Children hoping to catch Santa landing his present-packed sleigh at their house this Christmas may want to think twice about getting too close to his trusty reindeer.
That's because the reindeer -- the same species as caribou (Rangifer tarandus) in North America -- could be carrying the larvae of a bumblebee-like fly called Hypoderma tarandi.
As the fly's name suggests, its eggs laid in the hair of reindeer hatch into larvae that penetrate the skin like a hypodermic needle. After the larvae mature, flies burst out of the skin to begin the cycle again.
A fact relevant to kids looking to sneak out of bed upon hearing bells jingling outside their houses next week is that the flies have no problem with using humans as their breeding ground.
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In a letter in the New England Journal of Medicine, Dr. Boris Kan of Karolinska University Hospital in Stockholm and colleagues reported on five children who developed dermal swellings and ocular injury after visiting reindeer herding areas in subarctic regions of Norway and Sweden.
Infestation with H. tarandi was confirmed in each child "by assaying serum samples for antibodies against hypodermin C, an enzyme released by the larvae during migration in the host," the researchers wrote.
That adds to the 12 other human cases of myiasis -- human tissue becoming infested with fly larvae -- caused by H. tarandi reported in the literature since 1980.
Three-quarters of the previously reported patients developed ophthalmomyiasis. Of the five new patients, two developed the infestation of the eye, one of whom lost vision in the affected eye.
Although all five of the children visited reindeer herding areas, only four said they actually saw the animals. None recalled being attacked by a fly.
The patients developed swelling of the occipital lymph nodes and dermal swellings 2 to 5 cm in size that appeared 15 days to 3 months after exposure. The swellings appeared one at a time, lasted for up to 3 days, and then reappeared after 2 to 34 days.
In two siblings, the symptoms developed 3 months apart, even though they were exposed at the same time.
Four of the children required treatment with ivermectin (Stromectol) at doses of 200 to 350 µg/kg. One required three treatments and three required five treatments, including one child who underwent eye surgery.
After ivermectin treatment, the dermal swellings turned into hard nodules, "probably because of a 'foreign-body' reaction against the dead larva," according to the researchers.
They concluded, "Myiasis due to H. tarandi should be considered in patients presenting with migratory dermal swelling if they recently had visited an area frequented by reindeer."
So a peek at Rudolph and his buddies may not be such a good idea after all.