Global Health Threats

Remarkably, the outbreak that involved a virus that has been one of the worst killers ever known to man, was not at center stage after the plague had abated. Even though the flu of 1918 had been a life altering event for thousands of families everywhere in the world, second generations to this cataclismic event would hardly knew anything about it. It is difficult to understand this ignorance in the presence of such devastation where more americans were killed in 1 year than those who died in WWI, WWII, the Korean war and the Vietnam war combined! Equally difficult is to understand their lack of preparedness that meant devoting time to create theories as to its origins, stories that range from a mythical new weapon to german sabotage into aspirins.

Misleadingly nicknamed "Spanish Influenza", the 1918 influenza pandemic was caused by a type of influenza A(H1N1) virus capable of causing very severe disease. Although the pandemic only lasted from 1918 to 1920, it infected 500 million people worldwide and killed an estimated fifty to 100 million. The first cases of the pandemic were reported in the United States, quickly spreading to Europe and Asia. In less than a year, the disease had affected almost every inhabited corner of the globe. The 1918 influenza pandemic differed from previously seen outbreaks of flu in several aspects. First, the symptoms seen were much more severe than the usual flu-like manifestations. In addition to fever, cough, and colds, patients could experience extreme difficulty of breathing soon after being infected. Some would also show signs of hemorrhage in the stomach and intestines, as well as bleeding from the nose, gums, or ears.

The disease was also much more fatal and acted more quickly than seen before. Cases of people dying mere hours or days after showing signs of illness were reported. Countries all over the world saw their populations rapidly reduced. Previous cases of flu outbreaks killed less than one percent of the infected population; with the 1918 influenza pandemic, ten to twenty percent of those infected died. The most common cause of death was bacterial pneumonia following infection with influenza; however, there were also cases in which the virus directly caused lung damage and internal bleeding, leading to death.

In addition, the 1918 influenza pandemic differed in terms of the population affected. Usually, the very young and the very old are more susceptible to infection by influenza; consequently, they are also more likely to die of the disease. However, this influenza pandemic affected and killed a greater percentage of the young. Almost half of the deaths during the pandemic were adults aged twenty to forty years old; more than 99% of deaths occurred in people less than 65 years of age. One popular theory on why this was so related to the then-ongoing Great War (now known as the First World War). Otherwise healthy young men would be weakened by time spent in the trenches, enduring physical hardships and malnutrition. This made them more susceptible to infection and less capable of fighting off disease. In addition, the overcrowded conditions in the barracks made it easy for the virus to spread amongst soldiers. The end of the war in November 1918 also saw another chance for disseminating the disease as soldiers returned to their homes.

Another theory explaining this pattern of infection is that older adults had partial immunity against the 1918 influenza strain, as they had been previously exposed to a related strain in an influenza pandemic that had occurred decades earlier. Those who were not yet born at the time had no means of forming antibodies against the virus and thus, had no protection.

Even though this epic catastrophe happened almost a century ago, it still impacts us today. Epidemiologists and virologists studying the events of 1918 with the help of modern technology can further our understanding of viruses circulating today and have actually succeeded in linking the original 1918 strain to the most recent swine flu virus. Learning from the past also aids us in predicting, preventing, and responding to future pandemics.

The genus Ebolavirus consists of five types of viruses that can cause ebola hemorrhagic fever (EHF). Four of these viruses—the Zaire virus, the Sudan ebolavirus, the Ivory Coast ebolavirus, and the Bundibugyo ebolavirus—can cause disease in humans. The Reston ebolavirus does not cause disease in humans who are infected with it.

The Zaire virus was first identified in 1976, after an outbreak of disease in Yambuku, near the Ebola River Valley in the Democratic Republic of the Congo (then known as Zaire). There were 318 cases and 280 deaths. Since then, the Zaire virus has been responsible for the most outbreaks and the highest case-fatality rates among all the other Ebolavirus types. Subsequent outbreaks occurred in Gabon and the Republic of the Congo during 1994, 1995, 1996, 2001-2002, and 2003.

The year 1976 also saw the emergence of another type of Ebolavirus, the Sudan Ebolavirus. This virus caused an outbreak in Sudan, infecting 284 people and causing 151 deaths. This was followed by a smaller outbreak in 1979, involving 33 cases and 22 deaths. The Sudan Ebolavirus was not seen until 2000, wherein 425 cases of infection were reported in Uganda, with 224 deaths. The last known outbreak of this type of Ebolavirus was in 2004 in Sudan, with 20 cases and five deaths. The latest outbreak of disease caused by an Ebolavirus was in Uganda in 2007. It was discovered to be a new type of Ebolavirus, and was named the Bundibugyo Ebolavirus after the district where it was first discovered. By the time the epidemic ended in 2008, there had been 149 cases and 37 deaths.

Ebola hemorrhagic fever can cause very severe symptoms and is often fatal. The disease is spread among humans by coming into contact with the body fluids (such as saliva or blood) of an infected person. A person may also be infected with the virus by handling the corpse of someone previously infected with an Ebolavirus. Contact with infected monkeys or other primates may also result in infection.

