The power of viruses – as enemies, companions, and beneficials

At some point, probably between 1900 and 1930, a hunter killed a chimpanzee in the northern Congo or in Cameroon. Today it is still not unusual to hunt for wild animals in central Africa, because their meat is in great demand and is sold in local markets.

But the hunting event in question, which occurred about a century ago, is still devastating the world today. It unleashed a pandemic that struck Africa first and then countries far beyond it and since then has caused more than 35 million deaths all over the world.

That’s because the chimpanzee that was killed and eaten back then was the carrier of a certain virus — a variant that apparently leaped across to human beings with unusual ease. Inside these new hosts, it radically destroyed the human immune system, thus triggering Acquired Immune Deficiency Syndrome (AIDS).

The following facts clearly illustrate the dimensions of this pandemic: During the talk I gave at the Mercedes-Benz Museum concerning the current status of virus research, which took me an hour, more than 100 people died of AIDS and more than 200 people were newly infected with AIDS all over the world. Today’s blog post is based on my talk about viruses, which was part of the event series “Dialogue in the Museum,” which is organized jointly by the Daimler and Benz Foundation, Daimler AG, and the Mercedes-Benz Museum. For us, the season of colds is just around the corner.

The media especially enjoy producing dramatic reports about viruses and epidemics. If there’s a local outbreak of an illness such as Ebola or avian flu, we’re sure to see striking headlines such as “The beast from the jungle,” “A deadly epidemic” or “Attack of the killer viruses.” Headlines like these raise the readers’ blood pressure and the click rates of the Internet magazines, but from an epidemiological viewpoint there are greater challenges to master — pathogens that infect far more people and lead to far more deaths.

It doesn’t help anyone if we overdramatize this topic and lose our sense of perspective. Whereas Ebola has caused at total of about 13,000 deaths since 1976, seasonal flu claims about 400,000 victims all over the world every year. Many of these deaths could have been prevented by vaccination. In recent decades, tremendous progress has been made in the struggle against epidemics caused by viruses.

Thanks to comprehensive vaccination campaigns, smallpox has been eliminated since 1977; the polio virus, which causes infantile paralysis, now exists in only three countries on earth; and chronic Hepatitis C can now be cured in almost all patients as long as they have access to the necessary therapy. Moreover, today an HIV infection is no longer a death sentence if the patient receives appropriate medical treatment. Infected patients who are receiving such treatment can lead a normal life. Many challenges remain, but today we also have previously undreamed-of opportunities in the fields of research and medicine.

Ebola virus

The question of whether or not a virus is a living being can be answered in very different ways. The only thing we know for sure is that a virus consists of genetic information — often a very small amount of genetic information — that is packed inside a protein shell. In other words, viruses have a very simple structure.

We can regard them as a biochemical compound that is somewhere in the transitional area between living and nonliving matter. The most important thing for a virus is its host. That’s because once a virus meets an appropriate host organism, it reveals itself to be a radically “self-serving genome.” But without the host the virus is nothing, because the host is an incredibly efficient propagation machine.

HIV virus

Viruses are everywhere

Scientists estimate that there are about ten million times more viruses in the earth’s oceans than there are stars in the universe. There is hardly any habitat on the earth’s surface, no matter how extreme, that is not already populated by viruses. In other words, there are viruses almost everywhere — not only on our skins, under the rosebush in the garden, and on the nearest streetlamp, but also in the ocean depths, in acidic hot springs with a temperature of 80°C, in salt pans, and several kilometers under the earth’s surface.

That’s why it’s important to not merely regard viruses as possible pathogens. Instead, we should realize that they are a completely natural and elementary part of us human beings and our environment and that they have an important function for our daily lives and our survival.

Flu virus

For example, almost ten percent of the human genome consists of remnants of genetic information from ancient retroviruses that have long disappeared. A very long time ago, these remnants were left in an infected human cell and embedded themselves in the genome of their host. We have the process of gene transfer through viruses to thank for some of our evolutionary attributes, such as the formation of the placenta and helpful survival skills such as the ability to extract energy from potato starch.

Microorganisms and their viruses account for several kilograms of our body weight. However, the interactions between our bodies, viruses, and bacteria are so complex that we are only now gradually beginning to understand them. Nonetheless, it is certain that the vibrant stability of this micro-ecosystem has a significant influence on our health. There is still a lot of research to be done in this area.

Viruses are not always harmful

The application of useful attributes of viruses will become increasingly important for medicine in the future. Obviously the research in this area will experience failures and setbacks, but there will also be some very promising new approaches to therapy. Viruses are ideal vehicles for inserting genetic information, such as therapeutic genes, into diseased cells. This procedure can already heal certain blood diseases in some patients today.

Cancer cells

In the future, virus therapies will open up new opportunities for healing in tumor medicine as well. For example, genetic information can be inserted into cancer cells and induce them to self-destruct. Alternately, the viral infection can make the cancer cells visible to the body’s own immune system. Because of their rapid self-propagation, some kinds of cancer cells are especially vulnerable to the destructive operations of viruses.

In the area of virus research, we are far from having a detailed understanding of all the relationships involved. Nonetheless, today science has reached a point that is opening up entirely new horizons.

Podcast “The power of viruses”


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Hans-Georg Kräusslich is a virologist at the Department of Infectious Diseases, Virology Heidelberg University. His fields of interest are molecular virology, cell biology of virus infection, assembly, release and molecular architecture of HIV particles, HIV protease and antiviral resistance, HIV-cell interactions, role of lipids in HIV replication and transmission and therapy of HIV infection.