182 J Clin Pathol 1991;44:182-193 Opportunistic protozoan infections in human immunodeficiency virus disease: Review J Clin Pathol: first published as 10.1136/jcp.44.3.182 on 1 March 1991. Downloaded from highlighting diagnostic and therapeutic aspects A Curry, A J Turner, S Lucas Introduction AIDS. The AIDS epidemic has considerably Opportunistic protozoan infections are among increased our awareness of this organism, the most serious infections in patients with which is now known to be a common child- AIDS."A They cause severe morbidity and hood infection among the immunocompetent mortality; because many are treatable, it is in whom the infection is self-limiting.8 In important that early and accurate diagnoses patients with AIDS and in other immuno- are made. This is normally accomplished by compromised groups infection can be both direct microscopic visualisation of the parasite protracted and life threatening. It has a par- in infected tissues or body secretions. Rigid ticularly high incidence in HIV positive adherence to normal diagnostic procedures patients with diarrhoea in Africa" and it is may not be appropriate in patients with AIDS found in up to 10% of most series of HIV because the site and manifestation of some of positive patients with diarrhoea in the United these infections may be unusual. Experience Kingdom and the United States of America. of these conditions among histopathologists The gastrointestinal tract from oesophagus to and microbiologists is extremely variable. rectum, the biliary tract including intra- Furthermore, treatment of the protozoan hepatic ducts, and the bronchial tree can be infections in patients with AIDS is often com- infected in patients with AIDS.'2"3 Infection plicated by severe side effects and a high rate is caused by the ingestion of oocysts in food or of recurrence. water. We review the known protozoan infections Cryotosporidium under both the light in human immunodeficiency virus (HIV) microscope and the electron microscope seropositive people, the appropriate tissues to occupies an extracytoplasmic location within sample, the light and electron microscopic an intracellular parasitophagous vacuole (figs appearances, and briefly outline appropriate 1, 2, and 3). Laboratory diagnosis of Crypto- antibiotic treatment. The protozoa identified sporidium infection requires the staining of http://jcp.bmj.com/ to date in these patients are listed in the table. oocysts in faecal smears with modified Ziehl- Neelsen or auramine stains.'4 Monoclonal Predominantly intestinal infections Various infectious agents have been found in Protozoafound in HIV seropositive patients the gastrointestinal tract of patients with some which be Phylum sporozoa (alt: Apicomplexa) on September 23, 2021 by guest. Protected copyright. AID 5,-7 of may associated Class Coccidea with symptoms. For potential protozoan in- Order Eimeriida be Cryptosporidium fections, several stool samples should Isospora examined for cysts or oocysts before invasive Sarcocystis are considered. If microscopical Toxoplasma procedures Class Piroplasmea examination of wet preparations or fixed and Order Piroplasmida stained stool fails to show the Babesia samples Class Haemosporidea presence of an infectious agent, then biopsy Order Haemosporida may be necessary. A rectal biopsy specimen, Plasmodium which is easily taken, may indicate the Phylum Microsporidia (alt: Microspora) of a but it is not Class Microsporea presence protozoan infection, Order Microsporidia always the most appropriate site of the intes- Encephalitozoon Public Health tine to sample. For some protozoan infections, Enterocytozoon Laboratory, such as microsporidiosis, diagnosis is impossi- Phylum Rhizopoda Withington Hospital, Class Lobosea Manchester, M20 8LR. ble without biopsy of the small bowel. Entamoeba A Curry Coccidioses Coccidian protozoa are all Acanthamoeba A J Turner intracellular with complex life cycles parasites Phylum Metamonada Department of comprising asexual (schizogony), sexual Class Anaxostylea Histopathology, (gametogony), and sporogenous phases. At Order Diplomonadida University College and Giardia Middlesex School of some stage in their respective life cycles, all characteristic which can be Phylum Kinetoplasta Medicine, University possess structures, Order Trypanosomatida Street, London seen under the electron microscope. Trypanosoma S Lucas Cryptosporidium Now the most well recog- Leishmania Correspondence to: Dr A Curry nised of intestinal coccidia, °0 human Possible protozoon: Blastocystis infection was considered to Accepted for publication Cryptosporidium Protozoon or fungus: Pneumocystis 26 July 1990 be both rare and zoonotic before the advent of Opportunistic protozoan infections in HIV disease 183 Figure 1 Cryptosporidium