TAG: The OI Report - microsporidiosis

THE OI REPORT:
A Critical Review of the Treatment & Prophylaxis of
AIDS-Related Opportunistic Infections (OIs)

MICROSPORIDIOSIS
by Laura Morrison

MICROBIOLOGY & EPIDEMIOLOGY
Microsporidia are small protozoal parasites widely distributed in nature that cause disease in both animals and humans. There are more than 90 known genera of Microsporidia and close to 1000 known species (Manheimmer 1994). Only five genera of Microsporidia are known to occur in man: Encephalitozoon, Septata, Enterocytozoon, Pleistophera and Nosema. It is unclear how people become infected with Microsporidia, although it is speculated that the parasite is transmitted through oral ingestion of feces (e.g., rimming) bearing mature spores (Eeftinck Schattenkerk 1991).

Microsporidiosis is mainly seen in those who are immunocompromised and emerged as a significant cause of disease in humans at the beginning of the AIDS epidemic (Canning 1990). There is no definitive data on the prevalence of microsporidiosis in people with AIDS (PWAs), partly because it is difficult to diagnose and also because it is usually not the first AIDS-defining illness seen in HIV-positive patients. Most available prevalence data focus on intestinal microsporidiosis, the most common microsporidial disease in PWAs, though infection of the eye and other organs may occur.

Two species, Enterocytozoon bieneusi (E. bieneusi) and Encephalitozoon or Septata instestinalis (S. intestinalis), are known to cause intestinal microsporidiosis, although E. bieneusi is responsible for about 90% of reported infections (Orenstein 1994). One study of 67 people with AIDS-related diarrhea and no other evident enteric pathogens found that approximately 30% were infected with E. bieneusi (Orenstein 1990). In another study by Kotler and Orenstein, 39% of people with AIDS and diarrhea who had been referred for gastrointestinal evaluation were diagnosed with microsporidiosis: 36% with E. bieneusi and 3% with S. intestinalis (Orenstein 1994).

Are Microsporidia disease-causing agents? There has been some debate as to whether Microsporidia are, in fact, pathogens in PWAs. Rabenek and colleagues at Baylor University published a prospective study of 106 people with HIV, 55 of whom had chronic diarrhea and 51 of whom did not. They found no significant difference in the presence of E. bieneusi between the two groups and concluded that Microsporidia might be coincidental to, rather than a cause of, diarrhea (Rabenek 1993). Weber and Bryan retorted in "Microsporidial Infections in Immunodeficient and Immunocompetent Patients" that the Baylor study suffered from insufficient sample size and "other possible methodical limitations" (Weber 1994). Kotler and Orenstein then published a prospective study of people with HIV who had been referred for GI evaluation with results significantly different from Rabenek and colleagues (Orenstein 1994). One hundred and forty-one of Kotler and Orenstein's patients had AIDS and diarrhea, 53 had AIDS without diarrhea, and 56 did not have AIDS. Eighty-three percent of those with AIDS and diarrhea had an identifiable enteric pathogen, with Microsporidia being the most common (39%). Only 2% of the AIDS patients without diarrhea and 3% of the non-AIDS patients had an identifiable enteric pathogen. Kotler and Orenstein concluded that microsporidiosis is, in fact, a common cause of chronic diarrhea and weight loss in PWAs.

