Louse Infestation (Pediculosis)

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Infestation with the louse Haematopinus suis.


Infestation is common where husbandry and management are poor. The lice live only on swine although they may temporarily infest people handling swine. All age groups of swine are susceptible to infestation. Infestation is more severe in winter although it persists throughout the year. Presumably, the parasitism is worldwide wherever swine are raised.

Historical information

Prior to the development of good parasiticides, pediculosis in swine was very common. It was a common practice to use waste crankcase oil or diesel fuel as a topical spray on swine to reduce the number of lice. In at least a few instances, the practice resulted in terrible accidents when a match or cigarette was carelessly dropped where swine had been crowded together and soaked with these flammable liquids.

The relatively recent development of many effective parasiticides has made it possible for a producer to completely eradicate lice.

Products that control both internal and external parasites, including lice, have made control of lice more convenient.


Haematopinus suis is one of the largest species of lice, up to 6 mm long. Haematopinus suis is a sucking louse and obtains blood meals from the host through its penetrating mouth parts. The louse spends its entire life on the host. It can survive off the host for only a few days. The female louse lives about 23-30 days, lays three to four eggs (“nits”) per day and attaches them to hair shafts near their base. Eggs are 1-2 mm long and light cream to gray in color. They hatch in 12-20 days.


Hog lice, like most lice, are host specific. They usually spread among swine when the pigs are in close contact, as when they crowd together for warmth, shade or comfort. Also, lice can spread to pigs moved into quarters recently vacated by lousy animals. Infested animals added to a clean herd often introduce lice.

Lice living on a pig have certain preferred sites because they prefer to feed on thin-skinned areas. Favorite sites include the neck, jowl, flank, the inner side of the legs and ears. In the ears, they often reside in “nests.” Similar nests often are found on the abdomen, sometimes within the circles of pityriasis rosea lesions. Location within the ear offers lice protection from parasiticides because it is difficult to thoroughly wet the inner surface.


Lice annoy swine when they pierce the skin to take a blood meal. Dermatitis develops and leads to rubbing, scratching and some loss of hair. Loss of blood is not severe in most pigs but can lead to severe anemia in nursing pigs and may make them more susceptible to other diseases. Parasitized pigs are restless. They may lose weight and utilize feed less efficiently.

Lice are known vectors of agents that cause swine pox, African swine fever and eperythrozoonosis. It seems likely that other infectious agents may be transmitted as well.

Clinical signs

Persistent rubbing and scratching, patchy alopecia and pallor are signs of pediculosis. Because similar signs are seen with sarcoptic mange, it must be differentiated. Pediculosis and sarcoptic mange often occur concurrently. Hog lots and facilities with many rubbing sites also suggest that lice or mange are present.


Lesions include a rough, dull hair coat, often with patchy alopecia. A thorough examination reveals the lice and ova attached to the hair. Examination of the inner aspect of the ears often reveals the lice and it also is a good place to look for sarcoptic mange lesions.

It is a good practice to occasionally pick up a few small and growing pigs, turn them over and examine their undersides. Lice, as well as lesions of several other diseases, often are readily apparent on the posterior abdomen or on the inside surface of the legs.

At slaughter and removal of hair, the punctate cutaneous lesions caused by feeding lice are visible, especially in white skinned hogs.


Animals being introduced into a herd should always be treated with a parasiticide, preferably at least twice at two-week intervals, before being added to a herd. Many effective parasiticides are now available. A repeated treatment kills lice that emerge from eggs 12-20 days after an initial treatment.

Several parasiticides control external parasites other than lice (flies, mites and ticks). Injectable avermectins have been very effective in controlling both lice and mange and programs have been devised for eradicating both. See the table, Anthelmintics and Parasiticides. Directions for use should be followed carefully. Some parasiticides require withholding periods prior to marketing.