Thursday, May 19, 2011

EHV-1 vaccination

The question of the day seems to be about vaccination and EHV-1.  Here is my opinion:
There are two types of EHV-1 virus.  The first is the wild type EHV-1, which causes upper respiratory disease, abortion, and rarely, neurologic disease. The second is  neuropathogenic EHV-1, which is the virus identified in horses from the Ogden event.  This type has a genetic mutation that makes it much better at attacking the central nervous system, and therefore much more likely to cause neurologic disease, or EHVM (equine herpes virus myeloencephalitis).

 There is no vaccine known to protect against  EHVM.

The EHV-1 vaccines currently on the market have been shown to decrease the incidence of disease and the severity of signs in horses that get sick with wild type EHV-1.  There may be some cross-protection with these vaccines against infection with neuropathogenic EHV-1, but only if the horse is vaccinated at least 2 weeks prior to exposure to the neuropathogenic EHV-1, and even then this protection has not been proven.  Many horses currently clinically ill with EHVM were vaccinated against wild type EHV-1. Unfortunately, the interaction of the vaccine reaction and the neuropathogenic EHV-1 is very complex and not well understood.  If the vaccine is administered very close in time to exposure to the neuropathogenic EHV-1, vaccination may actually be harmful.

Based on this, here is my recommendation:
If there is any risk that your horse may have been exposed to neuropathogenic EHV-1 (the virus responsible for the current outbreak) do NOT vaccinate your horse. 
If there is NO risk that your horse has been exposed, and your horse is being housed in a closed facility so that there will be no new horses introduced within the next 2 weeks,  and your horse has not received a flurhino shot this year, then it is safe to proceed with routine spring vaccination.

I believe that education is the key to evolution. I believe that animals are the key to compassion. I believe the learning never stops.


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