World’s Most Dreaded Viruses on Earth

Medically reviewed By Pat F. Bass III, MD, MPH
World’s Most Dreaded Viruses on Earth...including statistics that will terrify you!



Viruses, in a general sense, are tiny organisms that cause illness in humans, plants, and animals that range from mild rashes to severely destructive conditions depending on the strength of the virus. But by definition, they are unique microscopic organisms made up of genetic material that consists of three parts:

  • Nucleic acid with either DNA or RNA that helps the virus reproduce
  • Protein that covers and protects the nucleic acid and sometimes have an envelope (spiky coating)
  • Lipid fat that surrounds the protein

Although viruses are known as microorganisms, microbiologists typically consider them “non-living” and microscopic infective agents because they need a host body to multiply and survive.

Structure of a virus

Viruses are considered the smallest of all microbes. Since they don’t have their own chemical machinery (commonly known as enzymes), they need a host cell, usually from humans or animals, in order to live, function and replicate.

The viruses attack the host cell and take over its functions. When the host cell is infected, it reproduces viral proteins and genetic material that is different from what the host usually produces. Such reproduction makes them parasitic in nature.

Size of a virus

A virus has no definite form, varying in shape, size and complexity. While they are commonly mistaken for bacteria, viruses are relatively smaller -- one-millionth of an inch and 16 up to 350 nanometers long. They are a thousand times smaller than most bacteria, and even smaller than a human cell. In fact, viruses are so significantly small that they can only be seen through an electron microscope.

Body’s response to viruses

The human immune system is designed to recognize and defend someone from foreign bodies and harmful substances, viruses included. It's made up of different types of white blood cells that are designed to attack viruses as soon as they are detected. With more persistent viruses, white blood cells called T and B lymphocytes rush in to strengthen immune response.

B cells are special proteins that produce antibodies which keep the virus from reproducing. T cells on the other hand either detect the virus or produce antibodies along with the B cells. After their first encounter with a virus, a certain number of B and T cells will remember the virus and will protect the body against any future threats.

Aside from the B and T cells, the immune system also respond in two ways:

  • Innate immunity is the first kind of defense against viruses. It has barriers that prevent harmful substances from entering the body
  • Adaptive immunity is developed from exposure to antigens. It eliminates and prevents the growth of pathogens. Additionally, it remembers the response to a pathogen which is used to create a better response to future encounters with a pathogen of the same kind.

How are Viruses Transmitted?

Viruses are small infectious organisms that cause several well-known human diseases such as hepatitis, polio, HIV-AIDS, smallpox, SARS, measles, etc. Some viruses can be swallowed, inhaled, or transmitted through a bite of a carrier. There are many different ways to come in contact with viruses. Here are some of them:

#1 Mother to child

Viruses can be transmitted from a mother to her child. Every human being comes in contact with viruses, and pregnant women are no exception to that. Viruses can travel through the placenta, birth canal, and may even be present in breast milk.

#2 Person to person contact

Viruses can be spread through airborne transmission and physical contact. Coughing, sneezing, and the exchange of saliva are some of the ways of spreading a virus. A cough or sneeze for example releases millions of particles in the air which spreads breathable viruses.

#3 Sexual or drug contact

Viral transmission can happen when a person’s infected bodily fluid is passed off to another person through sexual intercourse (e.g. saliva or semen) causing everything from herpes, gonorrhea, to HIV-AIDS. Drug users sharing needles and syringes tainted by infected blood are also at high risk of acquiring viruses.

#4 Insects and Pets

Mosquitoes also known to be vessels of viral transmission. Dengue, Malaria, and the Bubonic Plague are some of the most daunting diseases that are caused by mosquito bites. Parasites from an infected mosquito enter the body and infects the bloodstream. Fecal waste from mosquitoes also carries viruses and can be passed on to food (e.g. Salmonella and E.coli).

