Presence of Anti-T. cruzi Antibodies in Inhabitants and Dogs of Two Rural Settlements in the Sierra de Los Tuxtlas, Veracruz, Mexico.

PURPOSE: The aim of this study was to identify the risk factors associated with house infestation by Triatoma dimidiata as well as with Trypanosoma cruzi infection in humans and owned dogs in two rural communities from the municipality of Catemaco, Veracruz, Mexico. METHODS: One hundred and 16 human blood samples and 34 dog blood samples were collected. The presence of anti-T. cruzi antibodies was determined using four different ELISA assays. Moreover, reactive ELISA sera from humans and dogs were processed by indirect immunofluorescence (IFI) to confirm the presence of anti-T. cruzi antibodies. RESULTS: Serologic tests for T. cruzi infection showed a prevalence of 5.1% (6/116) in humans and of 50% (17/34) in owned dogs. CONCLUSION: The presence of animals (dogs, chickens and wild animals), as well as some characteristics of house construction were identified as risk factors for infestation and infection. Complementary studies must be carried out to allow a better understanding of the transmission dynamics in the state of Veracruz, Mexico, and the implementation of adequate control programs.

Natural infection with Trypanosoma cruzi in three species of non-human primates in southeastern Mexico: A contribution to reservoir knowledge.

The mechanisms of infection and dispersion of Trypanosoma cruzi among animals, especially in the sylvatic environment, are still not entirely clear, and various aspects of the transmission dynamics of this parasite in the sylvatic environment are still unknown. T. cruzi is a parasite with a great biological and genetic diversity that infects a wide variety of hosts, therefore, transmission cycles of this parasite are complex. The objective of this study was to determine the prevalence of T. cruzi infection and analyze the genetic variability of the discrete typing units (DTUs) of the parasite in three non-human primate species (Alouatta palliata, Alouatta pigra, and Ateles geoffroyi) in southeastern Mexico. A total of one hundred sixty-four serum samples (42 samples of A. pigra, 41 samples of A. palliata (free-ranging) and 81 samples of A. geoffroyi (hosted in care centers)) were analyzed for the detection of anti-T. cruzi antibodies by ELISA assays. The seroprevalence of infection was 23.39% in A. palliata, 21.40% in A. pigra and 16.27% in A. geoffroyi. Additionally, presence of parasite DNA was assessed by PCR, and the identification of DTUs was performed by real-time PCR coupled to High Resolution Melting (qPCR-HRM). Different DTUs (TcI, TcII, TcIII, TcV and TcVI) were found in the analyzed monkeys. In addition, infection of monkeys was not associated with age or gender, but it was associated with the species. This study reveals the risk of infection in the study area and that the different DTUs of the parasite can coexist in the same habitat, indicating that T. cruzi transmission in the study area is very complex and involves many ecological factors. However, there is a need for long-term studies of host-parasite interactions to provide a solid understanding of the ecology of these species and to understand the dispersion strategies of T. cruzi.

A survey of zoonotic pathogens carried by house mouse and black rat populations in Yucatan, Mexico.

The house mouse (Mus musculus) and the black rat (Rattus rattus) are reservoir hosts for zoonotic pathogens, several of which cause neglected tropical diseases (NTDs). Studies of the prevalence of these NTD-causing zoonotic pathogens, in house mice and black rats from tropical residential areas are scarce. Three hundred and two house mice and 161 black rats were trapped in 2013 from two urban neighbourhoods and a rural village in Yucatan, Mexico, and subsequently tested for Trypanosoma cruzi, Hymenolepis diminuta and Leptospira interrogans. Using the polymerase chain reaction we detected T. cruzi DNA in the hearts of 4·9% (8/165) and 6·2% (7/113) of house mice and black rats, respectively. We applied the sedimentation technique to detect eggs of H. diminuta in 0·5% (1/182) and 14·2% (15/106) of house mice and black rats, respectively. Through the immunofluorescent imprint method, L. interrogans was identified in 0·9% (1/106) of rat kidney impressions. Our results suggest that the black rat could be an important reservoir for T. cruzi and H. diminuta in the studied sites. Further studies examining seasonal and geographical patterns could increase our knowledge on the epidemiology of these pathogens in Mexico and the risk to public health posed by rodents.

A combination DNA vaccine encoding nucleoside hydrolase 36 and glycoproteine 63 protects female but not male hamsters against Leishmania mexicana.

Leishmaniasis is a group of diseases caused by protozoan parasites of the Leishmania genus. Previous studies have shown that a DNA vaccine encoding Leishmania donovani antigen nucleoside hydrolase 36 and L. mexicana glycoprotein 63 is protective in mice. We investigated here the efficacy of this DNA vaccine to induce protection in golden hamsters. Male hamsters were more susceptible to infection by Leishmania mexicana than females. Following immunization with two doses of the DNA vaccine, only females resulted protected while males developed normal lesions.

