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Proliferative enteropathy

ISSN 2398-2977


Proliferative enteropathy

Proliferative enteropathy is a bacterial infection in young horses caused by Lawsonia intracellularis. This condition can cause a range of clinical signs including ill thrift, lethargy, rough coat appearance, fever, weight loss, colic, diarrhoea and a common feature is swelling with fluid (oedema) of the lower limbs and beneath the abdomen.

A blood test can help diagnose proliferative enteropathy ©Chris Whitton

What is Lawsonia intracellularis?

Lawsonia intracellularis is a bacteria that infects young horse causing an intestinal disease known as equine proliferative enteropathy (EPE). 'Lawsonia' as the disease is commonly known, was historically considered a disease of pigs and has been associated with vast economic losses throughout the commercial pig industry. However, many species can be infected and its importance as an emerging disease in horses is now being recognized. Following infection the bacteria enter the cells of the small intestinal and cause them to proliferate. This results in 'hyperplasia' or thickening of the intestinal wall (intestinal hyperplasia) which leads to malabsorption and loss of proteins.

How common is this disease?

Over recent years reports of sporadic cases and outbreaks have been increasing and Lawsonia is now considered to be endemic on many horse farms. The disease is widespread with reports of occurence almost worldwide. Lawsonia has a seasonal occurrence and in the UK and Ireland is most frequently reported between August and late February. However recent reports have shown that this time frame varies by years and geographic region.

Where does the bacteria come from?

Transmission of disease is thought to occur through the ingestion of infected fecal material from wild or domestic animals. Exposure to pigs is not commonly reported in equine infections and studies have demonstrated the bacterial strains that infect foals vary from those that cause disease in pigs. However, the bacterial strain found in foals has been detected in numerous other species. In fact Lawsonia appears to be widespread among rodents, wildlife and birds and it is likely that they play an important role in the spread of disease, however the exact source of infection in horses remains to be determined.

Which horses are most at risk?

Young horses are most at risk of disease, with those between 4 and 9 months of age particularly susceptible. In piglets, multiple stress factors (such as weaning and mixing of groups) have been associated with clinical disease, and it is likely that similar risk factors play a role in the development of disease in young horses.

What are the signs of Lawsonia intracellularis infection?

Lawsonia intracellularis can cause a spectrum of clinical signs in foals, ranging from very mild through to severe. Reported signs include ill thrift, lethargy, rough coat appearance, fever, weight loss, colic, diarrhea and common feature is oedema (swelling) of the lower limbs and beneath the abdomen. Within a group it is the weaker foals that typically develop the most obvious signs of disease. However, these foals tend to be the tip of the iceberg and many other within the group are likely to be infected without developing over clinical disease.

How is infection diagnosed?

The presence of characteristic clinical signs in a young horse, combined with the detection of low protein on blood evaluation, and thickening of the small intestine detected on ultrasound examination are highly suggestive of Lawsonia infection. However, these signs alone are not always conclusive and diagnostic testing is used to confirm the diagnosis. There are two main laboratory tests used for the investigation of Lawsonia. The first involves the testing of faeces for the presence of bacterial genetic material or DNA (PCR testing). This is helpful for confirming active disease in sick foals. However, because the foal may no longer be shedding bacteria by the time of illness and testing, false negative results can occur. The second test is a blood test based on the identification of antibodies. The identification of antibodies simply tells you that the foal has been exposed to the bacteria but cannot differentiate active disease. Furthermore, it takes time for the foal's immune system to produce these antibodies and as a result it is possible for an infected foal to have a negative rest result in the early stages of infection. Although both of these tests have their limitations, they each play an important role in the diagnosis of Lawsonia infection and will often be used together.

Can it be treated?

In most cases foals with Lawsonia infection can be successfully treated with antibiotics and supportive care. Because the bacteria invade the cells of the intestine, antibiotic selection is important. The drug selected must be able to achieve therapeutic concentrations within the intestinal cells. The more severely affected foals will require intensive care and in particular, intravenous fluid therapy designed to manage the low protein concentrations.

What is the likelihood of recovery?

The overall prognosis for foals affected by Lawsonia intracellularis is good, with survival rates of up to 93% being reported. However, a worse outcome is predicted in those with complications or the more severe form of disease. When looking at the long-term outlook, research performed in Kentucky showed that there were no negative effects on race performance in horses that had been successfully treated for Lawsonia earlier in life.

Can the disease be prevented?

Although the role of wildlife and birds in the spread of infection is not fully understood, it would seem sensible to reduce exposure through the use of good pest control and biosecurity. Similarly, isolation of clinically affected foals is likely to help reduce environmental contamination. Vaccination is a commonly used strategy in the control of the pig form of the disease. The same vaccine has been tested in foals and has been used within the UK and Ireland for several years with encouraging results. Additional strategies such as minimizing stress and controlling heavy worm burdens may also help by reducing susceptibility to disease.