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The 10 Deadliest and Most Dangerous Viruses in the World

Larry Slawson received his Master's Degree from UNC Charlotte in 2018. He has a keen interest in biology, chemistry, and astronomy.

From Smallpox to Rabies, this article ranks the 10 deadliest and most dangerous viruses currently known to exist in the world.

From Smallpox to Rabies, this article ranks the 10 deadliest and most dangerous viruses currently known to exist in the world.

The 10 Deadliest and Most Dangerous Viruses in the World

  • Lassa virus
  • Rotavirus
  • Rabies
  • HIV (Human Immunodeficiency Virus)
  • Smallpox
  • Hantavirus
  • Influenza
  • Dengue virus
  • Ebola
  • Marburg virus

Understanding Deadly Viruses

Throughout the world there exists numerous viruses and diseases capable of inflicting serious harm (or death) on the human population at large. While treatment plans exist for a wide array of diseases, viruses offer a unique challenge to doctors and researchers as antibiotics and traditional medicines are often ineffective against their attacks on the human body.

This article explores the 10 deadliest and most dangerous viruses known to currently exist in the world today. After reading this work, it is the author’s hope that a better, more-developed understanding of viruses can be attained by his readers.

Selection Criteria

In order to select the viruses contained in this work, the author relies on several criteria for establishing the deadliest (and most dangerous) species of virus. Severity of symptoms, prognosis, and overall death rates (following the onset of sickness) are all taken into consideration, along with available treatment options (or lack thereof).

Long-term injuries, complications and death from these viruses in the absence of medical treatment are also considered for the purposes of this study. While imperfect, the author believes that this criterion offers the best means available for understanding the deadliest and most dangerous viruses of the world.

The infamous Lassa virus

The infamous Lassa virus

10. Lassa Virus

Common Name: Lassa virus

Realm: Riboviria

Phylum: Negarnaviricota

Class: Ellioviricetes

Order: Bunyavirales

Family: Arenaviridae

Genus: Mammarenavirus

Species: Lassa mammarenavirus

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Synonyms: Lassa virus


The Lassa virus, also known as “Lassa fever” or “Lassa hemorrhagic fever (LHF)” is a viral infection known to infect both humans and primates. Endemic to Western Africa, particularly the countries of Sierra Leone, Nigeria, and Liberia, it is estimated that approximately 300,000 to 500,000 new cases of the virus develop each year.

The virus alone is responsible for nearly 5,000 deaths per year. Currently there are no approved vaccines for the Lassa virus, as further investigation of the disease is needed.

The Lassa virus was first discovered in 1969 after a missionary nurse by the name of Laura Wine contracted a mysterious ailment during her visit to a village in Nigeria. She later died along with her nurse, Lily Pinneo, who had cared for Wine throughout the duration of the illness.

After samples of the mysterious virus were sent to Yale University, researchers later discovered that the virus originated with common African rats, which shed the virus through their urine and fecal matter. Humans are susceptible to the virus when they come into contact with areas contaminated by the rat’s urine and feces.

Lassa Virus Symptoms and Treatment

Because of its ability to rapidly replicate, the virus is extremely deadly to humans, causing hemorrhagic fever, deafness, weakness, fatigue, sore throat, coughing, headaches, and gastrointestinal illness in as little as a week after exposure. Bleeding in the eyes, gums, and nose, along with respiratory issues and neurological problems are also common.

Upon its entry into the body, the Lassa virus infects nearly every tissue of the human body, before it progresses to the body’s vascular system. Nearly 20 percent of individuals infected with the Lassa virus die after exposure, primarily from multi-organ failure attributed to the disease.

The highly contagious Rotavirus.

The highly contagious Rotavirus.

9. Rotavirus

Common Name: Rotavirus

Realm: Riboviria

Family: Reoviridae

Subfamily: Sedoreovirinae

Genus: Rotavirus

Species: Rotavirus A; Rotavirus B; Rotavirus C; Rotavirus D; Rotavirus E; Rotavirus F; Rotavirus G; Rotavirus H; Rotavirus I


The Rotavirus is a double-stranded RNA virus from the family Reoviridae. The virus is the most common cause of diarrheal illness in infants and children in the world. Nearly every child under the age of five is believed to be infected by the virus at some point in their life due to its prevalence and widespread distribution (with adults rarely being affected).

