Pathological Study On Intestinal Tract Of Broiler Chickens Artificially Infected With Infectious Bronchitis Virus ZZ2004 Strain Isolated From Duck

To study the pathogenesis of infectious bronchitis virus ZZ2004 strain isolated from duck that leads to growth suppression in chickens,fifty 7-day-old broiler chickens were infected with virus by nose/eye dropping as the experimental group and fifty with normal saline as the control in the same way.Experimental chicks were infected with 0.5 ml of virus(EID50 =10-186/0.2 ml)artificially.Clinical signs,autopsy changes were observed.Duodenum,jejunum,ileum,cecum and bowel were removed respectively at 24 h,72 h,168 h.240 h,336 h,504 h and 672 h after infection.Histopathology and ultrastructure examination were performed.The distribution and activities of succinate dehydrogenase(SDH),nonspecific esterase(NSE),and acid phosphatase(ACP)were studied by enzyme histochemistry methods.At the same time,virus distribution in small intestines were researched by immunohistochemistry study.The results showed that IBVZZ2004 strain isolated from duck could lead experimental chickens to spirit depression,respiratory distress and diarrhea from 24 h PI.From 168 h PI to 672 h PI at the end of the experimental period,the average weight of experimental chickens was 30.1%lower than that of the control chickens.Between 240 h and 312 h PI,the disease showed most serious symptoms.After that,the disease eased gradually and turned into the recovery phase.Different degrees of catarrhal and hemorrhagic inflammatory changes were observed in intestinal tract through autopsy.The intestinal epithelium exfoliated,villi shortened,villus of jejunum became shorter and thicker,inflammatory cells and goblet cells increased through light microscopy examination on the duodenum of dead chick 240 PI.Significant epithelial desquamation,the top of villi fractured,lamina propria exposed,lots of goblet cells openings existed between epithelial cells and lumped secretions discharged by scanning electron microscopy examination on the small intestine of dead chick 240 PI.So much mucus secretions were on the surface of the top of villi.The small intestinal epithelium microvilli of experimental chickens 240 h～312 h PI damaged seriously under transmission electron microscopy.Granules of rough endoplasmic reticulum dropped off and the smooth endoplasmic reticulum was intumescent as vesicle in which many virus-like particles proliferated.Chromatin agglutinated and perinuclear space widened.More virus-like particles could be detected in the perinuclear space when karyorrhexis occurred in epithelium cells.It was found that virus could proliferate in villous epithelial cells of small intestines and damage the normal structure by the immunohistochemistry staining.It should be noticed that jejunum showed stronger positive reaction.The activities of SDH,NSE and ACP were showed pathological increase or decrease by enzyme histochemistry in intestinal tract of the infected chickens.SDH activities were more sensitive to virus infection.SDH activity changes showed that the duodenum SDH activities was significantly higher(P<0.05)24 h～72 h P1,jejunum SDH activity at 72 h PI was significantly higher(P<0.05)and the remaining intestinal segments were no significant difference(P>0.05);jejunum SDH activity was significantly higher than that in the control group(P<0.05)168 h～240 h P1.duodenum SDH activity at 168 h PI and ileum at 240 h PI were significantly higher than the control group(P<0.05)and the rest of the intestinal segments were higher than those in the control group(P>0.05):SDH activity of experimental intestines were all low er than that in the control group between 336～504 h(P>0.05).ACP activity changes showed that every intestinal segment had no significant changes(P>0.05)24 h～72 h PI;ACP activities of small intestines were all higher than that in the control group between 168 h～336 h PI,in which duodenum were higher than the control activities between 240 PI and 336 PI(P<0.05),jejunum activity was significantly higher(P<0.01)at 240 h PI and the remaining intestinal segments were no significant difference(P>0.05).NSE activity changes showed that between 24 h PI and 72 h PI,NSE activity of every intestines had no significant changes(P>0.05);among 168 h～336 h PI,NSE activities of all intestine were higher than that in the control group,of which duodenum at 168 h PI and ileum at 240 h PI were significantly higher(P<0.01),jejunum at 240 h PI and 336 h PI was significantly higher than that in control group and the remaining small intestines were no significant difference(P>0.05)and at 504h PI,NSE activities were no significant difference between every small intestines(P>0.05).In summary,IBVZZ2004 strain isolated from duck can proliferate in the intestinal epithelial cells and cause a series of degenerative lesions,such as epithelium necrosis,shedding of epithelium,ultrastructure destruction and so on,along with structure damage,epithelial cells function decrease or loss,changing the enzymes activity about digestion and absorlption capacity.These changes lead to the disturbance of digestion and absorption in the intestinal tract,poor growth and even death in sick chickens.