General Information: Protozoans are single-celled,
free-living, animal-like organisms ranging in size from 0.005 mm
to 5 mm. All life-sustaining processes occur in one cell. Except
for some in wet soil, all protozoans occur in the aquatic
environment. Pathogenic protozoans comprise approximately 10,000
of the 35,000 species of protozoans known, and cause some of the
worst diseases (Mitchell et al., 1988).
Pathogens posing problems in drinking water are Giardia
lamblia, Entamoeba hystolytica, Cryptosporidium, and
Naegleria fowleri (AWWA, 1990).
Giardia lamblia: Causes Giardiasis, a
gastrointestinal disease. Giardia can exist as
a trophozite (9 to 21 um long) or as an ovoid cyst
(10 um long and 6 m wide). Ovoid cysts can survive in
water for one to three months. Humans become infected
after ingesting as few as 10 cysts. Giardiasis can be
transmitted by water and from person-to-person.
Entamoeba hystolytica: Causes dysentary and
ulceration of the colon and liver. E.
hystolytica survives in an amoeboid form in the
intestines. Spherical cysts are excreted in the
Cryptosporidium: When ingested, an oocyst
infects the cells of the digestive tract, epithelium,
liver, kidneys, and blood. The entire life cycle
occurs intracellularly. Excretion occurs in the
feces. Transmission occurs through ingestion of
oocyst-containing water (Kubek et al., 1990).
Naegleria fowleri: Causes the fatal disease
amoebic meningoencephalitis. N. fowleri gains
access to the brain tissues through nasal passages
(Mitchell et al., 1988).
Human Consumption: The maximum contaminant level goal
(not enforced) for protozoans is zero cysts per 100 ml sample
of drinking water. The maximum contaminant level (MCL) is
simply whatever level the best available technology can
achieve (Kubek et al., 1990).
Health Effects: Protozoans pose a hazard primarily in
areas lacking sanitary conditions. Pathogenic protozoans may
cause serious health problems, including gastrointestinal
disease (Giardia lamblia, Cryptosporidium), dysentary
and ulceration of the colon and the liver (Entamoeba
hystolytica), and amoebic meningoencephalitis (
Naegleria fowleri). Ingestion of and primary contact
with water are the primary methods of transmission.
Environmental Effects: Giardia and
Cryptosporidium can both infect mammals if the oocysts
are ingested. Infected animals experience symptoms similar to
those experienced by humans and act as vectors to enhance
transmission to humans(Kubek et al., 1990).
Agriculture: Protozoan cysts may originate in
livestock excrement from barnyards, pastures,
rangelands, feedlots, and uncontrolled manure storage
areas; and areas of land application of manure and
Residential and Urban: Failed on-site wastewater
disposal systems can contribute protozoan cysts to a
water body. Urban runoff may convey cysts from litter
and domestic pet excreta.
Other: Cysts in ground water may originate from
landfill oxidation ponds and deep well injection of
sewage. Other surface water sources include boats
that discharge raw sewage overboard; excreta from
wild animals in surrounding watersheds; and excreta
from wildfowl that congregate on the water body.
Point source: Sewered communities may
not have enough capacity to treat the extremely
large volume of water sometimes resulting from
large rainfalls. Periodically, treatment
facilities may find it necessary to bypass
treatment of their wastewater. In this case,
water containing protozoan cysts is discharged
directly into the surface water body.
Mode of Transport: Transport in
water: Water carries protozoan cysts to
surface water systems in overland flow (runoff),
unsaturated flow, and saturated flow. Cysts in
overland flow can be transported freely and within
organic particles. Overland flow is the most
direct route for protozoan transportation.
Underground flow is less direct because water flow
and cyst passage are impeded by soil permeability
and porosity constraints.
Waterborne diseases may be transmitted to
Drinking water: municipal, domestic,
industrial, and individual supplies.
Primary contact recreation: bathing,
Secondary contact: boating, fishing.
Ingestion of shellfish.
Analytical Techniques: Current methods for protozoan
detection are poorly standardized.
Isolation and identification of protozoa is difficult because
they are relatively few in number, even in polluted water.
Instead, other more plentiful organisms such as total
coliforms, fecal coliform, and fecal streptococci are often
used as indicator organisms. Detection of the indicator
organism suggests that protozoa might also be present.
Standard tests for coliforms are performed to assess probable
presence of protozoa (Tchobanoglous 1991).
Although methods are poorly standardized, to test for
protozoans, take your water quality sample to a qualified
laboratory for inspection.