الفهرس 
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Abstract
Newcastle disease (ND) is a highly contagious and widespread disease, which causes severe economic losses in domestic poultry, especially in chickens. The World Organization for Animal Health (WHO) lists it as a notifiable disease. Therefore, the purpose of this thesis is to make survey for the prescence of NDV in Egyptian provinces and molecular characterization of the isolates, in addition to, determination of phylogenetic diversity among islated strains and available commercial vaccines and evaluation of different vaccination programs against NDV genotype VII in broilers.
The study was carried on :
Fifty broiler chickens flocks suspected to be infected with Newcastle disease virus (NDv) in 5 Egyptian provinces Gharbia (7/50), El Behera(21/50), Kafr EL sheikh (8/50) and Matrouh (7/50) and Alexendaria (7/50) during the period of september 2015 to February 2017 were investigated for clinical and postmortem examination as well as virus isolation and molecular identification .These isolates were detected even in vaccinated flocks that indicate the possible causes of those outbreaks may be not only useless of vaccines, but also immunesuppression, use of heterogenous vaccines , improper application of biosecurity, moreover, may be arole in spreading of velogenic strain of NDv in Egypt .
The results of virus isolation on embryonated chicken SPF eggs (ECE) revealed that 16/50 samples had haemagglutinating agents by slide haemagglutination test by using specific antiserum against NDV.These haemagglutinating agents were confirmed as NDV by RT-PCR.
Analysis of the positive samples (16) by RRT-PCR using F-gene responsible for velogencity of virus and found that 7 isolates from 16 were velogenic while the other 9 isolates from 16 were lentogenic .
Sequencing of 8 selected isolates revealed that the deduced amino acid sequences of the fusion protein (7/8) isolates possessed the motif 112RRQKRI117at the cleavage site,indicating that these isolates are velogenic ,whereas the other (1/8) isolates carries the motif 112GRQGRL117indicating that is lentogenic .
Phylogenetic analysis demonstrated that the 7 strains belong to the NDv genotype VIId, and the other strain was of genotype II.
We made experimental design to evaluate different vaccination programs against ND genotype VII using the isolated strain NDV genotype VII with accession no MK977858. One hundred and forty one- day old commercial chicks were divided into fourteen groups each group contain ten chicks .all 14 groups were vaccinated by commercial vaccines except control group .All 13 groups experimentally challenged at 28- days- old 0.1 ml with infective dose EID50106/dose/chicks. Serum samples were collected from 8 chicks for each group for serological test (HI test ) to detect the presence of the antibodies at day 1 to evaluate MAbs, 14 , 21 and 28 days and also post challenge at 35 days age. The chicks and feed were weighted at day of challenge and after challenge by 7 days for calculation of weight gain and feed conversion ratio . The clinical signs were monitored and mortalities were recorded. At 3, 6and 9 days post challenge, tracheal swabs were collected from 3 chicks from each group to evaluate the viral shedding. We found Newcastle symptoms of greenish diarrhea and difficulty breathing in all infectious groups, but were more severe in the unvaccinated group (13) and that the mortality rate reached to 40% and when dissected we found hemorrhagic points on the gastric gland and enlargement of the spleen and hemorrhagic points like buttons in the intestine Significant decrease in weight in group 13 and significant difference in weight in groups (1,2,3,4,5,6,8,9,11), although no significant difference in groups (7,10) (12); Increasment of HI titer in group 5,6 which vaccinated by vectormmune than HI titer in group 3,4 which vaccinated by Innovax , The rate of shedding of the virus decreased on the sixth day after infection and disappeared on the ninth day after infection in the fifth group and disappeared on the sixth and ninth day in the sixth group, but in the remaining 13 infectious groups continued until the ninth day after infection, Shedding in groups 10-11-12 which vaccinated with dalguban (vaccine homologus to challenge virus ) lower than groups 7-8-9 which vaccinated by Nobilis Newvac (vaccine heterologus to challenge virus ). The use of 2 doses from dead vaccine with one dose from live vaccine give better feed consumption rate, rate of food conversion, increase in weight and reduce the shedding of the virus after infection than using 2 doses of inactivated vaccine only or using of inactivated vaccine with live vaccine only . The use of dead and live vaccine with Dalguban gave better results in the rate of feed consumption and the rate of food conversion and increase in weight and reduce the shedding of the virus after infection than the use of Dalguban with live vaccine only or with the dead vaccine only.
Finally, Continuous surveillance and vaccination-protection studies for NDV must be applied to control the new generation or multiple genotypes.