Possums, or opossums, are often misunderstood regarding their ability to carry the rabies virus. While every mammal can contract rabies, confirmed cases in possums are exceedingly rare. According to the Centers for Disease Control and Prevention (CDC), opossums account for less than 1% of all reported rabies cases in U.S. wildlife. This low incidence means the possum is not a primary vector for the disease compared to common carriers like raccoons, skunks, foxes, and bats. The scientific community generally points to a specific biological factor that explains this remarkable resistance to the fatal virus.
The Physiological Reason for Rabies Rarity
The rarity of rabies in possums is largely attributed to their unique internal body temperature. A possum’s average body temperature naturally ranges between 94 and 97 degrees Fahrenheit, which is several degrees lower than most placental mammals. This lower temperature creates an inhospitable environment for the rabies virus.
The rabies virus requires a relatively higher host body temperature to effectively replicate and spread throughout the central nervous system. When the virus enters a possum’s system, the cooler internal temperature often inhibits its ability to successfully incubate, hindering its progress to the brain. This makes it difficult for the infection to fully establish itself and become transmissible through saliva.
In contrast, mammals that typically maintain a core temperature closer to 100 to 102 degrees Fahrenheit, such as dogs, cats, and many wildlife species, provide the warmer conditions the virus needs to thrive. Although a possum can still be bitten by a rabid animal, the viral replication process is significantly stalled or stopped due to the thermal constraints. This biological defense mechanism is a major reason why possums are not considered a public health concern for rabies transmission.
Behaviors Often Mistaken for Rabies
The public often misinterprets several of the possum’s natural defense mechanisms as signs of neurological distress, which are the hallmarks of rabies. When faced with a threat, a possum may hiss and bare its fifty sharp teeth in a defensive bluff. This display is often accompanied by excessive drooling, which is a stress reaction, not a symptom of the virus.
The most famous behavior is the involuntary, catatonic state known as “playing ‘possum,” or tonic immobility. In this state, the animal collapses, its body becomes stiff, and it may appear to foam at the mouth or have a glassy-eyed stare. This reaction is a physiological defense mechanism intended to deter predators.
A possum that is truly sick or injured may still exhibit unusual behavior that causes alarm. They might appear disoriented, stagger, or become aggressive if cornered, especially if they are suffering from other common diseases or parasites. However, the drooling and staggering are often part of their fear response rather than a sign of a neurological infection.
Safe Practices When Encountering Possums
Regardless of the low risk of rabies, it remains prudent to treat all wild animals, including possums, with caution and respect. Rabies transmission occurs almost exclusively through the transfer of saliva from an infected animal, usually via a bite. Consequently, the best practice is to avoid any direct contact with a possum to eliminate the risk of a defensive bite or scratch.
Ensure that all pets are kept up-to-date on their rabies vaccinations, as they are far more susceptible to the virus than possums and can act as a bridge for transmission. If a possum appears sick, injured, or is trapped in an unusual location, you should never attempt to handle it directly. Instead, contact local animal control or a licensed wildlife rehabilitator. These professionals possess the training and equipment to safely assess and manage the animal without risk to themselves or the public.