Pathogenesis: Infections vary markedly in their presentation ranging from asymptomatic to mild acute to severe chronic disease. Endogenous intestinal stages may cause microvillus destruction, villus atrophy, impaired glucose and electrolyte transport, impaired carbohydrate and protein digestion manifesting in malabsorptive and maldigestive disease. Most clinical infections in immunocompetent individuals involve transient acute disease characterized by profuse watery foul-smelling diarrhoea or acute respiratory signs. Neonates and malnourished individuals are most susceptible, whereas older animals become resistant (immune) to infection. Infections may persist in immunocompromised individuals (those with congenital or acquired immunodeficiencies or those undergoing immunosuppressive therapy) resulting in protracted chronic disease which may prove fatal (especially in AIDS patients). In contrast, infections in reptiles (and possibly fish) cause chronic gastritis typified by postprandial regurgitation.

Mode of transmission: Oocysts excreted by infected hosts contaminate the environment and initiate infections when ingested by susceptible hosts (faecal-oral transmission). Some (thin-walled) oocysts are thought to be auto-infective and may excyst in the same host. Most infections are transmitted by fomites between individuals held in close confinement, such as in child day-care centres, hospitals, zoos, and intensive animal rearing facilities. In addition, oocysts are being detected with increased frequency in treated and untreated water supplies. Many water-borne outbreaks of public health significance have been reported involving contamination of potable and recreational waters (lakes, pools, water parks) by sewage and/or agricultural waste. While conventional methods of water treatment (filtration and chlorination) may reduce contamination levels (quantified by log removal and concentration-time parameters), the small tough oocysts are quite resistant and enough persist to pose a significant problem for water providers. Food-borne transmission has also been recorded (involving milk, cider, salads, sausages), probably attributable to contaminated water being used in food production.

Differential diagnosis: Infections are conventionally diagnosed by the detection of oocysts in smears or concentrates of faecal material or respiratory exudates. Unstained oocysts may be confused with yeasts but they are acid-fast and stain well with basic fuchsin stains. Alternatively, phase-contrast or differential interference contrast microscopy can be used to reveal internal oocyst features, as can vital dyes (DAPI) and fluorescent nucleic acid stains (MPR71059). Although some parasite species can be cultured in vitro (in tissue cultures) or in vivo (in laboratory or neonatal domestic animals), considerable variation has been observed in parasite infectivity and growth. More success has been reported in detecting oocysts in clinical and environmental samples using specific monoclonal antibodies for immunomagnetic separation or as fluorescent markers for microscopy or flow cytometry. Researchers have also developed several highly sensitive techniques using polymerase chain reaction (PCR) amplification of partial gene sequences followed by electrophoretic fingerprinting.

Treatment and control: There is currently no effective chemotherapeutic treatment for cryptosporidiosis, although variable success has been reported using paromomycin and nitazoxanide. Supportive treatment by oral or parenteral rehydration may help alleviate symptoms. Some promising results have been obtained using hyperimmune bovine colostrum for passive immunotherapy. Control measures include identification of the source of infection, isolation of infected individuals, maintaining high standards of hygiene, proper effluent disposal and disinfection of contaminated surfaces. Public health authorities also recommend boiling water during outbreak situations and also more regularly for high-risk patients groups (such as HIV-positive individuals).

< Back to top