Newcastle disease virus genotype VII.1.1 identified from backyard chickens with low antibody titer: Jimma Zone, Southwest Ethiopia.

backgroundNewcastle disease significantly impacts the global poultry industry and is prevalent in many African countries, including Ethiopia. The objective of this research is to determine the humoral immune response to Newcastle Disease Virus (NDV), identify the circulating NDV genotype, and evaluate the correlation between the diagnostic tests used in backyard chickens in the Jimma Zone, southwest Ethiopia.

methodsA total of 90 swab and blood samples were purposively collected from symptomatic backyard chicken in the period between February and April 2022. Samples were collected from Jimma town, Seqa Chekorsa and Tiro Afeta districts of Jimma zone. Enzyme linked immunosorbent assay (ELISA) was conducted and seropositivity was determined from the collected serum samples. From the swab samples, total RNA was extracted and the viral genomic material was detected by amplifying the Fusion gene by Reverse transcription polymerase chain reaction (RT-PCR). The interconnection between ELISA and RT-PCR was also analyzed. Further, positive swab samples were nucleotide sequenced and genotyped.

resultsOf the 90 serum samples, 62 (68.8%) were seropositive. From the 90 swab samples, 14 (15.5%) were RT-PCR positive. No statistically significant association between risk factors (breed, age, sex) and virus exposure was observed by RT-PCR (P = 0.41, 0.44, 0.67) or ELISA (P = 0.85, 0.19, 0.11). However, local breeds, young, and male birds were at higher risk according to RT-PCR results, while young and female birds were more likely to be seropositive. The antibody titer study showed that RT-PCR positive birds produced less than half the mean antibodies of negative birds (x̄=854 vs. 1885) and positive birds produced similar amount of antibody (σ = 626). Local (x̄=1978), adult (x̄=2558), and female (x̄=2620) birds had higher mean antibody titers than their counterparts. The agreement between RT-PCR and ELISA in identifying positive samples was minimal (k = 0.05). Nucleotide-sequenced isolates were nearly identical (99.7%) to each other and identified as velogenic based on the F-gene cleavage site (RRQKRF) with genotype VII.1.1.

conclusionNDV was circulating in the study area, infecting birds with low antibody titers. High viral similarity between neighboring countries emphasizes the need for regional disease control strategy.