NOV 16, 2016 9:50 AM PST

Brazil's feral pigs spur vampire bat boom, spreading rabies


A new study published in the journal Frontiers in Ecology and the Environment earlier this month examines the impacts of invasive feral pigs, a favorite prey of vampire bats, on ecosystems in rural Brazil. The distribution of feral pigs has increased five-fold since they were first recorded in Brazil in 2007. A group of Brazilian researchers found that not only might populations of vampire bats (Desmodus rotundus) explode as a result of this invasion of feral pigs, but the spread of infectious diseases could increase as well.
A vampire bat feeding on a feral pig, captured by camera trap. Photo: Alexine Keuroghlian, Wildlife Conservation Society - Brazil.
The wild boar is becoming a dominant mammal in Brazil’s Atlantic forest and could potentially invade the Amazon region, as well, according to Felipe Pedrosa, an ecologist from São Paulo State University in Brazil who studies the impacts of feral pigs on biodiversity and co-authored the study. As wild boars invade new territory, damage to crops such as maize, sugarcane, and soybeans as well as predation of native birds and mammals usually increases as well.

But the researchers are concerned about another consequence too: as pig numbers increase, they provide an ever-increasing blood supply to vampire bats, resulting in population growth for the bats as well. Additionally, previous studies have suggested that vampire bats may have a preferential taste for pig blood. One such study, published last year in Science, used a genetic technique to investigate what species the bats prey on most frequently. The results indicated that vampire bats were about seven times more likely to prey on pigs than one would expect would happen by chance alone — in other words, the bats were likely actively seeking out the boars.
A vampire bat feeding on a feral pig, captured by camera trap. Photo: Alexine Keuroghlian, Wildlife Conservation Society - Brazil.
Following The Washington Post, the researchers analyzed thousands of photographs and videos used to monitor wildlife in Brazil’s Pantanal region, a tropical wetland area mostly occupying the Brazilian state of Mato Grosso do Sul, and the Atlantic Forest, which runs down the Atlantic coast. They found that, in addition to preying on livestock like cattle, the bats also feed on wild animals including tapirs, deer and feral pigs. The videos and photos from the Pantanal region suggested there was about a 2 percent chance that a pig might be attacked by a vampire bat on any given night. In the Atlantic Forest, this chance rose to 11 percent.

Unfortunately, the chain of events doesn’t stop there. The study explains that “the common vampire bat is a major reservoir of rabies virus and is well known for spreading this deadly disease to several mammals upon which it feeds. The rabies virus is transmitted through the saliva of infected bats, and exposure to saliva through small wounds or scratches may occasionally result in rabies infection. Bushmeat hunters are exposed to saliva and other bodily fluids from their kills when they cut up the carcasses. Rabies-infected feral pigs may also occasionally bite hunters, their dogs, or even other predators of pigs. There is therefore a danger of the virus being transmitted to hunters and dogs via feral pigs.”

Mongabay News reports that incidences of rabies among vampire bats are about three for every two hundred individuals, or 1.4 percent of vampire bat populations. Because the species is relatively rare in the wild, and cattle and dog vaccination programs are practiced intensively in Brazil, the chances of humans contracting rabies are relatively low — but the researchers say their observations have led them to believe there is a significant chance of an increase in human rabies cases nonetheless, in addition to increased transmission of disease to other wildlife.
 

In 2005, a spate of attacks on humans in Brazil made international headlines by causing 23 rabies deaths in two months and leading to more than 1,300 people seeking medical treatment for rabies. The bites typically happen at night while people are sleeping, and are most common in children, who tend to sleep more soundly and are less likely to be wakened by the bats. While 2005 was an unusually alarming year for rabies scares, generally human infection with rabies remains rare.  
Nevertheless, a 37-year-old farmer in a rural area of Ceará state, Brazil has recently contracted rabies from a vampire bat, according to a UOL Noticias Ciencia e Saude report.The man was bitten in his sleep in mid-September, according to health officials. The patient did not seek medical attention until exhibiting symptoms a month later. He was admitted to the hospital and given human anti-rabies serum.The report does not say if he survived; however, since his symptoms started, his chances of survival are small.

As The Washington Post sums up nicely: ‘“In other words, it’s a classic example of how one human action — introducing a species that becomes an invader and colonizes new ecosystems in a destructive way — can have cascading and damaging effects that ultimately come back around and hurt humans, themselves.”

Sources: The Washington Post, Mongabay News, Outbreak News Today, Frontiers in Ecology and the Environment

 
About the Author
  • Kathryn is a curious world-traveller interested in the intersection between nature, culture, history, and people. She has worked for environmental education non-profits and is a Spanish/English interpreter.
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