Help study scratch an itch

AN ITCHING PROBLEM: Anson Koehler, a PhD student from Otago University with Norman Davis, Waimate, who is doing a study on duck itch.
AN ITCHING PROBLEM: Anson Koehler, a PhD student from Otago University with Norman Davis, Waimate, who is doing a study on duck itch.

Retired Waimate school teacher Norm Davis is trialling the use of sunscreens as a protection against duck itch and looking for willing volunteers.

Mr Davis is seeking people who have definitely had duck itch before and who would be willing to submit to the exposure trial.

"If you have had duck itch before, you will know how uncomfortable it can be and might be interested in participating in such a trial."

Mr Davis has been conducting a double blind test for the past three weeks, to see if three different lotions may be suitable for the job.

With an Otago University PhD in parasitology, he has spent more than 25 years studying duck itch (also known as swimmers itch), including doing a doctorate on duck itch in Lake Wanaka.

He has investigated the possibility of controlling the disease in selected swimming areas through either chemical or biological methods.

However, the cost of these methods is prohibitive, he said.

"A more practical method is being sought to protect individuals who spend time in the fresh waters of New Zealand lakes and rivers."

He said certain sunscreens may be effective in keeping the duck itch parasite from attacking human skin.

To find out if this is so, three different products are being tested in an exposure trial with human volunteers.

One is a plain lotion with no additives. The second is a lotion with Deet, an insecticide which has been shown elsewhere to repel swimmers itch and, the third is a sunblock designed to repel stinging jelly fish in salt water, which has also been shown to repel swimmers itch in Europe.

In Mr Davis' double blind test, the lotions are labelled by number so the volunteer and the tester do not know which is which.

"These lotions are applied to the lower forearm on small areas labelled by number."

A fourth control area has no lotion applied.

He said snails releasing the duck itch parasite are being collected from Lake Wanaka and can be kept in cold storage, for up to a week or two.

The duck itch parasite is harvested from them and a small number of parasites applied to the four test patches.

This is done by pipetting a small amount of water containing a few parasites into a 30mm diameter glass petri dish, applying one (dish) each to the marked areas on the lower under forearm, secured with tape.

The volunteer then sits forearm upright and horizontal for at least 40 minutes to give the parasites a chance to penetrate the skin.

The petri dishes are then removed and the areas allowed to dry. Any response is noted one hour to 24 hours after the exposure.

The reason trial volunteers must have had duck itch before is because the control area must show a response for comparison with the other three.

As an incentive for their assistance volunteers will receive a complimentary bottle of one of the sunscreens tested.

"The trials should completed within about two weeks, the sooner the better since the material available is limited."

Mr Davis can be contacted at 021 129 6822, 03 689 7877 or


South Canterbury