Lice in Pigs — Integumentary System — Merck Veterinary Manual

Lice in Pigs

Jennifer E. Thomas

, DVM, Oklahoma State University

Domestic pigs are infested with only one species of louse, Haematopinus suis, the hog louse. This very large (5–6 mm) sucking louse is common on domestic swine worldwide. Swine pediculosis is more common in smaller or backyard populations than in large, commercial operations. Nymphal lice are normally found on the inside of the ears (often in the ear canal), on the skin behind the ears, in the folds of the neck, and on the medial aspects of the legs. In severe infestations, H suis may be found elsewhere on the body.

H suis can cause severe anemia, especially in piglets, because of the amount of blood imbibed by this large louse species. Extreme pruritus and subsequent self-trauma (alopecia, erythema, excoriations, and crusting) can be seen as hogs alleviate the irritation associated with the lice feeding.

Pathogenesis and Disease Transmission:

H suis is a vector of swine pox virus, and it has also been implicated as a vector of Eperythrozoon suis and E parvum, the causative agents of swine eperythrozoonosis and of African swine fever virus in regions where these agents are endemic. Except for swine pox virus, transmission of these agents by H suis is considered rare.


A variety of compounds effectively control lice on swine, including synergized pyrethrins; pyrethroids; the organophosphates phosmet, coumaphos, and tetrachlorvinphos; and the macrocyclic lactones ivermectin and doramectin.

Amitraz is no longer available for use on swine in the USA. Although eprinomectin is used in cattle, this compound should not be used in unapproved animal species, because severe adverse reactions, including fatalities, may result.

For severe infestations in swine, dust formulations can be used to treat bedding. Husbandry and underlying health issues should be addressed.

Ascariasis from pigs FAQs

On this Page

Can people get ascariasis from a pig?

Yes. Ascaris suum is an intestinal parasite of pigs that can also infect people.

How is Ascaris suum spread to humans?

The adult Ascaris suum worm lives in the pig’s intestines and produces eggs that are passed in the pigs’ feces (manure). These eggs are deposited into the soil wherever the pig defecates. The eggs require days to weeks in the environment to become infective. Ascaris suum infection is caused by ingesting these infective eggs. This happens when

  • People don’t wash their hands thoroughly after handling pigs, cleaning pig pens, or handling pig manure; and
  • People consume fruits or vegetables grown in gardens fertilized with pig manure or in soil where pigs have previously been kept and that have not been carefully cooked, washed, or peeled.

Ascaris suum is not transmitted to people by eating pork or pork products because the worm eggs are not found in the meat.

How do I know if my pigs are infected with Ascaris suum?

Many infected pigs do not show any symptoms. Heavily infected pigs may have symptoms including the following:

  • Difficulty breathing, sometimes called “thumps”
  • Weight loss
  • Unthrifty (not strong or healthy)
  • Slow weight gain
  • Possibly passing whole worms in manure

A veterinarian can take a fecal sample from your pig(s) and look for evidence of roundworm infection. A veterinarian can also prescribe deworming medications for your pigs if they are infected.

Who is at risk for infection with Ascaris suum?

People who raise pigs or use raw pig manure as fertilizer may be at risk for infection with Ascaris suum.

How can I prevent infection with Ascaris suum?

  • Avoid contact with soil that may be contaminated with pig feces, including soil where pig manure has been used to fertilize crops.
  • Wash your hands with soap and water after handling pigs, cleaning pig pens, or handling pig manure, and always before handling food.
  • Teach children the importance of washing hands to prevent infection. Supervise children around pigs, ensuring that they do not put unwashed hands or other potentially contaminated objects in their mouths.
  • Wash, peel, or cook all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with pig manure.

Consult a veterinarian for recommendations on preventing and controlling Ascaris suum in your pigs.

This information is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the parasites described above or think that you may have a parasitic infection, consult a health care provider.


Examination of hair and scalp for head lice. Close examination of the hair and scalp is necessary to determine head lice infestation. (CDC Photo)

Misdiagnosis of head lice infestation is common. The diagnosis of head lice infestation is best made by finding a live nymph or adult louse on the scalp or hair of a person.

