Confronting host bats — Difficult to impossible

August 7, 2019 0 By S Harachand

In Malaysia, when the first-ever and the biggest outbreak occurred, authorities identified infected pigs acting as intermediary hosts predominantly transmitting infections to humans. 90% of the infected people in Malaysia were pig farmers. The finding resulted in the killing of a million pigs. No NiV outbreak has been reported from the South East Asian country since 1999.

Bangladesh, the other country which suffered a big toll from the virus, witnessed the recurrence of the outbreak for at least five consecutive years. Repeated outbreaks of NiV encephalitis and sporadic infections have been reported from Bangladesh almost every year, with high mortality and constituting a public health threat. Up to March 31, 2012, a total of 209 human cases of NiV infection were reported in Bangladesh. 161 (77%) of them died, according to WHO.

Date palm tree sap, the consumption of which in the raw was considered the source of the infection, is traditionally harvested by overnight collection. People there use a wide-mouthed container to collect the palm sap, which is easy to be contaminated by opportune bats, says Prof Arunkumar, Director, Manipal Institute of Virology, Manipal Academy of Higher Education.

Transmission happened directly from bats to human, no animals involved.

Repeated outbreaks occurred in different parts of West Bengal too in 2001 and 2007.

The population of large, wild-fruit bats, in which the pathogen resides, is ubiquitous in this part of the world. It is difficult to impossible to annihilate these reservoir host animals which are very much a part of the ecosystem.

“Bats are integral to our ecosystem. We cannot think of killing bats and get rid of the virus”, avers Prof. Arunkumar, Director, Manipal Institute of Virology, Manipal Academy of Higher Education.

In Malaysia, efforts have been made to reduce livestock interactions with bats; for example, restricting animals’ access to areas under fruit trees, covering water and feed containers to prevent contamination and not placing water and feed under fruit trees. However, the significant numbers of fruit trees and roosting bats on or near properties containing livestock made a complete separation of the wildlife and livestock populations near impossible.

Measures have been employed to prevent bats from accessing date palm sap collectors in Bangladesh, as well. Despite these, outbreaks continued to occur every year reflecting the difficulty of implementing the new practices.

As livestock have been identified as intermediate hosts for NiV, vaccination of livestock populations has been found to be a highly attractive strategy to mitigate both the disease as well as secondary transmission to humans.

However, in regions such as India and Bangladesh, where no intermediate host has been identified, the development of both effective therapies and vaccine strategies are required to combat
the infections.