Saturday, May 1, 2010

Gall Bites Man

Headline of Gall Bites Man?  Well not exactly.  But as Tim Gibb, a Purdue Extension entomologist, reported in 2007 an oak gall mite can cause a chigger-like reaction when it bites humans.  Formally known as Pyemotes herfsi, it is a parasite of a parasite.  Confused yet?  Stick with me.
A midge lays its egg on a pin oak and its egg produces the gall which harbors the insect larva.  The mite comes along and lays its egg, parasitizing the midge larva.  While the mite is known to attack this oak leaf gall, entomologists suspect it affects other gall larva as well.
This is all ready confusing enough but hang on.  "When there are not enough insects acting as hosts for the mites, humans and animals become secondary hosts.  These mites do not carry diseases and are very similar to chiggers.  They are strictly a nuisance and there is no need to stop outdoor activities."
It looks really threatening in the picture, but don't bother searching your body for it.  It is only 0.2 mm long, the equivalent of three human hair widths.  Although possibly spread in the air, the best way to acquire your own mite is by handling the galls.  They tend to attack the hair follicles and pores.
"Most people can't see the mite, but can feel it moving," Gibb said.  "When they get on people, they typically go to pores or hair follicles.
"Once they pick a spot they inject their saliva, which desensitizes the skin around it and then suck lymph from the body.  The person won't know until four- or five-plus hours later when the skin becomes sensitive and develops a rash or welt that itches."
Actually Pyemotes herfsi was identified in 1936 in Europe.  According to an article in Wikipedia the first US outbreak was identified in Kansas City, Kansas in 1992. Although not a serious health hazard, the CDC estimated that 54% of the county residents were affected.  There have been scattered outbreaks since then. 
Humans typically report itching from mite bites within 10 to 16 hours after contact. The victims often do not recall being bitten. The rash that results from the bites is usually described as a red patch with a small blister in the center, most often found on the neck, face, arms, or upper torso.  Washing with soap and water is said to kill the mites.
If you are wondering how they figured all this out, the USDA study makes interesting reading.  Are you feeling a little itch?

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