Rabies, influenza and smallpox: 12 of the deadliest viruses on Earth
Humans have fought viruses since ancient times. Often, vaccines and antiviral drugs prevented widespread infections and helped patients recover. And only one disease - smallpox - we were able to eradicate, ridding the world of new cases. Writes about it Live Science.
But humanity is far from victory in the fight against viruses. In recent decades, several viruses have passed from animals to humans and caused significant outbreaks that claimed thousands of lives. The viral strain that caused the outbreak of Ebola in West Africa in 2014–2016 kills up to 90% of the people it infects, making it the deadliest member of the Ebola family.
But there are other viruses that are equally deadly, sometimes even more deadly. Some viruses, including the new coronavirus, which is currently causing outbreaks around the world, have lower mortality rates, but still pose a serious threat to public health, as we do not yet have the means to combat them.
Scientists discovered the Marburg virus in 1967, when there were small outbreaks among laboratory workers in Germany exposed to infected monkeys brought from Uganda. Marburg virus is similar to Ebola in that both can cause hemorrhagic fever, that is, infected people develop high fever and bleeding all over their bodies, which can lead to shock, multiple organ failure and death.
According to the World Health Organization (WHO), the mortality rate during the first outbreak was 25%, but during the outbreak in the Democratic Republic of the Congo in 1998-2000, as well as during the outbreak in Angola in 2005, it exceeded 80%.
The first known outbreaks of Ebola among people occurred simultaneously in the Republic of Sudan and the Democratic Republic of the Congo in 1976. Ebola spreads through contact with blood, other body fluids or tissues of infected people or animals. Known strains are very different in mortality, said Elke Mülberger, an Ebola virus expert and associate professor of microbiology at Boston University.
From one strain, Ebola reston, people don't even feel the symptoms of the disease. According to the WHO, the death rate for the Bundibugyo strain is up to 50%, and for the Sudanese one - up to 71%.
The outbreak in West Africa began in early 2014, according to WHO, the largest and most complex outbreak to date.
Although rabies vaccines for domestic animals introduced in the 1920s helped make the disease extremely rare in developed countries, rabies remains a serious problem in India and parts of Africa.
“It destroys the brain. It's a very, very bad disease, ”said Mühlberger. “We have rabies vaccine and we have antibodies, so if someone is bitten by a rabid animal, we can cure that person.”
However, she said, "if you do not receive treatment for rabies, there is an almost 100% chance that you will die."
In the modern world, the most deadly virus can be HIV.
“It is still the leading cause of death,” said Dr. Amesh Adalya, an infectious disease physician and spokesman for the American Society of Infectious Diseases.
According to experts, 32 million people have died from HIV since the disease was first discovered in the early 1980s.
“The infectious disease that is currently causing the greatest damage to humanity is HIV,” said Adalya.
Powerful antiviral drugs let people live with HIV for years. But the disease continues to devastate many low- and middle-income countries, where 95% of new HIV infections occur. Almost one in every 25 adults in the African region, according to WHO, is infected with HIV, which makes up more than two-thirds of people living with the virus worldwide.
In 1980, the World Health Assembly declared the world smallpox free. But until that time, people had fought for millennia with smallpox, which killed about every third infected. The survivors received deep scars and, very often, blindness.
Mortality rates were much higher among populations outside Europe, where people had little contact with the virus before visitors brought it. For example, historians estimate that 90% of Native Americans died from smallpox brought by European researchers. In the twentieth century alone, smallpox killed 300 million people.
“It entailed enormous consequences on a planetary scale - not only death, but also blindness. This is what stimulated the launch of a campaign to eradicate the disease, ”said Adalya.
Hantavirus pulmonary syndrome (HPS) first gained widespread attention in the United States in 1993, when a healthy young Navajo man and his fiancee died within a few days from developing shortness of breath. A few months later, the health authorities removed hantavirus from a mouse living in the house of one of the infected people. According to the Centers for Disease Control and Prevention, in the United States, more than 600 people fell ill with HPS, and 36% died from the disease.
The virus is not transmitted from one person to another, people become infected by contact with infected rodents.
