Building Bovine Immunity

One of the most common diseases in animal agriculture is mastitis, an udder inflammation caused by bacterial infection. According to the U.S. Department of Agriculture, annual losses due to mastitis are estimated at more than $2 billion in the United States, and about 3 million dairy cows each year show visible signs of acute infection. Virginia Cooperative Extension calculates that the Virginia dairy industry loses $18.6 million annually to mastitis-associated costs that include treatment, loss of milk, veterinary bills, decreased milk quality, and purchase of replacement animals. Dairy scientist Isis Mullarky is taking a new approach to the mastitis problem and hopes to find some answers that may help cows and possibly humans.

The bacterium Staphylococcus aureus is one of the most common causes of mastitis in cows and, according to the Centers for Disease Control and Prevention, of skin infections in humans. In addition, methicillin (antibiotic)-resistant Staphylococcus aureus (MRSA) is responsible for many of the difficult-to-treat infections that are cropping up in hospitals and schools.

Mullarky, an assistant professor in dairy science, and her students are studying the cow’s immune system’s response to this troublesome bacterium.

During an infection, a cow’s natural immune response should kick in and eliminate the pathogen and prevent its spread, explains Mullarky. However, when a cow is infected with S. aureus, the bacteria may act to suppress the cow’s ability to fight the infection. Mullarky’s research looks at the cell-mediated and coagulatory components of the host immune response and the development of immune memory to S. aureus.

By learning more about a cow’s natural ability to fight infection, Mullarky seeks to identify new therapies and vaccines to help boost the cow’s immune response. She explains that by stimulating the natural immune response to S. aureus, the cow may be able fight the infection on its own, without the use of antibiotics. This means healthier cows, better milk quality, and more money in the dairymen’s pockets.

Mullarky’s team is currently taking two approaches to studying the immune response to S. aureus. In one study, the researchers infect bovine immune cells and evaluate the inflammatory and coagulatory responses. This approach will explain how the bacteria manipulate the cow’s immune response to cause infection and alter coagulation response to induce abscess formation.

In another study, they are evaluating the T lymphocyte response, a cell type important for development of immune memory and required for effectiveness of certain vaccines. Together, these two approaches will define the basic mechanisms of disease progression and provide targets for protection against staphylococcal infection in cows and humans.

The knowledge gained through this research will not only be beneficial for the treatment of bovine mastitis, but has human implications as well. With the number of MSRA and secondary infections on the rise, there is urgency to finding alternatives to antibiotics.

“Bovines are an excellent model for identifying alternative therapies and treatments to bacterial infections,” says Mullarky. “The bovine population, like humans, is naturally exposed to S. aureus, and certain individuals may be more resistant than others. Understanding the basis of this resistance may provide new options for disease prevention.”

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Virginia Cooperative Extension estimates that the Virginia dairy industry loses $18.6 million annually to mastitis-associated costs that include treatment, loss of milk, veterinary bills, decreased milk quality, and purchase of replacement animals.

Staphylococcus aureus (photo from the Centers of Disease Control and Prevention).