SARS on the Move
By Rear Adm. Joyce Johnson, D.O., M.A.

How do diseases move from place to place? Will severe acute respiratory syndrome (SARS) spread throughout the United States? 

Transmission of an infectious disease requires a pathogen (organism that causes disease), route of transmission (such as air, water, or food), and a host (person to get sick). Migration of disease usually depends on its route of transmission. There are almost no areas left on earth without regular outside commerce; this interaction and movement of people is one way — but not the only way — disease spreads.

Influenza, or flu, offers a good example of disease movement. Flu viruses mutate, and the new strains travel to other parts of the world (thus the need for an annual flu vaccine). 

Lyme disease, first recognized in 1975 in Lyme, Conn., spread to the far western United States when Connecticut deer were moved to a western reserve. The infected deer spread the disease to local ticks, which in turn spread the disease in their new surroundings.

Plant diseases and harmful insects also can migrate through fruits, vegetables, and plants. To prevent the spread of these diseases, tourists are restricted from bringing fresh fruit and vegetables into the United States. Commercially transported produce is inspected, and only if it is free of transmittable plant disease is it shipped into the United States. 

SARS is a current example of a migrating disease. Though it was first recognized in Vietnam on Feb. 28, 2003, the SARS epidemic may be traced to a patient in China in November 2002. As of April 30, 5,663 cases and 372 deaths have been reported from 27 countries. This febrile respiratory disease can be transmitted from close contact. The virus also has been identified in tears and feces, and some hypothesize it can be transmitted from environmental sources. 

The World Health Organization and many countries are implementing a range of precautions to prevent, or at least delay, international spread. These include global health and travel alerts, education of travelers about symptoms, contact tracing, and extensive epidemiological and laboratory study. The estimated cost to the world economy to date is $30 billion. 

Scientists and clinicians from all parts of the world are working together to learn more about SARS, its transmission, and its treatment. Today, the question is how far it will migrate. If we can understand the route of transmission well enough to prevent transmission, we may be able to reduce its spread. However, in our global society, it is difficult to keep infectious diseases from spreading.