Vesicular Stomatitis Update
Vesicular Stomatitis(VS) is a vesicular disease caused
by a rhabdovirus affecting horses, pigs, ruminants, and
camelids. The disease may cause vesicles to form on the
mouth, hooves, dental pad, and teats. These vesicles swell
and rupture, leaving exposed raw tissue, that causes animals
to become lame and refuse food and water. The virus concentrations
in the blood are typically very low, but high concentrations
can be found in vesicular fluid and saliva. Virus particles
disappear within a week after rupture of the vesicles. Transmission
is by animal contact, fomites, such as milk machines, and
insect vectors.
There are many differential diagnoses for VS. Contact dermatitis,
such as that associated with damp conditions or chemical
bums associated with the use of chemicals may mimic VS lesions.
In pigs, swine pox is a diiferential, although these lesions
are more papular than vesicular, and are distributed widely
over the body rather than being localized to certain areas
as in VS. The primary clinical sign of biotin deficiency
involves hoof lesions, which could be confused with the
vesicular lesions involving the hoof in VS. Finally, the
vesicular foreign animal diseases (FAD), such as foot and
mouth disease and swine vesicular disease, are important
diseases to include on a differential list.
The classification of this disease as a FAD is debatable,
because there is an endemic stain on the island off the
coast of Georgia.
It is still of regulatory concern because the clinical signs
mimic those of foot and mouth disease, and other vesicular
diseases. VS also causes significant economic loss to
affected herds due to poor weight gain, poor milk production,
and lameness, especially associated with secondary infection
of hoof lesions. The high morbidity (up to 80%) also contributes
to the economic loss. A VS outbreak occurred in the western
United States
from May through December of 1995. The last occurrence of
VS in the southwestern United
States was in 1985 and
a cyclic pattern of recurrence every eight to ten years
has been recognized.
Confirmed cases in the recent outbreak totaled 367, out
of 1,162 investigations, and involved horses, pigs, cattle,
sheep goats, and llamas. Several cases in people were also
confirmed. Clinical signs in affected people working with
affected animals consisted of an influenza-like illness
with a few people developing mouth lesions. Confirmation
of infection at the NVSL was by virus isolation alone, or
by complement fixation and/or serum neutralization in combination
with clinical signs. In the most recent US
outbreak, the first confirmed case was in New
Mexico in May 1995; the last confirmed
case was reported on November 30, 1995; the outbreak was declared over
on January 15,
1996. States in which there were confirmed cases
were New Mexico,
Colorado,
Wyoming, Utah,
Texas, and
Arizona. There
are currently no special interstate restrictions in place
regarding VS. Some countries still have trade restrictions
in place in response to the 1995 VS outbreak, which are
expected to be removed over the next 12 months. Certain
countries had trade restrictions in place regarding VS before
the 1995 outbreak occurred and these restrictions are not
expected to change. A published report documenting the
outbreak is expected to appear in JAVMA within the next
year.
In Indiana,
investigations of suspect VS infection of horses with oral
ulcers have most frequently revealed oral ulcers associated
with penetration of the oral mucosa by plant awns. We have
as yet not determined why the incidence of this occurrence
has increased this year, but are investigating it.
- Christine Yarger, Class of 1996
- Edited by H.L.Thacker,DVM,PhD
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