Viruses have been around for billions of years. They are biological infectious agents that replicate and thrive only inside living organisms such as animals, plants, bacteria and others. Scientists have so far described more than 5,000 virus species, each of which has several strains. Humans have witnessed dozens of virus-caused epidemics throughout history – with some wiping out a huge chunk of the world’s population. Here we take a look at some of the deadliest viruses in the world based on the fatality rate and how much threat they still pose to humanity.
Top 10 deadliest viruses
There are several strains of the Hantavirus. During the Korean War in the 1950s, a strain of Hantavirus infected about 3,000 soldiers and killed nearly 12% of them. It is transmitted through the droppings of infected mice. Different species of rodents carry different strains of this virus. The most common symptoms include hemorrhagic fever, lung disease, and kidney failure. The Hantavirus pulmonary syndrome (HPS) has a mortality rate of 38%, according to the Center for Disease Control and Prevention (CDC).
9- Spanish Flu
According to the World Health Organization (WHO), influenza kills nearly half a million people every year. But a new strain of flu emerged in 1918 that caused a massive epidemic across Europe and many other countries. Dubbed the Spanish Flu, it infected more than 40% of the world’s population between January 1918 and December 1920. The virus killed 50-100 million people. The pandemic is described as “the greatest medical holocaust in history.” The outbreak occurred during World War I, so most of the affected countries grossly under-reported its effects to maintain the morale of their people. But media in Spain, which was neutral, was free to report the real conditions.
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8- Yellow Fever
The Yellow Fever virus is spread by mosquitoes, and infects only humans and other primates. It is difficult to detect because symptoms are not visible in the early stages of infection. The symptoms include fever, chills, nausea, headache, and abdominal pain. It also leads to liver damage, which causes the skin to turn yellow. Affordable vaccines are now available for yellow fever. But according to the World Health Organization (WHO), it still infects about 200,000 and kills 30,000 people every year. Nearly 90% of infections and deaths occur in African countries.
Dengue is one of the deadliest viruses humanity has ever encountered. The virus spreads via mosquitoes. According to the Center for Disease Control and Prevention (CDC), more than 100 million cases of dengue fever are reported every year, mostly in tropical and subtropical regions. It kills about 20,000 people every year. The virus first appeared in the Philippines and Thailand in the 1950s, though dengue fever was described in the Chinese literature more than 2,000 years ago. It has since spread to several countries across the globe. Scientists have warned that dengue will spread further as the world warms.
6- Crimean-Congo Hemorrhagic Fever (CCHF)
This virus first emerged in 1944 in Crimea and then spread to Congo in the 1960s. The CCHF virus is transmitted by ticks. According to the WHO, it has a fatality rate of 40%. There is no CCHF vaccine available in the market yet. Though the virus is found all over the world, the CCHF occurs mainly in Asian countries such as India, where agricultural workers are frequently exposed to tick-bearing animals. Its progression is similar to Ebola and Marburg viruses. In the early stage, it causes pin-sized bleedings in the mouth, face, and pharynx. Other symptoms include intense fever, back pain, joint pain, enlargement of the liver, and vomiting.
The Human Immunodeficiency Virus (HIV) is still one of the biggest killers in the world. It has claimed more than 36 million lives since the virus was first recognized about 40 years ago. According to WHO, about 5% adults in the sub-Saharan Africa are HIV-positive. The HIV causes acquired immunodeficiency syndrome (AIDS), which deteriorates the victim’s immune system. Due to a weakening immune system, the victims suffer from numerous infections and eventually die. Though researchers have developed drugs that could extend the lives of HIV patients, the virus continues to wreak havoc in many African and Asian countries.
The first records of rabies could be traced back to 2300 BC, when Babylonians described people going mad and dying after being bitten by dogs. The rabies virus attacks the central nervous system and kills patients if left untreated for long. Fortunately, there are affordable rabies vaccines available today in the market, so the disease is preventable. Some of the symptoms of rabies are hallucinations, raging, violent behavior, and delirium. Rabies has become pretty rare in the US and other Western countries,
3- H5N1 Bird Flu
Influenza A virus subtype H5N1, also known as bird flu, has caused panic time and again in many countries. It has the mortality rate of above 70%, making it one of the deadliest viruses out there. The virus spreads through direct contact with poultry. According to scientists, the virus can also mutate into a strain capable of human-to-human transmission. Several companies and governments are working on bird flu vaccines. In June 2008, 11 outbreaks of H5N1 were reported in China, Vietnam, Indonesia, Pakistan and Egypt.
2- Marburg virus
The Marburg virus was recognized in 1967 when lab workers in Marburg, Frankfurt, and Serbia contracted a new type of hemorrhagic fever after coming in contact with imported African green monkeys. It also spreads through human-to-human contact. Marburg virus is classified as a CDC Biosafety Level 4 (BSL-4), meaning it’s one of the deadliest pathogens in the world. It has a fatality rate of a staggering 90%. The early symptoms include fever, headache, and a rash on the trunk. In later stages, the patient suffers from immense internal bleeding and multiple organ failure. There is no known cure yet.
1- Ebola virus
Don’t be surprised to see Ebola at the top of the list of deadliest viruses known. There are five known strains of this virus: Sudan, Tai Forest, Zaire, Reston, and Bundinbugyo. Zaire is the deadliest of them with the mortality rate of above 90%. The fruit bats are the natural Ebola virus hosts. The virus infects humans when they come in close contact with the secretions, blood, or other bodily fluids of infected animals such as fruit bats, monkeys, and chimpanzees. It then spreads through human-to-human transmission. Four of the five Ebola virus strains cause the Ebola Hemorrhagic Fever (EHF), which has claimed thousands of lives in Liberia, Guinea, Sierra Leone, Uganda and other African countries.