Top 10 Deadliest Viruses In The World

It seems like a new virus that's trying to kill us pops up somewhere in the world every other day. While the World Health Organization, the Centers for Disease Control and Prevention, and other health organizations monitor the new coronavirus, officials continue to announce the rapid spread of new COVID-19 infections and deaths around the world.

Despite modern sanitary practices, prevention strategies, and vaccines, there is much to fear from tiny imperialistic pathogens—invisible to all but the most powerful microscopes—that invades our cells to replicate, messing them up like a coke-fueled rock band destroys a hotel room after a concert.

All the hand sanitizer, face masks, and toilet paper in the world can’t save us from some of history’s nastiest viruses and the horrifying diseases they cause in humans.

Here are the 10 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

Marburg virus is a hemorrhagic fever virus of the Filoviridae family of viruses and a member of the species Marburg marburgvirus, genus Marburgvirus.

Marburg virus (MARV) causes Marburg virus disease in humans and nonhuman primates, a form of viral hemorrhagic fever. The virus is considered to be extremely dangerous. The World Health Organization (WHO) rates it as a Risk Group 4 Pathogen (requiring biosafety level 4-equivalent containment). 

In the United States, the NIH/National Institute of Allergy and Infectious Diseases ranks it as a Category A Priority Pathogen and the Centers for Disease Control and Prevention lists it as a Category A Bioterrorism Agent. It is also listed as a biological agent for export control by the Australia Group. 

The virus can be transmitted by exposure to one species of fruit bats or it can be transmitted between people via body fluids through unprotected sex and broken skin. The disease can cause bleeding (hemorrhage), fever, and other symptoms similar to Ebola. However, Marburg virus is not the same as Ebola, although similar.

Actual treatment of the virus after infection is not possible but early, professional treatment of symptoms like dehydration considerably increases survival chances.

 

 

Ebola Virus

Zaire ebolavirus, more commonly known as Ebola virus, is one of six known species within the genus Ebolavirus. Four of the six known ebolaviruses, including EBOV, cause a severe and often fatal hemorrhagic fever  in humans and other mammals, known as Ebola virus disease (EVD).

Ebola virus has caused the majority of human deaths from EVD, and was the cause of the 2013–2016 epidemic in western Africa, which resulted in at least 28,646 suspected cases and 11,323 confirmed deaths.

Ebola virus and its genus were both originally named for Zaire (now the Democratic Republic of the Congo), the country where it was first described, and was at first suspected to be a new "strain" of the closely related Marburg virus. The virus was renamed "Ebola virus" in 2010 to avoid confusion.

The members of the species are called Zaire ebolaviruses. The natural reservoir of Ebola virus is believed to be bats, particularly fruit bats, and it is primarily transmitted between humans and from animals to humans through body fluids. Because of its high fatality rate (up to 83 to 90 percent), EBOV is also listed as a select agent, World Health Organization Risk Group 4 Pathogen. 

 

Rabies Virus 

Rabies lyssavirus, formerly Rabies virus, is a neurotropic virus that causes rabies in humans and animals. Rabies transmission can occur through the saliva of animals and less commonly through contact with human saliva. 

Rabies lyssavirus, like many rhabdoviruses, has an extremely wide host range. In the wild it has been found infecting many mammalian species, while in the laboratory it has been found that birds can be infected, as well as cell cultures from mammals, birds, reptiles and insects.

In September 1931, Joseph Lennox Pawan of Trinidad found Negri bodies in the brain of a bat with unusual habits. In 1932, Pawan first discovered that infected vampire bats could transmit rabies to humans and other animals.

 

HIV

The Human immunodeficiency viruses (HIV) are two species of Lentivirus (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive.

Without treatment, average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.

In most cases, HIV is a sexually transmitted infection and occurs by contact with or transfer of blood, pre-ejaculate, semen, and vaginal fluids. Research has shown (for both same-sex and opposite-sex couples) that HIV is untransmittable through condomless sexual intercourse if the HIV-positive partner has a consistently undetectable viral load. 

Non-sexual transmission can occur from an infected mother to her infant during pregnancy, during childbirth by exposure to her blood or vaginal fluid, and through breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells.

  

Hantavirus 

Hantaviruses are a family of viruses spread mainly by rodents and can cause varied disease syndromes in people worldwide.  Infection with any hantavirus can produce hantavirus disease in people.

Hantaviruses in the Americas are known as “New World” hantaviruses and may cause hantavirus pulmonary syndrome (HPS). Other hantaviruses, known as “Old World” hantaviruses, are found mostly in Europe and Asia and may cause hemorrhagic fever with renal syndrome (HFRS).

Each hantavirus serotype has a specific rodent host species and is spread to people via aerosolized virus that is shed in urine, feces, and saliva, and less frequently by a bite from an infected host.

