† ‡ Other neglected tropical diseases Additional neglected tropical diseases include: Some tropical diseases are very rare, but may occur in sudden epidemics, such as the Ebola hemorrhagic fever, Lassa fever and the Marburg virus. There are hundreds of different tropical diseases which are less known or rarer, but that, nonetheless, have importance for public health. Relation of climate to tropical diseases The so-called "exotic" diseases in the tropics have long been noted both by travelers, explorers, etc., as well as by physicians. One obvious reason is that the hot climate present during all the year and the larger volume of rains directly affect the formation of breeding grounds, the larger number and variety of natural reservoirs and animal diseases that can be transmitted to humans (zoonosis), the largest number of possible insect vectors of diseases. It is possible also that higher temperatures may favor the replication of pathogenic agents both inside and outside biological organisms. Socio-economic factors may be also in operation, since most of the poorest nations of the world are in the tropics. Tropical countries like Brazil, which have improved their socio-economic situation and invested in hygiene, public health and the combat of transmissible diseases have achieved dramatic results in relation to the elimination or decrease of many endemic tropical diseases in their territory. Climate change, global warming caused by the greenhouse effect, and the resulting increase in global temperatures, are possibly causing tropical diseases and vectors to spread to higher altitudes in mountainous regions, and to higher latitudes that were previously spared, such as the Southern United States, the Mediterranean area, etc. For example, in the Monteverde cloud forest of Costa Rica, global warming enabled Chytridiomycosis, a tropical disease, to flourish and thus force into decline amphibian populations of the Monteverde Harlequin frog. Here, global warming raised the heights of orographic cloud formation, and thus produced cloud cover that would facilitate optimum growth conditions for the implicated pathogen, B. dendrobatidis. Prevention and treatment Vector-borne diseases Vectors are living organisms that pass disease between humans or from animal to human. The vector carrying the highest number of diseases is the mosquito, which is responsible for the tropical diseases dengue and malaria. Many different approaches have been taken to treat and prevent these diseases. NIH-funded research has produced genetically modify mosquitoes that are unable to spread diseases such as malaria. An issue with this approach is global accessibility