Summary

In Canada pigs are hosts to the large (5-6mm) sucking louse Haematopinus suis. The life cycle of lice occurs entirely on the host and transmission is usually by direct contact between hosts. Life cycle stages can, however, survive for short periods in the environment, including on fomites (e.g. barn fixtures), and these can be a source of the parasites. Clinically lice cause irritation, and attempts by the host to relieve this can cause additional skin lesions. Heavy burdens of sucking lice in pigs can lead to reduced feed efficiency and possibly even clinical anemia due to blood loss. There are several products approved in Canada for louse treatment in pigs. Lice are relatively host specific and so zoonotic transmission is unlikely.

Taxonomy

Phyllum: Arthropoda
Subphyllum: Uniramia
Class: Hexapoda
Order: Anoplura  

Within the Class Hexapoda, other orders containing parasites of importance in veterinary medicine are the Hemiptera (bugs), Siphonoptera (fleas), and Dipetera (flies). The Order Mallophaga contains all chewing lice, and the Order Anoplura contains all sucking lice. Mammals can be infested with both types of lice, but birds have only chewing lice. Lice are relatively host-specific.
In Canada, the only louse infesting domestic pigs is Haematopinus suis.

Morphology

Larval and adult lice are dorso-ventrally flattened and have six legs arising from the thorax.  The legs terminate in claws.  Adult H. suis are up to approximately 5-6 mm in length.

In common with other sucking lice, the head of H. suis is narrower than the thorax, is pointed anteriorly, and has two prominent, segmented antennae, one on each side.

The eggs (nits) of H. suis are whitish in colour, measure up to approximately 750 µm by 300 µm, and are fixed to the hairs.  Louse eggs are readily visible to the naked eye, particularly if present in large numbers.

Morphology: Haematopinus suis

Host range and geographic distribution

Haematopinus suis is the only louse found on domestic pigs throughout the world. 

Life cycle - direct

For H. suis, like other lice, the entire life cycle occurs on the host.  Lice probably cannot survive off the host for more than a few days.  Adult females lay eggs (nits) attached to hairs.  A larval stage develops in each egg, which hatches.  There are three larval stages before the adult.  All the larval stages and the adults feed on blood.  The life cycle is completed in a few weeks.  

Life Cycle: Haematopinus suis

Epidemiology

Infestation with lice is more common in pigs than is clinical disease, meaning that there are asymptomatic carriers.  Transmission of lice is usually direct pig-to-pig contact. An infested pig in a herd usually means that many other animals in the group are infested.

Pathology and clinical signs

Lice prefer parts of the body where the skin is delicate such as behind the ears, the throat, inside of the thighs, and under skin folds.

Clinically, attempts by the pigs to relieve the irritation by rubbing and biting leads to hair loss and damage to the skin. The constant efforts at relief may interfere with feeding and result in reduced growth rates.  The blood loss associated with sucking lice may, in heavy infestations, cause a clinically apparent anemia.

Diagnosis

Recovery of adult lice (which can easily be identified to species) or eggs is the best method.  

Treatment and control

Treatment and Control

There are several products approved in Canada for louse treatment in pigs.  Treatments need to be repeated, ideally three times at 10-day intervals, because the lice eggs, but not the hatched larvae, are resistant to the treatments.

Drug(s)	Product(s)
Carbaryl	DUSTING POWDER, SEVIN
Doramectin	DECTOMAX
Ivermectin	VARIOUS

Additional information is on the products mentioned is available from the Compendium of Veterinary Products (Twelfth Edition, 2011), or from the manufacturers.     
           
     

Public health significance

Lice of pigs are host-specific and are not known to be zoonotic, although pig lice may occasionally be found on people.

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