Cryptosporidiosis in perspective

In vitro activities of lytic peptides against the sporozoites of Cryptosporidium parvum

Cryptosporidium parvum is a protozoan parasite that causes mild to severe diarrheal disease in animals and humans. There are currently no effective chemotherapeutic agents available for the treatment of cryptosporidiosis. Recent studies have described small, naturally occurring antimicrobial lytic peptides with antiprotozoal activities. In the present study, the anticryptosporidial activities of three synthetic lytic peptides were determined in an in vitro sporozoite susceptibility assay. Sporozoite viability was assessed microscopically by the uptake of the vital dyes fluorescein diacetate and propidium iodide. Sporozoite viability was reduced by 93.5% following a 60-min exposure to 10 microM Hecate-1 at 37 degrees C. Shiva-10 reduced sporozoite viability by approximately 74.0% after a 60-min exposure at 100 microM and 37 degrees C. The cecropin-b analog SB-37 reduced sporozoite viability by 6.0% following a 60-min exposure at 100 microM and 37 degrees C. A control peptide showed no anticryptosporidial activity.

Asexual development of Cryptosporidium parvum within a differentiated human enterocyte cell line

Unremitting diarrhea with malabsorption is associated with Cryptosporidium parvum infection of the small intestine in patients with AIDS. The lack of a well-defined in vitro model of C. parvum infection has severely hampered research into the biology of cryptosporidial invasion of the host epithelial cell and development of new pharmacologic and immunologic therapies. The adherent human intestinal epithelial cell line HT29 when grown in glucose-free medium develops morphologic and functional characteristics of the small intestine enterocyte and was used to develop an in vitro model of infection. Cryptosporidium oocysts obtained from AIDS patients were applied to a monolayer of cloned, differentiated HT29.74 cells. Cells were fixed and stained to estimate the degree of parasite infection. Schizonts were easily distinguished from the host cell by light microscopy. Twenty-four hours after 10(5) oocysts were added to approximately 10(6) HT29.74 cells, Cryptosporidium infection rates varied from 50 to 120 schizonts per 1,000 cells. Among 14 different experiments, the mean infection rate was 91 (+/- 18) schizonts per 1,000 cells. Electron microscopy at 6 and 24 h confirmed intracellular localization and development of schizonts. The morphologic features of the cryptosporidial schizonts within HT29.74 cells, which included the presence of a dense band and feeder layer, were identical to those described during cryptosporidial infection of human enterocytes in patients with AIDS. Fewer schizonts were observed at 5 days and beyond. Infection of differentiated HT29.74 cells (62 and 65 schizonts per 1,000 cells at 24 and 72 h, respectively) was over five times more efficient than infection of undifferentiated HT29.74 cells (9 and 5 schizonts per 1,000 cells at 24 and 72 h, respectively). In vitro infection of differentiated HT29.74 cells will allow a better understanding of the mechanisms by which C. parvum infects the small intestinal epithelium and will allow a systematic evaluation of new therapeutic agents.

The prevalence of Cryptosporidium species in children in day care centres and primary schools in Salamanca (Spain): an epidemiological study

Cryptosporidium species was found in 1.8% (2/113 children in the first sampling) and 1.9% (2/107 children in the second sampling) of the children studied in 11 day care centres. All cases were observed in children younger than 3 years of age, who were immunocompetent and asymptomatic. No cases of parasitization by Cryptosporidium species was detected in 67 children aged 5-14 years attending 7 primary schools.

Coccidiosis and cryptosporidiosis in sheep and goats

The protozoan diseases, coccidiosis and cryptosporidiosis, are important enteric diseases of sheep and goats, resulting in diarrhea, inefficient weight gains, and occasionally death. Coccidiosis is a widespread, serious economic disease affecting animals who are preweaned, recently weaned, or in unsanitary, stressful, or crowded conditions, as well as after entering feedlots. The Eimeria species in sheep and goats are relatively host specific. Control is accomplished through sanitation and by incorporating one of the modern coccidiostats, such as lasalocid or decoquinate, in feed or salt to ensure an intake of approximately 1 mg of drug per kg of body weight per day for at least 30 consecutive days. Prevention and control of coccidiosis results in significantly greater weight gains and production, whereas disease with or without treatment is likely to result in inefficient production and economic loss to the producer. Cryptosporidiosis, caused by Cryptosporidium parvum, is primarily a disease of lambs and kids less than 30 days of age and is usually a milder disease than coccidiosis. Infective oocysts are passed in feces and are transmitted by oral ingestion. Oocysts readily infect a variety of animals, including humans. Cryptosporidiosis is a prevalent disease in neonatal ruminants and in humans. Effective treatments are not available, but because the disease is usually mild and self-limited, supportive care, primarily hydration, is important. Control is strict sanitation and quarantine of sick animals. Disinfection of contaminated housing with ammonia or formalin will kill the oocysts. The cyst-forming coccidia diseases, toxoplasmosis and sarcocystosis, utilize two hosts in their life cycles: sheep or goats and carnivores. Abortions and reproductive failures are major manifestations of disease. Control is through elimination of carnivore feces from the premises through management.

In vitro cultivation of Cryptosporidium parvum and screening for anticryptosporidial drugs

Sporozoites of Cryptosporidium parvum which were excysted in vitro from oocysts isolated from calves or patients with acquired immune deficiency syndrome underwent development in monolayers of the mouse fibroblast cell line L929. Asexual multiplication occurred, with the maximum numbers of parasites usually being observed between 24 and 48 h after infection. Gametocytes were also found, but their numbers were relatively small compared with those of the asexual stages. A study was made of the effect on parasite development of 20 antimicrobial agents, most of which were anticoccidial or antimalarial agents. The majority of the drugs had a limited inhibitory effect on parasite development, but usually only at high concentrations. The two most active drugs were monensin and halofuginone, which reduced parasite multiplication by more than 90% at high concentrations. In the case of monensin, however, inhibition of parasite development at higher concentrations was due, at least in part, to a toxic effect of the drug on the host cells.

Cryptosporidiosis and AIDS

Cryptosporidiosis in patients with AIDS presents as a chronic enteritis, with biliary complications in about 10% of sufferers. The disease is persistent and progressively fatal. Due to the widespread prevalence of the parasite in the community and amongst domesticated animals, persons with AIDS are constantly at risk. Treatment is extremely difficult in view of the apparent lack of a specific anticryptosporidial drug. Methods of immunomodulation are worth considering, but the main recourse may have to be a prolonged regimen of rehydration and parenteral nutrition. However, if T helper cell function improves, the disease may go into remission or the parasite could be eliminated. Vaccination of those at risk is not feasible at present.

Epidemiological aspects of human cryptosporidiosis

The coccidian protozoan parasiteCryptosporidiumhas been described in many host species since its discovery in the early part of the century, but it remained obscure until the recognition by veterinary workers in the 1970s of its importance as a cause of scours in young livestock animals [1–4].

Experimental cryptosporidiosis in hamsters

A new laboratory animal model for experimental cryptosporidiosis is described. Adult immunosuppressed hamsters were infected per os with 0.5 x 10(5) and 1 x 10(5) Cryptosporidium oocysts of calf origin. The mean numbers of oocysts shed per gram of feces per day and the patterns of infection are described. The susceptibility to Cryptosporidium infection, the total number of oocysts shed (a thousand times the infective dose), and the ease of handling in laboratory conditions make hamsters a good animal model for cryptosporidiosis.