infection is an uncommon skin condition that usually affects
cats which enjoy hunting small rodents. The skin lesions
resulting from infection usually disappear on their own
with time. However, when a cat's immune system is suppressed
by medicines or illness, then the infection can develop
in a severe and generalised way.
are a variety of pox viruses that can infect a number of
different animal species. Although cowpox virus infects
cattle, cattle are rarely implicated as a source of infection
for cats. Cowpox infection has been reported in domestic
cats and cheetahs, rodents, occasionally humans, and infrequently,
in recent years, cattle, dogs, elephants and a foal. Cats
infected with cowpox virus are usually avid hunters that
come into contact with prey, especially the bank vole (Clethrionomys
glareolus), field vole (Microtus agrestis)
and the wood mouse (Apodemus sylvaticus) which
are known to carry the infection. The infection can occasionally
be found in the house mouse (Mus domesticus). Such
rodents don't usually show any signs of infections. The
prevalence of cowpox infection in cats is considered to
be relatively low but varies geographically. There is no age, breed or sex predilection
for infection and clinical disease.
disorder is reported throughout western countries in Europe,
including Austria, Belgium, France, Germany, The Netherlands,
and Norway and western states in the former Soviet Union.
In the UK infection is most commonly seen from July to November
when rodents are most common. Infection may also be reported
throughout the remainder of the year.
with feline cowpox virus infection: Lesions on
head with focal encrusted plaques
secondary cowpox virus lesion. The hair has been
clipped to show the typical shape of a plaque lesion
with crust removed
cowpox infection with secondary lesions on the
limbs and tail, with focal crusted plaques
courtesy of Aiden Foster
Cowpox virus enters the skin through a bite wound from a rodent
usually on the cat's head, neck or limb. The viral infection
becomes apparent after a few days as a small nodule with
ulceration (broken and infected skin). This may be followed
by secondary bacterial infection, producing cellulitis (inflamed
red and sore skin) and an abscess may form. Once inside
the cat's body the virus will multiply in the lungs, nasal
passages and various lymphoid tissues for about five days
producing what is know as a transient systemic virus infection
or viraemia. The mouth, nasal passages, lungs and gut may
be affected with oral and gastrointestinal ulceration, nasal
discharge, pneumonia and diarrhoea. Usually the signs of
viraemia are mild and include serous (clear) to mucopurulent
(containing mucus and pus) discharge, pyrexia (high body
temperature), depression and a poor appetite.
initial infection, 10 days to several weeks later, there
may be numerous skin lesions consisting of oval to circular
ulcerated papules (small bumps) and plaques (flat areas)
up to 1 cm in size. Pruritus (itching) is not a major feature
of this disease and this may help to distinguish it from
other conditions. The plaques are usually covered with crust
material which will separate as the infection resolves.
There may be residual scarring and hair loss (alopecia).
These lesions may be observed on any part of the body.
usually resolves itself over six to eight weeks. Occasionally
the lesions can be mistaken for other skin conditions such
as eosinophilic granulomas and glucocorticoids are administered. This may lead to severe
generalised systemic infection. Concurrent infection with feline immunodeficiency virus (FIV) or feline leukaemia virus (FeLV) may affect the rate of recovery from cowpox virus
or skin samples can be used to confirm a diagnosis of cowpox
virus infection. These are used to check for the presence
of specific antibodies or the cowpox virus itself. Antibodies
are proteins found in blood that are produced by the body
in response to infection.
virus infection can be confirmed by:
A positive antibody titre (detection of sufficient numbers
of antibodies) is supportive of recent infection in at least
the previous six months. Antibodies are not cowpox specific
but indicate a pox virus infection. There are, however,
no other orthopoxviruses that infect cats in the UK. Titres
may be positive seven to 14 days after initial exposure.
Crust material taken from skin lesions and sent for analysis
to the laboratory in viral transport media or a sterile
container can be used for viral culture (growing virus in
the laboratory). It can take three to 10 days for positive
The diagnosis may also be confirmed, in many cases, with
skin samples (biopsies) especially of the generalised skin
lesions, because there are characteristic changes occurring
within the infected cells. Other causes of skin diseases
including, for example, bite wounds and skin tumours can
also be eliminated through microscopic examination of changes
in the cells.
Crust material submitted in viral transport media or a sterile
container can be examined by electron microscopy for detection
of typical pox virus particles, in many cases. This is a
quick technique compared with culture.
The crust from skin lesions can be used for detection of
orthopoxvirus DNA by a molecular technique called polymerase
chain reaction (PCR). This highly sensitive technique is
not routinely available.
The lesions usually heal without intervention within weeks
of initial infection.
Where there is secondary bacterial infection of older and
generalised lesions, broad-spectrum antibacterial therapy
can be useful.
Cats that are not eating may require hospitalisation and
intravenous fluid therapy.
There are no specific antiviral agents recommended for this
condition and response to such therapy (eg, interferons)
may be difficult to evaluate when most cases will spontaneously
Severe cases with respiratory involvement may have a poor
It is very important to avoid administration of glucocorticoid
therapy because the clinical signs may become much worse.
transmission may occur rarely but does not seem to be associated
with overt clinical signs. In general, cowpox virus infection
of humans is uncommon and its infectivity is considered
to be low. There are, however, occasional reports of human
patients who became infected after playing with an infected
cat and being scratched. These cases are usually very young
or elderly people receiving immunosuppressive therapy or
afflicted with immunosuppressive conditions, or individuals
with severe skin disease. Sadly in one case the infection
became generalised and the patient died. As a precaution
cats with suspected cowpox infection, where possible, should
be isolated from other cats and handled by people not at
risk of infection, wearing gloves and avoiding contact between
infected material and skin wounds or the eyes.
virus can survive for months to years at room temperature
and is resistant to many disinfectants, although hypochlorite-based
products should be effective.
Updated November 2008