Diclazuril is a member of the triazine class of antiprotozoals. In the U.S., it is FDA-approved for the treatment of equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona and as a coccidiostat in broiler chickens. Diclazuril prevents S. neurona infection in foals living in high exposure areas. In the UK, oral diclazuril suspension is approved for the treatment and prevention of coccidial infections in lambs caused, in particular, by the more pathogenic Eimeria spp, E crandallis and E ovinoidalis and as an aid in the control of coccidiosis in calves caused by E bovis and E zuernii.1

Background

In the 1960’s and 1970s, a clinical syndrome referred to as “segmental myelitis” was first described based on a studies involving groups of horses in the eastern United States.2 Protozoa were first reported in lesions from horses by researchers in 1974. The syndrome was well-described, but the parasite involved was misidentified as Toxoplasma gondii; later, it became clear due to the illustrations taken from studies that the protozoan causing EPM was in fact Sarcocystis neurona.3 One researcher called the syndrome“equine protozoan encephalomyelitis,”4 which was later standardized to equine protozoal myeloencephalitis, or EPM. 

Description and Symptoms

EPM is an extremely debilitating disease that is ubiquitous on horse farms and facilities in the Americas, although only a small percentage of horses that are exposed to the S. neurona organism will develop clinical disease. The S. neurona organism infects horses when they ingest the organism in contaminated feed or water. The definitive host of this organism is the opossum, which passes the organism in its feces.2 EPM presents with a variety of neurologic signs, depending on the infection. Signs can have a subtle, gradual onset, or be acute and severe. 

Most commonly, horses with EPM present with asymmetric hindlimb paresis (weakness) and muscle atrophy. Rarely, the first signs may be related to a cranial nerve deficit (blindness, facial nerve deficits) or a focal brain lesion (depression, seizures). Without treatment, EPM will progress to severe paresis (weakness) and possibly recumbency (an inability to rise).3 

Diclazuril Treatment for EPM

With diclazuril treatment, approximately half of infected horses will stabilize in their current state.2 The following treatment regimen is recommended for the treatment/prevention of EPM in the horse (adapted from Plumb’s Veterinary Drugs):

• Treatment of equine protozoal myeloencephalitis (FDA-approved): Top dress feed at the rate of 1 mg/kg/day for 28 days. 

• Prevention of equine protozoal myeloencephalitis in foals: Top dress feed at daily ration of 0.5 mg/kg, beginning at 4 weeks of age.

Vitamin E supplementation is also frequently recommended due to its antioxidant properties. Horses with severe, acute neurologic deficits may also be treated initially with flunixin, phenylbutazone, or DMSO.1

Where to buy Diclazuril

Diclazuril is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. DICLAZURIL 8.3% from NexGen Pharmaceuticals is indicated for the prevention and treatment of equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona in the horse.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

1Plumb’s Veterinary Drugs.

2Rooney, J.R., Prickett, M.E., Delaney, F.M., Crowe, F.W., 1970. Focal myelitis–encephalitis in horses. CornellVet. 50, 494–501.

3Dubey, J.P. , et. al. A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM) Veterinary Parasitology 95 (2001) 89–131.

4Mayhew, I.G., de Lahunta, A., Whitlock, R.H., Pollock, R.V.H., 1976. Equine protozoal myeloencephalitis. In:Proceedings of the 22nd Annual Convention of the American Association of Equine Practitioners, Dallas, TX, November–December, pp. 107–114.