05: Equine Protozoa

Common equine protozoal disease

Equine protozoal myeloencephalitis

Reportable equine protzoal disease

Equine piroplasmosis

Protozoal phylum that infects horses (at least that we talked about)

Apicomplexa

General Apicomplexa protozoal characteristics

• Unicellular

• Undulating locomotion

• Sexual and asexual reproduction

• Apical complex at anterior end helps them invade

Suffix for different parts of the apicomplexan life cycle

-zoite

Life stages of an Apicomplexan

• Merozoite

• Gametozoite

• Sporozoite

Apicomplexan life stage that is infectious

Sporozoite

Apicomplexan life stage that is asexually reproducing

Merozoite

Apicomplexan life stage that is sexually reproducing

Gametozoite

Apicomplexan process of going from sporozoite to merozoite

Sporulation and sporogony

Apicomplexan asexual reproduction

Merogony

Apicomplexan gametogenesis

Gamogony

Process of gametozoites forming a zygote → oocyst

Fusion

Where does sporogony have to happen

Definitive host

Apicomplexan definitive hosts

Possums and ticks

System affected by EPM

Nervous system

Etiologic agents of EPM

Sarcocystis neurona and occasionally Neospora hughesi

Global distribution of EPM

Western hemisphere

Why is EPM only in the western hemisphere

Only have possums in the Americas

Life cycle type of Sarcocystis neurona

Indirect life cycle

Intermediate hosts of Sarcocystis neurona

Cats, wildlife, otters

What type of host is the horse for Sarcocystis neurona

Accidental/dead end host

Where does Sarcocystis neurona live in the definitive host

Intestines

Where does Sarcocystis neurona set up shop in the horse

White and gray matter of spinal associated CNS

Demographic for EPM

Younger horses (1-5 years)

T/F: Sarcocystis neurona typically causes clinical signs

False, many horses test positive but few show clinical disease

Where does Sarcocystis neurona finish development in a normal intermediate host

Muscle tissue

Life stage of Sarcocystis neurona preset in the tissue of an intermediate host

Sarcocyst

Life stage of Sarcocystis neurona present in the tissue of an aberrant host

Merozoites (schizonts)

Routes of Sarcocystis neurona infection for the horse

Ingestion or vertical transmission

Length of time it takes for sporocysts from DH to become infectious to IH/AH

Immediately

Clinical signs associated with EPM

• Asymmetrical peripheral neuropathy: weakness, abnormal gait, paresis, atrophy

• Occasionally brain: cranial nerve deficits (dysphagia, head tilt, muzzle deviation)

Diagnostic for Sarcocystis neurona in the DH

Fecal

Diagnostic for Sarcocystis neurona in the IH

Sarcocysts in muscle, schizonts in endothelium

Diagnostics for Sarcocystis neurona in horses (AH)

• Diagnosis of exclusion: CS, hx, rule-outs

• Paired CSF and Serum Ab titers

What results constitute a positive EPM diagnosis in a horse

CSF Ab titers that are significantly higher than the serum titers

Parasiticide of choice for Sarcocystis neurona

Ponazuril

Considerations when treating a horse with ponazuril

Protozoa are dying in the sensitive nervous system, likely want steroids on board

EPM prognosis

Most improve, very few fully recover

Prevention and control of EPM

• Keep possums out of feed and feed bin

• Keep the barn clean

• Break any natural life cycles you can; control peri-domestic wildlife

Etiologic agent for equine piroplasmosis

Babesia caballi and Theileria equi

DH of Babesia caballi and Theileria equi

Tick

What role i the Babesia caballi and Theileria equi life cycle does the horse play

IH

Routes of Babesia caballi and Theileria equi infection for the horse

• Ticks

• Dirty, blood-contaminated equipment

Which EP agent can be transmitted vertically in ticks

Babesia Caballi

Why is EP reportable

Because it is bad and it is mostly not in the US

Life stage of Babesia caballi and Theileria equi that is identifiable in the horse

Merozoites

How are Babesia caballi and Theileria equi identified

As piroplasms in RBCs

What happens if you see, or think you see, a piroplasm on a blood smear

Call the state vet!!!!

Life stage of Babesia caballi and Theileria equi that is injected into the horse by the tick

Sporozoite

Life stage of Babesia caballi and Theileria equi that is picked up by the tick

Merozoite

EP etiologic agent that goes through lymphocytes before ending up in RBCs

Theileria equi

Cause of EP clinical signs

Merozoites asexually reproducing and destroying RBCs

Which EP agent is more damaging

Theileria equi (the smaller piroplasms are more damaging)

Clinical signs associated with Babesia caballi and Theileria equi

• Can be subclinical

• Anemia → icterus

• Fever

• Poor performance

• Hypoxemia → colic, constipation, abortion

Diagnostics for Babesia caballi and Theileria equi

• Blood smear

• PCR

• Ab testing

When is Ab testing useful for Babesia caballi and Theileria equi

When looking for carriers with low numbers of protozoa

Options for a horse with confirmed EP

State vet gets to decide

• Export

• Cull

• New treatment program

Parasiticide of choice for Babesia caballi and Theileria equi

Imidocarb

Prevention considerations for EP

• Follow importation guidelines and testing

• Tick control (hard in horses)

• Clean your equipment

EP prognosis

Imidocarb has a decent success rate, but it’s not guaranteed and it’s a long and expensive road