This is one of a series of articles prepared for Fishing Cairns by Dr Deborah Mills, author of the book, Travelling Well, and director of Dr Deb The Travel Doctor travel medicine clinics in Brisbane.

Insect Bites

Insect bites may be irritating, painful, set off allergic reactions, become infected, or even transmit disease.

It is relatively rare, but mosquitoes in Australia can carry Ross River Fever, Dengue Fever, or even Japanese B Encephalitis, with one case of JBE having been contracted while fishing at the mouth of the Mitchell River in North Queensland. He recovered fully, but the risk is present in tropical environments.

Being bitten by insects is avoidable if you take the appropriate precautions:

  • Ask the locals about the resident insect ‘pests’, especially spots to avoid and the times of the day that they are at their worst.
  • Cover up your skin. If you are outside between dusk and dawn, wear treated long sleeved shirts, long pants, and long socks. Light coloured clothes are best as dark colours attract mosquitoes. Strong scents attract mosquitoes too, so avoid aftershave.
  • Use mosquito repellent REGULARLY. It definitely doesn’t work if it just sits in your tackle box, and ‘DEET’ (Diethyl toluamide) is definitely the most effective mosquito repellent for applying to your skin.

    DEET based repellents, such as Repel and Rid, need to contain at least 30% DEET to be effective for protecting adults under conditions of high mosquito exposure. Repellents with over 50% DEET (such as Bushman) are needed in areas of really intense exposure.Apply regularly as per instructions on the bottle.

    When sunscreen is required, apply sunscreen first, wait 20 minutes and then apply repellent. Repellents decrease the number of bites you may get, but unfortunately, cannot stop mosquitoes entirely.

  • Sleep in accommodation with screens or air conditioning and use a ‘knock down spray’ to remove stray mosquitoes before retiring. Permethrin treated Mosquito nets are essential where the accommodation is not well screened. In completely unscreened conditions, burn mosquito coils, cover exposed skin in insect repellent, and sleep next to a fan.
  • Oral Vitamin B There has been quite a bit of discussion about the role of Vitamin B in mosquito avoidance. Taking large quantities of vitamin B orally unfortunately does not decrease the number of mosquito bites you get.Such an apparently simple solution to mosquito avoidance is appealing, but careful scientific trials have failed to show any mosquito repelling effects from taking oral vitamin B, including B1.There is some evidence that the use of B1 will make any bites feel less itchy, but the risk of picking up nasty diseases is just the same as if you did not use it.

Treating bed nets and clothes with Permethrin

Permethrin is a highly effective synthetic insecticide which can be used to treat fabric. It is related to the naturally occurring pyrethrum from the flowers of a type of Chrysanthemum, and fabrics treated with Permethrin (bed nets, bed sheets, clothes, curtains) will kills or repel mosquitoes.

Using treated items significantly decreases the number of bites you get.One study showed treated nets were four times more effective than untreated nets.Insects must touch the fabric for it to work, so when you wear treated clothes, you still need to use repellent on exposed skin. You can buy items pre-treated (especially bed nets) or treat items yourself with commercially produced Permethrin impregnation packs. Follow the treatment instructions carefully to get the full effect.

Articles which are treated and immediately sealed and stored in a plastic bag will retain effectiveness for 12 months until usage is begun. A permethrin impregnated mosquito net is effective for three to six months of regular use. The solution wears off as well as washes off.Clothes treated in this way are said to be fully active for about one month, remaining effective even after normal washing.

Once the fabric is treated and dried, permethrin has no vapour action and nets can be safely used even around sleeping children.Should a young child suck the net, they will not suffer any ill effects. Treated items are not more flammable. Very occasionally, some people do develop minor skin rashes from the use of treated clothes.

Dengue Fever

Dengueis present in many parts of the world, evenNorth Queensland, and it is spread from person to person by a mosquito (Aedes aegypti) which bites during the day.

About 1 week after the bite, a mild runny nose develops, followed a few hours later, by the sudden onset of a fever, a splitting headache and severe muscle and joint pains.After 2-3 days the fever and pains settle.The ‘recovery’ may only last 2 days, then symptoms return, though less severely.Small red spots may appear on the trunk and spread to face and limbs. There is no treatment.After a few more days the fever subsides and recoveryfollows.

Although an unpleasant illness, serious complications are rare. It is common to be tired for weeks afterwards. Immunity after an attack is not lifelong and second attacks are possible and tend to be more serious than the first.

There is no vaccine and the best protection is to avoid day biting mosquitoes via the use of repellents containing DEET (diethyl toluamide).

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