Concerned over the rapidly spreading swine flu, the World Health Organization (WHO) has upped the influenza pandemic alert to phase 5, just one step short of declaring a bona fide global pandemic.

"All countries should immediately activate their pandemic preparedness plans," said WHO Director-General Margaret Chan, calling on government ministries and manufacturers of vaccines and antiviral meds to mobilize resources immediately to deal with the rapidly evolving swine flu outbreak.

The World Health Organization (WHO) has confirmed swine flu cases in two more countries—the U.K. and New Zealand—bringing the total number of affected countries to at least six. Although the disease appears to be causing only mild illness in most areas (Mexico being the notable exception), experts warn the virus could still cause a catastrophic global pandemic.

Last night, there were 73 laboratory-confirmed cases of swine flu (40 in the U.S., 26 in Mexico, six in Canada, and one in Spain); the tally has since increased to 79, with one new case in Spain, two in the U.K., and three in New Zealand, Keiji Fukuda, the WHO's assistant director-general for health security and environment, told reporters this morning. Meanwhile, media outlets are reporting that Mexico may have as many as 2,000 suspected cases and 150 deaths.  

The World Health Organization (WHO) has raised the influenza pandemic alert level to phase 4, just two steps shy of a global pandemic alert, according to Keiji Fukuda, the WHO's assistant director-general for health security and environment. And while the WHO does not recommend countries close borders or restrict travel, they are moving forward with plans to produce a swine flu vaccine as soon as possible, he told reporters in a teleconference this evening.

According to the WHO Web site, a phase 4 alert describes a viral outbreak in which human-to-human transmission is efficient and sustained enough to cause community-level outbreaks. Level 3 describes a situation in which human-to-human transmission is limited and disease cases are sporadic and occur in small clusters. (Phase 6 designates a global pandemic.)  According to the WHO, there are at least 73 confirmed cases of human swine flu -- 40 in the U.S., 26 in Mexico (including seven deaths), six in Canada, and one in Spain. But Mexico has over 1000 suspected cases, according to Time Magazine, and 149 suspected deaths, according to Reuters.

Bubonic plague. AIDS. Yellow fever. Some of the greatest scourges mankind has ever faced – and those that may yet spark a pandemic, such as bird flu – all originated as infectious agents in animals that then made the jump into human beings. It’s no accident that close contact between man and rats in medieval towns led to the Black Death, and that people hunting primates in the African bush provided an avenue for AIDS to spread throughout the world.

What if scientists could identify the next killer bacteria or virus before it struck humans? Nathan Wolfe writes about how this early detection may be possible in the April issue of Scientific American. Wolfe is a professor of biology at Stanford University and director of the Global Viral Forecasting Initiative, an effort to take stock of animal diseases in hotbeds of human-animal proximity – the jungles of Africa and southeast Asia, for example – and to monitor local people for what germs they carry that came from the wild.

We've known since January that most of the flu circulating this season is resistant to Tamiflu, an antiviral drug typically used against the infection. What remained a mystery was whether the resistant flu strain made people sicker than forms that respond to the treatment — and why the resistant strain surged this year, a worry for public health officials who stockpiled Tamiflu in the event of a flu pandemic stoked by avian influenza.

A study published today in the Journal of the American Medical Association indicates that Tamiflu-resistant flu does not make people any more or less sick. But researchers say they're still in dark as to why Tamiflu-resistant infections are on the rise. A whopping 98 percent of this year's circulating H1N1 flu strains are immune to Tamiflu, compared with only 12 percent during the 2007-2008 flu season.

You can cut your risk of contracting the flu or other respiratory viruses by as much as 80 percent by wearing a mask over your nose and mouth, according to a new study.

"This is the first clinical trial to show a positive effect of masks on preventing the transmission of respiratory viruses," says Raina MacIntyre, an epidemiologist and head of the School of Public Health and Community Medicine at the University of New South Wales in Sydney, Australia, and lead author of the study published today in Emerging Infectious Diseases, the journal of the Centers for Disease Control and Prevention (CDC) .

A mild first wave of flu pandemic could reduce deaths from a future outbreak of more severe infection, a new analysis suggests.

A review of the effects of the 1918 flu pandemic on American soldiers and British sailors and civilians found that people who were infected during the first, milder spring and summer wave had a 35 percent to 94 percent lower risk of catching the more severe strain than those who weren't infected earlier. The higher end of that continuum is similar to the 70 percent to 90 percent protection offered by vaccines.

Their risk of death also was 56 percent to 89 percent lower, according to an analysis published in the Journal of Infectious Diseases. Scientists from the National Institutes of Health, George Washington University and Tulane and Xavier Universities in Louisiana conducted the analysis.