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 more 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.
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 is the main species that infects humans. Two main strains occur in NZ: one drives human-to-human transmission via contaminated drinking water around huts and campsites, while the other spreads via 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, rodents, and chamois, don’t carry the strains that infect 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.
The most common 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.
Infected hikers can contaminate surfaces like watertank taps, door handles, and benches through poor hygiene practices, but Giardia usually lasts only a day or so before dessication 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.
Pristine mountain water can 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 last for up to 3 months in cold water or a month in damp faeces.
More remote areas can be less risky. 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 or iodine. Give the chemicals plenty of contact time in cold water.
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 and 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. No one wants foul-smelling diarrhoea for weeks.