Introduction
Cats and humans share a close bond when kept as pets and companions. While this companionship is rewarding, it also comes with risks, notably the potential for disease transmission between cats and humans. There are several viruses that can be transmitted from humans to cats.
These viruses lead to a variety of feline diseases, some mild and some potentially severe or fatal if left untreated. Respiratory infections, leukemia, rabies, ringworm, and gastrointestinal viruses are among the most common viral ailments transmitted from humans to cats.
Understanding these viruses, how they spread between humans and cats, and measures to prevent transmission is important for protecting the health of both pets and people.
Feline Upper Respiratory Infections
Feline upper respiratory infections (URIs) are one of the most common viral illnesses in cats. The primary viruses that cause URIs in cats are feline herpesvirus (FHV-1) and feline calicivirus (FCV) [1].
Feline herpesvirus is highly contagious and spreads through direct contact and respiratory secretions. It can cause symptoms like sneezing, discharge from the eyes and nose, conjunctivitis, fever, and loss of appetite. The virus remains latent in the body even after recovery and can reactivate during times of stress [2].
Feline calicivirus is also very contagious and causes oral ulcers, nasal discharge, conjunctivitis, and fever. It mutates frequently so cats may not develop full immunity after an initial infection. Severe cases can lead to pneumonia [2].
Feline Leukemia
Feline leukemia is a viral disease that is caused by the feline leukemia virus (FeLV). FeLV is part of the retrovirus family and is most commonly spread between cats when an infected cat sneezes or coughs. The disease is also commonly transmitted through saliva or blood contact, such as sharing food and water bowls or acquiring bites from an infected cat. Mother cats can also transmit FeLV to kittens before birth or when nursing. Signs and symptoms of FeLV infection include lethargy, persistent fever, loss of appetite, weight loss, swollen lymph nodes, and anemia. Sadly, many FeLV-positive cats will succumb to diseases of the blood cells or lymphoma
In the past, feline leukemia was typically fatal within 2-3 years of diagnosis. However, there have been great strides in the management and treatment of the disease in recent years. Anti-viral drugs, nutritional supplements, immunotherapy, and supportive care can help extend and improve quality of life for FeLV-positive cats.
Fortunately, FeLV is species-specific and cannot be transmitted from cats to humans or other animals. Humans may handle and live with FeLV-positive cats by taking precautions including vaccinating cats against FeLV, avoiding direct exposure to saliva and blood from infected cats, and getting regular veterinary checkups.
Feline leukemia testing and vaccination is highly recommended by veterinarians, especially for cats going into shelters or multicat households where exposure risk is higher.
Rabies
Rabies is a viral disease most often transmitted through the bite of a rabid animal. The rabies virus is found in the saliva of infected animals and can be transmitted through broken skin or mucous membranes when an infected animal bites or scratches another animal or human. According to the CDC, rabies virus is transmitted through direct contact with saliva or neural tissue from a rabid animal.
Cats can become infected with rabies if they are bitten by a rabid animal like a bat, raccoon, skunk or fox. The virus is transmitted through the infected saliva entering the cat’s wound. Once in the body, the virus travels to the brain and spinal cord where it multiplies, then spreads through the nerves to the salivary glands. An infected cat can then transmit rabies to humans or other animals through bites or scratches that break the skin and expose them to the virus-laden saliva.
According to the CDC, rabies virus from infected saliva enters the wound and travels through the nerves to the spinal cord and brain where it multiplies before spreading to other tissues. Rabies causes inflammation of the brain and can result in symptoms like aggression, impaired movement, excessive salivation, and paralysis in infected cats. There is no cure for rabies once symptoms appear. Therefore, preventing rabies through prompt vaccination and wound care is critical for cats and humans.
Ringworm
Ringworm is a common fungal infection that can spread between cats and humans. It’s caused by dermatophyte fungi that infect the skin, hair, and nails. In cats, ringworm often presents as circular bald patches with broken hairs, redness, and scaling (source). The fungi disrupt the hair follicles leading to hair loss. Ringworm is very contagious and can spread through direct contact or by touching contaminated objects like bedding.
Cats typically catch ringworm by coming into contact with infected soil or spores from another infected animal. The spores can survive in the environment for long periods. Young cats and those with weakened immune systems are most susceptible (source). Ringworm often resolves on its own within 2-4 months, but treatment with oral antifungal medication can speed healing. Keeping the cat isolated during treatment is important to avoid spreading ringworm to other pets or humans.
Toxoplasmosis
Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii. This parasite can infect most warm-blooded animals, including cats and humans. Cats are the only known definitive host for T. gondii where the parasite can complete its lifecycle. According to the CDC, over 40 million Americans may be infected with T. gondii.
