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Epidemiology

The virus spreaders

Identified the wild rodents that are spreading the viruses of the epidemic that has recently arrived in the Federal District

luiz pereira/alHosts: rice ratluiz pereira/al

During the Corpus Christi holidays, a few weeks ago, biologists from the Adolpho Lutz Institute, in São Paulo, spread hundreds of traps a little larger than a shoe box in the environs of the houses on the outskirts of São Sebastião, a town neighboring Brasilia, where, at the beginning of May, new cases arose of hantavirus infections – a grave form of infection caused by a kind of virus, the hantavirus, which kills half the people contaminated in two or three days, on average. In three nights, attracted by the smell of the bait – oatmeal mixed with peanut paste -, 510 animals fell into the aluminum plate cages. At least one third were hairy-tailed bolo mice (Bolomys lasiurus ), which transmit one of the Brazilian types of hantavirus, the Araraquara,so-called for this being the city, in the interior of São Paulo, where it was found for the first time, in 1995.

It is the same rodent with a dark brown fur that disseminates the Leishmania (Viannia) braziliensis protozoon, which causes American tegumentary leishmaniasis, the most common kind of leishmaniasis in human beings in Brazilian territory.Installed in a shed annexed to the Papuda Penitentiary Complex and protected with masks, blue overalls and double gloves – while, next door, policemen fulfilled yet another stage in their target shooting training -, the researchers collected blood and samples of entrails from the animals, for an analysis in the laboratory.

But the fact that they had found the hairy-tailed bolo mouse is a strong indication that the virus circulating in Brasilia is probably the Araraquara, since each type of hantavirus is associated with a species of wild rodent. Furthermore, the Bolomys , an animal about 12 centimeters long, without counting the 5 centimeter tail, lives mainly in the cerrado, the vegetation of the Federal District, the west of São Paulo, and of three other states – Minas Gerais, Mato Grosso and Goiás – where there have been cases of hantavirosis in human beings caused by the Araraquara variety.

“In July last year”, says Akemi Suzuki, a biologist from the Lutz who took part in the capture, “we worked in Campo Alegre de Goiás, 220 kilometers from Brasilia, and we found the Bolomys and the Araraquara virus.” The recently collected blood samples from the animals are in the care of researcher Ivani Bisordi, who, in a few weeks, will say whether these animals really are the hosts of the virus from the town where there have already been eight confirmed cases of hantavirosis and four deaths. In this period of time, another virology team from the institute, a national point of reference in diagnoses in this area, did the tests with blood samples from people suspected of having been contaminated with hantavirosis all over Brazil.

The group from São Paulo is presenting the Bolomys publicly in a scientific article about to be published, together with another reservoir host, as the animals that carry the hantaviruses without becoming sick are called. This is the small-eared pygmy rice rat ( Oligoryzomys nigripes ), a rodent with rust-colored fur and a tail 11 centimeters long, longer than its own body, which measures 8 centimeters. This rodent lives in the Atlantic Rain Forest, sometimes carrying the Juquitiba hantavirus, identified in 1994 in the environs of the town in São Paulo, which later emerged in Paraná – currently the state with most cases registered (92) -, in Santa Catarina and in Rio Grande do Sul.

More two types of virus
In parallel, a team from the Evandro Chagas Institute, of Belém, identified two new types of hantavirus found in Maranhão, when hantavirosis emerged in 2000 and affected seven persons, of which five died – until then there had been only one Amazonian hantavirus, the Castelo dos Sonhos, the same name as the town on the border of Pará and Mato Grosso, where the virus appeared ten years ago, with an as yet unidentified host. One of the new viruses is the Anajatuba, the same name as the municipality located in an inundated area known as the Baixada Maranhense, similar to the Pantanal in Mato Grosso, 100 kilometers to the south of the capital, São Luís. Its transmitter is the Oligoryzomys fornesi, a rodent of the same genus as the host of the hantavirus that is typical of the Atlantic Rain Forest.

The other virus found in Maranhão is the Rio Mearim, the name of the main river of the region, which cuts the central area of the state, is propagated by means of the Holochilus schiureus, a small aquatic rodent – this is the first demonstration of an aquatic rodent harboring hantavirus, according to virologist Pedro Vasconcelos, the coordinator of the team from the Evandro Chagas that identified the new varieties, described in an article to be published shortly. “In view of the high diversity of rodents in Brazil”, claims Vasconcelos, “we can imagine that we are still going to find new types of hantavirus in other states.”

The most recent discoveries made the Federal District, with four cases confirmed up to the end of June, the newest territory of an emerging disease that arose in the country in 1993 and has already spread over ten states, with 158 deaths – this year there have been 12 cases, seven of them fatal. Six years ago, when hantavirosis arrived at the municipality of Guariba, in the northwest of São Paulo, leaving a balance of 16 deaths, physician Luiz Tadeu Figueiredo, from the Ribeirão Preto Faculty of Medicine of the University of São Paulo (USP), asked whether this virus caused only devastating cases. “It ought not to be true”, he thought.

