The Ultimate Guide to the Worst Viruses in the World

worst viruses


They’ve been around for billions of years. They preexist humans and to this day continue to evolve, outwit and adapt to its victims.

Some viruses are more likely than others to cause severe outbreaks that could result in epidemics and pandemics. Especially alarming are the many viruses that can be lethal yet have no vaccine or treatment of any kind.

Read on for a list of the 10 worst viruses that will probably give you nightmares. Just pray you don’t ever come into contact with any of these.

1. Zika

A few years ago, no one had even heard of Zika virus. Then, in 2016 the CDC reported 36,512 Zika virus disease cases (with symptoms) in US territories. Considering that this disease had not made an appearance in the US before 2015, this virus is serious business.

The World Health Organization have declared Zika as a global public health emergency, especially due to the high risks of birth defects and severe health problems. Zika is linked to microcephaly, a birth defect that results in a smaller head than normal and lack of full brain development.

Zika is passed on to humans via infected mosquitos. Only 1 in 5 people who are infected will get symptoms. This is alarming because even symptomless, the virus can pass to fetuses.

2. Marburg Hemorrhagic Fever

This virus is named after Marburg, Germany where the first case was discovered. Marburg is passed from fruit bats to humans. Then it spreads from person-to-person through contact with someone who is infected.

The alarming mortality rate for this virus is up to 88%. What’s worse, death happens less than 10 days after the person first experiences any symptoms.

Symptoms include severe fever and intense head and muscle pain. Extreme lethargy and bleeding are also common symptoms.

There is no vaccine or treatment available.

3. Ebola Virus Disease

It’s no wonder that Ebola makes the top of the list. This killer virus has been sweeping through Africa for years. Widespread outbreaks in West Africa are common with the first ones in 2015-2016.

This virus has a 50% average mortality rate. Yet, in some outbreaks, that rate has been as high as 90%.

Most alarming is that scientists are not certain how Ebola spreads. Contact with the bodily fluids of dead animals seems to be related to how the virus is transmitted. Once a person is infected, it can be passed to other humans.

At this point, there is no vaccine. Drug therapies are in the works.

4. Crimean Congo Hemorrhagic Fever

This deadly fever spreads through ticks and livestock and is found all over the world. The symptoms come on fast and can prove lethal. Up to 40% of cases end in death.

Symptoms include swelling of the liver, fever, aching muscles, and vomiting.

There is no current vaccine for CCHF.

5. Lassa Fever

The scariest thing about Lassa fever is that the majority of people don’t know they have it. Around 80% of infected people never have any symptoms. This makes this virus extremely difficult to detect.

One way that scientists figure it out is through pathology. Read more here.

Though the fatality death is low (only around 1% of cases), most of the infected people can spread the virus without knowing it.

It is transmitted to humans via contact with rat urine or feces. Then it spreads among people through blood or fluid transfer.

Symptoms are often mild such as low fever and fatigue. Serious cases include bleeding from the eyes, nose or gums. Deafness, seizures, and comas are also possible symptoms.

Death usually occurs within 14 days of onset of this virus in fatal cases. This is one deadly virus for women at the end of their pregnancy. Both mother and infant die in over 80% of cases during the third trimester.


Middle East respiratory syndrome (MERS) is one of the types of pathogens that cause upper respiratory illnesses.

The illness spreads easily through sneezing and coughing. Roughly 36% of reported MERS cases have died.

There’s no vaccine or treatment currently available.

7. Chikungunya Virus

Chikungunya (pronounced chick-un-goon-ya) virus is spread to humans by contact with mosquitos.

Symptoms include fever and debilitating pain in the joints. While most patients recover, this is one of the worst diseases for longevity. Pain can last for months or even years!

This virus was first found in the Caribbean in 2013. Then in 2015, a major outbreak occurred in the Americans. There is currently no treatment.

8. Machupo Virus (Bolivian Hemorrhagic Fever)

This deadly virus is sometimes called the black typhus. It causes heavy bleeding and severe fever. So far this has only popped up in South America.

Rodents often carry this and can be passed from one person to another once someone is infected. You don’t have to come in direct contact with a rat to contract the disease. Airborn dust particles from the feces or saliva of infected rodents will do the trick.

9. Dengue Fever

Dengue is a fast emerging pandemic-prone viral disease. It doesn’t discriminate between urban or rural areas. This is one of the worst diseases to keep your eye on in you plan to travel to the tropics.

It is, like others on this list, transmitted by mosquitos and affects 50-100 million people each year in over 100 countries. In other words, 50% of the world’s population is at risk.

This virus comes with severe flu-like symptoms. It can be fatal if it results in a complication called severe dengue.

10. Rotavirus

Rotavirus claims the lives of over 500,000 children every single year. This deadly virus causes diarrhea in children and is often fatal in areas where proper medical care is non-existent.

Infection happens by coming into contact with infected stool. This virus is on the list of pathogens that can live without a host for extended periods. That means that if a surface or food or water is contaminated, a person can get the virus even days later.

Final Thoughts on Worst Viruses in the World

We hope you found this list of 10 worst viruses informative and eye-opening.

Are you interested in reading more curiosities for curious minds? Visit Curiosity Humans for a bucketload of interesting information on a wide range of topics.

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