Prevention

Vaccines

    The main commercial vaccines available, and the label instructions:

       1) Calvenza EIV/EHV (Boehringer Ingelheim) (6)
  calvenza
Type - killed vaccine, intra-muscular or intra-nasal
Dose - three doses each 3-4 weeks apart; then once annually
Age - for horses over 6 months of age; safe in pregnant mares
Combos - combined with influenza
Purpose - for respiratory disease caused by EHV 1 and 4
      


       (i2)

        2) Fluvac Innovator 6 (Fort Dodge) (7)
              fluvac
Type - killed vaccine, intra-muscular
Dose - two doses 3-4 weeks apart; then once annually
Age - not specified
Combos - available with eastern, western, venezuelan encephalomyelitis, influenza, and tetanus
Purpose - for respiratory disease caused by EHV 1 and 4


     
       (i3)

        3) Pneumabort K (Fort Dodge) (8)
          pneumabort
Type - killed vaccine, intra-muscular
Dose - three doses 1 month then 6 months apart; then once annually
    (three times annually at the 5th, 7th, and 9th months for pregnant mares)
Age - not specified
Combos - none
Purpose - for respiratory disease and abortion caused by EHV 1

         (i4)

      4) Prestige V with Havlogen (Intervet) (9)
             prestige
Type - killed vaccine, intra-muscular
Dose - two doses 3-4 weeks apart; then once annually
Age - for horses over 6 months of age
Combos - available with eastern and western encephalomyelitis, equine influenza, and tetanus
Purpose - licensed for prevention of respiratory disease from EHV 1 and 4

      


       (i5)

        5) Prodigy with Havlogen (Intervet) (10)
           
prodigyType - killed vaccine, intra-muscular
Dose - three doses 4-6 weeks apart
      (three times annually at the 5th, 7th, and 9th months for pregnant mares)
Age - for horses over 6 months of age
Combos - none
Purpose - for respiratory disease and abortion caused by EHV 1



       (i6)

        6) Rhinomune (Pfizer) (11)

rhinomuneType - modified live vaccine, intra-muscular
Dose - 2 doses 3-4 weeks apart; then every three months
Age - for horses over 3 months of age; safe for pregnant mares after second month of             gestation
Combos - none
Purpose - for prevention of respiratory disease from EHV 1

(licensed in the USA; NOT licensed in Canada) (12)

        (i7)

    Making decisions about vaccines:

      
Unfortunately, conclusive data about the effectiveness of the available vaccines is scarce... more studies are clearly needed. Many of the studies that have been done are inconclusive due to problems with the design and analysis of the trials (13). However, it is thought that none of the currently available vaccines consistently prevent infection or disease (1, 13, 14).

       In one recent study looking at the respiratory disease defence by Calvenza, Fluvac and Prestige, very low antibody levels (considered too low to protect from infection) were detected after vaccination by any of these three vaccines. This study used two doses of vaccine, and the researchers state that the poor response may indicate that a three dose series should be used (14).

        Another section of this study looked at the abortion defence by Prodigy and Pneumabort. An interferon response to these vaccines was shown, which indicates that cell-mediated immunity may have been conferred. Basically, this means that these vaccines may protect somewhat against abortion. However, this protection was only seen after the third dose, so if the third dose is not given until the ninth month of pregnancy, protection would not result until the last few weeks of gestation. Since abortion can occur by the fifth month of pregnancy, these researchers state that vaccination may be needed earlier in pregnancy. This study also points out that the vaccines labelled for abortion give much higher antibody levels than the vaccines labelled just for respiratory disease, which may mean that the vaccines labelled for abortion should be used in all situations (14).

        The American Association of Equine Practitioners recommend giving three initial doses regardless of the manufacturer's recommendations, and then re-vaccinating weanlings, yearlings, and performance horses every 3-4 months. They recommend vaccinating pregnant mares at the fifth, seventh, and ninth months of gestation, and state that a dose at the third month of gestation is optional (15).

       None of the available studies indicate effectiveness of the current vaccines against the neurological form of the disease, although this could be due to welfare concerns about experimentally reproducing this aspect of the disease. None of the licensed vaccines are labelled to protect against the neurological form of the disease (13). However, since they may decrease spread, they may help contain the disease (1,3).

      
More efficient, long-lasting, effective vaccines for this disease are obviously needed. Vaccines that will meet these goals are currently being researched and will likely involve modified live virus vaccines. Such vaccines will likely be available in the foreseeable future (16).

       Right now, individual vaccinated animals are still susceptible to respiratory disease and abortion. However, it is true that a combination of the widespread use of intramuscular vaccines and improved management has appeared to have reduced the incidence of abortion storms caused by this virus in the United States by 75%. This is thought to be due to the vaccine reducing the amount of virus shed from the nose (13). As well, vaccination does appear to reduce the severity of clinical signs in some individual animals (14). Because of these things, vaccination should still be strongly considered.


Management


        Most horses are latently infected with equine herpesvirus, which means the virus is in their bodies but they do not have the disease. Stress may cause the virus to reactivate, allowing spread and occasionally symptoms of the disease to occur (2).

       To protect against this disease, any new horses or horses returning to the property should be quarantined for 3-4 weeks before being allowed to mix with the other horses, and especially before being allowed to mix with pregnant mares. As well, pregnant mares should be kept separate from the weanlings and yearlings on the property (2).

       If an outbreak of respiratory disease or abortions does occur on an individual property, affected horses should be isolated from the other horses on the property, and the entire property should be quarantined. No horse should leave the property for at least three weeks after the last sick horse has recovered (2) or for at least thirty days after the last abortion (1). Contaminated premises should be thoroughly disinfected with detergents, and aborted fetuses and fetal fluids should be disposed of in a heavy-gauge plastic bag or burned (1).

       If there is a large outbreak of disease in the area, there are suggested guidelines for horse owners to follow. Ideally, all barns in the area should introduce footbaths for people entering and departing, all dogs and other animals should be kept out of barns, and hands, barn equipment, tools, drinking bucket, and manure buckets should be sanitized between stalls. Worried owners should not transport their horses long distances to get them out of harm's way, since stress is a known trigger factor for the disease. Twice-daily temperature taking is helpful in identifying early onset. Vaccinating because of a known outbreak in the area is not advised if there was no prior vaccination against the disease, since the vaccine itself might cause temperature fluctuations that could false diagnoses (17).


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