Download Equine Viral Diseases

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
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Equine Herpes Virus (EHV)
Equine Encephalomyelites
Equine Influenza
Equine Infectious Anemia
West Nile Virus
Equine Viral Arteritis
Rabies
Equine Herpes Virus
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Species Specific
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Three Subfamilies: alpha, beta, gamma
9 documented strains, but only 5 affect domestic
horses
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EHV-1 ()
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Subtype 1
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Rhinopneumonitis (respiratory form)
Abortion
Birth of weak foals
Peracute vasculitis
Neurological
EHV-1…
 EHV-1 is common throughout the world
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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
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EHV-2 and EHV-5
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Gamma Family
“Ubiquitous” but rarely causes disease
Found in nearly 100% of healthy foals
Can cause problems in the following
diseases:
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Conjunctivitis in young foals
May act as a forerunner infection that leads to
Rhodococcal (through immune suppression)
Equine Herpes Virus
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EHV-3
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Venereal Disease
Equine Coital Exanthema
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Rare but important
($$)
Doesn’t cause
death
Self-limiting
Characteristic
lesions on
genitalia of
stallions and mares
Equine Herpes Virus
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EHV-4
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Respiratory infection only (“Rhino”)
Non-fatal
Severe, widespread outbreaks in young
horses
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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 (5075% fatal)
Zoonotic Diseases!
 Transmitted by mosquitoes!
 Not horse-horse or horse-human
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:
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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
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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
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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
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Zoonotic Diseases!
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?
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