Search

SUMMARYWest Nile virus (WNV) was probably introduced in southern and northern Mexico from the USA in two independent events. Since then, WNV activity has been reported in several Mexican states bordering the USA and the Gulf of Mexico, but disease manifestations seen there in humans and equids are quite different to those observed in the USA. We have analysed WNV seroprevalence in asymptomatic, unvaccinated equids from two Mexican states where no data had been previously recorded. WNV IgG antibodies were detected in 31.6% (91/288) of equine sera from Chiapas and Puebla states (53.3% and 8.0%, respectively). Analysis by plaque reduction neutralization test (PRNT) showed good specificity (99.4%) and sensitivity (84.9%) with the ELISA results. Further analyses to detect antibodies against three different flaviviruses (WNV, St Louis encephalitis virus, Ilheus virus) by haemagglutination inhibition (HI) tests on a subset of 138 samples showed that 53% of the 83 HI-positive samples showed specific reaction to WNV. These data suggest continuous expansion of WNV through Mexico. [ABSTRACT FROM AUTHOR]

Chikungunya virus (CHIKV) was isolated from humans in an outbreak of a febrile illness during July and August 2015 in the central valleys of Chiapas, Mexico. Sera obtained from 80 patients were tested for CHIKV RNA by reverse transcriptase polymerase chain reaction (RT-PCR) and for IgM and IgG antibodies by an enzyme linked immunoassay and a commercial indirect immunofluorescence test for CHIKV and dengue virus (DENV). Of the 80 patients, 67 were positive, including 50 for RNA and 17 for IgM. In addition, one patient was coinfected with CHIKV-DENV and 40 patients were positive for IgG antibody to DENV. The clinical manifestations included a high fever, polyarthralgia, headache, myalgia, rash, digestive disorders, conjunctivitis, and adenopathy associated with cervical and axillary inguinal regions. Complete nucleotide sequences of two of the CHIKV isolates showed that they belonged to the Asian lineage but did not group with other Mexican CHIKV isolates from the Chiapas coast. Our findings documented that different Asian lineage strains of CHIKV were circulating simultaneously during the 2015 outbreak in the Central Valley of Chiapas, Mexico. The 2024 cases suggest an explosive scenario of re-emergence of thousands of new Chikungunya and dengue fever (DENF) cases associated with deaths, and a dangerous increase of the four DENV serotypes throughout the Americas, especially in South American countries that have shown a high influx of human migration to southern Mexico. In Mexico, the state of Chiapas and other southern regions are the most vulnerable., Competing Interests: Conflicts of Interest The authors declare no conflict of interest.

We report the 1st records of Aedes tormentor and Culex panocossa throughout vector surveillance events carried out in putative foci of eastern equine encephalitis in Tamaulipas, Mexico. Formerly, Ae. tormentor had been reported in, at least, 2 Central American countries and Mexico. In Mexico, reports were from the states of Campeche, Chiapas, Quintana Roo, and Veracruz. Records of Ae. tormentor in these 4 Neotropical states were recently reviewed and eliminated; thus, the southernmost geographic distribution for this species is considered to be the state of Tamaulipas Mexico in its neotropical zone. Further, Cx. panocossa had been collected in Guerrero, Tabasco, and Veracruz. In Tamaulipas, there are 82 species of mosquitoes, being the 4th state accounting for the highest mosquito species diversity of 11 states in which comprehensive studies have been conducted on the subject of mosquito distribution., (Copyright © 2024 by The American Mosquito Control Association, Inc.)

Background: Mosquito-borne diseases, such as malaria, dengue, Zika and chikungunya, pose significant public health threats in tropical and subtropical regions worldwide. To mitigate the impact of these diseases on human health, effective vector surveillance and control strategies are necessary. Traditional vector control methods, which rely on chemical agents such as insecticides and larvicides, face challenges such as resistance and environmental concerns. Consequently, there has been a push to explore novel surveillance and control tools. Mass trapping interventions have emerged as a promising and environmentally friendly approach to reducing the burden of mosquito-borne diseases. This study assessed mass-trapping interventions using autocidal gravid ovitraps (AGOs) on Aedes aegypti populations in Reynosa, Tamaulipas, Mexico., Methods: Four neighborhoods were selected to evaluate the effects of three treatments: AGO mass-trapping, integrated vector control (IVC), which included source reduction and the application of chemical larvicide and adulticide, and AGO + IVC on Ae. aegypti populations. A control area with no interventions was also included. The effectiveness of the interventions was evaluated by comparing Ae. aegypti abundance between the pre-treatment period (9 weeks) and the post-treatment period (11 weeks) for each treatment., Results: Only treatment using AGO mass trapping with an 84% coverage significantly reduced Ae. aegypti female populations by 47%, from 3.75 ± 0.32 to 1.96 ± 0.15 females/trap/week. As expected, the abundance of Ae. aegypti in the control area did not differ from the pre- and post-treatment period (range of 4.97 ± 0.59 to 5.78 ± 0.53); Ae. aegypti abundance in the IVC treatment was 3.47 ± 0.30 before and 4.13 ± 0.35 after, which was not significantly different. However, Ae. aegypti abundance in the AGO + IVC treatment increased from 1.43 ± 0.21 before to 2.11 ± 0.20 after interventions; this increase may be explained in part by the low AGO (56%) coverage., Conclusions: This is the first report to our knowledge on the effectiveness of mass-trapping interventions with AGOs in Mexico, establishing AGOs as a potential tool for controlling Ae. aegypti in Northeastern Mexico when deployed with sufficient coverage., (© 2024. The Author(s).)

