Infectious diseases, also known as communicable diseases, or tainting/transmissible diseases comprise clinically evident illness (i.e. characteristic medical signs and/or symptoms of disease) resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism. In certain cases, infectious diseases may be asymtomatic for much or all of their course. Infectious pathogens include some viruses, bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins known as prions. These pathogens are the cause of disease epidemics, in the sense that without the pathogen, no infectious epidemic occurs.
Transmission of pathogen can occur in various ways including physical contact, contaminated food, body fluids, objects, airborne inhalation, or through vector organisms. Infectious diseases that are especially infective are sometimes called contagious and can be easily transmitted by contact with an ill person or their secretions.
The below diseases are so viral that there is a high percentage chance that you will die from the complications. Some of these diseases have vaccinations, some have preventive measures while others are simply deadly with little chance of survival. To be included on this list, the virus has to have been a major cause of death in history with ranking based on fatality rates and impact worldwide.
This variola virus had many forms and continues to be a required vaccination for many countries. Smallpox in its worse forms – hemorrhagic and flat – had the highest fatality rates with only a 10 percent or less chance of survival. Fortunately this disease has been the only one on this list to be completely eradicated from nature since it is only contagious through humans. It is known to have two virus variants, Variola major and Variola minor.
Smallpox localizes in small blood vessels of the skin and in the mouth and throat. In the skin, this results in a characteristic maculopapular rash, and later, raised fluid-filled blisters. Variola major produces a more serious disease and has an overall mortality rate of 30–35%. Variola minor causes a milder form of disease (also known as alastrim, cottonpox, milkpox, whitepox, and Cuban itch) which kills about 1% of its victims.
9. Typhoid Fever
Perhaps one of the least lethal diseases on this list along time, the fatality rate of typhoid fever is only 10-30 percent. But the symptoms show up in stages over a period of three weeks and, in most cases, are not fatal. That said, the disease can stay dormant in a person who has overcome it and then be passed on to another person. The most famous case of this was the American cook in the early 1900s known as “Typhoid Mary” Mallon. It is transmitted by the ingestion of food or water contaminated with the feces of an infected person, which contain the bacterium Salmonella enterica enterica, serovar Typhi.
Leprosy, also known as Hansen’s disease (HD) has been around since biblical times; so has the stigma against them. For centuries, the disease was believed to be a curse. Stories abounded about the terrifying symptoms: skin lesions turn to dying flesh and into fallen limbs.Yes, that’s right. Your leg might just fall off.
Suddenly, those leper colonies make a lot more sense. In reality, leprosy doesn’t actually cause limbs to drop left and right.
The disease, also known as Hansen’s disease, is caused by Mycobacterium leprae, a bacteria that infects the peripheral nerves. Without functioning nerves to feel pain and temperature, patients can often inadvertently injure themselves and opportunistic infections can take hold, sometimes leading to the loss of a finger or toe (hence, the fallen limb rumors). It’s not a highly infectious disease, but can spread in areas with poor hygiene and close living conditions. Things changed a lot for lepers in the 1950s with the rise of antibiotics such as dapsone.
Today, we treat it with a multi-drug regimen and, though colonies still exist, far fewer people lose life or limb to the disease.
7. Influenza (the Flu)
Perhaps the scariest virus on this list is one that anyone anywhere can contract – influenza. Luckily, the flu is easily identified and in most countries easily combated. However, young children and the elderly are particularly susceptible to flu. And the most famous strain was the Spanish Flu, which was estimated to have killed 2-5 percent of the human population in 1918-1919. Thankfully that strain has never been seen again; however, the flu virus is famous for mutating from animals to humans.
6. Bubonic Plague
This plague is transmitted through infected fleas and kills about 70 percent of its victims in 4-7 days. The most well known epidemic was the Black Death in Medieval times and it swept through Europe in the 14th century killing an estimated 75 million people, 45-60% of the European population. The bubonic plague is often characterized by swollen lymph nodes though the modern world has seen few breakouts.
Because the plague killed so many of the working population, wages rose and some historians have seen this as a turning point in European economic development.
