What is the connection between fruit bats and Nipah virus?

What is it?

  • As the name suggests, fruit bats, or Pteropodidae, are a bat family that eats fruit.
  • Since the Nipah virus broke out in Kozhikode, Kerala, fruit bats have attracted attention as the wildlife reservoir for the virus.
  • This means the virus survives in the bat’s body without causing disease, allowing it to jump to susceptible mammals like humans or pigs, when bats come in contact with them.
  • Such contact is becoming increasingly frequent as agriculture and urbanisation destroy bat habitats, forcing them into human dwellings.
  • In the world’s first Nipah outbreak, which occurred in 1998 in Malaysia, virologists isolated the virus from the urine of the Island Flying Fox, a fruit bat species.
  • In Bangladeshi outbreaks, researchers found antibodies to Nipah in the Indian flying fox.

How did it come about?

  • All bats can carry viruses, some of them deadly. The Marburg virus, a relative of Ebola, was isolated in 2009 from the Egyptian Rousette, a fruit bat, in Uganda’s Kitaka Cave.
  • After the 2003 outbreak of Severe Acute Respiratory Syndrome (SARS) in China, researchers found antibodies to the SARS Coronavirus in cave-dwelling insectivorous bats.
  • Similarly, Ebola antibodies were found in species like the Hammer-headed fruit bat. In the case of SARS and Ebola though, the virus was never isolated from the mammals.
  • This means other animals may also play a critical role in the outbreaks.

Why are so many emerging diseases linked to bats?

  • For one thing, with around 1,200 species, bats comprise 20% of the earth’s mammalian diversity.
  • So, it ought not to be surprising that they host many viruses.
  • Not all of these viruses are threats to humans.
  • The bigger question is how bats stay healthy despite carrying these pathogens.
  • The Indian Flying Fox, for example, hosts over 50 viruses.
  • So far, researchers have only hypotheses to explain this viral diversity in bats.
  • One explanation — the “flight as fever” hypothesis — suggests that long periods of flying raises the temperatures of bats, boosting their immune responses.
  • This helps them survive the microbes’ pathogenic effects.

Why does it matter?

  • Identifying the source of the Nipah infection will help prevent future spread. In the Kozhikode epidemic, the virus seems to have moved from bats to humans in one “spillover” event.
  • After this, it moved from one human to another. Nipah spreads differently in different countries.
  • In the 1998 Malaysian outbreak, the virus moved to pigs first — perhaps after a domestic pig consumed fruit contaminated with bat saliva.
  • Once it spread widely on pig farms, the virus began jumping to humans who came in contact with the animals.
  • Around 260 people fell ill after such contact, but no person-to-person transmission seems to have occurred in Malaysia, unlike in Kozhikode.

What next?

  • Officials are trying to identify the bat species behind the outbreak. Even if the outbreak is eventually linked to these mammals, the transfer of bat viruses to humans is a rare event.
  • Given how critical bats are to ecosystems, the Kerala government has taken a stand against culling bats in response to the outbreak.

Source:TH