Figueiredo began five years ago with a serological survey in Jardinópolis, a town with some 30,000 inhabitants close to Ribeirão Preto, and gathered blood samples from 880 residents. Analyzing the results, published at the beginning of this year in the Journal of Medical Virology, he was surprised to see that 14.3% of the persons had antibodies against the viruses, in an indication that they had already been in contact with the causal agent of hantavirosis, without, however, showing any symptom. “Serious disease is rare, but infection is common”, the researcher claims. His team also discovered that even those who survive the more severe attacks of hantaviruses show sequelas, years later, like physical indisposition, weakness, and fibrous scars in the lungs.

“There will always be new cases of hantavirosis, because it is impossible to eliminate all the rats from nature”, comments Luiz Eloy Pereira, a scientific researcher who coordinated the team from the Lutz in the expedition to São Sebastião, which was also made up with biologists Renato Pereira de Souza and Matheus Ferroni. But the disease is transmitted only by means of wild rodents – and not by means of contaminated water, as was commented when the epidemic appeared in São Sebastião. “Neither city rats nor house mice transmit the hantaviruses”, claims Pereira, who spent a good part of the last few 25 years – he is 54 years old – in the middle of the forest, in search of spiders, insects, ticks, birds, monkeys or rats that can spread viruses that are harmful to human health: at the end of June, he was in the forest of Foz do Iguaçu, western Paraná, after migratory birds that may propagate the West Nile virus, another serious emerging disease whose arrival in the country the specialists regard as certain.

At first, it may be possible to hold back the Nile virus, keeping one’s distance from the birds that transmit it, but is appears to be difficult to escape from the hantaviruses: the hantaviroses are due, above all, to the expansion of the towns over the spaces of the wild rodents. Losing space, the animals that live with the hantaviruses without any problems draw close to the houses and food stores, after food and shelter.

Even when they do not find them, the animals leave feces, urine or saliva with particles of the viruses, which can contaminate human beings when inhaled together with the dust raised with the movement of rugs or wrappings with food. This was how hantavirosis reached the municipalities that are neighbors to continuously growing urban centers like Uberaba and Uberlândia, in the Triângulo Mineiro. This was also the way that it appeared at the toll plaza of a highway close to Sertãozinho, in the interior of São Paulo: the rats slipped into the holes of the lamp posts and left feces that contaminated one of the attendants.

In the field
Hantavirus infections s is also associated with plantations of soybeans, corn and beans or pastures with brachiaria grass, which the rodents feed on. In Cajuru, in the north of São Paulo, there was only an asphalt road separating a pasture from a condominium of popular houses, where in 1999 two persons were contaminated with the Araraquara. At other times, the cause is deforestation. Four years ago, in General Carneiro, in the south of Paraná, rats entered the improvised houses of peasants who were cutting down the araucaria forest.

Generally speaking, the rodents with their viruses appear when there is some instability, including momentary climatic alterations, as happened in 1993 in a desert area of the United States. For having rained more than usual, the plants grew a lot, and, with abundant food, the animals proliferated. But afterwards the aridness returned, and the famished rats drew close to the houses: in less than one year, about 180 persons were contaminated. “Hantaviruses are a problem all over the world”, says Akemi, from the Adolpho Lutz. “Luckily, in Brazil, the cases are isolated and sporadic.”

In the Americas, the hantaviruses – about 15 types have now been identified, each one carried by specific species of rodents – cause the so-called hantavirus pulmonary syndrome (HPS), which leads to the collapse of the lungs and of the heart, unlike the European varieties, which damage the kidneys. The problem is that hantavirosis, for causing fever, pain in the back, nausea and vomiting, is easily mistaken for flu, dengue or leptospirosis, increasing the risk of transmission between people, which is still a remote possibility, with just one case confirmed, in Argentina, in 1996. As there are no specific medicines, it is only the symptoms that can be treated.

In case of doubt, the specialists’ recommendation to the doctors is for them not to ask the patients to take a lot of liquid – hydration can be fatal, if hantavirosis is confirmed. It is not yet very well known why, but, after they are lodged in the lungs, the hantaviruses increase cell permeability, allowing the water from the inside of the cells to accumulate in the lungs.But there are ways of holding back the advance of the rodents, which cannot be eradicated, as they are abundant and live spread out. According to the team from the Lutz, people who live close to forest, plantations or pastures, should plug up any gaps in their houses to prevent the animals from entering, as well as keeping foodstuffs in closed places and not leaving leftover food scattered about. Another simple and effective measure is to keep the plantations at a minimum distance of 60 meters away from the house and its annexes.

It is also important to keep the surroundings of the house free of undergrowth, or even without any grass or shrubs. Pereira says that these wild rodents are agile when they are in the undergrowth, avoiding even the smallest twigs, but that when they find themselves on bare earth they act stupid and anxious to find some refuge.

The Projects
1. Genetic Diversity of the Virus Genome (Hantavirus); Modality
Special Project; Coordinator Luiz Tadeu Moraes Figueiredo – FMRP/USP; Investment R$ 1,557,340.73
2. Epidemiology of the Viral Hemorrhagic Fever, Caused by Arbovirus, Hantavirus, and Arenavirus and Studies of the Virus-Host Association in Hantavirus Investigations associated with HPS in the Municipality of Anajatuba; Coordinator Pedro Vasconcelos – IEC; Investment R$ 500,000.00 (CNPq and Ministry of Health)

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