A new study says about $2.5 billion was spent worldwide in 2007 on research and development of treatments for tropical diseases, but that most of the funds went towards only three diseases.

Researchers from Australia's George Institute for International Health published a report Wednesday saying that 80 percent of the funding was spent on HIV/AIDS, tuberculosis and malaria.  The rest of the money was used for an array of tropical diseases - including sleeping sickness, parasitic illnesses, leprosy, rheumatic fever and skin diseases, leaving some deadly diseases underfunded.

Researchers wrote that for some diseases killing millions of people in developing countries, funding was not enough to create even one new product.

The report says advocacy and fundraising groups often influenced investment, along with epidemiological considerations.

The survey was funded by the Bill and Melinda Foundation.  It says public and philanthropic donors provided 90 percent of the funds for tropical diseases in 2007.

The United States provided most - about 70 percent - of the public funding.  Researchers said some of the world's wealthiest nations failed to enter the list of top 10 donors.

The George Institute survey was released in London and published by the international publication PLoS (Public Library of Science) Medicine.

Some information for this report was provided by Reuters.