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Biology and Control of Giardia and Cryptosporidium Miodrag Belosevic, PhD, FRS(TMH), Department of Biological Sciences University of Alberta Waterborne Protozoa Cryptosporidium Giardia Entamoeba Naegleria Toxoplasma Acanthamoeba The Course of Protozoan Infections in Different Hosts Latent Period Acute Phase Elimination Phase Characteristics of Infection low numbers of parasites required to initiate infection multiplication in the hosttransmission self-limiting - except immundeficient individuals Zoonosis - cross-species transmission Cryptosporidium: Public Health Significance Worldwide prevalence about 10% Zoonosis, human and animal genotypes Oocysts ubiquitous in surface waters Difficult to remove, and hard to kill Drinking water - amplifier for disease Up to 20% of general population may be considered at higher risk Cryptosporidiosis: The Disease Serious disease in the young, pregnant women, patients undergoing chemotherapy and elderly Potentially fatal in immundeficient hosts Infectious dose in healthy humans is low: ID50 about 130 oocysts No effective chemotherapy available Giardia: The Organism obligate intestinal parasites of all classes of vertebrates more than 100 described species two stages in the life cycle: the motile trophozoites that inhabit the small intestine of the host, and the resistant cysts found in the environment Giardiasis: Public Health Significance Worldwide prevalence about 8%, much higher in endemic areas Zoonosis Most prevalent in day care centers, mental institutions, male homosexuals Children, elderly and immunodeficient persons more susceptible Transmitted by direct contact, food or water Chemotherapy available- some drug resistance Giardiasis: The Disease asymptomatic: largest group symptomatic: self-limiting infection, diarrhea, abdominal cramps,fever, nausea and weight loss symptomatic: chronic infection, immunodeficient individuals, malabsorption, food intolerance, chronic inflammation of the mucosa Parasites in Water Detection in Environment Inactivation Efficacy Viability Assays Animal Infectivity Measures of Viability ANIMAL INFECTIVITY: expensive, very reliable EXCYSTATION: not accurateoverestimates viability CELL CULTURE: underestimates viability, contamination NUCLEIC ACID DYES: inexpensive, convenient & rapid Animal Infectivity Answers the public health question: will the organism cause an infection? Depends on the dose-response in susceptible animal hosts Complex, labor intensive, timeconsuming Infectivity Assay • Infectivity in neonatal CD-1 mice • Flow cytometry of lower half of intestine Modern Concept of Inactivation Organisms are organic particles Sources in water supplies include: human wastes from point-sources uncontrolled non-point source pollution from agriculture and natural sources disposal/recycling of water treatment wastes View microbial reduction as a system of multiple processes designed to eliminate/inactivate infectious particles Control of Protozoa In Drinking Water Multiple barrier approach: – Filtration – Chemical inactivation- ozone, combination of disinfectants – Medium-pressure ultraviolet light (UV) Monitoring: – Presence of protozoa in raw water – Viability assessment in finished water Factors Affecting Chemical Inactivation Water quality dissolved organic carbon pH temperature turbidity Concentration of oxidant Contact time Degree of Microbial Inactivation Required for 1:10,000 Annual Risk /Person Overall oocyst treatment 5 4 Adequate protection 3 2 Inadequate protection 1 0 0.01 0.1 1 10 100 1000 Influent oocysts (no./100 L) From: C.N. Haas et al. 1996. Journal of the American Water Works Association, 88(9): 131-136. Microbial Reduction Goals Health effects criteria: serum antibody surveys of communities parasitological survey of communities Quantitative risk assessment: concentration of parasite in source water assume annual per person risk level of 1:10,000