Plague is an infectious disease caused by the bacterium Yersinia pestis. Symptoms include fever, weakness and headache. Usually this begins one to seven days after exposure. In the bubonic form there is also swelling of lymph nodes, while in the septicemic form tissues may turn black and die, and in the pneumonic form shortness of breath, cough and chest pain may occur. Transmission of Y. pestis to an uninfected individual is possible by any of the following means. droplet contact – coughing or sneezing on another person direct physical contact – touching an infected person, including sexual contact indirect contact – usually by touching soil contamination or a contaminated surface airborne transmission – if the microorganism can remain in the air for long periods fecal-oral transmission – usually from contaminated food or water sources vector borne transmission – carried by insects or other animals.
The Spanish flu, also known as the 1918 flu pandemic, was an unusually deadly influenza pandemic. Lasting from January 1918 to December 1920, it infected 500 million people – about a quarter of the world's population at the time. The death toll is estimated to have been anywhere from 17 million to 50 million, and possibly as high as 100 million, making it one of the deadliest pandemics in human history.
Ebola virus disease (EVD), or simply Ebola, is a viral hemorrhagic fever of humans and other primates caused by Ebola viruses. Signs and symptoms typically start between two days and three weeks after contracting the virus with a fever, sore throat, muscular pain, and headaches. Vomiting, diarrhea and rash usually follow, along with decreased function of the liver and kidneys. At this time, some people begin to bleed both internally and externally. The disease has a high risk of death, killing 25% to 90% of those infected, with an average of about 50%. This is often due to low blood pressure from fluid loss, and typically follows six to 16 days after symptoms appear.
SARS-CoV is thought to be an animal virus from an as-yet-uncertain animal reservoir.
Corona-viruses are a group of viruses that cause diseases in mammals and birds. In humans, the viruses cause respiratory infections – including the common cold – which are typically mild. Rarer forms such as SARS, MERS and the novel corona-virus causing the 2019–20 Covid-19 Virus outbreak can be lethal. In cows and pigs corona-viruses cause diarrhea. In chickens they cause an upper respiratory disease. There are no vaccines or antiviral drugs that are approved for prevention or treatment.