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Although rare in the developed world, amebiasis continues to be a leading cause of diarrhea and illness in developing nations with crowding, poor sanitation, and lack of clean water supply. Recent immigrants or travelers returning from endemic regions after a prolonged stay are at high risk of developing amebiasis. A high index of suspicion for amebiasis should be maintained for other high-risk groups like men having sex with men, people with AIDS/HIV, immunocompromised hosts, residents of mental health facility or group homes. Clinical presentation of intestinal amebiasis varies from diarrhea to colitis and dysentery. Amebic liver abscess (ALA) is the most common form of extraintestinal amebiasis. Various diagnostic tools are available and when amebiasis is suspected, a combination of stool tests and serology should be sent to maximize the yield of testing. Treatment with an amebicidal drug such as metronidazole/tinidazole and a luminal cysticidal agent such as paromomycin for clinical disease is indicated. However, for asymptomatic disease treatment with a luminal cysticidal agent to decrease chances of invasive disease and transmission is recommended., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Globalization has contributed to the emergence of specific parasitic diseases in novel geographical areas, and in these regions, these infections in travelers and immigrants may cause a considerable burden of disease. Timely diagnosis and treatment of protozoan infections to decrease mortality and prevent associated complications are essential. In this respect, the increased availability of specific DNA-detection procedures has improved the diagnosis of many imported parasitic infections. Travelers and immigrants with associated comorbidities or immunosuppression may pose a special challenge regarding management. An updated review of the main protozoan infections in mobile populations (malaria, Chagas disease, leishmaniasis, enteric protozoan infections) is provided, focusing on the changing epidemiology of these diseases, recent developments in diagnosis and management and the possibility of local transmission of imported infections.

Competing Interests: The authors have declared that no competing interests exist.

Acanthamoeba, one of free-living amoebae (FLA), remains a high risk of direct contact with this protozoan parasite which is ubiquitous in nature and man-made environment. This pathogenic FLA can cause sight-threatening amoebic keratitis (AK) and fatal granulomatous amoebic encephalitis (GAE) though these cases may not commonly be reported in our clinical settings. Acanthamoeba has been detected from different environmental sources namely; soil, water, hot-spring, swimming pool, air-conditioner, or contact lens storage cases. The identification of Acanthamoeba is based on morphological appearance and molecular techniques using PCR and DNA sequencing for clinico-epidemiological purposes. Recent treatments have long been ineffective against Acanthamoeba cyst, novel anti-Acanthamoeba agents have therefore been extensively investigated. There are efforts to utilize synthetic chemicals, lead compounds from medicinal plant extracts, and animal products to combat Acanthamoeba infection. Applied nanotechnology, an advanced technology, has shown to enhance the anti-Acanthamoeba activity in the encapsulated nanoparticles leading to new therapeutic options. This review attempts to provide an overview of the available data and studies on the occurrence of pathogenic Acanthamoeba among the Association of Southeast Asian Nations (ASEAN) members with the aim of identifying some potential contributing factors such as distribution, demographic profile of the patients, possible source of the parasite, mode of transmission and treatment. Further, this review attempts to provide future direction for prevention and control of the Acanthamoeba infection.

Vector-borne diseases cause over 700,000 deaths annually and represent 17% of all infectious illnesses worldwide. This public health menace highlights the importance of understanding how arthropod vectors, microbes and their mammalian hosts interact. Currently, an emphasis of the scientific enterprise is at the vector-host interface where human pathogens are acquired and transmitted. At this spatial junction, arthropod effector molecules are secreted, enabling microbial pathogenesis and disease. Extracellular vesicles manipulate signaling networks by carrying proteins, lipids, carbohydrates and regulatory nucleic acids. Therefore, they are well positioned to aid in cell-to-cell communication and mediate molecular interactions. This Review briefly discusses exosome and microvesicle biogenesis, their cargo, and the role that nanovesicles play during pathogen spread, host colonization and disease pathogenesis. We then focus on the role of extracellular vesicles in dictating microbial pathogenesis and host immunity during transmission of vector-borne pathogens., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)

Balamuthia mandrillaris is a free-living amoeba that lives in soil and water near human settlements. B. mandrillaris was first isolated from a mandrill baboon that died at the San Diego Zoo Wildlife Park in California in 1986, and the first human infection was reported in 1990. Although reported B. mandrillaris infections are often not properly characterized, it appears that B. mandrillaris invades the living body from the soil and water, either via a wound or the nasal cavity. Most confirmed infections have originated in South and North America. B. mandrillaris inhabits warm climates and is recognized as a pathogen in warm areas such as desert climates and tropical climates. B. mandrillaris has been isolated from environmental samples since 2000, most of which originated from warm areas such as step climates, tropical climates, and desert climates. However, B. mandrillaris may survive in diverse environments, although fewer granulomatous amebic encephalitis patients have been reported in colder Japanese and Northern European regions. In the present study, we conducted a survey of 13 soil samples in Aomori Prefecture located at the northernmost tip of Japan Honshu and successfully isolated one strain of B. mandrillaris from soil for the first time in Japan. In addition, B. mandrillaris gene was detected from several soils. This confirms that B. mandrillaris is capable of spreading to a wider climatic region.

