EHV-1 Outbreaks in Pennsylvania

By Britanni Kirkland and Aliza Simeone

Multiple EHV-1 outbreaks have occurred in the last few months. Monitor your horses and take proper precautions.

There have been several outbreaks of equine herpesvirus (EHV) nationwide over the last few months, including more than 30 confirmed cases of EHV-1 in Chester County, Pennsylvania this March. But what is this virus and how can horse owners protect their horses?

Equine herpesvirus is a highly contagious respiratory virus that can cause different types of illness in horses depending on the type of virus and the interaction of that virus with each particular infected horse. There are many subtypes of EHV, but EHV-1 and EHV-4 are the two most common. Infection with EHV-1 or EHV-4 most commonly causes respiratory disease (rhinopneumonitis or "rhino") but can also cause abortion in mares and, much less commonly, neurological disease.

Equine herpesvirus is transmitted from horse to horse through nasal discharge or contact with contaminated objects. It can also be spread through respiratory droplets in the air. Clinical signs vary widely between infected horses and may include any of the following:

• Fever (this is often the first sign of illness and may not be obvious)
• Increased respiration rate
• Nasal discharge
• Cough
• Depression/Lethargy
• Abortion (usually occurs in late pregnancy)
• Swelling, often in one or more limbs, but can be elsewhere
• Neurological disease: incoordination, paralysis or weakness of hind limbs, toe-dragging, inability to stand up, staggering, and abnormal body positions (dog sitting, leaning on surfaces, etc.), inability to urinate normally

These signs may not appear immediately but can occur 1 to 14 days after infection. In some cases, horses may not show clinical symptoms at all. This means that a seemingly healthy horse could infect other horses at a show, or after coming home from a show, without anyone knowing. This is why it's so important to always follow biosecurity protocols even when there is no known outbreak and, of course, to follow all required protocols during a known outbreak.

What happens if there is an outbreak?

When EHV-1 is associated with neurological disease, it is a reportable disease in Pennsylvania. This means that if a veterinarian suspects that a horse may be showing signs of neurological disease associated with EHV-1 infection, they are required to report it to the Pennsylvania Department of Agriculture (PDA). An investigation will occur, and if the neurologically impaired EHV-1 case is confirmed, then a quarantine will be placed for that horse and other equine animals that may have been exposed on that property and on other properties identified as having had potential exposure. Horses on those premises must be monitored closely for signs of illness including taking temperatures at least twice a day. During a quarantine, horses are not able to be transported on or off the property except with a special permit from PDA, for example, to move for emergency medical care at an approved veterinary hospital.

In Chester County in March 2021, there were several premises affected with EHV-1 through routine movement of horses. As of April 1, 2021, only the first recognized neurologically impaired horse was affected significantly enough that it had to be euthanized. Since then, more than 30 other horses being monitored under quarantine due to known or suspected exposure have developed fevers or mild neurological impairment and tested positive for EHV-1, but so far all have recovered.

Reporting of EHV-1 and regulatory response varies by state. In some states, even respiratory cases of EHV-1, not known to be associated with any neurologic case may be quarantined or have other restrictions placed. For information on each state’s reportable equine diseases, visit Reportable Diseases | Equine Disease Communication Center.

In general, any horse that has been diagnosed with or exposed to EHV should not be moved and biosecurity measures should be implemented immediately to reduce chance of disease spread. If you suspect your horse has EHV, contact your veterinarian immediately.

What should horse owners do?

1. Assess your horse regularly and recognize if he is showing any abnormal physiological or behavioral signs . It is best to take your horse’s temperature  regularly to recognize what their average temperature is so you can easily detect deviations that may be caused by EHV.
2. Make sure your horse is up to date on vaccinations and speak with your veterinarian about any risk-based vaccines they might recommend. There is a vaccine available for the respiratory and abortion forms of EHV to help reduce severity of the disease, but your horse may still contract the virus and spread it and vaccination does not protect against EHV-1 neurological disease.
3. Do your best to keep your horse healthy! Reduce stress on your horse as much as possible and always ensure they are getting a well-balanced diet.
4. Always implement biosecurity measures , whether you are at the farm or at a horse show. Some biosecurity measures include:

-- Taking your horse’s temperature twice daily while at horse shows.

-- Do not share equipment (tack, muck buckets, pitchforks, feed buckets, etc.)

-- Do not let your horse touch noses with other horses to say "hi."

-- Try not to let other people pet your horse.

-- Wash your hands frequently! You can spread the virus from horse to horse.

-- If possible, keep your horse at the trailer as much as possible when getting ready to show. Park your trailer at least one bus length (approximately 35 feet) away from the trailer next to you if possible.

-- Do not use communal water troughs or let the hose touch the water in your horse’s bucket when filling it.

-- Disinfect items BEFORE leaving the horse show. Think buckets, pitchforks, even the soles of your boots! Make sure you follow the disinfectant label instructions for the most effective use.

-- Quarantine your horse from others on the farm when you return from a horse show (21 days of quarantine is recommended). -- Continue to monitor your horse’s temperature twice daily upon returning home. Again, this is often one of the first signs of illness.

               5.Call your veterinarian if you suspect your horse might be ill or if you         have been to a show where there has been a case reported. It is best to always seek advice from a veterinary professional. The investigation and quarantine may seem like a major inconvenience, but by reporting you could be saving horses’ lives.