Equine Viral Diseases

INAG 120 – Equine Health Management

September 19, 2011

What’s a Virus?VIRUS

Structure Outer layer

(envelope) is spiky Protein coat DNA/RNA

Electron micrograph of a rotavirus. The one on the right has antibodies attached which prevent it from infecting cells© GrahamColm

What’s the difference between a virus and a bacterium?

VIRUS BACTERIUM

More About Viruses

VIRUS VERY small REPRODUCTION

Depend on host cells for reproduction Attach to a cell and inject genes or are

absorbed Host cell mass-produces virus

Equine Viruses

Equine Herpes Virus (EHV) Equine Encephalomyelites Equine Influenza Equine Infectious Anemia West Nile Virus Equine Viral Arteritis Rabies

Equine Herpes Virus

Species Specific Three Subfamilies: alpha, beta, gamma

9 documented strains, but only 5 affect domestic horses

EHV-1 () Subtype 1

Rhinopneumonitis (respiratory form) Abortion Birth of weak foals Peracute vasculitis Neurological

EHV-1…

EHV-1 is common throughout the world Can be sudden and deadly High temperature “Fulminating” respiratory disease May see all 5 of the syndromes at once Horses of all ages are affected Mares 3-9 months pregnant most

susceptible Abortion storm virus first identified in the 1940s

EHV-1…

Viral incubation for 2-10 days: Fever (102 - 107º F for 1-7 days) Malaise, depression, anorexia Congestion and serous discharge from the

nostrils Swollen lymph nodes Mild incoordination to severe ataxia, paresis

and paralysis Loss of bladder tone, tail tone, skin

sensation in hind limbs

EHV-1

Treatment and prognosis: Supportive nursing If horse remains standing, prognosis is good NSAID’s to control malaise and fever

Encourages eating Fluid therapy if dehydrated Antibiotics to prevent secondary bacterial

infection (especially if respiratory disease) Corticosteroids to reduce nerve inflammation

Equine Herpes Virus

EHV-2 and EHV-5 Gamma Family “Ubiquitous” but rarely causes disease Found in nearly 100% of healthy foals Can cause problems in the following

diseases: Conjunctivitis in young foals May act as a forerunner infection that leads to

Rhodococcal (through immune suppression)

Equine Herpes Virus

EHV-3 Venereal Disease Equine Coital Exanthema

Rare but important ($$)

Doesn’t causedeath

Self-limiting Characteristic

lesions on genitalia of stallions and mares

Equine Herpes Virus

EHV-4 Respiratory infection only (“Rhino”) Non-fatal Severe, widespread outbreaks in young

horses Foals 3 years old in training Not a problem in older horses (develop

immunity)

EHV-1 Outbreaks: USA & UK # outbreaks caused by

Five-year interval

# Outbreaks Wild-type Mutant

1970-1975 1 0 1

1976-1980 3 0 3

1981-1985 4 2 2

1986-1990 6 1 5

1991-1995 5 1 4

1996-2000 6 2 4

2001-2005 32 2 30

EHV in Ohio

University of Findlay, January 12, 2003: 138 horses quarantined at the English riding facility

35-40 horses showed obvious neurological signs

12 horses died Within 5-6 days of first horse showing symptoms,

80-90% of horses had fevers

Strain confirmed as EHV-1 Respiratory and neurological symptoms

Not sure where the strain came from

All horses were current on vaccinations!

EHV in Maryland

Montgomery County, March 2004: 12 horses exhibit signs of neurologic illness 5 horses died Farm houses mostly polo ponies

Strain confirmed as EHV-type 1 Confirmed after multiple tests on July 8 Not sure where the strain came from Hindlimb ataxia, inability to stand, coma

All horses were current on vaccinations!

EHV in Maryland Howard County, Columbia Horse Center

March/April 2005 – June 2005 Facility strictly quarantined 4? horses euthanized

Pimlico, Eastern Shore, January 2 – March 2006 EHV-1 detected in one barn 4 Barns quarantined (but not quickly enough)

EHV-1 spreads to training farm on the Shore, leading to the euthansia of 2 horses.

