Evaluation of Virulence of Tanzanian Strains of Fowlpox and Pigeonpox Viruses in Chickens

Aim: To evaluate the virulence characteristics of recently isolated Tanzanian strains of fowlpox virus (FWPV) and pigeonpox virus (PGPV) in chickens.

Study Design: Experimental.

Place and Duration of Study: Faculty of Veterinary Medicine, Sokoine University of Agriculture, Morogoro, Tanzania; between January 2015 and April 2015.

Methodology: Ten-day embryonated chicken eggs were used for In ovo evaluation. The eggs were randomly grouped into four groups (I, II, III, and IV) of 5 eggs each. Each egg in group I, II, and III was inoculated with 0.1 ml of 106 EID50/0.1 ml of reticuloendotheliosis virus (REV)-free FWPV inoculum; REV-integrated FWPV inoculum; and PGPV inoculum; respectively, through chorioallantoic membranes (CAMs). Group IV eggs served as control. All eggs were incubated at 37ºC for 7 days, thereafter CAMs and chicken embryos were examined for gross pathological changes. One hundred and forty chicks were used for In vivo evaluation. At 26 days of age the chicks were randomly grouped into four groups (I, II, III, and IV) of 35 chicks each. Each chicken in group I, II, and III was inoculated with 0.1 ml of 106 EID50/0.1 ml of REV-free FWPV inoculum; REV-integrated FWPV inoculum; and PGPV inoculum; respectively, subcutaneously. Chickens in group IV served as control. Thereafter from day zero to day 28 post-inoculation, the chickens were examined for development of clinical signs and deaths; followed by necropsy of dead chickens and examination of samples of cutaneous nodular lesions from chickens inoculated with REV-free FWPV or REV-integrated FWPV for the presence of FWPV by using standard procedures.

Results: Extensive pock lesions and severe haemorrhages were evident on CAMs and embryos, respectively, of eggs inoculated with REV-integrated FWPV. Chickens inoculated with REV-integrated FWPV developed a severe disease, characterized by mortality rate of 57%.

Conclusion: REV-integrated FWPV strains are more virulent in susceptible chickens than REV-free FWPV strains.