Bats: Friend or Foe?
Bats. They’re not my favourite animal and let’s be honest they’re not the cutest of animals. The majority of us would see them as small, harmless flying rodent-type-things that dwell in caves. In the most part they are harmless. However, they play a huge role in driving the emergence of globally important diseases, most recentlyEbola virus and Middle Eastern Respiratory Syndrome (MERS).
First, let’s consider the initial transmission event.
These emerging diseases originate from developing countries, countries that retain the tradition of consuming bush-meat or countries that have close contact with animals but have poor hygiene standards. Many countries in Africa and Asia either consume bush-meat as a means of survival or due to certain meats being considered a delicacy.
It is thought that Ebola virus originated from bats. Not many people realise that Ebola has actually been around since the 70s. The first cases were small and contained within countries so didn’t pose a threat to global health. However, the most recent outbreak has been the most severe due to the ease of transmission from person-to-person. This meant that the disease was able to rapidly spread from The Democratic Republic of Congo to countries like Sierra Leone and Guinea, as well as America and isolated cases in Europe. The initial transmission event isn’t actually clear. Scientists know it involved a bat but are unsure as to whether it came from the consumption of the infected meat or from a young boy playing with an infected bat. Either way, close contact with an infected bat meant the virus hopped from one species to another.
MERS only emerged in 2012 in Saudi Arabia and is thought to be more deadly than the Severe Acute Respiratory Syndrome (SARS) outbreak that occurred in 2003 in southern China. Despite MERS being considered an extremely dangerous disease the development of a vaccine is not yet underway. Instead efforts to create vaccines to tackle current emerging disease outbreaks are focused heavily on Ebola virus. One of the two potential vaccines for Ebola is now in Phase II of clinical trials.
To understand the ease of transmission from one species to another we have to go into a bit of detail – sorry non-biologists, I’ll keep it simple. Commonly, DNA is what makes up most genetic material in living organisms. Some viruses have DNA genomes, however viruses with an RNA genome cause the majority of newly emerging diseases and so these are called RNA viruses – RNA being like a simpler form of DNA. DNA synthesis involves a proofreading phase using DNA polymerase. This means mistakes in copying genetic information is kept to a minimum. RNA synthesis lacks this vital step and this means that any mistakes that are made persist in the genome and can be passed on to viral progeny. These mistakes could mean the virus is now able to infect a human. Other factors such as selective advantage also play a role. In summary, mutations in the RNA viral genome mean viruses are more able to infect a wider range of organisms, and in the case of Ebola and MERS, these were humans.
Preventing Disease Emergence
Bats are successful reservoirs of many viruses due to their inability to develop symptoms of disease from carrying such viruses – in other words they are resistant. This means the virus can successfully replicate in the host without killing it – which is advantageous as death of the host likely means death of the virus too.
Since vaccination of the global bat population would be impossible, warning people of the risks of consuming bush-meat and not coming into close contact with bats is generally advised. But with increased deforestation this means bats are forced to seek habitats overlapping with our own, and the issue of poverty is still a driver in the consumption of bush-meat.
Broadening our understanding of the bat-virus relationship is needed to strengthen our ability to control – and prevent – the emergence of new viral diseases; as well as addressing issues such as extreme poverty and deforestation. Until this is done, we will continue to see the emergence of viruses that could potentially pose a threat to global health.
Friend or Foe?
Despite their ability to spread harmful diseases, bats are actually contributing to medicinal research, so it’s not all bad. Their ability to resist the development of disease symptoms despite being infected by viruses could help lead to a vaccine against these globally important diseases. Additionally, other unique aspects of bats can be exploited. Researchers are looking into specific components of the bat saliva to contribute to a treatment for blood clotting disorders and stroke. So, to sum up bats in general are relatively harmless but their ability to carry viruses, yet sustain resistance, could hold the key to future anti-viral vaccines.
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