Washington: The number of infectious disease outbreaks and the number of unique illnesses causing them appear to be increasing around the globe, scientists, including one of Indian-origin, have found.
The findings also showed that even though the globe faces more outbreaks from more pathogens, they tend to affect a shrinking proportion of the world population. For the study, Brown University researchers analysed more than 12,000 outbreaks affecting 44 million people worldwide over the last 33 years.
They found that 65 per cent of diseases in the dataset were "zoonoses," meaning they come from animals. In all, such diseases caused 56 per cent of outbreaks since 1980, researchers said.
"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 Katherine Smith, assistant professor of biology and co-lead 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," Smith said. To perform the analysis, the team worked to derive quantifiable data from the prose reports of outbreaks stored in the Global Infectious Disease and Epidemiology Online Network (GIDEON).
They developed a "bioinformatics pipeline" to automate the creation of a database comprising 12,102 outbreaks of 215 infectious diseases involving 44 million cases in 219 countries between 1980 and 2013. The raw numbers showed a steep rise in the number of outbreaks globally.
"GIDEON defines an outbreak as an increase in the number of cases of disease beyond what would normally be expected in a defined community, geographical area, or season," said co-lead author of the study, Sohini Ramachandran, assistant professor of biostatistics.
Between 1980 and 1985 there were well under 1,000 such instances, but for 2005-10, the number surged to nearly 3,000. In those same timeframes, the number of unique diseases causing the trouble climbed from less than 140 to about 160. Smith and her colleagues reasoned, the increase could be due to factors such as better reporting of outbreaks and information sharing.
To account for that, they paired the outbreak data with data on each country's GDP, press freedom, population size, population density, and even Internet use (after 1990). Even after controlling for those factors, the numbers of outbreaks and unique causes rose significantly over 33 years.
"Our data suggest that, despite an increase in overall outbreaks, global improvements in prevention, early detection, control, and treatment are becoming more effective at reducing the number of people infected," the authors wrote in the Journal of the Royal Society Interface.
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