The population dependency of measles, syphilis, and amebiasis was expressed as P = kN m , where P, N, and m were number of patients, population size, and a constant (～2 for measles, and 1.3～1.4 for syphilis and amebiasis), respectively. The population size dependency emerged only when conditions other than population size, such as infant mortality, hygienic condition, vaccination practices, and others, improved to the same level in all the prefectures in Japan. The formation of prefectures and municipalities was well simulated by the random coin toss assuming that people are attracted to a community with a probability proportional to the number of the residents to the 1.3rd power. When the number of inflow population was plotted against the number of the resident population in a prefecture, or when the number of coins that were added in a round was plotted against the number of coins that were present before the coin toss, the plots fell on a straight line with the slope ～1.3, which was almost the same as the slope obtained when the number of cases of syphilis or amebiasis was plotted against the population size.

Amebiasis is caused by Entamoeba histolytica infection and can produce a broad range of clinical signs, from asymptomatic cases to patients with obvious symptoms. The current epidemiological and clinical statuses of amebiasis make it a serious public health problem worldwide. The Entamoeba life cycle consists of the trophozoite, the causative agent for amebiasis, and the cyst, the form responsible for transmission. These two stages are connected by "encystation" and "excystation." Hence, developing novel strategies to control encystation and excystation will potentially lead to new measures to block the transmission of amebiasis by interrupting the life cycle of the causative agent. Here, we highlight studies investigating encystation using inhibitory chemicals and categorize them based on the molecules inhibited. We also present a perspective on new strategies to prevent the transmission of amebiasis., Competing Interests: The authors have declared that no competing interests exist.

Background: During 2009 and 2010, 2 clusters of organ transplant-transmitted Balamuthia mandrillaris, a free-living ameba, were detected by recognition of severe unexpected illness in multiple recipients from the same donor., Methods: We investigated all recipients and the 2 donors through interview, medical record review, and testing of available specimens retrospectively. Surviving recipients were tested and treated prospectively., Results: In the 2009 cluster of illness, 2 kidney recipients were infected and 1 died. The donor had Balamuthia encephalitis confirmed on autopsy. In the 2010 cluster, the liver and kidney-pancreas recipients developed Balamuthia encephalitis and died. The donor had a clinical syndrome consistent with Balamuthia infection and serologic evidence of infection. In both clusters, the 2 asymptomatic recipients were treated expectantly and survived; 1 asymptomatic recipient in each cluster had serologic evidence of exposure that decreased over time. Both donors had been presumptively diagnosed with other neurologic diseases prior to organ procurement., Conclusions: Balamuthia can be transmitted through organ transplantation with an observed incubation time of 17-24 days. Clinicians should be aware of Balamuthia as a cause of encephalitis with high rate of fatality, and should notify public health departments and evaluate transplant recipients from donors with signs of possible encephalitis to facilitate early diagnosis and targeted treatment. Organ procurement organizations and transplant centers should be aware of the potential for Balamuthia infection in donors with possible encephalitis and also assess donors carefully for signs of neurologic infection that may have been misdiagnosed as stroke or as noninfectious forms of encephalitis., (Published by Oxford University Press for the Infectious Diseases Society of America 2016. This work is written by (a) US Government employee(s) and is in the public domain in the US.)

Acanthamoeba genus is divided into 20 genotypes (T1-T20) on the basis of the gene encoding 18S rRNA sequence. Using of at least 2 kbp gene fragments is strongly recommended to identify new genotypes and 5% difference is commonly used as a criterion of new genotypes, however, this value is questionable. In this paper, Polish Acanthamoeba strains described earlier on the basis of ~850 bp Ami fragment of 18S rRNA gene as T4, T11 and a new T16 genotype, have been analyzed using near-complete sequence of the gene. This analysis was needed because the Ami fragment does not reveal full variability within 18S rRNA gene. Phylogenetic analysis based on Ami fragment is biased by artifacts in the construction of the tree, so the fragment should not be used for identification of new putative Acanthamoeba genotypes. The analysis confirmed that the Polish sequences represent T4 and T11 genotypes and that the strains described earlier as T16 genotype are in fact a new subgroup of the T20 genotype and that this genotype should be divided into two subgroups: T20a (two strains described by [J. Eukaryot. Microbiol. 62 (2015) 69]) and T20b (11 Polish strains described in this study). The T20b subgroup was isolated from both clinical samples and water bodies used by people as bathing places and there is a risk of infection for humans during contact with water., (© 2015 The Author(s) Journal of Eukaryotic Microbiology © 2015 International Society of Protistologists.)

Primary amoebic meningoencephalitis (PAM) is a fatal infection in most cases, caused by the amoeba flagellate Naegleria fowleri. This report describes the first cases of PAM in Algeria, in a cow and a ewe from Batna, north-eastern Algeria. The death of both ruminants occurred a week after the first clinical manifestations. The cerebrospinal fluid, after staining with May-Grünwald-Giemsa, showed the presence of amoebae cells. Histological sections revealed numerous amoebae in all parts of the brain. The presence of N. fowleri was confirmed using a species-specific real-time PCR in histological tissue sections. The two PAM cases were reported during the hot season, and the source of infection is very likely the water where the cattle came to drink. Particular attention should be focused on this type of infection in aquatic environments when the temperature is high and preventive measures must be taken to avoid the proliferation of N. fowleri., (© M. Benterki et al., published by EDP Sciences, 2016.)

