OCCURRENCE, PATHOBIOLOGY AND DIAGNOSIS OF AVIPOXVIRUS INFECTION IN BIRDS AROUND JAMMU
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Date
2017
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Sher-e-Kashmir University of Agricultural Sciences and Technology of Jammu
Abstract
A total of 610 fowls, 998 pigeons and 70 turkey birds (April 2016 to May 2017) were screened for the Avipox infection from different parts of Jammu region. The overall prevalence of avian pox in fowl was 18.52%, 45.36% in pigeons and 57.14% in turkey birds. The mortality rate was 41.96% in young fowls, 45.36% in young pigeons, whereas 20.00% mortality was seen in adult turkeys while 100% was recorded in poults. Both cutaneous and diphtheritic forms of the disease was seen in fowl, pigeons and turkey birds. The wet form was particularly prevalent in young birds only. The lesions were conspicuous by presence of nodular or pock lesions on skin. However, the wet form was not easily discernible, especially when unaccompanied by skin lesions which otherwise prompted a closer inquiry. The oral lesions in the wet form were characterized by small, slightly elevated, white opaque patches that often coalesce together to form a diphtheritic membrane. This could often extend to the upper respiratory tract and crop. A confirmatory diagnosis was made by PCR amplification by targeting a highly conserved P4b gene amongst all Avipoxvirus and also conserved across all present isolates in the study. The amplified product was detected in all samples yielding a predicted 578 bp product. Conventional diagnosis of Avipoxvirus was done by crush smear preparations which revealed red A-Type intra-cytoplasmic inclusions in epithelial cells, and proved to be a very rapid diagnostic technique from direct clinical samples. Elementary bodies (Borell body) were demonstrable arranged particularly around the periphery of the inclusions. The putative Avipoxvirus isolates from Fowlpox and Pigeonpox were also inoculated on the chorio-allantoic membrane (CAM) of 10-12 day old chicken embryonated eggs for three passage levels. The Fowlpox isolates were associated with oedema and haemorrhages in the initial passage, which developed by third passage to small, round, raised circular white lesions or ‘pocks’, of varying morphology. Whereas, with Pigeonpox isolates, pock lesions were sometimes visible from first passage itself, which developed to larger pocks with focal areas of necrosis, oedema and opaque thickening on CAM through third passage. Pathobiology of isolates showed that Fowlpox and Pigeonpox isolates readily grew on chicken embryonic CAM, with the Pigeonpox isolate showing earlier and aggravated lesions. The CAM lesions were confirmed by PCR. Histopathology was also employed to study the different skin and diphtheritic lesions from affected birds (fowl, pigeons, turkeys) and infected CAM. The underlying tissue response revealed varying degrees of hyperplasia and hypertrophy of the epithelium with associated inflammatory response. Skin and diphtheritic lesions showed inflammatory changes consisting of swollen, pale keratinocytes with vacuolated cytoplasm and eosinophilic A-type intra-cytoplasmic inclusion bodies (Bollinger body). These inclusions were very conspicuous and often filled up the entire swollen cell, resulting in its degeneration. The microscopic lesions in fowl was particularly severe in naked neck fowls with atypical connective tissue proliferation in the dermis and presence of epitheloid cell islands and deposition of large, globoid, hyalinised materials. In PGPV inoculated CAM, massive proliferation of fibroblasts, presence of epithelial cell islands containing intra-cytoplasmic eosinophilic inclusions were marked in the mesoderm. CAM lesions in Fowlpox were milder with no inclusion demonstrable in observed specimens. The PCR products of P4b gene were sequenced commercially and aligned after BLAST search from published sequences in the public library. It was observed that Fowlpox and Turkeypox isolates from Jammu were related to other Fowlpox sequences, while Pigeonpox isolate was related to other Pigeonpox sequences. Experimental infection for detection of host specificity of FWPV and PGPV isolates in reciprocal infection in fowl and pigeons were conducted in pigeon squabs, and fowl chicks showed host specificity of FWPV to fowls and PGPV to pigeons, with characteristic development of lesions. The results indicate that the FWPV and PGPV isolates differ pathobiologically and probably are different at species level. The lesions were also confirmed by PCR.
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