Lice

Sucking Lice

The sucking lice share the characteristics of all ectoparasites, but differ from chewing lice by their mouthparts and width of their heads. The chewing lice have large, heavily sclerotized chewing type mandibles for gnawing on the host. Consequently, they possess large muscles to move the mandibles and a large head that is needed to house the muscles. Sucking lice have small needle-like mouthparts to suck the blood of their host and, correspondingly, have smaller mouthpart muscles and a smaller head. With Mallophaga and Anoplura, the head is wider and narrower than the thorax, respectively.

A comparison of width of head of a sucking louse and a sucking louse.

Crab Lice.

Sucking lice are chiefly found on mammals. Almost all are host specific, with three types attacking humans: namely the head, body and crab lice. Crab lice (Pthirus pubis), also known as pubic lice, attack humans and a few species of gorillas. The broad squat bodies, large claws on the middle and hind legs, and characteristic sluggish movements have resulted in the pubic louse aptly being called the crab louse. Infestations typically are restricted to the groin and perianal area in adult humans; however, in very heavy infestations they can be found all over the body. If a child who hasn’t reached puberty is attacked, the lice frequently are found on the eyelashes. Apparently this is because one critical factor in crab louse environment is the distance between, and thickness of, individual body hairs. This distance and coarseness in eyelashes is ideal and consequently is occupied in the absence of pubic or other body hair.

Females lay a small number of eggs (100 to 150) on body hairs. Development is quite rapid with the life cycle being completed in 30 to 40 days. Crab lice are nearly immobile and typically attach to body hairs with their opposing claw-like tarsi and tibia while feeding. They frequently become buried in their own excrement and can only live for a short time off the host.

Because of host dependency and relative immobility, these lice normally are acquired by sleeping with an infested person. It is possible (but not probable), that crabs could be contacted from situations such as using the same shower towel immediately after an infested individual, using a toilet seat immediately after use by a heavily infested individual or similar situations. As might be expected, there is a correlation between the degree of crab louse infestation in the general public in a given area or during a particular era and the degree of sexual promiscuity. For example, crab lice infestations in the United States during the 1960’s and 1970’s were more common than today. The 60’s and the 70’s were the decades of social unrest, sexual experimentation and “free love.” Today, we are much more careful because our awareness of more serious repercussions (AIDS, for example) has risen.

Crab lice do not vector any disease but can cause a rash and corresponding itching. As do most blood sucking insects, crabs inject a saliva when they feed that contains both an anticoagulant to keep the host’s blood flowing and an anesthetic to minimize detection of their presence. Prolonged infestations of this species can result in subcutaneous blue spots ranging in size from 1/16 to 1/2 inch in diameter. Of course, the blue spots are a result of the anticoagulant in the saliva which results in bruising.

Crab lice can be treated with Permethrin 1% cream rinse and pyrethrins. They can be used for this purpose and are the drugs of choice for pregnant or lactating women. These agents should be applied to the affected areas and washed off after 10 minutes. Shaving off or grooming any hair in the affected areas with a fine-toothed comb is necessary to ensure full removal of the dead lice and nits. Resistance of pubic lice to pyrethroids must be, if at all, very rare. A second treatment after 10 days is recommended. It is also crucial to make sure that all the bed sheets are changed. The sheets used before the first application of the treatment must be put away in a plastic bag, without air and well shut. They should be left alone for 15 days before washing to avoid the reproduction and survival of lice eggs that may have been left on the sheets and lead to reinfestation.

Pubic lice on the eyelashes can be treated with a permethrin formulation by applying the solution to the infested hair with an applicator.

Lindane shampoo (1%), a pediculicide, although banned in more than 50 countries, is approved by the U.S. Food and Drug Administration (FDA) as safe and effective when used as directed for the second-line treatment of pubic lice (“crabs”). While serious side effects have been reported, they are considered to be rare and have almost always resulted from misuse of medication, such as excessive application and oral ingestion. To minimize this risk, Lindane medications are now dispensed in small single-use bottles. The Centers for Disease Control and Prevention (CDC) notes that Lindane should not be used immediately after a bath or shower, and it should not be used by persons who have extensive dermatitis, women who are pregnant or lactating or children aged under two years. The FDA similarly warns against use in patients with a history of uncontrolled seizure disorders and premature infants, and recommends cautious use in infants, children, the elderly, and individuals with other skin conditions (e.g., atopic dermatitis, psoriasis) and in those who weigh less than 110 lbs (50 kg).

Head Lice.

