الفهرس 
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Abstract
Avian leucosis virus, a member of the Alpharetroviruses, is an economically significant virus to the poultry industry. The disease incited by this viruswithin the chicken is known to causea variety of neoplasms, which result indecreased production traits, condemnations atslaughter, and tumormortality. The pathogenic forms of this ALV are classified into fivesubgroups, those being A, B, C, D, and J.Avianleucosis virus subgroup A and B responsible for lymphoid leucosis especially in egg-type chickens and broiler breeder chickens, While ALV-J, the recent subgroup of avian leucosis virus was discovered in 1991, is responsible for causing myeloid leucosis especially in meat type chickens, and particularly important in disease significance. Importation ofcontaminated great grandparent (GGP) and grandparent (GP) meat breeder lines has however enabled ALV-J to enter many countries. Verticaltransmission via egg-semen-embryo is the major means of persistence of ALV-J infections and control requires the removal of ALV’s from broiler genetic stocks. Retroviruses such as ALV-J are inherently predisposed to genetic mutation, and ALV-J isolates from various locations around the world now show a diversity of molecular-antigenic characteristics.
Progeny broilers infected with ALV-J also tend to show reduced growth, unevenness of growth rates within flocks and a greater susceptibility to developing serious diseases when challenged by immunosuppressive viruses or secondary bacterial invaders.
With this background knowledge of avian leucosis virus and the clear potential of ALV (A,B and J) to cause significanteconomic losses through mortalities and reduced productivity in Egyptian chicken meat industry,
The current study was undertaken during 2011-2015 with the following data.
For virological examination 730 (632 serum, 76 egg albumin, 12 cloacal swabs and 10 blood samples) were collected.For histo-pathological examinationtissues samples on formalin were collected from 34 flocks of commercial broiler chickens located at different governorates in Egypt.
These samples were prepared for virological diagnosisand histopathological examination and the obtained results were present in 3 chapters as follow;
A- Results of serological examination;-
1- Detection of antibodies to ALV-subtype A/B in serum samples of commercial broiler chickens by IDEXX commercial ELISA kits;
The positive ratio for ALV-A/B reach to 90% from total tested samples.
2- Detection of antibodies to ALV-A/B in serum samples of commercial broiler breeder chickens;-The positive ratio for ALV-A/B reach to 91.7% from total tested samples.
3- Detection of ALV-AG for all ALV-subtypes in serum samples of commercial broiler chickens by IDEXX ELISA kits;
The positive ratio for ALV-AG reach to 74% from total tested samples.Also 12 cloacal swabs of one day old broiler chicks show 100% negative result.
4- Detection of ALV-AG in serum and egg albumin samples of commercial broiler breeder chickens;-
The positive result for ALV-AG reaches to 100%. While 76 egg albumin samples were tested show 100% negative result.
5- Detection of antibodies to ALV-subtype J in serum samples of commercial broiler chickens by commercial IDEXX ELISA kits;
The positive ratio for ALV- J ranged from6% to 50% from the collected tested samples.
6- Detection of antibodies to ALV- J in serum samples of commercial broiler breeder chickens;-
The positive ratio for ALV- J ranged from 9.7% to 60%from the collected tested samples.
B- Results of virus isolation and molecular examinations by polymerase chain reaction test;
1- Detection of avian leucosis virus in liver samples by PCR test;-
5 liver samples were collected from 6 weeks old broiler chickens and tested by conventional PCR test, and the 5 samples show negative result.
2- Detection of avian leucosis virus in buffy coat of blood samples by PCR test;-
2 samples were tested by conventional PCR test and gave one faint positive and one negative result.
3- Isolation of avian leucosis virus on cell line CER (chicken embryo rough);-
a-First Inoculation of samples in cell line tissue culture; Liver samples(2 samples)from 6weeks old broiler chickens and one buffy coat sample from 6weeks old broiler chickens were taken and inoculated to 3 flasks of CER culture ,after 72 hours the 3 samples show cell changes( cell rounding and cell aggregation) under light microscope.
b- Second inoculation occurs by inoculation of samples from first 3 CER culture to another CER culture; the same changes of cells (rounding and aggregation) were seen in 2 samples by light microscope after 72 hours, and then these culture were tested by PCR test.
c- Detection of avian leucosis virus in tissue culture PCR test; 2 tissue culture samples from 3 previous samples were tested by PCR test and show positive result for 2 samples.
