Giardia in water supplies
What is Giardia
Giardia is a waterborne parasite found widely distributed around the world including South Africa. It is found in man, dogs, pigs, sheep, beavers and in many other domestic mammals and birds (AWWA, 1999: Cox 1991). Giardia cysts are found in large numbers in untreated and treated sewage effluent (Robertson et.al 1995). When ingested it can cause an unpleasant illness referred to as giardiasis (often referred to as travellers diarrhoa). Infection is transmitted by tiny spore-or egg-like cells called cysts. Giardia cysts are oval in shape with a length of 9-12 micrometers (FWR ROCK document 2002).
The Giardia life cycle
The life cycle of Giardia in contrast to Cryptosporidium is very simple involving two stages, a flagellate (Trophozoite), which multiplies in the intestine and an infective thick walled cyst which is shed intermittently in large numbers in the faeces.
After ingestion the cyst passes through the stomach where it ex-cysts to produce two throhozites which colonise the small intestine. They are about 12 –18 micrometers in length and pose a sucking disk which they use to adhere to the mucous membranes of the small intestine thus inhibiting the adsorption of nutrients. (FWR ROCK 2002)
Similar to Cryptosporidium oocysts, the Giardia cysts also have thick protective walls which ensure their survival in the environment and which are also highly resistant to the disinfectants used to treat drinking water.
Does Giardia pose a health risk?
Yes and it has resulted in various outbreaks of gastrointestinal disorders throughout the world.
How is Giardia contracted?
Consumption of contaminated drinking water is but one of several routes through which transmission can occur. Recreational waters, including swimming pools are also emerging as an important source of giardiasis. Other routes include direct contact with infected human carriers, pets and occasionally contaminated food. The most likely source of giardiases remains the use of untreated water contaminated with animal and human waste.
Are all Giardia Oocysts infectious to humans?
As with most infective agents there is a so-called infective dose which will vary from person to person depending on the physical condition of the person and the state of their immune system. The infective dose has been set between 10 and a 100000 viable cysts. One or two cysts are unlikely to cause an infection unless the individuals’ immune system is severely compromised.
What are the symptoms of Giardiasis?
The symptoms of giardiasis are acute diarrhoea with abdominal cramps, bloating and excessive flatulence. The severity of the illness can vary considerably and only 25% of the infected people show symptoms of the illness. Malabsorption of food can lead to considerable loss of weight. The incubation period can be anything from 1 to 75 days with a median of 7 – 10 days. (FWR ROCK 2002)
Treatment of Giardiasis
Unlike cryptosporidiosis, giardiasis is not regarded as a disease which may be fatal although left untreated the victim may suffer for an extended period of time. Unlike cryptosporidioses, giardiasis can be treated with drugs, some drugs which have been shown to be affective include albendazole, quinacrine , metronidazole, trinidazole and paramomycin (AWWA 1999).
How do we prevent Giardia entering water supplies?
The implementation of a multiple barrier approach from catchment to tap is recognised internationally as the only real means of minimising the risk of Giardia contamination. With the protection of the catchments from human and animal wastes a priority.
How big is our risk?
Rand Water derives its potable water from the Vaal Dam Catchment, which is rural in nature with a few small towns bordering the dam. Although animal husbandary forms part of the agriculture in this area it is dry land farming which dominates the catchment. The area in question is also arid limiting the contamination caused by run-off. This coupled to long retention times in the Vaal Dam is to our advantage as Breeman et al 1998 found that storage reservoirs markedly reduced both Giardia and Cryptosporidium densities. Retention times of 24 weeks (retention times in Vaal Dam is well in excess of 24 weeks) reduced densities by up to 2log10 units. The biggest threat to our catchments remains contamination by untreated or poorly treated sewage, which currently is a major problem that needs to be addressed.
Monitoring for Cryptosporidium and Giardia has placed Rand Water at the cutting edge of technology in its quest to ensure safe drinking water. Presently Rand Water participates in the LEAP scheme (Laboratory Environmental Analysis Proficiency testing scheme) which is a UK-based proficiency scheme focussed on Cryptosporidium testing methodology.