Because adult and nymph lice are very small, move quickly, and avoid light, they may be difficult to find. Use of a fine-toothed louse comb may facilitate identification of live lice.

If crawling lice are not seen, finding nits attached firmly within ¼ inch of the base of hair shafts suggests, but does not confirm, the person is infested. Nits frequently are seen on hair behind the ears and near the back of the neck. Nits that are attached more than ¼ inch from the base of the hair shaft are almost always non-viable (hatched or dead). Head lice and nits can be visible with the naked eye, although use of a magnifying lens may be necessary to find crawling lice or to identify a developing nymph inside a viable nit. Nits are often confused with other particles found in hair such as dandruff, hair spray droplets, and dirt particles.

If no nymphs or adults are seen, and the only nits found are more than ¼ inch from the scalp, then the infestation is probably old and no longer active — and does not need to be treated.

Identifying Swine Lice, Ticks, and Fleas

Identifying Swine Lice, Ticks, and Fleas

Swine Lice or Hog Lice are relatively large external blood sucking parasites.

A lice infestation causes itchy discomfort for the pigs. Infected pigs will rub against their surroundings trying to relieve the itch. Left untreated they will rub their hair off and create sores. Lice are vectors for disease such as swine pox.

Lice can be treated and prevented with ivomec, brand name Ivermectin. This is the same medication, at the same dose, that is used to treat and prevent mites. See dosage here. Pigs get lice from other pigs. Swine lice are species specific and cannot live on any other animals or humans.

Lice are identified by their size, body shape, movement, and the sticky eggs left in the pig’s hairs. They are the largest blood sucking louse found on domestic animals, much larger than the lice found in human hair.

  • Grayish brown
  • Measure around 1/4 inch long, visible to the naked eye
  • Elongated, segmented, soft body w/ oblong head
  • 6 legs and 2 antennae
  • Does not engorge or swell
  • Runs fast through the hairs
  • Leaves sticky eggs attached to hair follicles
  • Cause extreme itching and hair loss
  • Transmits infections and diseases to pigs
See also:  How To Kill Fleas On Cats (Safely And Effectively) - All To Do With Cats

Ticks are soft bodied blood sucking arachnids. They are found in all environments outside, feasting on mammals, birds, and humans.

Ticks should be removed promptly if found attached to your pig. Prevention is through environmental management. Make your yard unappealing to ticks, and/or use tick repellent products or natural homemade recipes to keep ticks off your pigs. Read the info here.

  • Varied colors/patterns, usually black or brown
  • Teardrop shape body, small compact head
  • 8 legs and no antenna
  • Dramatic changes through life cycle
  • Starts flattened and gorges to the size of a swollen raisin
  • Abdomen is not segmented
  • 1 mm to up to 3/4 inch in size
  • Crawl slowly until they attach firmly to the pig’s skin
  • Stay attached until engorged
  • Does not cause itching
  • Transmits infections and diseases to pigs

Overview of Lice


Jennifer E. Thomas

, DVM, Oklahoma State University

Numerous species of lice parasitize domestic animals. Lice are largely host specific, living on one species or several closely related species. Lice are obligate ectoparasites and depend on the host to complete their life cycle. Recent taxonomic changes have complicated the orders and suborders of lice. In general, lice are divided into two categories: bloodsucking (or sucking) lice (order Anoplura) and chewing (or biting) lice (formerly the order Mallophaga, now composed of three suborders). Bloodsucking lice are parasites of mammals, whereas chewing lice infest both mammals and birds. Lice live within the microenvironment provided by the skin and its hair or feathers, and are transmitted primarily by contact between hosts. All life stages occur on the host, although lice may survive off the host for a period of time. In temperate regions, lice are most abundant during the colder months and often are difficult to find in the summer. Infestations are most often seen on stressed animals, and husbandry and individual health are important in treatment and management of these parasites. (Also see Ectoparasites.)

