Image caption A mosquito feeding on human blood

Novel measures are needed to tackle malaria hotspots in countries with low levels of the disease, scientists say.

Countries such as Malaysia and Bhutan have seen malaria levels fall - but pockets of infection remain, mainly among men living or working outdoors.

Writing in the Lancet, the scientists say this means that measures, such as nets, that help in homes are ineffective.

Instead, treated hammocks or clothing could be more useful.

'Hot pops'

In countries where there are high levels of malaria, it is largely women and young children who are affected.

But in places where there has been success in reducing overall levels, it is adult men who bear most risk.

More sophisticated and targeted approaches to identifying those people who are infected, and responding promptly and effectively, must be put in place Prof Sir Richard Feachem , University of California, San Francisco

Those working in forests or plantations, or sleeping in fields overnight to protect crops, are all specific groups - known as "hot pops" (populations).

In the Philippines it was found that men who went to forests at night to hunt or gather wood were six times more likely to be infected than other men.

In Sri Lanka, where malaria incidence fell by 99.9% between 1999 and 2011, the proportion of infections in men rose from 54% to 93%.

The Lancet paper suggests this might be linked to the conflict in the island, which ran from 1983 to 2009.

Other groups who are disproportionately affected include ethnic or political minorities who are typically poor and often on the move.

Malarial burdens

The authors of the paper say different measures are needed compared with traditional malaria prevention work.

Prof Sir Richard Feachem, director of the Global Health Group at the University of California, San Francisco, the study's lead author, said: "The malaria control strategies implemented over the last decade have been highly successful in reducing malaria worldwide.

"However, these strategies must evolve to respond effectively to the changing patterns of infection in low transmission areas.

"More sophisticated and targeted approaches to identifying those people who are infected, and responding promptly and effectively, must be put in place.

"The good news is that these new approaches are being pioneered with great success in countries such as China, Sri Lanka and Swaziland."

In addition, a different type of malarial parasite is causing problems,

Traditionally, the Plasmodium falciparum parasite has been the one responsible for most malaria cases around the world.

But the success in controlling P. falciparum in many countries has resulted in an increasing proportion of infections from P. vivax, another malarial parasite.

P. vivax is less likely to prove fatal, but is also harder to detect and treat, and therefore more difficult to control and eliminate.

The researchers wrote in the Lancet: "As countries reduce their malaria burdens, strategies that address the changing epidemiology… need to be developed, validated and adopted."