Pediculus humanus capitis, and body lice, Pediculus humanus humanus are different subspecies of the same species. Placed side by side, they look almost exactly alike; however, they have quite different biologies and are easily distinguish from crab lice. It is thought that primitive humans were infested with head lice but, as we became more civilized and began wearing clothing, this opened up a different ecological niche that was occupied by body lice (body lice are found on clothing). Because they are both the same species, they are capable of inter-mating but their offspring all exhibit characteristics of head lice.

Head lice were called mechanized dandruff during World War II because typically they were found above the shoulders on scalp hair, mustaches, sideburns and beards. Heavily infested individuals may have the lice on all hairy parts of their bodies. They normally are gray colored, but tend to take on the color of the hair they are infesting.

The eggs (nits) typically are deposited on the base of the hair immediately next to the scalp. Generally, they hatch by the time the hair has grown 1/4 inch. Occasionally head lice will lay their eggs on long hair that is lying on the scalp, so that unhatched eggs can be found some distance from the base of the hair. Lice use cement that is impervious to normal influences such as shampoo; consequently, the eggshells remain attached to the hair long after hatching. Head lice are more prolific than crab lice because the females can deposit up to 200 eggs and development can be completed in as little as 30 days. It should be noted an infestation of head lice has no correlation to unsanitary conditions and these lice have no socio-economic barriers. The rich are as likely to be infested with these pests as are the poor.

There does seem to be a correlation between the probability of being infested with head lice and hair length. Probably this is due to the fact that these lice are more difficult to control in longer hair. Also it is less common to find head louse infestations in African-Americans: however, in Africa these lice readily attack black individuals. lndividuals infested with these pests harbor only 10 to 20 lice, but in heavy infestations the hair can become matted with nits, nymphs and adult lice. Typically, only the head or scalp of the host is infested, although the disease can occur in other hairy parts of the body, like leg hairs. Head lice feed on human blood (hematophagy), and itching from louse bites is a common symptom of this condition. Treatment typically includes application of topical insecticides such as a pyrethrin or permethrin, although a variety of folk remedies are also common.

Lice infestation in general is known as pediculosis, and occurs in many mammalian and bird species. The term pediculosis capitis, or simply “pediculosis”, is sometimes used to refer to the specific human pediculosis due to head-louse infestation. Humans are hosts for two other lice as well-the body louse and the crab louse.

Head-louse infestations are widely endemic, especially in children. It is a cause of some concern in public health, although, unlike human body lice, head lice are not carriers of other infectious diseases. These infestations are most frequent on children aged 3-10 and their families. Females get head lice more often than males, and infestation in persons of Afro-Caribbean or other black descent is rare because of hair consistency. But, these children may have nits that hatch and the live louse could be transferred by head contact to other children.

Head lice are spread through direct head-to-head contact with an infested person. Body lice are spread through direct contact with the body, clothing or other personal items or a person already carrying lice. Pubic lice are most often spread by intimate contact with an infested person. Head lice occur on the head hair, body lice on the clothing, and pubic lice mainly on the hair near the groin. Human lice do not occur on pets or other animals. Lice do not have wings and cannot jump.

From each egg or “nit” may hatch one nymph that will grow and develop to the adult louse. Full-grown lice are about the size of a sesame seed. Lice feed on blood once or more often each day by piercing the skin with their tiny needle-like mouthparts. Lice cannot burrow into the skin.

Diagnosis. In order to diagnose infestation, the entire scalp should be combed thoroughly with a louse comb and the teeth of the comb should be examined for the presence of living lice after each time the comb passes through the hair. The use of a louse comb is the most effective way to detect living lice. In cases of children with dirty, long and/or curly/frizzy hair, an alternative method of diagnosis is examination by parting the hair at one inch intervals to look for moving lice near the scalp. With both methods, special attention should be paid to the area near the ears and the nape of the neck. The examiner should examine the scalp for at least 5 minutes. The use of a magnifying glass to examine the material collected between the teeth of the comb could prevent misdiagnosis.

The presence of nits alone however, is not an accurate indicator of an active head louse infestation. Children with nits on their hair have a 35-40% chance of also being infested with living lice and eggs. If lice are detected, the entire family needs to be checked (especially children up to the age of 13 years) with a louse comb and only those who are infested with living lice should be treated. As long as no living lice are detected, the child should be considered negative for head louse infestation. Accordingly, a child should be treated with a pediculicide only when living lice are detected on his/her hair (not because he/she has louse eggs/nits on the hair and not because the scalp is itchy).

