Duck Itch

Below I have pasted a series of emails from Dr Norman E Davis PhD detailling an experiment which he is conducting this coming week in Wanaka in relation to duck itch. He has asked for help from people willing to act as guinea pigs! Perhaps guinea fish… So I will be arriving at the Sunday morning swim with a pen and paper hoping to gather as many names and phone numbers as possible of people willing to help. The emails below are in reverse order – latest email at the start – and detail exactly how Dr. Davis wishes to proceed. He will be setting up late on Sunday and is hoping to be able to start working with participants from Monday. His time frame is a little vague at the moment as he has to contend with the vagaries of species and weather! I will be participating and I have a few others willing to give it a go so hopefully we can get enough of us together to make it a valuable experiment. Apparently, if you have already had a reaction to duck itch, you are a perfect candidate! (Anna Kate!!) See you on Sunday morning!


  • I think we can keep the research participation as simple as possible.
  • I won’t need help finding snails, since I should have 500 or more by the time I arrive on Sunday.
  • I will need volunteers I can contact when I have found the parasites, hence the requirement for a list with phone numbers.
  • Since we are working with wild parasites there can be advantages and disadvantages.
  • An advantage is that these parasites are the ones we need to repel and not ones that may have been “weakened” by being maintained artificially through several generations in laboratory animals.
  • A disadvantage is the unpredictability of supply. There can be no guarantee that the parasites will be found when we want to find them. They are “ephemeral”, as an Otago University lecturer once told me.
  • I am pleased with the success I had finding the snails at Sailors Cutting. I never have been able collect as many of these snails in Lake Wanaka. I can dedicate the whole of next week to finding the parasites and can go back to sailors Cutting and replenish my snail supply in one full day if necessary.
  • I am hopeful of success because not only were the snails at Sailors Cutting but, three species of diving birds were there as well; NZ Scaup, Australian Coot and Crested Grebe. I know the scaup is almost 100% infected and I suspect the other two species of being infected as well. So all of the parasite hosts are definitely there. This might be the reason that swimmers and water skiers on Lake Benmore have been having such a bad time with duck itch this season.
  • So volunteers for the trials will be all I will need and then only when I have succeeded in finding the parasites being shed by the snails.


  • I have just returned home after a week in Wanaka attempting to get enough snails to work with. As you are aware, the wind and rain made it impossible to get any snails. I didn’t stop by because I was busy with experimental details and was also not sure I would have any snails for the experiment to proceed.
  • On my return home yesterday, I stopped by Sailors Cutting on Lake Benmore and was rewarded with several hundred lymnaeid snails which I now have in cold storage to slow down any parasite development. I can expect between 2 and 4% of the snails to be infected. While I was collecting snails at the pier, quite a few onlookers commented that they were having a particularly bad season with duck itch.
  • I plan to come to Bremner Bay on 21 January, stopping for several hours at Sailors Cutting to collect as many snails as possible to bring with me. I will set up my microscopes and equipment and will start inducing the snails to shed parasites on the next morning. I would like to be able to contact willing individuals on a few hours notice to come by and submit to exposure trials. Since the parasites are WILD and not laboratory raised, there is some unpredictability of availability. I may have to make a trip or two back to Sailors Cutting to collect snails during the week.
  • For this to be a success, I will need to know names and phone numbers of those who can drop by for a 30 minute treatment and exposure session, followed by another visit 2 hours, 24 hours and 48 hours post exposure to read results. I will have an informed consent form available giving the details commencing the 22nd of January.
  • Since the parasite shed has to be induced by placing snails into individual wells, I will be doing this each morning and looking for them under the microscope. I cannot guarantee when they will appear, but they do survive for up to 24 hours and may be infective from about an hour post shed. This is why I must be able to contact someone who can stop by within a few hours of my discovering the parasites.
  • Would you be willing to organize volunteers in your group and then let me know how I may contact them? If I had a list by 22 January, I could then carry on from there. I would prefer to have volunteers who have previously had duck itch, since they will definitely respond to exposure.
  • Volunteers can expect to have their fore arms teated in 4 cm square patches with 3 different sunscreens, Safe Sea, another sunscreen with DEET, and another sunscreen without any repellent. There will also be one patch of untreated skin exposed as a control. After the sunscreens have been applied, an estimated number of parasites will be placed in lake water into 3 cm petri dishes which will then be taped into place over each of the treated skin patches. The arms will then be turned over so that the water and parasites have access to the treated skin patches for at least 30 minutes. After 30 minutes, the petri dishes will be removed and the water will be allowed too dry naturally. Then the volunteer will be able to go about their business, stopping by for results to be recorded 2, 24 and 48 hours post exposure. Once a reaction has been noted, the experiment will be over for that individual.
  • And, yes, I plan to submit myself to the experiment.
  • If you think it would help, I am willing to meet, either at 17 Aubrey Road or another venue of your choice, at any time after the 21st to brief prospective volunteers on the trial. Or interested individuals can stop by while the work is going on.
  • I now have enough of the sunscreen “SAFE SEA” to be able to give a complimentary bottle to each participant.


