On the heals of scientists discovering that dogs can catch norovirus from humans, a team of researchers from the University of Pennsylvania School of Veterinary Medicine and Penn’s Perelman School of Medicine have discovered that an Epstein-Barr-like virus can infect dogs. The virus may also be responsible for causing cancerous lymphomas in canines.
The Epstein Barr virus is a herpes-type virus and is most commonly known as "the kissing disease" and for causing mononucleosis in people. Over 90 perscent of humans have antibodies for the virus. However, the virus has also been marked as causing more serious conditions in people, including Hodgkin’s, non-Hodgkin’s and Burkitt’s lymphomas.
Little is known about how EBV triggers these cancers. However, the new findings suggest that domestic dogs possess a similar biology to humans with respect to EBV infection. This discovery could allow scientists to study dogs to help uncover the mechanisms by which EBV leads to cancer in certain people. "Discovering that dogs can get infected with this virus like people do may provide us with a long-sought-after model for EBV-associated disease," said Nicola Mason, assistant professor of medicine and pathobiology, and one of the authors of the study at Penn Vet.
In people, the Epstein Barr virus infects B cells. After an acute phase of infection, of which many people are not even aware, the virus goes into a latent phase. Most people show no symptoms during this phase, but, in some people, EBV promotes unnatural growth of B cells, which contributes to the development of lymphoma.
Dogs seem to develop lymphomas that share some characteristics with the human equivalents. These conditions are relatively common in certain breeds. One out of eight Golden Retrievers, for instance, develops lymphoma.
"The paradigm up until now was that EBV only infects humans," Mason said. "It is an extremely successful virus, and most people are infected. Since humans and domestic dogs have cohabited for around 15,000 years, we hypothesized that the virus may have adapted to another host."
In their research Mason’s team obtained samples of blood from client-owned dogs of various breeds brought to Penn Vet for care. In 48 dogs with lymphoma and 41 without the disease, the researchers first looked to see if the pets had antibodies against proteins specific to the EBV capsid, the protein shell of the virus. The test is nearly identical to the one used to detect EBV in humans. They observed that eight of the dogs with lymphoma and three of those without it had high levels of antibodies against EBV proteins, indicating that a portion of the dogs had been exposed to a virus very similar to EBV.
The presence of antibodies confirms if a dog has been exposed to a virus or not. But the researchers wanted to know whether the virus had a direct association with the tumors in dogs with lymphoma. So next they tested the lymphomas to see if they could find virus in the dog tumors. Using DNA testing the researchers analyzed lymph nodes of dogs with B cell lymphoma and found a portion of DNA very similar to one in EBV in two sick dogs.
They repeated similar tests with other stretches of EBV DNA, and examined the cancerous B cells under an electron microscope. Both tests revealed what appeared to be viral indicators similar to what is found in humans with EBV-linked lymphomas.
Taken together the evidence points to dogs are natuarally infected with a virus similar or identical to EBV in people. And just like in people that develop lymphomas, the virus appears to be linked to cases of canine lymphomas as well.
The fact that the virus is so widespread in people, but only a small percentage of people develop cancers from the virus, indicates there may be a genetic component to being susceptible to developing an EBV-associated cancer. "With additional studies within certain breeds of dog we hope to provide insights into genetic factors that may predispose to virus associated lymphoma," said Mason. "Furthermore, this spontaneous dog model may help us evaluate new treatments for EBV-related lymphomas or investigate strategies to prevent those cancers from developing in the first place." The discovery is sure to have an impact on the research and care for both dogs and people affected with the cancer.
Mason’s team at Penn Vet included Shih-Hung Huang, Philip Kozak, Jessica Kim, George Habineza-Ndikuyeze, Charles Meade, Anita Gaurnier-Hausser and Reema Patel. The team also worked closely with Erle Robertson, professor of microbiology at the Perelman School of Medicine. Their work was published online March 8 in the journal Virology.
Shih-Hung Huang, Philip J. Kozak, Jessica Kim, Georges Habineza-Ndikuyeze, Charles Meade, Anita Gaurnier-Hausser, Reema Patel, Erle Robertson, Nicola J. Mason. Evidence of an oncogenic gammaherpesvirus in domestic dogs. Virology, 2012; DOI: 10.1016/j.virol.2012.02.013
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