Disease

           Other than natural disasters, diseases are the most known entities to cause mass death in the human population. Disease is an abnormal condition that affects the body of an organism. It is often considered a medical condition with each disease having its own specific symptoms and signs. Diseases can be caused by many things such as external sources, other infected people, or internal sources due to hereditary predispositions. There are four main types of disease: pathogenic disease, deficiency disease, hereditary disease, and physiological disease (Johnson 2002). A pathogen is an infectious agent (germ) that can cause disease in a host body. The host can be any plant, animal, human, or other microorganisms. Examples of pathogenic diseases are smallpox, influenza, chickenpox, and measles. Deficiency disease (nutritional disease) is a disease in humans that can be directly or indirectly caused by missing essential nutrients in the everyday diet. This disease is known for causing two extreme reactions, obesity and malnutrition. Hereditary disease is a genetic disorder. It can be caused by mutations and abnormalities in the genome. This disease is also characterized as a lifelong disease because it is usually present in the child from birth. These diseases are also heritable and can be passed down from generation to generation. An example of this disease is certain forms of cancer. A physiological disease is what the normal regulation of the body’s system is affected. This can result from certain organs in the body not working properly or if certain cellular structures change over time, it can cause illness. An example of a physiological disease is asthma or diabetes.

The top ten deadliest epidemics of all time are categorized by one of the four groups listed and has had extremely negative consequences on the human population. The biggest worldwide epidemic was smallpox. Smallpox is an extremely infectious pathogenic disease. Smallpox was characterized by a rash and after fluid-filled blisters which can cause blindness, scarring, limb deformities, and in many cases, death (Barquet and Domingo 1997). Smallpox is believed to have first been found in the mummified remains of Ramses V who died over 3000 years ago. Through trading routes between Egypt and India, it is believed that the disease spread and from there was introduced to China and then Japan. It is unclear how it began to spread to the rest of the world, but by the time of the Middle Ages, the population increased and around the 16^th century smallpox was well established throughout many regions in Europe. Smallpox continued to ravage the world and by the mid-18^th century it was a major endemic disease everywhere but Australia. In Europe during the 18^th century it was the leading cause of death killing at least 400,000 people per year. Death was rampant until the use of vaccinations. Through the push of the governments, and donations of vaccines to poorer countries, smallpox was finally eradicated in 1979. Smallpox was to blame for 300 to 500 million deaths during the 20^th century and at the height, about 15 million people contracted the disease per year and about 2 million of them died. Overall, smallpox was definitely a disease, during its height that affected the growth of the human population. It put natural holds on growth until its eradication and then once again the population began to grow (Barquet and Domingo 1997).

The second largest epidemic of all time was the measles. The measles is also a pathogenic disease which infects the respiratory system. Symptoms of the measles include fever, cough, running nose, red eyes, and rashes. Measles are also highly contagious and can by caught through transmission of respiratory fluids (Broy et al 2009). While the measles today are rarely fatal, it was not the same case throughout history. The first known case of the measles was known as the Plague of Galen around 165-180 AD. It killed one third of the population in certain areas and is the cause for extreme loss in the Roman army. In 1529, an outbreak of the disease in Cuba killed two-thirds of the native people there after they already survived a smallpox outbreak. From there it continued to ravage Honduras, Mexico, Central America, and the Incas. In the last 150 years alone, measles has been thought to have killed about 200 million people around the world. It has been extremely hard to eradicate measles completely because to date, 21 strains exist and can at any time produce more strains. While vaccines have definitely improved the mortality rate of those who contract measles, there are still outbreaks today. One of the most recent large outbreaks happened in Japan in 2007, in Bulgaria in 2009, and as recent as March of 2013 with over 1000 cases and one death. While death is not common last stage for the measles anymore, it still can produce some fatalities. There is no denying that measles definitely affected population growth (Broy et al 2009).

