Neglected tropical diseases are a medically diverse group of tropical infections which are especially common in low-income populations in developing regions of Africa, Asia, and the Americas. They are caused by a variety of pathogens such as viruses, bacteria, protozoa and helminths. Different organizations define the set of diseases differently. In sub-Saharan Africa, the impact of these diseases as a group is comparable to malaria and tuberculosis. Some of these diseases have known preventive measures or acute medical treatments which are available in the developed world but which are not universally available in poorer areas. In some cases, the treatments are relatively inexpensive. For example, the treatment for schistosomiasis is USD $0.20 per child per year. Nevertheless, control of neglected diseases is estimated to require funding of between US$2 billion to US$3 billion over the next five to seven years.