Lice Of Livestock

Although louse populations of a few hundred individuals commonly occur on healthy livestock, sometimes these numbers can reach into the thousands or, rarely, to more than a million per animal. It is under the latter conditions that detrimental effects to the host occur. These include restlessness, pruritus, anemia, low weight gain, low milk yield, dermatitis, hide or fleece damage, skin crusting or scabbing, and lameness. Large louse populations on domestic stock typically develop on juvenile, senile, sick, nutritionally deprived, or immunocompromised hosts.

Sucking louse infestations of cattle, such as those caused by the shortnosed cattle louse (Haematopinus eu-rysternus), the cattle tail louse (H. quadripertusus), and the longnosed cattle louse (Linognathusvituli) (Fig. 4.7H), can cause serious damage to the host. This can be manifested as frequent rubbing of infested areas, hair loss, scab formation, slow recovery from disease or trauma, and low weight gain. Younger animals are typically more severely affected than older cattle. Mixed infestations of both chewing and sucking lice on cattle, or of both lice and nematodes, can affect weight gains more severely than single infestations. In single or mixed infestations, weight gains are typically lower in stressed cattle and those on low-nutrition diets. Sometimes, cattle sucking lice cause severe anemia, abortions, or even death. Irritation can be caused by small numbers of lice in sensitive cattle and usually results in frequent rubbing and subsequent hide damage. This rubbing also damages livestock facilities. Severely infested cattle often have patches of bare skin and a greasy appearance which results from crushing lice and their feces during rubbing. Under laboratory or confined conditions, at least three pathogens can be transmitted by cattle sucking lice, i.e., the causative agents of bovine anaplasmosis, dermatomycosis {ringworm) (Table III), and, rarely, theiieriosis. The importance of cattle lice in transmitting any of these pathogens in nature is unknown but presumed to be low.

Lice of horses and other equids typically do not greatly debilitate their hosts except when they are present in large numbers. Pruritus, hair loss, and coat deterioration may occur in severely infested animals. Horses with severe louse infestations are nervous and irritable; they typically rub against objects, kicking and stamping. Hair can be rubbed from the neck, shoulders, flanks, and tail base, resulting in an unkempt appearance that may affect the value of the horse. No pathogens are known to be transmitted by equid lice.

Hog lice can imbibe significant volumes of blood from hogs, especially piglets, which often have larger infestations than adult pigs. Hog-louse feeding sites often cause intense irritation, leading their hosts to rub vigorously against objects, which can result in hair loss and reddened or crusty skin lesions. Haematopinus suis is a vector of the virus that causes swinepox (Table III), a serious and potentially fatal disease characterized by large pockmark lesions, mainly on the belly of infected animals. Some studies have implicated this louse as a vector of Eperythrozoon suis and E. parvum, causative agents of swine eperythro-zoonosis, and of African swine fever virus. However, transmission of these pathogens by lice appears to be rare, if it occurs at all, in nature.

All species of lice that parasitize sheep and goats (Tables I and II) can cause debilitation, even when present in relatively small numbers, because of the potential

FIGURE 4,15 Fleece damage (wool slippage) in a sheep, caused by-severe infestation with Linojjtiatbm africanm (Anoplura). (Courtesy of John E. Lloyd)

damage which they can cause to fleece and wool (Fig. 4.15). Some sheep develop hypersensitivity to the sheep biting louse (Bovicola oris) (Fig. 4.16). This louse causes most sheep fleece devaluation worldwide and is the major cause of cockle, an economically disfiguring condition of sheep fleece that is particularly prevalent in New Zealand. Any increase in skin lesions or body rubbing in response to lice generally devalues wool or mohair. Different breeds of sheep and goats exhibit contrasting levels of resistance or tolerance to infestation by lice.

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