Outbreak of equine herpes reported
Horses have been quarantined; four confirmed dead
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While horseback riding is more common in the mid-west, this playful activity is also available to Southern Californians at the Los Angeles Equestrian Center (LAEC). However, the horses that live at the LAEC have been temporarily placed out of commission.
According to the California Department of Food and Agriculture (CDFA), all horses at the LAEC were quarantined as of November 3, after a five year-old and a ten year-old Saddlebred displayed moderate to severe neurologic signs and tested positive for myeloencephalopathy (EHM), a neurological disease associated with Equine Herpesvirus-1 (EHV-1). The department immediately issued a quarantine for exposed horses at the facility and implemented enhanced biosecurity measures. Unfortunately, due to the severity of the disease, the 5-year-old horse was euthanized that same day.
According to United States Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS), this virus can cause four manifestations of disease in horses, including neurological, respiratory, abortion, and neonatal death. Myeloencephalopathy is the neurological form of the disease and is one of nine strains of equine herpes virus. It forms from mutation in the genome or neuropathogenic strains of EHV-1, which is said to be one of the three most dangerous strains of equine herpes virus, as it poses the most serious health risks for domesticated horses and can have significant economic impacts on the U.S. equine industry.
The USDA-APHIS also stated that by the age of two, almost all horses have been infected with EHV-1. Foals can become exposed to the disease from their mothers. The virus can then become inactive and remain in the horse’s body, forcing them to be carriers of EHV-1. Some do not show any external signs of disease when the virus is inactive. Although the virus can be reactivated during times of stress, such as strenuous exercise or long-distance transport, there is much lower risk of infecting other horses if they have a low viral load.
While EHV-1 can spread easily and most likely occurs through horse-to-horse contact it can also spread through human contact, still humans are not at risk of contracting the virus.
Horses can spread the virus via the respiratory tract, through direct or indirect contact with an infected aborted fetus and fetal membranes, secretions from their nose, and through the air; however, it is hard to determine the distance it can spread if airborne. Grooming equipment, feed and water buckets, and human contact are a few ways in which the virus can spread physically through human contact.
Signs of EHM include fever, decreased coordination, loss of tail tone, hind limb weakness, leaning against a wall or fence to maintain balance, and lethargy. Nasal swabs and blood samples are used to diagnosis the disease in live horses. Neurological signs result from damage to blood vessels in the brain and spinal cord. Interference with the blood supply leads to tissue damage and loss in normal function of areas in the brain and spinal cord.
IV fluids, anti-inflammatory, antibiotics, and antivirals are administered to treat the disease. Although there are vaccines that help control the respiratory and abortion manifestations of EHV-1, there is currently no vaccine that prevents EHM.
Since the outbreak, there have been six confirmed positive horses, four of which recently returned home on October 30 from a week-long horse show in Las Vegas. A total of nine horses are living in quarantined isolation after showing neurological signs and having an elevated temperature. One of the horses that was placed in quarantined isolation on November 3 also tested positive on both nasal swabs and blood samples for non-neuropathic EHV-1 as of November 9. Since this horse was originally moved to isolation from a barn on the facility that had not previously been identified with a confirmed EHV-1 case, the horse population under quarantine at LAEC was expanded to a total of three barns under quarantine.
All horses under quarantine are required to have their temperatures taken twice a day and any elevated temperatures reported to incident management. All other confirmed positive horses remain in quarantined isolation and are stable and responding to treatment. At this time, no additional EHV-1 cases have been confirmed in horses that performed at the Las Vegas horse show. CDFA has confirmed that the host facility has taken biosecurity measures of thorough cleaning and disinfection of the show facility. CDFA Animal Health Branch veterinarians are monitoring the quarantine and situation on-site.
To help stop the spread of the disease owners should limit horse-to-horse and horse-to-human-to-horse contact, avoid use of communal water sources and sharing of equipment among horses, wash hands before and after handling horses, changing clothes and footwear between horses, wearing gloves, using disinfectant, monitoring horses for clinical signs of disease and report any temperature over 102°F to a veterinarian, and isolating sick horses.
For more information, visit https://www.cdfa.ca.gov/ahfss/animal_health/equine_herpes_virus.html and https://www.aphis.usda.gov/aphis/home/