CLASS INSECTA

The Class Insecta is the second class of arthropods that we will discuss. They can be readily differentiated from arachnids by the following characteristics:

Adults have three body parts.
Adults have three pair of legs on the thorax.
Antennae and wings are present.
There is no sexual dimorphism.
Metamorphosis

Simple (incomplete)- egg, nymph, adult
Complete - egg, larvae, pupa, adult

LICE

Lice are significant to veterinary medicine for several important reasons. As pests, they are a significant annoyance to many animals, including man. Additionally, some species are important as vectors for significant disease agents effecting both man and animals.

There are two Orders of Lice covered in this class: Anoplura (Sucking lice) (below left), Mallophaga (Biting lice) (below right).

Members of the Order Anoplura (above left) can be recognized by having a head that is longer than it is wide while the Malophaga (above right) have a head that is wider than it is long.

All lice are wingless, flattened dorso-ventrally and well adapted to an existence on the body or body-hairs.. The head is narrow in proportion to the length of the mandibles and the body is not chitinized. Lice are very host and site specific.

A general life cycle involves eggs (nits - above left) which are oval in shape and white in color with a operculum or lid on one end. Eggs are deposited on an area of choice (attached to hairs, clothing, etc.). Eggs hatch in several weeks and young lice, that look like miniature adults (incomplete metamorphosis) appear. The young are ready to feed when hatched and feed several time a day. They molt (change in size) several times over a several week period. When adults, copulation occurs and eggs are laid in a few days. Adults (females) can live several months. Often the only indication of louse infestations is the presence of the nits attached to the hair (above middle). In cases of heavy infestations, both adults and nits are readily visible (above right).

Anoplura Human (above)

Pediculus humanus var capitis (head lice)
Pediculus humanus var corporis (body lice)

Human body lice can be involved in the transmission of epidemic relapsing fever, typhus, and various micotic and bacterial dermatologic conditions. These lice are vary host specific and transmission is directly from one human to another. The head louse is often involved in epidemics involving school children or families where close contact occurs.

Phthirus pubis (crab lice- above). This louse is of considerable aesthetic importance but not known to be involved in the transmission of disease agents. Infestations are by direct contact with other infested individuals. Non-human animals (dogs, etc.) are not infested with this species and as a result are not involved in the epidemiology of transmission.

Common genera of Anoplura of domestic animals:

Haematopinus
Linognathus
Solenoptes

Common genera of Mallophaga of domestic animals:

Bovicola
Damalania
Trichodectus
Menopon

Host list for lice of domestic animals:

Swine:

Haematopinus suis. Common on loose folds of skin at neck, jowl, ,base of ears, along the belly, and the inside of the legs. Eggs are usually located along the lower parts of the body and the base of the ears.

Sheep:

Damalania ovis. Referred to as the "red-headed sheep louse" since the head is red in color while the body is brown. Infestations are characterized by a marked irritation producing "taggy" wool. This usually leads to rubbing and biting, further compounding the condition of the wool and leading to secondary infections.
Linognathus pedalis. Called the "sheep foot louse" since it is usually found on the legs, especially around the claw region.

Horses:

Bovicola equi
Haematopinus asini. The sucking louse of horses.

Cattle:

Bovicola bovis. Called the "little red louse" due to the color of the head. They are most common around the base of the tail, withers and neck. Marked irritation which results in scab-like lesions are often seen in heavy infestations.
Haematopinus eurysternus. The "short nose" cattle louse.
Linognathus vituli. The "long nose" cattle louse. This louse is generally seen uniformly over the entire body unless infestations are of several species. In these cases, this louse is more restricted to the lower body regions.
Solenoptes capillatus. The "little blue" cattle louse.

Dogs:

Trichodectus canus. The common biting louse of dogs. It has been implicated as a possible intermediate host for the tapeworm Dipylidium caninum. The common use of flea colors and other treatments has made this once common parasite a rarity.
Linognathus piliferus. The common sucking louse of dogs. Small in size and yellow to pink in color.

Poultry:

Menopon sp. A common problem in all poultry. Infestations are often an unrecognized cause of poor condition in domestic and wild birds. There are many species involved but diagnosis and control is similar.

Each of the large domestic animals except the horse and goat has only one species of biting lice that infest it. The horse has two and the goat several. Hogs are not parasitized by biting lice while only biting lice infest poultry.

Control and Treatment

Most louse infestations in dogs and cats can be controlled with carbaryl dust or dioxathion (shampoo, spray or dip). Repeat treatment in about 7 days. Most products that control fleas are also effective in controlling lice.

Louse infestations in cattle are usually mild but numbers can increase through winter months. Treatment with most insectacides is usually effective. Ivermectin treatment is successful against most species of Anoplura lice.