Infectious Diseases

Infectious diseases are caused by living organisms, they pose two problems to medicine and public health. First, pathogens can grow and replicate, allowing them to evolve drug resistance or change just enough to be unrecognized by our memory immune cells. Second, they are contagious and potentially lead to outbreaks. Human-to-human transmission is outlined in more detail in the figure below. There is even human-to-animal transmission.

Modes of Infectious Disease Transmission (A) Pathogens can be transferred by environmental factors, such as wind and water. They can also be transferred between humans, as well as from humans to animal vectors. Animal vectors can further spread the disease through migration (if carried by birds or fish) or trade. (B) Human-to-human transmission has been classified into five main modes . These five modes are not mutually exclusive; for example, the Ebola virus can be spread through direct contact and, potentially, through droplet transmission. How pathogens can be transmitted mostly depends on how “hardy” they are outside a human body. Some cannot survive for long periods of time, so they require direct contact, droplet transmission, or transmission through an animal vector. Others, such as flu, can survive for long periods of time on surfaces – making them extremely contagious. Fecal-oral pathogens are a large problem in developing countries, but not in developed countries such as the US.

In order to control outbreaks, we often call upon epidemiologists. Epidemiologists observe how health-related events are distributed in the population and use that information to determine their causes and control their spread. In fact, John Snow (described in the first paragraph) is celebrated as one of the fathers of epidemiology. Drawing from John Snow’s example, we can see that the solution to fighting epidemics requires coordination between multiple agencies, including citizens, scientists, physicians, and government officials. In the US, this job often falls to the CDC, and internationally, the World Health Organization (WHO).

In conclusion, infectious diseases are caused by microorganisms that can hijack the nutrients and cellular machinery in our bodies. Fortunately, our immune system and current therapies can keep us healthy. In fact, according to the WHO,  infectious, maternal, neonatal, and nutritional-related diseases combined caused about 23% of deaths around the world . However, the recent Ebola outbreak has shown us that infectious diseases are still a major threat. This is especially important with an increasing amount of global travel and a lack of new drugs . We can do our part by taking sick leave or avoiding travel when ill, taking antimicrobial drugs properly (finishing the course), getting the appropriate vaccinations to protect those vulnerable in the population (through herd immunity), and asking scientists and politicians to make infectious diseases a priority. source: http://bit.ly/2MMverR