Since the first reports in early April of several unusual cases of flu in Mexico’s Veracruz state, the world has been increasingly transfixed by the outbreak of a highly contagious and potentially lethal new type of influenza. Here’s a Wired.com primer on what you need to know about H1N1, or swine flu:

Approximately 1,600 cases have been reported so far in Mexico, and 103 people have died. Not all  the cases have been officially confirmed, but it’s believed that the same virus strain is responsible. Many of those who died were between the ages of 25 and 45. This is especially concerning, because flu doesn’t usually kill people in their prime. Twenty cases have been reported in the United States. All of those people were quarantined and, according to the Centers for Disease Control and Prevention, have recovered.

The World Health Organization says swine flu has the potential for becoming a worldwide epidemic. It has urged national public health systems to be vigilant and watch out for flu outbreaks in demographic groups other than children and the elderly. However, WHO says it’s too soon to know if a new vaccine is warranted or international travel should be restricted.

The U.S. Department of Health and Human Services declared a public health emergency on Sunday. Homeland Security Department Secretary Janet Napolitano said at a news conference that the declaration is not reason for alarm, but is standard operating procedure required to allow the release of government funds and drug stockpiles.

WHO and CDC are now scrambling to profile the new strain of swine flu. They know that it contains a cocktail of genes from human-, swine- and bird-flu strains. Though it was originally reported that the strain contained a cocktail of human-, swine- and bird-flu genes, it appears to be a novel combination of two existing swine flu strains. Mortality rates appear directly related to delay of treatment. If caught in time, the disease can apparently be treated with relative ease.

Speaking of preparedness, congressional Republicans stripped the economic stimulus plan of $900 million for state and local pandemic-readiness programs, and $462 million for the CDC. What does a pandemic have to do with economic recovery? So far, the prospect of worldwide swine flu is causing market panics.

Mexican newspapers report the flu may have originated in high-density pig farms run by Smithfield Foods, the world’s largest hog producer. Some residents in the region allege that it jumped to humans through water supplies contaminated by pig waste, or by flies. Similar pig farms exist in the United States, and have been blamed for the rise of lethal, drug-resistant staph infections.

A great deal of information on the swine flu epidemic is on the internet. The most reliable is the CDC’s dedicated swine flu page. They also have a Twitter feed. In general, people might want to avoid Twitter-wide swine flu coverage, which tends toward the sensational and has a very low signal-to-noise ratio. The Biosurveillance blog, maintained by disease-surveillance company VeraTect, is a good source of news and analysis. So are the Aetiology and Effect Measure blogs.