Pets can also carry viruses like rabies that can be transmitted through saliva or bites from infected animals, such as rodents, dogs, and cats.

#5 Food

Food and water can also be contaminated by viruses. Microbes, like humans, also consume food in order to grow, which puts the food we take at high risk of being contamination. Food poisoning and diarrhea are two of the most common diseases caused by food contamination.

Faulty preparation processes like the use of dirty kitchen utensils and unwashed hands help viruses spread. Moreover, disease-causing microbes also infiltrate sewage and water systems, causing water-borne diseases like cholera and typhoid fever.

Existing Viruses on Earth

The Earth holds an innumerable number of viruses. There are up to 5,000 viruses known to infect humans, animals and plants. According to studies,10,000 new viruses are produced by a virus infected cell, which can go up to a trillion in a few days or weeks time. Although millions of viruses have infected people, there are still a few considered horrifying because of how destructive and fatal they are.

Here is a list of some spine-chilling diseases that will make your skin crawl:

#1 Marburg Virus

The Marburg virus causes severe bleeding or hemorrhage, organ failure, and subsequent death. The first cases of Marburg virus disease were recorded in Germany, Belgrade and Serbia and attributed to a shipment of monkeys from Uganda. The virus is classified under the Filoviridae family, where the Ebola virus is from. Both the Marburg and Ebola viruses are rare, but when an outbreak occurs, they are almost instantly fatal.


The virus is said to live in animal hosts and can be acquired by contact with contaminated needles and syringes or body fluids from an infected person or animal.


A person with Marburg virus will have:

  • Fever
  • Muscle pains
  • Severe headache
  • Malaise

Within 5-7 days, the patient develops:

  • Severe hemorrhagic manifestations
  • Bleeding from several parts of the body, such as the nose, eyes, and gums.
  • Inflammation of intestine, eyelid and membrane, and liver
  • Gastrointestinal hemorrhage
  • Vomiting
  • Dehydration

Although some survive, most of them develop muscle weakness, hepatitis, ocular disease, hearing loss, and psychosis to name a few.

Fatality rate

Extensive hemorrhage in the skin, internal organs, and intestines, as well swelling of the kidneys, brain, and lymph nodes causes death for Marburg disease patients. Recorded fatalities have grown from 25% in 1967 to 80% in 1998-2000 in Congo, and 90% in 2005 in Angola.


Treatment is yet to be discovered for the virus. However, there are therapies that help ease complicating infections, including supplemental oxygen, and maintaining fluids and electrolytes.

#2 Ebola Virus

Ebola is a rare and fatal virus. It originates from animals but has since spread through human to human contact. In the human body, it damages both the immune system and organs and causes fata,l uncontrollable bleeding.

The virus first manifested in Sudan and Congo in 1976 while the first recorded outbreak was recorded in the tropical rainforests of Central Africa. The 2014 outbreak was also deemed catastrophic. It was recorded in both the urban and rural parts of West Africa, spreading out globally soon after. Liberia, Sierra Leone, and Guinea were severely affected, with patients suffering from genuinely ineffective health systems and a lack of resources


Source of the virus is yet to be identified, but it is believed to have originated from wild animals like fruit bats, apes and monkeys.

It can be transmitted through contact with infected objects, blood, organs, bodily fluids, or secretions from infected, ill, or dead animals and infected people. It can also be sexually. In fact, Ebola virus has been found in the semen of some men. People who die from Ebola could continue spreading the disease until cremation or full burial.


Patients initially suffer from:

  • Muscle pain
  • Sore throat
  • Fever
  • Fatigue
  • Headaches
  • Lack of appetite

Followed by:

  • Rashes
  • Internal and external bleeding
  • Impaired kidney and liver
  • Vomiting
  • Diarrhea
  • White blood cell and platelet count suddenly drops.

These symptoms may appear and last around 5-20 days depending on the severity.

