Outbreaks of animal-related illnesses--a trend in infectious diseases.

As more outbreaks of emerging infectious diseases--from severe acute respiratory syndrome to monkeypox--are linked to animal sources, veterinary public health officials are warning that more such diseases could be inching their way toward humans.

In early July, CDC confirmed that recent cases of monkeypox that occurred among residents of Illinois, Indiana, and Wisconsin were most likely passed to humans via a shipment of small mammals imported into the United States in April. About a month earlier, researchers in China and Hong Kong announced that the coronavirus that causes SAPS was present in civets, a small mammal that people sometimes eat, suggesting the animals may have had a role in the global outbreak.

Combined with recent reports in Canada of bovine spongiform encephalopathy--a form of which can be transmitted to humans through beef consumption--and the continuing spread in the United States of West Nile virus, which is linked to birds via mosquitoes, the occurrences demonstrate that animals have become a primary source for modern-day emerging infectious diseases.

In fact, according to scientific estimates, as many as 75 percent of all emerging infectious diseases are zoonotic--passed from animals to humans. Some of the other recent diseases infecting people in the United States, such as West Nile virus, are vectorborne--passed from animals to humans via insects.

Among the factors that are playing a role in the emergence of the animal-related diseases is human activity, according to Frederick A. Murphy, Ph.D., D.V.M., former director of CDC's National Center for Infectious Diseases and a professor of veterinary medicine at the University of California at Davis. As humans around the globe increase their geographic range and rapidly transport goods and people from place to place, the conditions are becoming more favorable for animal-related diseases to spread, said Murphy.

While incidences of animal-related diseases being passed to humans are far from new, the frequency with which they are being detected and diagnosed is. Some of the change can he linked to improved diagnostic and surveillance tools, and some may be due to greater general awareness among public health officials, according to John Herbold, Ph.D., D.V.M., M.P.H., F.A.C.E., who is an associate professor of epidemiology at the University of Texas School of Public Health and associate director of the Center for Biosecurity and Public Health Preparedness.

For example, when hantavirus was being transmitted from mice to humans in the U.S. Southwest in 1993, it took public health officials months to isolate the virus that was causing the illness. By comparison, CDC officials were able to identify monkeypox as the cause of the recent rashes and illnesses in the Midwest, as well as determine how the disease was introduced into the United States, in just weeks.

The recent U.S. emphasis on bioterrorism and preparedness has put public health officials on alert for unusual diseases, especially those that include fevers or rashes, which may also contribute to faster identification of animal-related diseases, said Herbold, who is chair of the American Public Health Association's Veterinary Special Primary Interest Group.

"We probably have had things like SAPS in the past, but we just didn't recognize it," Herbold said. "Or we recognized it, but we just didn't identify the virus that caused it."

The investments that have been made in the nation's public health infrastructure since September 11, 2001, have improved the ability both to detect bioterrorist activities and to identify naturally occurring diseases, according to David Fleming, M.D., CDC deputy director for public health science.

"This is confirmation of, number one, the need to invest in our system, and number two, the effectiveness of that system," Fleming said during a June CDC briefing on the monkeypox investigations.

For more on the monkeypox, West Nile virus and SAPS investigations, visit http://www.cdc.gov/.

(Adapted from The Nation's Health, August 2003.)