U.S. health officials are busy trying to contain three infectious diseases that Americans were unaware of only a few years ago. A top government public health expert says fighting emerging and re-emerging infections is now the norm.

The chief of the U.S. government's disease tracking agency, the Centers for Disease Control, is like a general fighting a three-front war. Dr. Julie Gerberding has good news on one of the fronts but is worried about the other two.

The good news is about SARS, the Severe Acute Respiratory Syndrome epidemic that came from East Asia earlier this year. Beijing, China is now the only area that the World Health Organization recommends a traveler avoid.

"We are seeing increasing evidence of global containment of this problem. There is less and less transmission," said Dr. Gerberding. "The other provinces of China have been taken off the advisory status, and we think that represents a remarkable achievement on the part of all the officials and personnel in those areas who have worked extremely hard to accomplish what looked like a very daunting task at the beginning."

Still, Dr. Gerberding says this could be a seasonal lull in SARS transmission, and CDC is maintaining strict surveillance in the event it returns.

At the same time, the Centers for Disease Control is tracking monkeypox, a smallpox-like virus that recently arrived in the Western Hemisphere from West Africa. It is spreading throughout the U.S. midwest, with nearly 90 cases reported. Like SARS, monkeypox jumped from animals to people and has not killed anyone in the United States, as it has in Africa. In addition, monkeypox has not been transmitted between people. U.S. officials have traced it to a burrowing rodent known as a prairie dog, which is thought to have been infected in an Illinois pet store by a giant imported Gambian rat.

With summer approaching in the Northern Hemisphere, Dr. Gerberding is also concerned that West Nile Virus will reappear in the United States. The Centers for Disease Control has detected it in animals, birds, and insects in half of the 50 U.S. states. Officials fear it will become a worse human epidemic this year than last because of the excessive spring rainfall in the eastern part of the country. Last year, the virus infected more than 4,000 Americans and killed nearly 300 others.

"All of this is part of the new normal of emerging infectious diseases where not only are we dealing here with infectious diseases that were imported into the United States through various means, but it is a global community and all of these illustrate the tendency for a problem in one corner of the world to emerge as a problem in another corner of the world," she said.

U.S. public health officials are also implementing a nationwide smallpox prevention program because the virus causing the disease, although eradicated in the late 1970s, is considered a potential bioterrorist threat. To deal with the possibility, the Bush administration and Congress have allocated $1 billion extra to strengthen the country's public health system. Ironically, the measures taken to protect against this human threat over the past year have helped in the fight against nature's triple infectious onslaught.

"We're sitting here talking about three infectious diseases that we are simultaneously coordinating through our emergency operations center, three diseases with global importance, three diseases that are new in our society, and three diseases that all of us are working very hard to contain and prevent," explained Dr. Gerberding. She called this an unprecedented time in the history of her agency.