January, 1999
In southwestern Ethiopia a program to eradicate sleeping sickness has apparently turned up a drug-resistant form of the disease. In a large experimental program using both drugs and tsetse fly traps, one group of treated cattle had a resurgence of the disease, implying that the drug may no longer be useful in curing the disease, according to a report from the Panafrican News Agency (PANA). While this may not yet represent a major set-back in the continent-wide effort to control sleeping sickness, it may be an important case of emerging drug-resistance, an issue that is of increasing concern in many contexts.
Sleeping sickness is properly known as trypanosomiasis, after trypanosomes, a protozoan that causes the disease. The protozoan is transmitted to cattle and to people by biting tsetse flies. Once in the body, trypanosomes attack the nervous system, causing drowsiness and eventually death. Tens of millions of people and livestock risk exposure to the disease in Africa, and some estimate that up to 50,000 people a year may die from the disease.
Because trypanosomiasis is so widespread and lethal, it is the subject of major disease control efforts. One of these is in Ethiopia's Ghibe valley, where the International Livestock Research Institute has engaged 3,500 households in a research program. This group has been using two drugs, cypermethrin and deltamethrin to prevent trypanosomiasis in cattle. In cattle treated with the latter drug, deltamethrin, trypanosomiasis recurred in some cases. Although drug resistance is not proven to be the cause of this failure, it is the main explanation reported by PANA.
Drug resistance occurs when a species of bacteria or a parasite develops immunity through long exposure to the drugs intended to kill it. A pest becomes resistant when random genetic changes happen produce a strain that survives exposre to the drug. As widespread use of the drug kills off non-resistant strans, the pest population becomes dominated by resistant strains, and the drug becomes increasingly useless. Drug resistance is a concern because it is becoming increasingly common as antibacterial chemicals (including those used in household antibacterial soaps) and pesticides become more widely used.
Ironically, trypanosomiasis may play a significant role in environmental protection in Africa. Although the disease exacerbates poverty and sickness in already poor populations, in some regions the disease has, consequently, kept both human and animal populations low. The result is moderated grazing and agricultural pressures on the land. Although complete eradication of the disease remains a distant dream, success in these efforts could have important ecological ramifications.
In related news, the February issue of the journal Nature reported a breakthrough in genetically disabling the trypanosome protozoan. Although use of this genetic alteration in preventing disease is probably some time off, this breakthrough was hailed as a promising step toward controlling trypanosomiasis.
For further information, see these related web sites:
Report on drug-resistant trypanosome from PANA
Report on problems with African diseases, including epidemics caused by war
World Health Organization news on infectious diseases, including trypanosomiasis
General information on trypanosomiasis
To read more, see
Environmental Science, A Global Concern, Cunningham and Saigo, 5th ed.
Infections organisms: pp. 184-87
Map of hunger in Africa: p. 215
Pesticide use for controlling diseases; development of resistance: pp. 253-56
Environmental Science, Enger and Smith, 6th ed.
Resistance to pesticides: pp. 275-77
Graph of increase in insecticide resistance: p. 276
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