The most characteristic symptom of infestation is itching on the head which normally intensifies 3 to 4 weeks after the initial infestation. The bite reaction is very mild and it can be rarely seen between the hairs. Bites can be seen, especially in the neck of long-haired individuals when the hair is pushed aside. In rare cases, the itch scratch cycle can lead to secondary infection with impetigo and pyoderma. Swelling of the local lymph nodes and fever are rare. Head lice are not known to transmit any pathogenic microorganisms.

The most common symptom of lice infestation is itching. Excessive scratching of the infested areas can cause sores, which may become infected.

Head lice may cause local infections, but are not a vector for epidemic microbial disease (see below). Head lice per se are a disease only if they cause symptoms. In the absence of discomfort or skin lesions, infestation is therefore only a condition and cosmetic problem for the carrier (not strictly a disease), though they may present a disease-transmission-risk for those others who will develop symptoms, if infected.

The number of cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually. There is no product or method which assures 100% destruction of the eggs and hatched lice after a single treatment. However, there are a number of treatments that can be employed with varying degrees of success. These methods include chemical treatments, natural products, combs, shaving, hot air, and silicone-based lotions.

Treatment. Lice on the hair and body are usually treated with medicated shampoos or cream rinses. Nit combs can be used to remove lice and nits from the hair. Laundering clothes using high heat can eliminate body lice. Efforts to treat should focus on the hair or body (or clothes), and not on the home environment. Some lice have become resistant to certain (but not all) insecticides used in commercially available anti-louse products. A physician or pharmacist can prescribe or suggest treatments. Because empty eggs of head lice may remain glued on the hair long after the lice have been eliminated, treatment should be considered only when live (crawling) lice are discovered. There are many home remedies for lice control most of that are ineffective and some can be dangerous. The authors have a Turkish friend who had head lice as a child and the method used on him consisted of soaking the head with kerosene. Unfortunately, the chemical caught on fire and the individual has been blind for virtually all his life. Other flammable materials such as alcohol are also not advisable.

Prevention. Examination of the child’s head at regular intervals using a louse comb allows the diagnosis of louse infestation at an early stage. Early diagnosis makes treatment easier and reduces the possibility of infesting others. In times and areas when louse infestations are common, weekly examinations of children, especially those 4-13 yrs old, carried out by their parents will aid control. Additional examinations are necessary if the child came in contact with infested individuals, if the child frequently scratches his/her head, or if nits suddenly appear on the child’s hair. Keeping long hair tidy could be helpful in the prevention of infestations with head lice. In order to prevent new infestations, the hair of the child could be treated with 2-4 drops of concentrated rosemary oil every day, before he/she leaves for school or kindergarten. The oils can be combed through the hair using a regular comb or brush. Clothes, towels, bedding, combs and brushes, which came in contact with the infested individual, can be disinfected either by leaving them outside for at least 3 days or by washing them at 60°C (140 degrees F) for 30 minutes. An insecticidal treatment of the house and furniture is not necessary.

Prevalence. Despite improvements in medical treatment and prevention of human diseases during the 20th century, head louse infestation remains stubbornly prevalent. In 1997, 80% of American elementary schools reported at least one outbreak of lice. Lice infestation during that same period was more prevalent than chicken pox.

About 6-12 million people, mainly children, are treated annually for head lice in the United States alone. High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia. Normally head lice infest a new host only by close contact between individuals, making social contacts among children and parent child interactions more likely routes of infestation than shared combs, brushes, towels, clothing, beds or closets. Head-to-head contact is by far the most common route of lice transmission. The number of children per family, the sharing of beds and closets, hair washing habits, local customs and social contacts, healthcare in a particular area (e.g. school) and socio economic status were found to be significant factors in head louse infestation . Girls are 2-4 times more frequently infested than boys. Children between 4 and 13 years of age are the most frequently infested group.

The United Kingdom’s National Health Service, and many American health agencies, report that lice “prefer” clean hair, because it’s easier to attach eggs and to cling to the strands, however, this is often contested.

Because head louse infestation occurs primarily in children, much of the effort to prevent head lice transmission has focused on school and day care settings-places where large numbers of children come into close contact. Schools in the United States, Canada, and Australia commonly exclude infested students, and prevent return of those students until all lice, eggs, and nits are removed. This is the basis of the “no-nit policy”. Data from a primarily American study during 1998-1999 found that no-nit policies were present at 82% of the schools attended by children suspected of louse infestation. A separate 1998 survey revealed that 60% of American school nurses felt that “forced absenteeism of any child who has any nits in their hair is a good idea.

