Prevalence and clinico-pathological manifestations of avian leucosis in Chicken in Nairobi And Surrounding Counties
Avian leucosis (AL) is an important disease causing high morbidity, mortality and reduction in chicken production. There is scanty information in Kenya on the status of the disease in chicken to enable its prevention and control. Objectives of this study were to determine the prevalence of AL in chicken in the year 2003 to 2012; determine its seroprevalence; and the clinical and pathological manifestations of the disease in sero-positive and negative chicken in Nairobi and surrounding counties. Determination of AL prevalence, involved retrospective retrieval of post mortem records from January 2003 to December 2012 in the Department of Veterinary Pathology, Microbiology and Parasitology, Faculty of Veterinary Medicine, University of Nairobi (VPMP) and Central Veterinary Investigation Laboratories (CVL). Seroprevalence determination involved blood sampling from 385 birds comprising indigenous (180), broilers (103) and layer chicken (102) from Nairobi and surrounding counties. The blood was tested for AL p27 antigen using an enzyme linked immunosorbent assay (ELISA). To determine clinical and pathological manifestations; ten AL suspect farms were visited, questionnaire administered, clinical examinations undertaken, and fifty birds acquired for serology, post mortem and histopathological examination done at VPMP. A total of 3,721 chicken cases were examined in the period of 2003 to 2012. Of these, 5.05% (188/3721) were diagnosed with AL. There has been a rising trend in the number of AL cases over the period. Of these, commercial layers comprised 92.5% (174/188) (8-52 weeks old), broilers 3.7% (7/188) (3-36 weeks old), indigenous chicken 1.1% (2/188) (age not indicated) and 2.7% (5/188) chicken whose type and age were not indicated. Kiambu County was the main source of these birds with 56.4% (106/188), followed by Nairobi County 27.1% (51/188), Machakos County 10.1% (19/188) and Kajiado County with 6.4% (12/188). Majority of these cases were reported in the rainy season (April-June; October-December) 53.2% (100/188) while the dry season (January-March; July-September) recorded 46.8% (88/188). In seroprevalence determination, one hundred and five (58.33%) indigenous chicken (12-96 weeks old), nineteen (18.63%) commercial layer chicken (8-65 weeks old) and seven (6.8%) broilers (6-10 weeks old) were positive for avian leucosis virus (ALV) p27 antigen. Among the sampled birds, Kajiado County had the highest seroprevalence rate of 77.78% (35/45), followed by Nairobi County 52.94% (27/51), Machakos County 45.35% (39/86) and Kiambu County 14.78% (30/203). Of the ten farms visited, sixteen (32%) out of fifty birds from six farms tested positive to ALV p27 antigen. Main clinical manifestations were whitish or brownish diarrhoea, anorexia, unthriftiness, paralysis, dullness and ruffled feathers. Common pathological lesions observed were emaciated carcasses, renomegaly, hepatomegaly with nodular liver lesions, enteritis, cardiomegaly and congestion of visceral organs (spleens, lungs and kidneys). Main histopathological manifestations comprised lymphocytic and lymphoblastic infiltrations with occasional mitotic figures in various organs (spleens, livers, kidneys, lungs, ovaries and sciatic nerves). There was correlation between seropositivity and observed clinical, pathological and histopathological manifestations of unthriftiness; enteritis, renomegaly and cardiomegaly; and lymphocytic infiltration in various organs respectively. In conclusion; AL is prevalent among poultry flocks in Nairobi and surrounding counties and has been increasing with time, with over 30% of sampled birds testing positive. Majority of seropositive chicken were indigenous. Some clinical and pathological manifestations had a significant correlation among seropositive birds. This study recommends effective screening of imported birds to prevent entry of infected birds into the country, culling of infected birds with proper disposal and standard biosecurity measures in hatcheries and farms to prevent primary exposure.
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