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  • Lawsonia intracellularis infection in horses

Lawsonia intracellularis is a species of bacteria. It can infect a range of animal species but in horses it can cause problems in foals and weanlings.

The strain of the bacteria that infects weanlings can also be found in wildlife. These birds and rodents are an important reservoir for infection on horse farms. In all species the infection establishes itself in the intestinal tract, inside the cells of the intestine, as the name states, intracellularis, and it spreads from animal to animal via the ingestion of infected faecal matter. Infection with Lawsonia or Equine Proliferative Enteropathy occurs when the foal ingests the organism and it enters the small intestine where it causes thickening of the intestinal wall. This causes the foal to be less able to absorb nutrients. The damage to the intestinal wall results in protein loss as well.


Foals can become depressed and reluctant to eat. They can have a fever, develop diarrhoea and colic. Because of the protein loss the foal can also develop swollen limbs and/or face. The disease is mostly seen from August to late February and the incubation period is 2 to 3 weeks. Healthy foals will often be able to fight off the infection without any assistance. It is usually the weaker foals that become ill or a period of stress such as being weaned or transported tip the scales and cause the foal to develop clinical signs.


When a foal is severely ill the clinical signs and the low level of protein in the foal’s blood will often be enough to rouse suspicion of Lawsonia infection. An ultrasound examination will provide further evidence when showing thickened small intestines. Faeces can be tested for the presence of bacterial DNA. This test is known as a PCR test and is very helpful in confirming the infection in sick foals. Another test that can be performed is based on the identification of antibodies (proteins made by the infected animal’s immune system as it tries to fight off the infection) against Lawsonia in a blood sample.


Foals can be treated with antibiotics. Some severely ill foals will need intensive care to receive fluids and extra support when their protein levels are low. An infection with Lawsonia can dramatically affect the weanlings growth preventing them reaching their predicted height.


Thought should be given to where the infection could have come from and if there are rodents or birds that could have introduced the bacteria. Ideally the foals would be kept away from these possible sources and a foal with an infection should be kept away from the rest of the young stock. There is a vaccine that could possibly help to reduce the prevalence of the Lawsonia but this is for now still an unlicensed product.