Rotavirus is also capable of infecting livestock animals. Commonly referred to as the “stomach flu,” the virus is known to damage the lining of the small intestine, resulting in gastroenteritis. Despite the availability of treatments, nearly 215,000 children worldwide die each year from the virus, particularly in third world countries, where proper medical treatment is not available.

Vaccinations have become available in more recent years to combat the effects of the virus, with promising results.

Rotavirus Symptoms and Treatment

There are nine different species of the Rotavirus, with humans being affected primarily by Rotavirus A. Because the virus is transmitted via fecal-oral route, poor hygiene and lack of sanitation procedures are often the primary transmitter of the disease. Initial symptoms of the virus begin approximately two days after exposure, and include nausea, fever, vomiting, and extreme diarrhea.

Because diarrhea often lasts four to eight days, dehydration is a major concern for those infected (and is the most common cause of death for those infected with the virus). Diagnosis is done by testing stool samples, whereas treatment primarily involves the management of symptoms along with a focus on maintaining adequate hydration levels (since antibiotics are ineffective against viral illnesses).

Microscopic image of the deadly Rabies Virus.

Microscopic image of the deadly Rabies Virus.

8. Rabies Virus

Common Name: Rabies

Realm: Riboviria

Phylum: Negarnaviricota

Class: Monjiviricetes

Order: Mononegavirales

Family: Rhabdoviridae

Genus: Lyssavirus

Species: Rabies lyssavirus

Synonyms: Rabies Virus


The Rabies virus is a neurotropic virus from the Rhabdoviridae family. The virus is extremely deadly, and is known to infect birds and all warm-blooded animals, including humans. Common hosts for the virus include infected bats, monkeys, foxes, skunks, wolves, coyotes, dogs, and cats. The virus is primarily found in the nerves and saliva of infected animals, and is usually transmitted via bites.

In human infections (following a bite from a rabid animal), the virus enters the peripheral nervous system, affecting the host’s central nervous system, and eventually the brain (causing encephalitis, or swelling of the brain).

Because the virus remains asymptomatic for approximately one to three months (sometimes as much as a year), diagnosis is difficult. This is problematic because once symptoms begin, treatment is ineffective (with a mortality rate of 99 percent). Nearly 17,400 people die worldwide from Rabies each year, with the majority of these cases involving bites from rabid dogs.

Rabies' Symptoms and Treatment

Once symptoms of Rabies begin (approximately one to three months after infection), common symptoms include fever and headache in its initial stages. Once the virus progresses to the brain, however, inflammation of the spine and brain, along with paralysis, severe anxiety, sleeplessness, confusion, agitation, paranoia, hallucinations, and terror are common.

Death usually occurs within two to ten days after symptoms appear, with the final stages of the virus being delirium, hydrophobia (fear of water) and coma. Until 1885, nearly all cases of rabies were fatal to humans. Following the vaccination developed by Louis Pasteur and Emile Roux, however, fatality rates have declined significantly (assuming proper medical care is sought out immediately).

For individuals exposed to rabies, rapid treatment is needed (within ten days), and includes a fourteen-day series of vaccinations known as HRIG (Human Rabies Immunoglobulin). These vaccinations are highly effective, with a 100 percent cure rate when administered promptly.

Pictured above is HIV (green) attacking healthy cells in the human body.

Pictured above is HIV (green) attacking healthy cells in the human body.

7. HIV (Human Immunodeficiency Virus)

Common Name: HIV (human immunodeficiency virus)

Phylum: Incertae sedis

Class: Incertae sedis

Order: Ortervirales

Family: Retroviridae

Subfamily: Orthoretrovirinae

Genus: Lentivirus


The human immunodeficiency virus (HIV) is a species of virus from the Retroviridae family that affects the immune system of infected individuals. HIV is believed to have originated from chimpanzees living within Central Africa, and may have been present on the continent as far back as the 1800s. The virus has existed in the United States since the 1970s.

