There's something in the water

by gabeatkinson / 27 December, 2012
Enjoy the summer swimming, but watch for dangers, too.
There's something in the water

Now is the season for swimming, but there are things lurking in our cleanest, greenest waters that you, and your dog, should know about.


The grey side-gilled sea slug, or Pleurobranchaea maculata, rose to prominence a few years ago after a population explosion on Auckland’s north shore beaches resulted in the poisoning, and death, of several dogs. The sea slug was first identified in Captain Cook’s time, but only in recent years have scientists discovered just how toxic it is, and identified the toxin as tetrodotoxin (TTX), also found in puffer fish,  terrestrial newts, frogs, flatworms and ribbon worms, among other species. “We call it New Zealand’s most toxic animal,” says Cawthron Institute scientist Susie Hill.

Curiously, slugs tested in the South Island aren’t toxic but those found in the North Island are, and they can be lethal. “The most toxic slugs we’ve tested contain enough toxins to kill  four adults,” says Hill. This would require eating one, which humans are unlikely to do. If you do touch one, wash your hands thoroughly before putting them anywhere near your mouth. And try to keep the dog away.


Blue-green algae, or cyanobacteria, occurs naturally in a range of water quality conditions, more commonly in the summer months. It’s not always blue-green and it’s not actually an algae, having a structure that is more like bacteria. Taxonomically, it’s known as phormidium. In lakes, it is typically bright green, and in the right weather will clump together and form something that looks like a paint spill, often along shorelines. In rivers, it forms thick brown-black slimy mats on rocks and stones. It only takes a little rainfall to detach the mats, which float downstream and gets caught up in other debris.

The mats do die and dry out, but are still harmful to humans and animals. In recent years a number of dog deaths have been linked to phormidium in rivers such as the Hutt River and, more recently, Nelson’s Waimea River. Phormidium produces a number of toxins. In rivers, it often releases neurotoxins that can lead to paralysis – dogs typically die of respiratory arrest. Humans don’t tend to ingest phormidium and are more commonly affected by hepatotoxins, which can result in skin irritation, asthma-type symptoms and gastroenteritis.


Duck itch, sometimes known as swimmers’ itch, is caused by a parasite that lives in various animals in different parts of the world. It is also known as pelican itch, beaver lice and rice paddy itch. Waimate-based Norman Davis did his PhD on the pertinent parasite, mainly studying it at Lake Wanaka, and has identified the New Zealand scaup as the parasite’s preferred host here. These tiny parasitic worms go through various stages: they release eggs inside the blood vessels of the bird, which are then discharged by the bird. These hatch into tiny larvae that swim to find a particular species of snail to burrow into. When they reach the next stage, they are released by the snail and swim around hoping to bump into a passing scaup.

Unfortunately, they can bump into a passing human. Our immune system quickly kills the parasite in the skin, but it still manifests in a fiery, distressing itch that can last up to 10 days. Duck itch can wreck a holiday, but it really is a matter of being in the wrong place at the wrong time. You’re more at risk in the shallow warm waters on a lake’s windward side. This makes children vulnerable, but the parasite is less likely to penetrate areas covered by a swimsuit, and Davis says there is evidence wearing an insect repellent that contains DEET might repel it.

The snails are more likely to release the parasites from late morning to midday, but it doesn’t mean they won’t shed them at other times, too. According to Davis, natural biocontrol mechanisms seem to check the population by late summer. Until then, he suggests, beware of spending too much time in waters frequented by the New Zealand scaup. Duck itch is best treated with a light rinse of rubbing alcohol followed by calamine lotion. Baking soda paste, antihistamine or mild corticosteroid creams might also help.

Health Briefs


An analysis of the Nurses’ Health Study has shown the risk of sudden cardiac death was significantly greater among smokers than among those who had never smoked, but the risk steadily declined after quitting. After 20 years, the risk was comparable to that of those who had never smoked.


University of Alberta researchers have found a drug designed for diabetes, which never made it to market, appears to restore memory in Alzheimer’s brain cells, at least in mice. The team took brain tissue from animal models with the disease and tested the tissue in the lab, using shock memory tests to look specifically at the cells’ memory capacity. When the drug known as AC253 was given to brain cells with Alzheimer’s, memory was restored to levels of normal cells. The researchers are now looking to see whether the drug will also affect behaviour and cognition in animals with the disease. They noted that AC253 can’t cross the brain barrier, so pharmaceutical companies  would need to design a similar drug that can.


Although rates of heart disease and stroke continue to fall, unhealthy lifestyles look likely to reverse the trend, according to an American Heart Association report. Over 10 years, death due to cardiovascular disease fell by about 33%, and stroke mortality dropped 37%. However, more than two-thirds of American adults are overweight or obese, a third say they don’t exercise, and risk factors from being overweight are on the increase.
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