Madagascar is one of the last places where outbreaks of human bubonic plague still happen regularly. Fleas carrying the plague bacterium Yersinia pestis can spread the disease through their bites. And while a species commonly known as "the rat flea" has been fingered as the main culprit in plague outbreaks, a species known as "the human flea" may play a secondary role.

Household flea infestations also promote the overuse of insecticides. Surveys by the researchers reveal that 80% of the households use insecticide to try to battle the fleas. Many people are buying liquid insecticides that are repackaged in empty plastic or glass containers, without labels or instructions for how to apply them, and sold in small, open-air markets. Improper use of insecticides is a health risk to people who may be overexposed to the chemicals. "Overuse of these chemicals is also dangerous because some fleas are developing resistance to insecticides -- the frontline tools for battling plague outbreaks," Miarinjara says.

The researchers painstakingly removed each drowned flea using tweezers, set them to dry on absorbent paper, and then transferred them to test tubes for laboratory identification and analyses. The results showed that around 95% of the species collected in households were human fleas, mixed at times with a few rat fleas and a few from a third species that prefers to feed on cats and dogs. Collections were conducted in both the dry and rainy seasons with similar results. "We're now looking deeper into what's going on with insecticide use in households," Miarinjara says. "We want to both sort out what is driving insecticide resistance among fleas and find ways to help people use insecticides safely and more effectively."