Transcript Document

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