Sunday, June 9, 2013

Answer to Case 261

Answer:  Pediculus humanus, either P. h. humanus or P. h. capitus, the body and head lice respectively. 

This little arthropod can be readily identified by its elongated body (which is dorso-ventrally flattened, like someone stepped on it), lack of wings, and 'raptorial' legs adapted for grasping hair shafts.

Interestingly, you can't reliably tell head lice and body lice apart morphologically, and you might be tempted to think that they are the same organism.  However, in nature they occupy very distinct geographical niches (body and clothing vs. head respectively) and they will only breed with each other under laboratory conditions.

In this case, Vanessa pointed out that "You could make a tentative argument for it being a head louse rather than a body louse as it's still alive. Body lice die very quickly off the host and I think head lice are slightly more resilient."  Also, head lice are much more common in the U.S. (particularly in school-aged children), whereas body lice are found in settings of war, extreme poverty, and homelessness, thus making this specimen more likely to be a head louse.

Florida Fan noted quite correctly that this is a male rather than a female because it has a rounded rather than notched posterior end.

You can very easily tell Pediculus sp. lice apart from their pubic lice counterparts by their body size and shape as shown below:

Figure:  A body louse (left) and pubic louse (right).  Note the notched posterior end, indicating that these are female specimens.

Now, for our poem by Blaine Mathison:

War! It’s such a nasty political device!
Regardless of the outcome everyone pays the price!
Are you exhibiting a rash and feeling icky?
Well, you may just have Rickettsia prowazekii
Caused by an outbreak of Pediculus, a.k.a. body lice

No comments: