Pathogenesis of two strains of avian paramyxovirus serotype 2, Yucaipa and Bangor, in chickens and turkeys

Abstract

Nine serologic types of avian paramyxovirus (APMV) have been recognized. Newcastle disease virus (APMV-1) is the most extensively characterized virus, while relatively little information is available for the other APMV serotypes. In the present study, we examined the pathogenicity of two strains of APMV-2, Yucaipa and Bangor, in 9-day-old embryonated chicken eggs, 1-day-old specific-pathogen-free (SPF) chicks, and 4-wk-old SPF chickens and turkeys. The mean death time in 9-day-old embryonated chicken eggs was more than 168 hr for both strains, and their intracerebral pathogenicity index (ICPI) was zero, indicating that these viruses are nonpathogenic in chickens. When inoculated intracerebrally in 1-day-old chicks, neither strain caused disease or replicated detectably in the brain. This suggests that the zero ICPI value of APMV-2 reflects the inability of the virus to grow in neural cells. Groups of twelve 4-wk-old SPF chickens and turkeys were inoculated oculonasally with either strain, and three birds per group were euthanatized on days 2, 4, 6, and 14 postinoculation for analysis. There were no overt clinical signs of illnesses, although all birds seroconverted by day 6. The viruses were isolated predominantly from the respiratory and alimentary tracts. Immunohistochemistry studies also showed the presence of a large amount of viral antigens in epithelial linings of respiratory and alimentary tracts. There also was evidence of systemic spread even though the cleavage site of the viral fusion glycoprotein does not contain the canonical furin protease cleavage site.

Fig. 1. Growth kinetics of APMV-2 strainsYucaipa and Bangor in the brain of 1-day-old chicks and comparison with that of APMV-1 strain Beaudette C

Twelve 1-day-old chicks were inoculated with 0.05 ml of 1:10 dilution of 2⁸ HA units of APMV-1 strain Beaudette C(BC), APMV-2 strains Yucaipa and Bangor via intracerebral route. Brain tissues were collected by sacrificing three birdsfrom each group on 1, 2, 3 and 4 days post inoculation (dpi) or as and when the birds died of infection. Each time point represents the geometric mean of the individual virus titration from the brains of three birds. ^† All birds infected with APMV-1 strain BC were dead by 3 dpi.

Fig. 2. Immunofluorescence of frozen tissues samples using monospecific antibody raised against APMV-2 nucleocapsid protein in rabbits

2A: Lung from chicken no. 3 infected with APMV-2 strain Yucaipa, 4 dpi; 2B; Caecal tonsil from chicken no. 3 infected with APMV-2 strain Yucaipa, 4 dpi; 2C: Trachea from chicken no. 1 infected with APMV-2 strain Yucaipa, 4 dpi; 2D: Colon from chicken no. 2 infected with APMV-2 strain Yucaipa, 4 dpi; 2E: Brain from chicken no. 2 infected with APMV-2 strain Bangor, 4 dpi. * dpi: Days post infection

Fig. 3

Alignment of the F protein cleavage site sequence of APMV-2 strains with that of APMV-1 strains. Basic amino acids (R=arginine and K=lysine) are underlined and in bold. Numbers indicate amino acid position.