Etiology and Pathogenesis:

Lice are wingless, flattened insects, usually 2–4 mm long, although the species infesting animals may range from 1–8 mm long. The claws of the legs are adapted for clinging to and moving among hairs or feathers; the size and shape of the claws tend to be specialized for the average width of a hair shaft of the host species. This characteristic plays an important role in host specificity. The mouthparts also aid in attachment to the host. Chewing lice have ventral chewing mandibles; they feed on epidermal debris, primarily skin scales, sebaceous secretions, and feathers, if applicable. The heads of chewing lice have a blunted appearance, with the head being wider than the thorax. As the name implies, bloodsucking lice have piercing mouthparts that allow them to feed on the blood of their host. In contrast to the heads of chewing lice, those of bloodsucking lice have a pointed appearance, and the heads are narrower than the thorax. When not in use, their mouthpart stylets are retracted within the head. The distinction between chewing lice and bloodsucking lice is important when choosing an effective therapy for treatment of pediculosis.

On mammalian hosts, louse eggs, sometimes called «nits,» are glued to hairs near the skin surface and are pale, translucent, and suboval. The three nymphal stages, of increasing size, are smaller than adults but otherwise resemble adults in habits and appearance. Approximately 3–4 wk are required to complete one generation, but this varies by species. Adult lice are visible to the naked eye, but magnification is often required to identify the species.

Pediculosis can result in dermatologic disease, production loss, and occassionally anemia due to blood loss. Additionally, lice may be vectors of more arthropod-borne infections than previously believed. Lice have been shown to transmit viruses, bacteria, fungi, and protozoa. Most of the research has focused on agents transmitted by human lice species that are known to transmit a variety of pathogens to their hosts, including the causative agents of epidemic typhus (Rickettsia prowazekii), louse-borne relapsing fever (Borrelia recurrentis), and trench fever (Bartonella recurrentis), among others. Until recently, relatively few diseases were known to be vectored by domestic animal lice. A number of agents are now known or suspected to be vectored by lice.

Clinical Findings and Diagnosis:

Pediculosis is manifested by pruritus and dermal irritation, with resultant scratching, rubbing, and biting of infested areas. A generally unthrifty appearance, rough coat, and lowered production in farm animals is common. In severe infestations, there may be loss of hair and local scarification. Extreme infestation with bloodsucking lice can cause anemia. In sheep and goats, rubbing and scratching often results in broken fibers, which gives the fleece a “pulled” appearance. In dogs, the coat becomes rough and dry and, if lice are numerous, the hair may be matted. Sucking lice cause small wounds that may become infected. The constant crawling and piercing or biting of the skin may cause restless behavior in hosts.

Diagnosis is based on the presence of lice. The hair should be parted, and the skin and proximal portion of the coat examined under good lighting conditions. The hair of large animals should be parted on the face, neck, ears, topline, dewlap, escutcheon, tail base, and tail switch. The head, legs, feet, and scrotum should not be overlooked, particularly in sheep. On small animals, the ova are more readily seen. Occasionally, when the coat is matted, the lice can be seen when the mass is broken apart. Biting lice are active and can be seen moving through the hair. Sucking lice usually move more slowly and are often found with mouthparts embedded in the skin. Diagnosis may be aided by use of a magnification device. An otoscope, without the otoscopy cone, may be useful for this purpose.

Pediculosis of livestock is most prevalent during the winter; severity is greatly reduced with the approach of summer. Infestations of both chewing and sucking lice may become severe. In dairy herds, the young stock, dry cows, and bulls may escape early diagnosis and suffer more severely. Young calves may die, and pregnant cows may abort.

Transmission usually occurs by host contact. Lice dropped or pulled from the host die in a few days, but disengaged ova may continue to hatch over 2–3 wk in warm weather. Therefore, premises recently vacated by infested stock should be disinfected before being used for clean stock.


Successful louse control is a multifactorial process. Factors to address include treatment of the affected animal(s), treatment of contact animals, environmental control, and properly addressing the stressors that either permitted initial infestation or exacerbated infestation. Effective treatment results in prompt improvement of clinical signs. Specific pediculosis treatments are discussed below.

