Fowl pox is an economically
important disease of poultry because it leads to a drop in egg production and
to mortality. Fowl pox is a slowly spreading disease characterised by the
development of:
- - Discrete nodular proliferative skin lesions on the non-feathered parts of the body (cutaneous form) or
- - Fibrino-cerotic and proliferative lesions in the mucous membrane of the upper presiratory tract, mouth and oesophagus (diptheric form).
Transmision
Because of its genetic make up
and inherent stability, fowl pox virus (FPV) can persist in the poultry house
and become a source of infection for suspectible future flocks. The increased
frequency of the disease is perhaps due to the closer confinement of chickens,
especially in multiple-age complexes. Such conditions provide opportunities for
the transmission of disease directly from bird to bird as well as in the air.
High poultry densities and dirty house increase the chances of spreading the
disease.
Types of vaccines
Live virus vaccines are used for
the immunisation of birds against fowl pox. These contain a minimum
concentration of 10 EID/ml to establish a satisfactory take and good immunity,
Fowl pox and pigeon pox virus
vaccines labelled ‘chick embryo origin’ are prepared from chorio-allantoic
membrane. Fowl pox virus vaccine labelled ‘tissue culture origin’ is prepared
frominfected chicken embryo fibroblas culture. If fowl pox appears in a flock
in an initial outbreak and only a few birds are affected, the remaining birds
should be vaccinated.
The ‘chick embryo origin’ vaccine
contains live fowl pox virus capable of producing serious disease in a flock if
it used incorrectly.
Fowl pox virus vaccine is
commonly applied by the wing web method to 4 week old chickens and to pullets
about 1-2 months before the expected onset of lay. This vaccine must not be
used for hens already laying.
Attenuated fowl pox virus
vaccines of cell culture origin can be used effectively on chicks as young as
day-old, sometime in combination with Marek’s disease vaccine.
Pigeon pox vaccine contains live,
non-attenuated, naturally occuring virus form pigeon. The virus is less
pathogenic for chickens. The vaccine may be applied by the wing web method and
can be used in chickens of any age. It is usually administered to chicks at 4
weeks of age or about one month before the onset lay.
A case study
On a breeder farm, severe fowl
pox occurred in a flock of grower at 6 weeks of age. The birds had not been
vaccinated and so the infection spread rapidly through the flock. The lesions
were mainly on the non-feathered parts of the legs and there were a few cases
on the face. Though there was no mortality, the disease disturbed the scheduled
operation for the flock. Virucidal spray, antibiotics and additional vitamins
were measures taken to control the outbreak and within 6 weeks, almost all the
birds recovered with desquamation of the scales of the lesions (Figure 1, 2 and
3)
For the next flock, pigeon pox
vaccine was used subcutaneously at 18 day of age. Only 9 days later, the first
sign of pox were noticed, with lesions similar to the previous batch. Clearly,
the birds were in the incubation period when the pigeon pox vaccine was
administered. For the next flock, the pigeon
pox vaccine was given on day 13. Symptoms of fowl pox were observed, but not
until week 5 and only in a mild form. It should be noted that the
growing birds were raised adjacent to a layer operation. The layers were
vaccinated against fowl pox in weeks 7 and 13.
From this study, it appears that pigeon pox
vaccine offers potential as a tool for the control of fowl pox.
