Ask the Experts: Marie Pizzorno on viruses, bacteria
September 09, 2010
LEWISBURG, Pa. — Marie Pizzorno, an associate professor of biology and a molecular virologist, explains the differences between viruses and bacteria, how some bacteria are "good," and why it's difficult to predict the next epidemic.
Q: What is virology and what is the difference between viruses and bacteria?
A: Virology is the study of viruses. I am a molecular virologist and I specifically study viruses that infect eukaryotes, or higher-order cells, that have a nucleus in them, such as in plants, animals, funguses and insects. Bacteria are simple, one-celled organisms that don't have a nucleus, which is the part of the cell that stores the DNA. Bacteria have all of the machinery they need to carry out the basic processes of life. They can use energy; they can make new proteins; and they can replicate. Viruses are much more limited in that they do not have the capacity to be independent life forms. They need a living cell to infect. Typically, in a normal virus infection, the virus goes into the cell and takes over the cell's machinery. Instead of the cell making cellular stuff, it makes viral stuff. A single virus infection can produce anywhere from 100 to 10,000 new virus particles. So, viruses can replicate very quickly, which is why virus infections in humans tend to take off really fast.
Q: Where are bacteria found and when are they beneficial?
A: Bacteria live in the water, soil, on our skin and inside us. They are everywhere. Most people think all bacteria are bad, but they are not. We have bacteria in our guts that we are now learning actually make things that are important for our bodies. And anybody who has taken an antibiotic and wiped out all the bacteria in their gastrointestinal system, in their stomach, knows the negative effect of not having those bacteria there. The only time we really get upset is when bacteria are in a place they shouldn't be and in a part of our body where they're growing too much and causing an illness. So we take antibiotics to kill bacteria when we have pneumonia or bronchitis or other things like that. But for the most part bacteria do good things and killing off all the bacteria is not always in our best interest.
Q: How do you know when you have a virus versus a bacterial infection? And why should you not take antibiotics when you have a virus?
A: You sometimes don't know whether you have a virus or a bacterial infection. There are some diagnostic tests a doctor can do. If you can grow bacteria in the laboratory, then you obviously have bacteria. Viruses are much more difficult to grow, so sometimes the tests they do for viral infections look for signs that the virus has been there. If you want to know if you have mononucleosis, for example, you don't look for the presence of the virus, you look for the antibodies against the mononucleosis virus. It's really hard for the average person to know whether they have a viral infection or a bacterial infection, but patients should not automatically ask for antibiotics. Fevers and chills and aches and pains can often be the sign of a viral infection. If it goes on for more than a few days, you should go to a doctor and find out if antibiotics are a good idea. Because bacterial cells are so different from our cells, we can fairly easily find drugs that will kill off the bacterial cells but not hurt our cells. Viruses literally get into our cells and replicate themselves, so if you inhibit the virus, you also inhibit your own cells.
Q: In recent years, health officials have warned against potentially serious viruses, including SARS, avian (bird) flu and H1N1 (swine flu). How serious were these threats and should we expect more events like this?
A: This is a field called emerging infectious diseases: new infections that appear to come out of nowhere. Many of these emerging infections are viral. SARS kind of threw the virology community for a loop. It came from an organism that lives in China and it seems now that it may have started in bats. I don't think anyone could have predicted that SARS was going to come about, and it seems to have died out. It's not really clear that it's going to be a problem in the future, but I think it teaches us a lesson about how to handle these weird viruses that come out of nowhere. Bird flu does not transmit very well between humans. So, if I got bird flu, I couldn't give it to you very easily. Most people who get bird flu get it directly from a bird and don't pass it on to a human, but if the bird influenza virus became capable of going from human to human really well, that could become a really big threat.
H1N1 was another virus that we predicted was going to be one of the next pandemics. The pandemic did not turn out to be quite as bad as people thought it was going to be, which is a good thing. Ebola is a great virus for making really scary movies and books, but it's only killed 1,000 people and maybe infected 1,500 to 2,000 people throughout our knowledge of it. The thing with Ebola is it kills quickly. It is actually not to a virus' advantage to kill you quickly because if you get really sick, you don't go out and interact with other people. You just want to go home and crawl under the covers.
I don't know if swine influenza is going to come back or come back in a different form. One of the reasons flu is so dangerous is that it changes so quickly. What we had last year might not be what we get this year, or there could be a whole new virus that comes completely out of nowhere, which happens about every 20 or 30 years. That's what they think happened with the Spanish flu of 1918. It's a completely different flu that no one had ever seen, so no one has prior immunity.
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