Human Lice Types, Management and Public health

Since no verified fossils of lice have ever been found we can only speculate when they originated. We do not know the ancient Egyptians and Greeks wrote of them and they were found on prehistoric American Indian mummies. There are three kinds of human lice which feed on man.

1. The head louse ( Pediculus humanus capitus )
2. The body louse ( Pediculus humanus humanus )
3. The crab or pubic louse ( Pthirus pubis )

Public Health Importance:

Louse-transmitted diseases are presently not a serious threat in the United States. In other parts of the world, however, lice do transmit typhus fever (a disease which has killed many millions of people), epidemic relapsing fever, and trench fever. Lice cause much discomfort to humans due to their bites, which are irritating, causing and sleeplessness. Scratching often leads to secondary bacterial infections.

Biology:

Lice have simple or gradual metamorphosis. The immature and adults look similar, except for size. Lice do not have wings or powerful jumping legs so they move about by clinging to hairs with their claw-like legs. Head lice prefer to live on the hair of the head although they have been known to wander to other parts of the body. Head lice do not normally live within rugs, carpet, or school buses. Body lice live in the seams of clothing, generally where it touches the skin, and only contact the body to feed; usually holding on to the clothing while they do this. The eggs of lice are called nits. They are oval white cylinders (1/16 inch long).

The eggs of head lice are usually glued to hairs of the head near the scalp. The favorite areas for females to glue their eggs are near the ears and back of the head. The eggs of body lice are laid on clothing fibers and occasionally on human body hairs. Under normal conditions the eggs will hatch in seven to 11 days. The young lice which escape from the egg must feed within 24 hours or they will die. Newly hatched lice will periodically take blood meals and molt three times before becoming sexually mature adults. Normally a young louse will mature in 10 to 12 days to an adult (1/8 inch in length). Adults range in color from white to brown to dark gray.

Female lice lay six to seven eggs (nits) per day and may lay a total of 50 to 100 eggs during their life which may last up to 40 days. Adults can only survive one to two days without a blood meal. The nymphs and adults all have piercing-sucking mouthparts which pierce the skin for a blood meal. The reaction of humans to louse bites can vary considerably. Persons previously unexposed to lice experience little irritation from their first bite. After a short time individuals may become sensitized to the bites, and may react with a general allergic reaction including reddening of the skin, itching, and overall inflammation.

Head Lice  

The female head louse will deposit from 50 to l50 eggs or nits in her lifetime. Head lice glue their eggs to the base of hairs. Only one nit is glued to any one hair. Eggs hatch in five to ten days when the temperature is between 95× and 100×F. Below 74×F, most eggs will not hatch. People finding nits on hairs wonder if they are old nits which have already hatched or new nits which may still hatch. Since human hair grows about 1/2 inch per month, any nits found on a hair 1/4 of an inch from the scalp would be approximately 16-days old, and would have hatched already, or will not hatch. These nits are glued tightly to the hair shaft and can only be removed by combing. A special fine-toothed comb must be used which has teeth 0.l mm apart. A vinegar rinse is not effective. The life cycle for the head louse (from egg to adult) takes from 16 to 21 days.

Body Lice 

Body lice spend most of their time on the underclothing, next to the body, particularly along the seams. From here they periodically visit the hosts’ body for blood. They usually glue their eggs (up to 300 in a lifetime) to the fibers of clothing, but may occasionally glue them to body hairs as does the head louse.

Crab Lice 

These lice are found mostly in the hair of the pubic area. They may also be found under the armpits, in the beard or mustache and on the eyebrows and eyelashes. Their development from egg to adult normally requires from 30 to 41 days. Adult crab lice live about 30 days. Females deposit 30-50 eggs (in her lifetime).

How Do People Get Lice?

Anyone can get lice no matter how clean they are about their personal hygiene and their homes. Lice do not feed on dirt; they feed on blood! People get lice from people. They don’t come from pets. (Dog and cat lice do not infest man.) Head lice are transferred between persons who share items such as hats, hairbrushes, combs, or wigs. Body lice spread from clothing, particularly underclothing. If infested clothing is left lying about, body lice can migrate and thus, spread to other clothes and people. Crab lice usually are transmitted from person to person by sexual contact, however, they can be found on toilet seats and in beds, and from there, spread to people.

Disease Transmission: 

The body louse is the vector of three human diseases — epidemic or louse-borne typhus, caused by Rickettsia prowazeki de (Rocha-Lima); trench fever, caused by Rochalimaea quintana (Schmincke) Krieg (long known as Rickettsia quintana); and louse-borne relapsing fever, caused by Borrellia recurrentis (Lebert). These diseases are not presently being reported from the United States, but their introduction at some future time is not impossible if body louse infestations should become sufficiently prevalent. Although head lice have been experimentally infected with Rickettsia prowazeki, neither head lice nor pubic lice have been implicated directly in active disease transmission. Although body lice may pose the most serious health threat in many countries, head lice appear to be the greatest nuisance, particularly among school children in highly developed countries where their presence is considered intolerable.

Management:

Shampoo products containing either prescription or over-the-counter preparations are the standard treatment for head lice. Body lice and crab lice are controlled using lotions which contain an insecticide. Contact your physician or pharmacist to determine which of these products will be most effective. Washing clothes in hot water, 123 degrees F. or higher, will kill anybody lice and their nits. Clothes which can’t be laundered should be dry cleaner. Body lice can often be controlled by frequent changes and washings of clothes. Head lice, on the other hand, are not killed by frequent showers. Cutting the hair will not eliminate head lice (unless the head is actually shaved).

Conclusion:

Current research on human louse biology has focused on the long-standing debate about speciation of head and body lice but using new tools of DNA and enzyme analysis. These studies have indicated that head and body lice from the same geographical zone may be more closely allied than insects inhabiting the same ecological niche in other regions. However, the majority of research over the past decade has involved clinical aspects including transmission, treatment, and the appearance and identification of resistant strains within populations of lice. Despite advances, there is a need for a better understanding of louse biology, as existing therapies fail and lice remain potential vectors of disease for millions of people.

This article is collectively authored by Asim Munawar^1*, Aqsa Arshad¹, Muhammad Ishaque Mastoi², Shehbaz Sharif¹ and Muhammad Ali^3_1Department of Entomology, University of Agriculture Faisalabad. ²Department of Plant and Environmental Protection, NARC, Park Road Islamabad. ³ Department of Clinical Medicine and Surgery, University of Agriculture Faisalabad.