Nearly 6 million people living in Nepal's Terai Belt are vulnerable to Kala-azar, an official said here Monday.

"The disease, affecting mostly those from the economically disadvantage community could spread among 150 million people if prompt action is not taken," Krishna Kumar Rai, executive director of Insect-borne Disease Investigation and Training Center, told reporters.

Health officers are concerned about the problem faced during the research and control of malaria, Kala-azar, Japanese encephalitis and dengue, among others, Rai noted, adding that a coordination is needed at the district, regional and central levels to have an effective control of the disease.

Over 80 percent of the total population who live off agriculture are vulnerable to insect-borne diseases in Nepal.

A poor family is forced to spend over 25 percent of its annual income on prevention and treatment of malaria, Rai noted.

Nearly 50 percent people are threatened by mosquitoes but there are only two mosquito experts in Nepal, he said.