Nipah outbreak: How hunger, stress among flying foxes started killing humans

Nipah virus has killed at least 10 persons in Kerala. This virus is believed to have come from fruit bats found in South-East Asia after they faced hunger in the wake of massive deforestation in the region.

Hunger is a known killer. Psychological stress also kills. These two have combined to create a typical biological stage among fruit bats, taxonomically belonging to Pteropus genus and Pteropodidae family, to unleash Nipah viruses on humans.

Nipah virus outbreak has hit India. Two districts of Kerala have reported at least 10 deaths due to Nipah virus infection. These 10 victims were from the group of 12 persons, whose samples gave positive results in the test for Nipah virus infection in Kozhikode and Malappuram. The condition of the other two persons was said to be critical today.

Nipah virus outbreak is relatively a new phenomenon. The first outbreak was recorded in 1998 in Malaysia's Kampung Sungai Nipah village giving the virus its name.

A WHO report on 1998-outbreak said that "pigs were the intermediate hosts" for Nipah virus. Later, dogs, cats, rats and several other animals known to be living in humans' surroundings were found to be a host for Nipah virus. Human to human transmission of Nipah virus has also been established.

Development And Destruction

The WHO factsheet indicates that humans are responsible for the deadly outbreak of Nipah virus. Various studies on Nipah virus have found that the parent source of this virus are fruit bats. They have lived in Malaysian forests for centuries and were not particularly known to stray towards human settlements.

These flying foxes are, though, migratory in nature but they remained confined to forests till they had enough food. These bats are the parent source of Nipah virus or NiV.

"There is strong evidence that emergence of bat-related viral infection communicable to humans and animals has been attributed to the loss of natural habitats of bats," the WHO factsheet on Nipah virus states.

It further reads, "As the flying fox habitat is destroyed by human activity the bats get stressed and hungry, their immune system gets weaker, their virus load goes up and a lot of virus spills out in their urine and saliva."

Simply put, over the last two hundred years, the rate of deforestation has been unsustainable. Rapid development and population explosion led to destruction of forests across the globe. With the loss of natural habitat, the fruit bats faced persistent hunger leading to psychological stress in these mammals.

Hunger and stress in fruit bats resulted in fast multiplication of Nipah viruses inside their bodies. Now, overpopulated Nipah viruses inside fruit bats spilled out from their excreta and saliva, and reached humans to kill them.

Seasonal Variation

The WHO report further says that seasonal variations may also have a role in virus shedding by flying foxes due to the stressful physiological conditions. Evidence of seasonal preference of transmission of Nipah virus was found in a study conducted in Thailand.

The period between April and June is understood to be the suitable time for Nipah virus outbreak with the month of May showing highest infection.

However, first Nipah virus outbreaks in India (2001) and Bangladesh (2004) were recorded during winters. In India, the Nipah virus outbreak happened in West Bengal's Siliguri. Drinking of fresh date palm sap led to transmission of Nipah virus to humans. Out of 65 persons infected by Nipah virus, 45 died in Siliguri.

In both India and Bangladesh, human-to-human transmission of Nipah virus was also suspected. In the current outbreak in Kerala too, a nurse who was treating a Nipah virus-infected patient contracted the infection and lost her life.