New strains of illnesses and resulting infectious disease outbreaks are on the rise around the globe, Brown University researchers discovered after analyzing data from the last 33 years. Bruised as your eyes feel after reading that, also know there’s a general trend whereby each outbreak affects fewer people (the current Ebola crisis excepted).

To perform their analysis, the team turned to supercomputing to help them derive quantifiable data from the prose reports stored in the Global Infectious Disease and Epidemiology Online Network known as GIDEON. They began by creating what they called a "bioinformatics pipeline;" this is an automated database comprising 12,102 outbreaks of 215 infectious diseases involving 44 million people in 219 countries between the years 1980 and 2013. An outbreak, by the way, is defined as an increase in the number of cases of disease beyond what would normally be expected in a community, geographical area, or season.

Having created the dataset, the researchers next went about analyzing it. Immediately, the team observed a spike in the number of outbreaks occurring around the world.

Pathogens from Animals

Between 1980 and 1985, for instance, well under 1,000 epidemics occurred, but between 2005 and 2010, the number of instances surged to nearly 3,000. Within the same timeframes, the number of unique diseases causing the trouble climbed from less than 140 to about 160. Analysis of the origins of disease also revealed that 65 percent of new diseases recorded in the dataset came from animals, and since 1980, these zoonotic diseases caused more than half (56 percent) of all the outbreaks.

"We live in a world where human populations are increasingly interconnected with one another and with animals — both wildlife and livestock — that host novel pathogens," said Dr. Katherine Smith, assistant professor of biology and co-author of the study. "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."

Naturally, working on computers themselves, the team of colleagues speculated better information sharing and better reporting of outbreaks might account for the steep rise in infectious disease incidents. Looking again at the data, this time they included data on each country's GDP, press freedom, population size, population density, and even Internet use. Even after factoring out these possible confounders — as well as latitude, since more infectious diseases occur in lower latitudes — the number of outbreaks and unique causes rose precipitously over 33 years.

The team of intrepid researchers did not stop there. Instead, they compiled top 10 lists of diseases for each decade.

Changing Disease-scape

In the decade ended 2010, salmonella topped the list of zoonotic illnesses followed by e. coli, influenza A, hepatitis A, anthrax, dengue fever, shigellosis, tuberculosis, chikingunya, and trichinosis. The researchers noted that chikingunya, a mosquito-borne virus common to the Caribbean and Central America, appeared on the list as a newcomer. For human-specific infections during this same time period, gastroenteritis led the list, trailed by cholera, measles, enterovirus, bacterial meningitis, legionellosis, typhoid, and enteric fever, rotavirus, mumps, and pertussis. Meanwhile, adenoviruses and rubella fell from grace.

“A warmer world, a world with altered landscapes, and a more urban world will undoubtedly have a new disease-scape to consider,” Smith said, promising to continue the research and track how global patterns of disease shift as land use changes.

Source: Smith K, Ramachandran S, Bauer C, et al. Journal of the Royal Society Interface. 2014.