Lice infestation

Also known as pediculosis and nits, lice infestation is a parasitic skin disease in horses. Biting and sucking lice can infest a variety of hosts, including cats, dogs, horses and people. Lice are host-specific, for example dog lice only affect dogs, and horse lice only affect horses! This means that humans can’t be infested with lice from animals.

Two species of lice can infect horses:

  • Damalinia (werneckiella or bovicolaequi – a biting louse that attaches to the host’s hair and eats skin debris and secretions.
  • Haematopinus asini – a blood-sucking louse that attaches to the host’s hair and uses its mouthparts to pierce the skin and drink blood.

An adult louse attaches itself to the host and feed, and reproduction occurs. The female lays eggs (‘nits’) that stay on the hair until they hatch. When fully developed adult lice emerge to continue the cycle. The entire life-cycle takes about 3-5 weeks to complete.

Signs of infestation can vary in severity, and may be limited to skin problems. You may notice the following signs in your horse:

  • Scratching, rubbing, biting
  • Stress caused by irritation
  • Hair loss
  • Skin wounds and raw areas caused by self-trauma
  • Rough coat
  • Weight loss
  • Poor bodily condition

Horses that are heavily infested with blood-sucking lice can become anaemic due to the amount of blood the lice drink.

Infestation is usually caused from being in contact with other infected horses, but there are other ways your horse could be infected. Infestation can occur as follows:

  • Horses in overcrowded environments where direct contact is inevitable.
  • Transmission via fomites, eg objects such as shared combs, brushes, blankets or tack.
  • Lice can be transmitted via surfaces such as stalls or fences if a horse has been rubbing against such an area, however this is rare.
  • Horses that travel may be exposed to infested horses or areas.
  • Sick, old or debilitated horses are also more likely to become infested.
  • Infestation is common in long haired horses which gives lice a place to hide, allowing them to go undetected.

Diagnosis is usually possible by a quick examination by your vet. Lice can be seen by looking closely at the skin and hair with a magnifying glass. Lice can be found anywhere on the body, but sucking lice are usually found on the mane, tail and fetlocks, and biting lice are mainly found on the back. In severe cases, lice can be found anywhere on the body. Your vet may also find nits attached on the hairs of your horse.

Yes! There are many products that can safely and effectively treat lice infestations in horses; options include sprays, shampoos, powders and wipes. It is important to ask your vet about the best choice for your horse, and you should only use products that are approved for use in horses using the manufacturer’s recommended usage guidelines to avoid skin irritation and other adverse effects.
You must also thoroughly clean your horse’s stable, rugs, brushes/combs, tack, etc. and any other fomites (objects capable of carrying infectious organisms) that your horse has been in contact with.
If you horse has acquired a severe infestation, become anaemic or debilitated, it may need hospitalisation for initial intensive care, however this is a rare occurence.

Regular use of products that control lice infestations can help prevent your horse from becoming infected if exposure occurs. New horses arriving at a yard should be examined thoroughly before being introduced into the herd; a period of quarantine may be advised.
Your vet may recommend treating all horses on a yard even if only one horse is infected because lice are easily transmitted from horse to horse. In the meantime, the affected horse should be separated from other horses until the infestation has been resolved.
Luckily, lice are host-specific, so you are not at risk of infestation. However, anyone handling an infested horse should take appropriate precautions to avoid transmitting lice from one horse to another.