There is currently no cure for the virus; however, effective treatments have been established to control the disease known as ART (antiretroviral therapy).

Each year, there are approximately 1.8 million new cases of HIV worldwide. The virus, which eventually progresses to AIDS (if left untreated), is responsible for an estimated 940,000 deaths per year, with the largest number of deaths occurring in Sub-Saharan Africa (66 percent of all cases).

HIV is a life-threatening virus, and is spread via bodily fluids. Upon entering the human body, the virus attack’s the body’s immune system, destroying CD4 cells (also known as T-Cells). The virus progresses through three different stages that include: Acute HIV infection (Stage 1), Clinical Latency (Stage 2), and finally, Acquired Immunodeficiency Syndrome [AIDS] (Stage 3).

As more and more cells in the immune system are attacked (and destroyed) by the virus, the body’s response to infections and other diseases becomes strained. At the final stage (AIDS), the immune system is compromised to a point where even a common cold can become a life-threatening ordeal.

HIV Symptoms and Treatment

Diagnosing HIV is difficult as the disease often shows no signs or symptoms in its early stages. Occasionally, people experience flu-like symptoms during the first two to four weeks of infection, including fever, chills, rash, muscle aches, sore throat, fatigue, mouth ulcers, and swollen lymph nodes. Routine blood-tests should be conducted if an individual believes they were exposed.

The infamous (and deadly) Smallpox Virus.

The infamous (and deadly) Smallpox Virus.

6. Smallpox

Common Name: Smallpox (Variola virus)

Family: Poxviridae

Subfamily: Chordopoxvirinae

Genus: Orthopoxvirus

Synonyms: Variola Virus; Variola Minor; Variola Major


Smallpox is an ancient virus (caused by the variola virus) believed to have originated in Egypt during the third century BC. The last known case of smallpox occurred in October 1977, with the World Health Organization (WHO) claiming a complete eradication of the disease in 1980 (globally).

Over the centuries, smallpox has often occurred in outbreaks, with a fatality rate of approximately 30 percent. During the 18th century alone, Europe experienced nearly 400,000 deaths per year from the disease. During the virus’s final 100 years of existence, the disease is believed to have killed 500 million people worldwide.

Smallpox Symptoms and Treatment

Before the eradication of the smallpox virus, scientists believe that the disease spread following face-to-face contact with other humans (via coughing or sneezing). Initial symptoms often wouldn’t appear until seven to nineteen days later, and included high fevers, headaches, muscle aches, and vomiting.

After about the fourth day, a rash containing small red spots began to appear on both the mouth and tongue of individuals infected with the virus. These spots later turned into sores that would break open and spread along the arms, legs, hands, and feet of the victim’s body.

After 24 hours, these sores would then fill up with a thick fluid making the bumps round and solid to the touch. After about 10 days, the sores begin to scab over, falling off within a week (often leaving lifelong scars on the skin).

Although smallpox has been eradicated worldwide, the potential for an outbreak remains. Bioterrorist attacks, where viruses and bacteria are intentionally released by terrorist groups or countries, remains an ever-present (though unlikely) threat during the modern age. For this reason, vaccinations and antiviral drugs have been safely stockpiled in the event of a bioterrorist attack in the future.

The deadly Hantavirus.

The deadly Hantavirus.

5. Hantavirus

Common Name: Hantavirus

Realm: Riboviria

Phylum: Negarnaviricota

Class: Ellioviricetes

Order: Bunyavirales

Family: Hantaviridae

Subfamily: Mammantavirinae

Genus: Orthohantavirus


Hantaviruses are an incredibly dangerous disease from the Hantaviridae family. The viruses, which are found predominantly in Europe and Asia, are believed to be spread through various rodents (via saliva, feces, and urine).

Some strains of the virus are known to cause HFRS (Hantavirus Hemorrhagic Fever with Renal Syndrome), as well as HPS (Hantavirus Pulmonary Syndrome) which both have high fatality rates of 36 to 38 percent, respectively.

First observed in South Korea during the 1950s (and named after South Korea’s Hantan River), the Hantavirus is a relatively new form of virus with cases occurring worldwide (including the United States). Due to the small number of cases that have occurred, however, little is known about its overall impact on humans.