It is the practitioner’s duty to recommend a safe and effective treatment regimen. In the USA, ectoparasiticides are regulated by the Environmental Protection Agency (EPA) or the FDA Center for Veterinary Medicine. As a general rule, if a product is applied topically to an animal to treat ectoparasites, and the compound is not absorbed systemically, it likely falls under the jurisdiction of the EPA. If a product is administered parenterally, or if it is applied topically for systemic absorption, it likely falls under the jurisdiction of the FDA. This distinction is important for practitioners to recognize, because there is no legal extra-label use of products regulated by the EPA. Label directions must be followed regarding species treated, product concentration, product dosage, individuals allowed to administer application, and re-treatment interval. Because products regulated by the FDA are approved animal drugs, extra-label use may be allowed under the Animal Medicinal Drug Use and Clarification Act (AMDUCA) (see Ectoparasiticides and see Anthelmintics). The Food Animal Residue Avoidance Databank (FARAD) can be consulted for extra-label drug use recommendations and calculated meat and milk withdrawal times.

See also:  The Largest Insect Ever Existed Was a Giant Dragonfly

Treatment of individual animals may be aided by debulking the infested coat if weather and coat type permit. Clipping an infested animal’s long, heavily soiled, or matted coat can immediately reduce the parasite burden on an affected animal, allow topical products to be distributed evenly, and allow for treatment of secondary infections if present. Many compounds effectively kill adult and nymphal life stages, but few have been tested for ovicidal capabilities. Therefore, many sources recommend re-treatment at intervals of 7–10 days until the infestation has been controlled. Contact animals should also be treated to prevent spread of infestation within a herd, flock, or household. Animal equipment or bedding should be washed frequently with hot, soapy water until infestation is controlled. Finally, addressing animal overcrowding, poor feed quality, and underlying health issues are the final steps to manage pediculosis and prevent recurrence. New animals should be quarantined and inspected for infestation before herd or flock integration.

External Parasites of Pigs

An overview on mange (sarcoptic and demodectic), lice, ringworm and ticks in pigs by Dr Amanda Lee, Pig Health Coordinator for the New South Wales Department of Primary Industries in Australia.

The importance of external parasites in pig production varies greatly among regions because of differences in climate and systems used to raise pigs. Sarcoptic mange caused by Sarcoptes scabiei var suis is the most important external parasite of pigs worldwide. Other external parasites include demodectic mites, lice, fungi and ticks.

External parasites produce a range of clinical signs in pigs including rubbing, scratching, and skin lesions. Some parasites also cause significant economic effects due to reduced growth rate, reduced feed efficiency, and loss of carcass value at slaughter.

Sarcoptic Mange

Two clinical forms of the disease are recognised: a hyperkeratotic form that most commonly affects multiparous sows and a pruritic or hypersensitive form that primarily affects growing pigs. The sarcoptes mite is a small, greyish-white, circular parasite about 0.5mm in length and just visible to the naked eye when placed on a dark background.

Hyperkeratotic encrustations in the ears of multiparous sows are the main reservoir of mites within a herd.

The boar helps to maintain infection in the herd because he is constantly in direct skin contact with breeding females and he remains a chronic carrier. If pigs are housed in groups, there is increased opportunity for spread. Piglets become infested during suckling.

Environmental spread is less important but exposure for as little as 24 hours to pens that have been immediately vacated by previously infected pigs can result in infestation.

The mite dies quickly away from the pig; under most farm conditions in less than five days. This is an important factor in control. If a herd is free from mange, it is one of the easiest diseases to keep out because it can only be introduced by carrier pigs. However, once it is introduced, it tends to become permanently endemic unless control measures are taken.

Acute disease

The common signs are ear-shaking and severe rubbing of the skin against the sides of the pen. Approximately three to eight weeks after initial infection, the skin becomes sensitised to the mite protein and a severe allergy may develop with very small red pimples covering the whole of the skin.

These cause intense irritation and rubbing to the point where bleeding may occur.

Chronic disease

After the acute phase, thick encrustations develop on the ear, along the sides of the neck, the elbows, the front parts of the hocks, and along the top of the neck.

Diagnosis of sarcoptic mange is confirmed by demonstrating the presence of the mite in the herd. The best method is to use a flashlight to examine the internal surface of the ears of breeding animals for encrusted lesions. A teaspoon is an ideal instrument to scarify material from the interior of the ear. This material can be spread onto a piece of black paper and left for 10 minutes. Turn the paper upside down to remove the material. Any mange mites present will be left adhering to the paper by the suckers on their feet. Mites can be observed directly or with a magnifying glass.

