By Dr Eddy Bajrovic*
Picture this: A female fly catches a female mosquito.
But, instead of making the luckless mozzie her next meal, the lady fly secretes glue-like substance that fixes her eggs onto the insect’s body before releasing it.
And, as mosquitoes do, she soon bites an animal or person to take a blood meal, and one or more of the tiny larva that have hatched from the fly’s eggs then burrow in through the puncture wound or simply into the skin.
As snug as a bug under the skin of its unwitting host, the larvae begin to grow… and grow.
Over the next 5-8 weeks a red sore becomes a boil-like lump. Then something rather peculiar happens: a pin-sized hole appears on the top.
It allows the now-plump maggot to breathe until, finally, it emerges as a Mini Me-sized version of the extra-terrestrial creature from Alien.
Eeeeeek! Where’s Sigourney Weaver when you need her?
“There’s a what in there?”
As a 52-year-old Melbourne businessman discovered earlier this year, this nightmarish scenario is up there with the more bizarre medical issues a traveller might encounter.
Called myiasis, it’s an invasion of living tissue or organs by fly larvae and every year there are a handful of cases among Australian travellers.
The Victorian, whose case was described recently in an Australian medical publication, was host to two bot fly larvae which hitched a ride to Australia on the back of his neck after he holidayed in Central America.
The otherwise healthy man recalled being bitten by various insects, including flies and mosquitoes, while swimming at a waterfall in Belize.
Fascinating femmes fatales
Several species of flies can cause myiasis, each with a fascinating life cycle and an intriguing method of getting its eggs hatched.
With a range extending from Mexico south to northern Argentina and Trinidad, the human bot fly (Dermatobia hominis), is the only species that uses other insects as a courier for its eggs.
The Tumbu or ‘Putzi’ fly (Cordylobia anthropophaga) and the Lund fly (Cordylobia rodhaini), which are found only on the African continent, lay eggs in soil or sand, or on clothes drying outdoors. The eggs hatch when the garment touches warm skin, or as the eggs are walked or sat upon, burrowing into multiple sites.
(Myiasis is one reason Africa’s safari camps and lodges have laundry facilities and return guests’ clothes neatly ironed. But, if you’re on a self-drive safari or spending an extended period living or working in rural areas of East or Central Africa, it’s definitely worth taking steps (see below) to avoid ‘putzis’.)
In the Americas, the New World screw worm fly (Cochliomyia hominivorax) also lays its eggs on the ground and relies on contact with bare feet to find a host.
Symptoms usually mild
People with untreated and open wounds are more likely to get myiasis, but the larvae can penetrate otherwise intact skin.
However, it can also result from accidentally swallowing the larvae or having them enter the body directly through the nose or ears.
Infection typically starts as an itchy sore. As the larva increases in size under the skin, the growing lump can be painful and often oozes.
As unpleasant as myiasis sounds, most people develop only mild symptoms and have no long-term health issues after their stowaway is removed.
However, myiasis can be more serious. Cochliomyia and Wohlfahrtia larvae feed under the host's skin for about a week, but may then migrate to other parts of the body, potentially causing severe damage in the process.
A little dab’l do it
Treating myiasis is remarkably straightforward.
Typically, the breathing hole is covered with Vaseline, cutting of the off the air supply to the now-plump maggot. Once it starts to emerge it can be squeezed out completely or removed with tweezers.
Alternately, it can be surgically removed by a doctor under local anaesthetic.
Left unmolested, the mature maggot eventually emerges to develop into an adult fly.
The maggot can leave behind a sizeable wound and ongoing hygiene is important to avoid secondary infection. Depending on the species of fly involved, medication also may be prescribed.
5 ways to avoid myiasis
If you are travelling to a region where myiasis occurs and plan to spend a lot of time outdoors, preventing infection involves the following steps:
- Apply a personal insect repellent containing an effective active ingredient such as DEET (N;N-diethyl metatoluamide), Citriodiol (extract of lemon eucalyptus), or Picaridin to exposed skin.
- Cover up with long sleeves and pants, and wear footwear to limit the areas of exposed skin.
- Wear footwear at all times when outdoors.
- If your accommodation is not securely screened, sleep under a permethrin-treated bed net.
- In Africa, hang up wet clothes indoors, away from flies. If that’s not possible, thoroughly iron clothes you’ve dried outdoors – the heat will kill eggs laid on the material, a common source of infection.
Avoiding all insect bites in the tropics is important to prevent a number of diseases, ranging from malaria to dengue, Chikungunya, Zika, and Lymphatic filariasis – all spread by mosquitoes.
Reminder of a plane fact
The Victorian case is yet another reminder of how easily insect-borne diseases can cross the globe on planes.
It also highlights the importance of providing a detailed travel history to your doctor if you become ill days, weeks or even months after you return home.
Myiasis does not occur in Australia and local doctors are not required to report cases to State or Federal health authorities. However, making our health, quarantine and agriculture authorities aware of myiasis infections enables them to keep track of the different species of foreign flies entering Australia with travellers.
It would be disastrous if any of these fly species became established here.
Getting rid of them would require a lot more than Vaseline and tweezers.
* Dr Bajrovic is the Medical Director of Travelvax Australia.
Find out more about myiasis and other potential health risks for overseas travel by calling Travelvax Australia’s free advisory health service on 1300 360 164. You can also book a one-stop pre-travel medical consultation at your nearest Travelvax clinic.