Progress report intestinal protozoa

Cystoisospora belli infections in humans: the past 100 years

Cystoisospora belli is a coccidian parasite of humans, with a direct fecal-oral transmission cycle. It is globally distributed, but mainly found in tropical and subtropical areas. Many cases of C. belli infections have been reported in patients with HIV, and in patients undergoing immunosuppressive therapy for organ transplants or those treated for tumours worldwide. Unsporulated or partially sporulated oocysts of C. belli are excreted in feces. When sporulated oocysts in contaminated water or food are ingested, asexual and sexual stages of C. belli are confined to the epithelium of intestines, bile ducts and gallbladder. Monozoic tissue cysts are present in extra-intestinal organs (lamina propria of the small and large intestine, lymph nodes, spleen, and liver) of immunosuppressed humans. However, a paratenic host has not been demonstrated. Cystoisospora belli infections can be persistent, lasting for months, and relapses are common; the mechanism of relapse is unknown. Recently, the endogenous stages of C. belli were re-examined and attention was drawn to cases of misidentification of non-protozoal structures in the gallbladder of patients as C. belli. Here, we review all aspects of the biology of C. belli, including morphology, endogenous stages, prevalence, epidemiology, symptoms, diagnosis and control.

Lipid analysis of Giardia lamblia and its culture medium

The neutral lipid and phospholipid composition of Giardia lamblia and its culture medium were analysed by a thin-layer chromatography flame-ionized detection system. Both lipid compositions of the parasite differed from that of the culture medium. Sterol was found to be the major neutral lipid, and phosphatidylcholine, phosphatidylethanolamine and sphingomyerin were also present. Fatty acid composition of G. lamblia and its culture medium were also analysed by gas liquid chromatography. Oleic and palmitic acid were the major fatty acids in the total lipid of the organism. The influence of porcine and bovine bile extracts on the lipid composition of G. lamblia was studied. The addition of bile to the medium caused no change in lipid composition of the parasite. Lipid composition of the culture medium was studied both before and following growth of the parasite, and it became evident that consumption of phosphatidylcholine occurred in the growth medium supplemented with bile extract. These results indicate that the presence of bile extract may possibly accelerate consumption by G. lamblia of lipid in the environment.

Giardia lamblia in children in day-care centres in southern Ontario, Canada, and susceptibility of animals to G. lamblia

In 1982, Giardia lamblia cysts were found in the faeces of eight of 97 children (two to five years old) in day-care centres in Guelph, Ontario, Canada. None of the infected children showed any of the classical signs of giardiasis. The survey was repeated in 1983 in the Kitchner-Waterloo area, Ontario. In this survey nine of 147 children were infected with G. lamblia. Experimentally established Giardia-free colonies of mice, hamsters, rats, cats (adults and kittens) and dogs (adults and puppies) could not be infected with Giardia cysts from clinical and non-clinical patients. Also, kittens, hamsters, and mice could not be infected by trophozoites from an axenic culture. However, five-day-old suckling rats can be infected with G. lamblia. Also, the Giardia-free rats and dogs are susceptible to their own Giardia (G. simoni and G. canis respectively). This proves that cats and dogs are not reservoirs of G. lamblia and consequently are not responsible for the spread of the infection in the human population.

The adherence of Giardia lamblia trophozoites to nylon fibre microcolumns: effect of temperature, fluoride, cyanide and metronidazole

A simple rapid method for the measurement of adherence of Giardia lamblia trophozoites is described. Microcolumns are prepared from 10 mg amounts of nylon fibre packed into 100 microliter size disposable pipette tips. The kinetics show that 30 min is the optimum contact time for the experiments. Maximum adherence occurred at 37 degrees C, minimal at 4 degrees C, and intermediate at 25 degrees C, suggesting that adherence is an energy-dependent process. Adherence was fluoride-sensitive but cyanide-insensitive, suggesting that this parasite derives its energy from the glycolytic pathway, and not the oxidative pathway. Metronidazole, one of the mainstays for chemotherapy of giardiasis, produced significant inhibition of adherence at 10 micrograms/ml and 100 micrograms/ml concentrations after one hour pre-incubation.