in a rectal biopsy specimen. Note the superficial location of this parasite J Clin Pathol: first published as 10.1136/jcp.44.3.182 on 1 March 1991. Downloaded from (haematoxylin and eosin). antibodies have been used on faecal smears in ethnic groups within countries, however, and paraffin wax sections, but they stain only isosporiasis is relatively common in patients oocysts and not the smaller trophozoites.15 A with AIDS.'8 In the United States of America rectal biopsy specimen shows the parasite in the incidence among Hispanics with AIDS is many cases, but a duodenal biopsy specimen 8%; the incidence among others with AIDS is is probably more sensitive; both tissue biopsy 1%.19 A similar high incidence of I belli has specimens and faecal smears can identify a been noted in Haitian patients with AIDS small proportion of organisms that the other (12%) and in Africa." 161820 This organism has has modality missed.'6 also been recorded in patients with AIDS in http://jcp.bmj.com/ Attempts to treat Cryptosoporidium infec- the United Kingdom (S Lucas, personal ob- tion have met with limited success. Most servations). The zoonotic reservoir-if there reports concern the use of spiramycin17; is one-is unknown. relapses are common, occurring in up to 50% Chronic watery diarrhoea is the major of patients at three months. Although a large symptom of isosporiasis. Infection is pre- number of other drugs have been used, there sumably through ingestion of oocysts in food is no established effective treatment. or water. The infected enterocytes of the small on September 23, 2021 by guest. Protected copyright. Isospora Before the advent of AIDS there intestine (the main organ infected) show com- were few recorded human intestinal infections pletely intracellular and intracytoplasmic caused by Isospora belli.5 In some countries or parasites (figs 4-7). There is some evidence for ,.. k.,:., .1 ..V4 ~~.E " W~~~n'Ss~Ir-i 44 t l.*- Figure 2 Electron micrograph of a human rectal biopsy Figure 3 Electron micrograph ofa schizont of specimen showing intracellular but extracytoplasmic Cryptosporidium. location of a late trophozoite stage of Cryptosporidium. 184 Curry, Turner, Lucas J Clin Pathol: first published as 10.1136/jcp.44.3.182 on 1 March 1991. Downloaded from Figure 4 Four zoites of Isospora seen in cross section Figure 6 Early schizonts ofIsospora-largegranular (arrowhead) within a duodenal enterocyte mononuclear cells arrowed (haematoxylin and eosin). (haematoxylin and eosin). latency, as isosporiasis may develop several Laboratory diagnosis of Isospora depends months or years after presumed exposure.'9 on faecal examination for oocysts (fig 8) or a Mild to severe mucosal inflammation, often biopsy of the small intestine where the enteric with eosinophilia, and crypt hyperplastic stages may be found in the gut wall. Com- atrophy occur; the parasites vary in abun- petent histological diagnosis is complicated by dance. Extraintestinal infection by Isospora the similarity of this organism to both Sarco- http://jcp.bmj.com/ has been described in a patient with AIDS in cystis and Toxoplasma; it is larger than micro- whom both the small and large bowel were sporidia. Like Cryptosporidium, tissue biopsy infected; the organism was also found in specimens and faecal smears identify small mesenteric lymph nodes.2' numbers of cases the other modality has on September 23, 2021 by guest. Protected copyright. Figure S Six sickle-shaped zoites ofJsospora seen in Figure 7 Multinucleatedgametocyte of Isospora in an longitudinal section in a duodenal biopsy specimen enterocyte (haematoxylin and eosin). (arrowhead) (haematoxylin and eosin). Opportunistic protozoan infections in HIV disease 185 Figure 8 Faecal smear patients with AIDS. Enterocytozoon bieneusi, withfour ovoid oocysts of Isospora belli (modified which was first described in such a patient,2526 Ziehl-Neelsen). seems to be the commonest human micro- sporidian infection. This organism has only J Clin Pathol: first published as 10.1136/jcp.44.3.182 on 1 March 1991. Downloaded from been found in symptomatic patients (up to 6 5%)27 in whom the major features are mal- absorption and diarrhoea. Its role in the pathogenesis ofdiarrhoea is still being debated. It seems to replicate and produce spores exclusively within the small intestinal wall without evoking any major tissue response. A duodenal or jejunal (not rectal) biopsy specimen is therefore necessary for diagnosis. Demonstration of the organisms within small intestinal enterocytes is possible using simple histological strains27 (figs 11 and 12), but elec- tron microscopical examination is required for definitive diagnosis, and is more sensitive (figs 13 and 14).28 Faecal smear examination is not useful because the small size of