Fowl pox is a highly contagious viral disease of
chickens and turkeys caused by a DNA virus of the genus Avipoxvirus of the family Poxviridae.
It is one of the oldest known viral disease of chickens and is endemic in Kenya
and most developing countries. The disease is slow-spreading and is characterized
by low mortality (1%- 5%), formation of proliferative lesions and scabs on the skin
(cutaneous/dry form), and diphtheritic lesions in the upper parts of the
digestive and respiratory tracts (diphtheritic/wet form) of chickens.
Risk
factors
Presence of a naive or highly susceptible chicken population
Introduction of an infected incubatory bird
Poor biosecurity with free mingling of wild birds
and chickens
The disease is spread by mosquitoes and scabs from
infected birds. Mosquitoes (Culex and
Aedes species) can harbor the virus
for more than a month after feeding on an infected bird. Fighting among birds,
cannibalism and the use of feed and water utensils or other equipment that
might scratch or injure the birds increase the risk of spread.
Diphtheritic
form: coughing and gasping, marked drop in egg production
in the layers and retarded weight gain in broiler chicken. Grossly, yellow
caseous plugs obstructing the larynx and trachea. This form of the disease
maybe confused clinically with Infectious Laryngotracheitis because of the
coughing and gasping respiration.
Cutaneous
form: Wart-like proliferative nodular lesions on the combs and wattles, base of the
beak, on the outer surface of the eyelids and other featherless areas of the
body. There is scab formation on the eye lesions. Chickens with eye lesions (ocular
form) may show no other lesions elsewhere on the body, making it easily be
confused with Ammonia Burns. Eye lesions, if extensive, may destroy the eyeball
and cause blindness.
Presence of typical pox lesions on featherless areas
of the body of affected chickens is practically diagnostic. Demonstration of
large intracytoplasmic inclusion bodies (Bollinger bodies) in Giemsa or H&E
stained thin sections of the cutaneous and diphtheritic lesions is confirmatory.
Eye lesions: Prompt removal of the scab-part of the lesion and
applying freshly prepared 15% Argyrol solution to the infected area may save
the eyeball.
Since there is no satisfactory treatment for Fowl
pox, it is best to prevent the disease by vaccination. An annual vaccination
program is advisable on poultry farms and in localities where fowl-pox has
already made an appearance. Vaccination is not a treatment for sick birds.
Chickens are usually vaccinated either at 8 to 12 weeks of age or at about one
month before the birds are expected to come into egg production. Vaccination
should be done when the chickens are in good health.
Control
- Eliminate standing water and all mosquito habitats to control mosquitoes.
- Isolate or cull infected birds to remove the source of the virus.
- Disinfect feeders, waterers, birdbaths and cages with a 10% bleach solution.
Dr.
Moses Bwana
Post-grad at the University of Nairobi,
Applied Microbiology, Virology Option
Cell: +254729246187
Email: bwanamoses@gmail.com
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