Animation of the infection route of viral respiratory disease, such as the 2019-20 Wuhan coronavirus. The virus particles are present in the air in a fine aerosol of water droplets. They infect cells in the respiratory tract, hijacking their cellular machinery to produce more virus particles. These erupt from the cell, killing it and infecting more cells. The new virus particles are then exhaled, coughed or sneezed out, allowing them to infect other people. Symptoms typically include coughing and sneezing, fever, breathing difficulties and in severe cases, pneumonia, which can be fatal.