EHV-1 Outbreak In California: Why Does It Feel Like We’ve Been Here Before?
We have been dealing with a global pandemic for the past two years. COVID-19 has resulted in upwards of 6 million confirmed deaths and over 480 million cases around the globe, with the pandemic still ongoing.
The horse community in California has been experiencing a different kind of viral outbreak. Since January Equine Herpes Virus (EHV-1) has been spreading in the state. It has resulted in the illness and deaths of horses and has significantly disrupted the equine industry. According to the California Department of Food and Agriculture (CDFA), the first positive case of EHV-1 in the recent outbreak was confirmed on January 19th.
But what is EHV-1? With the season is just getting started, we’ve all been eager to get as much training in as necessary. But just because you’ve been able to move your horses, does that mean you should? And for those who have been willing to risk it and break bio-security measures to even travel between states to get some extra training in, will they get the season underway with an unfair advantage..?
What is EHV-1?
EHV-1 is a viral infection in horses that can cause respiratory disease, abortion in mares, neonatal foal death and neurological disease. The neurological form is called Equine Herpes Myeloencephalopathy (EHM). EHM is most often attributable to the neuropathogenic strain of EHV-1, but it can occasionally be caused by the non-neuropathogenic strain of the virus.
EHV-1 is endemic in equine populations where mature horses develop immunity through repeated natural infection, but may become a source of infection to susceptible horses as asymptomatic carriers. This is how EHV-1 outbreaks can happen among even closed populations of horses.
Galway Downs, 2021
There is a vaccine for EHV-1, but there is not a vaccine for EHM. Why EHV-1 causes severe neurological symptoms in some horses is not understood at this time, though mature or aged horses tend to develop neurological symptoms more than juvenile equines. While vaccination for EHV-1 is widespread, especially for breeding and young horses along with competition horses, the presence of post-vaccinal antibodies against EHV-1 is “not indicative of protective immunity.” Repeated and regular vaccination does reduce the frequency and severity of EHV-1, but does not prevent the disease and potential outbreaks. In this way EHV-1 vaccination is much like vaccination for COVID-19 among humans.
Horses with EHV-1 tend to display signs of a fever, but it is also possible for them to have the virus and be asymptomatic or to have atypical presentation of EHV-1.
Dr. Nicola Pusterla, Professor of Medicine and Epidemiology, UC Davis Veterinary Medicine notes that “infection does not always translate into disease, meaning that adult horses can shed EHV-1 without displaying any abnormal clinical signs.” Much like the challenges we have experienced with asymptomatic cases of COVID-19, even after vaccination, the invisibility of asymptomatic EHV-1 cases means that the virus can be spread unknowingly.
What kinds of biosecurity measures mitigate the spread of EHV-1?
EHV-1 is spread primarily through nasal secretions and is extremely contagious. The virus can be spread directly from horse to horse, or through items such as halters, or even via people and any surface that has infected nasal secretions.
The incubation period (the time it can take clinical signs to develop) for EHV-1 is 2 to 10 days. After that, an infected horse can shed the virus for 7 to 10 days. Because of this variability and the long duration, the California Department of Food and Agriculture (CDFA) currently recommends a twenty-one day isolation period of confirmed positive cases.
Additionally, the latent form of EHV-1 can reactivate at a later date, suggesting that further isolation is a good precautionary measure. However, the latent form has a low viral load, which poses a far lessened risk of infecting other horses.
The CDFA recommends that participants at horse events follow basic biosecurity protocols, including limiting horse-to-horse and horse-to-human-to-horse contact, avoiding use of communal water sources, and avoiding sharing any equipment. The virus can also live in the environment for up to 7 days, so environment cleaning and disinfecting is an important step in the mitigation of spread of the virus.
If travel between barns or to horse shows is necessary, changing or disinfecting shoes and outer clothing can also help to decrease spread. The virus can even travel to other locations on vehicles or trailers. The CDFA also advises owners to report any temperatures of over 102°F to a veterinarian and monitor for any other signs of disease.
Can humans contract the virus?
Humans are not at risk of contracting the virus. Importantly, humans can indirectly transmit it. This risk of transmission means that humans should be especially careful when working with multiple horses, and should thoroughly clean and disinfect clothing, equipment, and hands.
EHV-1 has serious implications for the horse industry
There are obvious economic impacts due to the EHV-1 outbreak. Shows cannot run as they usually do - there is quite literally a freeze on the industry. In this way it’s a bit of 2020 deja vu when shows were cancelled due to the pandemic.
The sales, lesson, and training portions of trainers’ businesses have all but halted in affected barns. In addition, staff at affected barns have increased labor demands to meet biosecurity measures and care for horses that are ill.
Beyond the economic cost, there is a huge emotional toll. Horses’ lives have ended in this outbreak and their human connections are devastated. The owners of horses that have been ill are extremely concerned about them. And the owners of healthy horses are worried because the virus could spread to their horses. Sadly, grief, loss and worry accompany any serious disease outbreak.
Knowingly increasing the risk of spreading EHV-1 to continue training is both unfair and unethical
Galway Downs, 2021
On March 3, the USEF announced a 14-day suspension of all USEF competitions in California. In the eventing world, both Twin Rivers HT and Copper Meadows HT were cancelled. On March 16 the California Department of Food & Agriculture issued an extension of recommended caution for California equine events through March 31. As of the writing of this article, Galway Downs International and Horse Trials is scheduled to run April 2nd and 3rd with required health certificates dated no more than 72 hours prior to any horses arriving on-site and additional biosecurity measures.
While many shows and equine activities have been cancelled, it is difficult to stop horse owners from shipping their horses, including to train at different locations. It is up to individuals to act appropriately during this or any disease outbreak. Even if you technically can move your horses or yourself around, that does not mean that you should if it may put others at risk of disease exposure.
It is a privilege to ride and compete with horses. But it is an even bigger privilege to be their custodians and/or their owners.
Remember that a horse does not choose to get on a trailer and be shipped somewhere where they may be exposed to a virus any more than he chooses to be ridden. They don’t have a choice, so it is up to their owners to make the right choices for them.
We have been here before, and rather recently. It is not worth putting horses’ lives at risk to get to a horse show or go train at someone else’s farm, just as has not been worth the risk of exposing others to COVID-19 by not following biosecurity measures.
This current EHV outbreak will pass, and horse shows will resume shortly, though due to the nature of EHV it is only a matter of time before another outbreak occurs and we are faced with similar challenges. What can we take away from this year’s outbreak as learnings for future episodes? Your answer is as good as ours, but equine welfare and fairness of sport must be what govern the decisions for how these outbreaks are handled in future.
