Epidemics, bacterial

An epidemic is the occurrence of an illness among a large number of people in the same geographical area at the same time. Bacterial epidemics have probably been part of the lives of humans since the species evolved millions of years ago. Certainly by the time humans were present, bacteria were well established.

On example of a bacterial epidemic is the plague. Plague is caused by the bacterium Yersinia pestis. The bacterium lives in a type of rodent flea and is transmitted to people typically via the bite of the flea. People who come into contact with an infected animal or a flea-infested animals such as a rat can also contract the disease.

Plague has been a scourge on human populations for centuries. In the Middle Ages, the so-called Black Plague (Bubonic plague ) killed millions of people in Europe. The crowded living conditions and poor sanitation that were typical of the disadvantaged populations of the large European cities of that time were breeding grounds for the spread of plague.

While often thought of as an epidemic of the past, plague remains today. Indeed, in the United States the last epidemic of plague occurred as recently as 1924–1925 in Los Angeles. The widespread use of antibiotics has greatly reduced the incidence of plague. Nonetheless, the potential for an epidemic remains.

As for plague, the use of antibiotics has reduced bacterial epidemics. However, this reduction generally tends to be a feature of developed regions of the world and regions that have ready access to health care. In other less advantaged areas of the globe, bacterial epidemics that have been largely conquered in North America and Europe, for example, still claim many lives.

An example is bacterial meningitis . The bacterial form of meningitis (an infection of the fluid in the spinal cord and surrounding the brain) is caused by Haemophilus influenzae type b, Neisseria meningitides, and Streptococcus pneumoniae. Antibiotics that are routinely given to children as part of the series of inoculations to establish immunity to the infection readily kill all three types of bacteria. But, in regions where such preventative measures are not practiced, meningitis epidemics are a problem. In 1996, the largest meningitis epidemic ever recorded, in terms of the numbers of affected people, occurred in West Africa. An estimated 250,000 people contracted meningitis and 25,000 people died of the infection.

Leprosy is an example of a bacterial epidemic that used to be common and which is now on the way to being eliminated. The disease is caused by Mycobacterium leprae. The bacterium was discovered by G.A. Hansen in 1873, and was the first bacterium to be identified as a cause of human disease.

Epidemics of leprosy were common in ancient times; indeed, During the first century A.D., millions of people were afflicted with the disease. Nowadays, the number of leprosy patients in the entire world has been reduced some ninety percent over earlier times through a concerted campaign of diagnosis and treatment that began in the 1990s. Still, leprosy remains at epidemic proportions in six countries: Brazil, India, Madagascar, Mozambique, Myanmar, and Nepal. In these countries an estimated half million new cases of leprosy appear every year.

In contrast to leprosy, tuberculosis is an epidemic that is increasing in prevalence with time. Tuberculosis is caused by another mycobacterium called Mycobacterium tuberculosis. The lung infections caused by epidemics of tuberculosis kill two million people each year around the world. The number of cases of tuberculosis is growing because of the difficulty in supplying health care to some underdeveloped areas, the increase of immunocompromising diseases such as Human Immunodeficiency Syndrome, and the appearance and spread of a strain of the bacterium that is resistant to many of the drugs used to treat the infection. Estimates from the World Health Organization indicate that if the tuberculosis epidemic continues nearly one billion people will become infected by 2020. Of those, some 35 million people will die of tuberculosis.

The re-emergence of tuberculosis is paradoxical. Whereas other bacterial epidemics have and are being controlled by modern methods of treatment, such methods are exacerbating the tuberculosis epidemic. Part of this is also due to the target of the bacterial infection . Lung infections are harder to conquer than infections of the skin, such as occurs in leprosy. Moreover, when the immune system is not functioning properly, due to the presence of another infection, the lung infection can become deadly. Thus, tuberculosis is an example of a bacterial epidemic whose scope is changing with the emergence of other infections and treatments.

The tuberculosis epidemic also underscores the danger of ineffective treatment and the effect of modern life on the spread of disease. Poorly supervised and incomplete treatment has caused the emergence of the drug-resistant strains of the bacteria. The bacteria can remain in the lungs and so can infect others. With the greater movement of people around the globe, the spread of the disease by carriers increases.

A final example of a bacterial epidemic is cholera. The disease caused by Vibrio cholerae is an example of an ancient bacterial epidemic that continues today. The intestinal infection produces a watery diarrhea that can lead to a fatal dehydration. An epidemic of cholera caused by an antigenic version of Vibrio cholerae known as El Tor has been in progress since 1961. Indeed, the various epidemics are so widespread geographically that the disease can be considered pandemic (a simultaneously outbreak of illness on a worldwide scale). The latest epidemics have included countries in West Africa and Latin America that had been free of cholera for over a century.

Cholera is spread by contaminated food or water. Thus, the sanitary condition of a region is important to the presence of the epidemic. As with other bacterial epidemics of the past and present, underdeveloped regions are the focus of epidemic outbreaks of cholera.

See also Bacteria and bacterial infection; Biological warfare; Vaccination; Water quality