Nosogeographic Distribution

the sum of areas that either contain at present or did contain in the recent past active geographical focuses of a disease. The concept of nosogeographic distribution is applied chiefly to infectious diseases and infestations. When speaking of a collective nosogeographic distribution, we take into account the individual nosogeographic distributions of several closely related diseases. The extent of the nosogeographic distribution of an anthropozoonosis coincides with the extent of the range of the causative agent. In a zoonosis, the range of the causative agent is generally smaller than the nosogeographic distribution of the disease.

The nosogeographic distribution of a disease can be global—affecting all the populated areas of the world—as in measles or influenza; zonal—confined to a certain geographic zone—as in yaws, which is confined to the tropical zone; or regional—confined to certain regions—as in sleeping sickness, which occurs only in certain regions of tropical Africa. The extent of the nosogeographic distribution of a disease changes under the influence of various natural and socioeconomic factors. For example, schistosomiasis has become more widespread, while the distribution of malaria has become smaller. When discussing diseases that are becoming less widespread, a useful concept is the original nosogeographic distribution of that disease.

Within the area over which a disease is distributed, nosogeographic focuses can exist in which certain factors vary, such as the reproductive rate of the causative agent and the persistence of the epidemic. The study of the nosogeographic distribution of diseases is one of the main topics of medical geography (seeGEOGRAPHY, MEDICAL).