Definition

Pediculosis capitis, or head lice, refers to an infestation of lice in the head, caused by parasites that can cause disease. Head lice are small, wingless, blood-sucking arthropods that feed off blood on the scalp. The adult louse has dimensions comparable to a sesame seed, although its eggs or nits can be compared to a small dandruff flake.

"Pediculosis" refers to an infestation of lice, whereas "capitis" means "head". Pediculosis capitis is a condition that affects the human head, eyebrows, and eyelashes resulting from the infestation of lice belonging to the species Pediculus humanus capitis. Additionally, pediculosis may manifest in other areas, including pubic hair (attributed to Pthirus pubis) and the body (attributed to Pediculus humanus corporis). 

Pediculosis capitis is a highly prevalent condition that dates back thousands of years. The estimated annual incidence of pediculosis capitis falls within 6 to 12 million cases. Pediculosis capitis exhibits a high degree of contagiousness, particularly among children in the preschool and elementary school age groups, and has the potential to spread to other individuals residing within the same home.

Causes

An infestation of head lice called Pediculus humanus capitis results in the development of Pediculosis capitis. These lice are brown or gray with similar size to sesame seeds. They can feed on human blood from the scalp. Female lice can produce a sticky substance that firmly attaches each egg to the base of the hair shaft, which is located 5 millimeters or less than 1/4 inch from the scalp.

The life cycle of head lice

The life cycle of head lice consists of three distinct stages, they are:

1. Eggs (nits)

The shape of the eggs is oval with small size, and they are strongly attached to the hair shaft. The minuscule size makes them unnoticeable to the eye. There is a common misconception that nits are synonymous with dandruff, scabs, or hair spray droplets. The hatching period for the eggs typically ranges from 8 to 9 days. Typically, eggs with a high probability of hatching are situated within a maximum distance of 0.5 cm from the base of the hair shaft.

2. Nymphs

Nymphs are lice that hatch from their eggs in an immature state. Nymphs bear a resemblance to adult head lice, albeit with a smaller physical size. Feeding on human blood is a necessity for their survival. The maturation period for nymphs is approximately 9-12 days following their hatching from the eggs.

3. Adult lice

The size of adult lice is equivalent to that of a sesame seed. They possess six legs and exhibit a greyish-white color. Adult lice may appear darker on individuals with dark hair compared to those with lighter hair. Adult lice also require blood to survive. The lifespan of adult head lice on a person's head is approximately 30 days, however, they will die within a day or two if they are dropped from the head. Typically, adult female head lice exhibit greater size compared to their male counterparts and can deposit approximately six eggs every day. 

Transmission of Lice

Head lice are capable of crawling, but are unable to jump or fly. Head lice are frequently transmitted by direct head-to-head contact, particularly in familial settings or among youngsters that have activities in close proximity, which includes recreational areas or schools. Rarely, head lice can be transmitted via the shared use of personal objects, including:

• Hat and scarf
• Brush and comb
• Hair accessories
• Headphones
• Pillows
• Towels

The spread of head lice can also occur when you store various clothes in the same storages. Lice can spread, for instance, through hats or scarves kept in the same locker or hook. Cats and dogs or other pets do not contribute to the transmission of head lice. 

Risk factor

Head lice can affect individuals of all ages, however it is most prevalent among children between the ages of 3 and 11. Because lice claws are better in capturing specific hair types, individuals with curly hair do not get infested with lice much compared to those with finer hair types.

Additionally, head lice is more prevalent in females compared to males, potentially due to the tendency of females to possess longer hair. Head lice infestations are frequently observed in environments with frequent close contacts, including schools, residential dwellings, playgrounds, sport facilities, and recreational camps. Lice exclusively sucks human blood. Consequently, pets and other animals are incapable of transmitting head lice.

Symptoms

Typical signs and symptoms of head lice may include the following:

• Pruritus
• Visible nits that can be seen on the scalp or hair shafts
• The presence of lesions on the scalp, neck, and shoulders. Scratching can result in the formation of tiny red bumps that may occasionally be infected with bacteria
• The sensation of a tickling or perceptible movement within the hair
• Enlarged lymph nodes 

itchiness on the scalp, neck, and ears is the most common symptom of head lice. This symptom manifests as an allergic response to the bites of lice. In the initial stages of lice infestation, individuals may experience pruritus that could last between 4 to 6 weeks. Typically, lice can be observed on the scalp, however they are typically challenging to detect due to their small size, rapid movement, and they usually avoid light.

Nits are stuck to the hair shaft and can be difficult to spot due to their small size. They are most easily identifiable around the ears and neck hairline. Finding empty nits is easier due to their lighter coloration and empty nits are usually farther from the scalp. Nevertheless, the existence of nits does not automatically indicate the presence of live head lice.

Diagnosis

In the process of establishing a diagnosis, the physician will start by question you. They will inquire about your symptoms, the course of your symptoms, and will also search for potential triggers that may contribute to the onset of pediculosis. This will be followed by a physical examination, during which time they will specifically check for lice on the hair. If there are live nymphs or adult lice on the head, diagnosis of pediculosis can be established. This is challenging, though, because head lice can move swiftly and frequently avoid light. Among the things that can be done to facilitate the detection of head lice are:

• Wet the hair to help make lice more visible and stop them from scattering
• The patient should sit in a brightly lit area
• Divide the hair into halves, partially comb out the hair, section by section, starting from the scalp
• Use a wet paper towel to clean the comb after each combing, take a close look at the paper towel, comb, and scalp

Management

Treatments for pediculosis capitis typically are given twice. After seven to nine days, the second treatment will eliminate all freshly hatched nits. The following are some treatment options for pediculosis capitis, the following are:

• Over-the-counter (OTC) medicine
• The synthetic lice repellent permethrin is approved and safe for use on patients starting from two-month-old babies and older individuals.

• Prescription medications: 
• Benzyl alcohol lotion, which could be used to treat head lice in six-month-old babies or older individuals.
• Malathion is a treatment for lice in six-year-old children and older individuals. It is not advised for pregnant women and breastfeeding mothers to use this medication.
• Lindane is often reserved as a last resort. Serious adverse effects from this medication include convulsions and death. Premature babies and individuals with a history of seizures should not use lindane. 

Complications

Individuals affected with head lice infestations typically have severe itchiness. The act of scratching the itchy scalp caused by the head lice could potentially break their scalp and risk getting infected.

Prevention

Preventing the spread of head lice poses significant challenges, particularly among children who frequent daycare facilities and schools due to the significant degree of close contact involved. The possibility of indirect spread resulting from sharing personal belongings is quite uncommon. In order to prevent the spread of head lice, it is advisable to tell your child to:

• Separate their clothes from other children's clothing, they could hang their clothes on separate hooks
• Refrain from sharing their hats, scarves, combs, brushes, and such items with other people
• Avoid lying on beds, sofas, or cushions that have come into contact with children or individuals infected with head lice

When to see a doctor?

Seek medical advice if you encounter symptoms indicative of pediculosis capitis in yourself or your children. The physician will determine the root cause of the symptoms, as head lice can occasionally resemble dandruff and various other medical disorders.

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