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Plague-Carrying Fleas In Madagascar Developing Resistance To Several Insecticides

Disease Control: Scientists find fleas are unscathed by six of 12 commonly used insecticides, and only one insecticide is effective on all of the country’s fleas

by Bethany Halford
February 8, 2016 | A version of this story appeared in Volume 94, Issue 6

Credit: Pest and Diseases Image Library,
Xenopsylla cheopis.
A picture of the Oriental rat flea Xenopsylla cheopis.
Credit: Pest and Diseases Image Library,
Xenopsylla cheopis.

Despite decades of work trying to control plague, the illness is still a major health concern in Madagascar. A 2014 outbreak in that country infected more than 335 people at its peak and claimed at least 79 lives, according to the World Health Organization. Plague is primarily transmitted to people from rats via the Oriental rat flea Xenopsylla cheopis. Efforts to keep the disease in check focus on controlling the flea population with insecticides. But a study by Adélaïde Miarinjara and Sébastien Boyer, of the Pasteur Institute of Madagascar, reveals that of 12 standard insecticides, six—including the most commonly used insecticide deltamethrin—are ineffective against local fleas (PLOS Neglected Trop. Dis. 2016, DOI: 10.1371/journal.pntd.0004414). Miarinjara and Boyer studied eight flea populations from around the island and found that only one insecticide—dieldrin—was 100% effective on all populations. Dieldrin is an organochlorine compound that’s toxic to mammals and known to accumulate in the environment. It hasn’t been used in Madagascar since 1993. To prevent the spread of plague, Miarinjara and Boyer recommend exploring alternatives to insecticide dusting in homes, including rat control and insecticide-laced bait boxes for rats, which would reduce overall insecticide use.


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