An experiment with a bold objective of predicting the next global pandemic is about to commence, involving over fifty Jamaican fruit bats scheduled to be transported to a laboratory in Bozeman.
Bats around the globe play a crucial role in transmitting viruses from animals to humans, with the potential to be fatal for humans even though they typically do not harm bats themselves. In China, horseshoe bats are considered a probable source of the COVID-19 pandemic. Experts speculate that the combination of climate change and human encroachment on bat habitats has heightened the occurrence of viruses transferring from bats to humans, leading to the emergence of zoonotic diseases.
“Spillover events are the result of a cascade of stressors — bat habitat is cleared, climate becomes more extreme, bats move into human areas to find food,” said Raina Plowright, a disease ecologist and co-author of a recent paper in the journal Nature and another in Ecology Letters on the role of ecological changes in disease.
Montana State University immunologist, Agnieszka Rynda-Apple, intends to establish a breeding colony of Jamaican fruit bats in Bozeman this winter. This initiative, in collaboration with a team of 70 researchers across seven countries known as BatOneHealth, led by Plowright, aims to expedite their laboratory’s studies. Their ultimate goal is to identify methods for predicting the potential transmission of deadly viruses from bats to humans.
Rynda-Apple explained that they are working together to investigate the fascinating role of bats as disease carriers. Their primary focus is to comprehend the factors within bat immune systems that allow them to harbor viruses and determine the circumstances under which they transmit the virus.
Researchers create various diets to examine the impact of nutritional stress. They then proceed to infect the subjects with the influenza virus and analyze factors such as the amount of virus shed, the duration of viral shedding, and the subjects’ antiviral response.
Expanding their research, breeding bats will enable her and her colleagues to further delve into experiments they have already been conducting.
Understanding how environmental change contributes to nutritional stress and predicting spillover is a challenging task that requires careful effort. Andrew Hoegh, an assistant professor of statistics at MSU, emphasizes the importance of comprehensively grasping all the components involved in order to develop effective eco-counter measures that can disrupt the cycle of spillovers. Hoegh is currently constructing models to explore potential spillover scenarios.
The researchers at MSU collaborate with a researcher from the National Institutes of Health’s Rocky Mountain Laboratories in Hamilton as a small team.
The recent papers published in Nature and Ecology Letters focus on the Hendra virus in Australia, which is where Plowright was born. Hendra is a respiratory virus that causes flu-like symptoms and spreads from bats to horses, and then can be passed on to people who treat the horses. It is deadly, with a mortality rate of 75% in horses. Of the seven people known to have been infected, four died.
Plowright’s work was driven by the question of why Hendra virus emerged in horses and humans in the 1990s, despite bats being long-term carriers of the virus. The research reveals that environmental changes are the underlying cause for this phenomenon.
In 2006, Plowright initiated her study on bats. She and her colleagues found that the virus was rarely present in samples taken from Australian bats known as flying foxes. However, after Tropical Cyclone Larry devastated the bats’ food supply in 2005-06, a significant number of these animals vanished. Interestingly, they did come across a small group of weak and malnourished bats infected with the Hendra virus. This discovery prompted Plowright to shift her attention towards nutritional stress as a significant factor in the transmission of the virus.
After extensively examining 25 years of data on habitat loss, spillover, and climate, she and her team made an intriguing observation. They found a connection between environmental change-induced loss of food sources and the presence of elevated viral loads in bats that are struggling to find enough food.
In the year after an El Niño climate pattern, with its high temperatures — occurring every few years — many eucalyptus trees don’t produce the flowers with nectar the bats need. And human encroachment on other habitats, from farms to urban development, has eliminated alternative food sources. And so the bats tend to move into urban areas with substandard fig, mango, and other trees, and, stressed, shed virus. When the bats excrete urine and feces, horses inhale it while sniffing the ground.
The researchers aim to demonstrate a universal principle through their study on Hendra-infected bats: the correlation between the destruction and modification of nature and the heightened risk of deadly pathogens transferring from wild animals to humans.
The three most likely sources of spillover are bats, mammals, and arthropods, especially ticks. Some 60% of emerging infectious diseases that infect humans come from animals, and about two-thirds of those come from wild animals.
The notion that pandemics are driven by deforestation and the invasion of human activities into natural habitats is not a novel concept. One illustrative instance is the belief among experts that HIV, the virus responsible for AIDS, initially transmitted to humans through the consumption of chimpanzees in central Africa. Another example is the Malaysian outbreak in the late 1990s, wherein the Nipah virus, originating from bats, spread to pigs. The pigs acted as amplifiers, leading to human infections, resulting in 276 cases and 106 fatalities during that particular outbreak. Presently, a new understanding is emerging, emphasizing the correlation between environmental changes and the stress they induce on the emergence of such diseases.
Spillover events occur as a consequence of a sequence of stressors. As bat habitats are destroyed and the climate becomes increasingly severe, bats are compelled to venture into human-populated areas in search of sustenance.
DISEASE ECOLOGIST Raina Plowright
The immune systems of bats are an essential component of this intricate puzzle. By studying Jamaican fruit bats at MSU, researchers can gain a deeper understanding of how nutritional stress impacts their viral load.
Vincent Munster, a member of BatOneHealth and the head of the virus ecology division at Rocky Mountain Laboratories, is currently examining various bat species to gain a deeper comprehension of spillover ecology. According to Munster, the 1,400 distinct bat species exhibit substantial variations in their ability to carry coronaviruses or Ebola virus. Additionally, there are notable distinctions between bats that reside in large colonies of hundreds of thousands and those that lead relatively solitary lives.
At the same time, Gary Tabor, Plowright’s husband, holds the position of president at the Center for Large Landscape Conservation, a nonprofit organization which utilizes disease ecology research to safeguard wildlife habitats. One of their objectives is to ensure the sufficient nourishment of wildlife and prevent virus spillover.
Tabor expressed concern that the pressing issue of habitat fragmentation, which is not being adequately addressed, remains a significant threat to planetary health, especially considering the ongoing unprecedented levels of land clearing worldwide.
With advancements in outbreak prediction, various strategies emerge as viable options. For instance, the development of models capable of forecasting potential spillover locations for the Hendra virus could pave the way for vaccinating horses in those specific areas.
Hoegh mentioned another potential remedy, known as the “eco-counter measures,” which involves the extensive planting of flowering eucalyptus trees. This approach aims to discourage flying foxes from searching for nectar in urbanized regions.
Plowright stated that currently, the global attention is primarily directed towards finding ways to prevent future pandemics. Regrettably, the subject of safeguarding or reviving nature seldom finds a place in these discussions.
