Isolation and Molecular Characterization of Marek's Disease Virus in Central Ethiopia and Evaluation of its Vaccine Trial
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Date
2015-06
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Addis Ababauniversity
Abstract
The present study was conducted to isolate Marek's disease virus from outbreak samples and to evaluate HVT FC 126 vaccine strain against local isolates. The outbreak investigation was performed in six purposively selected sites (Addis Ababa, Akaki, Dukem, Bishoftu, Mojo and Adama) on the basis of outbreak report. Complete random design was employed for pathogenicity and efficacy trial on Bovans brown chickens. A characteristics clinical signs of MD was observed on sick chickens. White foci of tumour on liver, heart and lung and enlargement of spleen were the post mortem findings of euthanized sick chickens. Based on vaccination history morbidity in non-vaccinated flocks ranges from 22.2% to 51% and mortality as high as 29%. In vaccinated flocks morbidity ranges from 0.7% to 3.3% and mortality as high as 0.4%. From 46/30 pooled samples collected 93.3% were confirmed to be MDV through virus specific genotyping methods, targeting the ICP4 gene of MD virus (318bp) using conventional PCR. 130 chickens were assigned in seven experimental groups to evaluate the pathgenicity of the six new cell culture-grown local isolates. Challenge was performed in two alternative doses (500 and 1000 pfu) by inoculating intraperitoneally at 8 day of age. Death was observed from 30% -50% and post mortem lesion 50%-70% at 1000 pfu. No death and post mortem lesion was observed from 60%-80% at 500 pfu. Thus, all six isolates at 1000 pfu dose fulfilled the criterion to be standard challenge strain. The evaluation of the efficacy of trial vaccine formulated from HVT FC 126 was performed on 70 chickens. Chickens immunized at day old through subcutaneous route with 2000 pfu were challenged in respective of the six local isolates at 7 day of post vaccination. None of the chickens were dead while only Addis Ababa, Dukem and Adama isolates caused tumour lesions in one chicken from their group. The actual MD incidence was rated from 0-10% in challenged groups. The protective index reaches to 95%. Thus the trial vaccine provided efficient protection against MD. However, the vaccine effectiveness shall be evaluated in the context of the existing poultry production system.
Key words: Marek’s disease, chicken, pathogenicity, efficacy, vaccine, CPE, PCR, Ethiopia
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words Mareks, disease chicken, pathogenicity efficacy, , vaccine CPE PCR, Ethiopia