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? VIRUSBACTERIUM

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 ( º 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 cause death  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-typeMutant

EHV in Ohio  University of Findlay, January 12, 2003:  138 horses quarantined at the English riding facility  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 23 rd (reopens February 8 th )  Pennsylvania and Kentucky Tracks not accepting horses from Maryland or allowing horses to race in Maryland  EHV shows up at Laurel Park, January 25 th  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% die Zoonotic 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 ( º)  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