Isolation of H5 Highly Pathogenic Avian Influenza from Cattle Egret (Bubulcus Ibis) in the Vicinity of Affected Broiler Chicken Flocks in Egypt

Background: The role of free-living birds in the spread and epidemiology of H5N1 Highly pathogenic avian influenza is often neglected. Cattle egret is one of the free-living birds that is often present in the vicinity of commercial chicken farms with a possibility of catching and or helping the spread of avian viral diseases, especially H5N1 AIV; this is augmented by broken biosecurity which is often in small and medium production levels. 

 

Objective: To investigate the possible role of cattle egrets in the spread and epidemiology and to try virus isolation if possible.

 

Methods: Rapid test strip for detecting avian influenza antigen was used to test 15 tracheal pool samples collected from 15 commercial broiler flocks showing rapid increase in mortality, respiratory and enteric manifestation in Desouk and Qallin, Kafr-el-Shiekh Province, Egypt from 2014 to 2015. Another 60 swab samples (oropharyngeal as well as cloacal swabs) were collected from 30 cattle egrets in the vicinity of these flocks. Trials for isolation of AIV was conducted on collected samples via allantoic sac inoculation in 9-11 days old specific pathogen free (SPF) embryonated chicken eggs (ECEs) followed by identification by hemagglutination (HA) and hemagglutination inhibition (HI) using specific polyclonal antisera against AIV H5 and H9 and confirmation by RT-PCR. Two positive AIV H5 (cattle egret isolate and broiler chicken isolate) were selected for sequencing of HA gene fragment.

 

Results: The rapid field test revealed detection of AIV in one broiler flock (6.67 %). Isolation revealed 2/15 (13.3 %) AIV H5 isolates from broiler chicken flock samples, whereas 1/60 (1.67 %) AIV H5 isolate from cattle egret samples. Phylogenetic analysis, that revealed clustering in the same subclade 2.2.1/ C with Egyptian highly pathogenic avian influenza virus (HPAIV) H5N1 isolates from 2011-2013.

 

Conclusion: Isolation of HPAIV H5 from cattle egret shed the light on the possible epidemiological role of this resident bird in transmission of AIV to susceptible chicken. Further detailed analysis is required to detect the complete antigenic/ genetic characteristics of cattle egret H5 influenza isolate.