In a letter to the editor of the American Journal of Gastroenterology, Carlson and Craig questioned Kotler and Orenstein's conclusion (Carlson 1995), noting that in Kotler and Orenstein's study, 17% of patients with AIDS and diarrhea had no detectable pathogen, suggesting that there is a non-microbial cause of diarrhea, and citing a recent study of their own about 12 patients with AIDS-associated diarrhea, which suggested the presence of intestinal enterocyte dysfunction without an infectious pathogen (Carlson 1994). Kotler and Orenstein replied that it was incorrect to conclude from the 17% of patients in their study without an identified pathogen that there is therefore "a mechanism of diarrhea in these patients unrelated to the presence of pathogens," since they did not test for all possible pathogens that could cause diarrhea. Conceding that their study was not ideally designed to determine cause and effect, they noted that "absolute criteria for cause and effect have not been satisfied for many enteric infections known to affect AIDS patients, including cryptosporidiosis, cytomegalovirus, mycobateria, and others, although few would doubt their pathogenicity." They also questioned the thoroughness of Carlson and Craig's search for pathogens in the 12 patients they reviewed, and stressed that their own, much larger study showed a strong correlation between the presence of Microsporidia and chronic diarrhea. They concluded that "comprehensive studies using the most sensitive and specific techniques available" are necessary to make the case that Microsporidia are not a cause of diarrhea" (Kotler 1995).

CLINICAL MANIFESTATIONS
The most common manifestation of intestinal microsporidiosis in PWAs is profuse, watery, non-bloody diarrhea, sometimes accompanied by abdominal pain and cramping, nausea, vomiting, and weight loss. Species of Microsporidia have been tied to disseminated disease, cholangitis (inflammation of the bile ducts), keratoconjunctivitis (inflammation of the cornea and conjunctiva), hepatitis, peritonitis (inflammation of the membrane lining the abdomen and internal organs), and infection of the lungs, kidney, liver, muscles, and the brain. Presence of Microsporidia, however, does not always correlate with symptomatic disease.

DIAGNOSIS
The microsporidial spores that are seen in humans are particularly small (1 to 2 microns in diameter) and difficult to detect because of their size and poor response to routine staining techniques (Weber 1994). Until recently, the only method for diagnosis was electron microscopy of a small bowel biopsy which was both invasive and expensive. Light microscopy with modified trichrome stain, Giemsa stain and Uvitex 2B stain are newer techniques which allow for identification of the Microsporidia in stools and duodenal fluids (Van Gool 1990; Weber 1992; DeGirolami 1995). Recent studies suggest polymerase chain reaction (PCR) is useful for detecting Microsporidia in stool (Velasquez 1996) and gut biopsies (Franzen 1996).

Carl Fichtenbaum suggests that despite advances in diagnostic techniques, many labs still fail to detect Microsporidia He contends that unless technicians are trained to look for Microsporidia or more advanced techniques are developed, it will not be reliably diagnosed (Carl Fichtenbaum, personal communication).

TREATMENT
There is no FDA-approved therapy and no standard of care for the treatment of microsporidiosis, though there have been several reports of partial success with several agents, including metronidazole, albendazole and thalidomide.

Metronidazole (Flagyl)
The antiparasitic drug metronidazole (Flagyl), was studied in 13 HIV-positive patients with mild microsporidial diarrhea who had 6 or fewer loose stools a day. Twelve patients were treated with metronidazole 500 mg thrice daily, and one patient with 250 mg twice daily. Ten of the 13 patients showed a reduction in diarrhea within two days of starting therapy, however, 5 of those who had follow up biopsies continued to show Microsporidia (Eeftinck Schattenkerk 1991). Blanchard and Gazzard responded that metronidazole was not effective in their patients with severe microsporidial disease. Their four patients received 800 mg metronidazole three times a day for three days or 400 mg metronidazole four times a day for seven days. In all four patients, there was no change in stool volume or frequency (Blanshard 1991). Side effects of metronidazole include neuropathy, bad taste and diarrhea.

Albendazole
Albendazole is a broad-spectrum antiparasitic agent. In 1992, Blanshard and colleagues published a report on six HIV-positive men with diarrhea and infection with E. bieneusi, who were treated with 400 mg oral albendazole twice a day for four weeks. All patients saw their symptoms resolve within one week of starting treatment. Post-treatment biopsies showed that none of the patients cleared the parasite, but many of the parasites appeared damaged under electron microscopy, suggesting that albendazole acts directly against the parasite (Blanshard 1991). Dieterich and colleagues treated 29 patients with AIDS and diarrhea due to E. beineusi with 400 mg oral albendazole thrice daily for a month. In the 26 evaluable patients, the mean number of bowel movements decreased from 7.0 to 3.8 stools per day. No post-treatment biopsy, however, demonstrated clearance of the parasite (Dieterich 1994).

