1. Marbug

Scientists identified Marburg virus in 1967 when small outbreaks occurred among lab workers in Germany who were exposed to infected green monkeys imported from Uganda

Like Ebola the virus, can cause hemorrhagic fever, meaning that infected people develop high fevers and bleeding into the gastrointestinal tract and skin that can lead to shock, disseminated intravascular coagulation, multiorgan failure and death.

The mortality rate in the first outbreak was 25%, but it was more than80 % in the 1998-2000 outbreak in the Democratic Republic of Congo, as well as in the 2005 outbreak in Angola, according to the World Health Organization (WHO). The latest cases were reported out of Uganda at the end of 2012.

Bats are thought to be the natural reservoir for the virus, but this hypothesis has yet to be confirmed. An American tourist who had explored a Ugandan cave full of fruit bats known to be reservoirs of the virus contracted it.

There is no cure, no antiviral therapy or other vaccine exists for the Marburg virus. However, the WHO says a range of potential treatments, including- blood products, immune and drug therapies are being evaluated

2. Ebola

The deadly virus is named after the Ebola River in the Democratic Republic of the Congo where it was first reported, and is classified as a CDC Biosafety Level 4, making it one of the most dangerous pathogens on the planet.

Symptoms of Ebola virus can be sudden, and include fever, fatigue, muscle pain, headache, sore throat, vomiting, diarrhea, rash, impaired kidney and liver function, and internal and external bleeding.

The average case fatality rate is approximately 50%, according to the World Health Organization (WHO). But fatality rates vary depending on the strain which are each named after countries and regions in Africa: Zaire, Sudan, Tai Forest, Bundibugyo and Reston. The Zaire strain has a fatality rate of 90%, while the Reston strain does not even make people sick. The Bundibugyo strain fatality rate is up to 50% and the Sudan strain up to 71%, according to WHO.

Scientists say flying foxes probably brought the Zaire Ebola virus into cities which currently is spreading through Guinea, Sierra Leone and Liberia, and beyond.

The outbreak underway in West Africa began in early 2014, and is the largest and most complex outbreak of the disease till date killing at least 11,000 people in Liberia, Guinea and Sierra Leone.

3. Rabies

Rabies has a long and storied history dating back to 2300 B.C., with records of Babylonians who went mad and died after being bitten by dogs.

According to the World Health Organization (WHO), 99% of humans who die of rabies catch it from dogs.

The incubation period is generally 2-3 months before virus affects the brain and spinal cord and moves to affecting the central nervous system.

The symptoms of an advanced infection include delirium, hallucinations and raging, violent behavior in some cases, which some have argued makes rabies eerily similar to zombification.

Humans infected with rabies may exhibit one of two forms of the disease; Furious rabies or Paralytic rabies. According to the WHO, individuals with furious rabies may exhibit signs of hyperactivity, excitable behavior, hydrophobia, and aerophobia, with death occurring after a few days due to cardiorespiratory arrest. Those with paralytic rabies—which accounts for 20% of all human cases—gradually become paralyzed, starting at the wound site. Following a coma, death eventually occurs.

Although rabies vaccines for pets were introduced in the 1920s and have helped make the disease exceedingly rare in the developed world, this condition remains a serious problem in India and parts of Africa.

4. Small Pox

The world battled smallpox virus, one of the most devastating diseases known to mankind, for thousands of years before the World Health Assembly declared the world free of it in 1980 as the result of successful worldwide implementation of the vaccine.

There are several different types of smallpox disease that result from an infection ranging from mild to fatal, but it is generally marked by a fever, rash, pus-filled blisters, and oozing pustules that develop on the skin.

The virus is only carried by and contagious for humans.

The disease killed about 1 in 3 of those it infected and left survivors with deep, permanent scars, often blindness.

Historians estimate 90% of the native population of the Americas died from smallpox introduced by European explorers. In the 20th century alone, smallpox killed 300 million people.

The last known natural case was in Somalia, East Africa in 1977

5. Hanta

The Hanta virus describes several types of viruses with many strains floating around in the wake of rodents that carry the virus.

It is named after a river where American soldiers were first thought to have been infected with the Hantavirus, during the Korean War in 1950.

While the virus was new to Western medicine when it was first discovered in the US in 1933, researchers realized later that Navajo medical traditions describe a similar illness, and linked the disease to mice. Few months later, health authorities isolated hanta virus from a deer mouse living in the home of one of the infected people.

