A novel flu virus has struck hundreds of people in Mexico, and at least 18 have died. It has also infected eight people in the US, and appears able to spread readily from human to human. The World Health Organization is calling an emergency meeting to decide whether to declare the possible onset of a flu pandemic.
Ironically, after years of concern about H5N1 bird flu, the new flu causing concern is a pig virus, of a family known as H1N1.
Flu viruses are named after the two main proteins on their surfaces, abbreviated H and N. They are also differentiated by what animal they usually infect. The H in the new virus comes from pigs, but some of its other genes come from bird and human flu viruses, a mixture that the US Centers for Disease Control and Prevention calls “very unusual”.
On Wednesday, the CDC announced that routine surveillance had uncovered mild flu cases during late March and April, caused by a novel swine flu virus. Those affected, aged 9 to 54, live in and around San Diego, California, and San Antonio, Texas, near the Mexican border. None was severe. Symptoms were normal for flu, with more nausea and diarrhoea than usual.