الفهرس 
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Abstract
1- The study was carried out on 800 one day old Fayoumi chicks. They were classified into three experimentalgr-
oups and control one.
a.Group I: This include 300 chicks. They were infect-ed with velogenic viscerotropic strain of NDV inadose of 0.5 ml of 106 EID50/bird intramuscularly in the breast muscle when their age was 20 days and their ma-terial immunity declined to zero.
b.Group II: This include 300 chicks. They were infec-
ted with mesogenic vaccinal strain ”Komarov” in a dose of 0.5 ml of 108.47 EID50/bird intramuscularly in the breast muscle when their age was 24 days and their maternal immunity declined to 0.5.
c.Group III: This include 100 chicks. They were vacci-nated with inactivated oil adjuvant vaccine in a dose of 0.5 ml intramuscularly in the breast muscle when their age was 17 days and their maternal immunity de-clined to zero.
d.Group IV: This include 100 chicks as a control.
2- Post mortem examination was performed on the dead and sacrified birds. Specimens for histochemical studies (including alkaline phosphatase enzyme, acid phosphatase enzyme, non-specific esterase and PAS) and histopatholo-gical studies by routine H. & E. were taken from the lympoid organs (including thymus, bursa, spleen, caecal tonsils and gland of harder) and parenchymatous organs (including brain, heart, lung, trachea, intestine, prov-entriculus, liver and the site of inoculation). Blood samples from sacrified birds were collected from which serum was obtained for detection of antibody by H1 test.
3-Deaths were observed only in the velogenic group, they reach maximum by the 3rd day. Peracute, acute and chro-nic courses of the disease were demonstrated. Signs were mainly nervous with extreme weakness and paralysis. The survivors, were few and encephalitic.
4-In the velogenic group the gross lesions were mainly in the form of congestion, hemorrhage and edema. Hemorrh- ages involve the caecal tonsils, proventriculus and heart. Acute general congestion was observed. The congestive and hemorrhagic phenomena subsided by the end of the 1st week. Mesogenic strain resulted only in congestion of the small intestine, thymus, caecal tonsil and heart The phenomenon subsided by the end of the 1st week. In-activated vaccine revealed nothing grossly. 5- Histopathological examination of the lymphoid organs re-vealed that these organs including the thymus, bursa , spleen, caecal tonsils and the gland of Harder suffered necrobiotic changes and exhausion of their lymphocytes. This necrobiosis started as early as the 1st day after velogenic infection and continue with variable degrees of severity, reaching a maximum from the 3rd to the 5th day, then subsided toward the end of the 1st week. After the 1st week the lymphoid organs became repopulated gra-dually till the end of the experiment at the 5th week . Reticular macrophagal reaction usually started at the 1st day and reach maximum by the 3rd and 4th days and subsi-ded at the end of the 1st week. Acidophilic intranuclear inclusion body was observed in these reticular macropha-ges. Congestive phenomenon was observed at the 1st week.
Mesogenic vaccinal strain caused only mild and spor-adic necrobiotic changes at the end of the 1st week from the 1st or the 2nd. injection. Congestive phenomenon was also observed during the 1st week. After that time the lymphoid organs were more or less normal. No histopath-ological lesions in the lymphoid organs were observed in the vaccinated group. 6- Histochemical examination of the lymphoid organs revealed that.-
a.Thymic and bursal lymphocytes were negative for alk-aline phosphatase, acid phosphatase, non specific esterase in the three experimental groups indicating that they were not competent cells.
b.Acid phosphatase and non specific esterase reactions demonstrated the macrophagal activity only in the
velogenic group in the thymus, bursa, spleen and caecal tonsils. The reaction reach maximum by the 3rd day and declined toward the end of the 1st week indicating that the only immunological reaction in the 1st week was macrophagal.
c.The periarterial and periellipsoidal lymphocytes in the spleen of the velogenic group were alkaline pho-sphatase positive from the 6th to the 8th day. In the mesogenic group they were stained from the end of the 1st week to the 4th week. The reaction in the vacc-inated group was prolonged to the 4th week. The rea-ction indicated that these cells were in transforma-tion.
Acid phosphatase positive lymphocytes appearedin the periarterial and periellipsoidal sheaths at the end of the 2nd week and increased in intensity to the 5th week. In the mesogenic group acid phosphatase
positive lymphocytes appeared at the end of the 1st week and continue to the 5th week. The follicular lymphocytes in this group were positive from the 2nd to the 5th week. The reaction was stronger and dif-fuser in the inactivated vaccine, it started at the end of the 1st week and continue to the 5th week . The follicular lymphocytes were positive from the 2nd to the 5th week.
For the three experimental groups the periarter-ial lymphoid sheath was esterase negative and these cells were categorized as T cytotoxic.Thereacticfn only demonstrated in the follicular lymphocytes from the end of the 1st week to 4th week in the velogenic group,only at the 5th week in the mesogenic group and allover the experiment in the vaccinated group. These cells were recognized as T helper.
d. Alkaline phosphatase reaction started to appear in
the lymphocytes of the diffuse lymphoid tissue of the caecal tonsils at the end of the 1st week, end of the 2nd week and at the 1st and 2nd weeks in the veloge-nic, mesogenic and vaccinated groups respectively and continue to the 5th week. The reaction indicating that these cells were in tranformation. Acid phosphatase positive lymphocytes start to ap-pear at the end of the 1st, at the end of the 2nd week and at the end of the 1st week in the velogenic, mesogenic and vaccinated groups respectively and co-ntinued allover the period of the three experiments. These cells were categorized as T cytotoxic. The fo-llicular lymphocytes were only positive in the meso-genic strain from the 3rd to the 5th week.
Non specific esterase reaction was only demonstr-
ated in the follicular lymphocytes from the 1st to
the 4th week; only at the 5th week and allover the
experiment in the velogenic, mesogenic and inactiva-ted vaccine group respectively indicating that they were T-helper.
e. The gland of Harder was negative for enzyme histoch-emical reaction in the 3 experimental group. PAS reaction was positive in the velogenic group in the lymphoid cells from the 4th to the 8th day. from the 2nd to the 5th week the gland was populated by PAS positive plasma cells. For the mesogenic and vacci-nated groups the gland was normally heavilly popula-ted by PAS positive plasma cells.
9- Histopathological examination of the other parenchyma-
tous organs in the velogenic group revealed that:-
a.Encephalitis, myocarditis, enteritis, typhilitis,al-lergic inflammation of the gizzard and hemorrhagic myositis at the site of inoculation.
b.Congestion, edema and hemorrhage of the visceral or-gans and brain.
c.The most selective lesion observed was the necrobio-sis and exhausion of the lymphoid collections in the secondary bronchi of the lung, subepithelial lymphoid tissue in the intestine and at the proventriculus esophgeal junction.
In the mesogenic group the visceral organs re-vealed congestion and edema. These organs were normal in the vaccinated group.