A double-blind, placebo-controlled trial of albendazole in people with AIDS and microsporidiosis is currently under way at sites in Boston, Houston, Los Angeles, New York, San Francisco and Washington, DC. Patients are randomized to receive either 800 mg albendazole or placebo twice a day for 28 days, followed by 62 days of open label albendazole at 800 mg twice a day. The objectives of the study are to determine albendazole's safety and effectiveness in treating intestinal microsporidiosis in people with HIV. The primary clinical endpoint is a greater than 50% reduction in baseline stool frequency with a maximum of four bowel movements a day for five consecutive days. Secondary endpoints include decreased stool volume, weight gain, reduced parasite counts and improved quality of life.

A recent study randomized eight HIV and E. intestinalis-coinfected patients to albendazole 400 mg twice daily with meals for three weeks or placebo. All participants were white gay men with diarrhea. Median CD4 count ranged from15.5 (albendazole) to 31.5 (placebo). At three weeks of treatment, 100% (4/4) albendazole-treated and zero placebo patients cleared their E. intestinalis. Treated patients gained a median of 3.5 kilograms and their diarrhea stopped. Placebo recipients later received open-label albendazole and all cleared their E. intestinalis for a 100% cure rate. The eight individuals were then randomized to long-term maintenance with albendazole (400 mg twice daily) or no treatment. No treated patients experienced a relapse, compared with 3/5 (60%) of the untreated individuals (p=0.04). Side effects included abdominal pain (1), headache (2), increased liver function tests (1) and thrombocytopenia (1) (Molina 1997).

Albendazole is available on a compassionate use basis from SmithKline Beecham. If a patient and his or her physician want access to albendazole, the company can be reached at 1-800-877-7074 ext. 6454.

While there is no evidence that antiretroviral therapies improve a patient's ability to fight microsporidiosis, Carl Fichtenbaum notes that the stronger one's immune system, the better able one is to fight infection. He recommends that any patient presenting with microsporidiosis initiate maximum antiretroviral therapy (Carl Fichtenbaum, personal communication).

Thalidomide (Synovir™, Celgene)
Thalidomide is an oral sedative and hypnotic drug which was removed from the market in the 1960s because it was shown to cause birth defects when taken by pregnant women. Thalidomide has been approved by the FDA for the treatment of HIV-associated oral aphthous ulcers, and is also used in treating leprosy, lupus and a variety of other conditions.

Noting that thalidomide had been shown to inhibit tumor necrosis factor alpha (Sampio 1991), Sharpstone and colleagues were determined to study thalidomide for the treatment of microsporidial diarrhea because a correlation had been established between microsporidiosis and increased levels of tumor necrosis factor-alpha (TNF-a). They treated 12 HIV-positive patients with microsporidial diarrhea - all of whom had previously failed on albendazole - with 100 mg thalidamide nightly for three weeks. All showed clinical improvement in the form of reduced bowel frequency, decreased use of antidiarrheals, more solid stools or weight gain. Many patients improved within 3 days, but one patient had a total relapse after one week of therapy. Four patients had adverse effects: one developed a rash and stopped therapy after three days, leading to a recurrence of symptoms; three complained of drowsiness and two chose to halve their dosage of thalidomide to 50 mg a day, with no recurrence of symptoms (Sharpstone 1994). They concluded that controlled trials of thalidomide for microsporidial diarrhea should be conducted, and suggested that in the meantime it may be used to provide symptomatic relief.

