This particularly virulent new strain of highly pathogenic avian influenza (HPAI H5N1) has spread throughout a large geographic area in Asia, Europe, and Africa since it was first documented in 1997 in Asia, and has caused the largest and most severe outbreaks in poultry on record.

SARS stands for severe acute respiratory syndrome. It's a new disease that doctors still don't know much about.

They are a lot like pneumonia or the flu. People get a very high fever -- at least 100.4 degrees. They also usually have shortness of breath or other problems breathing and a dry cough. Some people get other symptoms, including a headache, stiff or achy muscles, a loss of appetite, fatigue, a rash and diarrhea.

Antibiotics don't seem to work, which is usually the case with virus-caused diseases. One antiviral drug known as ribavirin may help, but doctors aren't sure yet.

Scientists discovered that the disease is caused by a previously unknown microbe known as a coronavirus. Coronaviruses usually just cause the common cold, but can cause serious respiratory illnesses in animals.

SARS is caused by a previously unrecognized coronavirus, called SARS-associated coronavirus (SARS-CoV). It is possible that other infectious agents might have a role in some cases of SARS.

The primary way that SARS appears to spread is by close person-to-person contact. SARS-CoV is thought to be transmitted most readily by respiratory droplets (droplet spread) produced when an infected person coughs or sneezes. Droplet spread can happen when droplets from the cough or sneeze of an infected person are propelled a short distance (generally up to 3 feet) through the air and deposited on the mucous membranes of the mouth, nose, or eyes of persons who are nearby.

A new outbreak of SARS is defined as the occurrence of one or more clinically compatible, laboratory-confirmed cases of SARS in any country based on definitive laboratory investigations. The reappearance of SARS in the human population would be considered a global public health emergency. For the purposes of the international reporting of SARS in the post-outbreak period, Member States are requested to inform WHO of laboratory-confirmed cases only." (Section 3.5, WHO Aug 14, www.who.

The disease is believed to have first emerged in Guangdong province in China in November and then spread to Hong Kong and elsewhere.