Viruses are obligate intracellular parasites, that is: they need to infect a cell and use all of its cellular machinery (proteins, enzymes, lipids, sugars, etc.) to reproduce and spread.
The development of vaccines and drugs over the years has allowed us to be able to effectively eliminate them from our body. However, there are no treatments for all virus infections, or for some they do exist and they are ineffective. Be that as it may, there are certain types of viruses that produce more severe infections than others, reaching mortality rates of up to 90%.
In this article we will talk about some of the most lethal viruses that humanity has faced.
The smallpox virus
The smallpox virus ( Variola virus ) infects only humans and causes smallpox, the disease from which the virus takes its name. It is a virus with multiple forms and different mechanisms of entry into cells, which has historically made it a very severe virus, causing large epidemics that devastated populations. It is estimated that 90% of the Native American population died from the smallpox virus, introduced by European explorers, against which they had no immunity.
Smallpox is a serious infectious and contagious disease, with a high risk of death. Its mortality rate is around 30%, with higher mortality in babies. Even among survivors, scars and other possible malformations can be observed (especially in fetuses). There are also cases of blindness.
Symptoms include fever and vomiting, mouth sores, and skin rashes. The rashes turn into bumps with dense fluid inside and later these bumps turn into pustules and then into scabs, which fall off and leave scars on the skin.
Its transmission between people is carried out through direct and prolonged contact and can also be transmitted through body fluids or contaminated objects.
The first modern vaccine was developed against the smallpox virus. In 1980 its eradication was confirmed worldwide.
Human Immunodeficiency Virus (HIV)
The human immunodeficiency virus (HIV) is a virus that infects specialized cells of the immune system (such as T helper cells, macrophages, and dendritic cells) and kills them, eventually causing immune system failure. This is known as acquired immunodeficiency syndrome (AIDS) and allows life-threatening opportunistic infections and cancers to develop.
Over the years, powerful anti-HIV drugs have been developed that allow the infected person to live with the virus in a more or less normal way. In some cases, stem cell transplants have managed to cure the disease and eliminate the virus from the body, although this is not common. It is an especially severe virus in underdeveloped countries that do not have the appropriate drugs at their disposal.
Transmission of the virus can only be carried out through body fluids that have a high viral concentration. The three forms of transmission are: sexual (unprotected sexual relations), blood and perinatal (from mother to child: during pregnancy, childbirth or breastfeeding).
Not all people infected with HIV develop AIDS. In fact, with proper treatments, HIV infection has gone from being fatal to chronic. Without treatment, a person would die about 10 years after being infected by the virus.
The rabies virus
Rabies is an infectious disease caused by the rabies virus (family Rhabdoviridae ). The rabies virus is found worldwide and is present in the saliva and secretions of infected animals. Humans are infected through the bite of an infected animal.
Rabies manifests itself with nonspecific symptoms during the first ten days: fatigue, headache, fever, anorexia, nausea and tingling at the site of the wound. This is followed by difficulties in swallowing, disorientation, visual or olfactory hallucinations, focal or generalized seizures, periods of excitability... After these clinical manifestations comes a coma and, in most cases, death.
For all of the above, it is essential to treat the disease with the utmost urgency. There is no specific treatment for rabies, so if a possible infection is suspected, doses of human rabies immunoglobulin should be given urgently in addition to four doses of rabies vaccine two weeks later. Once the patient presents symptoms, the virus will be lethal almost 100% of the time.
The Ebola virus
The Ebola virus produces a severe illness in humans, which begins between two days and three weeks after contracting the virus. Symptoms are: fever, sore throat, muscle aches and headache. Nausea, vomiting, and diarrhea then develop, along with liver and kidney failure. From there, hemorrhages arise that can be devastating.
The virus is contracted through contact with the blood or body fluids of infected animals (usually monkeys or fruit bats). The disease is contagious between people once a human has been infected.
Some strains of the Ebola virus have had mortality rates of up to 90%, causing outbreaks that have been declared a public health emergency of international concern by the WHO.
In 2020, a vaccine developed against the Ebola virus was approved and has proven to be completely effective.
Marburg virus
Marburg virus causes a severe hemorrhagic disease, called Marburg hemorrhagic fever, with high mortality. The symptoms of Marburg hemorrhagic fever are indistinguishable from those of Ebola, making them very similar viruses.
Most Marburg virus infections are associated with visits to caves or mines where the common pipistrelle (Rousettus aeguptiacus) bat is present , which is believed to be a host of the virus. The modes of transmission are similar to those of the Ebola virus, although Marburg is slightly more contagious.
There have been major outbreaks of Marburg haemorrhagic fever, some being excessively severe, with mortality rates of 100%.
There are currently no vaccines or treatments against the virus in humans.
