You know that life expectancy has increased over time. People today certainly live decades longer than people did at the start of the 20th century and much more than hundreds or thousands of years ago.

However, some diseases have had serious effects on large populations, and some of those epidemics continue to occur in the present day. You will learn more about this in the following activity. 

One of the major factors that contribute to the spread of disease in the world today is globalization, the term used to describe how easily and quickly people now travel from place to place and how in contact we are with people all around the world.

 The current lifestyle that allows for fast and frequent travel around the world leaves everyone vulnerable to the spread of disease. Globalization also means that people are now in more contact with more animals and, as a result, are also more likely to be exposed to more animal diseases.

The image above shows the spread of the Zika virus around the world.

Some examples of diseases are relatively recent. Health professionals continue to monitor these diseases to prevent them from becoming even more serious epidemics. They include these examples:

    HIV/AIDS — Human immunodeficiency virus and acquired immune deficiency Syndrome have been a concern since the early 1980s. The World Health Organization estimates that more than 40 million people worldwide have been infected with HIV and that the number of infections continues to rise every year.
 
 Avian influenza —  Sometimes called Avian flu or the bird flu, this contagious disease normally affects only birds. However, it is of concern because it occurs in many countries and kills many birds, even in places that had never before had cases of the disease. As well, there is concern that human health might be affected if humans get the disease from direct infection from birds (as has happened in some rare cases) or if the disease changes its form slightly so that it infects humans directly, leading to a pandemic that the world is not prepared to face.

Zika virus — Zika is spread mostly by the bite of an infected Aedes species mosquito. Mosquitoes kill an estimated 700,000 people a year by transmitting viruses that cause diseases like the Zika. Zika can be passed from a pregnant woman to her baby, and infection during pregnancy can cause certain birth defects. As of 2016, there has been no vaccine developed to prevent or medicine developed to treat Zika. With the help of the World Health Organization, researchers have discovered that mosquitoes artificially infected with a bacterium called Wolbachia do not transmit these diseases as easily. Wolbachia bacteria exist naturally, and it may be possible to create populations of mosquitoes that cannot transmit deadly viruses by infecting them with this bacteria.

  "Superbugs"  — There is concern that parasites, viruses, and bacteria are becoming more resistant to antibiotics and vaccines so that many cures for diseases are less effective than they used to be.