Head Lice Risk Factors & Diagnosis
Head lice (Pediculus humanus capitis) are ectoparasites (blood-feeders) that dwell on the scalp of the humans, most commonly behind the ears and near the neckline. Head lice infestation is medically termed “pediculosis capitis”, however it is commonly referred to as simply “pediculosis”. Although having head lice can be a physically aggravating, and emotionally embarrassing experience, pediculosis has not been linked to the transmission of any serious diseases. However this does not mean that having a head lice infestation is not a significant health hazard. The irritation caused by the head lice causes severe itching, and in many cases the victim scratches so vigorously that the skin is broken. This leaves the scalp tissue susceptible to infection, especially if the victim continues to scratch after the skin has been broken.
Once the scalp has become infected, the infection can spread to other parts of the body and cause serious illness, which if left untreated for an extended period of time may result in fatality. This kind of event rarely happens in the United States due to the ready availability of pediculosis treatments and antibiotics, but deaths have been recorded in less fortunate countries where treatment is difficult to acquire. Even so it is very important to treat head lice as soon as it is discovered, as the infestation can become severe rather quickly, and infection is still cause for concern, regardless of where you live.
Risk Factors
Head Lice infestations (pediculosis) in the United States is most commonly seen in preschool or elementary school children aged 3-12. However the infestation commonly spreads to the family members and friends of these children. Although head lice can occur in people of all races, African Americans rarely contract pediculosis. It has been theorized that this is due to the fact that the claws of a louse are more adept at grasping the hair follicles of other races. This has lead to the observation that lice do prefer certain hair follicle shapes and widths.
A common misconception is that head lice infestation is caused by poor hygiene and/or dirty environments. This myth has been repeatedly disproven, and the contraction of pediculosis is not related to cleanliness in any way. Another common misconception is that head lice can only be spread through direct contact with an infested person’s hair. Although transmission through indirect contact is not as common as transmission through direct contact, it does occur, especially in congested environments such as schools. The most common form of transmission is through direct contact with the head of an infested individual. This is the primary reason why head lice infestations are more common among children, who often play intimately during sporting events and other recreational activities like wrestling, and “horse-playing”.
Head lice can live for about 24 hours without a host, and although they are small they can move very quickly, which makes indirect contact a very plausible transmission method. For this reason, sharing items is the second most common form of pediculosis transmission. Head lice can spread from person to person through the sharing and direct contact of items such as hats, helmets, shirts, ear muffs, headphones, scarfs, brushes, combs, hair accessories, and towels among others. Lice can also be contracted by using furniture that has recently been in contact with an infested individual. For this reason, children that ride a bus or van to and from school are at an elevated risk for contracting pediculosis, through both direct and indirect contact.
Children who play sports in which helmets and equipment is shared, such as baseball and football, are also at an elevated risk. Studies have shown that children that have siblings or live with other children are more likely to contract pediculosis, and statistically girls are infested more than boys. The theorized reasons for this are; girls generally have longer hair and more intimate playing habits. The children with the lowest probability of contracting head lice are African Americans with very short hair. Head lice cannot inhabit a head without hair for long, so children without hair are considered immune to head lice infestation.
Identification
Head lice live for about month, and their spans are categorized into three stages; nit (egg), nymph, and adult. Adult female lice attach nits to the hair follicle base via a naturally secreted adhesive. The nits are laid very close to the scalp (generally within six millimetres), as to provide heat for the incubation of the eggs. Nits are yellowish-white, oval-shaped eggs, about 0.8×0.3mm in size, and they usually hatch within a week to ten days, becoming nymphs. After the nit hatches, the shell remains attached to the hair follicle, and it’s color dampens to a darker shade of yellow. Nymphs look identical to adult lice, except they are slightly smaller and may also be slightly lighter in color. A nymph will shed it’s exoskeleton three times before reaching adulthood within a week of hatching.
Once reaching adulthood, the louse will require about 5 blood-feedings per day. The adult louse uses it’s claws to pierce the skin, after which it injects saliva and then sucks the blood through it’s mouth. The saliva that injects is primarily responsible for the irritation and itching sensation experienced. Although lice do not swell like many other ectoparasites, they do turn to a darker rust-colored shade after feeding. Despite their small size they can travel fairly quickly, and an adult female louse can lay up to eight nits per day. Since the adult lifespan of a louse is about 3 weeks, this means that a female can lay more than 150 nits in her lifespan, resulting in rapid reproduction and severe infestation if not treated.
Symptoms
Most cases of pediculosis cause very irritating symptoms. Generally the victim’s reaction to these symptoms prompts the scalp inspection that leads to the discovery and diagnosis of pediculosis. Occasionally more minor infestations are discovered through routine inspections. The first noticeable symptom of pediculosis is an itchy scalp or the sensation of something crawling on the scalp. Anyone experiencing these symptoms should be inspected for pediculosis immediately, as delaying treatment could result in a severe infestation. It is important to note that the itching sensation results from an allergic reaction to the louse saliva that is injected into the skin prior to feeding. Therefore many people do not experience an itching sensation in the beginning of the infestation, because their body has not yet developed an allergy to this irritant. This is especially true for people that have never contracted pediculosis before.
Once a sensitivity to the louse saliva has been acquired, small red bumps begin to appear on the scalp, and on the back of the neck and shoulder area, where the lice most commonly feed. These bumps are very easy to puncture with a fingernail during scratching, and this leads to more noticeable signs of infestation such as red sores or scratches on the scalp/neck area. Bacterial infection contracted through these open sores can lead to swollen lymph nodes, which when seen in conjunction with the signs above, are a reliable indicator of a possible head lice infestation. All of these symptoms may cause overall irritability in the affected individual, which itself is an indirect symptom of pediculosis.
Diagnosis
An official diagnosis is made when the head lice is discovered visually upon inspection of the scalp. Finding a single louse in any stage of it’s life cycle constitutes a diagnosis of pediculosis. Due to the rapid reproductive nature of head lice, it is much more common to find more nits than nymphs or adult lice. Any nits found within 4 centimeters of the scalp indicate an infestation that needs to be treated immediately. Once these nits hatch, more than half of them may be females, which will produce an additional 90-150 nits each during their 30 day lifetime. Given these numbers, it is easy to see how an infestation can become severe in a short time period. However, usually infestations don’t get past a moderate level without noticeable symptoms appearing.
It can be difficult to spot nits because they are extremely small. Nits resemble dandruff in appearance, however they can easily be distinguished from dandruff, as they are attached to the hair follicle and will not move upon agitation. Usually inspections are conducted with high lighting and a magnifying glass, and hair ties and wooden sticks are used to separate and comb through hair. Lice move very quickly, so adults and nymphs can be hard to spot, but finding any nits close to the scalp, behind the ears or near the neck is a good sign that an active infection is present. If nits are found more than a quarter of an inch from the scalp, then the infestation may be expired and no longer requires treatment. If a conclusive diagnosis cannot be made at home, then the assistance of a medical professional should be sought.
Prognosis
Although an head lice infestation can be a very irritating and embarrassing experience, it is a very easy condition to treat. Most people with pediculosis are cured of the infestation within a matter of weeks. In rare cases the infestation may be severe which could require the head of the infested person to be shaved. Although secondary bacterial infections are possible, serious complications from head lice infections are very rare, and it has not been linked the transmission of any diseases.