Balancing Act: The Role of Bats in Global Health

Source: Why rising interactions between bats and humans pose major global health risks, PBS News

With over 1,400 species globally, one in five mammals are some form of bat, contributing to the stabilization of the majority of ecosystems on our planet. Yet their populations continue to decline, driven by fear of zoonotic disease transmission harming human populations. This poses the question: what can be done to balance the conservation of bats while protecting ourselves from fatal diseases? 

Bats in Global Public Health

Bats are a key species in the protection of global public health due to their contribution to ecosystem stability and pest control, benefiting agricultural systems and food security. At the same time, however, bats are also a top host for viruses, raising concerns about the transmission of emerging zoonotic diseases. These include thousands of viruses, many of which have the ability to cause human disease, such as the Nipah virus, Marburg virus, Rabies, and SARS-like viruses. 

Bat’s tendency to live in colonies allows for easy transmission of these viruses, and more surprisingly, they are able to survive high virus concentrations without symptoms of disease. According to the Duke Global Health Institute, a major contribution to a bat’s viral immunity stems from their physiological development of flight. In fact, bats are the only mammals actually capable of sustained flight, with other mammals (such as flying squirrels) having the ability to glide, but not actually fly. 

In bats, the capacity to fly is linked to significantly high metabolic rates, which in turn causes harmful DNA damage. To combat this, bats have evolved to possess gene variants that minimize and repair this damage, with the same variants also able to provide protection against viruses and boost their immune systems. This highly active immune system is what allows bats to host viruses that result in severe and fatal illness in humans and other animals, without showing any signs of infection themselves. Moreover, these antiviral properties further contribute to the selection for exceptionally high growth rate viruses, or those that replicate at higher rates to maximize transmission. 

Preventing Spillover: Bat Vaccines

These unique characteristics have sparked researchers’ interest in targeting bats to prevent disease spillover. Recently, a study published in the Science Advances Journal proposed a unique solution: vaccinating bats directly for rabies and Nipah viruses. Previous methods, such as culling bats to control rabies, have backfired, with transmission rates instead increasing due to human contact.

The key to vaccinating small, flying mammals, while simultaneously avoiding close human contact, lies in mosquitoes, which can carry the vaccine after exposure. After being fed blood containing the vaccine, mosquitoes continue to replicate it inside their salivary glands, transferring it when either biting or being eaten by a bat. 

Another potential mechanism involves saline drinking stations, an alternative for places unable to implement vaccine-carrying mosquitoes. The salty mist from these stations attracts bats, encouraging them to drink the oral rabies vaccine solution. Either way, both methods resulted in the development of antibodies in vaccinated bats, demonstrating potential for slowing transmission rates. 

Despite promising results, some scientists have questioned the feasibility of implementing this solution. Many point to the difficulties in acquiring regulatory approval and funding for the projects. Releasing vaccine-carrying mosquitoes would require extensive research on environmental safety and potential impacts on other animals. Others believe that this approach would be generally ineffective, considering the sheer number of bats and the viruses they can carry. Instead, they highlight the importance of minimizing human disruptions to bat habitats, which largely drive zoonotic disease risk, targeting human behavior rather than the bats themselves. 

Importance of Conservation

Regardless, it is critical to remember the importance of bats to global and environmental health. Critical pollinators, bats are key contributors to the existence of plants such as bananas, avocados, peaches, and other agricultural staples. They are also important parts of ecosystems, helping with the population control of mosquitoes, beetles, and moths, which helps limit the spread of mosquito-borne diseases and use of chemical pesticides in farming. Bats are even providing useful information to human health research, commonly used in studies relating to cancer and aging. 

The fear that bats are inherently harmful to humans drives down conservation efforts, and has currently left over half of the bat species in North America at risk of population decline. Efforts such as the vaccine study aim to mitigate harmful disease spread without harming bat populations, but a lot can be done on individual levels as well. Avoiding contact with bats, ensuring your pets are up to date on rabies vaccinations, and supporting habitat and wildlife conservation efforts are all ways we can work towards safely coexisting with these small, but mighty mammals.