Rabies in the Pantanal
Written by: Casiliana da Silva Recalde, Jamie Brown, Ana Paula Antunes Nogueira, Lindsey Holmstrom
Rabies is a severe neurologic disease, caused by a rhabdovirus, that affects all species of warm-blooded animals. Worldwide, rabies is responsible for the mortality of 50,000 cattle annually. Cattle industry costs associated with losses and control of the disease are estimated at US$ 44 million per year.
Rabies is endemic in the southwestern Brazil, and is spread primarily by hematophagous (vampire) bats. Hematophagous bats are found only in Latin America. In the state of Mato Grosso do Sul, the disease occurs with greatest frequency in the Pantanal and the peri-Pantanal regions. Flooding concentrates animals in the higher parts of the land and here they provide good concentrations for the hematophagous bats to feed. The most severe problems occur in regions where there are numerous caves, as that is the preferred habitat of the bats.
Rabies in the Pantanal is cyclic, occurring with increasing severity through a seven-year cycle. The cycle is thought to be due to concentration of the virus within the bat colony and numbers of bats. As the disease reaches epidemic proportion within the bat colony, there is a decline in bat numbers and then some years are required to build up to sufficient numbers for optimal transmission again. Because each female has only one offspring per year, the growth of the colony is slow.
On an annual basis, most cases occur in cattle in the months of April, May and June, and this is related to biology and behavior of the bats. During the breeding period, males fight for a "harem" and as they inflict bite wounds on one another, the virus can spread. Also, unsuccessful males must leave their colony to become incorporated into new colonies, and so there can be considerable inter-colony movement during this period, which may transport the virus from one group of bats to another. Subordinate males have been known to travel as far as 25km to establish themselves in a new location, so the virus can skip across considerable distance in these social undesirables.
Vampire bats feed at night. They approach the animals from the ground and as the cattle are lying down at night, they usually feed on the lateral body wall. Most cattle in the Pantanal have residual scars from vampire bat feeding. The bat does not make a huge wound and suck blood, as the term "vampire" might conjure up in the imagination. Rather, they make a small tear in the skin, and then lap the blood as it trickles down from the wound.
Recent wound inflicted by vampire bat Most cattle have scars due to vampire bat bites
In the Pantanal, the disease in cattle is primarily the paralytic form, characterized by paralysis of jaw, tongue, hindlimb ataxia, and flaccid tail. The vampire bats will feed on cattle of any age. Disease is seen primarily in calves, because there is a period of time between waning of maternal immunity and and vaccination in which they are immunologically susceptible. Disease is occasionally seen in adults as well – in these cases, it is often presumed that the animal was vaccinated while already incubating the disease.
Treatment for the disease does not exist. The control and prophylaxis consist of vaccinating cattle in areas where it occurs and reduction of population of bats.
Control of vampire bats is done through trapping in mist nets, painting the back of the bat with a coumarin paste, and then releasing. The bat travels back to its colony, where grooming is active. As other bats groom the coumarin, they ingest this powerful anticoagulant and die from internal bleeding several days later. It is estimated that for each bat treated with the paste, approximately 20-25 bats are eliminated. There is no desire to totally eradicate the vampire bats from the Pantanal as it is recognized that they are an integral part of the ecosystem. The aim of the treatment regime is to decrease the population and diminish the number of cattle infected with rabies.
Cattle were herded into an enclosure and a 6’ high mist net was erected all around the corral.
The owner of the fazenda, Hipolito, slaughtered a sheep and cooked a barbecue for all of the visitors, who slept in hammocks distributed in every room of his home. All through the night, the mist nets were checked hourly. Any bats found were brought back to the house, where biological parameters were recorded and then they were treated with warfarin paste.
Bat is removed from the mist bet. Carlão, chief rabies technician with IAGRO, displays bat for recording of data
Vampire bat removed fom cage. Back is painted with coumarin.
Group poses for photo the morning after, prior to departing by boat.

In some parts of the Pantanal, where there is extensive rabies infection in the bat populations, there have been human infections due to vampire bats. In these cases, the usual scenario is that all cattle are taken to market, and the vampire bats then go after a blood meal from another large warm-blooded animal, humans. These cases are usually children that have been bitten during the night. There are virtually no cases of dogs becoming infected by vampire bats – it is thought that the dogs are very sensitive to the bat’s approach and have excellent tactile sensations so that even if the bats approach while they are asleep, they become alert enough to defend themselves.

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