Objective: To describe the environmental conditions and the parasitic infection status of Xukuru-Kariri individuals living in the municipality of Caldas, state of Minas Gerais, Brazil., Methods: A cross-sectional study was carried out in March 2009. Sociodemographic and environmental data were collected through interviews. Water and fecal samples were collected for determination of environmental contamination and parasitic infection status., Results: The Xukuru-Kariri population living in Caldas included 86 people divided into 22 families. Of 22 heads of household, 81.8% had low schooling (not higher than elementary education). Of 26 water samples collected for microbiological analysis, 77.0% were positive for total coliforms and 4.0% for Escherichia coli. Residents of 27.3% of households defecated in the open. Trash was scattered in the yard of 54.5% of households. Fecal samples were collected from 60 individuals, with parasitic infection in 66.6%. The following prevalence rates were recorded: Entamoeba histolytica/dispar, 6.7%; Entamoeba coli, 60.0%; Endolimax nana, 1.8%; and Giardia duodenalis, 6.6%., Conclusions: The people included in this study faced environmental characteristics that contributed to their health vulnerability. Health actions as well as the implementation of public policies to provide sanitation, with quality water and adequate collection and treatment of human and household waste, are essential to prevent environmental degradation and improve the quality of life of these individuals.

A liver, heart, iliac vessel and two kidneys were recovered from a 39-year-old man who died of traumatic head injury and were transplanted into five recipients. The liver recipient 18 days posttransplantation presented with headache, ataxia and fever, followed by rapid neurologic decline and death. Diagnosis of granulomatous amebic encephalitis was made on autopsy. Balamuthia mandrillaris infection was confirmed with immunohistochemical and polymerase chain reaction (PCR) assays. Donor and recipients' sera were tested for B. mandrillaris antibodies. Donor brain was negative for Balamuthia by immunohistochemistry and PCR; donor serum Balamuthia antibody titer was positive (1:64). Antibody titers in all recipients were positive (range, 1:64-1:512). Recipients received a four- to five-drug combination of miltefosine or pentamidine, azithromycin, albendazole, sulfadiazine and fluconazole. Nausea, vomiting, elevated liver transaminases and renal insufficiency were common. All other recipients survived and have remained asymptomatic 24 months posttransplant. This is the third donor-derived Balamuthia infection cluster described in solid organ transplant recipients in the United States. As Balamuthia serologic testing is only available through a national reference laboratory, it is not feasible for donor screening, but may be useful to determine exposure status in recipients and to help guide chemotherapy., (© Copyright 2014 The American Society of Transplantation and the American Society of Transplant Surgeons.)

Primary amebic meningoencephalitis (PAM) caused by the free-living ameba (FLA) Naegleria fowleri is a rare but rapidly fatal disease of the central nervous system (CNS) affecting predominantly young, previously healthy persons. No effective chemotherapeutic prophylaxis or treatment has been identified. Recently, three transplant-associated clusters of encephalitis caused by another FLA, Balamuthia mandrillaris, have occurred, prompting questions regarding the suitability of extra-CNS solid organ transplantation from donors with PAM. During 1995-2012, 21 transplant recipients of solid organs donated by five patients with fatal cases of PAM were reported in the United States. None of the recipients developed PAM, and several recipients tested negative for N. fowleri by serology. However, historical PAM case reports and animal experiments with N. fowleri, combined with new postmortem findings from four patients with PAM, suggest that extra-CNS dissemination of N. fowleri can occur and might pose a risk for disease transmission via transplantation. The risks of transplantation with an organ possibly harboring N. fowleri should be carefully weighed for each individual recipient against the potentially greater risk of delaying transplantation while waiting for another suitable organ. In this article, we present a case series and review existing data to inform such risk assessments., (© Copyright 2013 The American Society of Transplantation and the American Society of Transplant Surgeons.)

On November 21, 2012, the U.S. Virgin Islands (USVI) Department of Health documented the first case and death from primary amebic meningoencephalitis (PAM) in the territory. PAM, a rare and almost universally fatal condition, results when Naegleria fowleri, a free-living thermophilic ameba found in warm freshwater, enters the nose and migrates to the brain. The patient was a man aged 47 years whose only reported freshwater exposures were the use of tap water for daily household activities and for ablution, a ritual cleansing that he practiced several times a day in preparation for Islamic prayer. Ablution can include nasal rinsing. On November 16, 2012, the patient had visited the emergency department with a headache; he was treated symptomatically and released. The following day, the patient returned to the emergency department by ambulance with fever, confusion, agitation, and a severe headache, for which he was admitted. Cerebrospinal fluid (CSF) studies were consistent with bacterial meningitis, and antibiotics were started. On November 18, neurologic findings included fixed nonresponsive pupils, no response in the upper or lower extremities, muted plantar responses, and no response to verbal commands. Microscopic examination of the CSF obtained from a second lumbar puncture revealed motile amebic trophozoites. CSF specimens sent to CDC for confirmatory testing were positive for N. fowleri by real-time polymerase chain reaction testing. On the morning of November 21, the patient was pronounced brain dead based on neurologic criteria.

