Circumstantial evidence suggests that roof rats may have spread the severe acute respiratory syndrome (SARS) coronavirus in the outbreak at Amoy Gardens in Hong Kong in March and April of this year.
Dr. Stephen K. C. Ng, of Columbia University School of Public Health, New York, presents this hypothesis in this weeks' issue of The Lancet. The SARS outbreak involved 321 residents of Amoy Gardens in over 150 apartments located both upwind and downwind of the first person to be infected (index patient) in an area encompassing thousands of square meters and rising over 100 meters into the air.
Ng comments that other theories, such as contaminated sewage droplets and fecal-oral contact through contaminated surfaces, cannot account for the dose, timing, and distribution of this outbreak. Furthermore, he notes, the index patient, an overnight visitor at the housing estate, "would have needed to excrete a tremendous amount of virus into the environment" to have served as a common source of the epidemic.
Instead, Ng suggests that a roof rat that entered the apartment visited by the index patient became infected by contaminated material and then transmitted the virus when running through sewage and water pipes and along clothes lines located outside each apartment.
As evidence, the researcher points out that the SARS coronavirus has been isolated from other animals in China. The virus, detected in rat droppings and in cultures from cats, a dog, and at least one rat in the area, is capable of genetic mutation. Further substantiating his theory is the significantly greater virulence of the disease in Amoy Gardens compared with outbreaks in other areas.
Given the strong possibility that his rat vector hypothesis is true, Ng recommends that "studies could be undertaken to identify behavioral risk factors and possible mechanisms for rat-to-man infections."
SOURCE: The Lancet, August 16, 2003.