A study from Brazil has revealed that the notion that flu epidemics begin in areas of high population density and extend outwards may not be appropriate for the tropics.
The study revealed that in Brazil, flu is triggered in less populated North area and moves later to the South region.
"This flips our understanding of influenza in tropical regions on its head and will hopefully improve control strategies," Nature quoted Mark Miller of the Fogarty International Center (FIC) for Advanced Study in the Health Sciences in Bethesda, Maryland, as saying.
Miller and his colleagues looked at Brazil, expecting highly populated cities to have the first cases of flu. But they discovered that southern states, containing Sao Paolo and Rio de Janeiro, developed epidemics a couple of months after flu cases occurred in appeared in Brazil's northern jungles.
"We were really surprised. The fact that influenza starts in the north may mean that seasonal epidemics arise from the tropics where the virus persists all year round," Miller said.
The team suggested that weather may determine how the disease travels south from the Equator. "More delicate experiments are definitely needed to tease apart the complex relationships being uncovered here. This research takes a nice first look at viral behavior in the tropics," said Eddie Holmes, evolutionary virologist at Pennsylvania State University, University Park.
The researchers also said that the study suggested that vaccines for 70 pct of the elderly across Brazil, may prove more effective if administered at different times in different regions.
The work will appear in the American Journal of Epidemiology later this month.