Atovaquone (Mepron^® Glaxo Wellcome
Atovaquone is a broad-spectrum antiparasitic agent which has been approved by the FDA for treatment of mild-to-moderate PCP in Bactrim-intolerant patients.

Anwar-Bruni and colleagues gave 750 mg atovaquone three times a day to eight gay male AIDS patients with symptomatic microsporidiosis and no other evident diarrhea-causing pathogens (Anwar-Bruni 1996). All eight experienced clinical improvement, including a decreased number of stools (from a mean of 10+/- 2.5 at baseline to a mean of 2+/-1 after treatment) and weight gain (mean increase of 3+/-2 kg). The mean beginning of symptomatic improvement was 13 days (+/-2 SEM) after beginning treatment. Although monthly stool exams revealed the parasite was not completely eliminated, a more in-depth analysis of two patients' stool samples showed the numbers of Microsporidia were reduced. Small bowel biopsies for four patients also showed the continued presence of Microsporidia, but only one displayed fewer parasites than the baseline sample. The researchers concluded that atovaquone is a promising therapy that deserves further study and noted that a double-blind, placebo controlled clinical trial is underway.

A proposed ACTG-sponsored study of Atovaquone for microsporidiosis was cancelled due to lack of interest from member sites.

Antiretroviral Therapy
There has been considerable speculation that improved immune function brought about by combination antiretroviral therapy including protease inhibitors may help people clear microsporidiosis. Two small, uncontrolled studies presented in early 1997 suggest this may be the case.

In a study of patients with cryptosporidiosis and microsporidiosis, Carr and colleagues treated seven patients with microsporidial diarrhea with combination antiretroviral therapy including a protease inhibitor (Carr 1997). Within 12 weeks, diarrhea improved for all seven but one has since relapsed.

In another study, Benhamou and colleagues evaluated fifteen patients with chronic cryptosporidiosis (n=9) or microsporidiosis (n=6) who had been taking triple antiretroviral therapy including either Crixivan (IndinavirTM, Merck) or Norvir (RitonavirTM, Abbott) for a mean time of 3.8+/-1.4 months (Benhamou 1997). Four of six patients with micrososporidiosis revealed no identifiable parasites in multiple stool examinations, and diarrhea resolved for 12 patients.

