Emerging viral diseases are always high value news items. However, how will viruses change over the next few years? In recent years, the most significant virus of them all, in terms of human cases and death toll, was the re-emergence of Ebola, which is causing the biggest outbreak of the disease in history. But there is also chikungunya fever, which appeared in the United States for the first time in July, and enterovirus D68, a previously rare disease causing an outbreak of respiratory illness among U.S. children.
Humans have come a long way in preventing viral diseases over the last one hundred years. Children receive vaccinations against nine viral diseases, including many that used to cause life-threatening complications, such as polio. But still, there are fewer treatments for viral diseases than for those caused by bacteria, and when infectious disease pandemics emerge, the pathogens that are the most lethal are the viruses.
Treatments for viral diseases have generally stayed far behind treatments for bacterial diseases. One reason for that is simply because scientists have been working on antibacterial treatments for longer. Viruses are also much smaller than bacteria, and they have fewer genes or proteins to target with treatments. Viruses also mutate much more quickly than bacteria, so any therapy that is developed may no longer work after a short time.
In addition, bacteria are living cells that divide on their own, and a lot of drug treatments against bacteria work by knocking out essential functions of those cells, such as the ability to replicate. But viruses are not made of cells, and they are even not exactly “alive” — they just hijack the machinery of their hosts’ cells in order to replicate, so researchers can’t target virus functions or replication in a traditional way.
When the first antibiotics were developed in the 1940s, they were considered something akin to a miracle cure for diseases that had once seemed unstoppable. A few decades later, scientists developed drugs against viruses, known as antivirals. However, although there are “broad-spectrum” antibiotics, which are single drugs that work against dozens of bacteria, the spectrum for antivirals is much narrower. Most antiviral drugs are specific for one type of virus, although some work against two or three.
Some of the most successful antiviral drugs inhibit a certain viral enzyme called reverse transcriptase, which synthesizes parts of the virus. Several drugs against HIV work in this way. However, only RNA viruses (HIV for example) use reverse transcriptase, so drugs against this enzyme will not work for DNA viruses. In addition, the structure of reverse transcriptase can be very different depending on the virus, which is why an antiviral that works against HIV might not work for Ebola.
Discovering antiviral drugs is easier today than it used to be, thanks to new technologies. That should continue to be a strong factor in favor of humanity when it comes to fighting diseases of the future. A few decades ago, researchers had to test potential drugs individually, and it could take three to six months to test three hundred potential drugs, Now, the process is automated with robots, so those same three hundred drugs would require only a few days to test.
In addition, researchers can now view three-dimensional models of viral components on a computer, and quickly design and “test” compounds with computer programs that simulate the binding of drugs to viral components. However, because new antiviral drug treatments may be years or decades away, public health organizations are focused on stopping pandemics before they start. New viral diseases typically emerge because of human activity that brings people into contact with wildlife, such as road building, hunting and agriculture expansion. About 75 percent of emerging diseases in people come from animals. So to reduce the risk of an outbreak, researchers need to figure out ways to reduce the activity that brings us into contact with wildlife, particularly in incredibly hot areas where diseases tend to emerge, such as tropical areas. Pandemics of the future will hang on the thread of researchers being able to fight the onset of the disease with all the technology that is available to them.