a group of diseases occurring exclusively or largely in the equatorial, subequatorial, and tropical regions. They include mainly infectious and parasitic diseases, most of which are transmissible. Among them are such viral diseases as yellow fever, such bacterial diseases as melioidosis, such rickettsial diseases as tsutsugamushi, such spirochetal diseases as yaws, such fungal diseases as coccidioidomycosis, such protozoan diseases as malaria, leishmaniasis, and sleeping sickness, and such helminthic diseases as schistosomiasis and filariasis.

Characteristics of tropical diseases are extensive lesions and a high probability of simultaneous infection with several species of causative agents. Tropical diseases also include diseases directly associated with a hot climate, such as dermatitis, and diseases caused by a protein or vitamin deficiency, such as kwashiorkor, beriberi, and sprue. Other diseases included among the tropical diseases are those caused by genetic anomalies of the blood, such as sickle-cell anemia, and those caused by the bites of poisonous snakes, spiders, and fishes.

The high incidence of tropical diseases in the developing countries results from natural causes as well as from the socioeconomic factors that are the heritage of the colonial system. The low level of sanitation, poor medical care, malnutrition, and traditional ways of life are responsible for the clinical course of many diseases. Tropical diseases are often the result of protein and vitamin deficiency, chronic metabolic disorders of parasitic origin, and anemia; the relations between cause and effect are often unclear. The hot, humid climate typical of the tropics is conducive to the rapid propagation of the causative agents of infectious tropical diseases, which constitute a potential threat to the health of the inhabitants of other countries. Soviet medical organizations are cooperating with the World Health Organization in adopting and implementing international programs to eradicate the most widespread tropical diseases. These diseases are no longer common in the USSR.