MICROSPORIDIOSIS

Microsporidia are worldwide ubiquitous intracellular protozoan parasit es infecting most major groups of the animal kingdom. In humans, micro sporidiosis has recently emerged as a significant cause of morbidity i n immunocompromised patients, and particularly in patients with acquir ed immunodeficiency syndrome (AIDS). Parasites of the genus Encephalit ozoon cause keratoconjunctivitis and disseminated infections. In 15 to 30 degrees of patients with advanced stage AIDS, Enterocytozoon biene usi is the causative agent of major chronic diarrhoea. Clinical manife stations include numerous (2 to 8) and abundant, irregular liquid or s emi-liquid stools without evidence of intestinal haemorrhage. Impaired absorption is aggravated by food intake causing the patients to restr ain from eating and subsequent weight loss is progressive and irrevers ible. The diarrhoea becomes permanent and leads to dehydration ad maln utrition. Spontaneous remissions have been observed but are always of short duration. Microsporidiosis has also been found in ocular localiz ations in patients with AIDS; these keratopathies may be due to Enceph alitozoon cuniculi, the only known species in mammals but E. hellem, a morphologically identical but antigenically different species has bee n identified. Other visceral localizations have been observed. Diagnos is of microsporidiosis relies on the demonstration of spores and/or in tracellular parasites in stools, urine or tissue biopsies. The respons ible agent can generally be identified by light microscopy, but differ entiation between species still requires electron microscopy, New ligh t and fluorescent microscopic techniques have been proposed for easier recognition of spores in various pathological samples. Immunodiagnost ic techniques are limited due to the lack of correlation between antib odies detection and clinical manifestations. Although the parasite can be identified and although its cycle has been carefully studied, no p rophylactic action can be taken because the mode of transmission remai ns largely unknown. Many treatment protocols have been tried but none have been found to be effective. Very little pharmacological data has been accumulated. Microsporidiosis is, and will remain, a major opport unistic infectious disease causing uncontrollable debilitating malnutr ition in AIDS patients unless an effective treatment can be found, a m ajor challenge for medical science.