Global infectious disease outbreaks on the rise since 1980

Salmonella and the flu are among the top 10 most common infections causing disease outbreaks, according to new research that finds the number of such outbreaks appears to have increased around the globe over the last three decades.

Animals and insects are the major sources of infections that affect humans, causing illnesses such as dengue, which is carried by mosquitos, and Ebola, which may have come from bats.

In fact, about 65 per cent of the diseases that appeared in the research were "zoonoses," meaning they come from animals.

In a world where humans are increasingly interconnected with one another and with animals, animal diseases are able to cross over to our species, according to Katherine Smith, a co-author of the study and an assistant professor of biology at Brown University.

"These connections create opportunities for pathogens to switch hosts, cross borders, and evolve new strains that are stronger than what we have seen in the past," she said in a statement.

From 2000 to 2010, the most common animal-derived infections among humans were:

Chikungunya, a mosquito-borne virus was a newcomer in the decade, as was influenza A. Other infections that had previously been common dropped off the top 10, including campylobacterosis, cryptosporidiosis, and hepatitis E.

Among infections that were specific only to humans, the top 10 were:

The good news is that while there has been an increase in overall outbreaks, the impact of those outbreaks is declining, affecting smaller proportions of people than previous outbreaks. The authors say that's likely due to improvements in infection prevention, early detection, and treatment.

To perform their study, the researchers took data from the Global Infectious Disease and Epidemiology Online Network (GIDEON), looking at 44 million infections in 219 countries between 1980 and 2013. They defined a disease "outbreak" as an increase in the number of cases beyond what would normally be expected of a certain community or a certain season.

Between 1980 and 1985, there were fewer than 1,000 such outbreaks. But between 2005 and 2010, the number surged to nearly 3,000.

The increase could have been due to such things as better reporting of outbreaks and better ability to share information, the researchers acknowledged. But they said that even after taking steps to account for these factors, it's clear the numbers of disease outbreaks rose significantly over the 33 years.

The full study appears in the Journal of the Royal Society Interface.