School Head Lice Policy. This involves a number of issues: Establishing criteria to infer infestation; screening asymptomatic children for evidence of infestation; establishing the circumstances under which children will be inspected; immediate exclusion of infested children; and establishing criteria to permit previously infested children to return to school (e.g., the no-nit policy).

All of these policies are controversial. In particular, a number of health researchers and organizations object to the required removal of nits (i.e., the no-nit policy). Opponents to the no-nit policy point out that nits, being empty egg casings, have no clinical importance. Transmission can only occur via live lice or eggs. Time-consuming nit removal, therefore, has no direct effect on transmission. This has led to the perception that the no-nit policy serves only to ease the workload of school nurses and punish the parents of infested children.

Proponents of the no-nit policy counter that only a consistently nit-free child can be reliably shown to be infestation-free. That is, the presence of nits serves as an indirect proxy for infestation status. Proponents argue that such a proxy is necessary because lice screening is prone false negative conclusions (i.e., failure to find lice present on actively infested children).For example, a 1998 Israeli study found that 76% of live lice infestations were missed by visual inspection (as verified by subsequent combing methods). Although lice cannot fly or jump, they are fast and agile in their native environment (i.e., clinging to hairs near the warmth of the scalp), and will try to avoid the light used during inspection. Lice colonies are also sparse (often fewer than 10 lice), which can contribute to difficulty in finding live specimens. Further, lice populations consist predominantly of immature nymphs, which are even smaller and harder to detect than adult lice.

Body Lice. The behavior of body lice, which are also called cooties, is totally different than that of head lice. Females lay up to 300 eggs and the life cycle can be completed in as little as 25 days. The eggs are deposited on clothing and the nymphs and adults remain on clothing, even while feeding. Body lice infestations are not common in California, but typically develop when a large number of people live closely together under poor sanitary conditions, such as during war time. One person can harbor a large colony of this species. Over 30,000 body lice have been removed from a single individual. Even though such an infestation is rare, these insects have such a rapid reproductive capacity that huge numbers can develop rapidly unless control is quickly initiated. Close contact with someone who is heavily infested can result in a transfer of several hundred lice to a non-infested individual.

As in the other two species that attack humans, body lice cause dermatitis and considerable irritation. Scratching can result in secondary infection and sometimes blood poisoning. In long term infestations a condition called vagabond’s disease may develop. The victim’s skin becomes thickened and deeply pigmented. This condition is not due to a microorganism, but to the skin’s reaction to the feeding of the lice. Finally, individuals who are heavily infested with lice may develop a systemic or overall body, effect. The following is taken from a report made by a scientist who recorded his symptoms after allowing 700 to 800 lice to feed on him two times a day. “I started feeding twice a day and almost immediately a general tired feeling was noticed in the calf of my legs and along the shin bones, while on the soles of my feet and underneath my toes the tired feeling was so intense as to often prevent sleep until late in the night. An irritable and pessimistic state of mind developed. An illness resulted with symptoms very similar to grippe and a rash similar to German measles was present, particularly over the shoulders and abdomen.” Once the experiment was discontinued the symptoms disappeared within a few days.

Epidemic Typhus. Epidemic typhus (also called “camp fever”, “jail fever”, “hospital fever”, “ship fever”, “famine fever”, “putrid fever”, “petechial fever”, “Epidemic louse-borne typhus,” and “louse-borne typhus”) is a form of typhus so named because the disease often causes epidemics following wars and natural disasters. Based on actual human deaths, this is one of the top three insect-vectored diseases in the world. The causative organism is Rickettsia prowazekii, transmitted by the human body louse (Pediculus humanus corporis). Body lice but not head lice are the main transmitters, perhaps because head lice are less mobile and they don’t reach the high populations on the body, therefore they are less frequently passed from person to person. Epidemics usually occur in the winter when people are huddled closely together and the lice migrate nightly from one pile of clothing to the next.

Feeding on a human who carries the bacillus infects the louse. R. prowazekii grows in the louse’s gut and is excreted in its feces. The disease is then transmitted to an uninfected human who scratches the louse bite (which itches) and rubs the feces into the wound. The incubation period is one to two weeks. R. prowazekii can remain viable and virulent in the dried louse feces for many days. Typhus will eventually kill the louse, though the disease will remain viable for many weeks in the dead louse.

Symptoms include severe headache, a sustained high fever, cough, rash, severe pain, chills, falling blood pressure, stupor, sensitivity to light, and delirium. A rash begins on the chest about five days after the fever appears, and spreads to the trunk and extremities. A symptom common to all forms of typhus is a fever which may reach 39°C (102°F).