Cryptosporidium waterborne parasite
What is Cryptosporidium?
Cryptosporidium is a waterborne parasite found widely distributed around the world including South Africa. When ingested it can cause an unpleasant illness referred to as cryptosporidiosis. Infection is transmitted by tiny spore or egg-like cells called oocysts. Cryptosporidium oocysts are small, roughly spherical in shape and about 4 to 6 micrometer in diameter.
The Cryptosporidium life cycle
The life cycle of Cryptosporidium is very complex and consists of a number of stages that may take 1-8 days to complete. The cycle is continually repeated so that the host re-infects itself. The oocyst is the infective stage which then either passes out with the faeces, or excysts (hatches out) and starts another cycle.
Oocysts 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 Cryptosporidium pose a health risk?
Yes it does and has resulted in various outbreaks of gastrointestinal disorders throughout the world.
How many Oocysts do I need to ingest to become infected?
There is usually a so-called “infective dose” with many infective agents. An infective dose for both Giardia and Cryptosporidium is relatively small. In a human volunteer study for Giardia the average infective dose was between 25 and 100 cysts although as few as ten cysts resulted in infections (Rendtorff, 1979). With regard to Cryptosporidium using C.parvum genotype 2 oocyst isolates 20% of the volunteers became infected following an oral dose of 30 C.parvum oocysts (DuPont, et al, 1995). A dose of 300 oocysts caused infection in 88% and 1000 oocysts produced infection in 100% of volunteers tested. The median effective dose was calculated to be a 132 oocysts. It should however be borne in mind that the infective dose depends on the physical condition of the person who is infected and the state of their immune system so the size of an “infective dose” will vary.
Available analytical methods for detecting oocysts in the environment are not very reliable. Furthermore, it is not possible to be certain whether or not any oocysts detected are viable, or the species composition of the oocysts so there is still considerable uncertainty on the levels of infective dose.
What are the symptoms of Cryptosporidiosis?
Cryptosporidiosis is associated with watery diarrhoea, rapid weight loss, dehydration and abdominal cramps. Less frequent symptoms also include low-grade fever, nausea, vomiting, anorexia and general fatigue. The incubation period of the disease is between 4 and 28 days with an average of 7 days.
Duration and severity of disease can vary but the diarrhoea is self-limiting and the infection is limited to the small and large intestine. In immunocompromised individuals, especially those with AIDS, infection may lead to dehydration, electrolyte imbalance, and eventually death.
Treatment of Cryptosporidiosis
No drug has been shown to be effective against Cryptosporidium infection and recovery from the illness is dependent on the body’s immune system.
How big is our risk?
Rand Water are at the cutting edge of technology to ensure safe drinking water. However, there are no guarantees regarding the water in the Vaal River.
Ref: Rand Water