A recent outbreak of sleeping sickness in eastern Uganda might be attributed to livestock movement from another part of the country where the disease is endemic, conclude authors of a study in this week’s issue of THE LANCET.
Sleeping sickness is a parasitic disease caused by two protozoa, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. The disease is transmitted by the tsetse fly in sub-Saharan Africa, and is fatal if not treated with drugs such as melarsoprol. Soroti District-where an outbreak of sleeping sickness began in late 1998-has been the subject of large-scale livestock restocking activities. Because domestic cattle are important reservoirs of T b rhodesiense, Eric Fèvre and colleagues from the University of Edinburgh, UK, and the Livestock Health Research Institute, Uganda, investigated the role of cattle in the origins of the outbreak.
The investigators identified the origins of cattle entering Soroti District in the 4 years preceding the outbreak. A matched case-control study was done to assess whether the distance of villages from the main market involved with cattle restocking was a risk factor for sleeping sickness. The spatial clustering of sleeping sickness cases was assessed at the start of the outbreak. Over 50% (1510 of 2796) of cattle traded at the market were reported to have originated from endemic sleeping-sickness areas. The case-control study revealed that distance to the cattle market was a highly significant risk factor for sleeping sickness, and that there was a significant clustering of cases (27 of 28) close to the market at the start of the outbreak. As the outbreak progressed, the average distance of cases moved away from the cattle market by approximately 0.4 km each month.
In an accompanying Commentary (p 603), Michael Barrett from the University of Glasgow, UK, cautions that prophylactic drug-treatment to prevent cattle acquiring the non-human form of sleeping sickness could result in the emergence of cross-resistance and reduce the efficacy of drugs such as melarsoprol. He states: “Fèvre and colleagues report that sleeping sickeness due to T b rhodesiense can be spread from one area to another through the mass movement of cattle. They therefore propose that cattle should be treated before transportation in order to diminish the risk of transmission of trypanosomes infectious in man. Since selection of resistance to diminazene in animals can lead to melarsoprol resistance in human beings, caution must be exercised in the choice of trypanocide used to clear cattle of trypanosomes. Therefore, although resistance to isometamidium and homidium can arise more quickly in cattle than can resistance to diminazene, these former drugs could be better choices in terms of implications for human health.”
Contact: Mr E M Fèvre, Centre for Tropical Veterinary Medicine,University of Edinburgh,Royal School of Veterinary Studies,Easter Bush Veterinary Centre,Roslin,EH25 9RG,UK;T) 44-131-650-7347;F) 44-131-445-5099;E) Eric.Fevre@ed.ac.uk
Dr Michael Barrett, Division of Infection and Immunity,Institute of Biomedical & Life Sciences,Jospeh Black Building,University of Glasgow,Glasgow,G12 8QQ,UK;T) 44-141-330-6904;F) 44-141-330-8016;E) m.barrett@bio.gla.ac.uk
Journal
The Lancet