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