Opossums, often simply called possums, are unique marsupials native to North America. They are widely recognized for their distinctive appearance and behaviors, including “playing possum” when threatened. A common belief among the public is that these animals are highly resistant to rabies. This observation has fascinated many, leading to questions about the underlying biological reasons for such apparent resilience.
A Unique Biological Shield
The primary scientific reason behind the opossum’s notable resistance to rabies lies in its body temperature. Opossums maintain a naturally lower average body temperature, typically ranging from 94 to 97 degrees Fahrenheit (approximately 34 to 36 degrees Celsius). This cooler internal environment creates a less hospitable setting for the rabies virus.
The rabies virus, a warm-blooded virus, struggles to replicate and spread effectively within a host that has a lower core temperature. While the virus can show some replication at temperatures as low as 27.2 degrees Celsius, maximal viral yields are generally observed at higher temperatures, such as between 34.0 and 39.8 degrees Celsius. The opossum’s consistent lower body temperature appears to inhibit the virus’s ability to efficiently multiply and cause widespread infection, thus limiting its progression to the central nervous system.
Rabies: A Broader Perspective
Rabies is a severe viral disease that attacks the central nervous system of mammals. It is primarily transmitted when an infected animal’s saliva, containing the virus, enters the body of another animal or human, most often through a bite. Once symptoms emerge, rabies is almost always fatal.
Common carriers of rabies in North America include bats, raccoons, skunks, and foxes. These animals typically have higher body temperatures than opossums, providing a more favorable environment for the rabies virus to thrive and replicate efficiently. This contrast underscores why the opossum’s resistance is noteworthy, as it deviates from the typical susceptibility seen in other warm-blooded mammals.
Rarity, Not Immunity
While opossums are highly resistant to rabies, it is important to understand that they are not completely immune to the disease. Cases of rabies in opossums are extremely rare. Scientific studies have shown that opossums have one of the lowest rates of rabies positivity among tested wildlife.
Other factors beyond body temperature also contribute to the low incidence of rabies in opossums. Their generally solitary nature and non-aggressive demeanor mean they are less likely to engage in fights that could lead to the transmission of the virus through bites. Furthermore, their nocturnal habits can reduce their interactions with common daytime rabies carriers. Despite their resistance, it is always prudent to observe any wild animal, including an opossum, from a distance and avoid direct contact.