The most important hantavirus in the United States that can cause HPS is the Sin Nombre virus, spread by the deer mouse.

 

Influenza

Influenza viruses are members of the family Orthomyxoviridae. This family represents enveloped viruses the genome of which consists of segmented negative-sense single-strand RNA segments. There are four genera of this family: types A, B, C and Thogotovirus, of which, however, only genera A and B are clinically relevant for humans.

Influenza viruses are assumed to be transmitted predominantly by aerosol infection, i.e. relatively large droplets (>5 μm) created particularly while talking, coughing, or sneezing, thus entering the mucosae through contact at small distances. Individual publications, however, have also suggested that transmission might occur by so called droplet cores which are smaller (<5 μm) and able to remain in the air for longer periods (aerogenic transmission).

In addition, transmission can occur by direct contact with virus-contaminated surfaces (e.g. shaking hands) and subsequent mouth-nose contact.

After infection the viruses replicate in the nasal and laryngeal mucosae. This replication also affects the lower airways as the infection progresses.

Human influenza virus infections have a world-wide distribution. Seasonal influenza epidemics occur regularly both in the Northern and the Southern hemispheres each winter.

Due to the seasonal shift, the winter influenza outbreak of the Southern hemisphere occurs during the summer of the Northern hemisphere. These influenza epidemics are estimated to cause approximately 500,000 deaths per year world-wide.

 

Dengue Virus

Dengue virus (DENV) is the cause of dengue fever. It is a mosquito-borne, single positive-stranded RNA virus of the family Flaviviridae; genus Flavivirus.  Five serotypes of the virus have been found, all of which can cause the full spectrum of disease. 

Nevertheless, scientists' understanding of dengue virus may be simplistic, as rather than distinct antigenic groups, a continuum appears to exist. This same study identified 47 strains of dengue virus. Additionally, coinfection with and lack of rapid tests for zika virus and chikungunya complicate matters in real-world infections.

Dengue virus has increased dramatically within the last 20 years, becoming one of the worst mosquito-borne human pathogens with which tropical countries have to deal.

Current estimates indicate that as many as 390 million infections occur each year, and many dengue infections are increasingly understood to be asymptomatic or subclinical.

 

Rotavirus

Rotavirus is a part of the Reoviridae family of viruses that commonly cause stomach and respiratory illness.Rotaviruses are the most common cause of severe diarrhoeal disease in young children throughout the world.

According to WHO estimates in 2013 about 215 000 children aged under 5 years die each year from vaccine-preventable rotavirus infections; the vast majority of these children live in low-income countries.

Rotavirus is highly contagious. It spreads through direct or indirect contact with an infected person’s feces (poop). It can happen if you touch a contaminated object, food, water, or the hands or mouth of an infected person. The virus enters your body when your unclean hand touches your nose or mouth.

Symptoms include watery diarrhea, vomiting, fever, and stomach pain. If your child has rotavirus, they also may be weak and cry more than normal. Dehydration (not getting enough fluids) is a symptom in more severe cases.

 

SARS-CoV

SARS corona virus, also known as SARS-CoV, is a virus which can cause severe acute respiratory syndrome (SARS). SARS coronavirus belongs to a family of enveloped corona viruses. Corona viruses are enveloped, single-stranded, positive-sense RNA viruses which belong to the subfamily Coronavirinae.

There are seven human corona viruses: HCoV-229E, HCoV-OC43, HCoV-229E, HCoV-OC43, SARS-CoV, HCoV-NL63 and HCoV-HKU1, other novel human corona viruses have also been discovered in recent years.

SARS-CoV is mainly transmitted among humans by the deposition of infected droplets or aerosols on the respiratory epithelium. In addition, transmission is infrequent during the first 5 days of illness, partly because of the low viral load in respiratory secretions during that phase.

There is no confirmed treatment that works for every person who has SARS. Antiviral medications and steroids are sometimes given to reduce lung swelling, but aren’t effective for everyone.

Supplemental oxygen or a ventilator may be prescribed if necessary. In severe cases, blood plasma from someone who has already recovered from SARS may also be administered. However, there is not yet enough evidence to prove that these treatments are effective.

 

Smallpox

Smallpox is an extremely contagious and deadly virus for which there is no known cure. The last known case occurred in the United States in 1949 and due to worldwide vaccination programs, this disease has been completely eradicated. Smallpox is also known as variola.

Since the time of ancient Egypt, smallpox has proven to be one of the most devastating diseases to humankind. Widespread smallpox epidemics and huge death tolls fill the pages of our history books.

Smallpox spreads from person to person by respiratory droplets or direct contact with body fluids. Contaminated clothing or bedding may also transmit the virus. Animals and insects are not known to carry or spread the virus to humans. The incubation period for smallpox is 7 to 17 days.