Equine piroplasmosis (EP)

Equine piroplasmosis (EP)

Equine piroplasmosis (EP) is a disease found in equine species such as horses and donkeys. The disease is caused by parasites (Babesia caballi and Theileria equi) found in the blood cells. Ticks feed on the blood of an infected animal and then become vectors of the disease. It can make horses very ill, but most infected horses will become carriers without actually displaying any symptoms of the disease.

Equine piroplasmosis not only affects the health and wellbeing of infected equine animals, but also causes economic damage to the horse sector around the world. Wageningen Bioveterinary Research (WBVR) tests horses (before export, for example) in order to combat and limit the spread of the disease.

Which animals are affected by the disease?

WBVR focuses on equine piroplasmosis in horses. Piroplasmosis (also known as babesiosis, theileriosis, tick fever or tick disease) also occurs in other animals such as dogs and cattle.

Equine piroplasmosis in horses is not a zoonosis and therefore cannot be transmitted to humans.

What causes equine piroplasmosis?

The disease is caused by two single-celled parasites (protozoa): Babesia caballi and Theileria equi (previously known as Babesia equi). These two parasites can trigger symptoms of equine piroplasmosis either independently of each other or at the same time (co-infection).

How do the parasites spread?

  • The parasites inhabit the blood cells of equine species. Ticks act as vectors. They feed on the blood of an infected animal, and then carry the parasite to other animals.
  • Transmission can also occur through the use of infected needles or blood transfusions using blood sourced from infected horses.

Neither of the parasites can survive independently of a host. For B. caballi, infected equine animals and ticks are both considered hosts. For T. equi, only the infected equine animals serve as hosts.

Can all ticks transmit the disease?

Several hard-bodied ticks of the Ixodes genus have been identified as vectors. Out of these, two species – Dermacentor and Hyalomma (known as the giant tick) – are found in the Netherlands.

What are the symptoms?

Equine piroplasmosis can occur in different forms. While the symptoms vary for each form, most symptoms can be attributed to hemolysis (destruction of blood cells) by the parasites, and to the anaemia that results from this. Horses usually don’t display symptoms when they get infected. Any symptoms that do arise will become evident after 1 to 3 weeks. Foals infected while still in the womb can show symptoms within a few days.

Acute form of equine piroplasmosis

The acute form of equine piroplasmosis manifests itself initially as a high temperature, lack of appetite, weight loss and oedema in the legs. Later, the effects of hemolysis and anaemia will become noticeable in the form of yellow or pale mucous membranes (jaundice), increased breathing rate and heartbeat, and brown or red urine. Blood spots can also appear on the mucous membranes, as a result of clotting problems.

Serious infections can also lead to problems with lung, heart, liver, kidney and gastro-intestinal tract function. The peracute form occurs in naïve animals, who have never been infected before, and is usually fatal after a very brief symptomatic phase.

Chronic form of piroplasmosis

The chronic form is often characterised by vague symptoms such as weight loss, a loss of appetite, and reduced performance.

Asymptomatic carriers pose a risk

Most horses infected with equine piroplasmosis do not develop symptoms. These horses are then considered carriers of the parasite(s). They pose a risk for the introduction of the disease into naïve populations. The animals appear to be healthy, but can still pass the parasites on to a tick.

Mares that are carriers can miscarry or pass the infection on to their foal.

Weight loss in horses can be a sign of piroplasmosis
Weight loss in horses can be a sign of piroplasmosis

Where is equine piroplasmosis found?

The B. caballi and T. equi parasites are both found all over the world. Because they are transmitted by specific ticks, their spread occurs in areas where those ticks are endemic. Equine piroplasmosis is considered endemic to Asia, South and Central America, Africa, southern Europe and certain parts of the southern United States.

Expansion of the ticks’ habitats and the international trade of horses are both risk factors for the introduction and spread of the disease. Only a handful of countries, including Norway, have never recorded the disease.

Is the disease found in the Netherlands?

Over the past decade several countries, including the Netherlands, have reported the presence of one or both of the parasites for the first time. In 2010 both B.caballi and T. equi were found in the Netherlands in horses that had never been abroad. This was confirmation of the first indigenous cases of equine piroplasmosis. No further cases have been reported in horses in the Netherlands since then. This means the Netherlands is currently considered to be free of the disease.

Is this a notifiable disease in the Netherlands?

Equine piroplasmosis is not a notifiable disease in the Netherlands. However, positive cases and outbreaks are reported to the World Organisation for Animal Health (OIE).

The range of the Dermacentor reticulatus tick is known to be increasing within the Netherlands. The Hyalomma, or giant tick, has also been seen several times in the Netherlands. Given that these vectors are present in the Netherlands and that the Dutch horse sector operates internationally, it’s important to keep a close eye on the status of equine piroplasmosis in the Netherlands.

Is there a vaccine?

No commercial vaccine is available.

How do you combat equine piroplasmosis?

Treatment is not always successful, and with T. equi in particular the treatment rarely eliminates the parasite. Screening horses before export to detect antibodies is one of the most important ways of preventing the spread of the disease.

Diagnostics: how does WBVR identify the parasites?

Wageningen Bioveterinary Research (WBVR) offers a variety of ways of testing horses for the presence of antibodies to B. caballi and T. equi in the blood, both for export and for screening and research purposes.

Serological tests include the IFT/IFAT (indirect fluorescent antibody test), the ELISA (enzyme-linked immunosorbent assay) and CBR/CFT (complement fixation test).