Rabies spreads

Researchers report first cases of transmission of the virus by marmosets in Ceará

Fabio colombiniWhite-tufted-ear marmoset: from the Northeast to other regionsFabio colombini

Kept as pets in the hinterland of the Northeast, the white-tufted-ear marmoset (Callitrix jacchus jacchus) have become a cause for concern: they can transmit the rabies virus. The most common of the marmosets caused eight deaths to inhabitants in Ceará between 1991 and 1998, according to an article published in the November/December issue of Emerging Infectious Diseases, of the Centers for Disease Control and Prevention (CDC), of the United States, signed by researchers from the Pasteur Institute of São Paulo, the State Department for Health of Ceará, and the Ministry of Health. It was the first account of a species of primates that is a source of infection by rabies in human beings.

As if the means of transmission were not enough, the characteristics of the virus – the so-called variant – are also new. On the basis of analyses carried out at the Pasteur Laboratory in São Paulo and at the CDC itself, Silvana Regina Favoretto, a researcher from Pasteur, shows that the virus found in the marmosets constitutes a single group, with no relation to the samples found in bats or terrestrial mammals.

This work reinforces the suspicion that the marmosets are a natural receptacle for the rabies virus: previous studies had already indicated that these monkeys are highly susceptible to intracerebral inoculation with the virus. The field reports that led to the discoveries came from the coordinator for zoonoses at the Department for Health of Ceará, Nélio Moraes, who warns of the risks of contagion and encourages vaccination in the case of being bitten by monkeys.This is not just a local problem.

At the beginning of last year, the Pasteur identified the same variant of the virus in a case of rabies in humans, already confirmed, in Piauí, also transmitted by a marmoset. In addition, the inhabitants of the poorer regions of the Northeast catch the marmosets that live in the thickets and sell them, illegally, to other regions. Highly adaptable, these monkeys also live close to plantations and green areas in cities like São Paulo and Rio de Janeiro.

Among the bats
The appearance of cases of rabies transmitted by primates in Ceará is one of the alterations in the epidemiological profile of the disease in Brazil. Urban rabies, transmitted by cats and dogs, is under control in the Southern and Southeastern regions. But as it is still intense in the other regions, these animals continue to be the main sources of transmission of the virus: they cause about 70% of the cases notified – there were, on average, 26 a year, between 1996 and 2001.

On the other hand, there has been growth in transmission by bats, one of the main receptacles for the virus in the wild, now responsible for about 15% of the cases. The cause is the expansion of the areas of occurrence,now including densely populated areas. “Bats are now on the move, and are found nowadays close to the city of São Paulo”, observes Ivanete Kotait, vice-director of the Pasteur Institute in São Paulo. There have been recent cases of rabies in cats and dogs, transmitted by bats, in Itapevi, Barueri and Santo André, neighboring municipalities to the city of São Paulo. “It will be no surprise if we find contaminated cats and dogs in the municipality of São Paulo.”

In Porto Alegre, in Rio Grande do Sul, the first case of rabies in 11 years has been registered – in a cat, probably contaminated by a bat, according to the studies now carried out. In particular, it is worrying that transmission by the Desmodus rotundus, one of the species central to the International Seminar on Bats as Transmitters of Rabies, held in São Paulo last December.Another problem that afflicts the researchers is that the hematophagous bats, called vampire bats, infect species that do not feed on blood. In the January issue of the CDC’s magazine, Chilean researchers reported the first case of human rabies in Chile to be caused by an insect-eating bat, Tadarida brasiliensis, which is the main receptacle of the virus there, like the Desmodus rotundus in Brazil.