Introduction
Parasites are organisms that live on or inside another organism, called the host, and benefit at the expense of the host. Parasites cannot live independently and rely on the host for survival. Some common parasites found in cats include roundworms, tapeworms, hookworms, heartworms, giardia, coccidia, ear mites, fleas, and ticks. These parasites are transmitted to cats through various modes of transmission such as ingestion, skin contact, from mother to kitten, and from the environment. Parasites can cause illness in cats and proper prevention and treatment is key.
Parasite Life Cycles
Cat parasites like toxoplasma gondii and various worm species have complex life cycles that involve multiple hosts. Toxoplasma gondii has an indirect life cycle where cats are the definitive host. The parasite reproduces sexually in the cat’s intestine and oocysts are shed in the feces. These oocysts can survive in the environment and be ingested by intermediate hosts like rodents. The parasite then forms tissue cysts in the intermediate host that are infectious to cats if ingested.
Intestinal worms like roundworms and hookworms have direct life cycles. Eggs are passed in the feces and larval stages develop in the environment. The larvae can then be ingested by the cat to complete the cycle. Fleas and ticks can act as intermediate hosts and transmit the larval stages when they bite the cat.
The key difference between direct and indirect life cycles is whether sexual reproduction and egg production occurs in the definitive host (direct) or in an intermediate host (indirect). For parasites with indirect cycles, the cat is essential to complete the sexual phase and continue the parasite’s life cycle.
Fleas
Fleas are perhaps the most common parasite that can transmit diseases to cats. Fleas can carry tapeworms, and if a cat swallows an infected flea during grooming, they can contract tapeworms as well. The flea life cycle begins when flea eggs are laid on the cat’s skin. The eggs hatch into larvae, which live in the cat’s surrounding environment. The larvae then molt into pupae before emerging as adult fleas that jump onto the cat and feed on its blood.
To prevent flea transmission of parasites, it is critical to use monthly flea control products on cats and treat the home environment as well. Vacuuming frequently can help remove flea eggs and larvae. Washing bedding in hot soapy water is also recommended. There are also environmental flea control products that can be sprayed inside the home.
Stopping the flea life cycle is key to preventing fleas from transmitting parasitic diseases to cats. With diligent flea control on the cat and in the home, flea transmission of parasites can be avoided. For more details on flea prevention, see Cat Owners – Fleas.
Ticks
Ticks are a common parasite found on cats that can transmit a variety of diseases. Some of the most concerning tick-borne diseases in cats include cytauxzoonosis, tularemia, Lyme disease, and anaplasmosis (PetMD). Cytauxzoonosis is caused by the parasite Cytauxzoon felis, which infects and destroys red blood cells, leading to severe anemia (VCA Animal Hospitals).
Ticks go through four life stages: egg, larva, nymph, and adult. After hatching from eggs, ticks must feed on blood at every stage to survive and advance to the next stage. Ticks transmit diseases when they attach to cats’ skin and feed. Cats typically get ticks from exposure to wooded, brushy areas. Prevention involves using tick preventatives, checking cats thoroughly for ticks, and keeping cats away from tick habitat.
There are a number of options for preventing ticks on cats, including spot-on liquid treatments, collars containing repellents, and oral medications. Ticks must be attached for at least 24 hours before disease transmission occurs, so prompt tick removal is critical for preventing illness. If a tick-borne illness is suspected, cats require veterinary care which usually involves medications and supportive therapies.
Ingestion
Many parasites are transmitted when cats ingest infected prey or feces containing parasite eggs or cysts. Common parasites transmitted through ingestion include:
- Toxoplasma gondii – This parasite infects rodents and birds which cats may eat. Cats can become infected by eating raw meat containing tissue cysts with T. gondii, or ingesting feces or soil contaminated with oocysts shed in the feces of infected cats (1).
- Toxocara cati – Cats ingest infective eggs from contaminated soil or feces. The eggs hatch in the intestines, larvae penetrate the intestinal wall and migrate to muscles where they encyst as infective larvae. These larvae are transmitted to new hosts when cats ingest paratenic hosts like rodents (1).
- Dipylidium caninum – Cats become infected by eating fleas or lice containing infective larvae. Larvae are released during digestion and attach to intestinal mucosa where they develop into adult tapeworms (2).
- Giardia – Cats ingest cysts shed in the feces of infected cats. The cysts excyst in the small intestines, resulting in infection (3).
Preventing ingestion of infected prey, proper fecal disposal and environmental disinfection helps reduce parasite transmission through contaminated food/feces (1,3).
(1) Source 1
(2) Source 2
(3) Source 3
Skin Contact
Some cat parasites can be transmitted through direct contact with breaks or wounds in the skin. For example, the mange mite Sarcoptes scabiei is a zoonotic parasite that causes scabies in cats. Humans can contract this mite from infected cats if there is skin-to-skin contact where one of them has an open wound. The mites burrow into the skin and cause intense itching and skin irritation in both cats and humans.
