Isolation of Avian Paramyxoviruses from village chickens and wild birds in Kenya

Abstract

The potential of village chickens in Kenya has not been fully exploited because most farmers do not practice disease control, supplementation, and there is no proper housing for the birds. Control of viral diseases especially Newcastle disease which is one of the major setbacks for village chicken farmers has not been dealt with. This work was designed to find out which strains of Avian paramyxovirus (APMV) occurred in the rural chickens and wild birds and if these chicken and wild birds could be potential reservoirs of virulent Newcastle disease virus (NDV). Field samples (cloacal and whole blood) were collected from live market village chickens at the time of slaughter. The samples were processed for virus isolation and the isolates recovered characterized using their haemagglutination-elution patterns, receptor specificity for red blood cells from different animal species, haemagglutinin thermo stability, virulence in 9-day old embryonated eggs, cross reactivity of the isolates among themselves and control strains tested by the haemagglutination inhibition (HI) test with homologous and heterologous and reference sera for paramyxovirus serotypes APMV -1 to APMV-9. One hundred and sixty two avian paramyxovirus serotype-1 (APMV- 1) and one avian paramyxovirus serotype-4 (APMV-4) were isolated from the rural chickens and wild birds composed of one hundred and forty six isolates from chicken, eleven from wild birds, five from Lake Bogoria water and one (APMV-4) from flamingo faeces. Haemagglutination-elution patterns showed that of the isolates recovered, 13 were fast eluters, 10 were moderate eluters, 41 were partial and 23 were non-eluters at 4°C. Elution appeared unrelated to any aspect of the virus history or other virus character. Receptor specificity of the isolates regarding red blood cells from seven species showed that all virus isolates agglutinated chicken red blood cells and in addition, dog red blood cells were agglutinated by most NDV isolates. Thermostability of haemagglutination activity of the isolates showed that at 56°C all the isolates were inactivated within 8 hours. Of the twenty-one NDV isolates tested for virulence, 10 were velogenic, 7 were meso genic and four were lentogenic. Flocks with velogenic strains constitute a reservoir of virulent Newcastle disease virus and this could be a potential danger to the chicken industry. The NDV isolates showed antigenic differences; however 8 pairs showed no cross-reactivity, 3 pairs of isolates were slightly related asymmetrically, and 33 pairs showed one-sided moderate relationship. Some vaccine strains were reacting asymmetrically with some of the isolates i.e. antisera against LaSota and F-strain vaccine strains could not neutralize B26, K2 and KII virus isolates. Serology served as a useful diagnostic function allowing detection of infections in unvaccinated flocks and also an indication of exposure. Three hundred and eighteen samples were screened and 87 serum samples were positive and some showed cross-reactivity with the APMV-2 to APMV-9. After adsorption of the antisera with NDV-L, only APMV-3 showed specific haemagglutination inhibition against B37, WI, WI7, KRI39 and B6, the other inhibitions against the other APMV isolates were crossreactions indicating the possibility that PMV-3 occurred in village chickens. NDV is widespread throughout Kenya. It was concluded that velogenic NDV strains are widespread in village chickens sold through live bird markets. Such birds are a reservoir of and can spread velogenic NDV and be a danger to the poultry industry. Wild birds harboured virulent NDV and pose danger to the poultry industry.