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Risk Factors for Infection with Highly Pathogenic Influenza a Virus (h5n1) in Commercial Chickens in Bangladesh

P. K. Biswas
Professor
Chittagong Veterinary and Animal Sciences University, Chittagong, Bangladesh

A. M. Habib
Central Disease Investigation Laboratory, Department of Livestock Services, Dhaka, Bangladesh

A. S. M. A. Hannan
Epidemiology Unit, Department of Livestock Services, Dhaka, Bangladesh

N. C. Debnath
Chittagong, Veterinary and Animal Sciences University, Chittagong, Bangladesh

S. S. U. Ahmed
Chittagong, Veterinary and Animal Sciences University, Chittagong, Bangladesh

A. Das
Chittagong, Veterinary and Animal Sciences University, Chittagong, Bangladesh

M. H. Rahman
Chittagong, Veterinary and Animal Sciences University, Chittagong, Bangladesh

H. Barua
Chittagong, Veterinary and Animal Sciences University, Chittagong, Bangladesh

J. P. Christensen
Department of Veterinary Pathobiology, Faculty of Life Sciences, Copenhagen University, Copenhagen, Denmark

M. Giasuddin
Principal Scientific Officer
Animal Health Research Division, Bangladesh Livestock Research Institute, Savar, Dhaka-1341

Abstract/ Executive Summary:

A matched case-control study was carried out to identify risk factors for highly pathogenic avian influenza A virus (subtype H5N1) infection in commercial chickens in Bangladesh. A total of 33 commercial farms diagnosed with H5N1 before September 9, 2007, were enrolled as cases, and 99 geographically matched unaffected farms were enrolled as control farms. Farm data were collected using a pretested questionnaire, and analysed by matched-pair analysis and multivariate conditional logistic regression. Two factors independently and positively associated with H5N1 infection remained in the final model. They were ‘farm accessible to feral and wild animals’ (odds ratio [OR] 5·71, 95 per cent confidence interval [CI] 1·81 to 18·0, P=0·003) and ‘footbath at entry to farm/shed’ (OR 4·93, 95 per cent CI 1·61 to 15·1, P=0·005). The use of a designated vehicle for sending eggs to a vendor or market appeared to be a protective factor (OR 0·14, 95 per cent CI 0·02 to 0·88, P=0·036).

Keywords: Avian influenza virus; Bangladesh; Highly pathogenic

Location: Bangladesh Livestock Research Institute

Start Date: 00-01-2007

End Date: 00-09-2007

Program Area: Animal Health and Management

Commodity: Chicken

Objectives:

1. To identify risk factors for highly pathogenic avian influenza A virus (subtype H5N1) infection in commercial chickens in Bangladesh.

Methodology:

Study population - The DLS provides subsidised veterinary services through Upazila Livestock Offices (ULO); an Upazila is a lower administrative unit, of which there are 472 in Bangladesh. From a ULO, a state veterinary surgeon and supporting staff deliver veterinary services. A commercial farm belonging to FAO system 2 was clinically suspected to have HPAI on January 15, 2007, and H5 was identified on March 13 by the National Reference Laboratory for Avian Influenza (NRL-AI) at Savar near the capital, Dhaka. When the diagnosis was confirmed as being HPAI subtype H5N1 at the National Institute for Animal Health (NIAH) in Bangkok, Thailand, Bangladesh was declared HPAI H5N1-infected. The owner of the index farm had delayed in reporting the mortalities to the local DLS office. Some days also passed in sending samples from the infected farm to the Central Disease Investigation Laboratory (CDIL), in getting the tentative and confirmatory diagnoses from the CDIL and the NRL-AI, respectively, and in reconfirmation from the NIAH. By September 9, 2007, 33 outbreaks (by date of clinical onset) had been identified on commercial chicken farms in nine districts: Jamalpur, Dhaka, Narayangonj, Gazipur, Tangail, Noakhali, Jessore, Rajbari and Bogra. All these farms were included as cases, defined as farms having high death rates and H5 identified by the NRL-AI. Diagnostic criteria and procedures for identification of case farms - Having received information of high mortality in chickens on a farm, the veterinary surgeon of the ULO examined the infected chickens. If HPAI was suspected, diseased and dead chickens were sent to the CDIL or any of the seven Field Disease Investigation Laboratories (FDILs) of the DLS, which provide subsidised diagnostic services. At the laboratory, oropharyngeal swabs were taken to test for avian influenza A virus antigen, using the avian influenza type A quick antigen detection kit (Synbiotics) (hereafter termed rapid antigen test). When this test was positive, tracheas from the dead chickens were referred to the NRL-AI, where H5 was detected using RT-PCR on pieces of tracheal tissue. Data collection and survey method - A preliminary questionnaire was administered to 10 of the HPAI-positive farms. Modifications were made to this questionnaire, incorporating new variables encountered during this pretesting, and the questionnaire (obtainable from the first author on request) was further modified for this study. Statistical analysis - The data were entered into a spreadsheet program (Excel 2000; Microsoft) and transferred into EpiInfo 2000 (Centres for Disease Control and Prevention) for analysis. Mantel-Haenszel matched-pair analysis (McNemar test) was applied to estimate the strength and statistical significance of associations between the risk factors and HPAI H5NI virus infection.

Source of Information: Veterinary Record (2009) 164, 743-746

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Two factors independently and positively associated with H5N1 infection remained in the final model. They were ‘farm accessible to feral and wild animals’ (odds ratio [OR] 5·71, 95 per cent confidence interval [CI] 1·81 to 18·0, P=0·003) and ‘footbath at entry to farm/shed’ (OR 4·93, 95 per cent CI 1·61 to 15·1, P=0·005).

Knowledge Management: Journal