Leaders and health officials around the world are urging people to take several precautions to help slow the spread of the sometimes deadly swine flu virus.
The U.S. Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) say swine flu is caused by a virus that normally causes outbreaks in pigs, but that this strain -- a combination of pig, human and bird viruses -- is passing from person-to-person.
Symptoms are generally similar to seasonal flu -- including fever, lethargy, lack of appetite and coughing. Some people with swine flu can also experience a runny nose, sore throat, nausea, vomiting and diarrhea. In some cases swine flu has led to severe pneumonia resulting in death.
Experts say everyone should cover their mouths and their noses when they sneeze, and wash their hands often. They also say anyone who feels ill should stay home from work and school and avoid other crowded areas.
The CDC says anyone experiencing difficulty breathing, sudden dizziness or severe vomiting should seek immediate medical attention.
The CDC and WHO say you cannot get swine flu from eating pork.
Scientists are working to develop a vaccine to contain the spread of the highly contagious respiratory disease but there are several antiviral medications that can be used to treat swine flu.
Most officials believe Mexico is the epicenter of the current outbreak.
In 1976, a swine flu outbreak in the U.S. state of New Jersey made 200 people seriously ill and caused one death.