Washington, Nov 16 A new study has found little evidence to show that factors like local rainfall and temperature have a significant impact on the incidence of dengue.

Large outbreaks of dengue, a vector-borne viral disease spread by the Aedes aegypti mosquito, occur every few years in many tropical countries.

Michael Johansson, of the Centers for Disease Control and Prevention in Puerto Rico, used a technique called "wavelet analysis" to probe associations between the local climate, El Niqo-Southern Oscillation - the climate cycle that occurs every three to four years as a result of the warming of the oceans in the eastern Pacific, and incidence of dengue in Mexico, Puerto Rico and Thailand - three countries where dengue is endemic.

They were able to separate and compare seasonal and multiyear components of each.

In all three countries temperature, rainfall, and dengue incidence varied strongly on an annual scale, showing association in the wavelet analysis.

On the multiyear scale however, the researchers found no association between El Niqo and dengue incidence in Mexico, a statistically insignificant association in Thailand, and an association in Puerto Rico only significant for part of the study period.

The researchers warned that the Puerto Rico outcomes should be viewed with caution.

They acknowledged that El Niqo could still play a role undetected by this research.

However, as Pejman Rohani of the University of Michigan - uninvolved in the research - states in a related Perspective, the absence of a predictable link between El Niqo and dengue transmission "is an important piece of information for the development of early warning systems".

The research has been published in PLoS Medicine. (ANI)