Establishment and maintenance of mange-free pig populations

The establishment and maintenance of mange-free herds is facilitated by three important facts:

  • Piglets are born free of mites
  • Mites are highly host-specific and do not survive long away from their host, and
  • Modern treatments are very effective.

Mange-free herds can be established with caesarean-derived piglets, by depopulation and repopulation from mange-free stock, by segregated rearing of treated pigs or by eradication using avermectins and other products registered for the purpose.

Biosecurity measures that focus on careful scrutiny of incoming stock and sourcing stock from a minimal number of herds are usually adequate to prevent re-introduction of the parasite.


Mange control involves identification of animals with chronic mange so that they can receive systematic and regular treatment to protect the younger animals in the herd. All control programmes must target the breeding herd.

Any animals with extensive hyperkeratotic lesions in the ears and over the body should be culled and the remainder of the sows treated simultaneously or alternatively in segregated groups prior to farrowing.

Contaminated bedding should be removed and the environment sprayed with insecticide.

  • Treat all pigs regularly to prevent a build up of numbers
  • Treat boars every three months
  • Always treat animals twice, 10 to 15 days apart
  • Leave pens empty for three days after infected pigs move out and spray the pen after washing with a mange dressing, and
  • Treat pigs in the hospital pens regularly

Demodectic Mange

In contrast to sarcoptic mange, demodectic mange is relatively unimportant in pigs. The mite is Demodex phylloides and it lives in hair follicles. The response to treatment is poor but the mite is sensitive to those acaricides used for sarcoptic mange control. Severely affected animals should be culled from the herd.

Lice in pigs are readily observed and often blamed for damage due to mange because both conditions cause irritation and rubbing. Lice are relatively uncommon in herds today; herds that treat routinely to control mange effectively seldom carry significant lice populations.

The louse affecting pigs is Haematopinus suis and it has piercing and sucking mouthparts. It is greyish-brown in colour with black markings. The females are about 6mm long and the males slightly smaller.

The whole life cycle from egg to adult takes 23 to 30 days. The pig louse is host-specific and cannot survive for more than two to three days away from pigs.

Lice are found on all parts of the body, but particularly in the folds of the skin around the neck, jowl, flanks and on the inner surfaces of the legs. They often shelter inside the ears, where they are sometimes seen in ‘nests’. The method of spread is by direct contact during huddling, although clean pigs placed in a yard just vacated by lousy pigs can become infested.

See also:  Feline Reactions to Raid Flea - Room Spray, Cuteness

Heavy infestations result in anaemia in young pigs and may affect growth rate and feed efficiency.

Treatment and control

Treatment and control of lice can be readily achieved because the parasites live on the skin surface and can survive only a few days away from their host. Registered therapeutic agents may be applied to the pig in the form of sprays, pour-ons, injections, and as in-feed medications. Two doses 10 days apart will eliminate lice. All acaricides are ineffective against eggs hence the need to treat twice. Control can also be assisted by placing granules containing insecticides in the bedding.

Control and eradication strategies listed for sarcoptic mange apply equally for lice. These include special attention to the ears, treatment of the boars, multiple treatment of sows prior to farrowing, segregation of clean and untreated animals if the whole herd is not treated at one time, and treatment of all introduced animals.


Fungal diseases are an uncommon zoonosis of pigs. They tend to be superficial mycoses involving the keratinised epithelial cells and hair only and are of little economic importance. Ringworm is found in both indoor and outdoor rearing systems.

All age groups can be affected and the incidence is higher in unhygienic environments where stocking rates are high and temperatures are moderate with high humidity. Bedding may be an important source of infection. Fungal spores can remain viable for many years in a dry and cool environment.

Microsporum nanum is the most common fungal infection in pigs. Lesions can be found on almost any part of the body. Typical lesions start as circumscribed spots which tend to enlarge in a circle, some to a very large size covering the complete side of the pig. The skin is reddish to light brown in colour, roughened but not raised. Dry crusts form around the periphery, the hair is usually not lost, and no pruritus develops. Chronic infections are often seen behind the ears of adult pigs and appear as thick, brown crusts that spread over the ear and neck.