Before him, another hantavirus caused an outbreak in the early 1950s, during the Korean War, according to a 2010 article in the journal Clinical Microbiology Reviews. More than 3000 troops were infected, and about 12% of them died.
This virus was new to western medicine. But when it was discovered in the United States, researchers realized that the Navajo medical traditions describe a similar disease and associate it with mice.
According to WHO, up to 500 people die from this disease during a typical flu season in the world. But sometimes, when a new strain of flu appears, a pandemic leads to a more rapid spread of the disease and often a higher mortality rate.
The deadliest influenza pandemic, sometimes called Spanish influenza, began in 1918 and caused up to 40% of the world's population to die, resulting in the deaths of about 50 million people.
“I think it's possible that something like the 1918 flu outbreak could happen again,” Mühlberger said. "If a new strain of influenza got into the human population and could be easily transmitted between people and cause serious illness, we would have a big problem."
Dengue virus first appeared in the 1950s in the Philippines and Thailand. Since then, it has spread throughout the tropical and subtropical regions of the globe. Currently, up to 40% of the world's population lives in areas where Dengue fever is endemic, and this disease (along with the mosquitoes that carry it) is likely to spread further when the temperature on the planet begins to rise.
According to the WHO, between 50 and 100 million people a year get sick of Dengue. Although the mortality rate from it is lower than that of some other viruses (within 2,5%), the virus can cause an ebola-like disease called dengue hemorrhagic fever. This disease has a mortality rate of 20%.
“We really need to think more about the Dengue virus because it is a real threat to us,” said Mühlberger.
The Dengue vaccine was approved in 2019 by the U.S. Food and Drug Administration for use in children 9-16 years old living in areas with Dengue fever and with a confirmed infection history. In some countries, an approved vaccine is available to everyone between the ages of 9-45, but, again, recipients must be prone to infection in the past. Those who have not contracted the virus before may be at risk of developing severe Dengue fever with the vaccine.
Two vaccines are currently available to protect children from rotavirus, which is the leading cause of severe diarrheal diseases in infants and young children. The virus can spread rapidly through what researchers call the fecal-oral route.
Although children in developed countries rarely die from rotavirus infection, this disease is a killer in developing countries where rehydration treatment is not available.
WHO estimates that worldwide, 453 children under 000 years old died of rotavirus infection in 5. But countries that introduced the vaccine reported a sharp decrease in hospital admissions and deaths from rotavirus.
The virus that causes severe acute respiratory syndrome, according to WHO, first appeared in 2002 in Guangdong Province, in southern China. Most likely, before infecting humans, he first appeared in bats, then infected nocturnal mammals called civets. Flaring up in China, SARS spread to 26 countries, infecting more than 8000 and killing more than 770 people in two years.
The disease causes fever, chills and body aches, and often progresses to pneumonia, a serious condition in which the lungs become inflamed and filled with pus. The death rate from SARS is estimated to be 9,6% and there is currently no approved treatment or vaccine. However, no new cases of SARS have been reported since the early 2000s, according to the CDC.
SARS-CoV-2 belongs to the same large family of viruses as SARS-CoV, known as coronavirus, and was first detected in December 2019 in the Chinese city of Wuhan. It probably originated in bats, as SARS-CoV passed through an intermediate animal before infection.
Since its inception, the virus has infected tens of thousands of people in China and several million around the world. The ongoing outbreak has caused extensive quarantine on the planet.
A disease caused by SARS-CoV-2, called COVID-19, has an estimated mortality rate of about 2,3%. Elderly people and those who have chronic illnesses are most at risk for a serious illness or complications. Common symptoms include fever, dry cough, and shortness of breath; in severe cases, the disease can develop into pneumonia.
The virus that causes the disease, called the Middle East Respiratory Syndrome, or MERS, caused an outbreak in Saudi Arabia in 2012 and another in South Korea in 2015. It belongs to the same virus family as SARS-CoV and SARS-CoV-2, most likely in bats. Disease infects camels before reaching people, and causes fever, cough, and shortness of breath in infected people.
MERS often progresses to severe pneumonia and has an estimated mortality rate of 30% to 40%, making it the most deadly known coronavirus that has passed from animals to humans. As with SARS-CoV and SARS-CoV-2, MERS does not have approved treatments or vaccines.
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