Field Guide to Venomous and Medically Important Invertebrates ...

Lice in the families Pediclulidae and Pthiridae (Order Phthiraptera) are exclusive and obligate
parasites of humans that are distributed worldwide wherever people live. Lice are wingless,
variously colored (usually gray, brown or black), equipped with prominent tarsal claws, and they
range in size from about 0.09-0.13 inch (2.5 to 3.5 mm). The eggs of lice, or nits, are cemented
to hairs in the case of head and pubic lice, and seams of clothing or bedding materials for body
lice. Nits hatch in only a few days and this allows lice populations to grow rapidly. People
infested with lice may experience itching, and develop reddened patches of skin, lesions and
wheals, and severe itching. Secondary infections may result from scratching of the bite sites.
Successful treatment of lice infestations must include both killing and/or removal of both the lice
and their nits. Body lice are always a threat when large numbers of people are crowded in
unisanitary living conditions such as after disasters and refugee camps. Under these conditions,
lice will spread rapidly from infested to uninfested people and, if epidemic typhus is introduced,
there is potential for an explosive epidemic of this deadly disease.
Head Louse (Pediculus humanus capitis)- Any human can become infested with head lice,
particularly refugees, prisoners of war, concentration camp detainees, and others in poor socio-
economic or stressful situations. However, infestations are most common among children
regardless of socioeconomic condition. Head lice can be controlled using any of various
chemical (pesticide) treatments, and through the use of louse (nit) combs. Permethrin-based
shampoo is a safe and effective choice for controlling head lice. Head lice are secondary vectors
of epidemic typhus although their role in the transmission cycle of this disease is not considered
to be significant.
Figure 73. Head louse (Pediculus humanus capitis). Photo: J. Kalisch.