Trichophyton mentagrophytes is the most common cause of trichophytosis in pigs. The size and shape of lesions vary; some measure up to 12.5cm across and are roughly circular. Typical lesions are red or covered by a thin brownish dry crust. The disease tends to be self-limiting and lasts about 10 weeks.

Candidiasis in pigs is caused by the yeast Candida albicans and appears to cause disease when the pig’s resistance is lowered.

Diagnosis is made by examining scrapings from suspicious areas under the microscope to look for fungal spores.

Treatment consists of removal of the crusts and local application of disinfectants or antiseptics.

Control is by maintaining good sanitation. Housing can be disinfected with phenolic disinfectant (2.5 to 5.0 per cent) or sodium hypochlorite (0.25 per cent solution).


Ticks infest many species of mammals and birds and are generally not host-specific. Compared with grazing species, pigs are not commonly parasitised by ticks and ticks essentially do not occur on pigs raised in confinement.

Ticks are readily seen by gross visual examination. They can be found on any part of the body, but they are more often seen around the ears, neck and flanks. The size and appearance vary according to the degree of blood engorgement.

The treatment and control of ticks in pigs are rarely necessary. If only a few ticks are present, these can be removed manually and the pigs confined away from infested pasture. Insecticides registered for lice control are usually effective. There are no registered tick treatments for pigs.

Other Pests

Mosquitoes, although considered primarily pests of humans, also attack livestock causing discomfort and irritation. In severe cases, affected carcasses of pigs must be skinned at slaughter.

Lesions appear on several or all of the pigs in the form of raised oedematous weals on the legs and abdomen. Mosquito bites can irritate nursing sows enough to result in increased overlays. Mosquitoes are important vectors in the transmission of Japanese encephalitis virus. Mosquitoes may also act as mechanical vectors in the transmission of Eperythrozoon suis.

There are several control measures that can be implemented to decrease the number of mosquitoes. Local councils may use larvicides and in areas where there is a disease outbreak fogging may be considered as an option in order to kill the infected adult mosquito population.

At the farm level, care needs to be taken because very few products used to control biting insects are registered for use in pigs. Several products (Inca Ban Fly insecticidal spray for animals in 250-mL and 500-mL quantities; Musca Ban insecticidal spray in 125-mL, 500-mL and five-litre quantities; Value Plus fly spray in the same quantities; Flygon insecticidal and repellent spray in the same quantities and Ecovet Insect Repellent in 500-mL quantities) contain a number of repellents and insecticides and are registered for direct application to pigs.

Baits/larvicides (such as cyromazine, thiamethoxam), knockdown sprays (such as dichlorvos), and residual insecticides applied to walls and surfaces where mosquitoes/flies rest (such as maldison, diazinon, trichlorfon or dichlorvos) can be utilised for pigs housed indoors.

‘Knockdown’ products can be sprayed into the pigs’ environment with some success. Foggers, coils and vapourisers may also be considered for use around the piggery. Where possible, the breeding ground of the mosquitoes should be identified. The larvae can be destroyed by either draining water reservoirs or covering the surface with oil.

Flies are a concern in pig production for several reasons and they tend to be used as a measure of hygiene by local health authorities. Some flies annoy animals by their vicious bite, while others act as a vehicle for transmission of infectious disease.

Flies make contact with faeces, skin, and discharges of the pig. If the number of flies in the environment reaches a high enough level they can become major transmitters of disease organisms, not only within a building, but also between buildings and sometimes between pig herds. Such infections include pathogenic strains of E. coli, B. hyodysenteriae, salmonellae, streptococci and rotavirus.

Major outbreaks of greasy pig disease and coccidiosis can be maintained by very high fly populations. When sows are sick with mastitis, flies are attracted to the udder and skin surfaces in great numbers and they can be responsible for enhancing severe outbreaks.

Fly control in all piggeries must be continuous in summer months. The aim is to prevent flies from breeding and to destroy adult flies. Breeding of flies can be prevented by regular removal of dung. Insecticides are effective in the form of sprays and baits.

No comments

Добавить комментарий

Your e-mail will not be published. All fields are required.