C- Histopathological examination;-
Tissue samples (livers, spleens, proventriculuses, lungs, tracheas, kidneys, eyes and bone marrows) of different breeds of broiler chickens at different ages were taken on formalin and examined histopathologically for detection of lymphoid and myeloid cell infiltrations.
The obtained results showed that;
1- Avian leucosis virus was detected in all tested samples collected from different breeds which present in this study representing different governorates in Egypt.
2- Avian leucosis virus was detected at early ages in first week and second week in commercial broiler chickens.
3- The histopathological changes due to avian leucosis virus infection in each organ were detected by figures which showed the different changes in the tested organs in each breed.
4- The histopathological changes due to infection of avian leucosis virus were diagnosed in most tissues in the broiler chickens of different collected breeds in this study, from the first week to the sixth week of age and collected in tables for comparison between breeds and organs by age.
from our study we concluded that;
1-Avian leucosis virus with its forms (lymphoid and myeloid leucosis) was detected and documented in commercial broiler chickens in tested samples of different tested breeds in this study at different ages and diagnosed by different virological tests and histopathological examination.
2-The growth lesions examination are not enough tests to indicate avian leucosis virus infection or not, but virological and histopathological examinations are best tests to detect infection in early ages.
3-We concluded that one test alone for detection of avian leucosis virus cannot give good and accurate diagnosis, but combinations between more than one test as virological tests (ELISA test, tissue culture isolation and PCR test) as well as histopathological examination give good and accurate diagnosis.
4-Avian leucosis virus type J was diagnosed by virological tests as ELISA and histopathological examination but the histopathological examination was very accurate as it can detect histopathological changes due to horizontal and vertical infection of avian leucosis virus type J, while ELISA test for detection of antibodies of avian leucosis virus type J detect only the antibodies due to horizontal infection while the antibodies due to vertical infection give sero negative.
5-In our study, it is the first time for isolation of avian leucosis virus on CER (chicken embryo rough) cell line.
6-We concluded in our study that ELISA tests for detection of avian leucosis virus antibodies or antigens give good and accurate results when operated from 4th week of age, while give negative or false results in first 3 weeks of age.
7-We concluded that PCR test for avian leucosis virus detection give good results when operated on buffy caught samples more than frozen tissues and this due to that avian leucosis virus was cell associated virus.
8-The intra-cytoplasmic inclusion bodies were detected very clear by histopathological examination in most tissues especially in heart and liver beginning from third week of age, these inclusion bodies are due to vertical transmission of avian leucosis virus.
9-Avian leucosis virus affect on immune organs (bursa of fabricius, spleen and thymus) causing depletion and neoplastic infiltration from first and second week and these changes lead to immune suppression of the broiler chickens then failure of vaccination and increasing of susceptibility of these flocks to other viral and bacterial infections leading to high mortalities and high economic losses.
10-In our study avian leucosis virus was detected by high percent reach to 90% for type A and B (lymphoid leucosis), and reach to 50% for avian leucosis type J (myeloid leucosis) in commercial broiler chickens samples in this study, these high percent of this virus which consider most important tumor virus in poultry may has relationship with high incidence of tumors in human being.
Our recommendations are;
1-Screening of breeder chickens for ALV, may also help in controlling the spread of ALV from dam to chicks as the virus is known to be transmitted vertically.
2-Genetic selection should be employed by poultry companies in to breed strains with improved live ability and reduced susceptibility to avian leucosis.
3-Efforts should be channeled into developing vaccines that will protect birds against the effect of this important group of retroviruses of chickens.
4-Preparing a protocol for testing the different breeds of broiler chickens with different virological and histopathological examinations before bringing it from other countries to Egypt.
5-As the avian leucosis virus is a great danger causing great losses and problems for poultry industry, we need from our Scientifics, researchers and all members concerned for poultry industry to put the avian leucosis problem under focus.