Found in 2021 in Parque Bosque dos Jequitibás, central region of Campinas, the body of a female white-eared opossum (Didelphis albiventris), mammal also known as saruê or possum, had the cause of death determined by a group of researchers from the Adolfo Lutz Institute and USP (University of São Paulo), as well as health professionals from public institutions in the municipalities of São Paulo and Campinas : meningoencephalitis caused by infection with the rabies virus.
Published in the journal Emerging Infectious Diseases, the result raises an alert about the presence of the virus, which is deadly to humans, in the urban environment.
“The dog rabies variant is no longer detected in the State of São Paulo due to the success of vaccination campaigns for domestic animals. Therefore, it is important to monitor other mammals that may be vectors of the virus, especially animals neglected by this type of surveillance, like opossums”, warns Eduardo Ferreira Machado, who conducted the work during his doctorate at the Faculty of Veterinary Medicine and Animal Science (FMVZ-USP) with a scholarship from Fapesp.
The neurological signs of the disease detected in the animal suggest the form that causes paralysis and is transmitted by bats. The detection of viral particles in other organs also indicated that the infection was in the systemic spreading phase.
The opossum was one of 22 tested for rabies and other diseases by the team in 2021, as part of an epidemiological surveillance project carried out in partnership with the São Paulo Municipal Health Department and the Campinas Zoonosis Control Center.
In the same year, the team also analyzed 930 bats, 30 of which tested positive for rabies. Among those infected, the majority (17 or 56.7%) were frugivorous species of the genus Artibeus. The other 13 (43.4%) were insectivores from three different genera.
Bridge to humans
Transmission between bats and opossums can occur through interaction between the animals, which compete for habitats, both natural (such as the top of trees) and those provided by humans (attics of houses, for example).
In 2014, a case of rabies in a cat was reported in Campinas (SP). The virus was a variant found in bats. Like cats, opossums can also prey on these animals, which leads to the most likely hypothesis for transmission.
The researchers also highlight that, of the 22 possums analyzed, 15 had been killed by dog attacks. “Dogs could be a bridge between opossums and us, bringing rabies and other diseases to humans. This is also why it is important to monitor wild animals that live in cities”, adds Machado.
According to José Luiz Catão Dias, professor at FMVZ-USP and Machado’s advisor, opossums are strategic for this type of surveillance, as they adapt very well to urban environments, without necessarily ceasing to interact with wild areas.
“Even so, they are very neglected. Almost nothing is known about the diseases they can have and, eventually, transmit to us”, says the researcher, who coordinates the project “Comparative pathology and investigation of diseases in neotropical marsupials, order Didelphimorphia: a proposal for surveillance in a group of mammals neglected in wildlife health studies”, supported by Fapesp.
The authors recall that a study from the 1960s suggested that opossums were resistant to the rabies virus, an argument that gained strength due to the fact that there are few reports of cases of the disease in these animals.
Low body temperature (between 34.4° C and 36.1° C) and the low chance of surviving an attack by a rabid animal have been suggested as the likely causes of the low occurrence of the disease in opossums in North America, since wild carnivores are natural reservoirs of the virus.
The Brazilian study, however, shows that transmission occurs and needs to be monitored.
Researchers continue to investigate dead animals that arrive at the Pathology Center of the Adolfo Lutz Institute, both to monitor the presence of rabies and other diseases.
One of the ideas for continuing studies is to establish partnerships with institutions in other countries that carry out surveillance of marsupials such as opossums, for example, Australia.
“There they have a lot of experience in this area and we can make comparisons that are useful for both countries”, concludes Catão.
The article Naturally Acquired Rabies in White-Eared Opossum, Brazil can be read here.