African swine fever: The threat posed by this viral disease
may sound remote, given its African origin and its health threat limited to domestic pigs. Nevertheless, ASF is near the top of the list of animal diseases that global agricultural organizations are seeking to prevent or control.
In domestic pigs, ASF is highly contagious and nearly always fatal—and there is no vaccine to prevent it. Like the Ebola virus in humans, ASF causes acute hemorrhage of internal organs along with high fever in swine.
An outbreak of ASF has a devastating impact not only on the swine industry but also on the international trade, overall economy, and even political stability of any country the disease hits. Although the virus has never been in the United States, there is a continuing epidemic in Russia, and the danger that the disease could spread to Western Europe and beyond is very real.
Because there is no vaccine, an outbreak would likely require widespread extermination of the pig population to limit the spread of the disease.
Dr. Daniel Rock, a professor at the University of Illinois College of Veterinary Medicine, conducts research that could provide a breakthrough in the search for an ASF vaccine.
“African swine fever is endemic in Africa, where a vaccine would bring tremendous relief,” says Dr. Rock. “For the United States and Western Europe, a vaccine would provide a tool for controlling the disease if it is introduced.”
Vaccine and disease control progress is hindered by lack of knowledge concerning the strain diversity in ASF and the antigens responsible for inducing protective immunity against ASF.
“To create a vaccine, there are two main things we need to know,” explains Dr. Rock. “We need to know how many strains there are of this virus and we need to know the viral proteins that produce a protective response to the virus in the pig.”
According to Dr. Rock, the ASF virus is very complicated and has more than 160 genes encoding many proteins. Dr. Rock’s laboratory is trying to identify which viral proteins could be used to make an effective vaccine.
Strains of the ASF virus can be categorized by serological groups based on antigenic properties. Research with ASF vaccines has shown that protective immunity extends to all viral strains in the same serological group. Recently, Rock’s laboratory and collaborators at the University of Connecticut–Storrs, the University of Nebraska-Lincoln, and the Institute for Veterinary Virology and Microbiology, Russian Federation identified two membrane proteins of the ASF virus—called CD2v and C-type lectin—that are responsible for serologic specificity. These research results were recently published in the Journal of General Virology.
“We found that the ASF virus membrane proteins CD2v and C-type lectin were both necessary for specificity of the virus. They can be used by researchers to differentiate among strains of the virus, a much simpler method of identification than was previously possible with ASF,” says Dr. Rock.
“Now that we have this information, these proteins are strong candidates for being protective antigens for ASF, and bring us one step closer to design of a vaccine.”
By Melissa Giese