Comparative Study of the Pathogenicity and Pathogenesis of a Local Nigerian Velogenic Newcastle Disease Virus in Guinnea Fowl Chickens

Abstract

The susceptibility, clinical signs, lesions, distribution and persistence of a local Nigerian Velogenic Newcastle disease virus KUDU-113 were studied in experimental infection in 6-week-old guinea fowls and chickens. Following inoculation intramuscularly, severe depression, whitish-green diarrhea, lethargy, hunched posture, tremors and torticollis were observed in infected chickens from day 3 PI. In infected guinea fowls depression, greenish diarrhea, dehydration, paralysis, torticollis and droopy wings were consistent clinical features. Morbidity was 100% and 91% in chickens and guinea fowls respectively, while the total mortality was 94.6% and 22.2% in chickens and guinea fowls respectively. Weight loss was highly significant in both infected groups (P<0.05). Post-mortem examination showed atrophy of the lymphoid organs (thymus, bursa of Fabricius and spleen) and congestion of kidneys in inoculated groups. Hemorrhages on the mucosa of proventricular glands, sharply-demarcated hemorrhagic ulcers in the intestine and in the caecal tonsils were observed only in infected chickens. Congestion in the brain vessels was always present in the infected guinea fowls. Histopathologically, endotheliosis, neuronophagia in the brain, atrophy of the lymphoid organs due to necrosis and depletion of lymphocytes, and ballooning degeneration in bursal folllicles were observed in infected chickens and guinea fowls. The highest antibody titers recorded on day 15 PI were considerably higher in infected chickens than that of the infected guinea fowls. On day 6 PI virus distribution was widespread and virus was detected in several organs including cloacal swabs. On days 15 and 19 PI there was anaemia in chickens. Leukocytosis, heterophilia and lymphopenia were common on days 3 to 15 in inoculated groups. Consequently, susceptibility to highly virulent NDV was shown to vary among chickens and guinea fowls. However, in general, disease among guinea fowls was less severe, despite the virus distribution in its several organs (bursa of Fabricius, thymus, spleen, brain and trachea/lungs), than in chickens. Intramuscular inoculat ion test showed high mortality in chickens with intestinal ulcers and hemorrhagic lesions which indicated that the KUDU-113 NDV strain is a velogenic viscerotropic virus. Key words: velogenic Newcastle disease virus; experimental infection; susceptibility; Guinea fowls; cockerels; Nigeria.