Background: Chagas disease or American trypanosomiasis, caused by Trypanosoma cruzi and vectored by triatomines, affects millions of people worldwide. In endemic countries including Mexico, infections in domestic animals, such as dogs, may affect the risk of human disease when they serve as a source of infection to vectors that subsequently infect humans. Materials and Methods: We conducted a cross-sectional study of 296 dogs from two cities near the northern and southern borders of Mexico: Reynosa, Tamaulipas, and Tuxtla Gutierrez, Chiapas. Infection was measured based on testing of blood using T. cruzi quantitative PCR (qPCR) and up to three antibody detection assays. The StatPak immunochromatographic assay was used to screen samples and the indirect fluorescent antibody (IFA) and multiplex microsphere immunoassay (MIA) tests were used as secondary tests on all samples that screened positive and a subset of negatives. Serologic positivity was defined based on reactivity on at least two independent tests. Results: Of the 280 samples tested for parasite DNA, two (0.7%) were positive, one of which (0.4%) was confirmed as T. cruzi discrete typing unit TcIV. Overall, 72 (24.3%) samples were reactive for T. cruzi antibodies via StatPak of which 8 were also positive using MIA and 2 were also positive using IFA (including one of the PCR-positive dogs). Overall, nine dogs (3.4%) met study criteria of positivity based on either/both serology or PCR tests. Positive dogs were found in both regions of Mexico; five (2.7%) from Reynosa and four (3.6%) from Tuxtla Gutierrez. We found no association between infection status and state of origin, sex, age group, breed group, neighborhood, and whether other pets lived in the home. Conclusion: Our results re-emphasize dogs' utility as sentinels for T. cruzi in Mexico and underscore the need for improved veterinary diagnostic tests and parasite surveillance at the household level in endemic countries.

Aedes albopictus is a vector of several pathogens of significant public health concern. In this situation, gravid traps have become a common surveillance tool for Aedes spp., which commonly use hay infusions as an attractant. Diverse grass infusions have been assessed to enhance the attraction to this vector mosquito. However, these studies have focused on the oviposition effect, and the attraction potential to gravid Ae. albopictus females has not been evaluated yet. Here we report the attractiveness of infusions of 4 different botanical species (Cenchrus purpureus, Cyanodon dactylon, Megathyrus maximus, Pennisetum ciliare) as baits in sticky ovitraps and autocidal gravid ovitraps (AGOs) under laboratory, semifield, and field conditions. In the laboratory, Cynodon dactylon showed attractiveness, whereas in semifield conditions, both C. dactylon and Megathyrsus maximus were similarly attractive for gravid Ae. albopictus. None of the infusions conducted with AGOs were able to lure Ae. albopictus and other species of mosquitoes in a 14-wk field experiment. Our results demonstrate the feasibility of finding more attractive infusions for Ae. albopictus females to improve the efficacy of AGO traps, but further testing of infusions in AGOs in field settings is needed., (Copyright © 2024 by The American Mosquito Control Association, Inc.)

We found serologic evidence of spotted fever group Rickettsia in humans and dogs and typhus group Rickettsia in dogs in Reynosa, Mexico. Our investigation revealed serologic samples reactive to spotted fever group Rickettsia in 5 community members, which highlights a potential rickettsial transmission scenario in this region.

SARS-CoV-2 mainly affects humans; however, it is important to monitor the infection of companion and wild animals as possible reservoirs of this virus. In this sense, seroprevalence studies in companion animals, such as dogs and cats, provide important information about the epidemiology of SARS-CoV-2. This study aimed to evaluate the seroprevalence of neutralizing antibodies (nAbs) against the ancestral strain and the Omicron BA.1 subvariant in dogs and cats in Mexico. Six hundred and two samples were obtained from dogs (n = 574) and cats (n = 28). These samples were collected from the end of 2020 to December 2021 from different regions of Mexico. The presence of nAbs was evaluated using a plaque reduction neutralization test (PRNT) and microneutralization (MN) assays. The results showed that 14.2% of cats and 1.5% of dogs presented nAbs against the ancestral strain of SARS-CoV-2. The analysis of nAbs against Omicron BA.1 in cats showed the same percentage of positive animals but a reduced titer. In dogs, 1.2% showed nAbs against Omicron BA.1. These results indicate that nAbs were more frequent in cats than in dogs and that these nAbs have a lower capacity to neutralize the subvariant Omicron BA.1.

Here, we report three near-full-length genome sequences of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) obtained in Mexico City, Mexico, during the pandemic of coronavirus disease 19 (COVID-19) in 2020, representing a zooanthroponotic transmission event between humans and a dog. All three genomes belong to the B.1.189 lineage based on the pangolin classification.

Of the documented tick-borne diseases infecting humans in México, Rocky Mountain spotted fever (RMSF), caused by the Gram-negative bacterium Rickettsia rickettsii , is responsible for most fatalities. Given recent evidence of brown dog tick, Rhipicephalus sanguineus s.l., as an emerging vector of human RMSF, we aimed to evaluate dogs and their ticks for rickettsiae infections as an initial step in assessing the establishment of this pathosystem in a poorly studied region of northeastern México while evaluating the use of dogs as sentinels for transmission/human disease risk. We sampled owned dogs living in six disadvantaged neighborhoods of Reynosa, northeastern México to collect whole blood and ticks. Of 168 dogs assessed, tick infestation prevalence was 53%, composed of exclusively Rh. sanguineus s. l. ( n = 2170 ticks). Using PCR and sequencing, we identified an overall rickettsiae infection prevalence of 4.1% ( n = 12/292) in ticks, in which eight dogs harbored at least one infected tick. Rickettsiae infections included Rickettsia amblyommatis and Rickettsia parkeri , both of which are emerging human pathogens, as well as Candidatus Rickettsia andeanae. This is the first documentation of pathogenic Rickettsia species in Rh. sanguineus s.l. collected from dogs from northeastern México. Domestic dog infestation with Rickettsia -infected ticks indicates ongoing transmission; thus, humans are at risk for exposure, and this underscores the importance of public and veterinary health surveillance for these pathogens.

We tested 294 domestic pet dogs in Mexico for neutralizing antibodies for mosquito-borne flaviviruses. We found high (42.6%) exposure to West Nile virus in Reynosa (northern Mexico) and low (1.2%) exposure in Tuxtla Gutierrez (southern Mexico) but very limited exposure to Aedes-borne flaviviruses. Domestic dogs may be useful sentinels for West Nile virus.

