Indian Pediatrics 2002; 39:941-944
Diarrheal diseases remain a leading cause of morbidity and mortality in children all over the world. Chronic diarrhea accounts for 3-23% cases of diarrhea and 36-56% diarrhea deaths in developing countries(1). Search in last decades for causative agents of severe, life-threatening and persistent diarrhea in immunocompromised individuals with special reference to patients with human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS) has highlighted the importance of opportunistic pathogens such as Cryptosporidium, Cyclospora, Microsporidia and Isospora spp. Intestinal coccidiosis causing diarrhea was infrequently reported before HIV infection. Isospora belli is the only species of Isospora that infects humans and is endemic in south east Asia, Africa and parts of the South America. It produces self-limiting watery diarrhea, malabsorption and weight loss in immunocompetent host(2,3). However, it is also responsible for chronic severe watery diarrhea, in immunocompromised patients (AIDS, hematological and lymphoreticular malignancies). Among HIV infected and AIDS patients, I. belli has been detected in 8-20% patients in Haiti and Africa, and 1-3% in USA(3). Human beings acquire the infection following ingestion of infective oocysts from either symptomatic or asymptomatic cases. To find out the prevalence of I. belli infection, fecal samples from both normal and immuno compromised individuals were examined during January 1990 to December 1999 in our laboratory. The clinical features and laboratory data of isosporiasis in children during this period are described.
Subjects and Methods
All cases with diarrhea irrespective of clinical features, HIV exposure and other immunocompromised states referred from the wards and out-patient departments were investigated. Diarrhea was defined as 3 or more watery to semisolid motions in 24 hours. Chronic diarrhea was defined as diarrhea occuring on at least 50% of the days in preceding month (i.e., either two weeks of continuous diarrhea or recurrent episodes for at least 15 days). Stool samples were collected from each individual; in more than 50% cases 3 consecutive stool samples were obtained. Most of these patients complained of abdominal pain, diarrhea, nausea, vomiting and flatulence. Detailed clinical history, relevant laboratory investigations and outcome of therapy were noted. Patients were also analyzed by their age, race, ethnicity, gender and HIV exposure. HIV serological status in vulnerable groups was determined.
Upon enrollment, stool samples were processed and examined using following methods: direct stool sample was examined within 1-2 hour for the presence of leukocytes (methylene blue stain); wet-mount preparations with both saline and iodine to look for motile trophozoites and larvae, ova, cyst and oocysts respectively. A part of the stool sample was processed by the formal-ether concentration technique(4). Saline and iodine wet-mount preparations of final formol-ether concentrate were examined microscopically for oocysts, cysts, ova and larvae. Modified acid-fast stain were also performed to fecal smear to look for Cryptosporidium, Cyclospora and Isospora. Each wet-mount preparation and stained fecal smears were examined by two microbiologists independently.
Seven children were diagnosed to have isosporiasis. Of 10126 patients whose stool was examined, 4112 (41%) were children. Seven children were positive for I.belli. The clinical data of patients with isosporiasis with or without HIV infection is summarised in Table I. Their ages ranged from 4 months to 8 years. Two children were HIV seropositive. Five children had diarrhea and were emaciated. Other laboratory parameters were within normal limits. Diagnosis of Isospora infection was made by visualisation of oocysts of I. belli. (both mature and immature forms) in either direct wet-mount or in wet-mount preparation of formal-ether concentrates under 400×magnification. Stool cultures for enteric bacterial pathogens were negative. Fecal leukocytes were not seen in any patient.
The patients showed satisfactory clinical response to treatment with oral cotrimoxazole.
Table I__Clinical Features and Course of Isosporiasis
* Failure to thrive # Lower respiratory tract infection
The diagnosis of isosporiasis is made following detection of oocysts (20-33 µm × 10-19 µm) of I. belli, which are passed in stool. Usually the oocyst contains only one immature sporont, but two may also be present. Continued development occurs outside the body with the development of two mature sporocysts, each containing four sporozoites. The sporulated oocysts is the infective stage, which upon ingestion excyst in small intestine, releasing the sporozoites that penetrate the mucosal cells and initiate the life cycle in the infected host. Intestinal infection due to I. belli is distributed world-wide and highest incidence has been described in underdeveloped countries. In the Indian sub-continent, few reports of isosporiasis have been cited in the literature(5-6). Very rarely disseminated extra-intestinal infections may occur(7). Disseminated infection occur because Isospora, like other coccidian parasites, may persist in a chronic state and reactivate during immunosuppression.
The present study showed only seven patients were positive for I. belli. In contrast, Cryptosporidium spp. has shown a slightly higher prevalence at this center (data not shown). The reason for a low prevalence in this study could be because immature oocysts are shed intermittently, which might not necessarily correspond to periods of clinical symptoms. Similarly, occysts may not be shed during initial phase of infection when the asexual phase of life cycle predominates, and the clinical symptoms become apparent. In addition, extensive use of cotrimoxazole for treating trivial illness and for Pneumocystis prophylaxis in immunocompromised patients may substantially reduce the occurrence of isosporiasis. Similar low prevlaence of isosporiasis have been reported from other part of the Asia-Pacific region(8-11).
The clinical presentation of HIV positive and HIV negative children in present study did not differ. However, both HIV-seropositive children had profuse diarrhea. Chronic isosporiasis has been reported in both immunocompetent and immunocompromised individuals. But, none of our patients showed recurrence or had extra-intestinal manifestations during 18 months follow-up. I. belli infection is more common among children and decreases with increasing age(12). Even in immunocompetent hosts, disease due to I. belli is more severe in infants and young children than adults, probably reflecting a complex interaction between I. belli infection and the host immune status.
On the basis of the numbers of stool specimens sent to our laboratory for examination, we conclude that infection with this organism is not frequent. Further studies are necesary for delineating the role of host defence against I. belli infection. The involvement of species other than I. belli and the potential role of paratenic (transport) host including domestic animals in the trans-mission of infection also needs to be investigated to establish modes of transmission other than contaminated food and water.
The authors would like to thank the laboratory staff of Parasitology, Department of Microbiology, AIIMS for their active assistance.
Contributors: BRM coordinated the design and interpretation of the study and will act as its guarantor. SKK assisted in collection of data. JCS helped in analysis of data and preparation of the manuscript.
Funding: Part of the study was supported by a grant from the All India Institute of Medical Sciences, New Delhi.
Competing interests: None stated.