Lake Chilwa, a Ramsar List recognized wetland area of international importance, is located in southern Malawi on the border with Mozambique and is the second largest lake in Malawi. The lake and its surrounding wetland are roughly 40 km across and 60km from north to south, giving a total area of 2400 km². In normal years, one third of the lake is open water, one third is swamp and marsh, and one third is floodplains.
The wetland and catchment area is home to large populations of breeding waterfowl and has a total estimated bird population of 1.5 million resident and migratory birds. Around 461 bird catchers rely economically on trapping and selling birds for consumption by local communities. It is estimated that around one million birds are trapped per year, a questionably sustainable practice at the current harvest rate. This fertile wetland is also used for agriculture with the primary crops grown being maize and rice. It is estimated that about 50% of the rice harvested in Malawi comes from the Lake Chilwa wetland.
In January of 2007 scientists from the United States Geological Service (USGS) - Western Ecological Research Center traveled to Lake Chilwa to study migoratory bird movements and to test for Highly Pathogenic Avian Influenza (HPAI) H5N1. This research was conducted out of the town of Zomba, west of the lake. Partners included Wetlands International, the University of Cape Town, Malawian veterinary specialists, and members of local village bird hunting clubs. Using local trappers a total of three common comb ducks (Sarkidiornis melanotos), two white-faced whistling ducks (Dendrocygna viduata) and one fulvous whistling ducks (Dendrocygna bicolour) were captured and fitted with satellite transmitters.
An additional 912 diagnostic samples were collected from birds at Lake Chilwa (mostly ducks), from December 2006 through February 2007. These samples were tested at the French Agricultural Research Centre for International Development (CIRAD) laboratory in France. Seven samples from seven different birds were found positive for type A Avian Influenza virus by RT-PCR. None of the type A positive samples was found positive for H5 nor H7.
All RT-PCR positive influenza samples were sent to the FAO/OIE reference laboratory, Istituto Zooprofilattico Sperimentale delle Venezie (ISZVe) in Padova, Italy, for confirmation and attempts for virus isolation. No virus isolates could be obtained.
In understanding the disease status and the movement of these birds and the relationship to avian influenza outbreaks that may occur along their migratory flyways, we hope to better understand the ecology of the AI virus and the role wild birds play in the spread of the disease.
Current locations of these birds are uploaded biweekly to the USGS website.