Opossums are not immune to rabies. They can catch it, and at least one case has been confirmed, though cases are unusual.1PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil The immunity idea is a half-truth built on how rarely rabid opossums turn up, not on any proof that they can’t be infected. Their real defences, like resistance to some snake venoms and a knack for killing most ticks that bite them, help explain why they get a reputation as near-invincible.
Proof That Opossums Can Get Rabies
In Brazil, an adult female white-eared opossum caught rabies in the wild and tested positive.2PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil She was 1 of 22 opossums tested in that area, about 4.5%.3PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil The same year, about 3.2% of local bats tested positive, and bats are the likely source.4PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil Opossums living near infected bats can pick up the virus.5PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil
One confirmed case matters more than a pile of negative tests. Immunity means an animal cannot be infected, so a single real infection disproves it.
The case was diagnosed by laboratory testing of brain tissue, the standard way rabies is confirmed in any animal. It does not show that opossums commonly get rabies, since one case says nothing about frequency.
There is wider evidence of contact with the virus too. In São Paulo state, about 1.6% of opossums (5 of 312) had blood signs of having met the rabies virus.6PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil Those tests looked for antibodies, proteins the body makes after meeting a germ. Antibodies show that an animal’s immune system met the rabies virus or something very like it, not that the animal was sick when tested. The animal may have been exposed and fought it off, so the finding is evidence of exposure, not a count of rabid opossums.
The idea of opossum resistance began with early lab experiments in the 1960s.7PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil Later evidence showed those early suggestions were wrong about immunity.8PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil
Why Rabid Opossums Are So Rare
An opossum’s body runs at about 94 to 97°F, cooler than most mammals.9PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil That cooler body is one suggested reason the virus does poorly in them.10PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil This is a likely contributor rather than a proven cause. A cooler body slows or discourages the virus rather than blocking it, as the Brazilian case shows.
Few opossums also survive the attack that would infect them. In North America, rabies mainly spreads among wild carnivores such as raccoons, skunks and foxes.11PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil An opossum attacked by one of these is unlikely to survive long enough to develop rabies.12PubMed Central. Naturally Acquired Rabies in White-Eared Opossum, Brazil
Rabies can take weeks or months to cause symptoms after a bite, so the animal has to survive that long. Opossums are fairly small, slow and short-lived, and a fight can easily be fatal or leave them open to predators and cars. Rabies is also slow in any body. It enters nerve endings near the bite and has to travel along nerves to reach the brain.13PubMed Central. Neuroglia infection by rabies virus after anterograde virus spread in peripheral neurons
Some people assume marsupials have simple immune systems that should make them easy targets. The opossum immune system is as complex as that of other mammals, not primitive.14CSIRO Publishing. Marsupial immunology bounding ahead
Opossum Behaviour That Looks Like Rabies but Isn’t
In one Brazilian city, police were called about an opossum roughly once every four days.15Animal Welfare. The welfare of an unwanted guest in an urban environment: the case of the white-eared opossum (Didelphis albiventris) Most of what frightens people is ordinary defence. Cornered opossums open their mouths wide, hiss and show their 50 teeth. They may sway slightly and growl, which looks aggressive but is a bluff meant to make you back away. They may also drool or foam a little when stressed, and that saliva by itself is not a dependable sign of rabies.
Playing dead is an involuntary response. The animal goes limp and can give off a foul smell. It may lie still for minutes to hours and look as if it has died, then get up and leave once the threat is gone. Seeing one in daylight is a weak clue on its own, because mothers with young, or hungry animals in cold weather, may be out looking for food.
Other signs do suggest illness: staggering, circling or seeming paralysed, approaching or attacking people or pets without provocation, or extreme lack of fear combined with odd movement. If you see any of these, keep away and call animal control.
If one is simply in your yard, leave it alone, since it usually moves on overnight. Bring pets in and secure trash and pet food. Never handle an opossum barehanded, even if it seems dead.
What to Do After an Opossum Bite or Scratch
Wash the wound right away with soap and running water for about 15 minutes. Then call your doctor or local health department the same day. Rabies is almost always fatal once symptoms start, but shots given soon after a bite prevent it.
If your dog or cat was bitten, call your vet even if its rabies vaccine is current. Vaccinated pets may need a booster after a possible exposure.
Rabies treatment after a bite starts with the wound wash and, for people not previously vaccinated, a dose of rabies antibodies put in and around the wound for immediate protection. A series of vaccine doses follows over about two weeks, for most people four doses, given as injections in the upper arm. The old idea of many painful shots in the stomach is outdated; modern treatment is much like other vaccines. Whether you need the rabies shots depends on the animal, whether rabies is present in your area, and whether the animal can be caught and tested or watched.
