Pathogenesis Of Velogenic Newcastle Disease Virus Infection In Cyclophosphamide Treated Chickens

ABSTRACT

The susceptibility, clinical signs, distribution and persistence of lesions of a local Nigeria

velogenic Newcastle disease virus (VNDV) strain (KUDU 113) were studied in 6 week old

chickens bursectomised by treatment with cyclophosphamide on days 2, 3 and 4 post-hatch.

Following intramuscular inoculation, depression, muscle tremor, greenish diarrhea and paralysis

were observed in the bursectomised infected (BI) chickens while severe depression, whitish to

greenish diarrhea, listlessness, hunched posture, tremors, paralysis and torticollis were observed

in the non-bursectomised infected (NBI) chickens. Morbidity was 97.5% in the BI chickens and

100% in NBI chickens, while mortality was 90% in the BI chicken and 100% in the NBI

chickens. Weight loss was highly significant (p< 0.05) in both BI and NBI chickens especially

on day 6 post inoculation (PI). The post mortem examination showed atrophy of the bursa from

day 5 to 9 PI, but not in the other lymphoid organs (spleen and thymus) in the BI chickens while

atrophy of all the lymphoid organs from days 4 to 9 PI, with initial enlargement of the spleen

from day 3 PI and congestion of the kidneys on day 5 and day 6 PI were observed in the NBI

chickens. Severely congested skeletal muscles were observed in the BI chickens from days 4 to 7

PI and from days 4 to 9 PI in the NBI chickens. Haemorrhages on the tips of proventricular gland

were observed in about 50% of the BI chickens necropsied from days 5 to 9 PI while all the NBI

chickens had the lesion from days 4 to 9 PI. Sharply demarcated haemorrhagic and necrotic

intestinal ulcers were observed in 3 and 4 chickens respectively of the 17 BI chickens necropsied

on day 6 PI while almost all the NBI chickens showed similar lesions from days 4 to 9 PI.

Haemorrhages of the caecal tonsil were observed in the BI chickens from days 5 to 7 PI while

same lesions were observed in all the NBI chickens from days 3 to 9 PI. Congestion in the

kidneys was observed in the NBI chickens on days 5 and 6 PI, but not in the BI chickens.

Parboiled liver lesions were observed in the NBI chickens from days 5 to 7 PI, but none was

observed in the BI chickens. Histologically, the lymphoid organs showed lymphocytic depletion

in both BI and NBI chickens.

The bursa of Fabricius, spleen, thymus and intestines were collected for virus isolation. The

bursa showed positive HA spot test on day 3 PI in BI chickens and on day 7 PI in NBI chickens.

The spleen did not show positive spot test in this experiment. The thymus showed positive spot

test on days 3 and 7 PI in both BI and NBI chickens and also on day 5 PI in the NBI chickens.

The intestine showed positive HA spot test on days 3 and 5 PI, only in the NBI chickens. The

pathogenetic pictures and severity of the velogenic NDV in the NBI chickens showed that Kudu

113 NDV strain is viscerotropic velogenic virus and the mild clinical signs and lesions presented

by the BI chickens indicated that bursectomy reduces the severity of the NDV infection but not

enough to prevent development of clinical NDV and subsequent mortality.