Introduction
Cats can carry certain fungal organisms on their skin, hair, and claws that may be harmful if transmitted to humans, a phenomenon known as zoonosis. The most common fungal organisms that cats carry and can spread to humans include dermatophytes like Microsporum canis, the fungus that causes ringworm. Several other fungal diseases like cryptococcosis, histoplasmosis, and blastomycosis can also be transmitted from cats to humans in some cases.
While not all fungi that live on cats are zoonotic, some can lead to skin, nail, and hair infections in humans if proper precautions are not taken. Understanding the fungal organisms that cats may harbor can help owners take preventive measures and seek timely treatment if symptoms do arise in themselves or their cats. Proper diagnosis and treatment of fungal infections in cats is also key to reducing risk of transmission.
Ringworm
Ringworm is caused by dermatophyte fungi and is highly contagious among cats [1]. It appears as a circular rash on the skin and causes hair loss and scaly skin. Ringworm is very contagious and can spread between cats and other animals through direct contact. The fungi that cause ringworm can also infect humans.
Ringworm often recurs because the spores can survive in the environment for long periods. Treatment involves both topical antifungal medications applied directly to lesions as well as oral antifungal drugs. Treatment may need to be continued for several weeks to fully eliminate the infection. The environment should also be thoroughly cleaned to remove spores. Careful monitoring is required to watch for recurrence of lesions.
Cryptococcosis
Cryptococcosis is a fungal infection caused primarily by two species of the fungus Cryptococcus, C. neoformans and C. gattii. This infection is relatively rare in cats and occurs when a cat inhales Cryptococcus fungal spores, which then lodge in the lungs and spread to other parts of the body. Cryptococcosis most commonly affects a cat’s respiratory and central nervous systems.
Unlike other fungal infections cats carry, Cryptococcosis very rarely spreads from cats to humans or other animals. The Cryptococcus fungus is naturally found in the environment, especially in soil or bird droppings. Cats primarily get infected when they come into contact with these sources. The fungal spores enter through the nasal passages when a cat sniffs contaminated material. From there, the infection can spread to the lungs and central nervous system.
In the lungs, Cryptococcus infection can cause pneumonia with symptoms like coughing, breathing difficulties, and fever. If the infection spreads to the brain and spinal cord, it can lead to meningitis or meningoencephalitis. Neurological symptoms include seizures, abnormal behaviors, weakness, paralysis, and loss of coordination. Without treatment, cryptococcosis can be fatal in cats. Veterinarians typically prescribe long courses of antifungal medications like fluconazole to treat this infection.
While Cryptococcosis is very rare in humans, people with compromised immune systems are at higher risk. There are only a few documented cases of Cryptococcosis transmitting from cats to owners, and this typically requires prolonged, close contact. Healthy individuals do not need to take any special precautions around cats with Cryptococcosis. As long as good hygiene practices are followed, owners face minimal risk of contracting this infection from their cats.
Sporothrix
Sporothrix is a fungal infection caused by the Sporothrix fungus. It is commonly transmitted to humans via scratches and bites from infected cats. The fungus is carried on cats’ claws and in saliva. When an infected cat scratches or bites, the fungus can enter the wound and cause an infection known as sporotrichosis in humans. Sporotrichosis causes skin lesions that start as small bumps or nodules around the area of the scratch or bite. Over time the lesions can develop into red, ulcerated sores or raised bumps that spread along the lymph nodes. According to the CDC, sporotrichosis cases have reached epidemic levels in some regions where infected stray and outdoor cats interact with humans. Proper treatment of infected cats and avoiding scratches and bites can help prevent transmission (CDC).
Aspergillosis
Aspergillosis is a respiratory disease in cats caused by the fungus Aspergillus. This fungus is commonly found in the environment, especially in soil, decaying vegetation, and household dust. When inhaled, the fungal spores can colonize the lungs, sinuses, or the space between the eyes and nose known as the sino-nasal cavity.
There are two main forms of aspergillosis in cats:
- Sino-nasal aspergillosis affects the nose and sinuses. It causes symptoms like nasal discharge, nosebleeds, loud breathing sounds, and masses in the nose or sinuses.
- Pulmonary aspergillosis affects the lungs. Cats exhibit coughing, rapid breathing, poor appetite, lethargy, and other signs of respiratory distress.
While aspergillosis can make cats very ill, it is not contagious to humans or other pets. The fungal spores are widespread in the environment. Aspergillosis mainly affects cats with compromised immune systems or other underlying health conditions. Treating the root cause of immune deficiency, along with antifungal medication, can help resolve aspergillosis in cats.
