Severe Acute Respiratory Syndrome (SARS) is a viral respiratory illness caused by a coronavirus, called SARS-associated coronavirus.
Spread: Originated in 2002-2003 in Southern China. Spread to Hong Kong, Vietnam, the US, the Philippines, Singapore, Mongolia, Switzerland. The SARS virus is thought to be transmitted most readily by respiratory droplets produced when an infected person coughs or sneezes.
Toll: Affected 8,300 people with 775 deaths, with a fatality rate of 9.6 per cent. No cure or protective vaccine available.
Symptoms: High fever, bodyache, headache, a characteristic dry cough after 2-7 days, runny nose, diarrhoea.
One of the strains of coronavirus, it causes the Middle East Respiratory Syndrome (MERS).
Spread: It originated in 2012 in Saudi Arabia. Countries affected in the Middle East include Iran, Jordan, Kuwait and the UAE. In Africa, the virus spread to Algeria, Egypt and Tunisia. In Europe, the disease spread to France, Germany, Greece and Italy. In Asia, cases have been reported from Malaysia and the Philippines.
Toll: 699 confirmed cases and 113 suspected ones, with 209 deaths reported to WHO.
Symptoms: Most people have respiratory problems, including runny nose, cough, fever and moderate to extreme shortness of breath.
The H7N9 virus is a subtype of influenza virus that has been detected in birds in the past. Most of these infections are believed to result from exposure to infected poultry or in markets where live birds were sold. Currently no vaccine exists, but the use of influenza antiviral drugs known as neuraminidase inhibitors in cases of early infection may be effective.
Spread: Reported for the first time in March 2013 from China. Affected areas included mainland China, Hong Kong and Malaysia.
Toll: A total of 133 cases were reported, with about 1/3rd resulting in death.
Symptoms: Cough, high fever, diarrhoea, muscle aches, breathing problems, runny nose.
Horses have been identified as the intermediate hosts, transmitting infection to humans through close contact during care or necropsy of ill or dead horses. The natural host of the virus are fruit bats of the Pteropodidae family. Without prompt medical treatment, the complications of Hendra virus can be fatal.
Spread: The first recorded outbreak of the disease was in Brisbane, Australia, in 1994. As of July 2008, 11 outbreaks have been reported, all confined to the east coast of Australia.
Toll: Without vaccines, the fatality rate has been 75 per cent.
Symptoms: Frothy nasal discharge, high fever, muscle spasms, difficulty with balance, sweating, increase in heart rate.
H1N1, swine flu
Until the 2009 pandemic, the influenza virus was never known to infect humans. Genetic analyses of the virus have shown that it originated from animal influenza viruses, specifically that of pigs, and is unrelated to the human seasonal H1N1 viruses that have been in general circulation among people since 1977. The virus was first detected in people in April 2009. Spreads as a droplet infection.
Spread: The first case was reported in the US. By the time WHO declared a pandemic in June 2009, 74 countries had reported confirmed infections.
Toll: It caused 16,000 deaths by end of 2009.
Symptoms: Fever, cough, sore throat, runny nose, bodyaches, headache, chills, diarrhoea, vomiting.
Compiled by Pritha Chatterjee