PATHOLOGICAL AND MOLECULAR DIAGNOSIS OF FOWL POX IN BACKYARD CHICKEN
Loading...
![Thumbnail Image](assets/images/Item.jpg)
Files
Date
2023-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
In the present study, fowl pox was diagnosed in 119 birds out of 128 suspected
backyard chicken with an overall occurrence of 92.96% based on gross lesions,
histopathology, ultrastructural and molecular studies.
Fowl pox in backyard chicken was recorded in eight coastal districts of Andhra
Pradesh and the highest occurrence of fowl pox was found in Krishna district (100%),
followed by West Godavari (96.8%), Bapatla (93.75%), Konaseema (92.3%), Kakinada
(90%), Prakasam (88.8% ), Anakapalli (75%) and Visakhapatnam (66.6%).
The highest occurrence of fowl pox in the present study was in the winter season
(47.9%), followed by summer (29.4%), and rainy seasons (22.7%). Occurrence of
cutaneous form of fowl pox in backyard chicken was mostly seen in chicks of ≤ 9
weeks of age (97.10%), followed by adults aged > 28 weeks (92.30%) and growers
aged 9-28 weeks (80.0%) whereas diphtheritic form of fowl pox was mostly noticed in
chicks followed by growers and mortality rate was also highest in chicks when
compared to others.
Both cutaneous (85.71%) and diphtheritic forms (14.28%), of fowl pox was
recorded in the present study. Among 102 cases of cutaneous form, highest occurrence
of pock lesions were observed at the eye lids (33.4%), followed by beak (25.5%), corner
of the mouth (11.77%), shank region (8.824%), feet (6.87%), comb and wattles
(4.95%), at the wings (3.93%), cloacal aperture (2.95%) and ventral aspect of abdomen
(1.97%). The highest occurrence of diphtheritic form was observed on mucous
membrane of the laryngeal orifice (29.42%), trachea (29.42%), oral cavity (23.53%) and
oesophageal tract (17.65%) in a total of 17 cases.
Backyard chicken affected with fowl pox exhibited clinical signs like stunted
growth, emaciation and decline in egg production in laying hens. Birds affected with
cutaneous form of fowl pox revealed alopecia, ocular discharges, closure of eyes,
blepharitis and blindness. Respiratory signs like nasal discharges, gasping and other
clinical signs like swelling of infraorbital sinuses swelling of head, difficulty in
swallowing and asphyxia were also noticed.
Grossly, cutaneous form of fowl pox revealed pock lesions ranging from initial
small erosions to large developed nodular, proliferative wart like projections on eyelids,
beak, corner of mouth, comb, wattles, wings, shank region and feet, whereas nodular to
purulent, cheesy patches at laryngeal orifice, trachea, oral cavity and oesophageal tract
were noticed in diphtheritic form.
In the present study, pock lesions from both cutaneous and diphtheritic forms of
fowl pox cases revealed characteristic histopathological features. Majority of tissue
sections from cutaneous form of fowl pox (25.5%) revealed severe congestion of blood
vessels and haemorrhages in epidermis and dermis, ballooning degeneration of
epidermal cells, hyperplasia of epidermis (acanthosis) in focal areas along with presence
of medium to large singular or multiple intracytoplasmic eosinophilic inclusion bodies
(Bollinger bodies).
Degenerative changes and necrosis of the cells of uropygial glands and feather
follicles were also seen in addition to numerous Bollinger bodies in 56 (54.9%) cases
whereas liquefactive necrosis of epidermal cells, microabscess development and severe
infiltration of heterophils was noticed in 18 (17.64%) cases. Proliferative wart like
lesions (1.96%) exhibited finger like projections of epithelium due to severe hyperplasia
and connective tissue proliferation. Superficial mineralised and necrotic layers were
observed over the hyperplastic epidermal cells in large firm crusted nodules whereas
increased fibrous connective tissue, increased collagen was noticed in epidermis and
dermis in healing lesions.
Microscopically, all the diphtheritic pock lesions revealed characteristic
changes like severe congestion of blood vessels, haemorrhages and degeneration of
epithelium of mucous membranes of oral cavity, tongue, oesophagus, trachea and
laryngeal orifice along with presence of small to medium solid or ring shaped Bollinger
bodies. Severe necrosis of mucosal cells was evident and was covered by haemorrhagic,
fibrinoheterophilic exudate in purulent pock lesions. Diffuse loss of cilia from lining
epithelium and disorientation of ciliated epithelium in focal areas in addition to
proliferation of epithelial cells in mucosa of trachea was noticed. Demonstration of
characteristic intracytoplasmic inclusion bodies was performed by Lendrum’s phloxine
tartrazine stain that revealed both solid and lipid associated ring shaped inclusion bodies
in skin and oesophageal sections.
Four cutaneous pock samples collected from fowl pox affected birds were
subjected to transmission electron microscopy and all the sections revealed medium to
large intracytoplasmic inclusions in epidermal cells. A few affected cells revealed
filaments and tonofibrils arranged as loose bundles in cytoplasm whereas various stages
of viral particles were observed in cytoplasm of epithelial cells in all the sections.
Majority of cells revealed degenerative changes in mitochondria like swelling of the
organelle, partial loss of cristae and coalesced mitochondria forming large
mitochondrion along with incorporated incomplete virions as an earliest evidence of
inclusion body formation. Immature viral particles contained eccentric nucleoid
surrounded by halo whereas mature viral particles contained typical inner dumbbell
shaped core and two lateral bodies. Characteristic large inclusions contained more
virions at the periphery than in central zone. Shedding of extra coats of the mature
virions as the broken segments of inner membranes of inclusions resulted in rodlets.
In the present study, inoculation of 10 day old embryonated chicken eggs with
skin pock suspension resulted in death of embryo between 5 to 7 days of post
inoculation. Grossly, the CAM showed severe congestion, haemorrhages, edema and
necrosis in first, second and third passages respectively. Microscopically, congestion of
blood vessels in ectoderm, edema in mesoderm and haemorrhages in mesoderm was
observed on the CAM in the first, second and third passages respectively.
Molecular diagnosis of fowl pox disease in skin, oesophagus, trachea and virus
propagated CAM tissue samples by using primers specific for P4b gene of fowl pox
virus obtained a desired amplicon of 578bp. Nucleotide sequencing and phylogenetic
analysis of four cutaneous fowl pox samples revealed that they were in close relation
with the FPV isolates from Singapore, North America and USA (KY464130,
MH175285 and KC017961 with an identity of 97.28%, 97.21% and 97.16%
respectively) when compared to FPVs isolated from Portugal, Brazil, Jammu and
Kashmir and India (KM974727, KX863706, MF496042 and HM481406 respectively
with an identity of 96.66% to 96.86%).
In the present study fowl pox was diagnosed based on the gross, histopathology,
electron microscopy and molecular studies in backyard chicken with an overall
occurrence as 92.96%.