Bats have recently gained more attention in the world of scientists and in the news. But where does this recent surge of interest in bats originated? Are they new exotic trendy pets?
Surprisingly enough, bats well deserve public attention, given their abundance and diversity, which makes them one of the most representative vertebrate species on earth (accounting for 20% of all mammalian species). These extremely versatile creatures have recently been accused to be the reservoir of novel viruses that might be threatening the lives of humans and live-stocks. The first evidence that bats may transmit infectious agents causing diseases in humans was reported back in the 20s, when rabies virus was found in bats from South and Central America. Since then, an increasing number of viruses causing diseases in humans have been lead back to a bat origin.
As the traditional means against bats comprising loads of garlic have not been proven to be effective, funding and research activities have increased on bat-borne viruses. How does it come that only during the last 20 years the number of newly discovered bat originated viruses has increased tremendously? One of the driving forces has been the development of novel techniques, such as pan-virus primers and next generation sequencing, that allow scientists to detect viruses with unprecedented sensitivity. These techniques permit avoiding the tedious and not always applicable detection methods used in the past, which involved virus isolation or identification of virion-like structures with electron microscopes. Nevertheless the use of these recently developed methods have also been shown to be error prone and results have to be analyzed with precautions (Naccache et al. JVI 2013).
So far 66 different bat viruses have been isolated, belonging to 15 virus families of different genomic origin (10 families of RNA viruses and 5 families of DNA viruses). Whether each single bat virus represents a risk to humans is unlikely, nevertheless the diversity of viruses that have so far been identified is astonishing, and an impressive number of viruses sharing moderate similarity to known mammalian viruses in their genetic code have been reported.
Some scientists believe that bats must exhibit special characteristics, which render them extremely attractive and comfortable for viruses, which otherwise don’t despise other guests, such as rodents (representing themselves a significant source of arenaviruses and several different hantaviruses), insects or plants.
For instance their permissiveness to a huge range of viral species might render them a “breeding ground”, allowing extensive diversification and co-evolution of the guest with its host over many millions of years. The exceptionally high average life-span of bats (in some cases up to 35 years) together with the huge number of individuals in each population, might have also played important roles, giving viruses enough time to become fitter and to spread to younger individuals, preserving themselves and continuing their evolution. Viruses in fact are intrinsically prone to find a perfect balance with their host in which enough multiplication can occur without prematurely killing the victim. Hence the chance that the virus might persist, without being too virulent for its host, might have rendered bats the perfect carriers, with occasional and unfortunate infections to other un-prepared mammals, such as humans.
Mass extinctions might also have played a role, by drastically reducing the biodiversity, and with it the number of viruses. During the last mass extinction, when 70% of species world-wide were lost, fossil evidences suggest that bat ancestors might have had characteristics allowing them to survive the extreme conditions.. Another favorable characteristic is definitely their capability of flying, which allows a high mobility to select suitable habitats. This in turn permits the interaction of bats with themselves or other mammals that could lead to spill-overs of bat originated viruses. Co-evolution of viruses and their hosts might have been further supported by the presence of very efficient mechanisms against oxidative damage of DNA in bats contributing to their longevity. In short, bats and viruses might have established a fruitful symbiotic relation.
Recently, the association of human pathogens with bats as their reservoir has increased public interest, therefore funding and research have grown significantly. In the near future, the study of bats may help to reveal currently unsolved issues in the field of cancer biology, virology, and molecular biology. For example, the identification of novel viruses in bats and the evolutionary trend of bat viruses can be used as the indicator for the existence of similarly originated human and animal virus which have not been identified yet. As mentioned above, the insight knowledge of bat’s characteristics will provide a new understanding of the virus-host interaction in mammals. This will lead us to develop new strategies for antiviral drug discovery research.
As this is still in the very early beginning we suggest to the broad public to keep a diet rich-in-garlic and to prevent close contact with this surprising and resourceful creatures.
1. Wang, L. F., Walker, P. J., and Poon, L. L. Mass extinctions, biodiversity and mitochondrial function: are bats ‘special’ as reservoirs for emerging viruses? Curr Opin Virol 1(6), 649-57.
2. Naccache, S. N., Greninger, A. L., Lee, D., Coffey, L. L., Phan, T., Rein-Weston, A., Aronsohn, A., Hackett, J., Jr., Delwart, E. L., and Chiu, C. Y. The perils of pathogen discovery: origin of a novel parvovirus-like hybrid genome traced to nucleic acid extraction spin columns. J Virol 87(22), 11966-77.