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Normally a human gets cholera from eating or drinking infected food or water. And untreated, the disease will progress from massive diarrhea to shock in 4-12 hours and possibly death within 18 hours or several days. Luckily, with oral rehydration therapy, a person can survive from cholera; however, in its most severe form, cholera can kill within three hours. But good sanitation practices can curb an outbreak. As the old saying goes – don’t drink the water – in many underdeveloped countries.
Primary treatment is with oral rehydration solution and if these are not tolerated, intravenous fluids. Antibiotics are beneficial in those with severe disease. Worldwide it affects 3-5 million people and causes 100,000-130,000 deaths a year as of 2010. Cholera was one of the earliest infections to be studied by epidemiological methods.
Foaming at the mouth, difficulty swallowing, a maniacal fear of water, anger and hostility, delusions and hallucinations, general all-round insanity.You may recognize these symptoms from that pack of rabid raccoons in your backyard, but a couple of hundred years ago, a lot more humans found themselves acting like those unfortunate animals.Back before Louis Pasteur’s groundbreaking vaccine hit the scene in 1885, rabies was a widely feared disease (and it still is in some parts of the world). Spread through saliva (usually through dog bites), the rabies virus attacks the nervous system; once it’s gotten to your brain, it’s pretty much over. Today, mandatory animal vaccination programs have pretty much wiped out the disease in humans in the developed world, but the disease still kills millions of animals and up to 50,000 people worldwide each year. Consider that a reminder to vaccinate Fluffy.
While anthrax can be produced in vitro and has been used as a biological weapon before, a person dies from anthrax after inhalation of the spores or through eating or coming in contact with animals who have ingested the spores.
Once contaminated, the bacteria quickly multiples and kills its host by producing two lethal toxins. Death can take from two days up to a month from the cold like symptoms, which then lead to serious breathing problems, shock and the eventual fatality. Large amounts of antibiotics have been shown to be able to stop the disease. A vaccine is known, then again there are also antibiotic-resistant strains of anthrax.
The dead body of an animal that died of anthrax can also be a source of anthrax spores.
2. Ebola, Hanta & Hemorrhagic Fevers
Drowning isn’t fun and neither is bleeding. Hemorrhagic fevers find a way to mix the two: as the entire body oozes and bleeds, the lungs can bleed into themselves, causing some victims to literally drown in their own blood. Hemorrhagic fevers are the result of some very scary viruses like Ebola and Hanta, most of which are spread via animal feces and transmitted either through the air or through direct contact.Once in the body, the viruses attack the cells that line blood vessels, causing internal organs throughout the body, from the intestines to the kidneys to the brain, to ooze blood.There’s no band-aid big enough to stop that bleeding.
1. HIV (Human immunodeficiency virus)/AIDS (Acquired immune deficiency syndrome)
HIV leads to AIDS, which cripples a human’s immune system. AIDS has been categorized as an epidemic by the CDC and the life expectancy has been extended despite the lack of a vaccination or cure. While on its own, the Ebola virus is much more deadly in the short term, most AIDS victims eventually succumb to death from an AIDS related sickness.
This condition progressively reduces the effectiveness of the immune system and leaves individuals susceptible to opportunistic infections and tumors. HIV is transmitted through direct contact of a mucous membrane or the bloodstream with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal fluid, and breast milk. This transmission can involve anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, breastfeeding or other exposure to one of the above bodily fluids.
AIDS is now a pandemic. As of 2009, AVERT estimated that there are 33.3 million people worldwide living with HIV/AIDS, with 2.6 million new HIV infections per year and 1.8 million annual deaths due to AIDS. In 2007, UNAIDS estimated: 33.2 million people worldwide had AIDS that year; AIDS killed 2.1 million people in the course of that year, including 330,000 children, and 76% of those deaths occurred in sub-Saharan Africa. According to UNAIDS 2009 report, worldwide some 60 million people have been infected, with some 25 million deaths, and 14 million orphaned children in southern Africa alone since the epidemic began.
Genetic research indicates that HIV originated in west-central Africa during the late nineteenth or early twentieth century. AIDS was first recognized by the U.S. Centers for Disease Control and Prevention in 1981 and its cause, HIV, identified in the early 1980s.