Background: Aedes aegypti mosquito-borne viruses including Zika (ZIKV), dengue (DENV), yellow fever (YFV), and chikungunya (CHIKV) have emerged and re-emerged globally, resulting in an elevated burden of human disease. Aedes aegypti is found worldwide in tropical, sub-tropical, and temperate areas. The characterization of mosquito blood meals is essential to understand the transmission dynamics of mosquito-vectored pathogens., Methodology/principal Findings: Here, we report Ae. aegypti and Culex quinquefasciatus host feeding patterns and arbovirus transmission in Northern Mexico using a metabarcoding-like approach with next-generation deep sequencing technology. A total of 145 Ae. aegypti yielded a blood meal analysis result with 107 (73.8%) for a single vertebrate species and 38 (26.2%) for two or more. Among the single host blood meals for Ae. aegypti, 28.0% were from humans, 54.2% from dogs, 16.8% from cats, and 1.0% from tortoises. Among those with more than one species present, 65.9% were from humans and dogs. For Cx. quinquefasciatus, 388 individuals yielded information with 326 (84%) being from a single host and 63 (16.2%) being from two or more hosts. Of the single species blood meals, 77.9% were from dogs, 6.1% from chickens, 3.1% from house sparrows, 2.4% from humans, while the remaining 10.5% derived from other 12 host species. Among those which had fed on more than one species, 11% were from dogs and humans, and 89% of other host species combinations. Forage ratio analysis revealed dog as the most over-utilized host by Ae. aegypti (= 4.3) and Cx. quinquefasciatus (= 5.6) and the human blood index at 39% and 4%, respectively. A total of 2,941 host-seeking female Ae. aegypti and 3,536 Cx. quinquefasciatus mosquitoes were collected in the surveyed area. Of these, 118 Ae. aegypti pools and 37 Cx. quinquefasciatus pools were screened for seven arboviruses (ZIKV, DENV 1-4, CHIKV, and West Nile virus (WNV)) using qRT-PCR and none were positive (point prevalence = 0%). The 95%-exact upper limit confidence interval was 0.07% and 0.17% for Ae. aegypti and Cx. quinquefasciatus, respectively., Conclusions/significance: The low human blood feeding rate in Ae. aegypti, high rate of feeding on mammals by Cx. quinquefasciatus, and the potential risk to transmission dynamics of arboviruses in highly urbanized areas of Northern Mexico is discussed., Competing Interests: The authors have declared that no competing interests exist.

The ongoing Coronavirus Disease 2019 (COVID-19) pandemic threatens the health of humans and causes great economic losses. Predictive modeling and forecasting the epidemic trends are essential for developing countermeasures to mitigate this pandemic. We develop a network model, where each node represents an individual and the edges represent contacts between individuals where the infection can spread. The individuals are classified based on the number of contacts they have each day (their node degrees) and their infection status. The transmission network model was respectively fitted to the reported data for the COVID-19 epidemic in Wuhan (China), Toronto (Canada), and the Italian Republic using a Markov Chain Monte Carlo (MCMC) optimization algorithm. Our model fits all three regions well with narrow confidence intervals and could be adapted to simulate other megacities or regions. The model projections on the role of containment strategies can help inform public health authorities to plan control measures., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

During ecological investigations for arboviruses conducted in coastal Chiapas, Mexico, in 2007, isolate MP1078 was obtained from a pool of Psorophora varipes mosquitoes. Based on antigenic characterization, this isolate was classified as a strain of Patois virus (PATV) ( Orthobunyavirus genus, Peribunyaviridae family). Recently, we conducted nearly complete genome sequencing of this isolate to gain further insight into its genetic relationship with other members of the Patois serogroup. Based on the genetic characterization, we determined that MP1078 contains S, M, and L genome segments that are genetically distinct from other viruses within the Patois serogroup. Serological analyses confirmed the taxonomic classification of MP1078 as a new virus and species within the Patois serogroup, and we propose the name Barrita virus (BITV).

Mosquito-borne viruses are emerging or re-emerging globally, afflicting millions of people around the world. Aedes aegypti , the yellow fever mosquito, is the principal vector of dengue, Zika, and chikungunya viruses, and has well-established populations across tropical and subtropical urban areas of the Americas, including the southern United States. While intense arboviral epidemics have occurred in Mexico and further south in the Americas, local transmission in the United States has been minimal. Here, we study Ae. aegypti and Culex quinquefasciatus host feeding patterns and vertebrate host communities in residential environments of South Texas to identify host-utilization relative to availability. Only 31% of Ae. aegypti blood meals were derived from humans, while 50% were from dogs and 19% from other wild and domestic animals. In Cx. quinquefasciatus , 67% of blood meals were derived from chicken, 22% came from dogs, 9% from various wild avian species, and 2% from other mammals including one human, one cat, and one pig. We developed a model for the reproductive number, R 0 , for Zika virus (ZIKV) in South Texas relative to northern Mexico using human disease data from Tamaulipas, Mexico. We show that ZIKV R 0 in South Texas communities could be greater than one if the risk of human exposure to Ae. aegypti bites in these communities is at least 60% that of Northern Mexico communities. The high utilization of non-human vertebrates and low risk of human exposure in South Texas diminishes the outbreak potential for human-amplified urban arboviruses transmitted by Ae. aegypti .

Venezuelan equine encephalitis (VEE) complex alphaviruses are important re-emerging arboviruses that cause life-threatening disease in equids during epizootics as well as spillover human infections. We conducted a comprehensive analysis of VEE complex alphaviruses by sequencing the genomes of 94 strains and performing phylogenetic analyses of 130 isolates using complete open reading frames for the nonstructural and structural polyproteins. Our analyses confirmed purifying selection as a major mechanism influencing the evolution of these viruses as well as a confounding factor in molecular clock dating of ancestors. Times to most recent common ancestors (tMRCAs) could be robustly estimated only for the more recently diverged subtypes; the tMRCA of the ID/IAB/IC/II and IE clades of VEE virus (VEEV) were estimated at ca. 149-973 years ago. Evolution of the IE subtype has been characterized by a significant evolutionary shift from the rest of the VEEV complex, with an increase in structural protein substitutions that are unique to this group, possibly reflecting adaptation to its unique enzootic mosquito vector Culex (Melanoconion) taeniopus. Our inferred tree topologies suggest that VEEV is maintained primarily in situ, with only occasional spread to neighboring countries, probably reflecting the limited mobility of rodent hosts and mosquito vectors.

