Lice in Deer

This fact sheet was created on 2/18/2020.

Cause

There three types of lice reported in deer; one sucking louse (Solenopotes binipilosus) and two chewing lice (Tricholipeurus lipeuroides and T. parallenus). The sucking louse feeds on the blood of the animal and the chewing lice feed on the skin.

Significance

At the population level, lice are not considered detrimental to deer herd health. However, heavy infestations can indicate the presence of other parasitic diseases, malnutrition or compromise of the animal’s immune system, any of which could be affecting local deer populations.

Species Affected

Lice are very host specific and these species (S. binipilosus, T. lipeuroides and T. parallenus) are adapted to only infect deer.

Distribution

Lice infestations have been described in deer across North America.

Transmission

Lice are transmitted by direct contact with infected deer. They spend their life cycle near the skin surface. The eggs (nits) are closely attached to the hairs and the larvae undergo several moults before becoming adults. Louse populations fluctuate with season. Infestations are commonly noted during later winter and early spring when infected animals are congregated in winter yards or at feeding stations.

Clinical Signs

Most infested deer do not develop clinical signs, but those that do can either look moth-eaten or have very dramatic large patchy areas of complete hair loss. A protein in the saliva of lice acts as an allergen and elicits a hypersensitivity (severe allergic reaction) in deer causing the release of compounds such as histamine. This results in skin irritation and itching. Itching causes varying degrees of self-trauma; excessive grooming and rubbing on inanimate objects results in loss of guard hairs (alopecia), and sometimes the underfur. This results in a patchy appearance to the pelage with yellow or white patches along the sides. Over time, usually when hair is completely lost, the skin may also become darkened (due to chronic inflammation and deposition of the pigment melanin) and thickened. These changes are reversible once the infestation is reduced or eliminated.

With low level infestations, the immune system can kill or repel the parasite through grooming. However, when the number of parasites is overwhelming or there is a diminished initial immune response due, for example, to poor nutrition, that immune response can be inadequate. Deer that are heavily infested may be suffering from malnutrition, other parasitic infection, or disease.

Diagnosis

Due to their small size lice are difficult to detect with the naked eye. Lice should be suspected when deer are observed to have hair loss especially when the coat takes on a patchy appearance. The insides of the legs are also commonly affected sites. Species identification is done by a magnified examination of specimens preserved in 70% alcohol or 5% formalin.

Treatment

There is currently no practical method of delivering effective doses of medication to free-ranging wild deer. Many affected animals will resolve their lice infestation and the hair will grow back without intervention when their immune systems function normally.

Management

Management is not only impractical but likely unnecessary since lice affect individual animals, and have not been documented to have a significant impact on wild deer populations. Discouraging supplemental feeding would help reduce opportunities for direct transmission of lice from one affected individual to another. Because they are host specific there are no known health risks to humans, predators or scavengers, or from eating meet from a deer infected with lice.