Introduction:-- A new strain of swine flu that has killed as many as 81 and sickened more than 1,324 in Mexico has spread to the United States and is raising fears of a possible pandemic. Learn more about the disease and why it is causing concern among health officials.

What is it: -- Swine influenza is a respiratory disease of pigs first isolated in swine in 1930, according to the Centers for Disease Control and Prevention. The illness is caused by four different type A influenza strains that can cause outbreaks in pigs, though subtypes H1N1 and H3N2 seem to be more common. The death rate among pigs is low, with most infections occurring in the late fall and winter. Symptoms of infected pigs include fever, depression, coughing (barking), sneezing, difficulty breathing, red or inflamed eyes, lack of appetite and discharge from the nose or eyes.

How do people get infected: -- Human infection happens intermittently, with most cases occurring when patients have direct contact with pigs. But cases of an infected person transmitting the swine flu to others have also been documented, says the CDC. (A 1988 outbreak in pigs in Wisconsin led to multiple human infections, and there was evidence that a patient transmitted the virus to health care workers.) Human-to-human infections do occur similar to the way the human seasonal flu virus is transmitted — through coughing, sneezing and coming in contact with a person or object with the virus.

People cannot become infected by eating pork or pork products. Cooking pork to an internal temperature of 160 degrees Fahrenheit kills the virus as well as other bacteria, notes the CDC.

What are the symptoms: -- Symptoms are similar to those of the regular human influenza virus: fever, lethargy, lack of appetite and coughing. Some who have been infected with the swine flu also reported having a runny nose, sore throat, nausea, vomiting and diarrhea.

How is it diagnosed: -- A respiratory specimen must be collected within the first four to five days of illness, when the infected person is most likely to be shedding the virus. However, some patients (such as children), may shed the virus for 10 days or longer, according to the CDC. Specimens must be sent to the CDC for laboratory testing in order to identify swine flu.

How is it treated: -- Four antiviral drugs are licensed to treat the disease in the U.S.: amantadine, rimantadine, oseltamivir and zanamivir. Most of the viruses are susceptible to all four, but the CDC currently recommends oseltamivir or zanamivir to treat and prevent swine flu infections. The antivirals should be taken as soon as possible symptoms appear.

Tamiflu, the generic name for oseltamivir, appears to be effective against the new strain when taken early, says the CDC. There is currently no human vaccine for swine flu, but the flu vaccine may provide some protection against the H3N2 strain, though not the H1N1 strain.

For additional information go the the WHO or CDC websites