Abstract: The American opossum Didelphis virginiana is the marsupial species with the largest geographic distribution in North America, a very important natural host and key to the maintenance and transmission of many zoonotic pathogenic microorganisms of importance in public health, and one of the wild mammals with the greatest adaptation to the human environment, but despite all that very little is known about some physiological aspects in their free-ranging populations. In the present study, basic haematological parameters of 201 opossums from a synanthropic population of D. virginiana in a rural locality of the state of Yucatan, are first described. The average values of haemoglobin, packed cell volume, red blood cells, and eosinophils were higher in males and adults (except eosinophils) than in females and juveniles, respectively, and juvenile opossums had higher values of lymphocytes, neutrophils, and platelets than males. Non-pregnant females had significantly higher values of mean corpuscular volume, lymphocytes and platelets than pregnant ones, while red blood cell count and segmented neutrophils showed higher values in pregnant females. The establishment of the basic haematological parameters for free-ranging populations of D. virginiana is a very useful reference for both the health monitoring of the populations and further studying the host-parasite relationship of some zoonotic pathogens present in the Yucatan Peninsula.

Abstract Introduction Participatory Research (PR) is a tool that can be approached for the analysis of sociocultural, environmental, and public health processes. The participation of school-age childrens in the appropriation of knowledge for the prevention of Chagas’ Disease (CD) can break the cycle of transmission. CD is a public health problem that mainly affects rural endemic communities of developing countries. Objective To develop a strategy for the acquisition and transfer of new knowledge in childs, due to the lack of information about the transmission cycle of the EC. Materials and Methods A cross-sectional study was carried out with a group of 48 childrens from a community in extreme poverty in Yucatan, Mexico. Through PR tools and with the support of parents, ejidal and school authorities, educational workshops were given to children of the basic education to know the cycle of transmission, and to prevent CD due to the abundance of the vector in the study area. A program called “Small Investigators” was implemented to initiate processes of appropriation and socialization of knowledge in the community. Results The new knowledge acquired by the group of children was used and disseminated to their families, partners, and social circles, promoting the prevention of the disease. 182 triatomas were collected at home and peri domicile. Conclusions The new knowledge, attitudes and practices acquired by children under participation schemes is beneficial for the prevention of the Chagas Disease. The official sector is recommended to design the promotion health programs in children under the scheme of the present study in developing countries.

Resumen Introducción La Investigación Participativa (IP), es una herramienta que puede abordarse para el análisis y mejoramiento de procesos socioculturales, medioambientales, y de salud pública. La participación de niños en edad escolar en la apropiación del conocimiento sobre la Enfermedad de Chagas (EC), puede romper el ciclo de transmisión. La EC es un problema de salud pública que afecta principalmente a comunidades rurales endémicas de países en desarrollo. Objetivo Desarrollar una estrategia para la adquisición y transferencia de nuevos conocimientos en niños y niñas, debido a la falta de información acerca del ciclo de transmisión de la EC . Material y Métodos Estudio socioambiental, realizado con un grupo de 48 niños y niñas de una comunidad en pobreza extrema en Yucatán, México. Mediante herramientas de IP y con el apoyo de las familias, autoridades ejidales y escolares, se impartieron talleres educativos a niños y niñas de educación básica para conocer el ciclo de transmisión de la EC y ayudar a prevenirla, debido a la abundancia del vector en el área de estudio. Se implementó un programa denominado “Pequeños Investigadores”, para iniciar procesos de apropiación y socialización del conocimiento en la comunidad. Resultados El nuevo conocimiento adquirido por el grupo de niñas y niños fue aprovechado y compartido a sus familias, compañeros de escuela, y círculos sociales, fomentando la prevención de la enfermedad. Fueron recolectados 182 triatomas a nivel domiciliar y peri domiciliar. Conclusiones Los nuevos conocimientos, actitudes y prácticas adquiridos por los niños y las niñas bajo esquemas de participación, resulta benéfico para la prevención de la EC. Se recomienda al sector oficial la participación en la promoción de la salud en niños y niñas bajo el esquema del presente estudio en países en desarrollo.

Rickettsia felis is an emergent pathogen and the causative agent of a typhus-like rickettsiosis in the Americas. Its transmission cycle involves fleas as biological vectors (mainly Ctenocephalides felis) and multiple domestic and synanthropic mammal hosts. Nonetheless, the role of mammals in the cycle of R. felis is not well understood and many efforts are ongoing in different countries of America to clarify it. The present study describes for the first time in Mexico the infection of two species of opossum (Didelphis virginiana and D. marsupialis) by R. felis. A diagnosis was carried out from blood samples by molecular methods through the gltA and 17 kDa genes and sequence determination. Eighty-seven opossum samples were analyzed and 28 were found to be infected (32.1%) from five out of the six studied localities of Yucatan. These findings enable recognition of the potential epidemiological implications for public health of the presence of infected synanthropic Didelphis in households.

In México, the role of mammals in the transmission cycle of Trypanosoma cruzi is poorly known. In the State of Yucatán, an endemic area of Chagas disease, both Didelphis virginiana and D. marsupialis occur sympatrically. However, until now, only the former species had been found infected with T. cruzi. To evaluate the role of D. virginiana in a peridomestic transmission, nine periods of capture-recapture were performed around the village of Dzidzilché, Yucatán. The sex, age, reproductive status, location, and presence of infection with T. cruzi were recorded for each opossum. The chromosome morphology was used to identify the opossum species. T. cruzi was identified by the presence of pseudocysts of amastigotes in cardiac muscle fibers of Balb/c mice inoculated with strains isolated from opossums. However, xenodiagnosis was the best diagnostic method. Triatoma dimidiata, the vector, were collected in and around the opossums' nests, and human dwellings; and were checked for T. cruzi. From 102 blood samples of D. virginiana examined 55 (53.9%) were positive to T. cruzi, the only two D. marsupialis captured were negative. Significant differences were found between infection, and both sex and reproductive condition. Eight out of 14 triatomines collected in peridomestic nests (57.1%), and 32 of 197 captured inside houses (16.3%) were found infected, suggesting a peridomestic transmission. The statistically high abundance of infected opossums and triatomines during the dry season (March to May) suggested the existence of a seasonality in the peridomestic transmission of T. cruzi in Dzidzilché.