Giardia: All you need to know

Avoid Giardia!

It’s a microscopic, single-celled parasite that probably won’t disrupt a tramp, since the incubation period is usually a week or two and you may get home; but once Giardia hits, you will know about it! Watery or greasy, foul-smelling diarrhoea, severe abdominal cramps and bloating, fatigue, and significant weight loss. The only good news: any initial vomiting doesn’t persist.

The ensuing illness, Giardiasis, lasts 2 to 6 weeks but, if not treated with anti-parasitic drugs, can drag on for three or more months. You remain infectious for that time.

Giardia first arrived in New Zealand with introduced mammals, including humans, and was first recorded here during the 1970s.

Several species and strains exist, but Giardia duodenalis (also known as Giardia lamblia or Giardia intestinalis) is the main species that infects humans. It’s generally just called Giardia in New Zealand. Two main strains occur in NZ: one drives human-to-human transmission via contaminated drinking water around huts and campsites, while the other is in the reservoir of introduced animals like deer, possums, pigs, and stoats defecating in or near water. Both are found to some extent across New Zealand backcountry catchments.

Other species, like birds, frogs, and chamois, aren’t infected by the strains that cause illness in humans.

You get Giardiasis by ingesting as few as 10 to 25 microscopic cysts, which are single parasites wrapped in a tough protein protective shell. The shell protects against stomach acid. Once past that, the cysts hatch, divide into two parasites, and attach to the small intestine wall to start dividing prolifically.

How?

Probably the most common way is that previously infected hikers can contaminate surfaces in or around huts because of the long incubation periods and then returning to the track before the parasite is completely eradicated from your digestive system. The obvious high-risk surfaces are the inner toilet door latch, the toilet seat and internal surfaces, watertank taps, hut door handles, and benches. Giardia usually lasts only a day or so before desiccation or UV light kills it. It can last longer in damp, cold conditions.

Another common method of infection is walking through animal faeces and transferring cysts directly onto your footwear. Wash your hands with soap after taking off your footwear and before handling food.

One route of infection is drinking water downstream from heavily used campsites or huts, where human waste and poor sanitation habits contaminate the water. Slow-moving water on the boundary between farmland and forest, and rivers passing through dairy farms, are also of concern.

Pristine mountain water can possibly be contaminated by mammals defecating into or near a water source. Depending on the mammal, millions to billions of cysts can be shed in a single day. These can theoretically last for up to 3 months in cold water or a month in damp faeces. But in reality, the more remote areas can be less risky due to generally low animal numbers. Fast-flowing alpine streams, where high water volume quickly dilutes and disperses cysts, and other high-altitude areas with high UV radiation can disrupt the parasite’s DNA.

Because the cysts are relatively large, filtering works, as do UV purification and chemical drops like chlorine. Give the chemicals plenty of contact time in cold water, like 40 minutes.

And keep dirty and clean water bottles apart.

You can filter water from streams and rainwater tanks, but make sure you also practice good personal hygiene.

Hand sanitiser doesn’t kill Giardia, it just smears it around your hands.

Even soap don’t kill the tough cysts, but rubbing your hands in soapy water for 20 seconds forces the cysts into the lather, then you rinse them off.

So, take precautions, particularly in and around huts. No one wants foul-smelling diarrhoea for weeks.