Isolation and Molecular Detection of Newcastle Disease Virus and Vaccine Immunogenicity Evaluation in and It’s Surrounding Bishoftu, Ethiopia
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Date
2023
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Addis Abeba University
Abstract
Newcastle disease (ND) is an economically important endemic viral disease of chickens that has a potential threat to village chickens and commercial poultry farms in Ethiopia. Despite intense ND vaccination, most clients were raising their doubt regarding efficacy of the current National Veterinary Institute (NVI) ND vaccines against the circulating viruses. Therefore, in this research a cross sectional study was designed to isolate and molecularly detect ND virus and to assess the protective efficacy of ND vaccines in and its surrounding Bishoftu from October 2022 to May 2023. A total of 57 samples were processed using SPF embryonated eggs, hatched chickens and DF1cell culture methods to isolate NDV. The pathogenicity of the isolates was evaluated using intracerebral athogenicity index (ICPI) scoring (60 chickens) and embryo mean death time (MDT) determination. The isolates were further identified by molecular assay, targeting primers of the M-gene (~1100 p) of avian paramyxovirus-1 (APMV-1). The result of PCR revealed that from the total 11 ND suspected samples eight of them were positive. Vaccine efficacy was evaluated in 80 chickens hatched from SPF eggs. Chickens were immunized with lentogenic vaccines of NCH1, NCL and NCTH using three vaccination schedule groups and one control group. Standard dose of 106.5 EID50 per chicken was administered at day zero and boosted at days 14 and 35. At the end of experiment period all groups were challenged with isolated NDV (1010.6 ELD50 per chicken) through occulonasal route. The result revealed that the isolated NDV was characterized as very virulent (velogenic pathotype) based on the mean death time (MDT) and ICPI score. The geometric mean (GM) haemagglutination inhibition (HI) antibody titer was peaked post-second-boost and revealed a significance difference (P < 0.05)
compared to the control group. Thus, secondary boost produces higher antibody HI titer than the first boost. Besides, the challenge assay revealed that vaccinated chickens were protected against the challenge strain while unvaccinated chicken were deceased 100% within 6 days post challenge. Accordingly, it can be concluded that the current ND vaccine is efficient to protect vaccinated chickens against the circulating NDV in the study area. Thus, the study commends further investigations of ND outbreaks, training and awareness regarding ND and vaccine management.