Artificial Infection Of E. Coli In Different Ways The Dynamics Of Ducklings

Objective:This research investigated the dynamic pathohistology of 5-day-old Sichuan Ma-duck which were affected by respiratory tract infection and intramuscular injection of E. coli (018) artificially. This study have established the pathological model of E. coli infection in ducklings. Experimental procedure:Infected ducklings by intramuscular injection and respiratory tract infection.1. Taken the the main organs of the heart, liver, kidney, lung and immune organs of spleen, thymus, France's capsule. Simultaneously, weighed and counted the viable count of these organs after infected at 6h,12h,24h,36h,48h,60h respectively.2. At the time of 24h,48h,72h,96h, taken 1mL of the duck blood which was containning heparin to perform the peripheral blood lymphocyte proliferation test.3. At the time of 6h,12h,24h,36h, 48h,60h,72h,84h,7d, taken heart, liver, spleen, lung, kidney, brain, thymus, bursa, pancreas and were cut into pathological section. The results are as follows:The weight index of each organ in Ducklings:The ducklings of intramuscular group were lost of weight at 12h after infection, and the weight were descented to minimum value of 87.56g. then the weight started to rise after 84h, finally, the weight were recoverd to normal levels after 7d. Respiratory tract infection group began to were lost of weight at 24h, and the weight were descented to minimum value of 79.7g. then the weight started to rise after 84h, finally, the weight were recoverd to normal levels after 7d. The weight index of heart, liver, and kidney in both intramuscular group and the respiratory tract infection were significantly higher than the control group. But the weight index of thymus and bursa was significantly lower than the control group. Viable counting:After infection of 6h, except kidney, brain and bursa, the bacterias can be detected in the other organs of intramuscular group, kidney and bursa were detected pathogens at 12h and 24h respectively. But brain still can not detect pathogens. In the respiratory tract infection group, all of the organs did not detect pathogens except for lung at 6h after infection. After 12h, except kidney, brain and bursa, the bacteria can be detected in the remaining organs, which indicated that E. coli was firstly breakthrough the lung protective barrier and then in other organs to invade into the ducklings. After 12h, in the intramuscular group, except brain and bursa did not detect bacteria, the other organs were detected the bacterias, the viable counting in liver was reached to 8.34 x 104, followed by thymus, lung, pancreas, spleen, heart and kidney. In the respiratory tract infection group, except kidney, brain andbursa did not detect bacteria, the remaining organs were detected the bacterias. Among of them, the viable counting in thymus was reached to 3.94×104, followed by lung, liver, pancreas, heart and kidney. At 24h after infection, all of the organs can be detected pathogens except for brain in both Intramuscular group and respiratory tract infection group. The bacterias was mainly distributed in liver, about 6.01 x 10, followed by lung, bursa,'thymus, kidney, pancreas, heart, spleen. In the respiratory tract infection group, the bacterias was mainly distributed in liver too, reached to 5.69×10, followed by thymus, lung, spleen, bursa, pancreas, heart. All of these indicated that the optimal target organ of E. coli 018 is the liver and lung, and they were the preferred organ to detecte and isolate the pathogen. At 36h～48h, the pathogens in both the intramuscular and respiratory tract infection group were no changes compared to 24h. The pathogens were mainly distributed in liver, and thenumber of bacterias were 7.78×105,86.01 x 105 respectively. After 60h in both groups, except liver and lung, the other organs were not detected the pathogens. Intramuscular group reached the dincreased logarithmic phase at 0-6h, respiratory tract infection group reached the dincreased logarithmic phase at 6h-12h. While the bacteria of organs in intramuscular group grew slowly at 12h-48h, and the bacteria of organs in respiratory tract infection group grew slowly at 24h-48h. These results suggested that different injection methods induced different immune response time, and inhibited the rapid growth of the pathogen.Anatomical observation:the majority organs of infected ducklings can observed some slight pathological changes at 12h, such as the visible hyperemia and telangiectasia; the liver, spleen, heart, lungs, kidneys have various degrees of congestive swelling, the thymus and bursa was detected atrophy after 24h; the surface of heart, liver can be observed with a layer of white cellulose membrane; and the swelling of organs in resistant ducklings had significantly reduced, and the fibrin exudate of heart and liver decreased significantly after 48h. The overall law of pathological changes is:6h-24h, the invasion course of the intramuscular group was changed rapidly, and the pathogenetic condition was more serious, but the respiatory tract infection group were relatively moderate and mild lesions; 36h-60h, the morbidity course of the respiratory group was tardy, while the intramuscular group have a accelerated trend, and more serious than respiratory group; at 24h-72h, the intramuscular group reached the peak of morbidity; but the respiratory group became the most serious at 36h-84h; after 72h, there were no ducklings dead by invasion in muscle group, the resistant ducklings were beginning recovered, the pathogenetic condition was significantly moderate, while the respiratory group was gradually moderate after 84h. The obvious observation were fibrinous pericarditis, parahepatitis, airbags inflammation, lung congestion, serous fibrin exudation; renal glomerular congestion, tubular epithelial cell swelling and necrosis; thymus swelling congestion, false eosinophilic leukocyte infiltration; reduction of the bursal lymphoid follicles, reticular macrophages proliferation, epithelium mucosae cell degeneration; pancreatic cell swelling granular degeneration, capsule thickened, cellulose slurry leakage.These two routes of infection can invade the organs in ducklings to induce dysfunction of ducklings and induce ducklings dead. The incubation period of intramuscular group was 6h, the mortality was higher to 90%, this route can induce more serious injury on duckling' organs; the eclipse period of respiratory tract infections group was 12h, was longer than intramuscular group, the peak of death was laged than intramuscular group, and the mortality is relatively low, about 65%.