Climate change could increase foodborne illness by energizing flies

Warmer springs and summers could make house flies friskier, spreading diarrhea-causing bacteria to more places. As a result, foodborne Campylobacter infections could increase with climate change, proposes epidemiologist Melanie Cousins of the University of Waterloo in Canada. 

Cousins’ computer simulation, still a proof-of-concept version, focuses on how the warm weather surge in house flies and their activity affects the typical spring-summer rise in Campylobacter cases. Under a scenario of summers 2.5 degrees Celsius warmer on average than in 2003, the simulation predicts about 28 percent more Campylobacter cases in the Canadian province of Ontario by 2050, she and colleagues say February 13 in Royal Society Open Science.

Campylobacter infections are most often caused by contaminated food, perhaps by a fly that’s strolled on other tainted food, an infected animal or feces. Most people recover from an infection within about 10 days. The bacteria are the most common cause of gastrointestinal illness in Canada, with Ontario averaging more than 3,000 cases a year. The United States has some 1.3 million infections a year.

To set up a simplified simulation, Cousins used data from 2005 on reported Campylobacter infections in Ontario to estimate transmission rates and fly birth and death rates. She then plugged those rates into the simulation to predict subsequent years’ Campylobacter infections. Those results came close to the real data available through 2013, and allowed her to predict future infections under different warming scenarios. The simulation assumes flies become more active with climate change since, like other insects, they depend on ambient temperatures for heating and cooling. It also assumes bacterial increases with warming.

The study is just the latest to highlight consequences of warming on insect behavior. Other studies have predicted how climate change might increase pest attacks on crops (SN: 9/29/18, p. 8) and affect public health, such as Lyme disease’s creep into Canada (SN: 8/19/17, p. 16).