Preliminary Report on Neuraminidase, Erythrocyte Surface and Free Serum Sialic Acid Concentrations in the Serum of Healthy and Newcastle Disease Virus-Infected Chickens

Abstract

A survey was carried out in ten backyard poultry farms in Zaria metropolis to determine levels of neuraminidase, erythrocyte surface and free serum sialic acid concentrations in the serum of chickens. One hundred Shika brown layers, of which 50 were infected by the Newcastle disease virus (NDV) and 50 were apparently healthy, were used. Neuraminidase activity, erythrocyte surface and free serum sialic acid concentrations were determined for each chicken, using the thiobarbituric acid assay method. The packed cell volume (PCV) and antibody titers to Newcastle disease were also determined for each chicken by the microhematocrit and hemagglutination inhibition tests, respectively. The mean values of 8.079 ± 2.93 μmol/min and 0.129 ± 0.04 mg/ml obtained for neuraminidase activity and free serum sialic acid concentration, respectively, in NDV-infected chickens were significantly higher (P < 0.001) than the corresponding mean values of 0.849 ± 0.61 μmol/min and 0.041 ± 0.03 mg/ml obtained in apparently healthy chickens. On the other hand, the mean values of 0.009 ± 0.01 mg/ml and 21.96 ± 6.89% recorded for erythrocyte surface sialic acid concentration and PCV, respectively, in NDV-infected chickens were significantly lower (P < 0.001) than the corresponding mean values of 0.650 ± 0.04 mg/ml and 29.50 ± 5.53% recorded in their apparently healthy counterparts. In conclusion, the low mean values of PCV and erythrocyte surface sialic acid concentration obtained in NDV-infected chickens could result from the circulating NDV that produced neuraminidase in vivo, which, in turn, cleaved off the erythrocyte surface sialic acid, thus rendering the erythrocytes more prone to destruction by the reticuloendothelial system. Further studies are needed to isolate and characterize neuraminidases of NDV field strains in this local environment.