Opossums are widely believed to be highly resistant to rabies. As North America’s only marsupial, they are often seen in residential areas, prompting questions about their susceptibility. Their unique biological and behavioral traits explain why rabies is rarely observed in their populations.
Understanding Rabies
Rabies is a severe viral disease impacting the central nervous system of mammals. It typically spreads when an infected animal’s saliva enters another animal or person, most commonly through a bite. Once in the brain, it causes inflammation and neurological symptoms like aggression, confusion, and paralysis.
The virus travels along nerve pathways to the brain. Symptoms can appear days to over a year after exposure. Once clinical symptoms emerge, rabies is almost always fatal.
The Opossum’s Biological Edge
Opossums have a distinct biological characteristic contributing to their low incidence of rabies: a naturally lower body temperature. Unlike most mammals, whose body temperature is around 98.6°F, opossums maintain a core temperature of 94-97°F. This cooler internal environment makes it difficult for the rabies virus to replicate and spread.
The rabies virus prefers warmer temperatures, and the opossum’s lower body temperature inhibits its progression. While their robust immune system may also play a role, their lower body temperature is a primary factor in their resistance. This physiological trait means that even if exposed, an opossum is less likely to develop the disease.
Behavioral Defenses
Beyond their unique biology, opossums exhibit behaviors that reduce their chances of contracting rabies. They are generally non-aggressive, preferring to avoid confrontation. This means they are less likely to engage in fights with potentially rabid animals.
A well-known defense mechanism is “playing dead,” where an opossum will collapse and appear lifeless. This behavior helps them avoid physical conflict with predators, including those that might be rabid. By reducing aggressive encounters, opossums minimize exposure to the virus.
The Reality of Rabies Resistance
While opossums are remarkably resistant to rabies, no mammal is entirely immune. Cases of rabies in opossums are extremely rare, accounting for less than 1% of reported cases in the United States. Their high resistance means they are not common carriers or vectors for the disease.
While exceptional, documented instances of rabies in opossums exist. Their lower body temperature and non-confrontational behavior significantly reduce infection and transmission. This unique set of biological and behavioral adaptations means opossums very seldom get rabies.