Another example is the hookworm Ancylostoma tubaeforme. The larvae of this worm can penetrate intact skin and infect cats or humans, causing cutaneous larval migrans. This results in serpiginous, raised, itchy skin lesions as the larvae migrate through the skin. Wearing protective clothing and avoiding skin contact with areas contaminated by infected cat feces can help prevent transmission.
In general, good hygiene and avoiding direct contact with stray/unwell cats is important. Any wounds or scratches should be promptly washed and treated as they could allow parasite entry. Seeking medical care for suspicious skin lesions, especially those that are itchy or slowly migrating, can ensure proper diagnosis and treatment.
Mother to Kitten
Cats can transmit toxoplasmosis vertically from mother to kitten. When a pregnant cat is infected with Toxoplasma gondii for the first time during pregnancy, she can pass the parasite onto the developing fetuses through the placenta. Kittens infected this way are often stillborn or die shortly after birth. Kittens that survive may have symptoms like fever, enlarged liver and spleen, jaundice, central nervous system disorders, eye inflammation and pneumonia. Nursing kittens can also become infected by drinking milk from an infected mother cat. According to the Cornell Feline Health Center, around a third of kittens nursed by an infected mother cat will contract toxoplasmosis this way. However, kittens are only susceptible to infection from milk for the first few weeks of life before their immune system develops sufficiently. After this early stage, drinking milk from an infected mother does not pose a risk (Toxoplasmosis in Cats, 2023).
Environment
Contaminated environments play an important role in the transmission of Toxoplasma gondii, the parasite that causes toxoplasmosis in cats and humans. Cats shed infective oocysts in their feces which can persist in the environment and remain infectious for many months or even years (Shapiro et al., 2019). These oocysts contaminate soil, sandboxes, grass, fruits and vegetables that cats or other animals graze on, and water sources. Humans can then become infected through ingestion of contaminated foods or water, or contact with contaminated soil
Oocysts are very hardy and resistant to disinfectants, heat, and cold, allowing them to survive for long periods outdoors. They can then be transmitted when humans ingest contaminated soil on raw fruits/vegetables or from contaminated water. This environmental contamination is an important additional route of transmission beyond direct contact with cat feces (CDC, 2022).
Proper food handling hygiene like washing fruits and vegetables and cooking meat to safe temperatures can help prevent ingestion of oocysts. Cat owners should dispose of cat litter properly and keep cats indoors to prevent shedding oocysts into the outdoor environment. Since oocysts are so hardy, prevention of shedding is key as environmental contamination can persist for months.
Prevention
Preventing parasitic infections in cats requires vigilance on the part of the owner. There are several effective ways to help prevent cats from acquiring parasites:
Administer flea, tick, and heartworm preventative medication as prescribed by your veterinarian. Products such as Revolution, Advantage, Frontline, and others can repel external parasites and prevent infestation.
Keep your cat indoors and do not allow exposure to other cats whose health status is unknown. This prevents the spread of parasites through contact.
Thoroughly clean the litter box daily. Parasite eggs can linger in the litter and be ingested during grooming.
Do not feed your cat raw or undercooked meat, fish, or eggs. Freeze meat-based diets for several days to kill any parasites.
Maintain cleanliness in your home and yard. Regularly vacuum and wash your cat’s bedding. Keep soil coverings like mulch and sandboxes away from areas your cat frequents.
Schedule annual fecal exams with your veterinarian to detect parasites early before infestation.
Control rodents and fleas in your home and yard to reduce vectors that can transmit parasites.
Treatment
Discuss diagnosing and treating parasitic infections.
If a cat is showing signs of a parasitic infection, such as diarrhea, vomiting, or skin irritation, the first step is to take the cat to a veterinarian for an examination and diagnostic testing. The vet will check for parasites by examining a stool or skin sample under a microscope. Blood tests may also be run to check for antibodies against certain parasites.
Once diagnosed with a specific parasite, the vet will prescribe medication to kill the parasite. Common anti-parasitic medications include praziquantel, pyrantel pamoate, fenbendazole, ivermectin, milbemycin, and selamectin. These are typically given orally in pill or liquid form, topically as a spot-on, or by injection. It is important to follow the vet’s instructions carefully and give the full course of medication, even if symptoms improve. This ensures the parasite is fully eliminated.
In addition to medication, the environment should be thoroughly cleaned to prevent reinfection and transmission to other pets. Bedding should be washed in hot water and vacuuming should be done frequently. The vet may also recommend follow-up fecal exams to confirm the parasite has been eradicated.
With prompt diagnosis and treatment, most parasitic infections can be cured. However, some parasites are difficult to fully eliminate so monitoring and preventative medication may be recommended by the vet. Overall, working closely with your vet is key to successfully diagnosing and treating any parasitic infection in cats.