Rome-The Food and Agriculture Organization of the United Nations (FAO) has released the continental atlas of the distribution of tsetse flies in Africa, a vital tool in combatting an often-lethal parasitic disease among livestock that causes billions of dollars in economic losses for farmers in sub-Saharan Africa.
Tsetse flies (genus Glossina) are blood-sucking insects that act as incubators and carriers for trypanosomes, single-celled parasites responsible for causing debilitating and often fatal diseases. In humans, this disease is also known as "sleeping sickness," resulting in an illness that affects the nervous system and manifests symptoms such as fatigue, severe headaches, and coma. If not diagnosed and appropriately treated, the disease almost invariably leads to death.
While sleeping sickness is no longer considered a public health problem, with fewer than 2,000 cases reported each year in humans, the disease still severely affects livestock in Africa. Animal trypanosomosis, known as "nagana" in cattle, hinders milk and meat production, as well as the animals' ability to work. This leads to food insecurity and decreased income for millions of African farmers who depend on livestock.
Efforts to control and eliminate animal trypanosomosis require decisions based on sound evidence. However, the last continental maps of tsetse distribution in Africa were developed more than half a century ago, and no Africa-wide map of animal trypanosomosis occurrence has even been generated.
Years in the making, the FAO atlas is the first significant step in filling such data gaps.
Its data on tsetse distribution is based on 669 scientific papers spanning 31 years (from 1990 to 2020). It combines geolocation data such as Google Earth with entomological fieldwork, including stationary traps and fly rounds using mobile devices.
Tsetse fly distribution
In total, 7,386 sites across Africa were analysed, producing the most comprehensive maps to date of the tsetse fly's distribution on the continent.
Based on the data collected, the occurrence of the Glossina species was confirmed in 34 countries, spanning from a maximum latitude of approximately 15° north in Senegal (Niayes Region) to a minimum of 28.5° south in South Africa (KwaZulu-Natal Province). No published data on tsetse flies could be found for five countries in sub-Saharan Africa that are known or considered to be affected: Burundi, Guinea-Bissau, Liberia, Sierra Leone and Somalia. Furthermore, relatively limited information was found for several countries, especially Angola, the Congo, the Democratic Republic of the Congo and South Sudan. The atlas did not consider countries in northern Africa that have been historically free of tsetse flies.
Overall, relatively abundant data were available for the species of paramount veterinary and public health importance, especially for the riverine (palpalis) and savannah (morsitans) groups, while more limited information was found for the species of the forest (fusca) group.
With the available data, FAO developed continental and national maps for 26 of the 31 recognized species and subspecies of tsetse flies. The species with the broadest geographic distribution appear to be Glossina palpalis and Glossina tachinoides in western Africa, Glossina fuscipes in central Africa, and Glossina morsitans and Glossina pallidipes in eastern and southern Africa.
This kind of data will be vital for practitioners on the ground and policymakers in the affected countries, as well as for scientific researchers and international organizations such as the World Health Organization (WHO), with which FAO is working closely in the fight against sleeping sickness.
The atlas also provides a blueprint for the development of national information systems. Indeed, with FAO's support, veterinary authorities in Burkina Faso, Ethiopia, Ghana, Kenya, Mali, Sudan and Zimbabwe have already adopted FAO's methodological approach.
"We are hopeful that these tools will help reinvigorate initiatives aimed at removing this major hurdle to sustainable development in Africa and thus contribute to the vision of a healthy world, free of poverty and hunger," Thanawat Tiensin, the Director of FAO's Animal Production and Health Division, wrote in the atlas' forward.
Next steps
The atlas was developed by FAO within the framework of the Programme Against African Trypanosomosis (PAAT), with financial support from FAO, the Government of Italy, the European Union and WHO.
Updates to the atlas are planned, along with a new publication to fill the second significant data gap: continental maps of animal trypanosomoses.
