Biology and Control of Giardia and Cryptosporidium

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
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

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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

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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

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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

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Parasites in Water
Detection in Environment
Inactivation Efficacy
Viability Assays Animal Infectivity
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Measures of Viability

• ANIMAL INFECTIVITY expensive, very reliable
• EXCYSTATION not accurate-overestimates
  viability
• CELL CULTURE underestimates viability,
  contamination
• NUCLEIC ACID DYES inexpensive, convenient
  rapid

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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

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Infectivity Assay

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

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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

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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

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Factors Affecting Chemical Inactivation

• Water quality
• dissolved organic carbon
• pH
• temperature
• turbidity
• Concentration of oxidant
• Contact time

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Degree of Microbial Inactivation Required for
110,000 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.
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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 110,000