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United States Department of Agriculture

Agricultural Research Service

Healthy Animals 46

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Issue 46, July 2011
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Developing Vaccines to Combat Diseases in Animals

A healthy pig rests its snout on the back of another pig.

Research Briefs

Honey Bee Loss Levels Out. A recent survey shows that total losses from managed honey bee colonies nationwide are similar to total losses reported in surveys conducted in the four previous years.

E. coli-Cattle Feed Connection. Scientists are investigating the relation between the use of wet distiller's grains with solubles in feed and the incidence and persistence of Escherichia coli O157:H7 in cattle manure and on the animals' hides.

Let Poultry Eat Yeast. A dietary yeast extract could be an effective alternative to antibiotics for poultry producers.

Livestock Numbers by Weather. A new computer model could allow ranchers to test various scenarios involving forage yields and the weight gains of beef cattle and other livestock under various stocking and weather scenarios.

Forage Grass Rediscovered. Meadow fescue, a forage grass that's very winter-hardy and persistent, may be just right for today's intensive rotational grazing.

The old adage "an ounce of prevention is worth a pound of cure" may hold true for animals as well as humans, especially when it comes to using vaccines that help control and prevent the spread of disease.

Vaccinating animals can help improve the overall health of livestock and reduce high costs involved in treatment. However, some vaccines don't work very well or lose efficacy over a period of time. New vaccines are sorely needed.

Agricultural Research Service (ARS) scientists are addressing these issues by developing more effective vaccines to combat troublesome diseases such as anaplasmosis in cattle and Newcastle disease in poultry.

A New Vaccine to Fight Newcastle Disease

Newcastle disease (ND), which can be deadly for domestic and commercial poultry as well as wild bird populations, is a major concern worldwide for the poultry industry. Newcastle disease virus (NDV), which typically affects the respiratory, gastrointestinal and/or nervous system, causes disease in more than 250 species of birds.

Symptoms of ND can include coughing, gasping, diarrhea, lack of appetite and drooping wings. Severe cases can result in mortality rates that exceed 90 percent in susceptible chickens. To complicate matters, a quick diagnosis of an ND outbreak may be difficult because it can be confused with a clinically similar disease—avian influenza.

Commercial poultry producers now use vaccines that protect vaccinated birds from disease, but these vaccines do not prevent poultry from becoming infected and carrying virulent NDV or shedding it in their feces. Infected birds can still spread the disease to healthy, unvaccinated birds.

ARS scientists at the agency's Southeast Poultry Research Laboratory in Athens, Ga., have developed a new vaccine that reduces mortality and severity of ND symptoms in poultry. The vaccine also decreases the amount of virulent virus shed from birds.

Microbiologist examining recombinant Newcastle disease virus vaccine candidates in infected cells.
Microbiologist Qingzhong Yu examines recombinant Newcastle disease virus vaccine candidates in infected cells.

Microbiologist Qingzhong Yu in the ARS Endemic Poultry Viral Disease Research Unit and his colleagues in the ARS Exotic and Emerging Avian Viral Diseases Research Unit used reverse genetics technology to create a new vaccine that replaces a gene in the vaccine with a similar gene from the virulent NDV circulating in the environment today.

"Currently, most vaccines used in the United States are formulated with NDV isolated in the 1940s, which is similar to the virulent NDV circulating at that time," Yu says. "Unfortunately, with time, new NDV strains have emerged that are genetically very different from commonly used vaccine strains.

"We found that when the new vaccine, which contains gene sequences similar to the virulent virus, was used in vaccination studies, the vaccinated birds were protected from disease and shed less of the virulent virus after challenge," Yu says.

Vaccines have been used for more than 50 years to control ND and are successful in reducing mortality and the severity of symptoms, Yu says. However, ND continues to threaten the commercial poultry industry.

The most recent U.S. outbreak in 2002-2003 affected poultry in several states: Arizona, California, Nevada and Texas. The industry suffered a devastating blow when more than 3.4 million birds had to be destroyed. California alone spent more than $160 million to control the outbreak.

The new vaccine protects birds from ND and reduces virus shedding, which will ultimately decrease the spread of the virulent virus.

Progress Made on Potential Anaplasmosis Vaccine

Chickens
The new vaccine for Newcastle disease reduces mortality and severity of symptoms in poultry, and decreases the amount of virus spread in poultry.

Research is under way at the ARS Animal Disease Research Unit in Pullman, Wash., to develop a vaccine that protects cattle against anaplasmosis, a tick-transmitted disease that threatens the health, wellbeing and production of cattle in many parts of the world.

At this time, there is no widely accepted vaccine for anaplasmosis. The disease, which is caused by the microbe Anaplasma marginale, can result in severe anemia, fever, weight loss and death in cattle.

ARS molecular biologist Susan Noh collaborated with scientists at Washington State University to identify significant proteins to include in a potential vaccine that is being tested on animals. They found that small groups of the outer surface proteins of A. marginale induce an immune response that reduces symptoms and also prevents A. marginale infection in some animals.

Among the vaccines being tested, some of those with the most potential have protected 80 to 90 percent of the animals from clinical disease and have prevented infection in up to 40 percent of the animals, Noh says.

"This is significant because infected animals may have no clinical evidence of infection, yet serve as sources of infection for others," Noh says. "No vaccine has ever prevented infection from A. marginale in cattle."

In other countries, an attenuated (weakened) strain (A. centrale) has been used as a vaccine that protects against clinical disease, but not infection, Noh says. Attenuated vaccines are prepared from live microorganisms or viruses that are cultured in the lab in such a way that they lose their virulence, but still confer disease immunity.

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So far, scientists have only tested the vaccine against one strain of Anaplasma, whereas many strains coexist in the field. Their next step is to determine whether this particular group of proteins will protect cattle from various strains of Anaplasma.

This research is part of ARS National Program Number 103, Animal Health.


About This Newsletter

ARS Animal Health Research Laboratories

Healthy Animals Archive

Last Modified: 7/13/2011
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