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Cache Valley virus (CVV), a mosquito-borne orthobunyavirus, causes epizootics in ruminants characterized by congenital malformations and fetal death in North America. Only seven human infections have been identified; limited information exists on its potential as a human teratogen. Diagnosis of CVV infections relies on the plaque reduction neutralization test (PRNT), which requires live virus, is time-consuming, and cannot differentiate between recent and past infections. To improve diagnostics for CVV, we developed an IgM antibody capture ELISA (MAC-ELISA) for detection of anti-CVV human IgM in diagnostic specimens that can be performed faster than PRNT and is specific to IgM, which is essential to determine the timing of infection. Conjointly, a cell line constitutively expressing human-murine chimeric antibody with the variable regions of monoclonal antibody CVV-17 and constant regions of human IgM was developed to provide positive control material. The new cell line produced antibody with reactivity in the assay equivalent to that of a human serum sample positive for anti-CVV IgM. Five of seven archived human specimens diagnostically confirmed as CVV positive tested positive in the MAC-ELISA, whereas 44 specimens confirmed positive for another arboviral infection tested negative, showing good initial correlation of the CVV MAC-ELISA. Two of 27 previously collected serum samples from febrile patients in Yucatán, Mexico, who tested negative for a recent flaviviral or alphaviral infection were positive in both the MAC-ELISA and PRNT, indicating a possible recent infection with CVV or related orthobunyavirus. The MAC-ELISA described here will aid in making diagnostics more widely available for CVV in public health laboratories.

We provide evidence of concurrent and close sequential infections between SARS-CoV-2 and select arboviruses-namely, chikungunya virus (CHIKV); dengue viruses 1, 2, and 3 (DENV1-3), and Zika virus (ZIKV)-in patients in Guerrero, southwest Mexico, in 2020-2021. The study population consisted of 176 febrile patients with laboratory evidence of SARS-CoV-2 infection. Sera from all patients were serologically and antigenically tested for seven arboviruses known to occur in Guerrero. Eighteen patients contained CHIKV IgM, six of whom also contained CHIKV RNA. Another 16 patients contained flavivirus antigen. The flaviviruses responsible for the infections were identified by plaque reduction neutralization test as DENV1 (two patients), DENV2 (five patients), DENV3 (three patients), ZIKV (three patients), and an undetermined flavivirus (three patients). In summary, we identified patients in Guerrero, Mexico, with concurrent or recent sequential infections between SARS-CoV-2 and select arboviruses, exemplifying the importance of performing differential diagnosis in regions where these viruses cocirculate.

The local public health authorities reported nine cases of chikungunya in Mexico in 2019, none of which occurred in Guerrero, a coastal state in the southwest. To test the hypothesis that chikungunya is grossly underreported in Mexico, acute sera were collected from 639 febrile patients from low-income households in Guerrero in 2019 and serologically assayed for chikungunya virus (CHIKV). Analysis of the sera by plaque reduction neutralization test revealed that 181 (28.3%) patients were seropositive for CHIKV. To identify patients with acute CHIKV infections, a subset of serum samples were tested for CHIKV-specific IgM by ELISA. Serum samples from 21 of 189 (11.1%) patients were positive. These patients met the chikungunya case definition established by the WHO. In conclusion, we provide evidence that CHIKV remains an important public health problem in Mexico and that the true number of cases is severely underestimated.

