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Roughly 232 avian species
in 23 orders have been reported to acquire a natural poxvirus infection. It is
likely that many more species are susceptible to avipoxviruses. Many of these
reported avian species belong to the order of Passeriformes.9
Poxvirus infections are
reportedly particularly common in canaries (Serinus canarius)
and other Fringillidae.32 Of clinical importance to the avian practitioner is canary pox.5
The disease is mainly
transmitted from latently infected birds by bloodsucking insects, including
mosquitoes and red mites.57 Transmission can also occur through
direct contact with an infected bird or indirect contact with contaminated objects
such as gloves or hands. Because poxviruses are not capable of penetrating
intact epithelium, they must enter the skin through abrasions (eg, caused by
cannibalism, territorial behavior, feather picking, aggressive preening or
handling and consumption of scabs).99 Theoretically, pox infections can
occur during the whole year. However, most outbreaks are diagnosed in the late summer
and autumn, because of the prevalence of mosquitoes. Birds of all ages can
develop disease, but young birds (older than 3 weeks) are especially
susceptible.
Clinical
Disease
The three different
clinically recognized symptoms are the cutaneous or external form, the internal
diphtheroid form and the septicemic form.59 Where as
finches often develop
the cutaneous form, canaries will often develop the internal diphtheroid or
septicemic form, making pox infections in canaries a disease with a high
mortality.
Cutaneous Form
This form is localized on
the toes and legs and around the eyes, nares and beak .These unfeathered body regions are easily accessible
to blood-sucking insects. As the lesions progress they develop from papules of
roughly 2 to 4 mm diameter to vesicles that open spontaneously, dry out and
then become crusts. Tumor-like pox lesions that do not develop vesicles and crusts
have also been described.The contaminated
birds rub their eyes and beaks against the perches. They also may pick the
lesions on their legs until they start bleeding. The lesions can be treated
locally with iodine, but often the bird will lose a nail or even a digit. The mortality
rate, however, is low in this form and the lesions will heal spontaneously
after 3 to 4
weeks.17
Diphtheroid Form
Lesions occur on the mucosa
of the tongue, pharynx and larynx. The fibrinous lesions are gray to brown and
caseous.51 In severe cases birds have difficulty swallowing or exhibit dyspnea. Note: The birds
should be treated at the same time through the drinking water and through the
food.
Septicemic Form
This is the predominant
form diagnosed in canaries. Birds show severe dyspnea and become apathetic and cyanotic.
They are unable to eat or drink, and mortality can be as high as 90 to 100%. In
contrast to other disorders, such as tracheal mites or bacterial infections of
the upper respiratory system, the breathing is silent without clicking or
growling sounds.
Diagnosis
Antemortem in-house
cytology and postmortem histopathology often reveal intracytoplasmic inclusions
(Bollinger bodies) in epithelial cells.59 Macroscopic
post-mortem findings
are often unspectacular .
Prophylaxis
Attenuated live vaccinesc
that are applied using the wingwebmethod are commercially available for canaries and
crossbreeds. A whitish
swelling or scab at the injection site observed 8 to 10 days post-vaccination
indicates a successful vaccination. Protection lasts approximately 6 months.
Vaccination should be performed early in the year, prior to mosquito season.
Solid immunity develops 2 to 4 weeks after vaccination. Fledglings should be at
east 4 weeks old. Vaccination can be repeated without any risk if vaccination
status is unknown. A new needle should be used for every bird so that
blood-borne diseases, including poxvirus, are not transmitted. Vaccinated birds
should be separate from newly acquired non-vaccinated birds.17
Treatment
There is no therapy for the
septicemic poxvirus infection. Only a preventive vaccination offers solid
protection. In case of an outbreak, the following measures should be taken:
separate diseased birds (gasping birds and birds with cutaneous lesions),
consider emergency vaccination and begin antimicrobial therapy against secondary
bacterial and fungal infections. Multivitaminm (especially vitamins A and C)
supplementation may help with epithelial turnover and immune system support. Iodine
should be applied locally to cutaneous and mucosal pox lesions. Non-steroidal
antibiotic eye ointment may be applied. Access to blood-sucking insects must be
prevented, and cages and perches much be thoroughly disinfected. An emergency
vaccination in the face of an outbreak is controversial. This may result in the
recombination between field and vaccine virus strains, inducing severe disease
in the entire flock.51 handling of the birds can also induce skin abrasions.
Differential
Diagnoses
The following should be
considered as differentials for the cutaneous form of poxvirus infection:
bacterial and mycotic dermatitis, Knemidokoptes mites,
fiber constriction and
conjunctivitis. Trichomonas and Candida should
be considered as differentials for the diphtheroid form, and for the septicemic
form, consider bacterial upper respiratory disease, Atoxoplasma,
Trichomonas, Sternostoma,
Chlamydophila, Aspergillus, Syngamus and PMV infections.
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