  • I have been getting some good advice about the experimental method I should be using to determine effectivity of Safe Sea against the infective cercariae of swimmers itch.
  • I have also found some literature that indicates that Safe Sea is, in fact, effective against the genera Trichobilharzia, of which there are two species in Lake Wanaka. The effectivity of DEET is not as well supported by the literature.
  • It remains to be seen if either formulation is effective against the species here in New Zealand. Hence the requirement for experimentation. One never really knows until the work is done with the local species.
  • Such experimentation requires careful estimation of the numbers of cercariae that are attempting to penetrate the skin. Then statistical analysis can be applied to determine the validity of the findings. That cannot be done with swimmers moving through the water where the parasites may or may not be encountered.
  • This work will require that snails be gathered and induced to shed cercariae which will be identified and quantified and then used to challenge the skin of human volunteers who will have one formulation on one arm and another without the repellent on the other arm. This is a big ask since my earlier research indicates that several hundreds of lymnaeid snails will have to be investigated to find one or two that will be shedding.
  • So, any help that I can get in collecting snails from the shallows of Bremner Bay will be most welcome. The more snails I can get, the better the chances of their shedding the parasites I want. If there are any local people willing to help, not only with snail collection but as “guinea pigs” for infection trials when parasites are found, I would be most grateful. It would be good to know who they are and if they can be contacted at short notice to participate. I intend to experiment on myself since I know I will react.
  • Collection of the snails is simple, once an eye is developed to identify the ones being looked for. It requires a kitchen strainer, a plastic peanut butter jar, some simple forceps or fingers  for transferring the snails from the strainer to the jar, shin high gumboots and some perseverance. If someone wants to do their own unqualified experiment while collecting snails, they might try applying the two different sunscreens to their legs and then wade knee deep while collecting. It might be interesting to see if only one leg becomes infected ;-)).
  • I have attached a photo of the local lymnaeid, Austropeplea tomentosa, just in case anyone would like to start looking for them. This particular snail is 5mm from the front to the back of the shell. Notice the “bunny ear” antennae. They can be maintained in lake water in aquaria, large jars or plastic 2 litre ice cream containers. A bit of water weed and some oven dried lettuce will help to maintain them. Lake water,not tap water, is essential. Snails do not necessarily start shedding immediately upon capture. The parasite may not be fully developed yet. So, the more snails we can look at, the better.
  • When this work can be accomplished is yet to be determined. I am hoping that I will be prepared to start in mid January. This will depend upon the timely receipt of materials from the Safe Sea manufacturers, Nidaria.
  • If there is anyone who would like to participate in the work with me, I can be reached on my cell phone: 021 129 6822. I prefer text messages which I can check at any time.
  • BASED ON THE LITERATURE, I would suggest that swimmers, especially the ones who have had Duck Itch before, acquire Safe Sea and start using it through this season.

This page has been set up to monitor the occurence of the dreaded duck itch! I would appreciate it if you could take the time to just note on the comments on this page if you’ve had an attack, the date, and anything else you have the time/information to add. I will post on a running page and we can monitor to see if we can address and perhaps do something about it.

I will also check out any information on duck itch and post here for your perusal, we may be able to do something about it, such as cold water shower by the lake edge – we’ll need lots of research in the form of your comments for that – which we will need council help for.

So keep an eye on this page and add any comments below and I’ll add to the page. Just pop your name on the comment so we have a reference. – Good old Wikipedia! – God I love Google! And this particular article contains the advice below, but do have a look at the site:

What can be done to reduce the risk of swimmer’s itch?

  • Avoid swimming in areas where swimmer’s itch is a known problem or where signs have been posted warning of unsafe water.
  • Avoid swimming near or wading in marshy areas where snails are commonly found.
  • Towel dry or shower immediately after leaving the water.
  • Encourage health officials to post signs on shorelines where swimmer’s itch is a current problem.
  • Do not attract birds by feeding them in areas where people are swimming.

14 responses to “Duck Itch

  1. I got duck itched badly on Friday january 6th, swimming at 7am. Doused myself with water from home afterwards but came up later that day. Also, it stung badly just after a shower.Water very calm and warm, about 18C. Claire O’Connell

  2. Got just one spot after swimming on Tues 3rd Jan 6-7pm. Was prob about 17C and moderately rough. I just did my usual of drying straight after and having shower at home. Seems to take 12-24hrs to come up anytime I get it. Fi Hezinger

  3. Got duck itch on my neck and slightly on my face after early morning OWS Sat Jan 7. Towel dried right after exiting water, had a shower once at home. It subsided over the day and was really only bad in the 1-2 hours post-swim. Water conditions were very calm, clear water, and maybe 14-16C?

  4. Went swimming with Claire at 7am Friday and have got bad duck itch all over face on both sides and on hands and neck and feet. Took approximately 12 hours to manifest fully. Washed my face with water from home and towel dried straight after swim, then had shower at home. Also had swim on Thursday night 6th Jan in a reasonably rough swell – poor visibility and very mucky water; but same cleaning routine as I have been doing for the past 2 weeks. Ali Moore.

