Tuesday, May 22, 2012

Pediculus humanus

Photo of a mother picking the nits off of her child.
     Who doesn't love talking about these creatures? Better yet, who doesn't start obsessively scratching their head when talking about these creatures? (I'm sure that I'll have more people who have raised their hands to the latter question.) Pediculus humanus is found on humans and exists as one of two distinct subspecies: Pediculus humanus capitis (better known as the head louse) and Pediculus humanus humanus (better known as the body louse). This little guy has even gone so far as to invade the way we speak. The term "lousy" derives from the act of one being infested with lice (the plural form of the word louse, if you haven't caught that already). You may also have heard about people being "nit-picky". This comes from the eggs (also known as "nits") that are laid by these animals. The treatment for a lice infestation is to remove the nits, which could be a tedious process before the days of lice combs and treatment shampoos. This is why people who are said to be meticulous are termed "nit-picky".

P. humanus capitis

P. humanus humanus
      This species of lice is of course an animal belonging in the class Insecta under the phylum Arthropoda. It belongs in the order Phthiraptera with over 3,000 other species of lice. All members of this order are wingless ectoparasites of many different types of birds and mammals. Most lice are scavengers, feeding on dead skin and other debris, but P. humanus is one of the species that takes blood meals. There are four suborders currently recognized under order Phthiraptera: Anoplura (sucking lice found only on mammals), Rhyncothirina (found on elephants and warthogs), Ischnocera (chewing lice that parasitize mostly birds, save for one family that is found on mammals), and Amblycera (more chewing lice that parasitize mostly birds, but are found on some South American and Austrailian mammals). P. humanus belongs to suborder Anoplura. It belongs in family Pediculidae. The two subspecies of P. humanus will interbreed under lab conditions, but they do not interbreed in nature as they occupy very different niches on their hosts.

Copulation in P. humanus humanus (Female on top)

Life Cycle
     The  life cycle for Pediculus humanus involves three distinct stages. The eggs, or "nits", are laid on either the bases of hairs on the head (as in P. humanus capitis) or on the seams of clothing, particularly around the waistline or armpit areas of clothing (as in P. humanus humanus). After a week or two, the nits hatch and release little nymphs. These nymphs look identical to adults except that they lack mature genitals and are smaller in size. The nymphs feed on the host's blood. They nymphs will undergo 3 molts before maturing into adults after 9-12 days. As adults, they will mate and reproduce. As adults, the lice continue to live on blood meals from the host. If they become separated from the host, or if the host dies, the lice will die after a short while living at room temperature.

Pediculosis (Being infected with lice.)
Nits of P. humanus capitis
      A person becomes infected with lice through contact with others who have been infected or through sharing clothing or bedding that is infested. (Pediculosis can also refer to pubic or "crab" lice [Pthirus pubis] infections, but I did not cover that species in this post.) This is particularly problematic in places of high population, but substandard living conditions. This often occurs in transient populations of homeless individuals without access to regular bathing and clean clothing. Historically, it has been problematic for armies or prisoners exposed to substandard living conditions.

       Head lice are not known to carry any diseases, but do cause itchy scalps. Head lice are often found in children and spread quickly in schools and daycares. Head lice are able to live for about two
days off of their host in things like hats, hairbrushes, and pillows.
Nits of P. humanus humanus
     Body lice also cause itching, but unlike head lice, this subspecies is known to serve as a vector for several diseases. This little guy is responsible for louse-borne typhus and louse-borne relapsing fever. Louse-borne typhus has been largely eradicated in many parts of the world, but has existed, and continues to exist in impoverished areas or during times of war or civil unrest.
     The treatment for pediculosis includes an improvement in living conditions, the use of pediculocidal shampoos and lice combs, washing or burning of infected clothing and bedding, and regular bathing.

The Moral of the Story
     Keep yourself clean, wash your cloths, and don't share hats with children or homeless people. :p Being aware of how these animals live is half the battle with preventing or treating their infestations.

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