*

Anwar-Bruni D, Hogan SE, Schwartz DA, et al.: Atovaquone is effective treatment for the symptoms of gastrointestinal microsporidiosis in HIV-1-infected patients. AIDS 10:619-23, 1996.
Asmuth DM, DeGirolami PC, Federman M, Ezratty CR, et al.: Clinical features of microsporidiosis in patients with AIDS. Clin Infect Dis 18:819-25, 1994.
Benhamou et, al.: Effects of triple antiretroviral therapies including a HIV protease inhibitor on chronic intestinal cryptosporidiosis and microsporidiosis in HIV-infected patients [abstract]. 4th Conference on Retroviruses and Opportunistic Infections, Washington, 1997.
Blanshard C, Gazzard BG: Microsporidiosis in HIV-1 infected individuals. Lancet 337:1488-89, 1991.
Blanshard C, Ellis DS, Tovey GT, et al.: Treatment of intestinal microsporidiosis with albendazole in patients with AIDS. AIDS 6:311-13, 1992.
Canning EU, Hollister WS: Enterocytozoon bieneusi (Microspora): prevalence and pathogenicity in AIDS patients. Trans R Soc Trop Med Hyg 84:181-86, 1990.
Carlson SJ, Yokoo HJ, Craig RM: Small intestinal HIV associated diarrhea. Evidence for panintestinal entrocyte disfunction. J Lab Clin Med 124:652-59, 1994.
Carlson SJ, Craig RM: Prevalence of intestinal microsporidiosis in HIV-infected individuals [letter]. Am J Gastroenterol 90:1184, 1995.
Carr A, et al.: Resolution of antibiotic-resistant cryptosporidiosis and microsporidiosis with potent combination antiretroviral therapy [abstract]. 4th Conference on Retroviruses and Opportunistic Infections, Washington, 1997.
DeGirolami PC, Ezratty CR, Desai G, et al.: Diagnosis of intestinal microsporidiosis by examination of stool and duodenal aspirate with Weber's modified trichrome and Uvitex 2B stains. J Clin Microbiol 33:805-10, 1995.
Dieterich DT, Lew EA, Kotler DP, et al.: Treatment with albendazole for intestinal disease due to Enterocytozoon bieneusi in patients with AIDS. J Infect Dis 169:178-83, 1994.
Dieterich D, Cazen R, Conteas C, et al.: A double-blind, placebo-controlled trial of albendazole in HIV-positive patients with intestinal microsporidiosis [protocol]. New York University, unpublished.
Eeftinck Schattenkerk JKM, van Gool T, van Ketel RJ, et al.: Clinical significance of small-intestinal microsporidiosis in HIV-1-infected individuals. Lancet 337:895-98, 1991.
Franzen C, Muller A, Hartmann P, et al.: Polymerase chain reaction (PCR) for detection of microsporidian DNA in gastrointestinal biopsies of HIV-infected patients [abstract: D061]. 36th Interscience Conference on Antimicrobial Agents and Chemotherapy, New Orleans, 1996.
Kotler DP, Orenstein JM: Response to Drs. Carlson and Craig [letter]. Am J Gastroenterol 90:1184-85, 1995.
Manheimmer S, Soave R: Protozoal infections in patients with AIDS. Infec Dis Clin of North Am 8:483-98, 1994.
Molina J-M, et al.: Albendazole for the treatment and prophylaxis if microsporidiosis due to Encephalitozoon intestinalis in patients with AIDS [abstract I-148], 37th ICAAC, Toronto, 1997.
Orenstein JM, Kotler DP: Prevalence of intestinal microsporidiosis in HIV-infected Individuals referred for gastroenterological evaluation. Am J Gastroenterol 89(11):1998-2002, 1990.
Orenstein JM, Chiang J, Steinberg W, et al.: Intestinal microsporidiosis as a cause of diarrhea in human immunodeficiency virus-infected patients: A report of 20 cases. Hum Pathol 21(5):475-81, 1994
Rabenek L, Gyorkey F, Genta RM, et al.: The role of Microsporidia in the pathogenesis of HIV-related chronic diarrhea. Ann Intern Med 119:895-99, 1993.
Sampio EP, Sarno EN, Galilly R, et al.: Thalidomide selectively inhibits tumor-necrosis-factor-alpha production by stimulated human monocytes. J Exp Med 173:699-703, 1991.
Sharpstone D, Rashid N, Anhur G, et al.: Faecal tumor necrosis factor-alpha and faecal alpha-one-antitrypsin in HIV infection [abstract]. Gut 35:40, 1994.
Sharpstone D, Rowbottom M, Nelson M, et al.: The treatment of Microsporidial diarrhoea with thalidomide [letter]. AIDS 9:658-59, 1995.
Van Gool T, Hollister WS, Eeftinck Schattenkerk JKM, et al.: Diagnosis of Enterocytozoon bieneusi microsporidiosis in AIDS patients by recovery of spores from faeces. Lancet 336:697-98, 1990.
Velasquez J, Carnevale S, Labbe J, et al.: Detection of the microsporidian parasite Enterocytozoon bieneusi by PCR in patients with AIDS [abstract: Th.A.4030]. XI Int Conf AIDS, Vancouver, 1996.
Weber R, Bryan RT, Owen RL, et al.: Improved light-microscopical detection of Microsporidia spores in stool and duoduenal aspirates. N Engl J Med 326:161-66, 1992.
Weber R, Byran RT: Microsporidial infections in imunodeficient and immunocompetent patients. Clin Infect Dis 19:517-21, 1994.

TAG home page