Intestinal protozoan infections in the immunocompromised host

PURPOSE OF REVIEW: Intestinal protozoa are becoming increasingly recognized as significant pathogens in immunocompromised hosts. However, pathogenesis of infection is still poorly understood, diagnostic tests remain insensitive, and management continues to pose a challenge. RECENT FINDINGS: Invasion by intestinal protozoa can be facilitated by impaired host T-cell immune response, although the exact pathogenesis at the cellular level is unclear. HIV-infected and transplant patients have been reported to have the highest risk for developing severe disease. Cryptosporidium is the most common parasite encountered in the immunocompromised host, followed by Cyclospora and Isospora. In recent years, Microsporidia and Blastocystis have also emerged as important players, due in part to improved molecular diagnostic assays. Effective drugs against these parasites in immunocompromised patients have not been reported in recent years. When possible, reducing the level of immunosuppression seems to be the most effective treatment strategy in combination with adjunctive antiparasitic therapy. SUMMARY: Despite that intestinal protozoan infections cause greater morbidity and mortality in the immunocompromised host, their pathogenesis in the setting of immunosuppression is poorly understood and efforts to develop new therapeutic agents are rather limited. Improving detection and identification of species or subtypes by PCR will result in improved management decisions and a better understanding of the epidemiology of intestinal protozoa. Favorable clinical outcomes can be achieved by early detection and effective treatment of the infection. Further research on key aspects of pathogenesis at the cellular level in humans is needed.