Cats can become infected with T. gondii by ingesting infected prey, ingesting contaminated soil or water, or consuming an infected rodent. Once a cat is infected, the parasite forms cysts in muscles and brain tissue. These cysts contain bradyzoites which are the infective stage passed in feces. The cysts can persist for the life of the cat.
Humans can become infected by ingesting these infective oocysts through contaminated food or water or poor hygiene after cleaning a litter box. Pregnant women are at highest risk as the parasite can cross the placenta and cause severe birth defects. T. gondii can also rarely cause vision loss or neurological problems in some adults. Good hygiene and proper handling of cat feces is critical to prevent human infection.
Feline Immunodeficiency Virus
Feline immunodeficiency virus (FIV) is a lentivirus that affects domestic cats worldwide. It is very similar to HIV in humans. FIV weakens a cat’s immune system and makes it harder for the cat to fight off infections and diseases. As with HIV, there is no cure for FIV (1).
FIV is primarily transmitted through bite wounds, where the virus is present in the infected cat’s saliva. Casual contact such as sharing food bowls or grooming is unlikely to spread FIV (2). The virus can also sometimes spread from mother to kittens, either before birth or through nursing. However, many kittens born to FIV-infected mothers test negative for FIV after weaning (3).
There is very limited evidence that FIV can be transmitted from cats to humans. A few cases of possible human infection have been documented in laboratory technicians or veterinarians exposed to high levels of the virus, but routine household contact with FIV-infected cats poses little to no risk (1).
Gastrointestinal Viruses
Cats can catch viruses like norovirus and rotavirus that affect the gastrointestinal system and cause vomiting and diarrhea in humans. According to Cornell University, human norovirus and rotavirus strains are not thought to be contagious to cats [1]. However, cats can get their own strains of gastrointestinal viruses that produce similar symptoms. Feline panleukopenia virus, feline coronavirus, and feline calicivirus are examples of viruses that can cause gastroenteritis (inflammation of the stomach and intestines) in cats [2].
Symptoms of viral gastroenteritis in cats include vomiting, diarrhea, loss of appetite, lethargy, and dehydration. It is highly contagious between cats, but not believed to be transmissible from cats to humans. Proper hygiene like washing hands after cleaning litter boxes is still important to prevent any potential spread. Treatment focuses on supportive care with fluids, anti-nausea medication, probiotics, and bland diets. Most cats recover fully within 1-2 weeks, but kittens and older cats may suffer more severe effects [2].
While human norovirus and rotavirus are not directly contagious to cats, any illness resulting in vomiting or diarrhea could potentially expose a cat to the virus through environmental contamination. It’s a good idea to isolate sick individuals from household cats during gastrointestinal illnesses as a precaution.
Influenza
While rare, influenza transmission from humans to cats is possible. According to the CDC, while cats have occasionally been infected from humans with seasonal flu viruses, these cases are generally isolated and limited to individual cats or households where a human is sick. The CDC states that “There is no evidence that cats can give the influenza virus back to people once infected.”
The most common type of flu virus found in cats is the H3N2 canine influenza virus. But in 2022, the CDC reported cases of the H3N2 variant influenza A virus infecting cats in New York state shelters. This human-origin virus had acquired mutations that allowed it to spread among cats.
Influenza symptoms in cats can include fever, lethargy, sneezing, nasal discharge, and lack of appetite. It’s recommended to isolate cats displaying these symptoms from other pets. While most cats recover within 2-4 weeks, kittens, senior cats, and cats with other medical conditions are at higher risk of complications. Prevention involves avoiding contact with infected humans, quarantining new cats, and vaccination.
Sources:
[1] https://www.cdc.gov/flu/other/flu-in-cats/index.html
[2] https://www.cdc.gov/flu/other/flu-in-cats/h7n2-cat-faq.html
Prevention
There are several ways to prevent viruses spreading between cats and humans:
Vaccination – Cats should be vaccinated against common feline viruses like feline leukemia and rabies. Humans should stay up-to-date on vaccinations like influenza.
Hygiene – Wash hands before and after contact with cats. Clean litter boxes daily and wear gloves when cleaning. Disinfect surfaces a cat has been in contact with. Avoid contact with cat feces, urine, saliva, or blood.
Avoiding contact with strays – Stray and feral cats are more likely to carry viruses and parasites. Avoid contact with unknown cats and do not bring strays into your home before vet screening.
Keeping cats indoors, avoiding contact with sick cats, and maintaining good hygiene practices can limit viral transmission between cats and humans.