Variations in sex ratio, feeding, and fecundity of Triatoma dimidiata (Hemiptera: Reduviidae) among habitats in the Yucatan Peninsula, Mexico.

Chagas' disease is a major public health concern in most Latin American countries and its prevention is based on insect vector control. Previous work showed that in the Yucatan peninsula of Mexico, houses are transiently infested by adult Triatoma dimidiata, which then fail to establish sustained colonies. The present study was designed to evaluate the seasonality and possible causes of the dispersal of sylvatic T. dimidiata toward the houses and the subsequent failure of colonization. Dispersal was highly seasonal and correlated with temperature, pressure, and wind speed. Analysis of sex ratio, feeding status, and fecundity of sylvatic populations of T. dimidiata indicated a rather low feeding status and low potential fecundity, suggesting that seasonal dispersal may be associated with foraging for better conditions. Also, feeding status and potential fecundity tended to improve in the domestic habitat but remained largely suboptimal, suggesting that these factors may contribute to the ineffective colonization of this habitat.

Usefulness of community participation for the fine temporal monitoring of house infestation by non-domiciliated triatomines.

The irregular presence and low abundance of wild triatomines inside domiciles make their detection more difficult than that of domiciled species, so that vector surveillance and evaluation of Chagas disease transmission risk are more challenging. We compared timed manual searches, considered as the gold standard, with community-based collections, for their efficacy at monitoring domestic and peridomestic infestation by non-domiciliated Triatoma dimidiata, and community-based collection was the most sensitive and cost effective. Scaling up community participation permitted investigation of fine temporal variations in infestation by T. dimidiata in over 700 houses. We confirmed a large seasonal infestation during March-July, but weekly and daily collections showed a rather stochastic pattern of bug presence in the houses, even during this period. These data are of key importance for the successful implementation of vector control, and community participation is a method of choice for sustained monitoring of infestation by non-domesticated triatomines.

Dynamics and distribution of house infestation by Triatoma dimidiata in central and southern Belize.

Chagas disease is a major public health problem from South America to Mexico, with approximately 10 million infected people. Chagas disease is known to occur in Belize, but little is known about the prevalence of Trypansoma cruzi infection in the Belizean population or the Chagas vector in this region. An entomologic survey of triatomines in the central and southern region of Belize was thus performed. Triatomines were collected by community participation in 37 villages of the Cayo (central) and Toledo (southern) districts and analyzed for infection with T. cruzi by microscopic examination and polymerase chain reaction. Two hundred fifty-six triatomines were collected in 34/37 villages, indicating a wide distribution, and all were identified as T. dimidiata. The majority (87%) were adults (42% males, 58% females), and 13% were larval stages. The infection rate with T. cruzi was 28%. Triatomines were more abundant during the hot season (March-July) compared with the cooler season (September-February). These results confirm that there is a significant risk for autochthonous Chagas disease transmission in central and southern Belize and suggest a pattern of seasonal infestation by nondomiciliated adult triatomines, which are likely to be closely related to T. dimidiata from Yucatan, Mexico. Further entomologic and epidemiologic studies should be performed to precisely determine T. cruzi transmission risk to humans, as well as the seroprevalence of T. cruzi infection and incidence of Chagasic cardiomyopathy in the Belizean population.

Urban infestation by Triatoma dimidiata in the city of Mérida, Yucatán, México.

The observation of widespread seasonal infestation by Triatoma dimidiata in rural villages around the city of Mérida, Yucatán, México, led us to reconsider the presence of Chagas disease vectors and the risk factors for house infestation in the city itself. Bugs were collected in 150 houses from 30 neighborhoods distributed throughout the city. We observed a widespread infestation by T. dimidiata in the city, with 38% of infested houses and 48% of the collected triatomines testing positive for Trypanosoma cruzi. House infestation by triatomines was greatest during the months of April-June. Infestation risk factors were related with backyard characteristics rather than housing type and quality of housing: houses located in the periphery of the city, with abandoned lots on the sides and large backyards, had a higher risk of being infested, while those with mosquito screens and occasional insecticide spraying in their yards had a lower risk. Several human blood meals were also identified and seropositive patients were distributed through most of the city, confirming the potential for urban transmission of Chagas disease to humans. This study shows that urban Chagas disease should not be neglected and surveillance programs should be implemented to further evaluate the magnitude of the problem.

In vivo and in vitro control of Leishmania mexicana due to garlic-induced NO production.