Chagas disease, caused by Trypanosoma cruzi, is endemic in southern parts of the American continent. Herein, we have tested the protective efficacy of a DNA-prime/T. rangeli-boost (TcVac4) vaccine in a dog (Canis familiaris) model. Dogs were immunized with two-doses of DNA vaccine (pcDNA3.1 encoding TcG1, TcG2, and TcG4 antigens plus IL-12- and GM-CSF-encoding plasmids) followed by two doses of glutaraldehyde-inactivated T. rangeli epimastigotes (TrIE); and challenged with highly pathogenic T. cruzi (SylvioX10/4) isolate. Dogs given TrIE or empty pcDNA3.1 were used as controls. We monitored post-vaccination and post-challenge infection antibody response by an ELISA, parasitemia by blood analysis and xenodiagnosis, and heart function by electrocardiography. Post-mortem anatomic and pathologic evaluation of the heart was conducted. TcVac4 induced a strong IgG response (IgG2>IgG1) that was significantly expanded post-infection, and moved to a nearly balanced IgG2/IgG1 response in chronic phase. In comparison, dogs given TrIE or empty plasmid DNA only developed high IgG titers with IgG2 predominance in response to T. cruzi infection. Blood parasitemia, tissue parasite foci, parasite transmission to triatomines, electrocardiographic abnormalities were significantly lower in TcVac4-vaccinated dogs than was observed in dogs given TrIE or empty plasmid DNA only. Macroscopic and microscopic alterations, the hallmarks of chronic Chagas disease, were significantly decreased in the myocardium of TcVac4-vaccinated dogs. We conclude that TcVac4 induced immunity was beneficial in providing resistance to T. cruzi infection, evidenced by control of chronic pathology of the heart and preservation of cardiac function in dogs. Additionally, TcVac4 vaccination decreased the transmission of parasites from vaccinated/infected animals to triatomines.

Transboundary zoonotic diseases, several of which are vector borne, can maintain a dynamic focus and have pathogens circulating in geographic regions encircling multiple geopolitical boundaries. Global change is intensifying transboundary problems, including the spatial variation of the risk and incidence of zoonotic diseases. The complexity of these challenges can be greater in areas where rivers delineate international boundaries and encompass transitions between ecozones. The Rio Grande serves as a natural border between the US State of Texas and the Mexican States of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. Not only do millions of people live in this transboundary region, but also a substantial amount of goods and people pass through it everyday. Moreover, it occurs over a region that functions as a corridor for animal migrations, and thus links the Neotropic and Nearctic biogeographic zones, with the latter being a known foci of zoonotic diseases. However, the pathogenic landscape of important zoonotic diseases in the south Texas-Mexico transboundary region remains to be fully understood. An international perspective on the interplay between disease systems, ecosystem processes, land use, and human behaviors is applied here to analyze landscape and spatial features of Venezuelan equine encephalitis, Hantavirus disease, Lyme Borreliosis, Leptospirosis, Bartonellosis, Chagas disease, human Babesiosis, and Leishmaniasis. Surveillance systems following the One Health approach with a regional perspective will help identifying opportunities to mitigate the health burden of those diseases on human and animal populations. It is proposed that the Mexico-US border along the Rio Grande region be viewed as a continuum landscape where zoonotic pathogens circulate regardless of national borders.

Background: The venom of Centruroides limpidus limpidus (Cll) is a mixture of pharmacologically active principles. The most important of these are toxic proteins that interact both selectively and specifically with different cellular targets such as ion channels. Recently, anticancer properties of the venom from other scorpion species have been described. Studies in vitro have shown that scorpion venom induces cell death, inhibits proliferation and triggers the apoptotic pathway in different cancer cell lines. Herein, after treating human cervical adenocarcinoma (HeLa) cells with Cll crude venom, their cytotoxic activity and apoptosis induction were assessed., Results: Cll crude venom induced cell death in normal macrophages in a dose-dependent manner. However, through viability assays, HeLa cells showed high survival rates after exposure to Cll venom. Also, Cll venom did not induce apoptosis after performing ethidium bromide/acridine orange assays, nor was there any evidence of chromatin condensation or DNA fragmentation., Conclusions: Crude Cll venom exposure was not detrimental to HeLa cell cultures. This may be partially attributable to the absence of specific HeLa cell membrane targets for molecules present in the venom of Centruroides limpidus limpidus. Although these results might discourage additional studies exploring the potential of Cll venom to treat human papilloma cervical cancer, further research is required to explore positive effects of crude Cll venom on other cancer cell lines.

Background: Chagas disease, caused by Trypanosoma cruzi, is endemic in Latin America and an emerging infectious disease in the US and Europe. We have shown TcG1, TcG2, and TcG4 antigens elicit protective immunity to T. cruzi in mice and dogs. Herein, we investigated antigenicity of the recombinant proteins in humans to determine their potential utility for the development of next generation diagnostics for screening of T. cruzi infection and Chagas disease., Methods and Results: Sera samples from inhabitants of the endemic areas of Argentina-Bolivia and Mexico-Guatemala were analyzed in 1(st)-phase for anti-T. cruzi antibody response by traditional serology tests; and in 2(nd)-phase for antibody response to the recombinant antigens (individually or mixed) by an ELISA. We noted similar antibody response to candidate antigens in sera samples from inhabitants of Argentina and Mexico (n=175). The IgG antibodies to TcG1, TcG2, and TcG4 (individually) and TcG(mix) were present in 62-71%, 65-78% and 72-82%, and 89-93% of the subjects, respectively, identified to be seropositive by traditional serology. Recombinant TcG1- (93.6%), TcG2- (96%), TcG4- (94.6%) and TcG(mix)- (98%) based ELISA exhibited significantly higher specificity compared to that noted for T. cruzi trypomastigote-based ELISA (77.8%) in diagnosing T. cruzi-infection and avoiding cross-reactivity to Leishmania spp. No significant correlation was noted in the sera levels of antibody response and clinical severity of Chagas disease in seropositive subjects., Conclusions: Three candidate antigens were recognized by antibody response in chagasic patients from two distinct study sites and expressed in diverse strains of the circulating parasites. A multiplex ELISA detecting antibody response to three antigens was highly sensitive and specific in diagnosing T. cruzi infection in humans, suggesting that a diagnostic kit based on TcG1, TcG2 and TcG4 recombinant proteins will be useful in diverse situations.

