Ehrlichiose Monocítica Equina: características biológicas de gastrópodes e trematódeos envolvidos na transmissão de Neorickettsia risticii

Abstract

Neorickettsia risticii is an obligatory leukocytes intracellular parasite, the etiologic agent of Equine Monocytic Ehrlichiosis (EME), known as "Potomac Horse Fever". It was first described in 1979 in the State of Maryland, in the vicinity of the Potomac River, United States. It is a disease of great importance in the creation of horses in the southern Brazil, especially the creole s breed, presenting the diarrhea as the main symptom, which can deteriorate and lead to death or complications such as laminitis. Contamination of animals possibly occurs by the oral route, being related to digenetic trematodes of aquatic environments, which in turn require more than one host to complete its life cycle. The location of the horses in overflowed regions provides an increase in the ingestion of aquatic vectors, making higher the chances of contracting the infection, especially in the months of higher temperatures, when the EME presents its characteristic seasonal peaks of occurrence. The objectives of this study were to investigate the species of Heleobia, the first intermediate host of N. risitcii in an endemic area for EME (rural property in Arroio Grande), in order to estimate its rate of parasite contamination. We evaluated the effect of salinity on the survival of mollusk of Heleobia piscium specie, as well as its reproduction and emission frequency of cercariae. Through the cultivation of trematodes in membrane chorioallantoic of chicken eggs, we sought the adult form of the parasite housed in gastropods. The snails found during the collections were classified as Heleobia piscium, noting that 6,24%, among 962 dissected gastropods presented themselves parasitized. Cercarial output occurred in an environment with variable salinity to 12 , which indicates partially the adaptability of the species in estuarine regions. There was no satisfactory results regarding the cultivation of trematodes in chorioallantoic membrane, possibly due to the high specificity of the technique required. Several parameters have been analyzed and the outcomes represent a starting point for the establishment of a specific methodology for obtaining the adult trematode. The results presented are important for the elucidation of the biological cycle of the parasite analysed in this study, contributing to highlight the epidemiology of EME, serving as the basis for future researches that aim to minimize its impact on the creation of horses in Rio Grande do Sul.