Giardia and Cryptosporidium in Drinking Water
These two microscopic organisms are protozoa pathogens that live in the gut of warm blooded animals including humans. They can cause intestinal illnesses with mild symptoms and often go unnoticed. However in some instances, symptoms can be more severe and are especially serious for immunocompromised individuals. Because both organisms can form protective cysts when released in faeces, Giardia and Cryptosporidium can survive for long periods in the environment.
Giardia
This is the most common enteric protozoan pathogen of humans, domestic animals and wildlife.
Once a person has ingested cysts of Giardia, they become flagellated pear shaped trophozoites which are the active feeding stage colonizing the upper part of the small intestine. Generally, only trophozoites are present in faeces when an infected person has diarrhea. When trophozoites pass slowly toward the large intestine, they develop into cysts.
Several studies have shown that there appears to be a certain proportion of the population (up to 20%) that carry Giardia, but of these, two thirds show no symptoms of infection. When an infection is noticed, symptoms are: indigestion, flatulence, nausea for a mild infection; or when more severe: vomiting, diarrhea, abdominal cramps and weight loss.
Possible sources of infection are person to person (faecal-oral transmission), untreated drinking water supplies, especially ones infiltrated with human waste. Children day care centers are also well known to be regular sources of infection due to the lack of adequate hygienic practices by young children. It has been shown that children are up to three times more susceptible to infection than adults, suggesting that immunity to infection is acquired over time.
Much of the current research now being undertaken is trying to elucidate whether cross-infections can occur between humans and other animals. Some recent work has indicated quite strong evidence for infections between humans and dogs.
Cryptosporidium
While recognized in animals for over a century, Cryptosporidium wasn’t identified as a threat to humans until the AIDS epidemic in the 1980’s. In 1993 a waterborne outbreak infecting more than 403,000 people in Milwaukee, Canada, has shown that it is a potential major hazard to the general population. It is now regarded as the most important water-borne human pathogen in developed countries.
In comparison to Giardia, Cryptosporidium has a more complex life-cycle. It has intracellular development in the gut wall as well as asexual and sexual reproduction.
Symptoms of cryptosporidiosis are: fever, loss of appetite, nausea, crampy abdominal pain and watery diarrhea.
Sources of infection are similar to Giardia, however Cryptosporidium strains that infect humans appear to have a much wider host range with other animals. Young dairy calves for example, are sources of large numbers of cysts of the same species that infect humans.
Treatment
Because both organisms are quite resistant to chlorine, the best water treatment processes are ones that can filter out these organisms prior to chlorination. Tweed’s Bray Park Water Treatment Plant has Membrane Ultrafiltration with a nominal pore size of 0.04 micrometers. This not only effectively excludes protozoa such as Giardia and Cryptosporidium, but also much smaller organisms such as bacteria.
Testing the Water
The methods for detecting Giardia and Cryptosporidium in water samples are still not reliable and expensive to perform. Moreover, routine testing cannot at this stage determine between species that are infective to humans or different hosts. For these reasons, no guideline values are given for either organism in the Australian Drinking Water Guidelines (NHMRC). Instead, potential threats to drinking water supplies are determined using indicators such as E. coli which are shed in huge numbers from faeces in all individuals (whether infected or not). The presumption is that if no E. coli are present in a water sample, then no recent faecal contamination has occurred.
Medical Advice
If you or a member of your family appears to have symptoms of infection from either pathogen or other illness, it is strongly recommended to seek professional medical advice.
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