Diseases carried

• Typhus
• Trench fever

Vector organisms

• The body louse(Pediculus humanus)
• The head louse (Pediculus capitis)
• The pubic louse (Pthirus pubis)

Life Cycle and Control

Eggs are laid by the head and body louse by gluing them to hairs or clothing.These hatch within 1-2 weeks (or longer if they are on discarded clothing.) A head louse will lay 50-150 eggs and a body louse will lay 200-300 in her lifetime. The nymph that hatches will take a blood meal and mature in 7-12 days. The louse is a true parasite and has to take blood meals from a healthy human host to survive. Males and females take blood meals from their hosts as needed at any time of day. If they take Rickettsia from an infected individual they may pass it on to another human after they leave a dead or fevered host. The microorganism is eventually passed out in feces after it has multiplied and damaged the digestive tract. The pathogen is then passed into the body when the host scratches.

Lice only move between people when the host becomes fevered or they die. They can only survive for brief periods without a host and are spread by direct contact.

Lice are a consequence of poor personal hygiene and can be easily controlled at an individual level by cleaning bodies and clothes with hot (>60°C), soapy water. In large-scale outbreaks spraying or dusting with pediculides may be necessary. Agents with low mammalian toxicity have to be used for dusting.

• DDT
• Malathion
• Temephos
• Propoxur
• Permethrin

Other Countermeasures

Other agents that are showing some effectiveness against lice are ivermectins, which can be taken orally.

A typical infestation will result in an individual carrying several hundred (up to 400-500) lice.

Other comments

Louse-borne disease, especially typhus, devastated a number of military expeditions from the 15th Century until World War I. They remained a problem in civilian populations in combat areas during the Second World War until widespread treatment with the first modern insecticide (DDT) was introduced.

It remains a concern in areas of poor public health and overcrowding. A particular concern is refugee camps.