Sources: https://vcahospitals.com/know-your-pet/aspergillosis-in-cats, https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/aspergillosis
Histoplasmosis
Histoplasmosis is caused by a fungus called Histoplasma capsulatum. Cats become infected by inhaling the spores of this fungus into their respiratory system. The spores are often found in environments contaminated with bird or bat droppings. Once inhaled, the spores spread through the cat’s lungs and cause flu-like respiratory illness. The disease can range from mild to severe depending on the amount of spores inhaled.
Histoplasmosis causes flu-like illness in humans as well. People contract it by inhaling the fungal spores from contaminated environments. The symptoms include fever, chest pain, dry cough, headache, loss of appetite, and fatigue. In rare cases, it can spread to other organs and become life-threatening if left untreated. But most individuals recover fully with antifungal treatment. So it is important to take precautions when cleaning areas contaminated with bird or bat droppings where fungal spores may lurk.
Source: https://vcahospitals.com/know-your-pet/histoplasmosis-in-cats
Source: https://www.pethealthnetwork.com/cat-health/cat-diseases-conditions-a-z/histoplasmosis-cats
Blastomycosis
Blastomycosis is a fungal disease caused by the fungus Blastomyces dermatitidis. This fungus thrives in moist soil, especially along rivers or lakes and in wooded areas. Blastomycosis is rare in cats, but when it does occur it can cause pneumonia, skin lesions, and eye infections. The fungus is contracted by breathing in spores from the environment. While blastomycosis spreads through the lungs, it only rarely spreads to humans through close contact with an infected cat [1]
Coccidioidomycosis
Coccidioidomycosis, also known as valley fever, is a fungal disease caused by the soil fungus Coccidioides immitis. This fungus is found in arid soils in the southwestern United States and parts of Mexico and Central and South America. The areas where the fungus is most commonly found include southern California, southern Arizona, New Mexico, and western Texas.
When soil containing the fungus is disturbed, such as during digging, the fungal spores can become airborne and be inhaled by humans and animals. The inhaled spores can then lead to flu-like respiratory illness in humans. The infection is also called San Joaquin Valley fever or desert rheumatism.
In humans, signs and symptoms occur within 1 to 3 weeks after infection and can include fatigue, cough, fever, shortness of breath, headache, night sweats, muscle aches, joint pain, and rash on upper body or legs. Most people recover, but in a small percent of individuals, the infection can spread from lungs to skin, bones and brain.
Cats become infected with coccidioidomycosis by inhaling the fungal spores. Clinical signs are variable, but often include lethargy, fever, weight loss, draining skin lesions, lameness, and swelling of limbs or face. The infection can disseminate throughout the body. Without treatment, the disease can be fatal in cats.
Diagnosis involves clinical signs, chest X-rays, blood tests, and culture or PCR detection of fungus. Treatment usually involves long-term antifungal medication such as fluconazole or itraconazole. The prognosis is guarded even with treatment. Prevention involves avoiding areas endemic for the fungus and minimizing exposure to dusty outdoor air. There is no vaccine available for cats.
Prevention
There are several steps cat owners can take to help prevent fungal infections in their cats:
Keep cats indoors. Outdoor cats are at higher risk of exposure to fungi in the environment. Keeping cats inside reduces chances of infection.
Clean litter boxes regularly. Scoop waste out of litter boxes daily and fully clean boxes once a week. This helps prevent buildup of fungi in litter.
Wash hands after contact. Some fungal infections like ringworm can spread to humans. Washing hands after petting or handling cats can prevent transmission.
Seek treatment for infections. If a cat has symptoms of a fungal infection like skin lesions, hair loss, or respiratory issues, take them to a vet for diagnosis and treatment. Treating infections quickly can prevent spreading.
Conclusion
Fungal infections in cats can be caused by several types of fungi such as Microsporum (ringworm), Cryptococcus, Sporothrix, Aspergillus, Histoplasma, Blastomyces, and Coccidioides. While most fungal infections are localized, some can become systemic and potentially life-threatening if left untreated. Thus, prevention through good hygiene and nutrition as well as prompt diagnosis and treatment are crucial in managing fungal diseases in cats.
Some key preventative measures include keeping cats indoors, regularly disinfecting their environment, avoiding exposure to other infected animals, and maintaining a healthy diet and lifestyle to boost their immune systems. Catching infections early and following veterinarian recommended treatment plans can help mitigate the spread and severity of fungal infections in our feline companions.