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).
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.