Bats as Viral Reservoirs

Drs. Norbert Herzog & David Niesel

Drs. Norbert Herzog & David Niesel

Medical Discovery News

In tales, bats are feared because they could be blood-sucking vampires in disguise. Obviously, Dracula isn’t real, but science has recently uncovered a dark secret that bats have been keeping: viral reservoirs.

Reservoirs are bodies of collected water. Viral reservoirs are a collection of viruses carried by one species. Bats are an important source for a variety of viruses that can infect other animals and humans, such as deadly viruses SARS, Ebola and MERS.

Bats are among the most abundant and diverse vertebrates on earth and are found on every continent except Antarctica. Their ability to maintain viruses may date back to ancient times. Viruses can cause persistent infections in bats or they can lay dormant. Since bats also have relatively long lifespans — up to 25 years — if they have a persistent virus they have a good chance of infecting others with it, especially since they can fly and travel long distances. Bats also live in close-knit communities, so they are likely to pass infections to other bats, thereby maintaining viruses in the population. Some viruses spread by direct contact, while others such as rabies can be spread by droplets of saliva, mucus, urine or feces.

While scientists have known for a while that bats are a source of the rabies virus, they have recently isolated nearly 70 other viruses from bats. Most of these only infect fellow bats, not other animals or people, but they do carry some dangerous human pathogens like Japanese Encephalitis, Chikungunya, Rift Valley Fever, Nipah viruses and Hendra viruses.

Henipaviruses were first discovered as the cause of an outbreak of an acute respiratory illness in two humans and 22 horses in Hendra, a suburb of Brisbane, Australia, in 1994. The virus kills 75 percent of horses who are infected and 60 percent of people. That’s an especially deadly virus. Since then, there have been 39 Hendra outbreaks in horses, two of which spread to people. That virus was later found to be genetically related to another virus called the Nipah virus, which emerged in Malaysia in 1999. There have been nine more outbreaks of the Nipah virus since then, killing almost half of the people infected. Bats were probably responsible for many of these outbreaks.

In the latest study, 42 percent of the 2,000 Straw-coloured Fruit Bats from 12 African countries harbored Henipaviruses. About one-third of the bats also carried a rabies-like virus called Lagos bat virus. Since Henipaviruses can be easily transmitted, people living near bat populations could be at risk of infection.

Before mass bat hunts begin, it’s important to know that bats play essential roles in the ecosystem and cannot be eliminated without drastic consequences. Therefore people need to be cautious and vigilant about potential exposure to bat viruses. Ongoing research will hopefully create new antiviral vaccines that protect people. As humans continue to invade wildlife areas, so will the possibilities of contracting new viral infections.

Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professor emeritus Norbert Herzog and professor David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at www.medicaldiscoverynews.com.

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