Climate change paves way for rise in infectious diseases: report

Rising temperatures and increasing levels of precipitation triggered by climate change may increase the spread of infectious diseases, Canadian researchers suggest in a paper published Tuesday.

"Any major change in the nonliving component of an ecosystem will affect living components, including microbes, insect vectors, animal reservoirs and susceptible humans, and change the incidence and distribution of infectious diseases," wrote researchers in the Canadian Medical Association Journal.

They explained that rising temperatures could spur a geographic spread, and longer life, for species that carry diseases transmissible to humans, and more rain could lead to flooding and the spreading of contaminants.

For example, warmer temperatures could mean that mosquitoes, and other insects that carry diseases transmissible to humans, can expand their breeding area and the length of time they can survive in a season.

Co-author Dr. David Fisman, a scientist at the Hospital for Sick Children's Research Institute in Toronto, said this could cause the number of mosquitoes carrying the West Nile virus to rise dramatically, and a longer summer could see the period the disease can spread be prolonged into October or November.

Another affected species could be ticks, which can carry Lyme disease.

Flooding a big issue

As for increasing precipitation, co-author Amy Greer, a research fellow at the hospital, said more rain in a short period of time could lead to flooding, "and those precipitation events or flood events have been linked to outbreaks of things like gastroenteritis [intestinal disorders]."

One example, she said, is when rain allows for agricultural run-off into the water system, such as in Walkerton, Ont., with E. coli bacteria being a worry.

While a time frame for these changes is difficult to specify, Fisman said, it could happen within the next several decades.

"We're not trying to predict the future," he said. "What we're saying is that there's a real possibility."

The researchers said federal and provincial health bodies need to strengthen surveillance methods in preparation, so new cases of existing diseases and the emergence of new ones can be properly tracked.

"Unless we are able to identify and count the number of cases of disease that we have and look for year-on-year trends, we're never even going to know whether things are getting worse at the population level until things get so bad it will be sort of a slap in the face," Fisman said.

Infectious diseases in livestock and pets must also be monitored, Greer said.

"Many of these pathogens do have animal or insect components to them or are pathogens that are able to be harboured by both animals and humans," she explained.

Greer said veterinarians, for example, should let the public health community know if they see an increase in the number of ticks on pets.