Cats that are allowed to roam outdoors are most likely to develop an infestation of kidney, or renal, parasites. Wild animals such as raccoons are hosts for these parasites and often pass their eggs through feces or urine to intermediate hosts, such as earthworms or frogs, that may become prey for cats. Cats that hunt and eat prey are vulnerable to ingesting parasites, placing themselves at risk of developing serious health conditions.

Parasites, such as Dioctophyme renale, can enter the kidneys of a cat, causing differing signs of infestation. Because parasite infestation doesn’t always result in noticeable symptoms, the condition can progress and cause the affected cat to become extremely ill, especially if it develops a significant infestation or experiences kidney failure.

Most cats are initially asymptomatic (showing no symptoms) when their kidneys are infested with parasites. Other cats may have vague symptoms that don’t point to a definite diagnosis:

Various kinds of parasites can enter the cat’s kidneys, developing into a significant infestation. Examples of kidney parasites include:

Capillaria plica  is a small parasitic nematode that more commonly affects dogs than cats. Infestation may resolve itself, though medication may be prescribed.

Dioctophyme renale is a parasitic roundworm that can grow as much as three feet long. Called “giant kidney worm”, this parasite can cause extensive kidney damage. Often, only one kidney is affected. The remaining, healthy kidney typically compensates for the loss of function in the damaged kidney, resulting in a lack of symptoms. Surgical removal is often required.

The eggs or larvae of parasites that affect a cat’s kidneys are generally acquired through ingestion of infected prey. Small prey animals, such as earthworms and frogs, act as intermediate hosts for the parasites after picking up eggs shed in the urine of wild animals such as raccoons and mink. 

Upon evaluating a cat’s symptoms, such as frequent or uncontrollable urination, a vet may first consider a urinary tract infection. Examining a urine sample from the cat may rule out infection and instead reveal the presence of eggs from parasitic worms. In some cases, eggs may be detected in the cat’s feces.

X-rays an abdominal ultrasound may be used to detect an enlarged kidney. Urine, stool, and blood samples may be collected for laboratory analysis. Often, Dioctophyme renale is only detected by observation during abdominal surgery, at which time it can be removed.

Vets commonly prescribe antiparasitic medications, which work by killing the worms inside the kidneys and abdomen. Anti-parasitic drugs are better known as deworming medications, which can have several uncomfortable side effects for the cat, such as an increase in salivation, upset stomach, diarrhea and a loss of appetite. These medications include ivermectin or fenbendazole.

Cats taking an anti-parasitic medication may also feel lethargic and less alert. If the cat develops body twitches or vomiting, it should be seen by the vet. Kittens should be watched closely by their owners for muscle tremors, white gums, blood in the stool, weakness, lowered energy and feeling cold or hot to the touch.

Surgical removal may be required for large Dioctophyme renale worms. If the affected kidney has been severely damaged, it can typically be safely removed while the cat’s remaining kidney assumes its function.

After receiving a diagnosis of kidney parasites, the cat’s owner should give the cat every dose of medication exactly as prescribed until the vet says the infestation has been completely eradicated. At-home care following surgery may require cage rest, modified diet, and the use of an E-collar to prevent the cat irritating the incision site. Follow-up visits will be scheduled to monitor the cat’s condition and check for evidence of parasites.

Once the infestation has been completely eliminated from the cat’s body, it’s vital that the cat’s owner prevent the cat from returning to hunting and killing wildlife outdoors. If the cat has been used to roaming out of doors, it may need to be retrained to become an indoors-only pet.

If the cat enjoys eating fish or frogs, both should be thoroughly cooked so that any parasites in either one are killed. Raw or undercooked fish or frogs can lead to another kidney parasite infestation. If raw fish are brought home for eating, the refuse (organs and other body parts) should be properly discarded to prevent the cat eating it.