deadliest virus on planet earth
WHAT IS A VIRUS?
Just a tiny bundle of RNA or DNA and a shell.
That uses host cells to reproduce itself.
That uses host cells to reproduce itself.
They aren’t living, or non-living: They’re the perfect
parasites
Viruses are everywhere, Over 5,000 have been described in detail
Millions and Millions Exist
Millions and Millions Exist
When they’re in the air, or on a doorknob
They’re inert = about as living as a rock.
They’re inert = about as living as a rock.
When they come into contact with host cells, They trigger the
cell to engulf them
Or fuse with the cell, Then use the cell’s machinery to reproduce
Or fuse with the cell, Then use the cell’s machinery to reproduce
The deadliest viruses on Earth
Humans have been
battling viruses since before our species had even evolved into its modern
form. For some viral diseases, vaccines and antiviral drugs have allowed us to
keep infections from spreading widely, and have helped sick people recover. For
one disease — smallpox — we've been able to eradicate it, ridding the world of
new cases.
But
we're a long way from winning the fight against viruses. In recent decades,
several viruses have jumped from animals to humans and triggered sizable
outbreaks, claiming thousands of lives. The viral strain that drove the 2014-2016 Ebola outbreak in
West Africa kills
up to 90% of the people it infects, making it the most lethal member of the Ebola
family.
But
there are other viruses out there that are equally deadly, and some that are
even deadlier. Some viruses, including the novel coronavirus currently
driving outbreaks around
the globe, have lower fatality rates, but still pose a serious threat to public
health as we don't yet have the means to combat them.
Here are some
worst killers, based on the likelihood that a person will die if they are
infected with one of them, the sheer numbers of people they have killed, and
whether they represent a growing threat.
Marburg virus
Scientists
identified Marburg virus in 1967, when small outbreaks
occurred among lab workers in Germany who were exposed to infected monkeys
imported from Uganda. Marburg virus is similar to Ebola in that both can cause
hemorrhagic fever, meaning that infected people develop high fevers and
bleeding throughout the body that can lead to shock, organ failure and death.
The mortality
rate in the first outbreak was 25%, but it was more than 80% 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).
Ebola virus
Disables
tetherin, a protein that disables the spread of the virus from cell to cell.
Spreads rapidly to cause hemorrhaging, extreme fever, and death.
The first known
Ebola outbreaks in humans struck simultaneously in the Republic of the Sudan
and the Democratic Republic of Congo in 1976. Ebola is spread through contact
with blood or other body fluids, or tissue from infected people or animals. The
known strains vary dramatically in their deadliness, ElkeMuhlberger, an Ebola
virus expert and associate professor of microbiology at Boston University, told
Live Science.
The outbreak
underway in West Africa began in early 2014, and is the largest and most
complex outbreak of the disease to date, according to WHO.
Hepatitis
Viral
hepatitis caused an annual 1.34 million deaths worldwide in 2015. While deaths
due to other infectious diseases have declined, deaths due to viral hepatitis
have actually increased—by 22%—since 2000, according to a WHO report.
Approximately
325 million people, or 4.4% of the world’s population, have viral hepatitis.
And 1.75 million new infections of hepatitis C alone occur each year.
Despite
a vaccine for hepatitis B and effective antivirals for hepatitis C, few people
with viral hepatitis get a diagnosis because of limited access to affordable
hepatitis testing. (Only 9% of people with hepatitis B and 20% with hepatitis C
have received a diagnosis, according to the WHO.) Consequently, treatment
reaches only a small fraction of those infected.
Rabies
Although rabies
vaccines for pets, which were introduced in the 1920s, have helped make the
disease exceedingly rare in the developed world, this condition remains a
serious problem in India and parts of Africa.
yearly
mortality: 55,000 deaths
How it works:
Enters the body and proceeds to the brain, replacing nerve cells in the process. By proceeding through the salivary glands it increases salivation, causing foaming at the mouth. This helps the virus spread through saliva. The most common form is the encephalitic or “furious” form of rabies in which agitation and aggression is heightened.
How it works:
Enters the body and proceeds to the brain, replacing nerve cells in the process. By proceeding through the salivary glands it increases salivation, causing foaming at the mouth. This helps the virus spread through saliva. The most common form is the encephalitic or “furious” form of rabies in which agitation and aggression is heightened.
"It
destroys the brain, it's a really, really bad disease," Muhlberger said.
"We have a vaccine against rabies, and we have antibodies that work
against rabies, so if someone gets bitten by a rabid animal we can treat this person,"
she said.
However, she
said, "if you don't get treatment, there's a 100% possibility you will
die."
HIV
Invades
important immune system cells and kills them.
Leaves patient open to death by other illnesses with lowered immune function.
Leaves patient open to death by other illnesses with lowered immune function.
In the modern
world, the deadliest virus of all may be HIV. "It is still the one that is
the biggest killer," said Dr. AmeshAdalja, an infectious disease physician
and spokesman for the Infectious Disease Society of America.
An estimated 32
million people have died from HIV since the disease was first recognized in the
early 1980s. "The infectious disease that takes the biggest toll on
mankind right now is HIV," Adalja said.
Powerful
antiviral drugs have made it possible for people to live 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 25 adults within the WHO African region is HIV-positive, accounting for
more than two-thirds of the people living with HIV worldwide.