A clinical, serological, and molecular investigation was performed to determine the presence of dengue virus (DENV) and other flaviviruses among residents of the city of Reynosa, Tamaulipas, on the Mexico-U.S. border in 2014-2016. The sample population consisted of 2,355 patients with suspected dengue, in addition to 346 asymptomatic individuals recruited during a household-based epidemiological investigation designed to identify flavivirus seroconversions. Sera were collected from patients with suspected dengue in the acute phase of illness and from asymptomatic individuals at enrollment and every 5-7 months for 19 months. Sera from suspected dengue patients were tested for DENV antigen by enzyme-linked immunosorbent assay (ELISA), and select antigen-positive sera were further tested using a serotype-specific, quantitative reverse transcription-polymerase chain reaction. Sera from the household cohort were tested for flavivirus-reactive antibodies by immunoglobulin (Ig) M and IgG ELISAs using DENV antigen. A total of 418 (17.7%) patients with suspected dengue had laboratory-confirmed DENV infections, including 82 patients who were positive for DENV RNA. The most frequently detected serotype was DENV-1 (61 patients), followed by DENV-2 (16 patients) and DENV-3 (five patients). A total of 217 (62.7%) asymptomatic individuals had flavivirus-reactive antibodies at enrollment, and nine flavivirus-naïve individuals seroconverted. Sera from a subset of dengue patients and household participants, including all those who seroconverted, were further tested by plaque reduction neutralization test, resulting in the detection of antibodies to DENV-1, DENV-2, and West Nile virus. In summary, we provide evidence for the co-circulation of multiple flaviviruses in Reynosa, Tamaulipas, on the Mexico-U.S. border.

A total of 1,090 residents of the city of Reynosa, Tamaulipas, on the Mexico-U.S. border presented at hospitals and clinics of the Secretariat of Health, Mexico, in 2015 with symptoms characteristic of dengue. Dengue virus (DENV) antigen was detected by enzyme-linked immunosorbent assay in acute sera from 134 (12.3%) patients. Sera from select patients ( N = 34) were also tested for chikungunya virus (CHIKV) RNA by quantitative reverse transcription-polymerase chain reaction. Thirteen (38.2%) patients, including five DENV antigen-positive patients, were positive. Sera from three CHIKV RNA-positive patients were further assayed by virus isolation in cell culture and CHIKV was recovered on each occasion. The genome of one isolate and structural genes of the other two isolates were sequenced. In conclusion, we present evidence of CHIKV and DENV coinfections in patients who live near the Mexico-U.S. border and provide the first genome sequence of a CHIKV isolate from northern Mexico.

The mosquito Aedes aegypti is the major vector of the four serotypes of dengue virus (DENV1-4). Previous studies have shown that Ae. aegypti in Mexico have a high effective migration rate and that gene flow occurs among populations that are up to 150 km apart. Since 2000, pyrethroids have been widely used for suppression of Ae. aegypti in cities in Mexico. In Yucatan State in particular, pyrethroids have been applied in and around dengue case households creating an opportunity for local selection and evolution of resistance. Herein, we test for evidence of local adaptation by comparing patterns of variation among 27 Ae. aegypti collections at 13 single nucleotide polymorphisms (SNPs): two in the voltage-gated sodium channel gene para known to confer knockdown resistance, three in detoxification genes previously associated with pyrethroid resistance, and eight in putatively neutral loci. The SNPs in para varied greatly in frequency among collections, whereas SNPs at the remaining 11 loci showed little variation supporting previous evidence for extensive local gene flow. Among Ae. aegypti in Yucatan State, Mexico, local adaptation to pyrethroids appears to offset the homogenizing effects of gene flow., (© The American Society of Tropical Medicine and Hygiene.)

The home, or domicile, is the principal environment for transmission of dengue virus (DENV) between humans and mosquito vectors. Community-wide distribution of insecticide-treated curtains (ITCs), mimicking vector control program-driven interventions, has shown promise to reduce DENV infections. We conducted a Casa Segura consumer product intervention study in Mérida, Mexico to determine the potential to reduce intradomicillary DENV transmission through ITC use in individual homes. Dengue virus infections in mosquitoes and in humans were reduced in homes with ITCs in one of two study subareas. Overall, ITCs reduced intradomicillary DENV transmission; ITC homes were significantly less likely to experience multiple DENV infections in humans than NTC homes. Dengue virus-infected Aedes aegypti females were reduced within the ITC homes where curtain use was highest. Some homes yielded up to nine infected Ae. aegypti females. This study provides insights regarding best practices for Casa Segura interventions to protect homes from intradomicillary DENV transmission.