The third largest epidemic was the Black Death. While it does not have any recent cases in the past couple centuries, the centuries that it was present, were devastating. The Black Death is a pathogen from bacteria that caused several forms of the plague. Symptoms of the disease were pustules formed in the groin, neck, and armpits which oozed pus and bled when opened. Other signs included spots, rashes, fever, and vomiting, but most of the time, death was certain from two to seven days after contraction. The Black Death had origins either in or nearby China. It spread to other parts of the world either through the Silk Road trade route or by ships (Herlihy 1997). There have been three major outbreaks of the plague. The first was the Plague of Justinian around the 6^th and the 7^th centuries. This outbreak is the first known attack of the Black Death as well as the first patterns of the bubonic plague. During this outbreak, almost forty percent of the population of Constantinople died from the plague. The plague continued till it wiped out about half of Europe’s population and then declined. The plague was not seen again in Europe until the Black Death in the 14^th century. Here the plague reached its peak. It had a drastic affect on the European population, decimating huge numbers of people. The plague had caused rampant death, despair, and persecution of minorities as scapegoats for the introduction of the plague into society. In the 14^th century alone, it is estimated that the Black Death reduced the world population from 450 million to 350 million. The third pandemic hit China around the late 1800’s and also affected India, but the plague stayed within the confines of the West. Since the last outbreak, there has only been limited number of cases in the past century. Overall the plague has killed over 100 million people within a small time period and is one of the more violent epidemics which have affected the world population (Herlihy 1997).

While all of the top ten epidemics have caused countless of deaths on the world population throughout history, there are a handful that still cause death today. In addition to small outbreaks of the measles, malaria, tuberculosis, and AIDS still wreak havoc in society today. Malaria is a mosquito borne infectious disease. It begins with a bite from a mosquito and the saliva of the infected insect travels through your blood. Malaria causes symptoms that typically include fever, headache, and can progress to a coma or death. The disease is widespread in certain tropical regions including many areas around the equator because the conditions prove to be a perfect breeding habitat for mosquitoes. In 2010 alone, there had been an estimated 219 million documented cases and around 1.2 million deaths from the disease. In total, there is an upwards of 80 million deaths from malaria. Currently there are no effective vaccines that exist for malaria although there is research being conducted to create one. There are other defenses against malaria such as antimalarial drugs, but countries without access to these drugs and with no vaccinations, malaria will continue to be a deadly epidemic (Sarkar et al 2009). Tuberculosis is a common and lethal infectious disease caused by different strains of the bacteria, Mycobacterium tuberculosis. Tuberculosis is characterized by attacking mainly the lungs and can also spread to other parts of the body. It can spread through the air and be transmitted from person to person. The symptoms of tuberculosis are coughing, fever, night sweats, and weight loss. It is believed that about one third of the world’s population was infected with tuberculosis with new infections happening at a rate of about one per second. Every year there are millions of cases of tuberculosis. In 2010, 8.8 million cases were reported and about 1.5 million deaths as a result either directly or indirectly from tuberculosis. Currently, under developed countries still have many cases of tuberculosis because of compromised and weak immune systems after contracting HIV and AIDS. There have been between 40 to 100 million deaths from tuberculosis (Lawn and Zumla 2011). The last of the major epidemics currently in existence is AIDS.  AIDS is a disease of the human immune systems caused by an infection of human immunodeficiency virus (HIV). With the initial contraction of HIV, there are influenza-like symptoms. After, there can be long periods without any symptoms at all while the virus slowly attacks the immune system.  The last stage of HIV is considered to be AIDS. HIV is transmitted through unprotected sexual intercourse and exchange of bodily fluids. Because HIV/AIDS attacks the immune system, a person is much more likely to be affected by other diseases and sicknesses because the body cannot fight against it. Since the discovery of AIDS, it has caused about 30 millions deaths as of 2009 and as of 2010, it is estimated that 34 million people are living with it around the world. There are no cures or vaccines as of now, but there are ways to slow the course of the disease (Baggaley et al 2006). 

Figure 5: Table of the top ten deadliest epidemics

           Disease, in the past and in the present, has affected populations. Disease alone is responsible for killing over a billion people in the world. It has wreaked havoc on population in the history through means such as small pox or the Black Death, and currently affects our population through AIDS, malaria, and tuberculosis. It is hard to infer if these diseases will become worse with time, or if new diseases will be formed, but disease is definitely a huge factor affecting the world population.