To increase our knowledge of the geographic distribution of hantaviruses associated with neotomine or sigmodontine rodents in Mexico, we tested 876 cricetid rodents captured in 18 Mexican states (representing at least 44 species in the subfamily Neotominae and 10 species in the subfamily Sigmodontinae) for anti-hantavirus IgG. We found antibodies against hantavirus in 35 (4.0%) rodents. Nucleotide sequence data from 5 antibody-positive rodents indicated that Sin Nombre virus (the major cause of hantavirus pulmonary syndrome [HPS] in the United States) is enzootic in the Mexican states of Nuevo León, San Luis Potosí, Tamaulipas, and Veracruz. However, HPS has not been reported from these states, which suggests that in northeastern Mexico, HPS has been confused with other rapidly progressive, life-threatening respiratory diseases. Analyses of nucleotide sequence data from 19 other antibody-positive rodents indicated that El Moro Canyon virus and Limestone Canyon virus are geographically widely distributed in Mexico.

Venezuelan equine encephalitis virus (VEEV) has been the causative agent for sporadic epidemics and equine epizootics throughout the Americas since the 1930s. In 1969, an outbreak of Venezuelan equine encephalitis (VEE) spread rapidly from Guatemala and through the Gulf Coast region of Mexico, reaching Texas in 1971. Since this outbreak, there have been very few studies to determine the northward extent of endemic VEEV in this region. This study reports the findings of serologic surveillance in the Gulf Coast region of Mexico from 2003-2010. Phylogenetic analysis was also performed on viral isolates from this region to determine whether there have been substantial genetic changes in VEEV since the 1960s. Based on the findings of this study, the Gulf Coast lineage of subtype IE VEEV continues to actively circulate in this region of Mexico and appears to be responsible for infection of humans and animals throughout this region, including the northern State of Tamaulipas, which borders Texas.

Enzootic Venezuelan equine encephalitis virus (VEEV) has been known to occur in Mexico since the 1960s. The first natural equine epizootic was recognized in Chiapas in 1993 and since then, numerous studies have characterized the etiologic strains, including reverse genetic studies that incriminated a specific mutation that enhanced infection of epizootic mosquito vectors. The aim of this study was to determine the mosquito and rodent species involved in enzootic maintenance of subtype IE VEEV in coastal Chiapas. A longitudinal study was conducted over a year to discern which species and habitats could be associated with VEEV circulation. Antibody was rarely detected in mammals and virus was not isolated from mosquitoes. Additionally, Culex (Melanoconion) taeniopus populations were found to be spatially related to high levels of human and bovine seroprevalence. These mosquito populations were concentrated in areas that appear to represent foci of stable, enzootic VEEV circulation.

West Nile virus (WNV) has caused disease in humans, equids, and birds at lower frequency in Mexico than in the United States. We hypothesized that the seemingly reduced virulence in Mexico was caused by attenuation of the Tabasco strain from southeastern Mexico, resulting in lower viremia than that caused by the Tecate strain from the more northern location of Baja California. During 2006-2008, we tested this hypothesis in candidate avian amplifying hosts: domestic chickens, rock pigeons, house sparrows, great-tailed grackles, and clay-colored thrushes. Only great-tailed grackles and house sparrows were competent amplifying hosts for both strains, and deaths occurred in each species. Tecate strain viremia levels were higher for thrushes. Both strains produced low-level viremia in pigeons and chickens. Our results suggest that certain avian hosts within Mexico are competent for efficient amplification of both northern and southern WNV strains and that both strains likely contribute to bird deaths.

American trypanosomiasis is a public health problem in Latin America and southern parts of the United States. Infection in triatomines (vector) and domestic dogs (reservoir host) is a good indicator of Trypanosoma cruzi circulation and human risk of infection. The State of Mexico, Mexico, has been considered free of T. cruzi, and no detailed epidemiologic study has been conducted to assess the intricacies of the transmission cycle of the parasite in the region. Such studies would enhance our understanding of the epidemiology of T. cruzi infection in this geographic region and provide regional sanitary authorities with stronger fundamental knowledge for making decisions and allocating funds for Chagas disease control programs in the State of Mexico. The objective of this study was to determine the prevalence of T. cruzi infection in dogs (seroprevalence) and triatomines (fecal parasites) in a previously identified, discrete endemic region of parasite circulation and to widen our studies in the Tejupilco Sanitary Region located in the southern part of the State of Mexico. Dog blood samples (n=102) were analyzed for the presence of anti-T. cruzi antibodies by two assays, namely indirect hemagglutination assay and enzyme-linked immunosorbent assay. Triatomines (n=88) were collected and fecal aliquots were analyzed for the presence of parasites by light microscopy. Average seroprevalence in dogs in the Tejupilco Sanitary region was 24.5%, and the overall triatomine infection rate was 34.01%. Triatoma pallidipennis was the only triatomine species found in this region. Our data demonstrate that T. cruzi is actively circulating in the Tejupilco Sanitary Region and emphasize the requirement for epidemiologic surveillance programs throughout the putative endemic areas of the State of Mexico.

Venezuelan equine encephalitis (VEE) is an emerging infectious disease in Latin America. Outbreaks have been recorded for decades in countries with enzootic circulation, and the recent implementation of surveillance systems has allowed the detection of additional human cases in countries and areas with previously unknown VEE activity. Clinically, VEE is indistinguishable from dengue and other arboviral diseases and confirmatory diagnosis requires the use of specialized laboratory tests that are difficult to afford in resource-limited regions. Thus, the disease burden of endemic VEE in developing countries remains largely unknown, but recent surveillance suggests that it may represent up to 10% of the dengue burden in neotropical cities, or tens-of-thousands of cases per year throughout Latin America. The potential emergence of epizootic viruses from enzootic progenitors further highlights the need to strengthen surveillance activities, identify mosquito vectors and reservoirs and develop effective strategies to control the disease. In this article, we provide an overview of the current status of endemic VEE that results from spillover of the enzootic cycles, and we discuss public health measures for disease control as well as future avenues for VEE research.