Fatality rates

Deaths have risen from 25% to 90% since the 2014 Ebola outbreak in Africa


Ebola virus is comparable to other infectious diseases, making it difficult to identify. A number of tests could identify the virus, namely:

  • Electron Microscopy
  • Serum Neutralization test
  • Antigen-capture Detectio test
  • Virus Isolation by Cell Culture, etc.

Treatments for Ebola virus are still in the works, but common interventions include managing the symptoms through oxygen, blood transfusion, and electrolytes. Immune and drug therapies are usually done on patients. Vaccines are now being tested for circulation.

#3 Smallpox

An acute contagious disease and often considered deadly, Smallpox is one of the most devastating diseases known to mankind. The World Health Organization has however proclaimed complete obliteration of Smallpox in 1980 after a global immunization campaign. In fact, the last case ever recorded was in 1977 in Somalia and 1978 in Birmingham.


Smallpox is a serious disease caused by Variola virus and transmitted through exposure to contaminated air, objects, or people. A person with the disease is the most contagious when rashes start to appear. It was also reported that the disease was used as a biological weapon, which is why military personnel are still given vaccines.


Symptoms only appear after 12-14 days after acquiring the disease, while it takes up to 17 days to fully recover.

Indication of Smallpox are somewhat the same as other serious diseases that last for 2-4 days:

  • Fever
  • Headache
  • Backache
  • Fatigue
  • Vomiting

Subsequently, rashes with red sores will start to appear and can spread within 24 hours. They usually appear on the face, hands, and forearms, eventually turning into small blisters with clear fluid inside. After 8-9 days, scabs will start to form but will eventually fall off and leave pitted scars.

Depending on the severity of the disease, Smallpox can also cause blindness, and eventually, death.

Fatality rate

There is no definite number on the actual victims of the disease but it is speculated that the number of victims is more than the number of the victims of other diseases combined.

Diagnosis and Treatment

The disease can be identified through rashes that appear and blister on the skin, usually crusted over and filled with fluid. Although similar signs manifest with chickenpox, the appearance and form of the blisters are relatively different.

A cure has yet to be discovered but there are medications available to relieve the symptoms. As a matter of fact, vaccines have since been created to fight the disease, preventing most of its signs, and damping the severity of the disease. Although vaccines are readily available, they are rarely given since nobody has been infected by the disease since 1980.


#4 HIV

Human Immunodeficiency Virus, also known as HIV, weakens and destroys a person’s immune system and the important cells which fight diseases and infection. If HIV is untreated, it can escalate to Acquired Immunodeficiency Syndrome, or AIDS. Unlike other viruses, HIV is something that cannot be completely eradicated but can be controlled.

HIV is classified into two types:

  • HIV-1 which is seen worldwide
  • HIV-2 which is more common in Africa, certain parts of India and Europe

HIV started to spread in Africa, eventually gaining recognition when it hit the US in the 1970s. The disease is commonly associated with unregulated sex work, drug use, and certain pockets of the kink and gay community.


HIV is believed to have been from a certain type of chimpanzee found in Central Africa but the disease has since been identified as Simian Immunodeficiency Virus or SIV. It was likely transmitted to people when humans hunted chimpanzees for food and came in contact with infected blood. SIV consequently mutated to HIV.

It known as a sexually transmitted disease but can also be transmitted through injection of syringe and needle for drug users. Certain bodily fluids such as semen, breast milk, rectal and vaginal fluids, are the common hosts for the disease. Bloodletting, transfusions, or blood contact with a carrier is also another way of passing the disease.

The disease is usually passed on through unprotected sexual intercourse.


Indications of HIV are usually felt 2-4 weeks after acquiring the virus but would only feel flu-like symptoms.

  • Fever
  • Sore throat
  • Fatigue
  • Rashes
  • Headaches
  • Swollen glands
  • Muscle pains

These symptoms may last for days, even for weeks. However, having these symptoms won't always point to HIV. Sometimes, HIV-related symptoms remain latent for up to 10 or more years.

