I grew up on Ferngully, Dr. Seuss’ The Lorax, the Wild Thornberrys, Studio Ghibli movies, and Avatar the Last Airbender. The theme of the interconnectedness of humans, animals, and the environment has been entrenched in me for most of my life. Furthermore, it is the foundation of One Health, an approach emphasizing collaboration between human health, animal health, and environmental health sectors. The scope of One Health includes significant issues such as antimicrobial resistance, food safety and security, and zoonoses.
Zoonoses, diseases that are spread between animals and humans, are responsible for 60% of known infectious diseases and 75% of new or emerging infectious diseases in people. Since bats are most likely the origin of our current pandemic and implicated in many previous epidemics (Ebola, rabies, SARS, Marburg, Nipah, Hendra, etc.), they are an easy target for fear and blame. While there are several reasons that bats can harbor so many viruses (e.g., their unique immune response to pathogens and sheer species diversity), the risk of spillover from any reservoir into a human population is determined by a series of within-host and between-host processes. These determinants of spillover are interacting and complex, each with multiple barriers for the pathogen to overcome; broadly, the pathogen must be able to survive outside the reservoir host, there must be an opportunity for a human to be exposed to the pathogen, and the human must be susceptible to that pathogen.
Anthropogenic and environmental factors, such as deforestation, fragmentation, and human encroachment of wildlife habitat, act to increase contact between wildlife, livestock, and humans, increasing opportunities for disease transmission. In Southeast Asia, for example, the proximity of fruit orchards, pig farms, and bat habitats allowed for a unique sequence of events. Fruit bats that were infected with Nipah virus nibbled on mangoes from the orchard, bits of contaminated fruit fell into the nearby pig pens, and sick pigs went on to infect farmers with a virus that had an average mortality rate of 75%. If this is familiar, it may be because it inspired the plot of the 2011 movie Contagion.
On the other hand, there is a concept to describe the benefits that wildlife provide humans called ecosystem services. Insect-eating bats are crucial sources of pest control against insects that may damage forests, spread diseases among humans and animals, and destroy crops. The Brazilian free-tailed bat, for instance, preys upon some of the most destructive agricultural pests in the Americas; in fact, a 2011 study estimated the value of bats to the US agricultural industry to be around $22.9 billion/year in reduced cost of pesticides, not including the costs associated with the public health and environmental impacts of pesticides. Additionally, nectar-feeding bats, such as the lesser long-nosed or Mexican long-tongued bat, are essential pollinators in tropical and desert climates. Succulents like the agave plant (used to make tequila) and over 300 species of fruit (including bananas) are dependent on these bats for pollination. Similarly, fruit bats, such as the straw-colored fruit bat, are essential for seed dispersal, contributing to the health and diversity of forests. We are all interconnected, for better or for worse: threats to bats (e.g., windmill turbines, entanglement in nets and barbed wire, habitat loss, climate change, hunting, and white-nose syndrome) are also a threat to human and environmental health.
Our current fragmented approach is “failing to meet today’s health challenges.” While silos between these sectors prove difficult to bridge, a One Health approach is required for effective and sustainable disease prevention and control strategies. A public health intervention that ignores ecology, for example, can even be counterproductive. Ecologists caution against the public and political pressure to disperse or cull bats to control Hendra virus in Australia, as there may be unintended consequences. Disrupting colonies could actually put stress on the bats, which may result in increased viral shedding and higher birth rates; instead, interventions such as conservation and restoration of bat feeding habitat should reduce the risk of nutritional stress and the motivation for bats to colonize human areas.
Increased public awareness and understanding of One Health, collaboration between sectors (e.g., OHHABS, NARMS), and prioritization of efforts to strengthen pandemic preparedness and global health security are essential in protecting all sides of One Health. For more information about programs that detect, identify, prevent, and respond to zoonotic pathogens and other One Health issues, visit EcoHealth Alliance and CDC’s One Health Office. For more context on epidemics, Dr. Erin Allmann Updyke and Dr. Erin Welsh’s This Podcast Will Kill You and David Quammen’s Spillover are excellent.