Microsporidiosis Encephalitozoonosis in Cats

Encephalitozoonosis affects the cat’s lymphatic, gastrointestinal, ocular, brain, urinary tract, kidneys, liver, and biliary systems. Once the infestation affects the kitten’s or cat’s brain or kidneys, the vet may recommend having the pet humanely euthanized.

This parasite can be passed from cats to human owners. People who know their cat has been infected should be careful about handling the cat and its waste, especially if anyone in the family is immunosuppressed.

Microsporidiosis encephalitozoonosis is a parasitic infection caused by the parasite Encephalitozoon cuniculi, leading to infestation in several parts of the cat’s body. Once the cat has ingested this parasite, it may begin showing symptoms ranging from kidney issues, slow growth, depression and neurological issues. If the cat is still a kitten when it is infected, quick treatment is needed. Fortunately, this parasitic infection is relatively rare in the U.S., but if the cat has come from another country, its owners should be watchful.

Kittens infected with Encephalitozoon cuniculi will have symptoms in most of their body systems:

• Renal failure
• Stunted growth
• Loss of appetite and weight loss
• Neurological issues
• Thin, dull fur

In kittens, infection may become obvious a few weeks after birth. 

Older cats may be asymptomatic (showing no symptoms of infestation or illness), but if symptoms do manifest, they include:

• Strange gait
• Eye problems (cataracts, blindness and inflamed eyes that rapidly get worse)
• Behaviorally aggressive (biting, hissing and yowling)
• Depression
• Walking in circles
• Loss of control in limbs and muscles
• Blepharospasm (severe, involuntary closing of the eyelids)
• Convulsions
• Paralysis

E. cuniculi infection in cats can be caused by one of several factors:

• Contact with wildlife that has been infested
• Inflation or ingestion of parasitic spores
• Coming into contact with spores found in the feces, mucus and urine of infected animals
• Passed to unborn kittens by infected queen (mother cat)
• Eating the infected tissues of rodents or rabbits
• High humidity
• Living in a crowded kennel or cattery
• Though rare, this parasite and resulting infection can be spread through the cat’s body tissues after traumatic injury.

These spores can survive outside the cat’s body for months, making a deep cleaning and sterilization necessary to prevent infection.

The vet needs to conduct several complex tests to arrive at the correct diagnosis. Along with a complete physical and routine bloodwork, the vet will carry out a urinalysis, fecal analysis and further testing on the blood sample drawn from the cat. The testing will cover the serum biochemistry, ALP elevations, which tell the vet has too much protein in the cat’s system, and elevated ALT markers, which will indicate to the vet that the cat has experienced a liver injury because of the infestation.

The fecal analysis will have spores from the parasites, if the cat has truly been infected. The cat’s urine may have blood in it. The vet should run a test to check for this, as well as for too much protein. 

Another specialized test that could reveal the presence of encephalitozoonosis is a laboratory examination of some of the cat’s tissues (called a histopathology). The cat will test positive with this test depending on where the spores are in its body and how severely it has been infected. Depending on the remainder of the cat’s symptoms, the vet will need to run other tests of the cat’s cardiovascular, respiratory, ocular and liver systems.

Two additional tests include TEM and ELISA testing. A vet with specialized knowledge can run them. However, the tests are expensive and take a long time to provide results to the vet.

A lengthy course of treatment with antifungal medications will help to eradicate the E. cuniculi parasites and spores from the cat’s body. The drugs of choice include fenbendazole, oxibendazole, itraconazole and albendazole. Ideally, the cat should begin these medications before infestation travels to the cat’s kidneys or brain. If this happens, it is too late for treatment to be effective.

The cat should be treated as an inpatient in an animal hospital to ensure that all medications and courses of treatment are properly administered. During treatment, it should receive sufficient fluids to aid in its recovery.

While the cat is being treated in the hospital, the home, cattery, or shelter should be thoroughly cleaned with a solution of 70 percent ethanol, 10 percent formalin, hydrogen peroxide and 10 percent bleach to make sure that every last spore is killed and eliminated. Once the cat’s environment has been cleaned, the cat owner or shelter workers should ensure that re-infestation does not take place.

Recovery from an infection of E. cuniculi is possible if the infestation was caught soon enough. It’s vital that the cat finish taking the entire course of every medication prescribed so that every single microorganism will be killed. Treatment can take up to three months.

Once the cat has returned home, strong sanitary practices will be necessary. Keep the floors clean and wash the cat’s bedding and every blanket it normally uses.

As long as the infection was detected and diagnosed before reaching the cat’s kidneys and brain, the cat has a good chance of recovery, with the ability to resume its normal life.

If the cat has been allowed to run free and kill prey, the owner should train the cat to live indoors. Because so many wild animals carry the E. cuniculi parasite, reinfection is possible if the cat is allowed to go back outside.