Why are infectious diseases resurging?

Global misuse of antibiotics cited

The reasons for the current global resurgence of infectious diseases are not fully understood, but contributing factors include population shifts, increased urbanization and crowding, environmental changes, and worldwide commerce and travel, according to a recent government report on the issue.1 Specific causes cited in the report include:

* Increased human intrusion into tropical forests (for mining, farming, settlement, and tourism), where people are most likely to come in contact with infected animals carrying microbes that cause diseases in humans. For instance, many scientists believe that the human immunodeficiency virus (HIV), which causes AIDS, is a zoonotic pathogen which was transmitted to humans from nonhuman primates.

* Population growth and changes in demographics. By some estimates, more than 50% of the population of the world is under 15 years of age, and the proportion is increasing. This means there are an enormous number of susceptible people living in poor and crowded urban areas, where infectious diseases thrive.

* Population shifts within and between countries, spurred by changing economic conditions or military conflicts.

* Inadequacy and deterioration of public health infrastructures worldwide, including a lack of communicable disease surveillance and control efforts for food- and waterborne diseases, and vaccine-preventable diseases.

* Erosion of expertise on diseases such as plague, rabies, malaria, yellow fever, and botulism.

* Misuse of antibiotics or other antimicrobial drugs, which can hasten the evolution of resistant microbes. This includes prescribing a drug without proper indications, prescribing the wrong drug or the wrong dose, or having poor patient compliance with treatment regimens.

* Ecological changes due to irrigation projects or deforestation. For instance, formerly dry areas may become excellent habitats for parasite-carrying insects, as well as for snails and other animals that serve as parasite hosts.

* Increased trade and expanded markets for imported foods, which occasionally contain bacterial or viral contaminants. Although modern, large-scale food technologies generally improve food safety, when contamination does occur, it may affect vast numbers of people.

* Long- and short-term or cyclical changes in climate and weather that affect infectious microbes and/or the insect vectors, and animal hosts that carry them.

* Continual evolution of pathogenic microorganisms.


1. National Science and Technology Council. Committee on International Science, Engineering, and Technology. Working group on emerging and re-emerging infectious diseases. Infectious Disease -- A Global Health Threat. Washington, DC; 1995. *