Human Rabies in Brazil: A Warning of Epidemiological Changes

Roxana Tabakman

July 27, 2022

Until 2022, there hadn't been a case of human rabies recorded in the Federal District of Brazil for 44 years. And already to date, there have been five cases nationwide: one teenager in Brasília and, according to the Ministry of Health, four in Minas Gerais. Although there has been a sharp decline in the number of cases in recent decades, and not one case of dog-mediated rabies since 2015, this zoonotic viral disease has not been eliminated in Brazil.

"Thanks to mass campaigns aimed at getting domestic animals vaccinated, Brazil has had great success controlling rabies in the last few decades," epidemiologist Marco Horta, MD, PhD, told Medscape Medical News. "However, these cases in Minas Gerais and in the Federal District call attention to the fact that rabies is showing up in places where, for many years — even decades — it hasn't been reported. In recent years, there have been human cases in the state of Rio de Janeiro, both in the city of Rio de Janeiro and the rural area of Angra dos Reis. Again, these are places where there hasn't been a report in a long time. So, [the disease] has been showing up in unexpected places."

In addition to epidemiology, Horta, a well-known researcher affiliated with the Oswaldo Cruz Foundation (Fiocruz), specializes in epidemiologic surveillance of emerging and reemerging diseases. In March, he published an article to raise awareness of the change in the epidemiological profile of rabies in Brazil (bats have become the main reservoirs of the disease today) and how it affects the surveillance and disease control actions.

According to Horta, canine and feline rabies may no longer be much of an issue for humans. Even in incidents involving cats, it is no longer the domestic animal variant of the virus that is being transmitted; instead, it is the bat antigenic variant. Postexposure prophylaxis (PEP) should be given if there is a chance that rabies has been transmitted (for example, through a bite or a scratch), and not only by dogs, cats, or bats (of any species), but also by marmosets, monkeys, foxes, raccoons, coati, opossums, or capybaras, even those that have been domesticated.

Horta emphasized that physicians need to know that this disease has appeared in unlikely places. Therefore, it is important to watch for the signs and symptoms, as well as to consider rabies as a possible diagnosis when treating patients.

Test Your Knowledge

Administering PEP can prevent rabies. This communicable viral disease is caused by a virus of the Lyssavirus genus within the family Rhabdoviridae and has a case fatality ratio bordering on 100%. PEP should be given whenever an individual has been bitten by a suspected rabid animal. Although they are the first to interact with victims of an animal attack, primary healthcare staff are far from having adequate knowledge and awareness of rabies and how to treat it.

This lack of preparedness came to light in a study that analyzed the more than 4 million antirabies medical consultations that were reported in Brazil from 2014-2019. Prophylactic procedure was inappropriate in 42.2% (n = 1,582,411) of cases. Inappropriate or insufficient prophylactic procedures can lead to cases of human rabies and patient death and, when excessive, can lead to shortage of immunobiological products.

Similarly, in another study, several knowledge gaps were identified, this time through questionnaires given to health professionals administering PEP in three Brazilian states: Rio Grande do Sul, Santa Catarina, and Rio Grande do Norte. Most of these individuals struggled to identify a "suspected" rabid dog, according to the Ministry of Health guidelines. The health condition of the dog and characteristics of the wound are essential criteria to guide the indication of PEP. The analyses showed that only 11% of professionals prescribed the appropriate PEP under various dog-bite patient scenarios.

Brazil is facing problems with PEP, both in terms of its excessive use and its limited availability. Researchers who analyzed 10 years (2008-2017) of national surveillance data on dog bites estimated that Brazil could save up to $6 million per year on vaccines by reducing the number of doses administered during prophylaxis and adopting the intradermal vaccine delivery technique following the latest World Health Organization recommendations. They also found that false positive cases were frequently reported to the national surveillance system.

In the most recent update to the "Brazilian Protocol for Human Rabies Prophylaxis: Preexposure, Postexposure, and Reexposure," the Ministry of Health provided all the recommendations for healthcare professionals as well as guidance indicating a four-dose PEP regimen — days 0, 3, 7, and 14 — with equine rabies immune globulin (eRIG) or human rabies immune globulin (hRIG).

Preserving the Gains

Despite the change in the epidemiological profile of rabies in Brazil, people should not stop getting their pet dogs and cats vaccinated. "If there's a lapse in vaccination campaigns, there's a huge risk that rabies will come back," said Horta.

Vaccinating the general population against rabies is not recommended, as the incidence rate in humans is very low. Nevertheless, if there is an attack in the area involving a suspected rabid animal, prophylaxis must be administered. In addition, individuals at risk for exposure to the virus should be vaccinated. This would include veterinarians, biologists, agricultural technicians, veterinary technicians, pet store employees, and ecotourism guides.

The number of rabies vaccine doses administered has been decreasing in recent years. From 2015-2020, the number of doses was 1 million, 583,000, 443,000, 335,000, 260,000, and 127,000, respectively. The risk of vaccine and antirabies serum stock shortage for rabies control is still a concern, as some municipalities have postponed or suspended animal rabies vaccination campaigns. This was either due to the lack of transfer of vaccines sent by the Brazilian Ministry of Health to state governments, or to the interruptions in dose administrations during the peak of the COVID‑19 pandemic.

Another Health Crisis?

Controlling the circulation of the virus among wild animals is very complicated, "practically impossible due to environmental issues," said Horta.

A multifactorial system — including deforestation, land use, exchange of natural ecosystems for pastures where intensive livestock production keeps a large number of animals, and changes in local/regional climate due to global warming — could alter areas of bat species. Indeed, in a climate change scenario, bat species might expand their ranges in response to increasing temperatures, leading to cases of human rabies arising in places that had seen no previous reports of the disease.

A recent study tested serum samples of free-ranging wild mammals from the state of São Paulo. Overall seroprevalence was 1.7% among 24 species surveyed, with individuals of six species having positive results indicating exposure to rabies virus.

São Paulo State University (UNESP)-Botucatu, in collaboration with the University of Glasgow, United Kingdom, published a study that belongs to the research project entitled, "Piloting a one health surveillance approach to support elimination of rabies from Brazil." With a focus on the impact of zoonotic viral diseases in people, animals, and ecosystems, this approach is currently considered vital to reducing the risk of zoonotic pandemics. Although it does not have a precise definition, the one health concept is based on several fundamental principles, including the related concepts of eco-health and planetary health.

"Rabies fits right into the one health concept," stated Horta. "In its current epidemiological profile, the disease is a direct result of the impact of human actions and behaviors, which are moving populations closer and closer to bats and are bringing bats closer and closer to cities. It's the poor quality of environmental health that's bringing rabies back to the human population."

Horta reported no relevant financial relationships.

Roxana Tabakman is a biologist, freelance reporter, and writer who resides in São Paulo, Brazil. She is the author of the books A Saúde na Mídia, Medicina para Jornalistas, Jornalismo para Médicos (in Portuguese), and Biovigilados (in Spanish). Follow her on Twitter: @roxanatabakman .

This article was translated from the Medscape Portuguese edition.

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