Blood samples from 4893 cricetid rodents were tested for antibody (immunoglobulin G) to Whitewater Arroyo virus and Amaparí virus to extend our knowledge of the natural host range and geographical distribution of Tacaribe serocomplex viruses in North America. Antibodies to arenaviruses were found in northern pygmy mice (Baiomys taylori), woodrats (Neotoma spp.), northern grasshopper mice (Onychomys leucogaster), oryzomys (Oryzomys spp.), deermice (Megadontomys nelsoni and Peromyscus spp.), harvest mice (Reithrodontomys spp.), and cotton rats (Sigmodon spp.) captured in New Mexico, Texas, or Mexico. Comparison of endpoint antibody titers to Whitewater Arroyo virus and Amaparí virus in individual blood samples indicated that the Tacaribe complex viruses enzootic in Texas and Mexico are antigenically diverse.

Coues rice rat (Oryzomys couesi), a species abundant throughout Central America, was evaluated experimentally for the ability to serve as an amplifying host for three arboviruses: Patois (Bunyaviridae, Orthobunyavirus), Nepuyo (Orthobunyavirus), and Venezuelan equine encephalitis virus subtype ID (Togaviridae, Alphavirus). These three viruses have similar ecologies and are known to co-circulate in nature. Animals from all three cohorts survived infection and developed viremia with no apparent signs of illness and long-lasting antibodies. Thus, O. couesi may play a role in the general maintenance of these viruses in nature.

Here we describe clinical and pathologic evidence of Chagas disease caused in dogs by circulating Trypanosoma cruzi from a newly recognized endemic area in Mexico. We show that the Zumpahuacan isolate, although less virulent than the Sylvio-X10 reference strain that caused acute myocarditis and death, was pathogenic in dogs. Dogs infected with the Zumpahuacan isolate exhibited electrocardiographic alterations, left- and right-ventricle dilation, and hydropericardium. Histologically, diffused perimysial and endomysial lymphoplasmacytic cell infiltration, cardiomyocyte necrosis, and amastigote nests were noted in Zumpahuacan-infected dogs. These findings suggest that the risk of T. cruzi infection and Chagas disease is present in the State of Mexico, and further research is needed to identify the T. cruzi bio-types circulating in southern State of Mexico.

In this study, we investigated whether inflammatory responses contribute to oxidative/nitrosative stress in patients with Chagas' disease. We used three tests (enzyme-linked immunosorbent assay, immuno-flow cytometry, and STAT-PAK immunochromatography) to screen human serum samples (n = 1,481) originating from Chiapas, Mexico, for Trypanosoma cruzi-specific antibodies. We identified 121 subjects who were seropositive for T. cruzi-specific antibodies, a finding indicative of an 8.5% seroprevalence in the rural population from Chiapas. Seropositive and seronegative subjects were examined for plasma levels of biomarkers of inflammation, i.e., myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS), and xanthine oxidase (XOD), as well as for oxidative (advanced oxidation protein products [AOPPs]) and nitrosative (3-nitrotyrosine [3NT]) biomarkers. The seropositive subjects exhibited a significant increase in MPO activity and protein level, the indicator of neutrophil activation. Subsequently, a corresponding increase in AOPP contents, formed by MPO-dependent hypochlorous acid and chloramine formation, was noted in seropositive subjects. The plasma level of 3NT was significantly increased in seropositive subjects, yet we observed no change in XOD activity (O(2)(-) source) and nitrate/nitrite contents (denotes iNOS activation and NO production), which implied that direct peroxynitrite formation does not contribute to increased nitrosative damage in chagasic subjects. Instead, a positive correlation between increased MPO activity and protein 3NT formation was observed, which suggested to us that MPO-dependent formation of nitrylchloride that occurs in the presence of physiological NO and O(2)(-) concentrations contributes to protein nitration. Overall, our data demonstrate that T. cruzi-induced neutrophil activation is pathological and contributes to MPO-mediated collateral protein oxidative and nitrosative damage in human patients with Chagas' disease. Therapies capable of suppressing MPO activity may be useful in controlling the inflammation and oxidative/nitrosative pathology in chagasic cardiomyopathy.

In 1993, an outbreak of encephalitis among 125 affected equids in coastal Chiapas, Mexico, resulted in a 50% case-fatality rate. The outbreak was attributed to Venezuelan equine encephalitis virus (VEEV) subtype IE, not previously associated with equine disease and death. To better understand the ecology of this VEEV strain in Chiapas, we experimentally infected 5 species of wild rodents and evaluated their competence as reservoir and amplifying hosts. Rodents from 1 species (Baiomys musculus) showed signs of disease and died by day 8 postinoculation. Rodents from the 4 other species (Liomys salvini, Oligoryzomys fulvescens, Oryzomys couesi, and Sigmodon hispidus) became viremic but survived and developed neutralizing antibodies, indicating that multiple species may contribute to VEEV maintenance. By infecting numerous rodent species and producing adequate viremia, VEEV may increase its chances of long-term persistence in nature and could increase risk for establishment in disease-endemic areas and amplification outside the disease-endemic range.

We used 5 diagnostic tests in a cross-sectional investigation of the prevalence of Trypanosoma cruzi in Tejupilco municipality, State of Mexico, Mexico. Our findings showed a substantial prevalence of immunoglobulin G (IgG) and IgM antibodies to T. cruzi in human (n = 293, IgG 2.05%, IgM 5.5%, both 7.1%) and dog (n = 114, IgG 15.8%, IgM 11.4%, both 21%) populations. We also found antibodies to T. cruzi (n = 80, IgG 10%, IgM 15%, both 17.5%) in dogs from Toluca, an area previously considered free of T. cruzi. Our data demonstrate the need for active epidemiologic surveillance programs in these regions. A direct correlation (r2 = 0.955) of seropositivity between humans and dogs suggests that seroanalysis in dogs may help identify the human prevalence of T. cruzi infection in these areas.