  5. Entered the water at the Purple Statue (Left of swimming bouys) before Xmas ( say 23 Dec) and both my daughter and I received a bad dose of DI…I have entered the water every other day since then departing from the right hand of swim bouys closer to the toilets…”no duck itch”… David Crawford

  6. Good to see some reporting happening. If you are interested, go to DoC Headquarters and have a look at the Duck Itch poster they have put up. I would be very interested to hear your comments .

    Norm Davis, PhD
    Duck Itch researcher

    • Thanks Norm, I’ll pass the word on and assume that you mean we can see it at DoC Hq in Wanaka, I’ll call in there over next few days. This rain may put a bit of a halt on it! Thanks again, Claire

    • Hi My daughter and I swam in Lake McGregor last weekend Sunday 1 Feb 2015, we have both suffered with Duck itch, I have 153 spots and my daughter has triple that. Having seen lots of tourists bathing in the lake we went for a swim. the itching started afterwards and lasted a couple of hours. we woke the next morning smothered in spots. Just wondering whether we should report this? It was been an awful week with medications and creams not making much difference to the extreme itching. Strangely our son also swam in the lake, he got out before us which was just before the wind started up. He doesn’t not have any spots. Some that I have accidently scratched have come up in 3-4cm welts!! Would it have been bad timing for us or would have all that had been in the lake now suffering from this? Thanks Amanda

  7. Hi Claire
    Yes the Wanaka DoC Hq.

    And, BTW, a possible way to avoid infection while swimming is to use a sunscreen you can get locally. It is put out by the Cancer Society in a GREEN tube. It combines DEET and sunscreen. The DEET is a insect repellant which should also repel the duck itch cercariae. If you rub it in to all skin areas that are exposed or under loose garments where lake water can reach – watch out for around eyes – then it “should help” and be good for at least an hour in the water.

    This has not been scientifically proven (double blind test), but it is the best hope.

    I would be interested to know if anyone tries it successfully. The results would have to be compared with other swimmers in the same group who do not use the sunscreen. Any volunteers?


    • I think some swimmers have already been using sunscreen – and a few other products – to try to stop the itch! It’s particularly nasty this year, I thought I was immune but unfortunately not! I’ll talk about it in the morning and see what I can find out and if we can get any sort of an organised group to trial products. Perhaps we can get a few guinea pigs over the next few weeks. Definitely next summer we can monitor from an earlier time.
      Thanks again for your interest Norm, much appreciated and I’ll keep in touch.

  8. Duck itch definitely back for the season. I swam on Sunday, Dec. 23 (calm and pretty warm) and got itchy in around the neck and ankles. Will be sure to wear a good waterproof sunscreen next time. Happy Holidays!

      • Hi Swimmers

        I have been in contact with the company, Nidaria, which manufactures Safe Sea, a repellent against jelly fish stings.

        They have indicated their interest in providing material for a trial to determine if Safe Sea also works against swimmers itch (duck itch).

        I have contacted the NZ Cancer Society, who produce a sunscreen with DEET. This might also be considered for a trial.

        Now I must plan an experiment.

        One way is to have a dedicated number of persons who are prepared to participate in a “double blind” test using Safe Sea and a sunscreen without repellent for a recorded number of exposures during the duck itch season.

        Naturally, I am hoping that there will be a dedicated group of swimmers who will be willing to cooperate. At this stage I am hoping to get an idea of how many would be prepared to do so.

        The duck itch season usually lasts from December through February and I am hoping that I can get started by mid January. Of course, that will depend upon availability of materials, a good experiment design, and willing participants. Should the time frame be too ambitious, there would be plenty of time to plan for such an experiment during the following season.

        My family own a Bach at 17 Aubrey Road, Bremner Bay, and I am prepared to base the trial from there.

        Bremner Bay is also an ideal area to conduct exposure trials as the water is shallow and children often paddle there all day long. Since children can suffer moreseverelythan adults with duck itch, they may be good trial candidates. It would be necessary to recruit parents to participate.

        A controlled laboratory experiment using snails which are releasing the swimmers itch parasite plus volunteer human subjects might be more conclusive. This would require collection of several thousands of snails during the season and on call volunteers to be exposed when snails are found to be shedding the parasite. In this case, it would be helpful if there were some volunteers willing to collect snails a few hours each day. Perhaps these same volunteers would be willing to be trial subjects.

        I am open to suggestion and hope this stimulates your interest and cooperation.


        Norm Davis PhD

        >________________________________ > From: Wanaka Lake Swimmers >To: >Sent: Monday, 24 December 2012 7:08 PM >Subject: [New comment] Duck Itch > > > >wanakasigns commented: “Thanks Anna Kate, will put through to FB and see if anyone else getting the bug!!” >

  9. Pingback: Duck Itch in Lake Wanaka – research project | Wanaka Lake Swimmers·

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