الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 164 |  |  |
| | | from | 164 | | |
Abstract
In this study samples from 25 broiler chicken flocks in Beni-Suef, governorate during March to May 2017 were clinically examined, tracheal swabs and organs were collected, respiratory viruses specific real time-RT-PCR was applied, E. coli was isolated and the virulence determinants were examined phenotypically and genotypically. Finally, the possible synergistic relationship of E. coli and AIV-H9N2 has been evaluated under experimental conditions in broiler chickens.
Clinical signs and lesions varied according to the infecting virus strain, the immune status of the flock and number of infecting pathogens. Mortality rates in the flocks under investigation ranged from 0.5 to 65%. The highest mortality was observed in a flock suffering mixed AIV-H5, AIV-H9 and IBV infection. IBV was detected in 96% (n=24), AIV-H9 in 44% (n=11), velogenic NDV in 12% (n=3) and AIV-H5 in one flock (4%). Mixed respiratory viral infection (at least 2 viruses) was detected in 52% of the flocks. Mixed IBV with AIV-H9 has been found to be the most common mixed infection (9 flocks) representing 69.23% of mixed infected flocks (13 flocks) and 36% of total investigated flocks. Single IBV infection was detected in 44% of the examined flocks. vNDV co-detected with IBV in 3 flocks. The onset of clinical disease started at 11-34 days of age. The highest number of flocks had respiratory disorders was observed at 16:30 days of age (20 flocks) compared to younger (n=2) and older (n=3) flocks with higher incidence of respiratory diseases in flocks aging 20:30 days of age (17 flocks). Flock age seems to affect the mortality rate in flocks infected with IBV and AIV-H9; low mortality rates have been observed in young ages (below 15 days of age) compared to older flocks.
E. coli was isolated from all flocks and biochemically identified. Ten E. coli isolates were selected from high mortality rate for serogrouping. Seven serogroups were identified among the investigated isolates (O27, O86a, O114, O119, O124, O125, O169). Serogroup O125 was detected in 3 isolates and O114 in 2 isolates. E. coli virulence determinants were examined phenotypically by Congo red biding and genotypically by PCR targeting four virulence genes; iss, iutA, tsh, vat. Twenty five isolates (100%) were positive for Congo red binding and also all of them were carrying iss gene. 23 isolates (92%) were carrier for iutA gene, 6 isolates (24%) were carriers for tsh gene and 5 isolates (20%) were carriers for vat gene. Results showed that two, three or four virulence genes were detected in E. coli obtained in this study. iss/iutA was the most detected constellation (n=15), iss/tsh pattern was found in 2 isolates, iss/iutA/tsh was found in 3 isolates, iss/iutA/vat was found in 4 isolates and iss/iutA/tsh/vat was found in one E. coli isolate. For iss/iutA, the mortality rates varied from 0.5% to 25.5 %. For iss/tsh, the mortality rates were 1.7% and 2.1%. For iss/iutA/tsh, the mortality rates were 1.3% and 10.5%. For iss/iutA/vat the mortality rates were 1.13% and 28.6%. For iss/iutA/tsh/vat, the mortality rate was 1%. For flocks that were infected with AIV-H9, the number of virulence genes in E. coli was associated with mortality rate in the flock, where the average mortality rates for AIV-H9 infected flocks in which E. coli carries two virulence genes is 4.9% with minimum 0.5% and maximum 10.75%, while for AIV-H9 infected flocks from which E. coli carries three virulence genes the average mortality rate is 11.6% with minimum 10.5% and maximum 13.8%. For other viruses, there is no clear correlation between the number of virulence genes in E. coli and the mortality rate caused by the virus in the same flock.
Three E. coli isolates (one E. coli O114 and two E. coli O125) were tested for their pathogenicity in one day old chicks. All of them were found pathogenic and the most pathogenic one (O125) has been selected for experimental infection with AIV-H9 in broiler chickens. The experiment was applied at 21 days of age chicks were grouped on 5 groups; Gp-A: kept as non-infected negative control, Gp-B: infected with E. coli O125 at 21d-old, Gp-C: infected with E. coli O125 at 21d-old and superinfected with AIV-H9N2 at 23d-old, Gp-D: infected with AIV-H9N2 at 21d-old and superinfected with E. coli O125 at 23d-old and finally Gp-E: infected AIV-H9N2 at 21d-old. Clinical examination and necropsy were performed after infection. Samples were collected pre- and post-infection for E. coli count, viral shedding, serology and histopathology.
Mild respiratory manifestations were observed in E. coli infected group while severe manifestations were observed in single AIV-H9 and co-infected groups specially at 7dpi. Feed intake was slightly decreased in the AIV-H9 infected groups (either single or co-infection) compared to the non-infected or the E. coli infected group. Significantly lower average body weight and higher FCR was recorded in the co-infected groups and AIV-H9 infected group then E. coli infected group compared to the negative control group at 35d old. Gross lesions were evident in different organs specially trachea, air sacs, kidneys and thymus glands. Lesions in trachea, thymus and kidneys were severe in AIV-H9 infected birds (either single or co-infection) while severe air sac lesions were recorded for E. coli infected birds (either single or c-infection). Lesions in trachea progressed with time in different groups and bronchial casts were observed in AIV-H9 infected groups at 7dpi. In the same groups thymus gland was initially inflamed and in the last 2 groups thymus atrophy was observed at 7dpi. There was significant increase in the tracheal, lung and organs E. coli count in the E. coli infected groups. Moreover, the E. coli count in lungs of chickens infected with E. coli and then infected with AIV-H9 was significantly higher than single E. coli infected group.
At 4dpi there was non-significant increase in the tracheal viral shedding between AIV-H9 infected groups (Gp-C, Gp-D and Gp-E). At 7dpi, significant increase in the tracheal viral shedding was reported in co-infected birds (Gp-C and Gp-D) than single AIV-H9 infected group (Gp-E). Moreover, the shedding in co-infected groups at 7dpi was higher than 4dpi while in single AIV-H9 group the shedding at 7dpi was lower than 4dpi.
AIV-H9 specific HI test was performed for sera collected at zero day old, 1d pre-infection and 7dpi. Low maternal HI Abs titers (3.38 log2 titers) was detected in zero day old chicks. Decay of the Abs was confirmed at 20d old. Seroconversion was reported in AIV-H9 infected groups (Gp-C, Gp-D and Gp-E) at 7dpi that was statistically higher than non AIV-infected groups (Gp-A and Gp-B) (P<0.001). In Gp-D the HI Ab titer was significantly higher than Gp-E (P<0.05). Non-significant variations (P>0.05) were reported between Gp-C and Gp-D and between Gp-C and Gp-E at 7dpi.
Conclusions:
• Poultry industry in Egypt is facing co-infection with many respiratory viruses. IBV and AIV-H9 are the most prevalent and they represent the major component of mixed infection.
• Under field conditions variable mortality rates are observed and they are high if AIV-H5 or vNDV is sharing in the infection process.
• APEC is highly prevalent in the respiratory tract of viral infected broiler chickens and many virulence traits specially iss and iutA genes do exist.
• Experimentally, co-infection with E. coli O125 and AIV-H9 had synergistic effect on the performance of broiler chickens and resulted in significant increase in the severity of clinical signs, poor FCR, higher lesion score, increased viral shedding and E. coli count than single infected groups.