Balamuthia mandrillaris is an opportunistic, free-living amoeba that can cause skin lesions and the typically fatal Balamuthia amoebic encephalitis (BAE) both in immunocompromised and immunocompetent individuals. Available data for BAE cases indicate that this disease is difficult to detect because knowledge of predisposing factors is lacking, causing a challenge for diagnosing BAE. The number of reported BAE cases is increasing worldwide, and this is a major concern because little is known about the pathogen, no standardized detection tools are available, and most of the treatments are almost empirical. The recently reported cases, novel diagnostics tools, and successful therapeutic approaches against BAE infections are reviewed here., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

This study provides a comprehensive epidemio-clinical picture of sporadic, domestically acquired cases of amoebiasis, cryptosporidiosis and giardiasis in one Canadian community based on patient symptom, outcome and exposure data from an enhanced surveillance system. It yields valuable data for estimating the burden of those diseases including the proportion of bloody diarrhoea, hospitalization, and disease duration. Age differences were observed by incidence rate and for some clinical information and exposures to risk factors. For each of the three diseases, the animal/environment-to-person route was the most common possible main transmission route according to the exposure reported, whereas the person-to-person route was the least common. Exposure was higher for the 10-24 years age group of giardiasis cases for swimming in recreational waters (79%) and attending a barbeque (50%). Therefore, comparisons between groups of cases or extrapolation of results when estimating the burden of illness should be adjusted for age.

Objective: To our knowledge, there is no study dealing with the prevalence of free-living amoebas (FLA) in water sources in Turkey, previous studies were mostly case presentations. The aim of the present study was to investigate the prevalence of FLA from tap water and natural water sources in different parts of the city., Methods: In the study, 250 samples were collected from the city centre, districts and villages. Two litres of water was collected from each source and filtered through a vacuum filtration system. The filter papers were washed in "Page's Amoeba Saline (PAS)" solution and incubated overnight. Filter papers were removed from the tubes and centrifuged; the final pellet was inoculated on non-nutrient agar (NNA) plates. The growth rate of FLA was checked after three days of inoculation and the flagellation test was performed to determine the presence of Naegleria spp. Heat tolerance of isolated strains was checked at 37, 42 and 52°C for the presence of pathogenic Acanthamoeba species. The cyst and trophozoite morphology of amoebas were examined under a light microscope and the genera was identified according to morphotyping keys., Results: FLA were found in 75 (30.0%) of examined water samples. Eleven (4.4%) were identified as Acanthamoeba spp., 25 (10.0%) as Naegleria spp. and 39 (15.6%) as Hartmannella spp. after microscopic examination., Conclusion: Our study revealed that FLA are common inhabitants of household water as they are in the environment, so their own potential risks as well as transferring bacteria as other pathogens is important for human health.

Primary amoebic meningoencephalitis (PAM) is a rare and rapidly fatal disease caused by the Naegleria fowleri amoeba. It is a diagnosis rarely seen by medical personnel, yet this amoeba is frequently encountered by people who frequent freshwater bodies of water in certain states. The disease primarily affects children and young adults who swim or take part in water sports in the waters in which the amoeba thrive. The disease presents with symptomatology similar to bacterial meningitis: headache, stiff neck, altered mental status, seizures, and coma with a quick progression to death. Rapid diagnosis is imperative to facilitate prompt treatment, although PAM has 95% mortality. There have been only 10 survivors reported in medical literature. This disease is a public-health risk to those living in affected areas of the country. Healthcare providers need to be cognizant of the disease as well, and, although recovery is rare, focus on prevention and risk reduction strategies is imperative. It is not completely understood why, of the millions of people are exposed to freshwater with the amoeba, only a few become infected with it. The Centers for Disease Control and Prevention have suggested that all freshwater areas should always assume a level of risk in waters, even when signage is not posted. This case study will review a fatal case of Naegleria fowleri infection in a young patient and will include the pathophysiology, diagnosis, treatment, nursing and public health implications, and organ procurement that occurred with the patient.

The authors describe the unique presentation of Balamuthia mandrillaris encephalitis in a kidney donor and two recipients. All three patients suffered acute clinical deterioration, with radiological or clinical evidence of intracranial hypertension. Brain autopsy in the donor and an urgent brain biopsy in a recipient established the diagnosis. First-tier therapy, with mannitol and CSF drainage, successfully treated the intracranial hypertension in both recipients, while administration of a combination of antiamebic drugs was associated with survival in the second recipient. For both recipients, neurosurgical management played a critical role in the rapid diagnosis and treatment of Balamuthia mandrillaris encephalitis.

