Capybaras found dead from rabies on Brazilian island underline need to monitor virus

Three capybaras (Hydrochoerus hydrochaeris) died from rabies on Anchieta Island in the municipality of Ubatuba, São Paulo state, Brazil, between December 2019 and January 2020. One was found dead, and two exhibited hindlimb paralysis before dying. Analysis of their brains conducted at Instituto Pasteur in São Paulo city showed the cause of death to be rabies encephalitis.

An article reporting the findings of the study is published in the journal Veterinary Research Communications. This is the third report of rabies in capybaras in the world, and the second in Brazil.

The study also detected that the strain of rabies found in the three animals was the same as the variant present in the Common vampire bat (Desmodus rotundus).

“In recent years there has been an increase in reported cases of rabies in wild animals, possibly linked to environmental disturbances that trigger an imbalance in the ecosystems in which D. rotundus lives,” said Enio Mori, principal investigator for the study. Mori is a researcher at Instituto Pasteur, an arm of the São Paulo State Department of Health, and a professor in the Program of Graduate Studies in Experimental and Comparative Pathology at the University of São Paulo’s School of Veterinary Medicine and Animal Science (FMVZ-USP).

Another recent case involved a White-eared opossum (Didelphis albiventris) infected with the rabies virus and found dead in Campinas, one of the largest cities in the state.

Anchieta Island is a state nature park. The capybaras died there not long after roof repair work was carried out on a previously abandoned building, forcing a bat colony to roost elsewhere.

“At times like these, bat colonies are severely stressed, fights are frequent, and they may infect each other with rabies, increasing the probability of transmission to other wild animals on whose blood they feed, such as capybaras,” Mori said.

Generally speaking, deforestation also contributes to a rise in rabies cases. Less forest means fewer wild animals, whose blood is the sole source of food for vampire bats. The bats have to find other prey, frequently turning to livestock and even humans, and potentially transmitting rabies to them in the process.

Variants

The infected capybaras were found by employees of Fundação Florestal, the agency that manages São Paulo’s conservation units, including Anchieta Island State Park. Samples of the animals’ brain tissue were sent to Instituto Pasteur, part of a network of rabies surveillance laboratories in the region. Researchers and technical staff there first tested the samples for the rabies virus antigen for triage purposes, concluding that all three cases tested positive.

Next, they isolated the virus for confirmation testing. One of the samples was in poor condition, making this test impossible, but they were able to sequence the genome of a viral particle. The tests confirmed the presence of the rabies virus variant found in vampire bats, pointing to possible transmission by bite.

The only other case of rabies in capybaras in Brazil was published in 1985. Elsewhere in the world, only one case has been reported, occurring in northern Argentina in 2009. The viral variant in question has been typed only in this latest study.

There have been no reports of human rabies transmitted by capybaras. However, accidents in which people are bitten by these animals usually cause severe wounds. Whether capybara saliva may contain the virus, as does bat saliva, is unknown (bats are the primary rabies reservoir in South America).

“Epidemiological surveillance must therefore continue, so we can find out what role capybaras play in the viral cycle, for example. It’s perfectly possible they’re a dead-end host and die without transmitting the virus to other animals. But we need more research to confirm this,” Mori said.