Different strains, carried by different rodent species, are known to cause different types of illnesses in humans, most notably Hemorrhagic Fever with Renal Syndrome (HFRS)—first discovered during the Korean War—and hantavirus Pulmonary Syndrome (HPS), which reared its ugly head with a 1993 outbreak in the Southwestern United States.

6. HIV/AIDS

In the modern world, the deadliest human immunodeficiency virus of all may be HIV, that attacks the immune system, specifically CD4 cells (or T cells).

Although powerful antiviral drugs have saved HIV positive people for years with HIV but the disease continues to devastate many low and middle income countries, where 95 % of new HIV infections occur. Nearly 1 in every 20 adults in Sub-Saharan Africa is HIV-positive, according to WHO.

An estimated 36 million people have died from HIV since the disease was first recognized in the early 1980s.In 2017 alone, nearly one million people diedfrom Aids-related illness globally, according to the World Health Organization (WHO).

However in 2000 to 2017, new HIV infections fell by 36% and Aids related deaths fell by 38, thanks to Anti-retroviral Therapy (ART) worldwide.

7. Influenza

According to the World Health Organization (WHO), up to 500,000 people die globally during a typical flu season and sometimes turn into a pandemic when a new strain emerges.

Four types of the virus exist: A and B, which are responsible for seasonal flu epidemics in people; C, which is relatively rare, causes a mild respiratory illness, and is not thought to cause epidemics; and D, which primarily infects cattle and isn’t known to affect people.

Most people easily survive infections using influenza vaccines but the virus is constantly mutating and creating new strains. Thousands of strains exist at any given time, many of which are harmless, and vaccines available in the US cover only about 40 % of the strains at large each year.

The outbreak of the Spanish flu, a strain of H1N1 influenza, in 1918 is generally considered to be one of the worst pandemics in human history, infecting 20 to 40 % of the world’s population and killing 50 million in the span of just two years.

8. Dengue

Dengue originated in monkeys and spilled over into humans as long as 800 years ago. Dengue virus first appeared in the 1950s in the Philippines and Thailand, and since then has spread throughout the tropical and subtropical regions of the globe. Up to 40 % of the world’s population now lives in areas where dengue is endemic— with the mosquitoes that carry it — is likely to spread farther as the world warms.

The virus causes a high fever, severe headache, and in the worst cases, hemorrhaging.

According to the World Health Organization (WHO), every year 50 to 100 million people suffer from dengue sickness, although the mortality rate is comparatively lower than other viruses.

There is no current vaccine, but large clinical trials of an experimental vaccine developed by French drugmaker Sanofi have had promising results.

The good news is that it’s treatable and not contagious. The bad news is there’s no current vaccine against dengue, but large clinical trials of an experimental vaccine developed by French drugmaker Sanofi have had promising results. One can, however, easily get it from the bite of an infected mosquito—which puts at least a third of the world’s human population at risk.

9. Lassa

Discovered in 1969 in Lassa, Nigeria, this pathogen causes hemorrhagic fever and multiorgan failure.

Lassa is carried by a species of rat in West Africa called Mastomys and is most commonly transmitted by exposure to the urine of the infected Mastomys in food or water sources. Scientists assume that 15 % of rodents in western Africa carry the virus.

The disease can also be spread via inhalation of air contaminated with infected rodent secretions. Specifically, airborne transmission may occur during cleaning activities such as sweeping. Human-to-human transmission is common in healthcare settings where proper personal protective equipment is not available or infrequently used.

No vaccine for this virus exists, with prevention taking the form of infection and rodent control.

Mortality due to the virus is high (15% to 50%), with death due to vascular collapse. The virus causes about 5000 deaths a year in West Africa, particularly in Sierra Leone and Liberia.

10. Japanese Encephalitis

The Encephalitis virus is the most frequent cause of epidemic viral encephalitis in several countries across Asia, with an estimated 68,000 clinical cases annually, according to the World Health Organization (WHO).

Symptoms include fever, neck rigidity, altered consciousness, headache, tremors, incoordination, and convulsions.

Not only is the death rate of this disease high (30%), but survivors (30% to 50%) experience serious neurologic or psychiatric sequela.

This disease is spread to humans by infected mosquitoes of the Culex species that live in Asian rice fields, with reservoirs including water birds and pigs.

An inactivated vaccine does exist for protection against this virus, and mosquito protection is recommended among those at high risk of exposure. Because no antiviral therapy yet exists for infected patients, treatment is symptomatic.

In fact, 24 countries in the South-East Asia and Western Pacific regions have endemic Japanese encephalitis virus transmission, putting over 3 billion people at risk for infection.