Dark Avenger: I am sorry for it. I never meant to cause tragic incidents. I never imagined that these viruses would affect anything outside computers. I used the nasty words because the people who wrote to me said some very nasty things to me first.
The first thing that comes to mind when we talk about how dangerous a virus is generally its lethality: if a person is infected, what is the risk of them dying? Some viruses are particularly worrying from this point of view. The rabies virus, which affects the nervous system, is almost 100% fatal once symptoms appear. The best defense against this disease is vaccination. Useful before or after exposure to the virus, it can be used in humans but also in animals likely to contaminate them, mainly domestic dogs1.
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HIV, the Human Immunodeficiency Virus, is also fatal in almost 100% of cases if left untreated. Less than one percent of patients seem to be able to spontaneously control the virus and avoid the development of Acquired Immunodeficiency Syndrome (AIDS)2. Fortunately, current treatments can control HIV so effectively that infected people may no longer have symptoms, no longer be contagious and no longer die because of the viral infection. Despite the absence of a vaccine, effective preventive approaches do exist, notably pre-exposure prophylaxis, or PreP. However, access to these therapies remains unequal across the world, and there is no treatment that can be used on a large scale to cure HIV.
The examples of rabies and HIV show that the intrinsic lethality of a virus can be greatly reduced when effective means of prevention or treatment are available. Progress is being made in these areas with another type of particularly lethal virus: filoviruses. This is the family of viruses that includes Ebola and Marburg, which do not cause disease in some African bats but do cause hemorrhagic fevers in humans. The average fatality rate is around 50%, but varies according to epidemic and strain, and has already exceeded 80%3. The WHO now recommends two monoclonal antibody-based treatments for the most dangerous strain of Ebola4, as well as two vaccines, although research is still underway to determine the best vaccine regimens5.
We can reduce lethality of various viruses thanks to vaccines and treatments. But we must not forget that they are extremely unevenly available around the world, and vary according to geographical area, geopolitical situation, or financial resources. Not all populations have the same opportunities when faced with the same infectious agent6.
Some viruses become particularly dangerous when they trigger specific diseases: the severe form of yellow fever or the pulmonary syndrome caused by certain Hantaviruses, transmitted by rodents7, can exceed 50% lethality. Fortunately, however, these clinical forms are relatively rare. This illustrates another parameter to be considered when assessing the danger of a virus: the number of people it infects and makes ill. The Crimean-Congo hemorrhagic fever virus, transmitted by ticks, is a cause for concern, with a fatality rate of around 40%. It is therefore being monitored and studied, but although it has been present for decades and is endemic in some countries, fewer than 20,000 cases have been recorded in total8.
The mortality rate of a virus is inevitably a significant factor, but it is far from the only parameter to be taken into account when assessing how dangerous it is. For example, the impact may be considered more serious when it affects certain populations, such as children. Rotaviruses, for example, do not appear to pose much of a threat if they are presented as the cause of gastro-enteritis. But they particularly affect children under the age of five, in whom they can cause severe dehydration leading to hospitalisation. More than 180,000 children died from them in 2017, mainly in low- and middle-income countries14.
Furthermore, how dangerous a virus is depends very much on its rate and modes of transmission. Measles is particularly impressive in this respect: one infected person can infect around fifteen others, making this disease very difficult to control. It is so contagious that its spread can only be stopped if 95% of the population is immunised. However, vaccination coverage is far from reaching this level everywhere in the world, including Europe15. As a result, no country has managed to rid itself of this deadly disease, which remains a cause for concern for health agencies16.
Finally, to assess how dangerous a virus is, we need to consider all its consequences, which, as the Covid-19 pandemic clearly showed, are not limited to mortality. Hospitalisation, which can overwhelm a healthcare system, and long-term after-effects, which have health implications as well as social and economic ones, can also be significant. This was the case with smallpox, which caused scars, particularly on the face, but could also lead to blindness. Polio, which has almost disappeared thanks to vaccination but is still circulating in Pakistan and Afghanistan, can cause permanent paralysis19. And Lassa fever, endemic in West Africa, causes deafness and myocarditis20.
