Sarcocystis bertrami em tecidos de equinos da Bahia: frequência de infecção, análise ultraestrutural e bioensaio em cães

Abstract

Horses are hosts of protozoa from the genus Sarcocystis, whose species are known as S. bertrami (synonymous: S. fayeri) and S. neurona. The first one has low pathogenicity for horses, being associated, sporadically, with the occurrence of myositis in this animal species; in humans, intoxication has been reported after consumption of raw or undercooked equine meat, containing viable cysts of the parasite. S. neurona, in turn, is the main agent of equine protozoal myeloencephalitis (EPM). The aim of the study was to characterize by morphological and molecular methods, Sarcocystis spp. with potential for the development of sarcocysts in equine muscles obtained in the state of Bahia, as well as the performance of a bioassay in dogs for morphological and molecular evaluation of the parasitic forms of Sarcocystis spp. excreted in canine stool. The study was carried out using muscle fragments collected from 51 horses, which were inspected macro- and microscopically through techniques such as squash, tissue maceration, acid pepsin digestion, histology and transmission electron microscopy - TEM for the presence of cysts or bradyzoites. Aliquots of these samples were processed for DNA extraction and molecular analysis. Part of the muscle tissue that had cysts was administered to the dogs in the bioassay, using the proportion of 40 grams/animal over three consecutive days. Infection by Sarcocystis spp. reached a frequency of 100% in the evaluated horses. In histological evaluation, several sarcocysts were noted, which were highly septate, randomly dispersed within the muscle fibers, with variable sizes and shapes according to the section of the cut. Through TEM, each cyst was delimited by the membrane of the parasitophorous vacuole, whose shape was wavy and covered by an electron-dense layer, a granular layer with variable thickness depending on the region of observation, and in some regions, projections were noted slanted or bent digitiform villous. Due to these characteristics, the cyst was classified as type 11. The dogs used in the bioassay received muscle fragments and excreted oocysts and/or sporocysts for 13 and 47 days, with pre-patent periods of 13 and 23 days. Inside the oocysts, two sporocysts, each containing four sporozoites, residual granules and absence of Stieda's body were observed. The sporocysts had similar dimensions to each other, with sizes of 12.78 - 15.28 (14.19 ± 0.53) x 8.95 – 10.86 (10.06 ± 0.44) µm. The excretion of oocysts/sporocysts over the days was quite variable, with an daily average amount of 1.8 x103 sporocysts/µL. The high frequency of infection by Sarcocystis spp. in muscle fragments of horses destined for human consumption may represent a risk to public health, due to the enterotoxigenic potential of this parasite for humans. Dogs act as large disseminators of the parasite in the environment, a proven fact in this present study, in which a relatively long excretion pattern (47 days) was observed when compared to other species of coccidia excreted by dogs, such as Neospora caninum and Hammondia heydorni, whose patent periods are approximately one to two weeks.