Pimlico closes on January 23rd (reopens February 8th) Pennsylvania and Kentucky Tracks not accepting horses from

Maryland or allowing horses to race in Maryland EHV shows up at Laurel Park, January 25th

EHV-1 at Marion DuPont Scott Equine Medical Center February 2007 – March 29, 2007

Equine Encephalomyelitis

Arthropod-borne viruses that cause Central Nervous System dysfunction and moderate to high mortality Western (20-30% fatal) Eastern (70-90% fatal) Venezuelan (50-

75% fatal) Transmitted by mosquitoes!

Not horse-horse or horse-human

Zoonotic Diseases!

Equine Encephalomyelitis Clinical Signs:

Generally occur 5 days after infection Death may occur within 2-3 days Ataxia, wandering, impaired

vision, reduced reflexes, circling, inability to swallow, drooling, fever

Paralysis usually followed by death

EEE

VEE – “Paddling”

Equine Encephalomyelitis

Diagnosis: Laboratory tests on blood samples or necropsy

tissues

Treatment: Successful for mildly affected animals Supportive nursing care

Control: Vaccination one month prior to mosquito season

Equine Influenza

Symptoms: Harsh, dry cough Loss of appetite Depression Watery nasal discharge

Can lead to pneumonia!

Normal trachea Image courtesy of Dr. Issel and Gluck Center

Trachea after cilia destroyed by flu

Image courtesy of Dr. Issel and Gluck Center

Equine Influenza

Treatment Fresh air, rest Avoid dust Antibiotics to control secondary infection

Prevention: Vaccination! Most vaccines are effective against multiple

strains

Equine Infectious Anemia

“Swamp Fever” Horses are the only known natural host! No treatment available to eliminate EIA from an

infected horse Horses surviving EIA can

relapse and/or pass it on to other horses Lifetime Quarantine Euthanasia

2006: Appeared in Ireland

EIA

Clinical Signs Sudden onset of high

fever of 104º - 108º Severe depression Depressed appetite Weight Loss Weak/incoordination Jaundice Ventral edema Rapid destruction of red blood cells

EIA – Ventral Edema

EIA – Symptoms

EIA

Subacute form is most common Similar symptoms to acute, but not as

severe Death not as common

Chronic EIA: Horses are unthrifty and lack stamina May have acute or subacute attacks

EIA – Method of transmission

Blood from infected horses

Blood-sucking flies, mosquitoes

Needles Surgical

instruments Dental floats Bridle Bits

EIA - Diagnosis

COGGINS TEST Dr. Leroy Coggins of Cornell University Only 10 cc of blood is needed for the test Results can be available in 48 hours Most states require a negative Coggins test for

transported horses Most shows require negative Coggins test for

participants Some states require negative Coggins for sales

West Nile Virus

Vector-borne virus first in this hemisphere in 1999

Humans, horses, and birds are incidental hosts

Many horses infected with WNV do not become ill

Approximately 33% dieZoonotic Diseases!

WNV

Control: Mosquito Control! Eliminate standing water Mosquitoes can breed in as little as an inch

of water Vaccination –95% control rate WNV Antibody for horses already infected

(from Novartis Animal Vaccines, Inc.)

September 24, 2004

November 1, 2005

September 19, 2006

November 27, 2007

September 16, 2008

Equine Viral Artereitis

Acute upper respiratory infection caused by a herpes virus

Similar to influenza and rhino Fever (102-106º) Nasal discharge All age groups susceptible Can cause abortion (approximately

50%) Edema of the limbs Increased respiratory rate Skin rash

EVA

Most common in Saddlebreds and Standardbreds

Most animals recover without treatment Vet may prescribe antibiotics to prevent

secondary infection Transmission:

Inhalation of droplets from infected horses STD!!!

Rabies

Neruotropic Rhabdovirus Saliva of infected animal horse Travels up the NERVES to the brain Reproduces in the brain Sheds virus through the salivary glands BLOOD TEST WON’T DIAGNOSE

DISEASE!!! Saliva test?

Zoonotic Diseases!

Rabies

Symptoms: Neurological disorder, choking, weakness,

staggering, unprovoked excitement Behavioral changes are most common May take 2-6 weeks or even 3 months to show

symptoms after infection

NO EFFECTIVE TREATMENT!! Prevention = annual vaccination Problem in horses in the Mid-Atlantic

Raccoon strain is predominant here