Hantavirus Symptoms and Treatment

Incubation time for the Hantavirus is believed to be approximately one to eight weeks, with symptoms occurring at any time during this span. Early symptoms include fatigue, muscle pain, fever, headaches, abdominal problems (including nausea, diarrhea, and vomiting), as well as dizziness, and chills.

In cases where the virus results in HPS, extreme coughing, chest pain, shortness of breath, and chest tightness begin to occur after ten days as the lungs begin to fill with fluid.

In cases of HFRS, similar symptoms occur that eventually progress to low blood pressure, shock, internal bleeding, and acute renal failure. No specific treatments for the Hantavirus group have been developed. Intense medical care focusing on hydration, oxygen therapy, as well as dialysis (to aid patients undergoing acute renal failure from HFRS) are the main source of care.

Controlling mice and rodent populations appears to be the number one source of prevention for this family of diseases.

Influenza (also known as the "Flu") under a microscope.

Influenza (also known as the "Flu") under a microscope.

4. Influenza

Common Name: Influenza

Realm: Riboviria

Phylum: Negarnaviricota

Class: Insthoviricetes

Order: Articulavirales

Family: Orthomyxoviridae

Genus: Betainfluenzavirus


Influenza (commonly known as the “flu”) is a deadly respiratory virus from the Orthomyxoviridae family. There are four different strains of the virus that have been identified by researchers (Including Type A, Type B, Type C, and Type D). Of these, only Type A, B, and C are known to actively affect humans.

Influenza has been around for centuries, with documents from even Hippocrates’ era (approximately 2,400 years ago) describing various pandemics during ancient times. Influenza is extremely contagious, and is believed to spread via coughing and sneezing, or through touching contaminated surfaces.

Nearly three to five million cases of the flu are diagnosed worldwide, with an estimated 375,000 deaths per year.

Influenza Symptoms and Treatment

Symptoms usually progress rapidly after exposure to the virus (beginning less than two days after infection), and include fever, runny nose, sore throat, muscle aches and pains, headaches coughing, sneezing, fatigue, vomiting, diarrhea, and abdominal pain.

In severe cases, the flu is capable of developing viral pneumonia, as well as secondary bacterial pneumonia (particularly in cases involving the young and elderly). Although flu vaccines have been shown to reduce the spread of the virus, doctors are limited in their ability to treat the illness, with the primary treatment involving management of symptoms.

Influenza can be extremely deadly for the elderly, young, and individuals with compromised immune systems. During pandemics, influenza has been known to devastate entire populations of people. During the 1918 flu epidemic, alone, nearly 500 million people were infected with the virus worldwide, and claimed an estimated 50 million lives.

To this day, influenza remains a constant threat each year that should not be ignored.

Influenza Quote

"Influenza pandemics must be taken seriously, precisely because of their capacity to spread rapidly to every country in the world."

— Margaret Chan

The dangerous Dengue Virus.

The dangerous Dengue Virus.

3. Dengue Virus

Common Name: Dengue Virus

Realm: Riboviria

Family: Flaviviridae

Genus: Flavivirus

Species: Dengue virus


The Dengue virus is an extremely deadly virus from the Flaviviridae family, and is responsible for an astounding 390 million infections each year, worldwide. The virus, which contains five different strands, is believed to be spread via mosquitoes, and is found predominantly in Asia and Africa due to the warm, tropical climates in these regions.

The most deadly effect of the Dengue virus is the development of “Dengue fever.” This disease occurs primarily during the rainy season, and is transmitted to humans through the bite of an infected mosquito (female).

Dengue Virus Symptoms

After being exposed to the virus, symptoms usually begin three to fourteen days later and include severe headaches, muscle and bone pain, rashes, and bleeding of the gums.

In more serious manifestations of the disease, which include the development of Dengue Hemorrhagic Fever, infected individuals are prone to shock, extreme bleeding, blood plasma leaking, as well as extremely low blood pressure. Occasionally, the disease also affects the brain, liver, and heart, resulting in organ failure or inflammation of the brain.

