Bats: as Vectors

Bats: as Vectors

Bat-bourne diseases are unparalleled in their virulence and destructive powers. They carry zoonotic viruses which covers Coronavirus, Ebola, SARS and Nipah virus. A particular reason why bats are the reason for several diseases is because of their social nature and a highly functional immune system. In fact, bats host more zoonotic viruses than any other taxonomic order. 

Viruses are always are constantly encountering new species and attempting to infect them. More often than not, this ends in failure. In most cases, the genetic dissimilarity between the two hosts is too great. For a virus adapted to infect humans, a lettuce cell would be a foreign and inhospitable landscape. But there are a staggering number of viruses circulating in the environment, all with the potential to encounter new hosts. And because viruses rapidly reproduce by the millions, they can quickly develop random mutations. Most mutations will have no effect, or even prove detrimental; but a small proportion may enable the pathogen to better infect a new species. 

The odds of winning this destructive genetic lottery increase over time, or if the new species is closely related to the virus’ usual host. For a virus adapted to another mammal, infecting a human might just take a few lucky mutations. And a virus adapted to chimpanzees, one of our closest genetic relatives, might barely require any changes at all. It takes more than time and genetic similarity for a host jump to be successful. Some viruses come equipped to easily infect a new host’s cells but are then unable to evade an immune response. Others might have a difficult time transmitting to new hosts. For example, they might make the host’s blood contagious, but not their saliva. 

However, once a host jump reaches the transmission stage, the virus becomes much more dangerous. Now gestating within two hosts, the pathogen has twice the odds of mutating into a more successful virus. And each new host increases the potential for a full-blown epidemic. Virologists are constantly looking for mutations that might make viruses such as influenza more likely to jump. However, predicting the next potential epidemic is a major challenge. There is a huge diversity of viruses that are just being uncovered. Researchers are tirelessly studying the biology of these pathogens. And by monitoring populations to quickly identify new outbreaks, they can develop vaccines and containment protocols to stop these deadly diseases.

Since bats are capable of flight, Their metabolic rate is far higher than other smaller terrestrial mammals, While this may seem as a double edged sword, since mammals having that kind of metabolic rate and small-bodied barely live that long, Bats seem to fly in the face of that and even live for 40 years. This has helped bats to remain immune to viruses since even viruses requires a specific temperature to replicate and while flying, A bat’s internal temperature cruises to about 40.C. Which, incidentally, means they can definitely weather a meagre human fever.

Bats also have a highly evolved interferon-alpha system. It is a protein common in mammalian immune systems used to signal to other cells throughout the body that they must fortify themselves against imminent attack. When mitochondria convert nutrients into energy, they also create by-products called reactive oxygen species. Mitochondrial exhaust fumes, in the form of reactive molecules which contain oxygen. The immune system uses them to rouse immune cells to action and kill bacterial invaders. 

But they can also cause a lot of damage. They can weaken cell membranes and damage proteins, and even break DNA, and because of that, they play an important role in diseases like cancer and arthritis. Cells can try to keep them in check with antioxidants — compounds that essentially neutralize these overeager molecules. But those can only do so much, and when the balance collapses, cells experience a condition called oxidative stress. This is when most of the DNA damage happens. 

The immune system protects the bats from viruses, but these viruses still linger in its body. Bat species that live longer, have greater body masses, smaller litter sizes and more litters per year tend to host more zoonotic viruses.

However, it is equally important to know that human inference has also played a high role in the spreading of disease. As humans’ approach closer and closer to their habitats, the increased stress causes the bats to shed more saliva, urine, and other bodily fluids. Conservation of these species is essential.

– PM Sayee Leshya

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