Smallpox
In
1980, the World Health Assembly declared the world free of smallpox. But before that, humans battled
smallpox for thousands of years, and the disease killed about 1 in 3 of those
it infected. It left survivors with deep, permanent scars and, often,
blindness.
Mortality rates
were far higher in populations outside of Europe, where people had little
contact with the virus before visitors brought it to their regions. For
example, 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.
"It was
something that had a huge burden on the planet, not just death but also
blindness, and that's what spurred the campaign to eradicate from the
Earth," Adalja said.
Yellow
Fever:The reemerging killer
Yearly Mortality: 30,000 deaths
How it works:
An acute hemorrhagic disease sometimes causing jaundice and living damage.
Yearly Mortality: 30,000 deaths
How it works:
An acute hemorrhagic disease sometimes causing jaundice and living damage.
Hantavirus
Spread through
rodent bites, droppings, or aerosolized rodent fecal matter. Can cause
hemorrhaging and death.
Hantavirus
pulmonary syndrome (HPS) first gained wide attention in the U.S. in 1993, when
a healthy, young Navajo man and his fiancée living in the Four Corners area of
the United States died within days of developing shortness of breath. A few
months later, health authorities isolated hantavirus from a deer mouse living
in the home of one of the infected people. More than 600 people in the U.S.
have now contracted HPS, and 36% have died from the disease, according to the
Centers for Disease Control and Prevention.
The
virus is not transmitted from one person to another, rather, people contract
the disease from exposure to the droppings
of infected mice.
Previously, a
different hantavirus caused an outbreak in the early 1950s, during the Korean
War, according to a 2010 paper in the journal Clinical Microbiology Reviews.
More than 3,000 troops became infected, and about 12% of them died.
While the virus
was new to Western medicine when it was discovered in the U.S., researchers
realized later that Navajo medical traditions describe a similar illness, and
linked the disease to mice.
Influenza
During
a typical flu season, up to 500,000 people worldwide will die from
the illness,
according to WHO. But occasionally, when a new flu strain emerges, a pandemic
results with a faster spread of disease and, often, higher mortality rates.
The most deadly
flu pandemic, sometimes called the Spanish flu, began in 1918 and sickened up
to 40% of the world's population, killing an estimated 50 million people.
In
the United States, at least 22 million people have gotten the flu in the
2019-2020 season so far and 12,000 have died from it—including at least 78
children—according to the most recent
report from the CDC.
While
there’s no treatment or yearly vaccine for COVID-19 like there is for the flu,
COVID-19 has warranted a high level of caution and extensive containment
procedures. If seasonal flu were given as much regard, fewer people would
likely die from it, experts say.
Dengue
Dengue
virus first appeared in the 1950s in the Philippines and Thailand, and has
since 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, and the disease — with the
mosquitoes that carry it — is likely to spread farther as the world warms.
Dengue sickens 50
to 100 million people a year, according to WHO. Although the mortality rate for
dengue fever is lower than some other viruses, at 2.5%, the virus can cause an
Ebola-like disease called dengue hemorrhagic fever, and that condition has a
mortality rate of 20% if left untreated. "We really need to think more
about dengue virus because it is a real threat to us," Muhlberger
said.
Rotavirus
Two vaccines are
now available to protect children from rotavirus, the leading cause of severe
diarrheal illness among babies and young children. The virus can spread
rapidly, through what researchers call the fecal-oral route (meaning that small
particles of feces end up being consumed).
The WHO estimates
that worldwide, 453,000 children younger than age 5 died from rotavirus
infection in 2008. But countries that have introduced the vaccine have reported
sharp declines in rotavirus hospitalizations and deaths.
SARS-CoV
The
virus that causes severe acute respiratory syndrome, or SARS, first appeared in
2002 in the Guangdong province of southern China, according to the WHO. The virus likely emerged in bats, initially,
then hopped into nocturnal mammals called civets before finally infecting
humans. After triggering an outbreak in China, SARS spread to 26 countries
around the world, infecting more than 8000 people and killing more than 770
over the course of two years.
The
disease causes fever, chills and body aches, and often progresses to pneumonia,
a severe condition in which the lungs become inflamed and fill with pus. SARS
has an estimated mortality rate of 9.6%, and as of yet, has 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
SARS-CoV-2 belongs to the same large family
of viruses as SARS-CoV, known as coronaviruses, and was first identified in December
2019 in the Chinese city of Wuhan. The virus likely originated in bats, like
SARS-CoV, and passed through an intermediate animal before infecting
people.
Since its
appearance, the virus has infected tens of thousands of people in China and
thousands of others worldwide. The ongoing outbreak prompted an extensive
quarantine of Wuhan and nearby cities, restrictions on travel to and from
affected countries and a worldwide effort to develop diagnostics, treatments
and vaccines.
The disease
caused by SARS-CoV-2, called COVID-19, has an estimated mortality rate of about
2.3%. People who are older or have underlying health conditions seem to be most
at risk of having severe disease or complications. Common symptoms include
fever, dry cough and shortness of breath, and the disease can progress to
pneumonia in severe cases.
MERS-CoV
MERS
often progresses to severe pneumonia and has an estimated mortality rate
between 30% and 40%, making it the most lethal of the known coronaviruses that
jumped from animals to people. As with SARS-CoV and SARS-CoV-2, MERS has no
approved treatments or vaccine.
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