Leishmania mexicana is the main causal agent of cutaneous leishmaniasis in the Yucatán peninsula in Mexico. Control of this disease is associated with a Th1-type immune response and garlic extract has been reported as a Th1 immunomodulator in BALB/c mice infected with Leishmania major. In this study, we investigated the effect of garlic extracts on L. mexicana infection in vivo and in vitro. Garlic extract reduced footpad lesions in L. mexicana-infected BALB/c mice by inducing IFN-gamma production from T cells. In vitro, garlic extract reduced macrophage infection through induction of nitric oxide (NO) production. Garlic extract may thus act on both T cells and macrophages to stimulate IFN-gamma production and NO synthesis for parasite killing. A 10- to 14-kDa fraction was identified as responsible for the in vitro effect of the whole extract and may lead to the identification of novel immunomodulating drugs and therapeutic alternatives for the treatment of leishmaniasis.

Leishmanicidal evaluation of extracts from native plants of the Yucatan peninsula.

Methanol extracts were prepared from different parts of 18 plants collected in the Yucatan peninsula and evaluated in an in vitro bioassay for leishmanicidal activity against Leishmania mexicana promastigotes. The ten most potent plant extracts (IC(50)<50 microg/ml) were Aphelandra scabra leaves, Byrsonima bucidaefolia bark, Byrsonima crassifolia bark, Clusia flava leaves, Cupania dentata bark, Diphysa carthagenensis leaves, Dorstenia contrajerva whole plant, Milleria quinqueflora roots, Tridax procumbens whole plant, and Vitex gaumeri bark.

Immunotherapy against visceral leishmaniasis with the nucleoside hydrolase-DNA vaccine of Leishmania donovani.

The nucleoside hydrolase (NH36) of Leishmania (L.) donovani is a vital enzyme which releases purines or pyrimidines of foreign DNA to be used in the synthesis of parasite DNA. As a bivalent DNA vaccine, the VR1012-NH36 was immunoprotective against visceral and cutaneous murine leishmaniasis. In this work we tested the immunotherapy against Leishmania (L.) chagasi infection, using two doses of 100 or 20 microg VR1012-NH36 vaccine (i.m. route), and, as a possible immunomodulator, aqueous garlic extract (8 mg/kg/day by the i.p. route), which was effective in immunotherapy of cutaneous murine leishmaniasis. Liver parasitic load was significantly reduced following treatment with 100 microg (91%) and 20 microg (77%) of the DNA vaccine, and by 20 microg DNA vaccine and garlic extract (76%) (p=0.023). Survival was 33% for saline controls, 100% for the 100 microg vaccine, and 83 and 67% for the 20 microg vaccine with and without garlic extract addition, respectively. Garlic treatment alone did not reduce parasite load (p>0.05), but increased survival (100%). The NH36-DNA vaccine was highly effective as a new tool for the therapy and control of visceral leishmaniasis, while the mild protective effect of garlic might be related to an unspecific enhancement of IFN-gamma secretion.

Comparative study of DNA vaccines encoding various antigens against Leishmania mexicana.

Leishmaniases represent an important public health problem in large parts of the world. In the south-east of Mexico, the major species isolated from patients is Leishmania mexicana mexicana, causing localised cutaneous leishmaniasis, and the development of a vaccine is a key objective for the control of this parasite. We thus performed a comparative study of DNA vaccines encoding L. m. mexicana gp63 and CPb, L. m. amazonensis gp46, and L. major LACK to define the best antigen(s) candidate(s). cDNAs encoding these antigens were subcloned into the VR1012 plasmid, and susceptible BALB/c mice were immunised with two i.m. injections of 100 microg of plasmid DNA. All mice immunised with VR1012-GP46, VR1012-CPb and VR1012-GP63 showed increased IgG levels against L. m. mexicana, but not those immunised with VR1012-LACK. Two to three weeks after the last immunisation, mice were challenged by the injection of 4 x 10(6) L. m. mexicana parasites in the foot pad to evaluate protection. Measurement of lesion size indicated that mice immunised with VR012-GP46, VR012-GP63 and VR1012-CPb were partially protected against infection, whereas the other plasmids had no effect. Thus, these plasmids represent good candidates for further development of DNA immunisation against L. m. mexicana.

Update on Chagas' disease in Mexico.

Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi, represents a major public health problem in most of the American continent. As transmission of the parasite is being interrupted in most of South America, the disease remains endemic in various areas of Mexico. We review here some of the information gathered in recent years. Seroprevalence of T. cruzi infection in humans remains relatively high in some areas, and there has been a general increase in the number of chronic cases reported to health authorities in recent years. In fact, chronic chagasic cardiomyopathy appears to be affecting a large number of patients with heart disease, but many cases may be misreported because of the unspecific nature of the clinical symptoms. Epidemiological monitoring of vector and reservoir populations, as well as of human cases is helping focus on endemic areas, but a better coordination and development of these efforts is still needed. Recent studies of parasite biology are in agreement with previous work showing the great diversity of parasite characteristics, and support the need for a regional approach to this zoonosis. Strong and continuing support from health and academic authorities is thus still needed to further improve our understanding of Chagas' disease in Mexico and implement efficient control programs.