The lice are an important group of arthropods that while not vectors of parasites, they are important ectoparasites that can cause great discomfort, lead to secondary infections, and can transmit some bacterial infections that can lead to serious illness. Infections caused by lice is called pediculosis.

Lice have an intimate relationship with the host in that it is their source of warmth and food consisting of blood meals and cutaneous cell fluids. Removed from their host the lice do not survive for very long.

Head louse (Pediculus humanus capitis) obtained from the head hair of a child visiting an outpatient clinic – Photo by W. Vientos

The body louse and the head louse are almost indistinguishable except for the location in which they are found on the host as described below. They are described as grey white translucent with an elongated body containing 6 legs. They are generally wider at the center with segmentation present. Two prominent antenna can be seen on the head directly after the eyes.

The Pubic louse however is distinctly identifiable by it more plump round shape.

The Body Louse (Pediculus humanus corporis)

Pediculus humanus corporis is the causative agent of body lice infestation. The louse is found to inhabit the fibers of clothing and move to the host body periodically to feed. Eggs (nits) are laid on the fibers of the clothing.

Pediculus humanus corporis infestation is an important vector for various rickettsial infections (epidemic typhus; trench typhus; and relapsing fever).

The adult louse is approximately 2.5 – 3.5 mm in length and are translucent in appearance (tan to grayish). They have six legs.

Body louse (Pediculus humanus corporis) obtained from the clothing of a homeless man visiting an outpatient clinic – Photo by W. Vientos

The Head Louse (Pediculus humanus capitis)

Pediculus humanus capitis is the cause of human head lice infections. These infections tend to occur mostly in the homeless, crowded conditions as in jails or extended care facilities, and schools or daycare centers where outbreaks occur frequently among children sharing hats or brushes.

The infestation is mostly a nuisance with secondary infections possible. Unlike the body louse which can transmit bacterial diseases, the head louse is not known to be a vector of either parasitic or bacterial diseases.

This is a photo of a louse nit of Pediculus humanus capitis – These eggs are laid along the shaft of the hair and in large infestations can number in the hundreds. Lice combs are meant to remove these nits from the hair in combination with a pediculicide. Repeat treatments are commonly needed to achieve full eradication of the infestation. – Photo by W. Vientos
A nymph stage of Pediculus humanus capitis – Photo by Wilson Vientos

Pubic louse or crab louse (Phthirus pubis )

The Pthirus pubis or the crab louse is a louse that has a predilection for coarse hairs. Specifically those hairs of the pubic area. Coarse hair infestation may also occur in other area in which there may be coarse hair such as the arm pits, beards/mustaches. and eyebrows. They are considered sexually transmitted however they can be acquired without sexual contact.

Pthirus pubis are predominantly a nuisance in that they cause irritation due to allergic reactions from saliva & feces. Some of these allergic reactions are extremely intense and can cause hallmark bruise marks around the pubic area. Additionally, if the itching is severe enough, breaks in the skin due to itching can lead to secondary infections with bacteria such as Staphylococcus aureus and Streptococcus pyogenes.

Phthirus pubis – Note the characteristically round body, hairs at the posterior, hooks on the legs to allow the louse to grab on securely to the rough hair. Two prominent antennae are present. 
Video by W. Vientos