Viruses are becoming stronger and stronger in recent times. And this is exactly how they are being depicted. Emergence and modification of more new deadly virus have scared the public healthcare officials but it may occur to you that how are we supposed to define the term deadly? Significant criteria for that includes the incidence fatality rate, the rate of reproduction (by measuring the potential for transmission), and time of incubation. Yet another significant determinant of fatality of virus is it’s mode of transmission. A scary thing about deadly viruses is that they get advanced after every transmission allowing quick spread after being mutated.

Most Deadly Virus

With time, urbanization, alterations in sexual behavior, increasing population worldwide, and mobility of virus have actually helped the viruses to advance and spread.

1. By Death Rate

Following are the seven deadly viruses which have increased the mortality rate up to millions each year.

HIV/AIDS: HIV/AIDS causes astonishing 1.6-1.9 million mortalities each year. Looking back at the last three decades, the virus has caused more than 25 million people to taste death. HIV-like viruses (lentiviruses) sprung in African primates many years ago, about 5-12 million years, but presented itself in the humans somewhere in the 20th century. There are around 34 million patients fighting HIV and most of them live in the sub-Saharan Africa (around 69%). Unfortunately, only half of the patients can reach antiretroviral therapy.

Hepatitis: A million people die of due to all types of hepatitis each year, according to an estimate. Hepatitis B causes death of 600,000 people and it has an infectious capacity of more than 50-100 times than any other Hepatitis virus. More so, 350,000 people die due to hepatitis C and about 70,000 due to hepatitis E.

Influenza: Irrespective to the fact that there are many vaccines available and being used since 60 years, the influenza virus results in 250,000-500,000 deaths each year. Older people and medically sick people are more prone to this virus.

Human Papillomavirus: It is true that infections caused by human papillomavirus (HPV) are not fatal, but chronic infection may result in cervical cancer. Apparently, HPV is responsible for almost all cervical cancers (approx. 99%). HPV results in 275,000 deaths per year.

Rabies: Death toll due to rabies is 55,000 each year. If no post-exposure prophylaxis (PEP) is given, this animal-caused disease—that progresses to acute encephalitis—is life-threatening after onset of symptoms.

Dengue Fever: The incidence rate of dengue has dramatically increased recently. Approximately, 50-100 million people get infected by dengue each year, causing 12,500-25,000 of them to die. The rapid rate of spread is also due to urbanization, although it got promoted by African slave trade. Spread was seen more during the Second World War and after it.

Rotavirus: Among infants, Rotavirus is said to be the most common reason of serious diarrhea worldwide. Every year, approximately 500,000 humans die due to rotavirus. There are vaccines available against rotavirus which has played quite a role in reducing mortality rate in children below the age of 5 in third world countries.

2. By Fatality Rate

Ebola virus: Ebola virus, results in fatal hemorrhagic fever. Due to no treatment, death toll has gone up to 90%. Spread is more common in poor villages located near rainforests, and thus the disease has a limited outbreak. Outbreaks are only seen in Africa, although some other cases from other continents have also been reported.

Henipaviruses: The genus Henipavirus comprises of 3 members which are Hendra virus (HeV), Nipah virus (NiV), and Cedar virus (CedPV). The second one was introduced in the middle of 2012, although affected no human, and is therefore considered harmless. The rest of the two viruses, however, are lethal with mortality rate up to 50-100%.

Marburg Virus: Quite clinically alike Ebola virus, the Marburg virus results in severe illness with serious hemorrhagic representation in a week when the symptoms appear. Mortality rate is 24% to 88%.

Lassa Virus: Lassa fever causes 5000 deaths per year. This virulent condition is endemic in the areas of West Africa—highest prevalent hemorrhagic fevers rate in that area. The fatality rate is about 15-20%, although some suggest it is up to 50%. The virus when enters the body affects all cells of the human body.

Lyssaviruses: This genus comprises of not only rabies virus (causing death of almost everyone who is infected) but certain other viruses such as Duvenhage virus, Mokola virus, and Australian bat lyssavirus. Although small number of cases are reported, but the ones reported have always been fatal. Bats are vectors for all of these types except for Mokola virus.

3. By Total Death

Humans have always struggled to win the battle against microbes but almost always failed in doing so because the microbes are getting stronger and stronger day by day but we aren’t. In old times, pandemics were not common due to less population. Alterations in techniques of farming and agriculture, growing population, and emergence of cities ­all of these have played a part in the spread of viruses. Following are four deadly viruses that are popular in history.

Smallpox: Smallpox became apparent around 10,000 BC and is still one of the most devastation disease of all time. It is very contagious and is spread through variola virus, and has caused many epidemics, beginning in ancient Egypt growing up to India, China, as well as Europe. Travelers from Europe going to the New World spread the virus there too, thus affecting native people of America. According to estimates, fatality rates were 80-90% when epidemics occurred. It killed around half of the native Australian population while in early years of British colonization, referring it to be the most common cause of death in Aboriginal populations in the year 1780- 1870. Smallpox caused 300-500 million people to die in the 20th century. The first vaccine for smallpox was developed by Edward Jenner in 1796 and after this, it was eradicated by the vaccination campaigns successfully and WHO certified its eradication in 1979.

Measles: Measles was first described by a Persian physician Rhazes (860-932 AD) who gave a scientific point of view regarding measles. History tells us that this was severely contagious disease that had incidence throughout the globe, resulting in millions of people to die. The Antonine plague (165-180 AD) caused by the measles virus was spread in Roman Empire by army men and troops coming back from the Near East. The estimated death toll is five million. Although vaccines are available, measles is referred as one of the leading reasons of death, among younger mass even today. A report by WHO describes 158,000 deaths caused due to measles in the year 2011.

Spanish Flu: Spanish flu was pandemic in 1918 mostly infecting the third world countries’ population causing 100 million people to die throughout the world, out of which more than 20 million died in World War I. The flu mostly targeted young adults. This was because the virus caused the immune system to overreact leading to very strong immunological reactions inside the body. This virus affected the world before it disappeared completely after 18 months.

Yellow Fever: Yellow fever is an acute hemorrhagic disease which caused high death toll in the United States as well as in Spain around 18th & 19th century. Yellow fever virus has not completely eradicated and according to an estimate, there are 200,000 incidences of yellow fever around the globe, taking lives of 30,000 people per annum.