Centers for Epidemiology and Animal Health
Equine Herpes Virus
Concern has been voiced within the U.S. horse industry
that the neurologic (also known as
myeloencephalopathic or paralytic) form of equine
herpes virus type-1 (EHV-1) may be increasing in
prevalence and/or morbidity and mortality. This concern
is based on an increased number of neurologic cases
reported in recent years, as well as the occurrence of
several high profile outbreaks of neurologic EHV-1
affecting several sectors of the U.S. equine industry.
These outbreaks are the first reported EHV-1 outbreaks
at large facilities or events involving neurologic cases
that resulted in euthanasia. At least part of the
increased interest and concern are related to these
highly publicized events. It is possible that reporting has
increased, as opposed to an actual increase in number
and severity of cases; more data is needed to determine
the actual situation.
Profile of Disease Emergence
The question of whether neurologic EHV-1 is emerging
can be evaluated using standard definitions of disease
emergence. A disease is considered to be “emerging”
when it meets at least one of three general criteria. The
first is when a disease is identified for the first time.
Recent examples of this would be SARS or Ebola.
Another criterion is when a disease evolves and
changes in virulence, host capable of being infected or
other pathogen behavior. The monkey pox outbreak in
prairie dogs in 2003 in the United States would be an
example of this type of disease emergence, as a new
species was infected. The third criterion is a change in
disease geographic range or incidence within a range.
The appearance of West Nile virus in the United States
in 1999 is a good