Dengue Virus Treatment and Prognosis

Diagnosis of the disease is often difficult to establish in its early stages, as the virus mimics many other viral infections. Moreover, treatment for the disease is non-specific, and often involves management of symptoms (i.e. maintaining proper fluid levels).

Although the fatality rate of Dengue fever is relatively low (at 1 to 5 % annually), approximately 25,000 people die from Dengue-based infections each year. Vaccinations and the maintenance of mosquito populations (combined with efforts to reduce mosquito bites) appears to be the best course of action in reducing the spread of the Dengue Virus.

For countries in Southeast Asia, however, such procedures will be difficult to implement in the years that follow due to the duration of the region’s rainy season.

The highly-infectious (and deadly) Ebola Virus.

The highly-infectious (and deadly) Ebola Virus.

2. Ebola

Common Name: Ebola

Realm: Riboviria

Phylum: Negarnaviricota

Class: Monjiviricetes

Order: Mononegavirales

Family: Filoviridae

Genus: Ebolavirus


The Ebola virus, also known as the “Ebola hemmorhagic fever,” is an extremely deadly virus found predominantly in Africa. First identified in 1976 during an outbreak in Congo and Sudan, the virus is believed to have originated with primates, and is transmitted via direct contact with bodily fluids (including saliva, mucus, vomit, feces, urine, breast milk, sweat, and tears).

There are currently four strains of the Ebola Virus, with the EBOV (Zaire ebolavirus) being the most dangerous to humans. Depending on the strain of Ebola, the virus carries an extremely high fatality rate that ranges from twenty-five to ninety percent.

As a relatively new strain, little is known or understood about the disease. As a result, treatment options are limited, with supportive care being the primary course of action for infected individuals.

Rapid detection and control of outbreaks has become a matter of national emergency in regions susceptible to viral outbreaks, and have proven effective in controlling the spread of Ebola strains.

Between 1976 and 2013, approximately 24 outbreaks have been reported to the World Health Organization (WHO) involving nearly 2,387 cases in West Africa. Of these cases, 1,590 individuals died. The largest outbreak in West Africa, occurring between 2013 and 2016 and involving 28,646 cases of Ebola, resulted in the death of 11,323 individuals.

Although vaccinations are currently in development to curtail the spread of Ebola during future outbreaks, there is still much to be learned about the virus before positive outcomes can be implemented with effect.

Ebola Symptoms and Treatment

Following exposure to the Ebola Virus, incubation takes approximately two to twenty-one days before the onset of symptoms first occurs. Initial symptoms involve a sudden flu-like stage that is characterized by extreme fatigue, high fever, muscle weakness and pain, sore throat, and decreased appetite.

As the virus spreads, nausea, vomiting, abdominal pain (and cramps), as well as diarrhea are also common, leading to severe dehydration in many cases.

Severe rashes, respiratory problems, and chest pain are also likely to develop within five to seven days, followed by the onset of internal and external bleeding. Bloody stools, coughing up blood, and vomiting blood usually result from the virus decreasing the blood’s natural ability to clot.

In severe cases, individuals often enter a coma in the final stages of the disease, followed by low blood pressure that often results in death.

In individuals that survive Ebola, lifelong complications are common, including liver inflammation, deafness, chronic fatigue, poor vision, and decreased appetite.

Microscopic image of the Marburg Virus; the deadliest and most dangerous virus in the world.

Microscopic image of the Marburg Virus; the deadliest and most dangerous virus in the world.

1. Marburg Virus

Common Name: Marburg virus

Realm: Riboviria

Phylum: Negarnaviricota

Class: Monjiviricetes

Order: Mononegavirales

Family: Filoviridae

Genus: Marburgvirus

Species: Marburg Marburgvirus


The Marburg virus is an extremely deadly disease from the Filoviridae family, and is considered the most dangerous virus in the world. The World Health Organization (WHO) currently rates it as a "Risk Group 4 Pathogen" (which requires biosafety Level-4 containment protocols), while the Centers for Disease Control and Prevention (CDC) lists the virus as a "Category A Bioterrorism Agent."

