Detection of Anti-Orthopoxvirus Neutralizing Antibodies in Three Dogs and One Cat from a Household with a Confirmed Human Mpox Case in Brazil

Mpox is a zoonotic infectious disease caused by the species Orthopoxvirus monkeypox (MPV), which is becoming an increasing public health concern. While human-to-human transmission of the virus is well established, the role of domestic animals in MPV infection remains poorly understood. Investigating how the virus is transmitted among humans, dogs, and cats can improve our understanding of the disease’s pathogenesis and help develop strategies to limit its dissemination during future outbreaks. In this study samples were collected from four domestic animals (three dogs and one cat) in May 2023. These animals lived in a household where a human mpox case had been confirmed by PCR in March 2023, approximately 2 months before animal sampling. A plaque reduction neutralization test (PRNT) using vaccinia virus was performed to detect anti-orthopoxvirus (OPV) neutralizing antibodies (nAbs). Our data demonstrated that anti-OPV nAbs were present in samples obtained from three dogs and one cat with neutralization titers ranging from 1:5 to 1:20. These results indicate that the domestic animals were exposed to OPVs after contact with an individual with confirmed mpox, suggesting possible human-to-animal transmission within a household. Nevertheless, due to the cross-reactive immune response among OPVs, and the endemic circulation of vaccinia virus in Brazil, it is not possible to determine the specific viral species based solely on PRNT results. Therefore, these serological findings should be interpreted as evidence of OPV’s exposure rather than confirmed MPV infection.