Legionnaires’ disease and Lyme disease are not new, but only recently have they become common enough to be recognized as distinct entities and for their bacterial causes to be identified. Legionella bacteria were able to flourish in water towers used for air conditioning. Regulations requiring antimicrobial agents in the water have been effective in limiting the spread of Legionnaires’ disease.
The conditions that promote the spread of Lyme disease, however, are more difficult to change. The pathogen that causes Lyme disease was identified in 1982 as a spirochete that is spread by the bite of an infected deer tick. The reservoir for Lyme disease is the white-footed mouse, on which the deer tick feeds and becomes infected. Deer, on which the ticks grow and reproduce, are an important step in the chain of infection, and it is because of the recent explosion in the deer population in suburban areas that Lyme disease has now become such a problem for humans.
The Institute of Medicine has undertaken several studies to address the environmental, demographic, social, and other factors leading to the emergence or re-emergence of infectious diseases. One of its conclusions is that most of the emerging infectious disease events have been caused by zoonotic disease pathogens those infectious agents that are transmitted from animals to humans.