MEXICO CITY A dangerous strain of flu never seen before has killed up to 60 people in Mexico and spread into the United States, where several people were reported ill.
Here are some questions and answers about the virus:
HOW MANY PEOPLE ARE AFFECTED?
Mexico has confirmed 20 deaths from the flu and has 40 other possible fatalities and 1,004 people reported infected. Most of those who died are aged between 25 and 45.
In California and Texas, eight people were infected with the new strain, but all of them have recovered.
WHAT KIND OF FLU IS IT AND HOW IS IT SPREADING?
The virus is an influenza A virus, carrying the designation H1N1 and is spreading from person to person. It contains DNA from avian, swine and human viruses, including elements from European and Asian swine viruses, according to the U.S. Centres for Disease Control and Prevention, or CDC.
The virus is being passed on by sneezing, coughing or physical contact. Though a link to swine flu was originally suspected, the Mexican government has now ruled out any risk of infection from eating pork.
HOW SERIOUS IS IT?
The CDC says it is too early to fully assess the threat posed by the new flu virus.
The Mexican government said on Friday the rate of deaths has slowed in recent hours and that it has a million doses of antiviral drugs, which is more than enough to treat all reported cases.
Central American countries were not reporting any cases of the new flu for the time being.
HAS MEXICO EVER SEEN AN OUTBREAK LIKE THIS BEFORE?
Mexico has not suffered a serious flu epidemic before.
Many Mexicans vaccinate themselves against common flu, which hits each year in a season that normally ends in February or March. Worldwide, seasonal flu kills between 250,000 and 500,000 people in an average year.
WHAT MEASURES IS THE MEXICAN GOVERNMENT TAKING?
Mexico City has closed universities and schools until further notice, suspended all major public events and advised people feeling flu-like symptoms to stay home from work.
Mexico City's busiest subway stations are handing out face masks to passengers to use on crowded train carriages. The city government has closed museums, including the popular Anthropology Museum.
Authorities recommend people avoid crowded places and have cautioned people not to shake hands or kiss when greeting or to share food, glasses or cutlery.
The government has also extended the deadline on filing tax returns by a month to the end of May.
WHAT IS THE REST OF THE WORLD DOING TO HELP?
The U.S. government said it was taking the situation seriously and monitoring for any new developments.
The CDC said it is working on a vaccine.
Geneva-based U.N. agency the World Health Organisation said it was in close contact with U.S., Canadian and Mexican authorities and had activated its Strategic Health Operations Centre -- its command and control centre for acute public health events.
The WHO says it is ready to use rapid containment measures if needed, including antivirals, and said Mexico is well-equipped to handle the outbreak.
SHOULD TOURISTS WITH TRIPS PLANNED TO MEXICO BE WORRIED?
The CDC and the WHO say there is no need to alter travel plans and Mexico said it saw no need to close its borders.
Canada's government has advised doctors to be on the alert for reports of illness from people who recently travelled to Mexico, but has not recommended cancelling trips.