The originally identified strain of EHV-1 appears to have mutated into a strain that replicates more rapidly and has a predilection for neurologic tissue. The mutated virus circulates at higher levels in the body earlier in the course of the disease and maintains the high level of virus within the body for a longer period of time.
However, both the mutated and original virus can cause neurological disease. The neurological form of EHV-1 traditionally has been less common. However, in the Findlay, Ohio outbreak, the respiratory outbreak of EHV-1 involved the neurological form and has been the most devastating outbreak to date. Neurological EHV-1 has been responsible for quarantines and horse mortality in most areas of the country during the past decade.
Most recently, a case was diagnosed in Ontario the end of February and a case was diagnosed at Michigan State University this the past week. Also, Ohio has had a couple of cases in the past week. The Michigan Department of Agriculture has quarantined the farm of origin for the Michigan case and is currently identifying all contacts the Michigan horse had and testing any horses that may demonstrate clinical signs suggestive of EHV The virus that caused the neurological disease in the Michigan horse was the original strain of the virus.
The incubation period for EHV-1 may be as short as one day or up to ten days. Typically signs are seen within the first week. The virus is shed for seven to 10 days but shedding has been documented for up to 28 days after clinical signs have been recognized. Initially, horses may present with fevers up to degrees Fahrenheit. Some horses will develop nasal discharge, depression and loss of appetite. Horses may also develop neurological signs, including toe-dragging, weakness, and incoordination of the hind end.
The nerves of the head cranial nerves are often not affected. Other neurological signs that may occur include a weak, floppy tail, inability to defecate and urinary incontinence. Once innervation to the urinary bladder is affected, the horses cannot urinate freely and the bladder becomes greatly distended. Please check with your state or provincial animal health office about which diseases are reportable.
A variety of inactivated vaccines are available, including those licensed only for protection against respiratory disease, and two that are licensed for protection against both respiratory disease and abortion,.
Performance of the inactivated respiratory vaccines is variable, with some vaccines outperforming others. A single manufacturer provides a licensed modified live EHV-1 vaccine.
It is indicated for the vaccination of healthy horses 3 months of age or older as an aid in preventing respiratory disease caused by equine herpesvirus type 1 EHV None of the available vaccines have a label claim to prevent the neurologic form of EHV-1 infection. It has been suggested that vaccines may assist in limiting the spread of outbreaks of EHM by limiting nasal shedding of EHV-1 and dissemination of infection. For this reason, some experts hold the opinion that there may be an advantage to vaccinating in the face of an outbreak.
If this approach is pursued, only afebrile and asymptomatic horses should be vaccinated and protection against clinical EHM should not be an expectation. Adult, non-breeding, horses previously vaccinated against EHV: Frequent vaccination of non-pregnant mature horses with EHV vaccines is generally not indicated as clinical respiratory disease is infrequent in horses over 4 years of age.
It is recommended that the following horses be revaccinated at 6-month intervals:. A 4 to 6 week interval between doses is recommended. Pregnant mares: Vaccinate during the fifth, seventh, and ninth months of gestation using an inactivated EHV-1 vaccine licensed for prevention of abortion. Many veterinarians also recommend a dose during the third month of gestation and some recommend a dose at the time of breeding. Maternal antibody passively transferred to foals from vaccinated mares may decrease the incidence of respiratory disease in foals, but infection is common in these foals and may result in clinical disease and establishment of the carrier state.
Barren mares at breeding facilities: Vaccinate before the start of the breeding season and thereafter based on risk of exposure. Stallions and teasers: Vaccinate before the start of the breeding season and thereafter based on risk of exposure.
Administer the third dose at 10 to 12 months of age. Immunity following vaccination appears to be short-lived and it is recommended that foals and young horses be revaccinated at 6-month intervals. The benefit of intensive vaccination programs directed against EHV-1 and EHV-4 in foals and young horses is not clearly defined because, despite frequent vaccination, infection and clinical disease continue to occur.
Becke and her small army of staff and volunteers are working in shifts to monitor the horses and administer the drugs to the surviving animals. At the same time, they must observe strict new protocols. It's not just nuzzling that's now forbidden: due to a horse's powerful sneeze, the animals require a physical distance of 11 metres between them.
Vapour barriers have been installed inside the barn, while stalls are deep-cleaned and disinfected regularly. There's even a sort of equine ICU. Veterinarian Carole Michon must also take extreme precautions to halt the further spread of the illness, including bagging her personal protective equipment and leaving it behind when she departs for the day.
Michon noted that while older horses are generally thought to be more vulnerable, the death of five-year-old Eddy shows how unpredictable the disease can be.
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