First discovered in 1967, the virus made noticeable outbreaks in the German cities of Marburg and Frankfurt, as well as Yugoslavia’s capital city of Belgrade. After German workers were exposed to infected Grivet Monkeys, seven of the thirty-one people infected by the virus died shortly after.

Although the virus has only had a handful of outbreaks over the last 50 years, mortality rates are incredibly high (an astounding 90 percent). The most recent outbreak involved the 2004-2005 cases in Angola, where approximately 252 individuals were infected by the virus.

Of these, 227 people died from the disease. In addition to primates, it is believed that fruit bats are the primary carriers of the virus. For this reason, individuals exposed to mines or caves for prolonged periods of time are particularly susceptible to the disease.

Marburg Virus Symptoms and Treatment

Although little is known about the virus, it is believed that the Marburg virus spreads between humans via direct contact with broken skin, bodily fluids, or contaminated surfaces (such as bedding or clothing that has been contaminated with blood, urine, or fecal matter). Incubation periods for the virus vary from two to twenty-one days.

Initial symptoms often begin rapidly, and include high fevers, headaches, fatigue, muscle aches, severe diarrhea, abdominal pain (and cramps), as well as nausea and vomiting. By the third day of symptoms, individuals are often characterized as showcasing “ghost-like” features, with sunken eyes, expressionless faces, and severe rashes (non-itchy).

After five to seven days, infected individuals often develop severe bleeding (both internally and externally) from the gums, nose, and genital regions. Severe bleeding near venipuncture sites is also common (due to the inability of the blood to naturally clot).

In the disease’s final stages, impairment of the central nervous system is common, and often results in confusion, aggression, and irritability. By the ninth day, death usually follows.

Marburg Virus Prognosis

Similar to the Ebola virus, supportive care remains the only form of treatment for the Marburg virus as no vaccines or drugs have been developed to combat the disease’s progression. Rapid response and control of outbreak areas remains the best option for controlling the spread of Marburg virus pathogens.

For these reasons (particularly its high death rate and lack of treatment options), the Marburg virus is an incredibly dangerous disease capable of eradicating large populations of people (particularly in the event of a bioterrorist attack).

Suggestions for Further Reading

Preston, Richard. Crisis in the Red Zone: The Story of the Deadliest Ebola Outbreak in History, and of the Outbreaks to Come. New York, New York: Random House, 2019.

Works Cited

Cunha, John P. "Dengue Fever Symptoms, Causes, Contagious, Rash, Prevention & Vaccine." MedicineNet. Accessed August 06, 2019.

"Ebola (Ebola Virus Disease) - CDC." Centers for Disease Control and Prevention. Accessed August 06, 2019.

"HIV." Centers for Disease Control and Prevention. July 23, 2018. Accessed August 06, 2019.

"Influenza (Flu) - CDC." Centers for Disease Control and Prevention. Accessed August 06, 2019.

"Lassa Fever." World Health Organization. March 05, 2019. Accessed August 06, 2019.

"Marburg Virus Disease." World Health Organization. December 11, 2017. Accessed August 06, 2019.

"Rotaviru/Gastroenteritis - CDC." Centers for Disease Control and Prevention. Accessed August 06, 2019.

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2020 Larry Slawson


Larry Slawson (author) from North Carolina on January 08, 2020:

Thank you, Lorna! So glad you enjoyed the article my friend :)

Lorna Lamon on January 08, 2020:

Such an interesting and well structured article Larry. The only one I wasn't familiar with was the 'Marburg Virus'. I love learning something new. Thanks for sharing Larry.

Larry Slawson (author) from North Carolina on January 07, 2020:

I agree 100-percent, Louise! I had heard of most of these as well. Marburg was a new one for me though. Some scary stuff for sure!

Louise Powles from Norfolk, England on January 07, 2020:

Some of them viruses I don't know about, but some I do. There are certainly a lot of deadly viruses out there. We need to be very careful.

Larry Slawson (author) from North Carolina on January 07, 2020:

Thank you so much Pamela :) Glad you enjoyed!

Pamela Oglesby from Sunny Florida on January 07, 2020:

This is an excellent article on the most serious viruses. I was somewhat familiar with most of them, but I still learned a lot from you well-written article.

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