On December 14, 2009, a physician in Mississippi contacted CDC to report possible transplant-transmitted encephalitis in two kidney transplant recipients who shared the same organ donor. Histopathologic testing of donor autopsy brain tissue at CDC showed amebae, and subsequent testing of specimens from the donor and the two kidney recipients confirmed transmission by transplantation of Balamuthia granulomatous amebic encephalitis (GAE), a rare disease caused by Balamuthia mandrillaris, a free-living ameba found in soil. One kidney recipient, a woman aged 31 years, died; the other recipient, a man aged 27 years, survived with neurologic sequelae. Recipients of the heart and liver from the same donor received preemptive therapy and have shown no signs of infection. The donor, a previously healthy boy aged 4 years, was presumed to have died from acute disseminated encephalomyelitis (ADEM), an autoimmune neurologic disease, after infection with influenza A. An investigation was conducted by the state health departments in Mississippi, Kentucky, Florida, and Alabama and CDC to characterize the cases, elucidate possible exposures in the donor, and develop recommendations for early detection and prevention. This is the first reported transmission of Balamuthia by organ transplantation. Clinicians should be aware of Balamuthia infection as a potentially fatal cause of encephalitis. Organ procurement organizations (OPOs) and transplant centers should be aware of the potential for Balamuthia infection in donors with encephalitis of uncertain etiology, and OPOs should communicate this elevated risk for infection to transplant centers so they can make an informed risk assessment in the decision to accept an organ.

On August 23, 2010, CDC was notified regarding two organ transplant recipients in Arizona who had encephalitis with multiple ring-enhancing lesions revealed by cerebral magnetic resonance imaging. The common organ donor, a Hispanic male landscaper aged 27 years, had died in Arizona from a presumed stroke on July 21. He had a large skin lesion for approximately 6 months on his back that he had attributed to an insect bite. The ill recipients, a male liver recipient aged 56 years, and a male recipient of a kidney and pancreas aged 24 years, received organ transplants on July 22. In addition, two other recipients received organs from this donor: an adult male heart recipient received his transplant in California on July 22, and an adult male kidney recipient received his transplant in Utah on July 23.

Free-living amoebae are widely distributed in aquatic environments and their hygienic, medical and ecological relationships to man are increasingly important. The purpose of this study was to isolate free-living amoebae from water-hyacinth root (Eichhornia crassipes) and the water of an urban lake in Mexico City. Five grams of wet root were seeded on non-nutritive agar with Enterobacter aerogenes (NNE). Water samples were concentrated by centrifugation at 1200g for 15min and the pellet was seeded on NNE. Of the 16 isolated genera, 10 were detected in both habitats. The most frequent were Vannella in root and Acanthamoeba and Naegleria in water. The total number of isolates and genera isolated from root was higher than that isolated from water. The differences between root and water are probably due to the morphological characteristics of water-hyacinth root, which provides a large habitat and refuge area for many organisms., (Copyright 2010 Elsevier Inc. All rights reserved.)

Some free-living amoebae, including some species of the genus Acanthamoeba, can cause infections in humans and animals. These organisms are known to cause granulomatous amebic encephalitis (GAE) in predominantly immune-deficient persons. In the present study, we isolated a potentially human pathogenic Acanthamoeba isolate originating from a public heated indoor swimming pool in Switzerland. The amoebae, thermophilically preselected by culture at 37 degrees C, subsequently displayed a high thermotolerance, being able to grow at 42 degrees C, and a marked cytotoxicity, based on a co-culture system using the murine cell line L929. Intranasal infection of Rag2-immunodeficient mice resulted in the death of all animals within 24 days. Histopathology of brains and lungs revealed marked tissue necrosis and hemorrhagic lesions going along with massive proliferation of amoebae. PCR and sequence analysis, based on 18S rDNA, identified the agent as Acanthamoeba lenticulata. In summary, the present study reports on an Acanthamoeba isolate from a heated swimming pool suggestive of being potentially pathogenic to immunocompromised persons.

Aims: This study aimed to assess the prevalence of amoebiasis among patrons visiting gay saunas in Taiwan., Methods: A cross-sectional survey was conducted using questionnaire interview and indirect hemagglutination assays and specific Entamoeba histolytica antigen assays of blood and rectal swab specimens, respectively, among patrons visiting 10 gay saunas between September 2006 and December 2006., Results: During the three-month study period, 208 blood and 120 rectal swab specimens were tested for E. histolytica infection. Amoebiasis was detected among 3.8% and 3.3% of the patrons by serologies and antigen assays, respectively. During the latest sexual encounter, more than 70% of the patrons had oral-anogenital sex, and only 20% used condoms during oral-anogenital contact., Conclusion: Our findings suggest that there is a potential risk of E. histolytica transmission among the patrons visiting gay saunas who do not practise safe sex consistently in Taiwan.

The majority of the world's population still live without access to healthy water and the contamination of drinking water with protozoan pathogens poses a serious threat to millions of people in the developing world. Even in the developed world periodic outbreaks of diarrhoeal diseases are caused by the protozoan parasites Cryptosporidium sp., Giardia duodenalis and Entamoeba histolytica. Thus, surveillance of drinking water is imperative to minimize such contaminations and ensure continuous supplies of healthy water world-wide. This article reviews the progress in technology for detection and surveillance of these important waterborne parasites.

Acanthamoeba is an opportunistic protozoan that is widely distributed in the environment and is well recognized to produce serious human infections, including a blinding keratitis and a fatal encephalitis. This review presents our current understanding of the burden of Acanthamoeba infections on human health, their pathogenesis and pathophysiology, and molecular mechanisms associated with the disease, as well as virulence traits of Acanthamoeba that may be targets for therapeutic interventions and/or the development of preventative measures.

