Page 67 - Medical Parasitology_ A Textbook ( PDFDrive )

60 7 Coccidia

(gametogony) in the cytoplasm of enterocytes and transform into macrogameto-
cytes and microgametocytes. After fertilization, a zygote is formed and develops
into an immature oocyst. These immature oocysts are excreted with faeces and
mature in the soil
Cystoisospora belli completes its life cycle in 1 host. Incubation period ranges
from 1 to 4 days.

Pathogenesis and Clinical Features

Once mature C. belli oocysts are ingested, they liberate sporozoites which invade the
enterocytes of the proximal small intestine. They become trophozoites, and asexual
multiplication (schizogony) produces merozoites which invade other uninfected cells.
Infection is usually asymptomatic. Clinical illness includes abdominal discom-
fort, mild fever, diarrhoea and malabsorption. Diarrhoea is usually watery with no
blood or pus and is self-limiting. Protracted diarrhoea can be seen in immunocom-
promised persons, particularly in HIV patients.

Diagnosis

1. Microscopic examination
To detect the oocysts in saline preparation of stool. Stool concentration tech-
nique may be required when direct wet mount is negative. The staining technique
used is modified Ziehl Neelsen stain or Kinyoun acid fast. Pink-coloured acid
fast oocyst can be demonstrated. Samples from duodenal aspirates and intestinal
biopsy can also be obtained for diagnosis.
2. Molecular diagnosis
PCR of the stool sample.

Treatment

Infection is self-limiting, hence, no treatment is indicated in immunocompetent per-
sons. Immunosuppressed patients with diarrhoea are treated with co-trimoxazole
(160 mg trimethoprim/800 mg sulfamethoxazole orally or i.v. 4 times/day for 10
days). Relapses can occur in persons with AIDS and co-trimoxazole is given for
maintenance therapy.

Prevention and Control

1. Proper faecal disposal
2. Personal hygiene