Symptoms of EHF may take up to three weeks to appear after contact with the infected person or animal. EHF first presents with flu-like symptoms such as fever, headache, muscle and joint pains, sore throat, and weakness. This is usually followed by diarrhea and vomiting, as well as the appearance of rashes. The patient may have blood in the stools or phlegm, or have other sites of bleeding such as the gums or the nose. Supportive treatment is given to patients suffering from EHF. Intravenous fluids or oral rehydration solutions are given, as most EHF patients are dehydrated. Other treatment may be given to replace blood loss and stop bleeding. Even with treatment, the mortality rate for EHF is very high, with an estimated fifty to 89% of cases dying. Research is currently underway for medication that can combat the Ebolavirus.

There is no known vaccine for humans against any strain of Ebolavirus. Currently, vaccines developed against Ebolavirus for use in humans are still in the clinical trial stage.

The bubonic plague is the most common manifestation of plague. Plague is an infectious disease caused by the bacterium Yersinia pestis. This bacterium most commonly infects rats, but can also be found in other rodents and small mammals. Yersinia pestis is spread by means of the rat flea, Xenopsylla cheopis. The rat flea lives off blood ingested from other animals. When a rat flea bites an animal already infected with Yersinia pestis, the bacteria multiply in the flea’s body. The flea then passes on the bacteria when it bites another animal.

In humans who have been bitten by an infected flea, the bacteria spread throughout the body via the lymphatic system. The bacteria then collect and multiply in the lymph nodes, causing them to swell. These painful, swollen lymph nodes are called buboes, from which the name of the disease derives. Buboes are most often found in the groin, armpits, and neck. As the disease progresses, the skin surrounding the buboes may have scabs, blisters, or collections of pus. The buboes may further swell and burst, and may leak out pus. Small blisters may also be seen around the area of the flea bite. The spleen or the liver may also enlarge, causing abdominal pain. Other symptoms of bubonic plague are high-grade fever and chills, headache, pain throughout the body, weakness, and diarrhea. Plague is treated with antibiotics such as streptomycin or doxycycline. Very large and swollen buboes may be incised and drained of pus. If left untreated, approximately fifty percent of patients die. However, with proper medication and supportive therapy, the mortality rate becomes as low as five percent.

The most famous outbreak of bubonic plague is probably the Black Death—a pandemic that spread throughout medieval Europe, killing up to sixty percent of the world’s population during that time. The Black Death peaked between 1348 and 1350, but recurring outbreaks followed over the next few hundred years. Other major outbreaks of bubonic plague in Europe occurred in 1665-1666, designated as the Great Plague of London, and in 1679, called the Great Plague of Vienna. A plague pandemic resurfaced in 1855, beginning in China then spreading to India, Southeast Asia, Africa, Australia, and North and South America. This so-called "Third Pandemic" lasted well into the first part of the twentieth century.

It was during the Third Pandemic that advances in the research of plague were made. In 1894, Alexandre Yersin discovered the bacterium causing plague, and so it was named Yersinia pestis in his honor. The bacterium’s means of spread—from fleas biting infected rats—was discovered by Paul-Louis Simond in 1897. Further knowledge used to combat the spread of the disease was researched by Waldemar Haffkine, who developed a plague vaccine in 1897.

Thanks to these discoveries, as well as other advances in medicine and sanitation, effective preventive measures against bubonic plague can be taken. These include the following: controlling the rodent population, especially in workplaces and residential areas; preventing flea bites by wearing protective clothing and using insect repellent; treating pets for fleas; and reporting human and animal plague cases to health authorities.

Worldwide, 1,000 to 3,000 new bubonic plague cases are reported annually, and ten to fifteen of those cases occur in the United States. However, with continued prevention and vigilance, it is hoped that those cases will further decline.

The Black Death is one of the most devastating pandemics in recorded history. Believed to have originated in Central Asia, the Black Death quickly spread throughout Europe and some parts of Africa. The height of its destruction was wreaked on Europe from 1348 to 1350. The Black Death killed approximately thirty to sixty percent of Europe’s population and had profound consequences on society, economics, and culture.

As with other types of plague, the Black Death was also caused by Yersinia pestis. This bacteria is carried by fleas and rodents, and can then be spread to humans. Depending on how a human is infected, plague can be manifested in one of three ways: bubonic plague, septicemic plague, or pneumonic plague. The bubonic plague was the most commonly seen form of the Black Death.

Pneumonic plague, the second most common form, was spread from person to person rather than from fleas to persons. A person already infected with any form of plague could spread the bacteria in the form of droplets from coughing or sneezing. As the name implies, this form of plague attacks the respiratory system. People suffering from pneumonic plague have symptoms such as fever and coughing up of blood and bloody phlegm.

The rarest form of the Black Death was septicemic plague. This form can be transmitted from a flea bite, like in bubonic plague, or by coming into contact with infected humans, like in pneumonic plague. In septicemic plague, no buboes are seen. Septicemic plague can cause disseminated intravascular coagulation—a condition wherein small blood clots form in blood vessels all over the body, with abnormal bleeding afterward. Symptoms of septicemic plague are high fever, vomiting blood, and purpura (small red or purplish spots caused by bleeding under the skin).

At the time of the Black Death, very little was known about the nature of infectious diseases. There was little concept of pest control or sanitation, enabling the carriers of the disease to spread throughout the population in a short amount of time. Overcrowding also contributed to the devastating impact of the disease, as just one infected person could rapidly transmit the disease to countless others. Some measures taken to limit the spread of the Black Death were the institution of quarantines and restrictions on trade and travel. However, as they did not directly address the cause of the disease, these measures were largely ineffective. As a result, by the time Black Death subsided in 1350, the world’s population was largely reduced.