A Cynopterus sphinx bat that is found in Nagaland.
Rabies is a fatal encephalomyelitis (inflammation of the brain and spinal cord) caused by the rabies virus. Most commonly, dogs are known to be the main source of rabies infection.According to the World Health Organization, more than 60,000 people die of rabies each year of which India accounts for almost one-third of all reported cases.
Studies inzoonotic disease outbreaks over past few decades revealed that bats are important reservoir hosts for human infectious diseases with instance of SARS outbreak in China, Hendra virus in Australia, Nipah virus in Malaysia, Ebola virus in West Africa, and MERS in Saudi Arabia attributed to bats. Theyareknown to transmit rabies in western countries for decades. More recently, evidence of infection with rabies virus or closely related lyssaviruses has been reported from bats from Asian countries including Vietnam, China, Cambodia, Thailand, and Philippines as well as our neighboring country Bangladesh, and Sri Lanka but no systematic surveillance for detecting rabies in bats in India.
As part of our initiative to understand the role of the Indian bats as carriers of zoonotic infections, we conducted a surveillance study to examine for any direct or indirect evidence of rabies infection or other related viruses in bats in the state of Nagaland. This Northeastern state with its rich biodiversity and high human-animal interaction through rapid land-use change and hunting provides an ideal setting to studyevidence of viral infection within the resident bat fauna. Studies have shown that widespread deforestation (destruction of forests for palm oil cultivation was responsible for Nipah virus outbreak in Malaysia); and human contact through hunting (spread of Ebola virus to humans) ismajor reasons for emergence of outbreaks of zoonotic diseases. In a recent study, video surveillance in Bangladesh revealed direct contact of bats with the palm sap and established a direct link between bats and Nipah virus infection in humans.
We collected bats samples from hunted bats across six different locations including two villages (Mimi and Salomi village) where traditionally the village communities hunt bats. Bat brain tissues and blood were collected from the hunted bats and tested for evidence of infection with rabies or related viruses at NIMHANS Bangalore – a WHO reference laboratory for rabies. Multiple diagnostic tests revealed evidence of rabies or related lyssaviruses circulating in some of these hunted bats. We found antibodies against rabies virus (indirect evidence) or closely related lyssaviruses in the common fruit bat Cynopterus sphinx (Greater short-nose fruit bat) and the insect bat Eptesicusserotinus (Serotine Bat). Antibodies are Y-shaped proteinsproduced by our immune system to help fight against any invader (antigens) from causing disease. Thepresence of rabies antibodies in some of the bats suggests that they were exposed to rabies virus in the past. The Cynopterus sphinx is ubiquitous throughout most of the human dominated landscape of the subcontinent as well as widely distributed across, while Eptesicusserotinusis found mostly in forest caves or tree holes in higher altitudes.
This is the first study reporting evidence of infection with rabies or related viruses in bats in India and has important implications in disease transmission and rabies control measures. Furthermore, it highlights the need for a more holistic view for effective management strategies and preventive measures with regards to infectious disease of animal origin to protect the health of humans, livestock, wild animals and the environment.
The reason for spill over infectionsto humans mainly occurs because human activities have destroyed natural habitats of bats and they are forced to live in close proximity to humans. The available space for wildlife is decreasing enormously. Hence, there is greater contact with wildlife and subsequently higherrisk/probability of transmission of infection to humans. Additionally, not all outbreaks are a result of direct contact. In many cases, infection spreads through livestock, which come in close contact with bats (especially with faeces, urine, saliva etc.), get infected and then transmit the same to humans. Bats are also known to shed more viruses when they are disturbed, which in many cases can be linked to human activities.
Although the risk of rabies transmission from bats to humans is very low, given the scale of contact in the region, it is foreseeable that transmission of infectious disease from bats could potentially occur. Transmission by bite is considered the most common means of acquiring rabies infection. Consequently,seekingprompt medical care may be worthwhile when bitten or scratched by bats.
There are more than a thousand species of bats and India alone accounts for about 120 species. These bats provide crucial services to humans, fruit bats are most important agents for pollination, seed dispersal and reforestation; similarly insect bats devour a wide range of insect pests and are extremely effective biological agents of pest management. Hence we need to find a way to coexist in a mutually beneficial way.
Further studiesto understand the magnitude of interactionbetween humans and bats in the region could provide interesting insightsinto the consequences of such close contact with bats.
The article “Serological Evidence of Lyssavirus Infection among Bats in Nagaland, a North-Eastern State in India” was published in January 2017 in the international journal epidemiology and infection, published by Cambridge University Press. It is available online
https://www.ncbi.nlm.nih.gov/pubmed/28228179
