The Virginia opossum (Didelphis virginiana), the only marsupial native to North America, is often mistakenly identified as a high-risk carrier for rabies. This is a common misconception, as these animals display a strong resistance to the virus. While any mammal can theoretically contract the disease, cases of rabies in opossums are exceedingly rare, with statistics showing that less than one in every thousand tested specimens are infected. This low incidence is due to a specific biological trait that prevents the virus from establishing itself.
The Physiological Reason for Rabies Resistance
The primary reason for the opossum’s resistance lies in its average body temperature, which is significantly lower than most other placental mammals. The typical core temperature of an opossum ranges between 94 and 97 degrees Fahrenheit. This relatively low temperature creates an internal environment unfavorable for the rabies virus, which is notably temperature-sensitive.
The rabies virus, a Lyssavirus, requires a higher temperature range to replicate efficiently and move through the host’s nervous system. When an opossum is exposed to the virus, its lower body temperature effectively slows down the viral replication process. This delay prevents the virus from multiplying sufficiently to reach the brain and cause fatal encephalitis.
Rabies Transmission and the Statistical Possibility of Infection
Rabies is a viral disease that attacks the central nervous system, typically transmitted through the saliva of an infected mammal via a bite. Despite their natural resistance, opossums are still mammals. If an opossum receives a severe bite that introduces a massive viral load or a bite directly to the central nervous system, the virus may overcome the animal’s physiological defenses.
Opossums account for a tiny fraction of all reported wildlife rabies cases in the United States, typically less than one percent. In a study of North American mammals, opossums constituted less than 0.02% of all positive cases detected. This low statistical incidence confirms that the opossum is not a significant vector or reservoir for the virus, especially when compared to animals like raccoons, bats, and foxes.
Identifying Illnesses Other Than Rabies in Possums
Because rabies is so uncommon in opossums, a sick or strangely behaving animal is far more likely to be suffering from something else. The opossum’s defense mechanism, known as “playing possum,” is a stress response where the animal enters a catatonic state, which can be mistaken for sickness or neurological distress. They may also drool or hiss as defensive bluffs meant to intimidate predators, not signs of a rabid infection.
If an opossum appears lethargic, disoriented, or is staggering, the cause is often an injury, shock, or another type of infection. Opossums are susceptible to several other diseases, including Leptospirosis, Murine Typhus, and Tularemia, which can cause symptoms that mimic neurological issues. If an opossum exhibits any unusual behavior, it is safest to avoid contact and call local animal control or wildlife authorities for guidance.