Emerging Infectious Diseases

An emerging infectious disease is one that has appeared recently, spreads rapidly, and is likely to make an impact on public health at the local, regional, or international level. It may be caused by the appearance of a new infectious agent (SARS, HIV), or may correspond to the identification of the infectious origin of an established disease (for example, determining that the bacterium Helicobacter pylori plays a role in stomach ulcers, the treatment of which now includes antibiotics). The first time an infectious agent known in a particular animal species (i.e., avian influenza) is transmitted to humans represents another instance of emerging infectious disease. It may also be, and in this case it is referred to in more precise terms as a re-emerging disease, a new form of a disease that has been known for some time (for example, the increasing frequency of severe hemorrhagic forms of dengue fever, an infection that has been observed since the beginning of the 20th century). Lastly, an emerging infectious disease may correspond to the outbreak of a disease in a geographic area where previously it had not been seen.
The phenomenon of emerging infectious diseases has always existed because infectious agents are highly proficient at adapting to their environment. Just one example: anti-microbial resistance, which is when certain bacteria develop resistance to antibiotics.

Impact on public health

Infectious diseases were responsible for the deaths of 17 million people worldwide in 2002 (accounting for approximately 30% of all deaths). In just a few decades, 30 or so new infectious diseases have been identified (the Ebola virus in 1976; HIV1 in 1983 and HIV2 in 1986; SARS in 2003, etc.). The SARS (Severe Acute Respiratory Syndrome) epidemic is the first very serious disease to emerge in the 21st century. In the space of just a few months, more than 8,000 people were affected in 30 or so countries, with several hundred deaths. The spectacular rise in international exchanges (1.4 billion air travellers in 2001) has given an international character to the threat posed by these new infections.

Diagnosis

Biological analyses help identify new infectious agents and detect genetic modifications of known infectious agents. Advances in the field of genetics have made it possible to monitor genetic modifications occurring spontaneously in infectious agents. In some cases, the modification alters very basic characteristics and may increase the infectious agent's virulence and ability to spread. The influenza virus provides a good example: it mutates often, so the influenza vaccine must be reformulated each year. More rarely, major changes to the DNA of an infectious agent may enable it to cause a global pandemic.
Among the methods used to identify and diagnose new agents, molecular biology is especially valuable. It studies the genetic components of a microorganism and compares them to known microorganisms, which makes it possible to develop diagnostic tests, some of which are then used routinely.