Microsporidiosis is a disease caused by any one of several microsporidia organisms, including Enterocytozoon bieneusi. The organisms infect the lining of the small intestine and can cause severe diarrhea and malabsorption (an inability to absorb nutrients). Some microsporidia organisms can also cause sinus, eye, and kidney problems. There have also been reports of microsporidiosis of the lungs.


It is not at all clear how people become infected with microsporidia. It is often found in feces of humans and animals and can be spread via feces-contaminated food and, quite possibly, oral-anal sex ("rimming").


People with compromised immune systems—usually people with a CD4 cell count below 100—may experience prolonged and severe bouts of diarrhea and malabsorption that can be difficult to treat. It's also important to note that not all people exposed to microsporidia, even if their immune systems are suppressed, experience symptoms of the infection.


What are the symptoms, and how is it diagnosed?

Watery diarrhea is a primary symptom of microsporidiosis, along with abdominal pain, weight loss, loss of appetite, dehydration, and passing gas (flatulence). More rarely microsporidiosis can lead to brain infections, eye infections, sinus infections, and whole body (disseminated) infections.


Microsporidiosis can be difficult to diagnose. Microsporidia are very small organisms and, in most cases, can only be detected using an electron microscope. Even then, some labs may miss the infection. Polymerase chain reaction (PCR), similar to viral load technology for HIV infection, can be used to help diagnose microsporidiosis.


How is it treated or prevented?

Unfortunately, these is no universally effective treatment for microsporidiosis. Many drugs have been studied in clinical trials. Some have been complete failures. Others have been shown to be effective for some but not for others.


The best treatment for microsporidiosis appears to be antiretroviral drugs used to treat HIV. By treating HIV effectively, it's possible to increase CD4 cell counts to levels above 100. In many cases, this has proven to work well for many HIV-positive people with microsporidiosis. Unfortunately, microsporidiosis can cause malabsorption and may decrease the level of HIV drugs that reach the bloodstream, so people should be monitored closely until their diarrhea has resolved. Antibiotics to treat microsporidiosis directly may also be used, but do not work consistently unless they are combined with ARV HIV treatment. It is also important with microsporidiosis to guard against dehydration, and oral rehydration solutions that include important electrolytes should be used aggressively.


There are actually three different approaches that can be taken when treating microsporidiosis: to treat the infection, slow the diarrhea, and correct the weight loss.


To treat the infection, some antibiotics have been shown to be somewhat effective. However, no antibiotics are approved by the U.S. Food and Drug Administration for the treatment of microsporidiosis. Antibiotics that have been shown in clinical trials to be somewhat effective include fumagillin (Fumagilin B; not available in the United States) and albendazole (Albenza). In disseminated disease, itraconazole (sporanoz) may sometimes be combined with Albenza.


To help control the diarrhea, perhaps in combination with antibiotic therapy, a number of antidiarrheal drugs can be taken. These include: diphenoxylate (Lomotil), loperamide (Imodium), paregoric, tincture of opium and Pepto-Bismol. And because diarrhea is the direct result of intestinal inflammation caused by the infection, some non-steroidal anti-inflammatory drugs (NSAIDS) may be helpful such as ibuprofen (e.g., Advil). Another drug that has been shown to greatly reduce diarrhea, due to its anti-inflammatory activity, is thalidomide (Thalomid). Women who take this drug should avoid becoming pregnant; thalidomide can cause severe birth defects.


Finally, to help correct the weight loss, there are two factors to consider: 1) eating healthy amounts of the right types of food, and 2) helping the body convert the nutrients in food into lean body mass (muscle). Making dietary changes may be necessary if you've lost weight because of microsporidiosis. To help determine how you should change your diet, you might want to ask your health-care provider to refer you to a registered dietitian. A registered dietitian can help identify weaknesses in an existing diet and make suggestions regarding dietary needs and how best to tailor them to meet individual tastes, schedules, and tolerances. Nutritional supplementation can also be extremely useful. A number of oral supplements - including Ensure, Sustacal, Citrisource, Jevity, and Replete - are widely available, but can be expensive. To meet individual dietary needs and/or restrictions, some are free of wheat, dairy (lactose), or other components that can be difficult to digest. Unfortunately, very few clinical trials of oral supplements have focused on whether or not they can sustain weight in HIV-infected individuals. If you need some help boosting your appetite, your health-care provider can prescribe medicines such as Marinol (gel-caps containing THC, the active ingredient in marijuana) and megestrol acetate (Megace).


Very often, HIV-positive people lose muscle—as opposed to fat—as a result of an illness that can cause weight loss. Losing muscle can be very serious, thus it is important to focus on increased muscle mass when attempting to regain weight. Research suggests that anabolic therapies, in combination with resistance exercise (e.g., weight lifting), are the most useful treatments to help boost muscle size as a component of reversing weight loss. The only anabolic therapy officially approved by the Food and Drug Administration (FDA) for the treatment of HIV-related wasting is human growth hormone (Serostim). Serostim has been shown to increase muscle and help the body convert fat into energy. The drug is usually taken once a day using a hypodermic needle. Other anabolic drugs being studied and used to help reverse muscle loss include: testosterone (either by injection, patch, or cream/gel), oxandrolone (Oxandrin), nandrolone (Deca-Durabolin), and oxymethalone (Anadrol). Interestingly, anabolic steroids appear to be better at increasing muscle mass than increasing overall weight. Therefore, they might be best used in combination with appetite stimulants and/or nutritional supplements to boost weight.


A syndrome—called immune reconstitution inflammatory syndrome (IRIS)—where antiretroviral treatment can actually exacerbate the symptoms of an opportunistic infection due to a strengthened immune response, has not been reported with microsporidiosis.


The most effective way to prevent microsporidiosis is to avoid its sources—mainly potentially contaminated foods or human feces. People should wash their hands frequently and avoid drinking unfiltered tap water or using ice made from unfiltered tap water. Meats and fish should be washed thoroughly, fruits and vegetables should be pealed, and oral-anal sex should be performed with a latex barrier (e.g., a dental dam or saran wrap). This is particularly true for HIV-positive people with compromised immune systems.


Are there any experimental treatments?

If you would like to find out if you are eligible for any clinical trials involving new treatments for microsporidiosis, visit ClinicalTrials.gov, a site run by the U.S. National Institutes of Health. The site has information about all HIV-related clinical studies in the United States. For more info, you can call their toll-free number at 1-800-HIV-0440 (1-800-448-0440) or email contactus@aidsinfo.nih.gov.

Last Revised: January 18, 2016