Papillomaviruses can cause cancer not only of the cervix, but also of the vagina, vulva, anus, penis and oral cavity. Vaccination against certain strains can now drastically reduce these risks.
The list of viruses whose consequences persist over time is a long one: we could add to it those that promote the development of cancers, such as papillomaviruses or hepatitis B and C viruses21, those likely to cause more severe symptoms when reactivated after the original infection (such as the chickenpox virus, also responsible for shingles) or those which, initially perceived as fairly harmless, actually appear to be linked to serious illnesses. The most recent example is the Epstein-Barr virus, a herpes present in 90% of the population, which is clearly associated with the development of multiple sclerosis22.
Once all these factors have been taken into account, it seems illusory to identify THE most dangerous virus. But having them in mind enables us to know which viruses to keep a close eye on, and to consider ways of making each of them as safe as possible, in particular by abolishing the inequalities in access to treatment and prevention tools that still divide the world. Obviously, this debate must be extended to non-viral infectious agents: bacteria, fungi, and other parasites, such as the Plasmodium responsible for malaria. The One Health approach is also a reminder that humans are part of ecosystems and that health issues must be considered on an environmental scale23.
Some viruses pose a bigger threat than others. The viral strain that drove the 2014-2016 Ebola outbreak in West Africa kills up to 90% of the people it infects, making it the most lethal member of the Ebola family.
But there are other viruses that are are even deadlier. Some viruses, including the novel coronavirus currently driving outbreaks around the globe, have lower fatality rates, but still pose a serious threat to public health because they infect so many people.
According to the World Health Organization (WHO), the Marburg virus was first identified by scientists in 1967, when small outbreaks occurred among lab workers in Germany who were exposed to infected monkeys imported from Uganda. Marburg virus symptoms are similar to Ebola in that both viruses can cause hemorrhagic fever, meaning that infected people develop high fevers, and bleeding throughout the body that can lead to shock, organ failure and death, according to Mayo Clinic.
The first known Marburg virus outbreak in West Africa was confirmed in August 2021. The case was a male from south-western Guinea, who developed a fever, headache, fatigue, abdominal pain and gingival hemorrhage before ultimately dying of the disease. This outbreak lasted for six weeks and, while there were 170 high-risk contacts, only one case was confirmed, according to Reuters.
In 1976, the first known Ebola outbreaks in humans struck simultaneously in the Republic of the Sudan and the Democratic Republic of Congo. Ebola is spread through contact with blood or other body fluids, or tissue from infected people or animals. The known strains vary dramatically in their deadliness, Dr. Elke Muhlberger, an Ebola virus expert and associate professor of microbiology at Boston University, told Live Science.
In December 2020, the Ervebo vaccine was approved by the U.S. Food and Drug Administration. This vaccine helps to defend against the Zaire ebola virus and a global stockpile became available from January 2021.
Dr. Elke M\u00fchlberger is a professor of microbiology and the director of Integrated Science Services at the National Emerging Infectious Diseases Laboratories (NEIDL) at Boston University. \nDr. M\u00fchlberger is a renowned expert in the field of BSL-4 hemorrhagic fever viruses. She has a strong research focus on the highly pathogenic filoviruses, Ebola and Marburg virus. She received her PhD in Virology from the Philipps University Marburg, Marburg, Germany in 1993 and continued to work on filoviruses as an independent PI and group leader in Marburg. In 2008, she joined the Department of Microbiology at Boston University."}), " -7-12/js/person.js"); } else { console.log('no lazy slice hydration function available'); }Dr. Elke MhlbergerSocial Links NavigationProfessor of Microbiology at Boston UniversityDr. Elke Mhlberger is a professor of microbiology and the director of Integrated Science Services at the National Emerging Infectious Diseases Laboratories (NEIDL) at Boston University. e24fc04721