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Equine Herpes Virus-1 Equine herpes virus type 1 (EVH-1) is a common herpes virus in horses, with respiratory, reproductive and neurological signs associated with it. Reproductive signs include abortion of virus-infected fetuses from infected mares and the birth of weak, nonviable, infected foals. Neurological signs include a paralytic neurological disease due to vasculitis (inflammation of the blood vessels) of the spinal cord and brain. Respiratory signs, the most common form of EHV-1, include a sudden onset of fever (often up to 106° F), a serous (clear) nasal discharge which may progress to mucopurulence (yellow). Coughing is usually absent. EHV-1 may be complicated by a secondary bacterial pneumonia, requiring antibiotic therapy. Horses with primary respiratory signs usually recover without complications. This virus is spread in secretions through the air (30-40 ft), by direct and indirect contact (hands, buckets, boots, etc). Neonatal foals infected with EHV-1 may appear normal at birth, but within the first week of life become weak and lethargic. The illness progresses to respiratory distress, increased heart rate, red mucous membranes and diarrhea. Prognosis is grave despite any attempts at treatment. Equine herpes myeloencephalopathy is the result of decreased blood flow to the spinal cord. Acute onset of ataxia (wobbliness) and tetraparesis is most commonly seen. The severity of clinical signs may vary. Signs usually appear 6-10 days after infection. Coughing and nasal discharge may accompany or precede neurological signs. Urinary incontinence, a flaccid tail, decreased anal tone and increased severity of signs in the hind limbs versus the fore limbs are common. The clinical signs may stabilize in 48 hours; some progression and deterioration may continue and result in death or euthanasia. Horses that are prone to recovery improve within 5-7 days and make a full recovery within several months. Horses that do not become recumbent have a better prognosis. EHV-1 is found in the majority of the equine population, and is transmitted through the respiratory system. The virus incubation period is 3-7 days. After inhalation, the virus attaches to and replicates in cells of the nasal passages, pharynx and tonsillar tissue. The virus is then transported to other organs by mononuclear cells (a type of white blood cell). Blood work results may indicate acute viral inflammation, such as a low white blood cell count. A fourfold rise in antibody titer from the acute to convalescent sera is indicative of infection. PCR of an aborted fetus may be useful if viral isolation is negative. Viral isolation from the white blood cell coat of the blood may be performed and may be diagnostic for 10-12 days post-infection. Attempts to isolate the virus using a nasal swab may be performed within this time frame as well. Diagnosis of the neurological form of the disease includes clinical signs, history and findings on physical examination. A CSF analysis usually shows an increase in protein and a normal to slightly increased white blood cell count. The CSF is often yellow in color. Treatment of the respiratory form includes the use of anti-inflammatory medications (flunixin meglumine or phenylbutazone) and antibiotics if a secondary bacterial pneumonia is present. In addition, rest for a minimum period of 3 weeks is recommended. Treatment of the neonatal form is typically unsuccessful and requires appropriate identification of EHV-1 in the affected foal. Treatment of the neurological form requires the use of anti-inflammatories (flunixin meglumine, dexamethasone and DMSO), supportive care (bladder decompression, nutritional support, evacuation of feces from the rectum and intravenous or oral fluids) and the use of antibiotics if the horse is recumbent or has urinary tract or respiratory tract disease signs present. Horses that are recumbent or unable to rise without assistance often require the use of a sling. Prevention is available in the form of vaccines for the respiratory and reproductive forms. Both killed and modified-live vaccines are available at this time. No vaccine is present on the market at this time to protect against the neurological form of EHV-1. Reducing the incidence of the disease requires reducing the risk of introducing or disseminating EHV-1 infection in a stable setting, minimizing stress and maintaining distinct herd groups based on age, gender and occupation. Ensuring that pregnant mares get adequate vaccines during gestation are essential, as well as ensuring that any new horses entering premises have a detailed vaccination history or are isolated from all other horses for a minimum of 3 weeks. Equine Herpes Virus EHV-1 RecommendationsVaccination and EHV-1: · The Flu/Rhino vaccine that is typically given twice yearly is a killed vaccine that offers some protection against EHV-1 and EHV-4, but unfortunately no vaccine offers complete immunity. Currently there is no vaccine available that prevents against the neurological form of EHV-1. · At this time, we are recommending the administration of a modified live vaccine to open herds and barns. An open herd/barn is a farm where horses are coming on and off the farm on a daily/weekly basis (outside horses using the indoor, going back and forth to other barns for lessons, showing, traveling between state lines, etc). This vaccine requires a booster 3-4 weeks after the initial administration. · Reasons to vaccinate with a modified-live vaccine: o Vaccination decreases the severity of the disease and decreases the mortality from EHV-1 o Horses vaccinated with a modified-live vaccine that contract the disease will not shed the virus in their nasal secretions: this significantly decreases the spread of the disease if a horse becomes infected · People who opt not to vaccinate: o Non vaccinated horses should not travel to open barns or show grounds that have the potential to have EHV-1 carriers. o Barns with non vaccinated horses should follow strict quarantine protocols outlined below. This includes horses that come just for a daily lesson. o Non vaccinated horses that contract the illness will have higher likelihood of mortality and will have a much higher index of viral shedding to other horses compared to vaccinated horses. o The best tactic for non vaccinated horses is to prevent any possibility of exposure to sick animals. Transport of Horses and New Arrivals: · Never Ship a horse with a fever. The horse should have a normal temperature <101.5 for five days prior to shipment. · Horse should have a health certificate and physical examination from a veterinarian prior to shipment. · All horses should be current on vaccinations. If the horse is being shipped from or to an area that has the possibility of exposure to EHV-1, vaccination with the modified live vaccine is strongly encouraged. · Quarantine in area that is 30-40 feet away from all other horses and with no access to the public. This area should have its own mucking equipment, brushes, blankets, etc. This horse should be dealt with last when cleaning the barn. All clothes, boots, and hands should be cleaned prior to working with other horses. · EHV-1 is contagious to other horses while the horse has a fever and for 14 days following the last day with a fever. Therefore, all horses should be quarantined for at least 15 days upon arrival. · Monitor temperature daily. · It is also recommended that all questionable horses have a titer and nasal swab taken. Attached is information of equine herpesvirus from the AAEP.
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