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Biology and Control of Giardia and Cryptosporidium

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. Latent. Acute. Elimination. Period. Phase.

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Biology and Control of Giardia and Cryptosporidium

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  1. Biology and Control of Giardia and Cryptosporidium Miodrag Belosevic, PhD, FRS(TMH), Department of Biological Sciences University of Alberta

  2. Waterborne Protozoa • Cryptosporidium • Giardia • Entamoeba • Naegleria • Toxoplasma • Acanthamoeba

  3. Latent Acute Elimination Period Phase Phase The Course of Protozoan Infections in Different Hosts

  4. Characteristics of Infection • low numbers of parasites required to initiate infection • multiplication in the host- transmission • self-limiting - except immundeficient individuals • Zoonosis -cross-species transmission

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. Parasites in Water Detection in Environment Inactivation Efficacy Viability Assays Animal Infectivity

  11. Measures of Viability • ANIMAL INFECTIVITY: expensive, very reliable • EXCYSTATION: not accurate-overestimates viability • CELL CULTURE: underestimates viability, contamination • NUCLEIC ACID DYES: inexpensive, convenient & rapid

  12. 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, time-consuming

  13. Infectivity Assay • Infectivity in neonatal CD-1 mice • Flow cytometry of lower half of intestine

  14. 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

  15. 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

  16. Factors Affecting Chemical Inactivation • Water quality • dissolved organic carbon • pH • temperature • turbidity • Concentration of oxidant • Contact time

  17. Degree of Microbial Inactivation Required for 1:10,000 Annual Risk /Person 5 4 Adequate protection 3 Overall oocyst treatment 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.

  18. 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

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