Contributed by Charlotte K

"cancer news: epstein-barr-virus infects-and-may-cause-tumors in dogs

Interesting and with huge implications. We already knew that the model for a transmissible tumor was in dogs. This is a case of a virus being transmitted possibly from people to dogs, and possibly causing tumors such as lymphoma in dogs. I received this link from another Cavalier person who got it from NAIA, from Penn site. Its a backwards way of looking at their lymphoma vaccine, if you follow me. There is much more to be learned, and the cancer link is a hypothesis, as yet, as I understand it.

http://www.upenn.edu/pennnews/news/penn-researchers-find-epstein-barr-virus-infects-and-may-cause-cancer-dogs

http://tinyurl.com/7w83obt

Now Peggy and other scientists can really explain this better than I!"


I finally had time to read this interesting post. I found it well explained and am not sure what parts I need to further explain, but here goes.

Cancer is sometimes linked to viral infection because viruses contain DNA or a similar molecule, RNA. A viral gene may cause an invaded cell to grow inappropriately, producing a tumor or, in the case of lymphoma, over-production of cells of the immune system. The system these investigators are studying involves B cells, the cells that produce antibodies. They have evidence of several types that a virus very similar to the Epstein -Barr virus of humans is found in B cells of dogs with lymphoma.

The first type of evidence involves antibodies. B cells make antibodies to foreign proteins. You can take the blood and test it for presence of antibodies to specific proteins quite easily. (This test works whether or not B cells are enhanced in the body.) For instance, the first screening test for HIV, the virus that causes AIDS, is an antibody test. This type of test, however, only shows that the person, or dog in this study, has been exposed to the viral proteins; it does not show that the virus is still in their body, as antibodies persist for a long time after the foreign material is gone. It's a good quick and dirty screening device, but if you get a positive result with the antibody, you would then follow it up with a technique that allows you to see if the virus itself is actually present.

That's what the DNA test was designed to do. You may know that DNA is a double-stranded molecule with 4 types of subunits linked together in a long chain. The subunits always pair specifically, A to T and G to C. Information is stored in the DNA molecule through the ORDER of the subunits. You use PCR, a technique that allows you to replicate a specific sequence of DNA, to make a probe, which is a single stranded piece of DNA labeled somehow so that you can detect it. If you make a probe from a part of the viral genome, you can use it to determine if a similar sequence of DNA exists in the blood of a human or a dog because the probe will bind specifically to its opposite strand if it is present, ie. if the DNA is similar. The researchers found in the blood of dogs that had lymphoma a sequence that bound to several probes that they made from the Barr-Epstein virus. This showed that the Barr-Eptein virus or one very similar to it was actually present in the blood.

Finally, they examined cells visually using the electron microscope, which is powerful enough to see viral particles. This technique does not tell you as certainly what the identity of the virus is, but it is able to tell you if the viral particles are actually in the cells, where they could control cell growth. There were virus particles in the cells.

There are several ways that cancer can occur. You can inherit a sequence of DNA that predisposes some cell(s) in your body to grow inappropriately. Most inherited forms of cancer are recessive. You inherit one bad copy of a gene that is designed to down-regulate cell growth, and the other copy mutates, leaving a cell that lacks some of its regulatory machinery. Also, DNA is constantly being repaired, especially in cells that are replicating. Mutations in genes required for DNA repair are often found in hereditary forms of cancer.

Carcinogens that cause cancer typically are mutagens, causing mutations. Also, the metabolic processes that have to go on in our cells all the time can produce molecules such as free radicals that can cause mutations. Most cancers are sporadic, caused by mutations that are more or less random. Usually there are multiple cell systems that have to be mutated in a single cell in order for cancer to occur.

Viruses can cause cancer by introducing a gene that disrupts the regulatory machinery that keeps cell growth in balance. Often this is a powerful gene that turns on other genes so that the virus can take over the synthetic pathways in a cell. And of course other mutations may need to occur before the cell becomes cancerous. So a virally caused tumor may occur many years after the initial infection.

Charlotte and CM, does this answer the questions you had?

Peggy, you're the best - tks so much! Can I repost your very clear and helpful response to others that are interested in this???