Abstract
Newcastle disease (ND) is a global threat to domestic poultry, especially in rural areas of Africa and Asia, where the loss of entire backyard local chicken flocks often threatens household food security and income. To investigate the genetics of Ghanaian local chicken ecotypes to Newcastle disease virus (NDV), in this study, three popular Ghanaian chicken ecotypes (regional populations) were challenged with a lentogenic NDV strain at 28 days of age. This study was conducted in parallel with a similar study that used three popular Tanzanian local chicken ecotypes and after two companion studies in the United States, using Hy-line Brown commercial laying birds. In addition to growth rate, NDV response traits were measured following infection, including anti-NDV antibody levels [pre-infection and 10 days post-infection (dpi)], and viral load (2 and 6 dpi). Genetic parameters were estimated, and two genome-wide association study analysis methods were used on data from 1,440 Ghanaian chickens that were genotyped on a chicken 600K Single Nucleotide Polymorphism (SNP) chip. Both Ghana and Tanzania NDV challenge studies revealed moderate to high (0.18 – 0.55) estimates of heritability for all traits, except viral clearance where the heritability estimate was not different from zero for the Tanzanian ecotypes. For the Ghana study, 12 quantitative trait loci (QTL) for growth and/or response to NDV from single-SNP analyses and 20 genomic regions that explained more than 1% of genetic variance using the Bayes B method were identified. Seven of these windows were also identified as having at least one significant SNP in the single SNP analyses for growth rate, anti-NDV antibody levels, and viral load at 2 and 6 dpi. An important gene for growth during stress, CHORDC1 associated with post-infection growth rate was identified as a positional candidate gene, as well as other immune related genes, including VAV2, IL12B, DUSP1, and IL17B. The QTL identified in the Ghana study did not overlap with those identified in the Tanzania study. However, both studies revealed QTL with genes vital for growth and immune response during NDV challenge. The Tanzania parallel study revealed an overlapping QTL on chromosome 24 for viral load at 6 dpi with the US NDV study in which birds were challenged with NDV under heat stress. This QTL region includes genes related to immune response, including TIRAP, ETS1, and KIRREL3. The moderate to high estimates of heritability and the identified QTL suggest that host response to NDV of local African chicken ecotypes can be improved through selective breeding to enhance increased NDV resistance and vaccine efficacy.
Highlights
Newcastle disease (ND) is caused by a virulent pathotype of an avian paramyxovirus type 1 (APMV-1) that belongs to the family Paramyxoviridae, subfamily Avulavirus, and genus Orthoavulavirus (Mayo, 2002; Davison et al, 2019)
As part of a large-scale study to understand the genetic basis of Newcastle disease virus (NDV) response traits for local chicken ecotypes in Africa, we recently reported estimates of genetic parameters and genome-wide association study (GWAS) results for response to lentogenic NDV infection in three Tanzanian local chicken ecotypes (Walugembe et al, 2019b)
One-Mb windows that explained more than 1% of genetic variance in Bayes B corresponded in location to 7 QTL identified in the single-SNP analysis across all traits analyzed
Summary
Newcastle disease (ND) is caused by a virulent pathotype of an avian paramyxovirus type 1 (APMV-1) that belongs to the family Paramyxoviridae, subfamily Avulavirus, and genus Orthoavulavirus (Mayo, 2002; Davison et al, 2019). It is a devastating poultry disease that causes various clinical signs in infected chickens, which vary with the pathotype of the viral strain (Marshal et al, 2009). Newcastle disease virus (NDV) strains are categorized into three pathological categories: lentogenic, mesogenic, and velogenic (Songhua et al, 2003; Brown and Bevins, 2017). Lentogenic strains are often used as vaccines and are characterized by subclinical infections or respiratory disease (Cornax et al, 2012). Mesogenic strains are characterized by low mortality, especially in young chickens, and can cause respiratory and neurological disease. Virulent or velogenic strains often cause systemic infections, with several clinical signs, including diarrhea, neurologic disease, hemorrhagic lesions in the gastro-intestinal tract, and sudden death (Miller et al, 2010). NDV is often transmitted among flocks through fecal-oral and respiratory routes and can be spread by other poultry species, wild animals, wild and feral birds, domestic animals, and communal water reservoirs (Awan et al, 1994)
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