Maryland Clears Annual Herpes Epidemic
|Herpes Query: Incubation Periods and Why Did Maryland & Virginia Responses Differ So?
The mid-Atlantic herpes crises ended in March, but our readers questions still linger.
Q: Isn't the incubation period for for EHV-1 (equine herpes) up to 17 days? If so, why did Maryland take hold orders off and release horses before the incubation period was over, whereas Virginia did not?
A: Maryland State Vet, Guy Hohenhaus, DVM, responds:
One must be careful when comparing the processes used by different states to manage similar, but not identical situations. States are sovereign entities, which have the right to manage most internal aff airs as they see their interests. Given that laws, regulations and authority vary between 2 states, and diff erent individuals make up the response management teams, it is no surprise that there would be some diff erences in approach. The real question you raise is to the reasonableness of the Maryland response to EHV-1.
The 17 day incubation time you cite is an extreme outside range, most being within a week or less and incubation to clinical disease. We are using test methodologies which detect current infection, not current disease or evidence of past disease. Th e time frames on this are thus much shorter. Only a fraction of infections lead to clinical disease, so using that yardstick could lead to missed or "silent" infections.
If an animal was exposed , there would be PCR evidence of that infection within a few days, but certainly within 7 days. We focused the testing and observation on the higher risk animals, those which had Leesburg exposure, rather than secondary contacts. If those animals had no evidence of the virus after 7 days away from Leesburg, there is a very high probability they were only exposed, but NOT infected. No infection=no EHV-1 disease; no EHV-1 disease =no transmission to others.
Thus, with a negative PCR 7+ days post Leesburg, we were very confi dent that a discharged EMC patient had not brought the virus home and the property could be released.
Additionally, if there was any evidence of fever, unexplained respiratory disease or neurologic disease on the property from the time the patient returned, that protocol cannot be employed, hence, 2 farms remained restricted longer.
Lastly, the best measure of success or failure is the absence or presence of new cases traced back to the original outbreak (outcomes). I would certainly expect that had our approach been overly "lenient," that we would have seen some evidence of sick EHV-1 horses by well before the 17 day post discharge time frame. We do not. We continue to receive reports from veterinarians, but to date, none has yielded a case of EHV-1. Th e outcomes experience in VA has been quite similar, with only very limited disease spread beyond the EMC, as evidenced by very low rates of infection in discharged patients.
Our goal is the same as Virginia's - to control this outbreak as quickly and eff ectively as possible, while minimizing the necessary negative impacts on the industry. We take our duty to protect the industry very seriously and that duty includes doing everything necessary, lawful and proper to respond. We also subscribe the Hippocratic notion of "First do no harm," in that we have determined that for purposes of protecting Maryland horses, anything additional would be unnecessary, a burden on the industry and ultimately harmful.
Remember, our authority is limited to that which tends to control livestock diseases. That said, individuals, businesses and other entities are free to make their own choices about restricting activities. Please consult with our staff in advance to determine the best way to accomplish the goal, which is motivating the decision to restrict activities.
To understand more about the annual Maryland herpes crises, please Visit equiery.com
© The Equiery 2010