The recent Nipah outbreak being reported from Kerala has brought into focus the role of bats in transmission of the Nipah virus infection. Here is a brief overview of their habitat, types and diseases of human importance (zoonoses) caused by them.

1. Bats are ubiquitous and are present throughout the world, except in the extremely cold regions.
2. They are found everywhere; tree hollows, caves and tunnels, rock crevices, old ruins of buildings, human dwellings (barns, sheds, attics and other outbuildings) are the natural habitats of bats.
3. Bats are mammals of the order Chiroptera. Their forelimbs are adapted as wings. So, they are the only mammals that can fly.
4. There are about 1,200 species of bats, which is one-fifth of all mammal species, ranging from the worlds smallest mammal, the tiny bumblebee bat to giant flying foxes with six-foot wingspans.
5. Bats have a long life, more than 30 years, so they can carry the pathogens for long time and also spread the infection longer.
6. Some bats can fly for long distances, even beyond 1000 km, and spread the diseases over a larger area.
7. Most bats are nocturnal in habit.
8. Bats are usually grouped into two: the megabats (also called fruit bats or flying-foxes) and the echolocating microbats.
9. Megabats mainly eat fruits, nectar and pollen, the microbats are mainly insectivorous. They mainly eat night-flying insects, such as mosquitoes and other insects that destroy crops. A single little brown bat can eat up to 1,000 mosquito-sized insects in a single hour. The vampire bats feed on blood.
10. Bats are important in their ecosystems for pollinating flowers and dispersing seeds.
11. Bats are carriers of many pathogens – mainly viruses, which can spread to humans and cause severe disease. Their droppings may contaminate the spaces in which they live.
12. Bats do not live in close contact with humans, but they can spread the infection through intermediate animal hosts (livestock, pets), which are in close contact with humans such as horses, pigs etc. This is believed to be the most common route of transmission of infection to humans. These intermediate hosts acquire the infection by eating food that has been partially digested by bats.
13. Aerosol transmission may occur when humans accidentally enter the bat roosting caves.
14. Infection may also occur via direct contact with bats, such as catching bats or been bitten by bats and scavenging of bat carcasses.
15. Bats are natural reservoirs of rabies and Hendra virus. Other diseases carried by bats include histoplasmosis, leptospirosis, Salmonella.
16. Bats are natural reservoirs of many viruses, many of which are emerging human pathogens. These include Ebola virus, Marburg virus, Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) coronaviruses, Nipah and Hendra viruses.
17. Some bacterial spps such as Salmonella, Pasteurella, Bartonella and fungal spps like histoplasma capsulatum are also known to spread by bats.