Viruses: Infection, Transmission & Diseases

Viruses are responsible for many infections as pathogens. Unlike bacteria, however, viruses behave absolutely immune to antibiotics. Vaccinations against some viral infections exist, but not against all viruses.

What are viruses?

Viruses are infectious structures that spread outside cells by transmission, but can only replicate within a suitable host cell. Pictured are red blood cells and viruses. Click to enlarge. Viruses are genetic parasites. They infect both bacteria and higher cells, and thus also organism including humans. They are biological packages that transport their genetic material (DNA) into the host cell. There, cell metabolism accomplishes what the viruses themselves cannot:

The host cell produces new viruses according to their DNA blueprint and dies. As a result, thousands and thousands of these copied viruses are released. Since viruses do not have their own metabolism and cannot reproduce themselves, they do not belong to the realm of living organisms. Nevertheless, they must have evolved from living cells, as their biochemistry clearly indicates. The cells of all life forms can be attacked by certain viruses that are “responsible” only for them. This strict specialization is another characteristic of viruses.

Significance and function

Viruses cause cells to self-destruct. Their importance as pathogens in humans, animals, and plants is therefore the primary focus of this review. To be sure, bacteria and fungi also pose a significant risk of infection. However, some of these microorganisms are vital for humans. Reference should be made here to the skin flora, which protects us humans from many infections. Better known is the intestinal flora, without which optimal digestion would be unthinkable. Among the naturally occurring viruses, on the other hand, there are no forms that are useful to humans in any way. As mere DNA transporters without independent metabolism, viruses cannot be eradicated by antibiotics either. This is because antibiotics are lethal metabolic poisons only for bacteria. The medical treatment of viral infections therefore has narrow limits. Antivirals are drugs that can inhibit the multiplication of viruses but do not lead to their complete elimination. Despite all the risks posed by viruses as infectious pathogens, their modern importance for research and medicine must not be overlooked. Genetically modified viruses are already used today to treat bacterial infections. Such viruses are used in particular to combat bacteria that have become resistant to antibiotics. However, there are also attempts to use specially modified viruses in cancer therapy. These “oncolytic viruses” attack and destroy only tumor cells and thus have a highly specific effect. Patients are thus spared the serious side effects of chemotherapy. Somatic gene therapy efforts are also promising: for example, hereditary diabetes should be curable in the future. In this approach, laboratory-engineered viruses serve as vehicles (“vectors”) that introduce healthy genetic material into organs with genetic defects.

Diseases

Viruses are nonetheless first and foremost a constantly lurking danger. With each infection, their multiplication rate runs into the millions, if not billions. The occurrence of such high numbers in a short period of time means that a wide variety of mutations take place. New virus strains can thus germinate at any time and unpredictably. The annual influenza waves are therefore basically unpredictable. The global Spanish flu pandemic of 1918 and 1919 claimed at least 30 million lives. The situation of people infected with HIV is a cause for concern today. Most of the approximately 50 million people affected live in the Third World. With a series of antivirals, doctors can inhibit the growth of the virus and significantly prolong the lives of patients. But the severe side effects of drug therapy usually turn HIV patients into early retirees. For most patients in poor countries, AIDS is still a death sentence: they cannot afford the expensive drugs. The most effective way to get the human disease under control would be a vaccine. However, developing such a serum has proven very difficult. Many viral infections have been virtually eradicated in the last century with protective vaccinations.For example, chickenpox, measles and polio hardly play a role anymore, at least in western industrialized countries. Improved vaccination morale could also push other serious infections such as meningitis (early summer encephalitis or TBE) or hepatitis A and B into the background. No vaccine can be developed against the causative agent of the common cold because of its variability. However, the pathogens are also not among the most dangerous among the viruses.