Agricultural Research Management Information System

Home
Research Summary
Search
About Us
- ARMIS
- Brochure
Contact Us
Report
User Request
Data Input
Help
- Operation Manual
  - PDF
  - Video
- Program Area & Commodity
We have reached 37600 number of research entries at this moment.

- Logout

Research Detail

Home
Research
Detail

The Space-time Clustering of Highly Pathogenic Avian Influenza (hpai) H5n1 Outbreaks in Bangladesh

S. S. U. AHMED
University of Copenhagen, Faculty of Life Sciences, Department of Large Animal Sciences, Frederiksberg C, Denmark and Chittagong Veterinary and Animal Sciences University, Faculty of Veterinary Medicine, Department of Medicine and Surgery, Chittagong, Bangladesh

A. K. ERSBØLL
1 University of Copenhagen, Faculty of Life Sciences, Department of Large Animal Sciences, Frederiksberg C, Denmark

P. K. B ISWAS
Chittagong Veterinary and Animal Sciences University, Faculty of Veterinary Medicine, Department of Microbiology, Chittagong, Bangladesh

J. P. CHR ISTENSEN
University of Copenhagen, Faculty of Life Sciences, Department of Veterinary Disease Biology, Frederiksberg C, Denmark

University of Copenhagen, Faculty of Life Sciences, Department of Veterinary Disease Biology, Frederiksberg C, Denmark

Abstract/ Executive Summary:

Bangladesh faced two epidemic waves of highly pathogenic avian influenza (HPAI) H5N1 in two consecutive years. The peaks of the waves were observed in February–July 2007 and January–April 2008, respectively. We examined the spatial and temporal patterns of the 293 outbreaks in 143 subdistricts in 2007 and 2008. Global clustering assessed by K-function was seen at distances 150–300 km between subdistricts. Significant local clusters were detected by space-time scan statistics. In both waves, significant primary clusters of HPAI outbreaks were identified in the central part of the country dominated by commercial production systems and in the northwestern part primarily in backyard production systems. Secondary clusters varied from the northwestern part in 2007 and the southern part in 2008. The findings are highly relevant for the successful planning and implementation of control, prevention and surveillance strategies by highlighting areas where detailed investigations should be initiated.

Keywords: Bangladesh, Clustering, Epidemiology, Sub-districts, H5N1 avian influenza

Location: In Bangladesh

Start Date: 00-02-2007

End Date: 00-12-2008

Program Area: Risk Management in Agriculture

Commodity: Diseases, Virus

Objectives:

The objective of the present study was to identify space-time clusters of HPAI outbreaks at the subdistrict level in Bangladesh to support existing surveillance and to suggest empirical strategies for HPAI.

Methodology:

Outbreak data and data management: Data on outbreaks of HPAI were collected from the website of the World Animal Health Organization (OIE). All laboratory-confirmed outbreaks were officially reported by DLS Bangladesh to OIE. Clinical AI cases were initially reported by farmers to a state veterinary surgeon working at the subdistrict livestock office (i.e. the ULO) who then examined the sick chickens on the farm. If AI was suspected, dead chickens were collected and sent to the National Reference Laboratory for Avian Influenza (NRL-AI) in Bangladesh. The virus was confirmed in tracheal samples from chickens on the suspected farms by the NRL-AI by RT–PCR using a primer set HA oligo-5k (5k-ACACATGCYCARG ACATACT-3k) and HA oligo-3k (5k-CTYTGRTTYAGTGTTGATGT-3k) described by Lee et al. [21]. Biswas et al. [4] described in detail HPAI case-reporting in chickens, laboratory techniques employed at the NRL-AI and diagnostic reconfirmation of the virus in some representative samples sent to the Veterinary Laboratory Agency in the UK. For administrative purposes, Bangladesh is divided into six divisions, 64 districts and 481 subdistricts [22]. We concentrated our study at the subdistrict level with a subdistrict of Bangladesh as the study unit. The location used for the subdistricts was the centroid of the respective subdistricts. Coordinates for the centroids were calculated from the subdistrict-level digital map in ArcMap 9. 2 (Environmental System Research Institute, USA). Coordinates were converted from latitude/longitude to Cartesian UTM coordinates using the WGM84 ellipsoid and UTM zone 46. We performed data management with SAS version 9.1 (SAS Institute Inc., USA). Of the 481 subdistricts, we excluded 17 due to lack of data available regarding centroids resulting in a sample of 464 subdistricts. A subdistrict was considered as infected (case) if it had at least one officially confirmed outbreak within the period of interest. The rest of the subdistricts were considered as non-infected (control). Descriptive analysis We constructed the epidemic curve for affected subdistricts in relation to the production system. We plotted the number of infected subdistricts identified per day as a function of time. A subdistrict with one or more laboratory-confirmed case(s) for a particular day was considered as an infected subdistrict. In the construction of the epidemic curve of the affected subdistricts, we applied a temporal moving average of the affected subdistricts. The latter method removes the dependency of frequency at some specific temporal points and transforms the frequencies into a continuous form. We used a window size of 30 days based on visual inspection of the smoothed plot. Finally, we calculated the prevalence of HPAI-infected subdistricts stratified by production systems. Cluster analysis: To examine the clustering of HPAI outbreaks at the subdistrict level in Bangladesh we used two approaches. First, we evaluated global spatial clustering using K-function analysis for each wave and production type. Second, in order to identify the exact location of clusters, we applied a local cluster detection technique using scan statistics.

Source of Information: Epidemiol. Infect. (2010), 138, 843–852. f Cambridge University Press 2010

Article Link (Online Journal): doi:10.1017/S0950268810000178

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

From February 2007 to December 2008, a total of 148 (31%) out of 481 subdistricts were officially confirmed positive for HPAI infection. The epidemic of HPAI in Bangladesh is characterized by two distinct waves between February 2007 and May 2008. The first wave began in February, peaked in March and ended in early July 2007. After that almost 2 months passed without any officially confirmed cases. The second wave started sporadically in September and continued to November 2007. The epidemic started in December 2007, peaked in February and ended in April 2008. After the second wave, there were still some sporadic officially confirmed cases in Bangladesh. The moving average indicated the first wave was between April and July 2007 and the second wave was between January and April 2008. The analyses were performed for the two waves individually.

Knowledge Management: Journal