Viral Diseases of Horses

Why is understanding viruses of horses so important?t

• human health and welfare: directly and economically

• animal health and welfare: directly since animals are getting sick and dying, economically via global trade and travel, and bioterrorism

Climate change allows for what?

• niches for vectors and hosts

• different breeds or strains of animal

Define zoonoses.

Infectious agent that can jump from an animal to infect a human

Which equine viruses that we discussed are zoonotic?

• rabies

• west nile virus (and japanese encephalitis)

• hendra virus

• vesicular stomatitis

• EEE, WEE, VEE

Which virus is described:

• uncommon cause of neurological disease in horses

• a large, cylindrical, Rhabdovirus

• an enveloped RNA virus

• Genus: lyssavirus

Rabies

How is rabies virus transmitted?

• saliva entering contaminated wounds

• aerosol droplets

• oral

• transplacental (cattle natural, mice and rats experimental)

How does rabies virus reach the CNS?

via retrograde axonal transport to brain and spinal cord

What causes the clinical signs of rabies virus?

caused by vascular damage, hemorrhage, thrombosis, edema, inflammation, neuronal and glial cell degeneration and dysfunction, apoptosis and necrosis

What is the tropism for rabies virus?

CNS

What is needed for any febrile/neurological horse exam?

PPE

What are the clinical signs of rabies virus?

• lameness to sudden death

• colic, hyperesthesia, ataxia, behavior changes

• paralysis or paresis

• encephalopathy

What are the reservoir hosts of rabies virus?

• animals that live on forest edges or habitats that border horse facilities like skunks, raccoons, and red fox

How do we diagnose rabies virus?

• fluorescent antibody on tactile hair of the face is unreliable

• necropsy diagnose aligning with history of inadequate vaccination (rule everything else out first)

Which virus is described:

• arbovirus with worldwide distribution

• typically transmitted between birds and mosquitoes

• horses are a dead end host

West Nile Virus

West Nile Virus has a predilection for what type of tissue?

nervous tissue

What are the clinical signs for West Nile virus?

• ataxia and weakness of all limbs

• asymmetric signs are often noted

• muscle fasciculations and tremors

• ascending paresis to paralysis

• depressed mental state

• behavioral changes and depression uncommon

The asymmetric signs noted for West Nile Virus, makes what a rule out?

EPM

How do we diagnose West Nile Virus?

IgM capture ELISA (test choice for recent exposure)

IgM used for ELISA testing usually declines by how many days post onset of clinical signs for West Nile virus?

by 30 days

Will West Nile Virus vaccination interfere with testing for diagnosis of disease?

Yes

How do we prevent West Nile virus?

control of mosquitoes via repellants, adulticides/larviides, and eliminating breeding sites

Which virus is described:

• zoonotic

• highly fatal

• BSL4

• epitheliotropic

• respiratory disease

• pyrexia

• vaccine available

Hendra Virus

Which virus is described:

• looks like FMDV (FAD)

• off feed (not milking)

• causes flu like symptoms in humans

vesicular stomatitis

The virus enters the body via what route for VEE?

olfactory route

The virus infects what cells for WEE and EEE?

endothelial cells

What is the incubation period for EEE, WEE, and VEE?

3-15 days

Where do EEE, WEE, and VEE replicate?

in macrophages

In the CNS, the equine Encephalitides (EEE, WEE, VEE) invade what?

grray matter of the cerebrum, thalamus, hypothalamus

What are the clinical signs of encephalomyelitis (EEE)?

• fever, depression, ataxia, staggering anorexia

• muscle tremors and fasciculations

• ataxia may progress to parlysis

What species is a dead end host for EEE?

horse

What is the mortality rate for EEE?

nearly 100%

What are the clinical signs for WEE?

• less severe than EEE

• fever, depression, ataxia, anorexia, muscle tremor, possible paralysis

What species is a dead end host for WEE?

horses

Which equine encephalitide is a reportable foreign animal disease?

VEE

What species is a natural host of VEE?

rodents

How is VEE infection transmitted?

from bites from infected mosquitoes

When horses are viremic enough to infect mosquitoes, what cycle of VEE is that?

epizootic

What is the mortality rate of VEE in horses?

85-90%

How do we diagnose the equine encephalides (EEE, WEE, VEE)?

• virus isolation

• PCR
  serology (IgM) antibody detection on serum or CSF

• post mortem exam of brain tissue for antigen, virus culture or specific antibody

How do we prevent the equine encephalides (EEE, WEE, VEE)?

• vaccination

• mosquito control

• surveillance and testing

Is influenza an RNA or DNA virus?

RNA

Which influenza type is typical in horses?

type A

Whihc influenza strain is most common in horses?

H3N8

What is the incubation period of equine influenza?

1-3 days

How long is equine influenza infective?

for 3-6 days after cessation of clinical signs

What are the clinical signs of equine influenza?

• coughing and fever often first signs

• secondary bacterial infections common

• often younger horses

How do we diagnose equine influenza?

• nasal swabs for paired VN and HA antibody titers, PCR for viral genome, and Benchtop antigen capture kit

Which strain of equine herpesvirus causes respiratory and neurological issues, abortion, and neonatal death?

EHV-1

Which strain of equin herpesvirus causes respiratory issues, but rarely abortion or neurological issues?

EHV-4

What is a key feature of equine herpesvirus?

latency

What are the clinical signs of rhinopneumonitis (EHV1, EHV4)?

• fever

• lethargy

• clear serous nasal discharge

• watery eyes

• cough

• occur 2-5 days post exposure

Equine herepes myeloencephalopathy is caused by what?

EHV-1

What are the clinical signs of equine herepes myeloencephalopathy caused by EHV 1?

• fever

• respiratory disease

• proprioceptive deficits, paresis, progressive ataxia

• urine dribbling

• decreased anal tone

How do we test fo equine herpes?

• nasal swab PCR

• whole blood PCR

• CSF tap

• necropsy

What strain of equine herpes virus 1 is the “wild type”?

N752

What strain of equine herpes virus 1 is a single gene deletion/point mutation in the virus, increases in level of replication in host, has a longer level of viremia in the horse, and is neurotropic?

D752

How do we control and prevent equine herpesvirus?

• vaccination

• early recognition

• quarantine

• testing

• temperature monitoring

• biosecutiry vital

Which virus is described:

• reportable

• respiratory disease

• abortion

• limb/ventral edema

• enteritis

equine arteritis virus (EAV or EVA)

How do we diagnose equine arteritis virus?

• serology

• virus isolation on semen

• qPCR on semen or dead foals

How is equine infectious anemia transmitted?

• biting flies

• Iatrogenic (blood products, reusing needles)

How do we test for equine infectious anemia?

• AGID

• ELISA

True or false: Equine infectious anemia is a life long infection.

True