The hog lice (Haematopinus suis) is the largest lice species (4 to 6 mm) that infests livestock. It is specific of domestic and wild pigs and occurs worldwide. Its prevalence in a given operation depends mainly on its hygienic and management conditions.
Being rather large, hog lice can be seen by the naked eye, as well as masses of eggs (nits) that look like a yellow crust.
Hog lice are not contagious for cattle, sheep, poultry or livestock other than pigs, nor for pets or humans.
Lice infestations are called pediculosis, and in the case of Haematopinus also haematopinosis.
Biology and life cycle of lice on pigs
Hog lice are small wingless, bloodsucking (hematophagous) insects that live on the surface of their hosts. They are obligate parasites, i.e., they cannot complete their life cycle off the host.
As all lice species hog lice undergo an incomplete metamorphosis and spend all their live on the host. Off a host they will not survive more than a few days.
Adult females lay eggs (nits), which they glue one by one to single hairs of the host, close to the skin. The eggs hatch 5 to 20 days later. Nymphs are bloodsucking as well, and they moult three times before reaching the adult stage in about 2 weeks.
The complete life cycle lasts about 30 days. Six to 12 generations can follow within a year!. Since domestic pigs remain mostly indoors and lice are always on the host at almost constant temperature and humidity, climatic or other environmental conditions have a rather small effect on their life cycle. Nevertheless hog lice tend to be more abundant in the cold season, probably because it favors overcrowding.
Preferential sites of hog lice are the skin folds around the neck and the dewlap, in and around the ears, the legs and the flanks where they can congregate in large masses. Transmission from one animal to another one is mostly by contact, typically from sows to the suckling pigs immediately after birth, or from boars to the sows.
Click here to learn more about the general biology of insects.
Damage, harm and economic importance of lice on pigs
Both male and female hog lice suck blood, up to four times a day, each time during about 10 minutes. Lice bites are very irritant for pigs. Infected animals are restless and scratch and rub continuously against objects around them.
When entering a pig house, it is often enough to listen to the noise that animals produce through rubbing to conclude that they have lice (or mange) problems. Intense rubbing can cause hair loss and skin wounds, which are susceptible of becoming infected with secondary bacteria.
In fact, little is known about the real economic impact of lice on pigs, e.g. regarding the economic threshold level. As already mentioned, damage as well as prevalence may vary from place to place. Nevertheless, there are indications that the stress caused by severe infestations reduces weight increase and makes the animals more susceptible to other diseases.
Hog lice are involved in the transmission of several infectious diseases such as swinepox and swine cholera.
Prevention and control of lice on pigs
Best lice prevention is keeping the animals healthy, well fed and in good hygienic conditions, because healthy pigs are less prone to become infested.
Infested animals can be treated with various parasiticides. It is very important to treat the whole pig population simultaneously, even if symptoms are detected only in a few animals. Treatment must be repeated 2 to 3 weeks later. This is required because lice eggs are not affected by whatever treatment: they have to hatch to become susceptible to treatments. To avoid introducing lice into a clean operation all incoming animals must be treated before they come in contact with the clean ones.
For spraying or dipping the animals there are numerous concentrates containing contact insecticides such as organophosphates, pyrethroids or amitraz. It is very important that treatment reaches the inner part of the ears and covers the whole body surface, which requires to use at least about 1 liter dilution per animal. There are also insecticidal dusts that can be used directly on the animals, but they are less affective than the liquids. There are also pour-ons (=backliners) mainly with amitraz, phosmet or phoxim that are effective against pig lice.
Nowadays macrocyclic lactones such as ivermectin or doramectin are widely used against lice on pigs. They are available as injectables or as feed additives. Macrocyclic lactones are highly effective and more convenient than sprays or dips, but also more expensive. For lice eradication repeating the treatment is highly recommended.
Research on the use of entomopathogenic fungi (Metarhizium anisopliae) for the biological control of lice has shown promising results. However, there are still no such commercial products in the market. Learn more about biological control of insects.
For the time being there are no vaccines that will protect pig by making them immune to lice. There are no repellents, natural or synthetic that will keep lice away from pigs. And there are no traps for catching pig lice, for the simple reason that they spend their whole life on the animals and therefore there are no stages in the environment searching or waiting for a host.
Click here if you are interested in medicinal plants for controlling lice and other external parasites of livestock and pets.
|If available, follow more specific national or regional recommendations or regulations for hog lice control.|
Resistance of pig lice to parasiticides
So far there are no reports on confirmed hog lice resistance to lousicides.
This means that if a particular product has not achieved the expected control, it is most likely because the product is not adequate or it was not used correctly, not because hog lice have become resistant.