Practical Parasitology

Introduction to the Medically Important Arthropods


Overview

In this section order Anoplura, the body and pubic or crab louse will be studied. Pediculus humanus and Phthirus pubis respectively. Although they do irritate the skin, they are also vectors of disease.

Order Siphonaptera, fleas are a nuisance to both pets and pet owners and are vectors of disease.


Pediculus humanus var. capitis/corporis (head and body louse)

Nit comparison P. pubis and P. humanus Pediculus humanus nymph P. humanus P. humanus

The life cycle from egg (nit) to nymph and adult takes approximately 2 weeks and is an incomplete metamorphosis. According to the CDC viable nits are located within 6 mm. of the scalp. Nits found further from the scalp suggest a previous infection. Transmission is usually person to person.

Laboratory diagnosis is accomplished by identifying the nits or adults from a specimen obtained from the infected person.

Treatment usually involves the application of a prescription or over the counter pediculicide. The prescription drug is usually stronger. All clothing and bedding that may have come into contact with the infected person should be cleaned thoroughly to kill any nits that may be present. A special comb is available to run through hair that may have nits present to remove them.


Phthirus pubis (pubic, crab louse)

Phthirus pubis adult

The crab louse is a 1 mm. long, six legged arthropod, and unlike the body louse it is more compact not elongated. They may be found anywhere on the human body and although they may be acquired from bedding or clothing they are associated with sexual activity.

Laboratory diagnosis is accomplished by identifying the nits or adults from a specimen obtained from the infected person.

Treatment according to the Sanford Guide to Antimicrobial Therapy 1999 is the same for P. humanus consisting of an application of a prescription drug or an over the counter product of lesser concentration. After the initial treatment and combing another treatment is performed 7 - 10 days after to kill any remaining lice.


Ctenocephalides felis (cat flea)

C. felis Egg Larva

Although this flea is more likely to attack your pet it readily attacks humans and has the potential to transmit disease, namely plague, typhus and tularemia. It is important to treat not only your pet but the building it resides in. The life cycle of the flea is important to know to realize this.

The flea undergoes complete metamorphosis. From egg to larva, pupa and adult in about 5 weeks. The eggs are laid on or in the habitat the animal resides in. Most if not all of the development takes place "off" the animal.