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Insecticide susceptibility of some vector fleas and mosquitoes in Burma
Abstract:
Rat fleas and mosquitoes are insect vectors of public health importance in Burma. Plague is endemic in Central Burma and DDT has been the principal insecticide used for its control to date. Dengue haemorrhagic fever, recently introduced and transmitted by Aedes aegypti, has been spreading to major towns since 1971. The rodents, Rattus rattus, R. exulans, Bandicota bengalensis, Mus musculus, as well as shrews were commonly caught during routine trapping in the country. Rattus norvegicus, prevalent in Rangoon City, is not found in Central Burma. The rat fleas, Xenopsylla cheopis and X. astia, were found to be infesting these rodents, the former being the principal vector of plague. Insecticide susceptibility tests have been carried out periodically in plague endemic areas and Rangoon since 1966 and it is now observed that rat fleas in most of these endemic towns and Rangoon Port are no longer susceptible to DDT. Subsequent rechecks in towns where fleas became resistance to DDT show that fleas are persistently resistant to the insecticide. Aedes aegypti is found to be highly prevalent both in rural and urban areas of almost every major town and townships below 900 meters. Insecticide susceptible tests on this mosquito in limited areas show that the mosquito is generally resistant to DDT but susceptible to other insecticides. With the development of DDT resistance in fleas, it is now necessary to change to an effective insecticide in the control of plague in Burma.
Insights
Rat fleas in Burma are no longer susceptible to DDT, the primary insecticide used for plague control. This widespread DDT resistance necessitates a shift to alternative insecticides for effective disease management.
Area of Science:
- Medical entomology
- Vector-borne disease control
- Insecticide resistance
Background:
- Plague and Dengue hemorrhagic fever are significant public health concerns in Burma, transmitted by insect vectors.
- DDT has historically been the primary insecticide for controlling plague vectors, primarily rat fleas.
- Aedes aegypti mosquitoes, vectors of Dengue hemorrhagic fever, are prevalent in urban and rural areas.
Purpose of the Study:
- To assess the insecticide susceptibility of rat fleas and Aedes aegypti mosquitoes in Burma.
- To evaluate the efficacy of DDT in controlling plague vectors given emerging resistance.
- To inform public health strategies for vector control in Burma.
Main Methods:
- Conducted routine trapping of rodents and associated fleas in plague-endemic areas and Rangoon.
- Performed insecticide susceptibility tests on rat fleas (Xenopsylla cheopis, X. astia) and Aedes aegypti mosquitoes.
- Monitored the prevalence of Aedes aegypti in various geographical settings.
Main Results:
- Rat fleas, particularly Xenopsylla cheopis (a key plague vector), exhibit widespread resistance to DDT in endemic areas and Rangoon Port.
- Aedes aegypti mosquitoes show general resistance to DDT but remain susceptible to other insecticides.
- Rodent species commonly found include Rattus rattus, R. exulans, Bandicota bengalensis, and Mus musculus, with Xenopsylla cheopis and X. astia as common flea infestants.
Conclusions:
- The development of DDT resistance in rat fleas poses a significant challenge to plague control efforts in Burma.
- Alternative insecticides are urgently needed to replace DDT for effective plague vector management.
- Continued monitoring of insecticide resistance in both fleas and mosquitoes is crucial for public health.