Female white-eared possum ( Didelphis albiventris ), found dead in 2021 in the Bosque dos Jequitibás park in the center of Campinas, one of the largest cities in the state of São Paulo, Brazil, died of rabies meningoencephalitis, according to a group of researchers from the University of São Paulo (USP) and Adolfo Lutz Institute (IAL), the regional reference laboratory working with health professionals associated with public institutions in the city of São Paulo and Campinas.
It is reported in an article published in the journal Emerging infectious diseases the finding serves as a signal of the presence of the virus, which is deadly to humans, in the urban environment.
Canine rabies is no longer found in the state of São Paulo thanks to the success of vaccination campaigns for domestic animals. For this reason, it is important to monitor other mammals that may act as vectors for the virus, particularly animals overlooked by this type of surveillance, such as opossums.”
Eduardo Ferreira Machado, first author of the paper
He conducted the research for his PhD at the School of Veterinary Medicine and Animal Husbandry (FMVZ-USP) with a scholarship from FAPESP.
The neurological signs of the disease found in the animal point to the form of rabies that causes paralysis and is transmitted by bats. Virus particles identified in other organs also indicate that the infection is in the phase of systemic spread.
The opossum was one of 22 tested for rabies and other diseases by the group in 2021 as part of an epidemiological surveillance project conducted in partnership with the Ministry of Health of the City of São Paulo and the Center for Zoonoses Control in Campinas.
That year, the team analyzed 930 bats, 30 of which tested positive for rabies. More than half of them (17 or 56.7%) belong to frugivorous species of the genus Artisanal . The rest (13 or 43.4%) were insectivorous and belonged to three different genera.
A bridge to the people
Transmission between bats and possums can occur through their interaction, as these animals compete for habitats in nature, such as treetops, and in man-made environments, such as roof gables or backyards, for example.
In 2014, a case of cat rabies was registered in Campinas. The infection was traced to a viral variant found in bats. Both cats and possums can hunt bats and this is the most likely route of transmission.
The researchers also noted that 15 of the 22 possums analyzed were killed by dogs. “Dogs can be a bridge between opossums and us, bringing rabies and other diseases to humans. That's why it's important to monitor wild animals that live in cities,” Machado said.
According to José Luiz Catão-Dias, co-author of the paper and advisor to Machado at FMVZ-USP, opossums are key to this type of monitoring because they adapt well to urban environments without necessarily ceasing to interact with forested areas.
“However, they are overlooked. Hardly anything is known about the diseases they can have and can transmit to us,” said Catão-Dias, who is principal investigator and recipient of the project “Comparative Pathology and Disease Research in Neotropical Marsupials, Order Didelphimorphia: Proposal for monitoring a group of mammals neglected in wildlife health studies', supported by FAPESP.
The authors note in the paper that a study conducted in the 1960s led to initial suggestions of resistance to the rabies virus among opossums, a suggestion reinforced by the paucity of reports of rabies in these animals.
The low prevalence of rabies among possums in North America, where wild carnivorous mammals are natural reservoirs for the virus, is explained by their low body temperature (34.4 °C-36.1 °C) and the minimal possibility of surviving an attack by a rabid animal . However, the Brazilian study shows that transmission does occur and should be monitored.
Researchers continue to analyze dead animals brought to the IAL Pathology Center to monitor for the presence of both rabies and other diseases. They plan to partner with institutions in other countries, such as Australia, so they can monitor opossums and other marsupials.
“The Australians have a lot of experience in this area. We can make comparisons that will be useful for both countries,” said Catão-Dias.
source:
São Paulo Research Foundation (FAPESP)
Journal reference:
Ferreira-Machado, E., and others . (2023). Naturally acquired rabies in a white-eared possum, Brazil. Emerging infectious diseases . doi.org/10.3201/eid2912.230373.