If the virus progresses, it develops into AIDS. An HIV-infected person reaches this stage if no prior medical interventions are made. AIDS causes the body’s immune system to slowly deteriorate. The following are its symptoms:

  • Pneumonia
  • Mouth, anus, and genitals feel sore
  • Unexplained fatigue
  • Swelling of lymph glands in neck, armpits, and groin
  • Sudden weight loss
  • Neurological disorders such as depression and memory loss
  • Week long diarrhea
  • Recurring fever
  • Tuberculosis

Fatality rate

Deaths caused by HIV from 1988-1995 went from 78% to 15% from 2005-2010

Treatment and Diagnosis

HIV's symptomatology shares a whole host of symptoms with other viruses, making definitive diagnosis difficult without purposive HIV testing.

Interventions for HIV often include preventive action and seeking proper medical care. Antiretroviral therapy is one of the current treatments available to HIV patients, helping them live longer lives while curbing the spread of the disease.

#5 Hantavirus

Hantavirus Pulmonary Syndrome is a disease that comes from infected rodent urine and droppings. The first case of hantavirus was recorded in 1993 in the US which saw hemorrhagic fever with renal syndrome in patients.

The virus itself isn’t typically contagious but there were cases in South America which saw infection between several individuals.


Hantavirus is from the Bunyaviridae family and is usually found in rural areas, where rodents commonly live. The US and Canada have the greatest number of Hantavirus victims. In the US, cases of Hantavirus were detected in rodents from several national parks, including the famous Yosemite Park. Cases of the disease were also recorded in Argentina, Bolivia, Chile, Uruguay, Panama, and Brazil.

Although rodents are the host of the virus, several animals such as deer mice are considered its reservoirs. Hantavirus can be acquired through airborne transmission, bites from a contaminated rodent, or contact with objects or food contaminated with rodent urine, saliva, or droppings.


Symptoms may develop up to 5 weeks after being exposed to the rodent’s urine, droppings, or saliva, including:

  • Fever
  • Muscle aches, especially thighs, back, hips, shoulders
  • Abdominal pain
  • Headaches
  • Nausea
  • Vomiting
  • Diarrhea

After 4-10 days, the following symptoms may occur:

  • Coughing
  • Shortness of breath
  • Chest pains

If the virus progresses, the following may appear:

  • Acute Respiratory Distress Syndrome
  • Low blood pressure
  • Kidney failure

Fatality rate

Recorded mortality rate has gone up to 38%

Diagnosis and treatment

Hantavirus is hard to diagnose since most of the symptoms are commonly mistaken for influenza. However, if the symptoms were felt after exposure to rodents, followed by shortness of breath, there is a great possibility that the person is infected with the virus.

There is no cure, treatment, or vaccine available for the virus but oxygen therapy in an intensive care unit relieves severe respiratory complications. Medications for kidney-related problems are also a popular option.

#6 Influenza

Commonly known as flu, Influenza is a disease that attacks the respiratory system. Although Influenza goes away on its own, some cases with complications have resulted to death. Children under 5 years old, adults older than 65 years old, pregnant women, and people with weak immune systems and have chronic illnesses are the ones prone to acquiring Influenza.


Influenza is a contagious disease that can be transmitted through person to person contact through coughing, sneezing, or by touching a contaminated object or airborne transmission. The illness can go from mild to severe depending on the age and intensity of the virus.


The following are the symptoms of Influenza:

  • High fever
  • Muscle pains
  • Headaches
  • Malaise
  • Sore throat
  • Rhinitis
  • Persistent non-productive cough

The virus typically infects a human host days before symptoms begin to appear and linger on 5 days after their peak. Some people can be contagious for as long as 10 days after the appearance of symptoms. For children and people with weak immune systems, they can be contagious for a relatively longer time.