Equine epizootics of Venezuelan equine encephalitis (VEE) occurred in the southern Mexican states of Chiapas in 1993 and Oaxaca in 1996. To assess the impact of continuing circulation of VEE virus (VEEV) on human and animal populations, serologic and viral isolation studies were conducted in 2000 to 2001 in Chiapas State. Human serosurveys and risk analyses indicated that long-term endemic transmission of VEEV occurred among villages with seroprevalence levels of 18% to 75% and that medical personnel had a high risk for VEEV exposure. Seroprevalence in wild animals suggested cotton rats as possible reservoir hosts in the region. Virus isolations from sentinel animals and genetic characterizations of these strains indicated continuing circulation of a subtype IE genotype, which was isolated from equines during the recent VEE outbreaks. These data indicate long-term enzootic and endemic VEEV circulation in the region and continued risk for disease in equines and humans.

In 1993 and 1996, subtype IE Venezuelan equine encephalitis (VEE) virus caused epizootics in the Mexican states of Chiapas and Oaxaca. Previously, only subtype IAB and IC VEE virus strains had been associated with major outbreaks of equine and human disease. The IAB and IC epizootics are believed to emerge via adaptation of enzootic (sylvatic, equine-avirulent) strains for high titer equine viremia that results in efficient infection of mosquito vectors. However, experimental equine infections with subtype IE equine isolates from the Mexican outbreaks demonstrated neuro-virulence but little viremia, inconsistent with typical VEE emergence mechanisms. Therefore, we hypothesized that changes in the mosquito vector host range might have contributed to the Mexican emergence. To test this hypothesis, we evaluated the susceptibility of the most abundant mosquito in the deforested Pacific coastal locations of the VEE outbreaks and a proven epizootic vector, Ochlerotatus taeniorhynchus. The Mexican epizootic equine isolates exhibited significantly greater infectivity compared with closely related enzootic strains, supporting the hypothesis that adaptation to an efficient epizootic vector contributed to disease emergence. Reverse genetic studies implicated a Ser --> Asn substitution in the E2 envelope glycoprotein as the major determinant of the increased vector infectivity phenotype. Our findings underscore the capacity of RNA viruses to alter their vector host range through minor genetic changes, resulting in the potential for disease emergence.

Following a period of inactivity from 1973-1991, Venezuelan equine encephalitis (VEE) reemerged during the past decade in South America and Mexico. Experimental studies of VEE virus (VEEV) infection of horses with virus strains isolated during these outbreaks have revealed considerable variation in the ability of equine-virulent, epizootic strains to exploit horses as efficient amplification hosts. Subtype IC strains from recent outbreaks in Venezuela and Colombia amplify efficiently in equines, with a correlation between maximum viremia titers and the extent of the outbreak from which the virus strain was isolated. Studies of enzootic VEEV strains that are believed to represent progenitors of the epizootic subtypes support the hypothesis that adaptation to efficient replication in equines is a major determinant of emergence and the ability of VEEV to spread geographically. Correlations between the ability of enzootic and epizootic VEEV strains to infect abundant, equiphilic mosquitoes, and the location and extent of these outbreaks, also suggest that specific adaptation to Ochlerotatus taeniorhynchus mosquitoes is a determinant of some but not all emergence events. Genetic studies imply that mutations in the E2 envelope glycoprotein gene are major determinants of adaptation to both equines and mosquito vectors.

West Nile virus (WNV) antibodies were detected in horses from five Mexican states, and WNV was isolated from a Common Raven in the state of Tabasco. Phylogenetic studies indicate that this isolate, the first from Mexico, is related to strains from the central United States but has a relatively high degree of sequence divergence.

Experimental studies evaluated the vector competence of Ochlerotatus taeniorhynchus (Wiedemann), Culex cancer Theobald, Culex pseudes (Dyar and Knab), Culex taeniopus Dyar and Knab, and a Culex (Culex) species, probably Culex quinquefasciatus Say, and Culex nigripalpus Theobald from Chiapas, Mexico, and Tocoa, Honduras, for epizootic (IC) and enzootic (IE) strains of Venezuelan equine encephalomyelitis (VEE) virus. Culex pseudes was highly susceptible to infection with both the IC and IE strains of VEE (infection rates >78%). Patterns of susceptibility to VEE were similar for Oc. taeniorhynchus collected in Mexico and Honduras. Although Oc. taeniorhynchus was highly susceptible to the epizootic IC strains (infection rates > or = 95%, n = 190), this species was less susceptible to the enzootic IE strain (infection rates < or = 35%, n = 233). The Culex (Culex) species were refractory to both subtypes of VEE, and none of 166 contained evidence of a disseminated infection. Virus-exposed Cx. pseudes that refed on susceptible hamsters readily transmitted virus, confirming that this species was an efficient vector of VEE. Although Oc. taeniorhynchus that fed on hamsters infected with the epizootic IC strain transmitted VEE efficiently, only one of six of those with a disseminated infection with the enzootic IE virus that fed on hamsters transmitted virus by bite. These data indicate that Cx. pseudes is an efficient laboratory vector of both epizootic and enzootic strains of VEE and that Oc. taeniorhynchus could be an important vector of epizootic subtypes of VEE.

To assess the role of horses as amplification hosts during the 1993 and 1996 Mexican Venezuelan equine encephalitis (VEE) epizootics, we subcutaneously infected 10 horses by using four different equine isolates. Most horses showed little or no disease and low or nonexistent viremia. Neurologic disease developed in only 1 horse, and brain histopathologic examination showed meningeal lymphocytic infiltration, perivascular cuffing, and focal encephalitis. Three animals showed mild meningoencephalitis without clinical disease. Viral RNA was detected in the brain of several animals 12-14 days after infection. These data suggest that the duration and scope of the recent Mexican epizootics were limited by lack of equine amplification characteristic of previous, more extensive VEE outbreaks. The Mexican epizootics may have resulted from the circulation of a more equine-neurotropic, subtype IE virus strain or from increased transmission to horses due to amplification by other vertebrate hosts or transmission by more competent mosquito vectors.

