Investigação da circulação silenciosa de ortopoxvírus: estudo em pequenos mamíferos em área endêmica para a vaccínia bovina, Minas Gerais, Brasil

Abstract

Vaccinia virus (VACV), belonging to the genus Orthopoxvirus (OPV), family Poxviridae, is the causative species of bovine vaccinia (BV), an emerging viral zoonosis that mainly affects dairy cattle and milking cattle in Brazil. Since the first records of the disease in the country, at the end of the 20th century, several relevant information about the virus has been revealed, however, the way in which VACV establishes itself in the wild environment is still unknown. On the other hand, studies demonstrate a great participation of rodents and marsupials in the epidemiological cycle of this and other zoonotic species of the genus. In this context, the present work investigated the presence of OPV in samples of small mammals, captured during four field expeditions carried out between February and September 2021, in dairy farms producing artisanal cheese in the municipality of Serro, located in an endemic area for cases of VACV infections in Minas Gerais, Brazil. The animals were captured, euthanized, had their organs collected and taxidermized. Liver and serum samples were submitted to viral DNA extraction and subsequently to qPCR tests for amplification of the C11R, A56L and E9L genes, which can be found in the OPV genome. In addition, serum samples were submitted to the plaque reduction serum neutralization test (PRNT) in order to detect neutralizing antibodies to OPV. Of the 210 captured animals, it was possible to collect 107 liver samples and 142 serum samples. In molecular tests, the tested samples did not show amplification of these genes. However, 5 of the 142 serum samples tested positive in serological tests, demonstrating potential to neutralize OPV. Positive samples were collected from animals captured on different dairy farms, in different environments and at different times of the year. Furthermore, the present work detects, for the first time, the presence of anti-OPV neutralizing antibodies in samples of Marmosops incanus, a marsupial species. The observed data reinforce the participation of small mammals in the wild cycle of VACV and discuss the expansion of the virus to new species of small mammals, however, the reservoir animal remains unknown. Such observations demonstrate the demand for further surveillance studies to develop preventive measures for VB outbreaks and a better understanding of how this virus maintains itself in the environment.