Histological studies of the brain, lungs, liver, kidneys, heart, and the spleen were carried out in mice previously infected with 6 pathogenic strains of free-living amoebae of the genus Acanthamoeba. The potential virulence of the strains studied was determined on the basis of re-isolation of the amoebae from the organs of the inoculated animals and by the extent of the histopathological changes inflicted. The most virulent was strain AD16, affecting all organs of the inoculated mice, while the least virulent was strain AD148 re-isolated from the brain of a single mouse. The extent of the changes in the brain depended upon the amoebae strain, while in the remaining organs it also depended upon the duration of the infection.

The roles free-living amebae and the parasitic protozoa Entamoeba histolytica and Balantidium coli play as agents of waterborne zoonotic diseases are examined. The free-living soil and water amebae Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris are recognized etiologic agents of mostly fatal amebic encephalitides in humans and other animals, with immunocompromised and immunocompetent hosts among the victims. Acanthamoeba spp. are also agents of amebic keratitis. Infection is through the respiratory tract, breaks in the skin, or by uptake of water into the nostrils, with spread to the central nervous system. E. histolytica and B. coli are parasitic protozoa that cause amebic dysentery and balantidiasis, respectively. Both intestinal infections are spread via a fecal-oral route, with cysts as the infective stage. Although the amebic encephalitides can be acquired by contact with water, they are not, strictly speaking, waterborne diseases and are not transmitted to humans from animals. Non-human primates and swine are reservoirs for E. histolytica and B. coli, and the diseases they cause are acquired from cysts, usually in sewage-contaminated water. Amebic dysentery and balantidiasis are examples of zoonotic waterborne infections, though human-to-human transmission can occur. The epidemiology of the diseases is examined, as are diagnostic procedures, anti-microbial interventions, and the influence of globalization, climate change, and technological advances on their spread.

Risk from Acanthamoeba keratitis is complex, depending upon the virulence of the particular strain, exposure, trauma, or other stress to the eye, and host immune response. Bacterial endosymbionts may also play a factor in the pathogenicity of Acanthamoeba. Which factor(s) may be the most important is not clear. The ability of the host to produce IgA antibodies in tears may be a significant factor. The immune response of the host is a significant risk factor for GAE infection. If so, then a certain subpopulation with an inability to produce IgA in the tears may be at greatest risk. There was no sufficient data on the occurrence or types of Acanthamoeba in tapwater in the U.S. Published work on amoebal presence in tapwater does not provide information on the type of treatment the water received or the level of residual chlorine. Assessment of the pathogenicity by cell culture and molecular methods of Acanthamoeba in tapwater would also be useful in the risk assessment process for drinking water. The possibility that Acanthamoeba spp. might serve as vectors for bacterial infections from water sources also should be explored. The bacterial endosymbionts include an interesting array of pathogens such as Vibrio cholerae and Legionella pneumophila, both of which are well recognized waterborne/water-based pathogens. Work is needed to determine if control of Acanthamoeba spp. is needed to control water-based pathogens in water supplies.

Background: Primary amoebic meningoencephalitis was first recognised by a South Australian pathologist. The histopathological appearances indicated that the organism, Naegleria fowleri, entered the central nervous system from the nasal cavity via the cribriform plate. But the mode of transmission remained unknown., Aims: To describe how the pathogenesis of this condition was discovered, and correct misinformation about the events and persons involved in this process., Hypothesis: We hypothesised that pipeline water supplying northern centres in South Australia was responsible for transmitting thermophilic amoebae during the summer months., Evidence: The evidence supporting our hypothesis was: domestic water pipelines were exposed to sunlight and became heated to 35-45 degrees C in summer which promoted the formation of vegetative forms of the amoebae; some patients described using tap water to flush their nasal cavities; and Naegleri fowleri were eventually recovered from domestic tap water supplies., Conclusion: A successful collaboration between general practitioners and laboratory scientists elucidated the pathogenesis of primary amoebic encephalomyelitis, a serious public health hazard in South Australia from 1947 until the early 1970s.

The use of wastewater and excreta in agriculture constitutes an important source of spread Salmonella strains and protozoan infections into the environment. This practice has been used in El Azzouzia (the wastewater-spreading area of Marrakesh city, Morocco) for several years. The available circumstantial evidence gained from epidemiological and microbiological investigations suggests that the use of untreated wastewater causes an excess of protozoan infections among children living in El Azzouzia (72%) compared with those from a control area (45%). The pathogenic protozoan infections observed were giardiasis (39%) and amoebiasis (28%). For Salmonella infection, 21.34% of the exposed children were infected, while this rate did not exceed 1.14% in the control group. The serogroups B and C were the most commonly isolated. The sewage farming children are therefore more exposed to detectable risk from pathogenic micro-organisms than the control children.

