Emerging infectious diseases are infectious diseases with an incidence which is on the increase, suggesting that something has changed about the disease, its environment, or its hosts. Numerous colleges and universities have departments which study emerging infectious diseases and it is also a topic of interest at government agencies which monitor public health, including health of animals, because some animal species serve as reservoirs for zoonotic diseases which can be caught by humans.
Generally speaking, infectious diseases remain in a state of balance with their hosts. From the point of view of a disease, it wants to keep hosts alive so that it can be passed to other hosts, and thereby spread. Thus, there are no benefits to a disease in causing more noticeable illness, which might result in more aggressive treatment, or in causing deaths. However, infectious agents can and do evolve to become more virulent and when they do, they often become emerging infectious diseases.
If the incidence of a disease has increased in the last 20 years, or it seems likely to do so in the near future, it is classified as an emerging infectious disease. Some reasons why incidence might increase include evolution of the organism as well as environmental factors like crowding, poor sanitation, changes in community lifestyles, and so forth. Emerging infectious diseases have also taken advantage of the jet age to rapidly transport themselves around the world in the bodies of travelers.
These diseases are a cause for concern for a number of reasons. Any increase in disease results in a corresponding decline in public health, which is not desirable. In addition, emerging infectious diseases are sometimes new or different enough from old pathogens that they are challenging to treat. While treatments are in development a disease can get a foothold in a population and may become a problem. Once a disease becomes entrenched it can be difficult to eradicate and it can even lead to social instability.
Control of infectious diseases is a concern in many communities and cultures. Zoonotic diseases can be an area of special interest because infectious agents can spread between animal and human populations and may cause widespread issues as a result. Numerous government agencies have strike teams available to respond to new outbreaks so that they can quickly address diseases when they strike. Governments also conduct epidemic surveillance, tracking infections to determine whether or not the incidence of disease is on the rise.