Dr Norman Davis (right) checks on two of his Wanaka duck
itch trial volunteers, Sharyn and Kevin Gingell-Kent, this
week. The pair had their forearms exposed to parasites
which cause duck itch, to test the effectiveness of bug
repellent-infused sunscreen against them. Photo by Lucy
Although duck itch researcher Dr Norman Davis' latest
round of Lake Wanaka trials appear successful in showing bug
repellants prevent the itchy rash, finding volunteers willing
to be exposed to the parasite that causes it has proved a
''People don't want to get duck itch again. They think it's
going to end up as bad as when they first got it,'' Dr Davis,
of Waimate, said.
Cercarial dermatitis, or duck itch, has been Dr Davis'
self-confessed ''labour of love'' since the 1980s.
He obtained his PhD in zoology from Otago University in 2000,
and regular visits to his Bremner Bay holiday home in Wanaka
over the past three decades have been used to conduct
unfunded research on the parasites, which cycle between the
native New Zealand scaup duck and lymnaeid snail and can
invade human skin, causing an inflammatory immune response.
Since mid-January, he has been carrying out the ''tedious''
job of collecting about 1800 tiny lymnaeid snails from the
bottom of Lake Wanaka. Among those, he found just eight that
were shedding duck itch-causing parasites which could be used
in his trials. He then put a call out to the Wanaka Lake
Swimmers club for subjects for his study and has had about 10
volunteers participate, the ''absolute minimum'' required.
His aim is to verify the results of a European study that
found a commercial sunscreen which contains repellent for
jellyfish stings deterred the parasite from penetrating human
He applied three different sunscreens to patches on
volunteers' forearms. The three patches and a control patch
not pre-treated with sunscreen were then exposed to lake
water containing the parasite. Dr Davis is carrying out a
''double blind'' study, which means the sunscreens have been
dispensed from a pharmacy in plain bottles, so neither he nor
the participants know which is which.
Based on preliminary findings, two of the sunscreens appear
to completely repel the parasite, while the third results in
fewer itchy spots than the control patch, which could suggest
even a simple sunscreen works, to some extent, Dr Davis said.
He will later have a colleague at the University of New
Mexico determine which parasites featured in his trials -
Trichobilharzia longicauda, which infects the host through
the blood vessels, or Trichobilharzia regenti, which infects
through the nerves and has caused paralysis in mice and
neurological impacts in birds.
Dr Davis believed medical researchers should be studying what
happened when T. regenti entered the human body.
''I haven't got the facilities or the funds to do all of it
myself. It requires good lab facilities and a dedicated