The pig louse Haematopinus suis is a large, yellowish-brown louse (5 mm) which moves about amongst hairs on the pig's skin and may be seen most readily on white pigs. It occurs only on the pig and is most common on the folds of skin of the neck or around the base of the ears, inside the ears, on the insides of the legs and on the flanks. Eggs are laid on the bristle and appear as a yellow crust in heavily infected areas and are particularly obvious in black pigs. The eggs hatch into nymphs in 12-20 days.
Causes of Lice
The pig louse Haematopinus suis is a large, yellowish-brown louse (5 mm) which moves about amongst hairs on the pig's skin and may be seen most readily on white pigs. It occurs only on the pig and is most common on the folds of skin of the neck or around the base of the ears, inside the ears, on the insides of the legs and on the flanks.
Eggs are laid on the bristles and appear as a yellow crust in heavily infected areas and are particularly obvious in black pigs. The eggs hatch into nymphs in 12-20 days. Following two further nymph stages, the life cycle is completed in 29-33 days. The lice can only live away from the host for 2-3 days.
In severe infestations, the constant irritation and itching results in scratching and rubbing against gates and rails and leads to damage to the skin. Localized ulceration is found inside the pinna of the ears where lice congregate to feed. Large numbers of lice may cause restlessness and a reduced growth rate.
The pig louse may act as a vector for the swine pox virus and Mycoplasma haemosuis, and has been found to transfer infection by Borellia burgdorferi.
Effects of Lice
Pigs with louse infestations may be seen to rub or scratch constantly. The rubbing may be sufficiently severe to cause long scratches on the flanks and the bristles on the flank are often broken or rubbed smooth. Infested pigs may lose condition.
The lice may be seen scuttling about on the skin of white pigs but are less obvious on dark-skinned pigs. On these the pale egg cases may be the most obvious feature and may be found attached to hairs on and behind the ear and on the neck.
When the ears are examined closely, small ring-shaped areas may be seen inside the pinna (ear flap). Groups of lice may be seen feeding at these and larvae and nymphs may also be present. In bright sunlight the lice tend to spread out over the body and may be found near the feet or inside the ears.
Diagnosis of Lice
Louse infestation is suggested by the presence of scratches on the flanks of sows in poor condition. The hair shafts are broken. Confirmation is by finding the lice. Lice may be seen as brown spots moving across the skin and may be seen within the ears.
Egg cases can be found most easily on hairs behind the ears or on the ears, but finding them does not confirm that presence of louse infestation as they may be empty and remain from a period prior to successful treatment. If lice cannot be found easily, examine the feet and inside the ears, as they may be hiding on the extremities. Re-examination at a different time of day may yield results.
Treatment & Control of Lice
Treatment has been carried out using a wide variety of insecticides, but those most commonly used at present are ivermectin, doramectin, and, where available, amitraz and phosmet.
- Ivermectin can be given by subcutaneous injection and orally.
- Doramectin, amitraz spray and phosmet pour-on can be used to eliminate lice from affected animals.
Control can be carried out by the routine treatment of all sows entering farrowing accommodation, boars every 4 weeks and weaners and growers at weaning and during the finishing period together with mange program.
Eradication is relatively straightforward and is the preferred option. A whole herd treatment by injection or in feed (ivermectin) should be followed by a second course 18-21 days later.
Breeding stock from infected herds should be treated on entry to isolation, treated 18-21 days later, then brought into the herd 7 days after the second treatment. Similar programmes can be carried out using the other agents.
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