We studied the cyst production of 340 asymptomatic carriers with single or mixed infections of Entamoeba histolytica/Entamoeba dispar, Endolimax nana and Entamoeba coli. It was found that the main source of transmission was a small group of 37 (10.9%) carriers who produced 70.2% of all cysts. Gender was an important factor for cyst production of Ent. histolytica/Ent. dispar, since males produced 6-fold more cysts than females. Females produced 'large' (13-15 microns) Ent. histolytica/Ent. dispar cysts and males small (10-12 microns) cysts when concentration was > 2000 cysts/g. When concentration was < 2000 cysts/g, cysts were the same size for both sexes (11.6 +/- 0.3 microns). In Ent. coli infections, an inverse relationship between the number and size of cyst was found for both sexes. Cysts of End. nana were not affected by gender or cyst concentration. Following cyst production by a carrier infected with Ent. coli and Ent. histolytica for 28 days, we identified synchronized cycles of cyst production for both species. Altogether, these data suggest that cyst-mediated transmission is a highly regulated process in which synchronization among different species and gender of the host have an important role in transmission.

Free-living Naegleria fowleri amoebae cause primary amoebic meningoencephalitis (PAM). Because of the apparent conflict between their ubiquity and the rarity of cases observed, we sought to develop a model characterizing the risk of PAM after swimming as a function of the concentration of N. fowleri. The probability of death from PAM as a function of the number of amoebae inhaled is modeled according to results obtained from animals infected with amoeba strains. The calculation of the probability of inhaling one or more amoebae while swimming is based on a double hypothesis: that the distribution of amoebae in the water follows a Poisson distribution and that the mean quantity of water inhaled while swimming is 10 ml. The risk of PAM for a given concentration of amoebae is then obtained by summing the following products: the probability of inhaling n amoebae x the probability of PAM associated with inhaling these n amoebae. We chose the lognormal model to assess the risk of PAM because it yielded the best analysis of the studentized residuals. Nonetheless, the levels of risk thereby obtained cannot be applied to humans without correction, because they are substantially greater than those indicated by available epidemiologic data. The curve was thus adjusted by a factor calculated with the least-squares method. This provides the PAM risk in humans as a function of the N. fowleri concentration in the river. For example, the risk is 8.5 x 10(-8) at a concentration of 10 N. fowleri amoebae per liter.

The present study addresses the impact of wastewater reuse in agriculture on the transmission of protozoan and helminthic infections. For this purpose, an epidemiological study was carried out on two populations of children totalling 608 individuals for protozoan infections and 528 for helminthic infections. Each population comprised an exposed group living in the wastewater spreading area of Marrakech and a control group. Results showed that 72% of the exposed group had protozoan infections. This rate did not exceed 45% in the control group. The pathogenic protozoan infections observed were giardiasis and amoebiasis. Regarding helminthic infections, 73% of the exposed children were infected compared with 30% of the control group. The risk attributable to wastewater reuse in the transmission of pathogenic protozoan and helminthic infections was 41% and 43%, respectively. Children of the spreading area are therefore more exposed to detectable risks from parasitic helminths and protozoa than the control children.

Intestinal protozoan disease diagnosed in pregnancy is mostly controlled by symptomatic treatment. Specific therapy can be delayed until after delivery. Only severe cases, i.e. continued diarrhea leading to malnutrition of either mother or fetus, require an immediate specific drug therapy, which might be harmful to the fetus due to toxic and teratogenic potentials. Vertical transmission of intestinal protozoa has not been described. Invasive protozoan infections can be lethal to the mother making immediate drug therapy mandatory, even if the potentials of fetotoxicity or teratogenicity are known. Vertical transmission occurs independent of maternal symptoms, causing clinical disease in the child either directly after birth or during the first months of life. The knowledge of endemic regions and of the maternal travel history is essential for early diagnosis and treatment of protozoan disease in pregnancy and of congenital protozoan infections.

Naegleria fowleri, Acanthamoeba spp. and Balamuthia mandrillaris are free-living amoebae that occasionally may induce pathology in human beings. CNS disease due to N. fowleri, called "primary" amoebic meningoencephalitis, is acquired after exposure to polluted waters in swimming pools, rivers, and lakes. The clinical course is acute, often fulminant and characterized pathologically by necrotizing hemorrhagic meningoencephalitis, involving mainly the base of the brain, brainstem and cerebellum. In contrast, some Acanthamoeba spp. and B. mandrillaris cause opportunistic, chronic "granulomatous" encephalitis in subjects pathologically or iatrogenically immunocompromised. There are, most likely, foci of protozoa in lung and skin reaching the CNS by hematogenous route. Only Acanthamoeba spp. can also produce severe, subacute keratitis, mainly today in contact lens wearers.

Acanthamoeba culbertsoni is one of the free-living amoebae which are known to be pathogenic to man, causing granulomatous amoebic encephalitis (GAE). In this study, Acanthamoeba culbertsoni was isolated from a water sample of El-Mahmoudia Canal in Alexandria, in July-1993. This was used to infect mice intranasally to study the histopathological picture of the brain and lungs. The neuropathological features consisted of chronic granulomatous encephalitis in which cysts and trophozoites were found. Associated Acanthamoeba pneumonitis with massive consolidation was also observed. Congenital infection of offsprings was reported for the first time in this study.

