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There are a variety of parasites that can infect our cats – especially those with the freedom to hunt and roam the world. Intestinal parasites can be especially debilitating for kittens, and on and off diarrhea is often attributed to yet to be diagnosed case of intestinal parasitism. External parasites such as ear mites are very bothersome and can be passed easily between cats and even infect the family dogs. Also, some of the parasites infecting cats can infect humans, so it is important to be aware of these little bugs!

Read below for some information on the parasites we commonly find in our cats.  

Intestinal Worms

There are several intestinal worms that we worry about infecting our cats – Roundworms and Tapeworms are the most common.  These intestinal parasites can affect growth and development in our kittens, cause decreased health in adult cats, and can also be a dangerous zoonotic risk if passed on to humans (especially children)!  Most infections can be found through routine fecal analysis looking for worm eggs. Treatment of intestinal worms often involves multiple treatments of medication spaced several weeks apart in order to ensure all adult worms are removed from the intestines. Below is some information on the most common intestinal worms we see in our cats.

Roundworms – Infection occurs through ingestion of infective eggs from the environment – either from contaminated soil (typically ingested through routine grooming), from ingesting an infected rodent, or through the mother’s placenta and/or milk ingested by newborn kittens. Once ingested, the larvae migrates throughout the cat’s intestines, liver and lungs (depending on species) before growing into an adult in the intestines and laying eggs that pass in the cat’s feces. These worms can grow up to 7 inches in the intestines.  This worm does pose a risk to humans! If a human ingests an infective egg, the larvae travel randomly throughout the body before dying, causing severe inflammation. Eggs are fairly hardy in the environment and can survive freezing temperatures.

Tapeworms – There are several types of tapeworms that can infect cats. All tapeworms go through a cycle which includes an intermediate host (that is, the cat sheds the tapeworm eggs, which are ingested by either a flea, a grazing mammal, or a rodent for example, where the tapeworm develops further. The cat must then ingest the immature tapeworms from the intermediate host to finish the life cycle). Luckily tapeworms are easily treated, but care must be taken to treat flea infestations and/or prevent hunting and scavenging of carrion to prevent re-infection from occurring. Tapeworms can also infect humans through the same mechanisms, but not directly from cats.  


Heartworm disease affects cats too! And it is a real risk in our area.  Immature heartworms are delivered directly to the blood of our pets via infected mosquitoes. The heartworm’s ideal host is a dog (or similar species), but can infect a cat. In cats, the larvae travel unpredictably throughout the heart and lungs, causing respiratory distress as well as heart disease. A respiratory crisis that appears to be ‘asthma attacks’ in our cats, may in fact be due to heartworm infection.  At this time, there is no way to treat heartworm infection in cats, which is very scary. This makes it very important to prevent it from occurring in the first place with monthly heartworm prevention. It is important to remember that the heartworm parasite lingers in the area mainly due to dogs who are not on prevention, and in our wild animals such as foxes and coyotes and of course the abundant mosquito population that circulates the parasite between animals. Also, because mosquitoes often make it indoors, it is still important for cats who mostly live indoors to be on prevention as well.

External Parasites

Because cats are fastidious groomers, they can be less severely infected by external parasites compared to other pets, but they are not immune. Often, we can visualize external parasites if we look closely enough. However parasites such as mites (which can burrow under the skin and hide) and even some cases of flea infections (they can jump on and off of our cats) can be almost impossible to visualize. Diagnosis often requires swabs or skin scrapings to look under the skin and in some cases medication trials. There are also several options for treatment that will prevent infection of fleas and ticks.  

Mites – There are many different types of mites that can infect our cats. Ear mites and mange mites are the two most common types of mites to infect cats. Some of these infections cause extreme itchiness and secondary infections. Some are transmissible to humans. Ear mites are particularly common in cats and easily transmissible between feline and canine family members. Ear mites can cause extreme discomfort, causing self-trauma with excessive scratching at the ears. 

Fleas – these little guys are often dropped off by infected wildlife and can quickly infest entire homes. Flea bites can cause allergic reaction in cats leading to intense itchiness. Furthermore, fleas are the intermediate host in one type of tapeworm infection. These guys will bite humans too and can give tapeworms to humans if ingested. 

Other Parasites

Giardia – this protozoan parasite is picked up from a contaminated environment (often dirty water), similar to other intestinal parasites that are passed in the feces. It typically causes diarrhea and, depending on the species, can readily infect humans. This parasite is hardy in the environment. 

Tritrichomonas – this little protozoan parasite is also picked up from a contaminated environment, often ending up on paws that are then licked clean, causing ingestion of the parasite. It can cause mucousy, bloody stool. Often infected older cats will no longer have diarrhea, but can still infect other cats in the household, and diarrhea can flare up during times of stress.

Coccidia – this small parasite infects the intestine, causing diarrhea (sometimes bloody). Small infections will not always cause diarrhea, but will act as a source of infection for other animals by contaminating the environment. Some species of coccidia can infect humans (cryptosporidium is a particularly unpleasant example). Routine fecal analysis often will lead to detection of these little oocysts.