Isospora spp. in chronic diarrhea: A case report.

Sir,

It is estimated that there are approximately 340 parasite species capable of infecting humans, with the majority of the infected population residing in developing regions of the world.[1] The immune system, through local and systemic responses has an important role to play in modifying the establishment of infection, controlling the disease, limiting the severity and in clearance of the parasite. Isospora belli is a coccidian, unicellular protozoan parasite that resides in the gastrointestinal tract of humans. It usually causes non-bloody diarrhea in tropical and subtropical climates. In immunocompromised patients, the disease can vary in severity from chronic intermittent illness to a severe life-threatening diarrheal illness.

A 17-years-old boy came to the gastrointestinal medicine out-patient department with complaints of chronic intermittent diarrhea since 8 months. Stools were non-bloody and watery. There were 10-12 episodes/day. The patient was severely dehydrated and cachexic with significant weight loss (12% in the last 3 months). Reports of routine biochemical investigations were within the normal limits. The patient was found to be human immunodeficiency virus (HIV) positive by the fourth generation enzyme linked immunosorbent assay. The stool sample was watery in consistency, a saline mount, iodine mount and modified Ziehl-Neelsen (ZN) stain or Kinyoun stain for coccidian parasites[2] was examined. Direct wet mount revealed large numbers of epithelial cells, pus cells (30-40/high power fields [HPF]) and red blood cells (5-10/HPF). Oocysts of I. belli, (predominantly immature) intermingled within the mucous were seen [Figure 1]. They were long, oval, measuring 20-31 μm × 11-19 μm. Modified ZN staining revealed acid fast Isospora oocysts [Figure 2]. Bacterial culture of the stool performed as per standard protocols did not grow any pathogenic bacteria. The patient was referred to integrated counselling and testing centre for his newly diagnosed HIV status. His CD4 count was 470/cumm. The patient was put on trimethoprim (160 mg)-sulfamethoxazole (800 mg) 4 times a day for 10 days. He improved considerably and was discharged for follow up at anti retro-viral therapy clinic.

Figure 1

Wet mount showing oocyst of Isospora belli

Figure 2

Modified Ziehl‑Neelsen stain showing acid fast oocyst of Isospora belli

I. belli is a protozoan parasite of the phylum Apicomplexa, class Sporozoa, subclass Coccidian and family Eimeriidae. The parasite invades the small intestine epithelium and completes its life cycle in the cytoplasm of the enterocyte. Oocysts excreted in feces develop into mature cysts outside the host; each oocysts containing two sporoblasts, which in turn contain four sporozoites. The sporulated oocysts are the infective stage, which upon ingestion exist in the small intestine. Intestinal infection due to I. belli is distributed worldwide, however higher incidence is reported from developing regions of the world.[3] The infection is typically self-limited in immunocompetent hosts, but can become chronic in the immunocompromised causing protracted wasting diarrhea. Incidence of Isosporiasis in HIV seropositive population in India has increased up to 26%.[4] In contrast to earlier reports of a higher incidence of Cryptosporidium spp. as primary etiological agent in HIV-associated diarrhea.[5] In the present case, the HIV status of the patient was discovered due to chronic diarrhea by Isospora. This confirms the status of Isosporiasis as an AIDS indicator disease. Another peculiar fact was that CD4 counts (470/cumm) were not as low as expected for a chronic opportunistic parasitic infection of 8 months duration; one which had led to significant weight loss. Probably this was the reason why the patient responded almost immediately to medication.