Stretching over 4,119,500 hectares in the midst of the Sahelian zone, The Inner Niger Delta (IND) in Mali is the largest continental wetland in West Africa and the second largest in Africa. The IND is a vast ecosystem of major ecological and economic importance, particularly for fish and livestock production. The region supports high numbers of Afro-tropical ducks and migrating Palearctic ducks in the northern winter and is on the Ramsar List of Wetlands of International Importance.
Many of the resident wild birds are hunted by local fishermen and hunters in the delta. Surveys conducted by Wetlands International and the Direction Régionale de la Conservation de la Nature (Regional Nature Conservation Department) of Mali have shown that several thousand birds are collected every year to feed local markets. This trade and the mixing of bird species at markets is a risk factor for disease crossover between a species making this an excellent site for virus ecology the of avian influenza at the wild bird/ domestic bird/ human interface.
The objective of the long-term monitoring project was to better understand the epidemiology and ecology of avian influenza viruses, including in wild bird populations. Three species were chosen for the study: garganey (Anas querquedula),whistling ducks (Dendrocygna sp.) and the common comb duck (Sarkidiornis melanotos), each of which represents a different type of migration route. The garganey, a teal, is a Europe-Asia-Africa intercontinental migratory bird which winters in Subsaharan Africa. The comb duck restricts its movements to Africa, but covers several regions, while the fulvous whistling duck, the most common African duck, tends to stay in the same region year round.
Information provided by birds equipped with telemetric units will help to further understand possible virus diffusion patterns within the African continent and across continents. Biological samples will be collected regularly to detect and characterize avian influenza virus strains circulating at different periods of the year, and in birds of different ages, of different species, and living in different habitats. Concurrent similar studies will be conducted in domestic and commensal birds, and the comparison of strains isolated from these different birds will help identify possible transmission patterns.
All these data, together with other information collected from studies on the role of the environment (water, mud, climatic conditions, etc), will be mapped and analysed by risk analysis and modelling methods in order to provide veterinary services with recommendations on how to best prevent or control the transmission of avian influenza in the region.
Argos transmitters were fitted on birds in collaboration by experts from the US Geological Survey (USGS) Western Ecological Research Center. The birds, only ducks, were caught in the Lake Walado-Débo area, near Banadji village, by a team of traditional hunters. At the end of each afternoon these hunters, who know the Inner Niger Delta and waterbird habits very well, set up a network of nets within the floodplains. During the night, flocks of ducks and waders would fall into the nets when they came to feed on fresh grasses, seeds and invertebrates. Early in the morning, the hunters returned to the site to collect the birds caught in the traps. Transmitters were placed on 23 ducks including 19 garganeys 8 comb ducks 3 fulvous whistling ducks (Dendrocygna bicolour) and 2 white-faced whistling ducks (Dendrocygna viduata). All 23 birds were also ringed, measured (tarsus-culmen-wing length and weight), and cloacal and tracheal swabs taken. Feather samples were also collected from nine species of birds, to determinate through future analysis their isotopic composition, which may provide information on diet, habitat use and geographic origin.
An additional 1871 samples were collected at the Niger delta (mostly from ducks), in both December 2006 and February 2007. These samples were tested at the French Agricultural Research Centre for International Development (CIRAD) laboratory in France. 34 samples from 34 different birds were found positive for type A Avian Influenza virus by RT-PCR. Two type A positive samples were found to be positive for H5 by RT-PCR.
All RT-PCR positive samples were sent to the FAO/OIE reference laboratory, Istituto Zooprofilattico Sperimentale delle Venezie (ISZVe) in Padova, Italy, for confirmation and viral isolation and were low pathogenic strains one H11N3 and the other H12N5.
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 available at the CIRAD website.