RESUMEN
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; REVintegrated 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 REVintegrated FWPV developed a severe disease, characterized by mortality rate of 57%. Conclusion: REV-integrated FWPV strains are more virulent in susceptible chickens than REVfree FWPV strains.
RESUMEN
Aim: To investigate molecular and evolutionary characteristics of genes of fowlpox virus (FWPV) isolates from chickens in Tanzania. Study Design: Experimental. Place and Duration of Study: Faculty of Veterinary Medicine, Sokoine University of Agriculture, Morogoro, Tanzania; between November 2011 and October 2013. Methodology: Samples of cutaneous nodular lesions were collected from featherless parts of chickens (n = 154) suspected to have fowl pox in 14 regions of Tanzania followed by virus isolation, DNA extraction, polymerase chain reaction (PCR) amplification of the P4b gene, gel electrophoresis of PCR products, purification of PCR products, sequencing of purified PCR products and finally analysis of sequence data using standard procedures. Results: The disease was confirmed in 12 regions, out of 154 investigated samples 66 (42.86%) were found to contain FWPV, indicating that the 66 chickens from which the samples were collected had fowl pox as a result FWPV infection. Sequence analysis revealed that the Tanzanian FWPV isolates were 99.65 – 100% identical to each other and 99 – 100% identical to several published sequences of FWPV isolates from various countries in different continents of the world, including Europe and Asia. Phylogenetic analysis revealed that all Tanzanian isolates belong to clade A, subclade A1. Conclusion: Based on the findings of this study it is concluded that currently fowl pox is prevalent in several regions of Tanzania, caused by FWPVs which are genetically and phylogenetically closely related. However, these findings do not rule out the possibility of existence of genetic divergence among FWPVs currently prevalent in Tanzania. In order to rule out or detect genetic divergence (if any) among FWPVs currently prevalent in the country, other studies aimed at investigating molecular and evolutionary characteristics of genes in other genomic regions are highly recommended.
RESUMEN
Aim: To investigate integration of reticuloendotheliosis virus (REV) in the Tanzanian fowlpox virus (FWPV) field isolates, and the imported commercial fowl pox vaccines currently used in the country. Study Design: Experimental. Place and Duration of Study: Faculty of Veterinary Medicine, Sokoine University of Agriculture, Morogoro, Tanzania; between June 2012 and October 2013. Methodology: Fifty five samples of FWPV isolates from naturally infected chickens, and two isolates of FWPV from samples of the imported commercial fowl pox vaccines were analyzed for integration of REV envelope (env) gene and REV 5'long terminal repeat (5'LTR). The study involved polymerase chain reaction (PCR) amplification of FWPV P4b gene, REV env gene, and REV 5'LTR; agarose gel electrophoresis of PCR products, purification of PCR products, sequencing of the purified PCR products, and sequence analysis using standard procedures. Results: Out of 55 analyzed field isolates 53 (96.36%) were found to have REV inserts. Most of them [38 (69.09%)] contained both REV env gene and REV 5'LTR inserts, 10 (18.18%) contained inserts of REV env gene only, and 5 (9.09%) contained inserts of REV 5'LTR only. Two isolates (3.64%) were found to be integrated with neither REV env gene nor REV 5'LTR. None of the screened FWPV isolates from the imported commercial vaccines was found to have REV inserts. Sequence analysis revealed that genomic fragments of REV integrated in the Tanzanian FWPV isolate were closely related (99– 100% identity) to REV sequences integrated in FWPV isolates from other countries. Conclusion: Currently there is a heterogeneous population of FWPV in Tanzania comprising of REV-integrated FWPV strains and REV-free FWPV strains. Since strain(s) of REV-integrated FWPV are more virulent than strain(s) of REV-free FWPV, further studies on the REV-integrated Tanzania FWPV isolates aiming at obtaining the appropriate isolate for development of autogenous fowl pox vaccine are highly recommended.