Recovery from Influenza can take 1-2 weeks even without medical treatment, but may take longer especially for children, elderly, and those with other medical condition.

Bacterial pneumonia, ear and sinus infection, heart failure and diabetes are some of the complications that can develop from influenza.

Fatality rate

From 1976 to 2006, up to 40,000 influenza-related deaths were recorded.

Treatment and diagnosis

Vaccines for influenza is taken in a yearly basis. They are made available to prevent and cure influenza, and protect the body from three (trivalent) and four (quadrivalent) different flu viruses.

  • Trivalent vaccine is for Influenza A (H1N1 and H3N2) and Influenza B virus
  • Quadrivalent vaccine is for two kinds of Influenza A and B viruses.

Antiviral and antibiotic medications are also given to relieve the symptoms. However, some antiviral medication may cause some unpleasant side effects such as nausea and vomiting but may be lessened by food intake.

#7 Dengue

Dengue, also known as breakbone fever or dandy fever, is generally known as a mosquito-borne disease with up to four different strains. It is a virus that goes for the bloodstream and takes over human cells. With over 400 million people affected by the dengue virus, it is considered one of the most pervasive global diseases in recent memory.

It started to emerge in the 1950s in Latin America, spreading across the globe and raking up to 96 million dengue-related illnesses every year across The Pacific Islands, China, Southeast Asia, India, Mexico, The Caribbean, and Africa.


Dengue comes from Aedes mosquitoes that are infected with the dengue virus. Once it reaches the human body, the virus immediately begins reproducing in the blood stream.

Unlike other diseases, dengue is not contagious and cannot be transmitted through physical contact


Symptoms don't typically occur until 4-6 days after infection, and may last up to 10 days:

  • Mild to high fever
  • Severe headache
  • Muscle and joint pain
  • Rashes
  • Pain behind the eyes
  • Fatigue
  • Low heart rate
  • Low blood pressure
  • Rashes that usually occur on the lower limbs and chest
  • Swelling of lymph nodes

Dengue hemorrhagic fever, characterized as severe dengue, have different symptoms:

  • Fever
  • Difficulty in breathing
  • Abdominal pain
  • Bleeding
  • Persistent vomiting

Sometimes, symptoms can be mistaken for other viral diseases, making it hard to identify since there are shared symptoms with diseases like Smallpox. Blood tests are highly recommended as soon as symptoms manifest.

Fatality rate

Over 50-100 million cases of dengue are recorded every year with mortality rates as high as 50%.

Treatment and diagnosis

Dengue is diagnosed through blood tests since the virus runs along the bloodstream. If the platelets are low, and symptoms occur, the patient is at high risk of dengue.

As for treatment, there is no specific cure or vaccine for dengue but there is medication for the pain and related symptoms. Some medications, like Aspirin, have contraindications that worsen bleeding for example.

#8 Rotavirus

Rotavirus is usually caused by severe diarrhea and usually occurs among infants and children. Children as early as 3 months old can be infected by the virus. It is highly contagious, so a person with rotavirus is usually quarantined up to 2 days. The virus, along with the symptoms, typically goes away after 3-9 days.


The virus usually affects the bowels, causing inflammation of the bowels and stomach known as gastroenteritis. Rotavirus can be transmitted through hand-to-mouth contact or contact with contaminated toys, which makes infants particularly vulnerable. Bad hand washing habits following toilet use and diaper changes account for many cases of infection.


For infants and children, the following are the indications of rotavirus:

  • Fever
  • Vomiting
  • Watery or bloody diarrhea that usually lasts for 3-8 days
  • Abdominal pain
  • Signs of dehydration such as lethargy, sunken eyes, infrequent urination or unresponsiveness

Adults can also acquire the disease but the symptoms are typically muted.

Fatality rate

Rotavirus causes about 500,000 child deaths per year.

Diagnosis and treatment

The virus comes with diarrhea, so it is important for the patient to remain hydrated, either through water intake or through fluid injection.

