Bats are a reservoir of various viruses like Ebola, Nipah, Coronavirus, etc., which are the deadliest viruses known. They are the primary culprits of zoonotic infections in humans. Most infected bats do not die but live a pretty healthy life. Most viral infections are non-symptomatic in them. The only virus which can affect them is rabies.
Though rabies can affect it, the mortality rate due to viral infections-like Coronavirus and Ebola virus- in bats is still low. Bats are not the largest reservoir of microorganisms; rodents are. Rodents carry many common illnesses, but bats carry various deadly viruses in them that could destroy human life one day.
Bats are present in lots of cities and countries except Antarctica, which is free of bats to date. In recent studies involving Coronavirus, scientists confirmed the source of the virus to be bats. The scientists in China now suspect another outbreak soon due to bats and unfortunately, believe China to be a likely hot-spot.
Anyway, we can’t blame bats entirely for putting our health at risk. It is us who have been invading their habitats, mainly the tropical. Having nowhere else to go, bats finally reached the towns and cities. Since they are significant reservoirs of many viruses, exposure to their fecal matter can be very challenging as well. The considerable outbreaks in the world can be traced back to bats. For instance, the Nipah virus & Ebola virus outbreaks shook the whole world.
What is the reason for viral outbreaks due to bats?
In some countries, people eat bats. It is the main reason behind an outbreak. Besides, the spread of commercial pig-farms into bats’ habitat makes pigs more prone to infections and carries it to humans. The pig-farms are the reason behind the Nipah outbreak in Malaysia and its spread to other countries due to contact. Primary victims of the Nipah virus are Malaysia, Singapore, Bangladesh, And India. Fortunately, Kerala (India) is the best survivor, with only 17 deaths among 18 affected individuals.
Ebola virus prevailed over the cities of the United States, Liberia, Guinea, Sierra, and Mali. The mortality rate is very high due to the Ebola attack. The hemorrhagic fever due to Ebola is fatal and can kill up to 90% of the infected individuals, while SARS-coronavirus has a lower mortality rate but spreads rapidly. Its spread during its incubation makes it a more dangerous virus.
How can bats survive harboring numerous deadly viruses like Coronavirus
Studies suggest the STING-interferon pathway and co-evolutionary adaptations and the ability to fly to explain bats resistance.
How did bats adaptation to fly help resist virus attack?
When mammals fly, they produce a lot of waste products that damage the DNA. But in the evolutionary process of bats to flight, they took the defense mechanism to another level by protecting their DNA from damage by the waste. In the same process, specialized cells also develop that fight against deadly viruses.
The optimum temperature for the growth of a virus is 37°C. But when bats fly, their temperature rises to 40°C. The thermolabile viruses die instantly, and the hardy ones (thermostable) live. Eventually, their flight gained them immunity. Simultaneously, the viruses also evolved to tackle the temperature and acquired resistance to fight against us.
How STING-interferon pathway help bats?
STING (Stimulator of interferon genes) is an integral part of innate immunity. In a case of infection, it starts producing type I interferons. Interferons are agents that fight off foreign antigens like viruses. Studies confirm the presence of a Serine residue, which plays a vital role in the release of interferons.
If any other amino acid replaces Serine, the production of interferon reduces to a significant number. There is a mutation in bats in the same region, and thus, they produce low amounts of interferons during an infection.
Whereas in humans, there exists an ‘overdrive’ response, which produces way more number of interferons than required during a viral infection. This overdrive triggers an inflammatory response, which further damages the system. Whereas, the system of bats is so well developed that it starts producing anti-inflammatory cytokines soon after an immune response, which compensates for the inflammatory response of the system.
What is DNA sensing in bats?
Simultaneously, there are theories of “DNA sensing”. When bats fly, a significant number of cells in the body breakdown and release DNA. The DNA is floating freely in the system. It is an indication of the invasion of a disease-causing organism. This response in bats is weak. This response allows the bats to maintain a balanced state of the immune response.
These various favorable conditions in bats, provide a suitable environment for viral growth. Also, bats love the company. Numerous bats cluster together in one place, making it a suitable environment for the viruses to feed and grow. This relationship conclusively means, the virus selected an appropriate host for its growth.
Related: Coronavirus Symptoms: The outbreak of early 2020 in China