We report a case of fatal primary amoebic meningoencephalitis (PAM) with Naegleria fowleri in a 13-year-old male, and review the clinical course and diagnostic autopsy findings. The boy developed the infection after swimming with relatives in the Rio Grande and in a holding tank containing water pumped from the river. The clinical and neuropathologic features of PAM are presented. The microscopic features of motile unicellular organisms with pathognomonic broad, lobate pseudopodia are diagnostic and, if recognized before death, allow for timely treatment. A public health investigation into this case implicated river water from the Rio Grande polluted with sewage as the infection source. Exposure to polluted river water from some areas of the Rio Grande may represent a risk factor for infection with Naegleria fowerli, because the high levels of coliform bacteria found in sewage and the warm, sluggish water of the river are favorable growth conditions for the amoebae. Because the Rio Grande is an international border, this case illustrates the importance of international cooperation in pollution control in the prevention of a potentially fatal infectious disease.

The pathogenicity of a Philippine isolate of Naegleria sp. was evaluated using 3-4 week-old mice as experimental animals. Results showed that only the massive doses of 10(6) and 10(7) amebae/mouse inoculated intranasally could successfully establish ameba infection in the brain and cause death after 2-6 days. The effect of the ameba on the mortality rate of inoculated mice was dose-dependent. The amebae were recovered in the brain when inoculated through intracerebral and intranasal routes and in the lungs, liver, and intestines when administered through intranasal and oral routes. By intraperitoneal inoculation, recovery of amebae was positive in all major organs except in the heart. Intravenous inoculation resulted to positive recovery in the lungs, spleen, liver, and heart. Infectivity of the ameba isolate in major organs was route-dependent.

An attempt was made to recover soil amoebae from the air during the harmattan in Zaria, Nigeria. Non-nutrient agar plates seeded with Escherichia coli were used as settle plates and exposed to the air for 30 minutes to four hours, after which they were incubated at 27 degrees C or at 37 degrees C. A total of 38 strains of amoebae were cultured: 21 of the genus Hartmannella, eight Naegleria, four Schizopyrenus, three Didascalus and two Tetramitus. Three pathogenic species, H. culbertsoni, N. fowleri and H. rhysodes, were also recovered and all killed mice. These results suggest the possibility of airborne primary amoebic meningoencephalitis infections in Nigeria.

Certain enteric ailments are particularly common among homosexual men. They are primarily infectious diseases and include not only such common venereal diseases as gonorrhea and syphilis but also infections not usually regarded as being sexually transmitted. Among the latter are shigellosis, salmonellosis, giardiasis, and amebiasis. Patients' symptoms are non-specific and seldom helpful in diagnosing particular diseases. The practitioner must be prepared to identify a number of infections with similar presentations that may occur singly or together in gay men. Gonorrhea is probably the most common bacterial infection in gay men. Carriage rates as high as 50% have been reported, and extra-genital carriage is common; this necessitates culturing the urethra, rectum, and pharynx. Procaine penicillin G is the treatment of choice for most patients; spectinomycin is probably the drug of choice in penicillin-sensitive patients. In contrast to other venereal diseases, syphilis may have a characteristic protoscopic presentation. Benzathine penicillin G is the treatment of choice for most patients. Lymphogranuloma venereum causes penile lesions and inguinal lymphadenitis in heterosexual men, whereas homosexual men are more prone to proctitis. The disease may mimic Crohn's disease. Recommended treatment includes tetracycline or sulfamethoxazole-trimethoprim. Shigellosis usually presents as an acute diarrheal illness. Patients generally require only supportive treatment with fluids. Herpes simplex viral infection is difficult to diagnose and has several different presentations, including lumbosacral radiculomyelopathy. Symptomatic treatment with sitz baths, anesthetic ointment, and analgesics is recommended. Venereal warts are believed to be caused by the same virus that causes verrucous warts; they are usually found in the anal canal or around the anal orifice. They are commonly treated with 25% podophyllin solution. Parasitic infections include giardiasis, amebiasis, and pinworm infections. Metronidazole may be used in the treatment of symptomatic giardiasis and amebiasis, but it is not approved for the former indication; quinacrine is approved for giardiasis. Pinworm infestation may be treated with pyrantel pamoate or mebendazole. Cure of enteric diseases in homosexual men must be documented.

A strain of Naegleria fowleri, isolated from a child who died of primary amebic meningoencephalitis in Florida, was instilled in the nostrils of a sheep to determine whether livestock are susceptible to infection with free-living amebae. The animal died 7 days later from amebic infection of the central nervous system. N. fowleri were recovered from the brain and spinal cord of the animal. A control, saline-instilled sheep that had been pair-caged with the infected animal remained healthy.

Hepatitis viruses, enteric pathogens, and anorectal infections may commonly be transmitted by various sexual practices. Because of their larger numbers of sexual partners and sexual practices such as anilingus and anal intercourse, homosexual men are at particularly high risk of acquiring hepatitis B, giardiasis, amebiasis, shigellosis, campylobacteriosis, and anorectal infections with Neisseria gonorrhoeae, Chlamydia trachomatis, Treponema pallidum, herpes simplex virus, and human papilloma viruses. The evidence for sexual transmission of these infections as well as their diagnosis and treatment are discussed.