What would a modern day plague look like?

If there was a plague today, it would be catastrophic or very short and quite small. Because of technological advances and new medication, the world has been good at suppressing a plague and quick with dealing with possible plagues, such as the swine flu. If a plague were to start today, as long as the world reacted quickly (unlike the government in Oran), it should be able to be contained. The other possible outcome of the plague could be almost apocalyptic. Technological advances can also spread the plague. People commute between places easily and therefore more people can come into contact with someone who is contagious. If someone who had the plague got on a plane, that person could infect many there and then infect even more people at the location they're traveling to. Transportation is easy to access, yet easy to spread diseases.
It depends on how the population would react as well. If everyone listened to the government and any regulations they set forth to contain the plague, theoretically the plague should be contained and not turn into a global plague.
In today's day, many areas don't have as many rats as other ages did. The rats often spread diseases. The fleas that diseased them looked for new hosts and then when there were no other viable sources of blood, they moved to humans. Because there are less rats in many affluent areas, the people there are in less of a danger. Unfortunately this is not the case globally. Humans don't have any natural resistance against this. In the case of rats, the ones with natural immunity survive and pass on this immunity through generations. Humans haven't been exposed to recent rats' diseases and therefore haven't acquired immunity. Thankfully, due to modern technology, scientists can create vaccinations to help increase our immunity and they can do so quickly. There are scientists specifically to try to prevent the spread of illnesses. Hopefully we have learned from past mistakes and will be able to prevent a global plague.

For more information about a modern day plague:
http://science.howstuffworks.com/life/cellular-microscopic/plague5.htm