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A bug in the bush

Over the summer holidays lots of Kiwis enjoyed camping and tramping trips and endured nothing more uncomfortable than blisters and a few insect bites. But Giardia, a bug that can be found in untreated water – especially streams and creeks in the great outdoors – might not be quite so easy to shrug off.

Giardia intestinalis, also known as G. lamblia, is a single-celled microscopic parasite that, once swallowed, attaches itself to the intestinal wall causing severe diarrhoea, stomach cramps and wind. Anyone is at risk of infection, though infants and children are more susceptible and the disease can be more serious in those who are immune-compromised.

Symptoms can take up to three weeks to appear and last for up to eight. In other instances the symptoms may be very mild but recurring, and some people can carry the parasite for years without showing any signs of infection. Antibiotics can be prescribed to treat it.

It can be found in soil, streams and rivers or in food that’s been contaminated in some way by human or animal waste. It can also be passed from person to person. The cysts can survive in the environment for months and favour cool, moist conditions. Ingesting as few as 10 of these cysts can be enough to cause infection.

Those who suffer severe diarrhoea risk losing weight, dehydration and malnourishment as a result of their inability to absorb nutrients. Almost half (40%) of sufferers find they are intolerant to milk or milk products for some time after recovery.

Few well-documented outbreaks have been reported – none of them in New Zealand where numbers of reported cases have been falling steadily since 1999 because of ongoing education about boiling stream water when camping (latest figures show 1230 reported cases in New Zealand in 2005). The disease is more generally of concern in developing nations where it contributes to malnutrition.

Infected food handlers have been implicated in the majority of food-related outbreaks overseas. As well as being found in untreated water, the disease can be carried in food, such as root crops, lettuces, strawberries and herbs that have been contaminated in some way (either through irrigation or during washing using untreated stream water). Cysts have been shown to survive on herbs for eight days.

There are several ways to kill off Giardia cysts. Boiling untreated water for at least three minutes is the most effective and is usually the method you’ll see promoted at more remote camp grounds and in educational material.

The cysts can be killed at lower temperatures but it takes longer and is less reliable in uncontrolled conditions such as when you’re using a portable gas cooker and a billy can.

Chlorine can kill the cysts but the necessary dose is quite high. Because the cysts are relatively large, a filter (of a particular size) can be effective for physically removing them. The cysts are relatively resistant to ozone treatment and UV light.

If you’re likely to be camping or tramping and using untreated water then boiling, filtering or using a chemical treatment is advisable.

Tramping shop and outdoor specialist stores sell a variety of gadgets for the purpose. These include iodine, chlorine or silver-based chemical treatments (some taste better than others) as well as filters of various makes and sizes, including a New Zealand-made plastic sipper bottle that is fitted with a carbon filter.

Resources

• Giardia pathogen data sheet

• Meet the bugs brochure (pdf 426 KB)

• Preparing food when water is unsafe

• Giardia – Ministry of Health brochure (pdf 1115 KB)

• Giardia – from the Bad Bug Book, USFDA

• Giardiasis – from Victorian Government health Information

Date updated: 7 February 2007