الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 136 |  |  |
| | | from | 136 | | |
Abstract
avian influenza H9N2 viruses have become endemic in poultry in many countries and represent a real threat to global poultry populations in addition to their transmissibility to humans. It is worth noting that there are many zoonotic viruses that are known to cause the death of many poultry in addition to humans, such as H5N1, H7N9 and H10N8, which in turn have acquired six internal genes from H9N2 viruses. Since the first detection of the H9N2 virus in late 2010 in Egypt, these viruses have become endemic in poultry. Despite the spread of these viruses in the Egyptian environment, the available information on the molecular characteristics and their ability to cause disease is still limited. Moreover, several reassortment events were detected in Egypt resulting in the emergence of genotype II and III of H9N2 viruses besides genotype I that circulated in Egyptian poultry in the period from 2010 to 2014. These viruses are still evolving genetically and antigenically. Therefore, active surveillance studies have become an effective approach for monitoring avian influenza H9N2 viruses in the Egyptian environment in addition to understanding genetic and antigenic evolution, host range, ability to cause disease, and transmissibility in order to reduce the risks of these viruses.
In this thesis, the study was divided into three sections:
In Section A: According to ongoing our active surveillance studies between 2017 and 2021:
1- A number of 173 H9N2 viruses were isolated from different hosts in a number of Egyptian governorates.
2- The complete genome sequences of 173 isolated viruses were analyzed phylogenetically to determine the extent of the evolution of these viruses.
3- The amino acid sites associated with increasing or decreasing virulence in different genes were studied.
4- Several mutations have been identified in different genes which responsible for enhancing the adaptation of these viruses in mammals
The results of that study were as follows:
1- H9N2 viruses isolated in 2017 belong to genotype II or III, while isolates between 2018 and 2021 belong to genotype III.
2- Some of the Egyptian H9N2 viruses have acquired mutations in different sites in their genes that make them able to transmit to humans and adapt to mammals, especially in the internal genes of these viruses
3- Some mutations associated with increased virulence of these viruses in birds have been identified in H9N2 isolates, in addition to changes in amino acids in other sites, which need further study to try to understand their effect on these viruses.
In section B:
1- The virological and pathobiological features of two H9N2 viruses were compared, one of them belongs to the most prevalent genotype (III) circulating in Egyptian poultry from 2017 to 2021, and the second belongs to genotype (I), which spread from 2010 to 2014.
2- The two viruses were inoculated into chickens, ducks and mice in order to study the differences in the pathobiological features of two different genotypes of H9N2 viruses.
3- The ability of viruses to replicate was compared in fertilized chicken egg embryos and mammalian cells.
The results of that comparison indicated the following:
1- The A17358 virus belonging to the genotype III was able to replicate in different organs of chickens, while the S4456B virus belonging to the genotype I was not detected in any of the chicken organs. Beside the absence of any clinical signs in chicken groups inoculated with either virus.
2- Both viruses lack the ability to replicate in the different organs of ducks.
3- The two viruses showed limited replication in the organs of mice. In addition, there was no significant change in the weight of mice infected with either of viruses.
4- Both viruses showed the ability to replicate in mammalian cells. However, genotype I showed a higher replication rate than genotype III in mammalian cells.
In Section C: Egyptian H9N2 viruses are still antigenically evolving into drifting viruses that in turn lead to failure of the vaccines used to suppress the spread of these viruses in the Egyptian environment, so commercial vaccines should be updated based on antigenic drifting viruses and the dominant genotypes of H9N2 viruses. Especially with the isolation of H9N2 viruses from poultry pre-vaccinated with vaccines against the H9N2 and H5N1 strains. Therefore, an inactivated H9N2 vaccine was prepared from the A17358 virus (genotype III), which is the most prevalent genotype in the Egyptian environment. We evaluated the protective ability of this vaccine for poultry against A17358 virus and S4456B virus (genotype I).
The results of the study indicated that:
1- The vaccine prepared by inactivated virus (A17358) belonging to genotype III has the ability to protect vaccinated chickens from infection with virus (S4456B) belonging to genotype I.
2-The results of the hemagglutination inhibition assay using sera from chickens vaccinated with the A17358 virus, showed a high level of immunity against both viruses.
The overall results of this thesis concluded and recommended:
1- Continuous evolution at the genetic and antigenic level of H9N2 viruses in Egypt. Therefore, many amino acids in the different genes of these viruses need further studies to evaluate their effects on the behavior of viruses in terms of virulence and adaptation to other hosts.
2- Genotype III of H9N2 viruses has the ability to adapt to poultry, unlike genotype I, which appears less poultry adapted.
3- H9N2 viruses need more mutations to adapt to mammals.
4-Vaccination strategies in Egypt that rely on inactivated commercial vaccines need to be constantly updated according to antigenic drifting viruses.
5- We hope in future studies to determine the role of each gene of the H9N2 virus in the pathogenicity.