Since 1954, scientists with USDA’s Agricultural Research Service (ARS) have conducted research at Plum Island, N.Y., to prevent and control foreign animal diseases that threaten U.S. livestock production and food security. A new article from ARS outlines progress, particularly in defending against foot-and-mouth disease (FMD).
In 2010, ARS scientists discovered that the FMD virus selectively infects epithelial cells in the back of the cow’s throat. There are seven FMD virus serotypes — O, A, C, Asia-1, SAT-1, SAT-2 and SAT-3. Scientists detected the infection site using serotype O and have since had the same success with serotype A. They believe understanding of the actual route of infection can aid in the development of new vaccines and, potentially, treatments to control the disease. “Blocking the initial site of infection is the best way to achieve complete protection,” says ARS veterinary medical offi cer Jonathan Arzt.
Researchers at Plum Island also have found that interferons, which are proteins made and released by host cells in response to the presence of viruses or other pathogens, act as antiviral agents that kill the virus or stop it from multiplying and reproducing. Vaccines, they note, typically take about seven days to stimulate a protective immune response and protection against FMD, and the scientists believe interferons, administered with vaccines, could provide early protection during an outbreak. They found that by inoculating swine with a viral vector containing the gene coding for swine type-l interferon, they can protect the animals from FMD within one day, with the window of protection from the interferon lasting about five days. That falls two days short of the seven needed for the vaccine response, so the researchers found that combining type-l and type-ll interferons with a vaccine would provide protection until the vaccine immune response developed.
That approach works in swine but not in cattle. However, the Plum Island team was the fi rst to report and identify a type-III interferon in cattle, and to demonstrate that type-III interferon is effective against FMD virus in cattle as early as one day after vaccination. The scientists inoculated cattle with a viral vector that delivered bovine type-III interferon and challenged with FMD virus 24 hours later. “We saw a significant delay in the appearance of clinical signs in animals that received type-III interferon as compared to those given type-I interferon or no treatment,” says microbiologist Teresa de los Santos. “In other experiments, where cows were naturally exposed to FMD virus, the type-III interferon treatment was even more protective.”
In other research, a team led by microbiologist Elizabeth Rieder cloned the FMD virus genetic material in a plasmid, allowing it to alter the virus. They discovered a sequence that, if removed, renders the FMD virus harmless to animals while leaving it capable of growing in cell culture, and have used the technology to produce a new FMD vaccine. Production of this vaccine is safer than conventional methods, since the attenuated FMD virus doesn’t cause disease in animals. Also, scientists have labeled the virus used in the vaccine with unique markers to differentiate it from wild-type virus, which would allow differentiation between vaccinated cattle and those exposed to the disease in an outbreak. The group has filed for a patent on the technology, which is being developed for vaccine production by a private company.