Vaccines have been made available for the rotavirus since 2006. There are two types of vaccine available for children up to 8 months of age:

  • RotaTeq
  • Rotarix

#9 Herpes Zoster

Herpes Zoster, commonly known as Shingles, is described as a cluster of painful, blister-like rashes. The virus is commonly mistaken for chickenpox and smallpox. According to research, one out of three people will have shingles per year. Shingles typically occurs once. There are cases where it has occurred up to three times, but instances like this are rare.


Shingles are caused by the varicella-zoster virus as a complication of chickenpox. After a person recovers from chickenpox, the virus remains dormant for a certain period of time. Shingles will typically manifest as soon as the virus becomes active. The reactivation of the virus itself remains unexplained.

Patients with shingles are typically people over 60 years old, with significantly weak immune system and a history of chickenpox. It usually appears on the abdomen, back, buttocks, and chest. Contrary to popular belief, shingles can only be acquired if one has had chickenpox in the past. People who come in contact with a shingles patient will only acquire chickenpox and not shingles.


Symptoms occur in stages:

  • At first, pain, tingling, or burning sensations will be felt on a certain part of the body which can be present even before the appearance of rashes
  • After, red, blister-like patches start to form. When sores from the patches begin to dry up, it will for crusts that will fall off after 2-3 weeks that may leave scars

Other indications may include:

  • Joint and muscle pain
  • High fever
  • Headaches
  • Swollen lymph nodes
  • Muscle weakness
  • Sensitivity to touch

If shingles affect the nerves of the face, the following may occur:

  • Loss of hearing
  • Complication or total loss of eyesight
  • Difficulty moving certain muscles of the face
  • Lack of taste

Diagnosis and treatment

Shingles are diagnosed through tests done on the skin. Blood tests can also fetch positive results if the white blood cells increase along with the antibodies fighting the chickenpox virus.

There are vaccines available that help reduce the reactivation of chickenpox and the development of shingles. Antiviral drugs are also given to fight the chickenpox virus and prevent it from spreading. These help reduce pain, shorten the life of the disease, and prevent any further complications. These should be taken 72 hours after feeling pain, tingling, or burning sensations; better if taken before rashes occur.

Aside from antiviral drugs, patients may also be given Antihistamines and pain relievers.

#10 Hepatitis C

Hepatitis C is caused by the infection of the liver. Unlike other diseases, it doesn’t come with clear symptomatology, making it hard to distinguish. About 15-45% of untreated patients clear the virus within 6 months without medication. Around 55%-85% develop Chronic Hepatitis C which can lead to liver cancer and cirrhosis.


Hepatitis C is a liver disease that can be either acute or chronic. It ranges from mild illness to severe cases that can last from a few weeks to an entire lifetime. Asia and Africa have the highest number of Hepatitis C cases.

The virus can be contracted through contact with bodily fluids from an infected person. It can be passed through sexual intercourse, needle and syringe sharing, and through mother and child interaction.

In some instances, Hepatitis C can be transmitted through blood donation and transfusion, unprotected sex, and intercourse with a person with HIV.

Additionally, it is believed that people born between 1945 and 1965 have higher risk of Hepatitis C.


Most people with Hepatitis C don’t exhibit any outward symptoms but there are signs to identify it which includes:

  • Flu-like symptoms
  • Stomach pain
  • Nausea
  • Fatigue
  • Loss of appetite
  • Jaundice (dark urine, yellow eyes and skin)
  • Pain in the upper right part of the abdomen

Diagnosis and treatment

Hepatitis C can be detected through liver tests or blood tests. There are also drugs and medications that cure the disease within 8-12 weeks but come with headaches and fatigue. About 90% of people diagnosed with Hepatitis C have been cured by antiviral medications and have reduced the risks of acquiring liver cancer and cirrhosis. However, vaccines are not yet available for Hepatitis C.