Although a new influenza virus, now called influenza D, was discovered first in pigs, researchers found it was more common in cattle. However, further research has identified antibodies to the virus in small ruminants, but not in poultry.
To identify exposure to the virus, South Dakota State University doctoral student Chithra Sreenivasan tests blood samples for influenza D antibodies. Working with the Minnesota Poultry Testing Lab, she found no evidence of the new influenza strain in poultry; however, she did find antibodies to the virus in sheep and goats from the Midwest through blood samples archived at Washington State University.
Sreenivasan co-authored a paper on those findings that was published in the international journal Veterinary Microbiology last year. In ongoing work, she and her colleagues have also identified antibodies in horses. For her work, she has received the Joseph P. Nelson Graduate Scholarship Award that recognizes original scientifc research.
"The virus has not been shown to be pathogenic in humans. No one should be afraid of this," professor Radhey Kaushik said. SDSU alumnus Ben Hause, now a research assistant professor at Kansas State University, discovered the virus, which he identified and characterized as part of his doctoral work under tutelage of his research adviser, professor Feng Li.
Li and Kaushik secured a National Institutes of Health grant for nearly $400,000 to continue this work. Both faculty members have joint appointments in the biology and microbiology and veterinary and biomedical sciences departments at South Dakota State.
Ultimately, the goal is to determine whether the virus can cause problems in humans, he explained. "If the virus can undergo reassortment in combination with a closely related human influenza virus, it may be able to form a new strain that could pose more of a threat to humans."
Identifying animal model, studying virulence
Using the bovine Influenza D strain, Sreenivasan proved that the guinea pig could be used as an animal model to study the virus. Though guinea pigs showed no symptoms, she successfully isolated antigens in tracheal and lung tissues. In addition, her research showed the virus is spread only through direct contact. Those results were published in the Journal of Virology, with Sreenivasan as the first author of the article.
Her current study uses the guinea pig model to compare virulence among bovine and swine Influenza D strains and human influenza C. She has just begun analyzing the data. Influenza D has about 50 percent similarity to human influenza C, Sreenivasan explained.
"Human C affects mostly children," she said, noting that the most common symptom is a runny nose. "It's not a serious disease. We all have some antibodies because we were infected as children."
In addition, she is developing a way to study the virus in living cells -- trachea and lung epithelial cells from swine and cattle. "I isolate the cells and allow them to grow and then infect them to study the genetic and biologic characteristics," she said.
Thus far, she's completed the swine cell cultures and will now begin work on bovine cells. Using the in vitro culturing system, Sreenivasan said, "We will see how the virus attaches and what the receptors are."
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