Multilocus genotyping of microbial pathogens has revealed a range of population structures, with some bacteria showing extensive recombination and others showing almost complete clonality. The population structure of the protozoan parasite Plasmodium falciparum has been harder to evaluate, since most studies have used a limited number of antigen-encoding loci that are known to be under strong selection. We describe length variation at 12 microsatellite loci in 465 infections collected from 9 locations worldwide. These data reveal dramatic differences in parasite population structure in different locations. Strong linkage disequilibrium (LD) was observed in six of nine populations. Significant LD occurred in all locations with prevalence <1% and in only two of five of the populations from regions with higher transmission intensities. Where present, LD results largely from the presence of identical multilocus genotypes within populations, suggesting high levels of self-fertilization in populations with low levels of transmission. We also observed dramatic variation in diversity and geographical differentiation in different regions. Mean heterozygosities in South American countries (0.3-0.4) were less than half those observed in African locations (0. 76-0.8), with intermediate heterozygosities in the Southeast Asia/Pacific samples (0.51-0.65). Furthermore, variation was distributed among locations in South America (F:(ST) = 0.364) and within locations in Africa (F:(ST) = 0.007). The intraspecific patterns of diversity and genetic differentiation observed in P. falciparum are strikingly similar to those seen in interspecific comparisons of plants and animals with differing levels of outcrossing, suggesting that similar processes may be involved. The differences observed may also reflect the recent colonization of non-African populations from an African source, and the relative influences of epidemiology and population history are difficult to disentangle. These data reveal a range of population structures within a single pathogen species and suggest intimate links between patterns of epidemiology and genetic structure in this organism.

Anopheles pseudopunctipennis was collected from Acapulco, Mexico and Sallee River, Grenada, West Indies and used in cross-mating experiments. Larvae from the cross, Mexico female X Grenada male, died in the third instar. However, adult progeny were obtained from the reciprocal cross Grenada female x Mexico male. These hybrid males had testes with apparently normal appearance but some without viable sperm. Polytene chromosomes obtained from hybrid females exhibited extensive asynapsis of the X chromosomes. Previously undescribed fixed inversion differences between the two populations were noted on the X chromosome. It is concluded that the two populations belong to different species. The Grenada population is designated An. pseudopunctipennis species C, since it is the third taxon recognized in this species complex.

To assess the relationship between mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) and clinical pyrimethamine-sulfadoxine resistance, polymerase chain reaction surveys and analyses for new mutations were conducted in four countries with increasing levels of pyrimethamine-sulfadoxine resistance: Mali, Kenya, Malawi, and Bolivia. Prevalence of mutations at DHFR codon 108 and a new mutation at DHPS 540 correlated with increased pyrimethamine-sulfadoxine resistance (P < .05). Mutations at DHFR 51, DHFR 59, and DHPS 437 correlated with resistance without achieving statistical significance. Mutations at DHFR 164 and DHPS 581 were common in Bolivia, where pyrimethamine-sulfadoxine resistance is widespread, but absent in African sites. Two new DHFR mutations, a point mutation at codon 50 and an insert at codon 30, were found only in Bolivia. DHFR and DHPS mutations occur in a progressive, stepwise fashion. Identification of specific sets of mutations causing in vivo drug failure may lead to the development of molecular surveillance methods for pyrimethamine-sulfadoxine resistance.

Crossmating experiments were conducted to determine if postmating reproductive barriers are involved in the maintenance of genetic divergence among populations of Anopheles pseudopunctipennis sensu lato, a primary malaria vector of the American continent. Reciprocal crosses were conducted between colony and wild strains from Mexico, Bolivia, and Peru. Hybridization experiments revealed unidirectional male/female hybrid sterility in crosses between Mexican females and South American males. The data presented provide the first evidence that genetic differences exist among geographic strains of An. pseudopunctipennis in neotropical America. There is a consistent pattern suggesting the presence of at least two allopatric sibling species. One species occurs in central Mexico, the other in the South American Andean Cordillera.

Enzyme electrophoresis and restriction fragment length polymorphism (RFLP) analysis of Anopheles pseudopunctipennis sensu lato from nine isolated populations in neotropical America confirmed previous observations that it constitutes a species complex. Electrophoretic studies showed fixed differences at two enzyme loci, glycerol dehydrogenase (Gcd) and phosphoglucomutase (Pgm), suggesting limited or no gene flow between populations from Mexico and South America. In addition, analysis of genetic distance showed two distinctive clusters, one from Mexico and the other from South America, separated at a Nei's distance level of 0.13, a value consistent in magnitude with that of other anopheline sibling species. The RFLP analysis revealed the presence of a ribosomal DNA fragment in Mexican strains that was absent in strains from South America. Two species have been identified through these studies, one provisionally named An. pseudopunctipennis A, a species from central Mexico, and the other An. pseudopunctipennis B, for the species found in the interAndean valleys and Andean slopes in regions of Peru and Bolivia. This research provides information required to elucidate the status of the different species of the An. pseudopunctipennis complex as vectors of malaria in the Americas.

This preliminary report provides information concerning genetic variation in the vector mosquito Anopheles pseudopunctipennis sensu lato that could have malaria control implications. Because of inconsistencies in malaria transmission patterns within geographic zones inhabited by this vector, the possibility that it represents a species complex was investigated. Hybrid crossing studies, electrophoretic analysis of enzyme variation, and DNA restriction studies were carried out in mosquitoes captured in nine areas of Mexico, Bolivia, and Peru. The findings demonstrated the existence of a species complex believed to have resulted from allopatric speciation. This research points to a need for establishing the geographic distribution of the newly recognized species because of their potential influence on malaria control.

In light of inconsistencies in the pattern of malaria transmission within geographical areas inhabited by Anopheles pseudopunctipennis pseudopunctipennis, a study was carried out to investigate the possibility that this vector constitutes a species complex. Hybrid crossing studies, electrophoretic analysis of enzyme loci, and DNA restriction analysis were conducted on mosquitoes captured at nine sites in Mexico, Bolivia, and Peru. The sterility of generations resulting from cross-mating of Mexican female mosquitoes and South American male mosquitoes; the results of electrophoretic analysis, which showed differences at two loci; and a genetic distance value of 0.13 confirmed the existence of a species complex, probably produced by allopatric speciation. It is concluded that the geographic distribution of this newly discovered species complex should be defined, in view of its potential effect on malaria control.