USDA Scientists Discover How Foot-and-Mouth Disease Virus Begins Infection in Cattle

ARS researchers have identified epithelial cells in the cow’s throat as the primary site where the foot-and-mouth disease (FMD) virus initiates infection in cattle. FMD is considered the most economically devastating livestock disease in the world.

WASHINGTON—U.S. Department of Agriculture (USDA) scientists have identified the primary site where the virus that causes foot-and-mouth disease (FMD) begins infection in cattle. This discovery could lead to development of new vaccines to control and potentially eradicate FMD, a highly contagious and sometimes fatal viral disease of cloven-hoofed animals that is considered the most economically devastating livestock disease in the world.

The discovery was made by scientists with the Agricultural Research Service (ARS) Foreign Animal Disease Research Unit at the Plum Island Animal Disease Center at Orient Point, N.Y. ARS is USDA’s principal intramural scientific research agency, and this research supports the USDA priority of promoting international food security.

Veterinary medical officer Jonathan Arzt, research leader LuisRodriguez and microbiologist Juan Pacheco found that after just six hours of exposure to the FMD virus through the cow’s nasal passages, the virus selectively infects epithelial cells in the nasopharynx, a specific region of the back of the cow’s throat.

“Because we have determined the actual route the FMD virus takes in infected cattle, we can now begin to target the virus-host interaction in an effort to develop better vaccines and biotherapeutic countermeasures against the disease,” Arzt said.

Although the United States has not had an FMD outbreak since 1929, the disease is still considered a serious threat. Epidemics in other countries have resulted in the slaughter of millions of infected and uninfected animals to prevent the virus from spreading. Outbreaks of this disease in previously FMD-free countries could cause billions of dollars in economic losses related to eradication efforts and trade bans.

Vaccines that offer temporary immunity for livestock have been developed, but there is no universal FMD vaccine against the disease. Because there are seven different types of FMD viruses and more than 60 subtypes, vaccines must be highly specific, matched to the type and subtype present in the area of an outbreak, to protect animals against developing clinical signs of disease. Blocking the initial site of infection may be the most effective way to achieve complete protection.

The research was published in the November issue of Veterinary Pathology and featured on the cover of that issue.

The findings have allowed Arzt and his colleagues to answer some basic, yet long-standing mysteries regarding how the FMD virus first invades and propagates in susceptible cattle. The scientists now are conducting further research to answer questions about why the particular epithelial cells are susceptible, and how the initial infection site can be blocked.

“The answers to these questions will result in a new era of FMD prevention in which highly effective vaccines will provide rapid and long-lasting immunity to even the most virulent strains of FMD virus,” Arzt said.

Research Leads to Fewer Yellowjackets on Christmas Trees

ARS entomologist Robert Hollingsworth and colleagues like Washington State University plant pathologist Gary Chastagner (shown here) have been testing how effective current methods are at keeping yellow jackets from hitching a ride on Christmas trees being shipped to Hawaii.

Hawaiians can now worry less about finding stray yellowjackets living in their Christmas trees shipped from the mainland United States, partly due to research by a U.S. Department of Agriculture (USDA) scientist and his university and state cooperators.

Every year, fir trees from the Pacific Northwest are shipped to Hawaii for use as Christmas trees. Although yellowjackets usually nest in the ground, mated queens who haven’t yet built their nests sometimes make fir trees their home during winter. So, when the trees are harvested in November for shipment to Hawaii, the yellowjacket queens get rounded up right along with them.

The western yellowjacket, Vespula pensylvanica, is considered an invasive insect in Hawaii, competing with native birds for insect prey and greatly reducing native insect populations. In an effort to keep more yellowjackets from reaching the islands, Hawaii officials required a percentage of trees to be either manually or mechanically shaken to dislodge insect pests. But there is no precise specification for how long the trees should be shaken, which makes a big difference in whether insects remain on trees.

Entomologist Robert Hollingsworth, who works for USDA’sAgricultural Research Service (ARS), teamed with university and state collaborators to examine the efficacy of the tree-shaking program and found that both methods failed to remove all yellowjacket queens from the trees, although mechanical shaking was significantly more effective than manual shaking. Hollingsworth is based at the ARS Pacific Basin Agricultural Research Center in Hilo, Hawaii. ARS is USDA’s principal intramural scientific research agency.

The scientists also tested pre-harvest insecticide sprays as a supplement to the shaking treatment. They found mist applications of an insecticide in the pyrethroid chemical class were 100 percent effective in killing yellowjacket queens, and remained effective even after heavy rainfall. Details of the study were published in the Journal of Economic Entomology.

Hawaii officials now require all fir trees destined for the islands to be shaken, regardless of shaking method. Future research plans include making shaking treatments more effective in the absence of an insecticide treatment.

Tactics to Safeguard Catfish and Tilapia Fillets from Foodborne Pathogens Explored

ARS food microbiologist Kathleen Rajkowski is investigating ways to keep America’s most popular fish fillets, catfish and tilapia, safe from foodborne pathogens.

On a chilly winter night, quick and easy-to-prepare broiled catfish or tilapia fillets—seasoned with ginger and garlic—might make a tasty and satisfying choice for your evening meal. U.S. Department of Agriculture(USDA) food microbiologist Kathleen Rajkowski works with these popular fillets in studies designed to prevent certain pathogenic microbes from contaminating them.

Foodborne illnesses are not commonly associated with either catfish or tilapia fillets. However, these fish products are the focus of the research because they are the two most widely consumed kinds of fish fillets in the United States, according to Rajkowski. She’s with the Agricultural Research Service (ARS), USDA’s principal intramural scientific research agency, and her research findings were reported in the October 2010 issue of Agricultural Research magazine.

Microbes that Rajkowski investigates include Listeria monocytogenesSalmonellaShigellaStaphylococcus, and Escherichia coli O157:H7, all of which can cause gastrointestinal illness in humans.

In an early experiment with both frozen and thawed tilapia and catfish, Rajkowski artificially inoculated fillets with L. monocytogenes, then determined the amount of ionizing radiation needed to reduce the pathogen’s population by 90 percent. The dosages needed to achieve that level of safety were nearly the same for both kinds of fish, Rajkowski found. Published in the Journal of Food Protection in 2008, the study was the first to identify the dosages that effectively reduce Listeria in these popular fish products. Her results were similar to those that reduce Listeria in ground beef.

Other tests examine the effectiveness of ultraviolet (UV) light in combating foodborne pathogens. Rajkowski’s current UV experiments build upon a study published in Ice World Journal in 2007. In that investigation, she applied a solution of Shigella sonneito the surface of frozen and fresh tilapia, then exposed the samples to medium-intensity UV light. The treatment resulted in a 99 percent reduction of the pathogen on the frozen fillets, but did not kill S. sonnei on the fresh tilapia. However, exposing the fresh fillets to pulsating beams of high-intensity UV light reduced the pathogen by 99 percent.

Rajkowski is based at the ARS Eastern Regional Research Center in Wyndmoor, Pa. Her research supports the USDA priority of ensuring food safety.