EQUINE | Equine Disease Quarterly
and pathologic findings, is sporadically seen in adult
horses without recent administration of an equine
origin biologic. These “non-biologic” cases tend to
mostly occur between June and November and can
occur in small outbreaks that span a few weeks.
Non-biologic cases seem to occur most commonly
on broodmare farms. The seasonal incidence of the
non-biologic cases suggests the possibility of insect
transmission of parvovirus in these “non-biologic”
cases.
Clinically affected horses with Theiler’s disease
frequently have both neurologic signs (hepatic
encephalopathy: head pressing, stumbling, blindness)
and jaundice (yellow gums and eyes). Once the
neurologic signs are noted, there is a rapid progression
to death in approximately 70 percent of the cases.
Horses that receive supportive therapy and survive for
five days after the onset of fulminant disease generally
recover and have no long-term effects.
Another recently discovered virus that causes
liver disease in horses is non-primate hepacivirus
(NPHV). NPHV is genetically the closest homolog of
human hepatitis C virus (HCV) discovered to date.
Experimental horse infections consistently result
in biochemical and histopathologic evidence of
hepatitis, but the disease is mild and clinical signs are
either absent or very mild in recently infected horses.
NPHV and equine parvovirus are present in some
healthy horses, indicating that horses can become
healthy carriers of these viruses.
The USDA Center for Veterinary Biologics has issued a
notice that all licensed equine blood products have to
test free of equine parvovirus and NPHV. This should
improve horse health by eliminating most of the blood
product-associated cases of hepatitis. Non-biologic
associated cases will likely continue to occur until
natural means of virus transmission are determined
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and necessary control methods implemented.
CONTACT: Thomas J. Divers, Joy E. Tomlinson and
Gerlinde R. Van de Walle, [email protected], (607)
253-3100, College of Veterinary Medicine, Cornell
University, Ithaca, NY
Importance of Protecting your Horse against
Eastern Equine Encephalomyelitis and West
Nile Encephalitis
The two most frequently encountered causes of
equine encephalitis or equine encephalomyelitis in
North America are Eastern Equine Encephalomyelitis
(EEE) and West Nile Encephalitis (WNE) viruses. Both
are mosquito-borne and neurotropic. The respective
viruses are not restricted to equids in terms of their
host range; each can be transmitted to humans and
certain other mammalian and avian species. Both
diseases are a source of concern for the equine
industry not only from the potentially life-threatening
consequences of either infection, but also from the
economic losses involved.
Eastern equine encephalomyelitis poses an annual
threat to equids in the Gulf and Atlantic coastal states
and the Great Lakes region, extending in certain
years as far north as eastern Canada. It is occasionally
recorded in some inland states such as Arkansas,
Oklahoma, Tennessee, Kentucky, and Iowa. Evidence
of EEE activity is most often reported in Florida, in
which it has been confirmed as early as January, as
recorded in 2018. Over the past 15 years, the yearly
incidence of EEE cases in equids has ranged from 60
(2011) to 712 (2003), with an annual average of 206
cases. In 2017, 86 cases of the disease were reported
in 13 states.
In temperate regions, transmission of EEE virus is
• Equine Health Update •