If the opossum is dead or can be safely contained, tell the health department, since testing it can show whether you need shots. Testing uses brain tissue, so avoid damaging the head if the animal has to be killed or is found dead. Use thick gloves or a shovel to move it into a sealed container, never bare hands. Don’t try to catch a live animal yourself, since a second bite adds risk; call animal control instead.
Rabies isn’t the only concern with a bite. Opossum mouths carry bacteria that can infect a wound, so watch for redness, swelling or pus over the next days. It’s also a good moment to check that your tetanus shot is up to date.
Diseases Opossums Do Carry
In California backyards, fleas on opossums often carried bacteria that cause a flea-borne, typhus-like illness.16Proceedings of the Vertebrate Pest Conference. Identification of Zoonotic and Vector-borne Infectious Agents Associated with Opossums (Didelphis virginiana) in Residential Neighborhoods of Orange County, California About half of the opossum droppings tested contained Salmonella, usually types that make people sick.17Proceedings of the Vertebrate Pest Conference. Identification of Zoonotic and Vector-borne Infectious Agents Associated with Opossums (Didelphis virginiana) in Residential Neighborhoods of Orange County, California
Fleas that live on opossums can drop off in yards, porches and under decks, where they move on to pets and sometimes people. The illness often shows up as fever, headache and rash, and it can be mistaken for the flu. A person is usually infected when flea droppings or bites contaminate broken skin, not by touching the opossum directly. Keeping pets on flea prevention is the most practical way to cut the chain, since pets are what bring fleas indoors.
Salmonella is passed in droppings, so the risk comes from touching contaminated soil, surfaces or pet bowls and then your mouth. Symptoms are usually diarrhea, cramps and fever starting within a few days, and most healthy people recover without treatment. Young children, older adults and people with weak immune systems can get much sicker. Children playing in the yard and putting hands to their mouths are the most likely to be exposed.
Opossums can also carry parasites that pass from animals to people, including Toxoplasma and dog hookworm.18PubMed Central. Didelphis spp. opossums and their parasites in the Americas: A One Health perspective In one Brazilian study, nearly 9 in 10 opossums had at least one gut parasite.19PubMed Central. Gastrointestinal parasites in the opossum Didelphis aurita: Are they a potential threat to human health?
These spread through contaminated soil or droppings, not through casual sight of an animal. Most healthy people who pick up Toxoplasma have mild or no symptoms, but it matters more during pregnancy and for people with weak immune systems. Dog hookworm larvae can burrow through skin, such as bare feet in contaminated soil, and cause an itchy rash.
Basic hygiene handles most of the risk: wear gloves when cleaning droppings and wash your hands afterwards, wear shoes outdoors, and clean up droppings promptly. Don’t leave pet food or water outside overnight, and keep children away from areas where opossums leave droppings.
The Real Opossum Superpowers
Several opossum species resist snake venoms thanks to proteins in their blood that block venom toxins.20PubMed. Bacterial expression of a snake venom metalloproteinase inhibitory protein from the North American opossum (D.virginiana) A blood-clotting protein in opossums has also changed in ways that stop pit viper venom from latching on.21PubMed Central. Adaptive Evolution of the Venom-Targeted vWF Protein in Opossums that Eat Pitvipers That means opossums can eat venomous snakes that would kill many other animals.22PubMed Central. Adaptive Evolution of the Venom-Targeted vWF Protein in Opossums that Eat Pitvipers
The blood proteins bind to venom components and neutralize them before they can do damage. The resistance is aimed at particular toxins, which is why it works against some snake venoms and not others, and it doesn’t make an opossum invulnerable to a snake bite in every situation. Researchers are interested in these proteins as a model for new antivenom treatments, though that work is still in development.
Opossums also kill about 83 to 96% of young blacklegged ticks that try to feed on them.23PubMed Central. Hosts as ecological traps for the vector of Lyme disease These ticks, which spread Lyme disease, often die before passing on infection.24PubMed Central. Hosts as ecological traps for the vector of Lyme disease Opossums groom themselves intensively and swallow many of the ticks they find on their fur. Still, they’re one of several animals affecting tick numbers, not a cure for Lyme risk. Neither venom resistance nor tick killing protects an opossum from rabies or other infections.
Opossums can be helpful neighbours, eating ticks, snakes and pests. Appreciate them from a distance rather than handling them, and don’t relocate one yourself; call wildlife services if needed.