Tropical environments, human activities, and the transmission of infectious diseases

Abstract

Throughout recent history, the tropical regions of the world have been affected more severely by infectious diseases than the temperate world. Much of the success of infectious diseases in that region is due to both biological and environmental factors that encourage high levels of biodiversity in hosts, vectors, and pathogens, and social factors that compromise efforts to control diseases. Several of these factors are described. Discussion then shifts to specific types of host-pathogen relationships. The most important of these in the tropics is the relationship between humans, a pathogen, and a vector that carries the pathogen from one human to another. Mosquitoes are the vector responsible for the transmission of many vector-borne human diseases. Characteristics of mosquito-human interactions are described, including cultural behaviors humans have developed that both increase the chances of transmission and help to limit that transmission. The transmission of water-borne diseases, fecal-oral transmission, zoonotic diseases, respiratory illnesses, and sexually transmitted diseases are also discussed. Attention is paid to how diseases with these modes of transmission differ in characteristics and importance in tropical human populations compared to those in temperate regions. Following this general discussion, three case studies are presented in some detail. The diseases chosen for the case studies include cholera, lymphatic filariasis, and dracunculiasis (guinea worm). These three case studies taken together provide examples of the diversity of human host-pathogen interactions as well as ways that human activities have both promoted their spread and helped to control them. The transmission of all three diseases is related to the nature and quality of water sources. The transmission of cholera, a water-borne disease, is related to sanitation practices, physical characteristics of the environment such as temperature and humidity, and modern shipping practices. Lymphatic filariasis, a mosquito-borne disease, has increased in frequency in parts of Africa in recent decades as a consequence of large-scale agricultural development projects that have shifted the nature and quantity of water sources and potential mosquito breeding sites. Dracunculiasis is transmitted by a small crustacean that contaminates sources of drinking water. Because its transmission can be prevented by a simple change in human behavior, filtering all water with a small piece of cloth before using it, dracunculiasis has been the focus of a major eradication effort that is near success.

Influence of temperature and rainfall on the evolution of cholera epidemics in Lusaka, Zambia, 2003–2006: analysis of a time series

“…1 It is well established that environmental factors, through seasonal variations or as a consequence of global climate change, play an important role in the resurgence and dynamics of infectious diseases. [2][3][4][5][6] On the other hand, in addition to being linked to climate 7 , cholera is closely related to poor environmental status and lack of basic infrastructure in developing countries. In this manner, high population densities as well as poor access to safe water and proper sanitation along with other environmental conditions contribute to the spread of cholera in Africa.…”

Life history theory and the immune system: Steps toward a human ecological immunology

“…High global rates of infectious disease (particularly in many populations of anthropological interest) immediately come to mind as a primary selective force, and as a major public health burden (Barrett et al, 1998;Inhorn and Brown, 1990;Sattenspiel, 2000). Although immune processes provide protection against infectious disease and some forms of cancer, they also contribute to allergy, asthma, and autoimmune disease, as well as the pathophysiology of cardiovascular disease (Bjorksten, 1994;Fergusson et al, 1997;Libby et al, 2002;Ross, 1999).…”

Allomaternal Nursing in Humans

“…Hadza women, although claiming in emergency situations that it might occur, have neither reported nor been observed engaging in allomaternal nursing. The authors go on to suggest that allomaternal nursing in tropical environments, with higher rates of infectious and parasitic diseases (Sattenspiel 2000), might bolster the immune systems of infants. Although no data on immune function of infants is available, the Hadza do have comparatively low rates of parasitic disease transmission (Work et al 1973).…”