Pesquisa de infecção por Cryptosporidium sp., achados epidemiológicos, clínicos e lesões associadas em bezerros

Abstract

Intestinal disorders that course with diarrhea in calves are complex and multifactorial. In recent years the protozoan Cryptosporidium sp. has emerged as an important cause of disease in calves in the first weeks after birth. This coccidian can act as a primary agent or in conjunction with enteropathogens such as Rotavirus, Coronavirus, Escherichia coli, and Salmonella spp. Of 38 reported species of Cryptosporidium, four cause infection in cattle; C. parvum, C. bovis, C. andersoni and C. ryanae, with variations in age of the affected animals and location in digestive tract. Newborn calves are more susceptible to C. parvum, identified as an important cause of diarrhea and high elimination rates around 15 days of age, in addition to its zoonotic potential. C. parvum binds to jejunal and ileal enterocytes, leading to villous atrophy, and binds to crypts in the colon. The aim of this study was to identify infection by Cryptosporidium sp. in calves up to one year of age sent for necropsy at the Veterinary Pathology Sector of the Department of Veterinary Medicine of the Faculty of Zootechnics and Veterinary Medicine of the Federal University of Lavras (SPV-DMV-FZMV-UFLA), through cytology and histopathology, identify related lesions, and whether cryptosporidiosis was the cause of death. Calves up to 12 months of age with a history of diarrhea or not, sent to the SPV-DMV-FZMV-UFLA, from properties of the Campo das Vertentes, South and Southwest regions of Minas Gerais, from April 2021 to May 2023 were examined. Samples of intestinal content were collected at necropsy, centrifuged and the sediment distended on microscopy slides, which were dried, fixed with methanol, stained with the modified Ziehl Neelsen technique (ZNM), and then, evaluated under a light microscope, with classification of the intensity of infection. Intestine fragments and other organs and tissues were collected, fixed in 10% buffered formalin, processed for histopathology and stained with hematoxylin and eosin (HE) for microscopic analysis. The Periodic Acid-Schiff (PAS) histochemical technique was used to demonstrate Cryptosporidium sp. in histological gut sections. During the study, 85 calves of up to 12 months of age were necropsied, with a predominance of females, Holstein breed and intensive rearing, with suckling calves kept in individual and collective pens. Structures of Cryptosporidium sp. were found in nine calves at microscopic evaluation. All positive calves were six to 21 days old. The ZNM staining clearly showed the protozoan in the intestinal contents, being an interesting technique for the diagnosis of the infection. In the histological evaluation in HE, structures of the protozoan were observed on the surface of the intestinal villi, rounded and weakly basophilic, and the PAS staining was a useful tool for highlighting these structures, which were stained in blue to purplish. The results showed that, although Cryptosporidium sp. is a pathogen often mentioned as a cause of diarrhea in calves, especially suckling calves of dairy herds, the infection was not the most important cause of illness or death, even in calves up to 30 days old, considered the most susceptible.