How Disease Shapes Wild Animal Suffering — and What We Can Do
Disease is among the largest sources of suffering for wild animals. Epidemics can kill millions of individuals, and sub-lethal disease causes prolonged suffering — weight loss, neurological deterioration, immune suppression, and the behavioral compromise that makes animals more vulnerable to predation and starvation.
The welfare implications of wildlife disease raise profound ethical questions: should we intervene in natural disease processes to reduce wild animal suffering? If so, how, and at what scale? These questions are increasingly central to wild animal welfare science.
CWD is a fatal prion disease affecting deer, elk, moose, and reindeer across North America and parts of Europe. Infected animals progressively deteriorate — losing weight, showing abnormal behavior, difficulty swallowing, and excessive thirst and urination — over months before death. There is no cure, and the disease is now present in 32+ US states and 4 Canadian provinces. Millions of deer likely carry the prion. The welfare implications are severe: affected deer suffer for extended periods before death.
WNS, caused by the fungus Pseudogymnoascus destructans, has killed an estimated 5.7 million North American bats since 2006 — some of the steepest wildlife population declines ever recorded. Affected bats wake repeatedly during hibernation (burning crucial fat reserves), often emerging in winter to die of starvation and exposure. The welfare dimension of this prolonged dying process is significant. Research into probiotic treatments and fungal resistance is ongoing.
Batrachochytrium dendrobatidis has caused the greatest vertebrate biodiversity loss in recorded history — contributing to the extinction of 90+ amphibian species and dramatic declines in hundreds more. Chytridiomycosis causes a painful thickening of the skin that disrupts electrolyte balance, leading to cardiac arrest. Research into probiotic bioaugmentation (applying beneficial bacteria to frog skin) shows promise as a welfare and conservation intervention.
Canine distemper virus affects lions, wolves, foxes, seals, and many other species. It causes neurological symptoms (seizures, paralysis), respiratory disease, and high mortality. Vaccination campaigns for domestic dogs near wildlife reserves have reduced spillover into wild populations in some areas — a successful welfare-positive intervention.
H5N1 avian influenza has caused massive die-offs of seabirds, shorebirds, and waterfowl since 2021-2022, with millions of individuals dying in what is one of the largest wildlife disease events in history. Seabirds including gannets, terns, and pelicans have been severely impacted. The welfare implications of this mass mortality are substantial.
Conservation biology has traditionally favored non-intervention in natural disease processes, viewing disease as part of natural ecosystem regulation. Under this view, intervening to save individual animals from disease risks disrupting ecological balance.
Wild animal welfare advocates argue that the capacity to suffer creates moral obligations regardless of whether suffering is "natural." If we can reduce suffering at reasonable cost without causing greater harms, we have reasons to do so — even in wild animals.
Climate change is expanding the geographic range of many wildlife pathogens, creating new disease exposure for previously unexposed populations. Warming temperatures extend tick ranges (Lyme disease), alter bat hibernation patterns (WNS dynamics), and stress immune systems — creating a compounding welfare crisis that makes disease management increasingly important.