Diseases caused by the environment

While many infectious diseases are caused by human-to-human transmission, others are caused by microorganisms that exist in the outside environment.

Scientists from a variety of fields, including medicine and the environment, must work together to address the challenges posed by these environmental pathogens, according to a new report, From Outside to Inside: Environmental Microorganisms as Human Pathogens, released today by the American Academy of Microbiology.

"The key difference between environmental pathogens and other human pathogens is their ability to survive and thrive outside the host. Their widespread occurrence in the environment makes them difficult to monitor and control," says Gerard Cangelosi of the Seattle Biomedical Research Institute at the University of Washington, one of the authors of the report. "The fields of medical and environmental microbiology need to be better integrated to stimulate the type of work that is required to combat environmental pathogens effectively, and the development and improvement of surveillance and reporting strategies should be a top priority."

Environmental pathogens are defined as microorganisms that normally spend a substantial part of their lifecycle outside human hosts, but when introduced to humans cause disease with measurable frequency. They are carried in the water, soil, air, food and other parts of the environment and can affect almost every individual on the planet. Some examples of environmental pathogens include Legionella pneumophila (the cause of Legionnaires disease, often found in air conditioning systems), West Nile virus, and Cryptosporidium parvum (a parasite that can be found in food, drinking water and recreational waters).

In addition to better integration of medical and environmental research, the report recommends more effective monitoring of pathogens in the environment to allow researchers to better understand the incidence and persistence of pathogens in areas that are considered to be at risk for harboring these organisms. Multidisciplinary research must also be fostered to better predict how changes in the environment may affect the frequency of environmental diseases.

"These threats to human health can only be assessed in a comprehensive multidisciplinary context in which ecology, epidemiology, and emerging areas in environmental engineering and microbiology are integrated. This combined approach can yield immediate and long-term health benefits by mitigating established environmental risks, identifying risky situations for disease emerging and finding the causes of diseases of unknown etiology," says Cangelosi.

The report is the result of a colloquium convened by the Academy in February 2004 to discuss environmental pathogens and the current state of research on these organisms. Scientists with expertise in infectious diseases, food microbiology, bacteriology, molecular biology, microbial ecology, pathogenic mycology and other areas in the microbiological sciences participated. Participants considered the knowledge gaps related to the incidence and epidemiology of environmental infectious diseases, dynamics of human pathogens in the environment, ways to alleviate environmental infectious diseases, research needs in the field and education and communication issues.