Update on Equine Herpes Virus-1 Jenifer R Gold DVM ACVIM Mountain Horse Medical Center May 2011
Update for Utah As of noon today 4 quarantined facilities (Box Elder, Davis, Kane and Utah Counties) 7 Confirmed cases on the quarantined facilities 8 Suspect cases on the quarantined facilities 2 cases euthanized due to recumbency/inability to rise
Update for Outbreak in General Confirmed EHV-1 or equine herpes myeloencephalitis (EHM) have been reported in 9 states (AZ, CA, CO, ID, OR, TX, UT, WA) Arizona has 1 confirmed EHM and 1 euthanized. California has no new confirmed cases since 5/23/2011. So far they have 18 confirmed EHM cases. These cases came from Odgen UT (16) and Kern County Cutting Event (2), Bakersfield, CA. 1 case has been euthanized. Colorado has 9 confirmed cases of EHV-1. 2 of those horses were euthanized after showing severe neurological signs. 22 suspect cases. (not confirmed) 12 quarantine and hold orders in 8 counties (Bent, Boulder, Garfield, Gunnison, Larimer, Mesa, Morgan and Weld)
Update for the Outbreak in General As of 5/26/2011 at 1 pm, Idaho has 5 horses on an EHV-affected facility already observing quarantine confirmed positive for EHV-1 in the past 24 hours. 2 of the horses attended the Ogden Cutting. 3 were stable mates at the same Idaho facility. Total of confirmed cases of EHV-1 in Idaho is 6. Three of the 6 have shown neurologic signs consistent with the neurological form of the disease. The other 3 have been febrile. New Mexico has 2 known positive cases, one has been euthanized , the other has been febrile with no other clinical signs. Oregon has 3 positive cases of EHV-1. None of the horses are showing clinical signs. 2 cases are in Clackamas and Umatilla County, the other is in Deschutes County.
Update for the Outbreak in General Texas has 16 horses that were known to attend the cutting in Odgen UT. Only 1 horse so far has tested positive. The others are under quarantine. Washington State has 7 confirmed cases with no deaths. 3 of the cases are at WSU. Others are in Spokane, Thurston, Chelan and Asotin counties. Thus total number of horses with EHV-1 (fever, respiratory signs) or EHM (neurologic disease) =51 horses Total number of horses euthanized=8 horses
What is Equine Herpes Virus? EHV-1 and EHV-4 are also known as Rhinopneumonitis EHV-1 causes respiratory disease, abortion and neurologic disease EHV-4 causes respiratory disease and infrequent abortions. Rarely (1 case) EHV-4 causes neurologic disease
Respiratory Disease Clinical respiratory herpesvirus infections most commonly occur in young horses, usually weanlings and yearlings Widespread outbreaks can occur in stressful and overcrowded environments Older horses are important in the outbreak They become sub-clinically infected (no clinical signs) but shed virus!
Respiratory Disease Clinical signs of respiratory disease Mild fever, coughing and nasal discharge Nasal discharge is typically clear Can progress to yellow thick purulent material
Respiratory Disease Incubation period may be short as 2 days or as long as 10 days. Outcome is dictated by minimization of stress and lots of rest. Exercising horses frequently can develop prolonged hypersensitivity of the lower airways May cause a subtle decrease in performance
EHV-1: Abortion There are usually no warning signs of abortion Can occur as early as 90 days Most cases occur between 7 and 9 months of gestation (Red bag abortion are common in horses infected with herpesvirus). In abortion storms over 50% of pregnant mares on the farm can have problems Red bag Aborted fetus
Neurologic Disease Neurologic form of this disease can to be fatal and is the greatest cause for concern at boarding facilities, racetracks and horseshows. Most horses experience respiratory signs of disease for one to two weeks prior to the development of neurologic signs.
Neurological Disease ~10% of horses get the neurologic form of herpes Stress (shipping or surgery) may trigger the onset of neurologic signs The virus will attack the spinal cord and brain stem.
Neurological Disease The clinical signs commonly seen are: Hind-end weakness Incoorination Toe-dragging Dog-sitting Urinary/fecal incontinence
Latently infected carrier horse Pregnant mares Latency Establishment Latency Reactivation ABORTION Recruitment of New Hosts Into Cycle Infection of young horses Neurologic disease
How is Herpesvirus Transmitted? Transmission occurs via respiratory route with infective droplets obtained from coughing and snorting horses. Shedding of the virus in nasal secretions can occur for 14 days. Contaminated hands and equipment (fomites) can spread the virus. Infection can be obtained from aborted fetuses, fluids and tissues. Mares that abort transmit infection via the respiratory route
Transmission In perfect conditions the virus can last in the environment for 35 days. Typically however it last several weeks All horses have the potential to be carriers of the virus regardless of whether they have clinical signs
Diagnosis Detection of virus from nasal swab or blood by viral isolation Polymerase chain reaction (PCR) tests can look for the virus in nasal secretions or whole blood buffy coat or placental and fetal tissue. Demonstration of a relative drop in lymphocytes and neutrophils (white blood cells) on a complete blood count (CBC) Demonstration of rising titers in serum collected two to four weeks apart
Treatment Because EHV-1 is a virus, antibiotics do not work Supportive treatment: Guided by the severity and range of clinical signs. Fluids NSAIDS-banamine, Valcyclovir Vitamin E Sling
Treatment In most cases, horses that do not become recumbent have a good prognosis However, recovery may take weeks to months Horses that become recumbent and are unable to stand have a poor to guarded prognosis
Vaccination Vaccinations for the respiratory form of EHV may not prevent the disease Will decrease the frequency, and severity of clinical signs Will decrease the shedding numbers of virus to other horses
Vaccination The American Association of Equine Practitioners AAEP recommends the following vaccination schedule for EHV-1 and EHV-4 in the prevention of respiratory disease Foals/weanlings: First dose 4-6 months of age Second dose 5-7 months of age Third dose 6-8 months of age Later at 3 month intervals
Vaccination Yearlings Every 3-4 months Horses in training Every 3-4 months
Vaccination All broodmares at the beginning of 3rd 5th, 7th and 9th month of pregnancy Currently there are 2 vaccinations labeled for the protection of abortion which are killed vaccines containing EHV-1 Currently there is 1 vaccine that is a modified live virus vaccine
Vaccination No vaccination currently available that is labeled to protect against the neurological form of equine herpes Preliminary work suggests the modified live virus vaccine may decrease clinical signs, but has not been totally confirmed The MLV has been shown to decrease viral shedding and potentially clinical signs… Controversial
Controlling an Outbreak Isolate all new arrivals to the farm for 28 days If farms are quarantined, must remain in quarantine for 28 days.NO horse coming or going! Disinfect all areas of the barns and transport vehicles with either bleach (one part bleach to 10 pars water) or phenolic based disinfectants Take rectal temperatures daily and isolate any horse with a fever
Controlling an Outbreak Disinfect all diagnostic tools such as endoscopes, after they are used on each horse Keep mares that abort in isolated areas away from the rest of broodmares
Controlling an outbreak If horses are transported during an outbreak Call ahead and confirm requirements Some states require: Coggins, Health Certificate and proof of vaccination seven to 90 days prior to travel Both Wyoming and Colorado right now require a health certificate less than 72 hours old