Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease was initially described in the 16th century and was the first animal pathogen identified as a virus. Recent FMD outbreaks in developed countries and their significant economic impact have increased the concern of governments worldwide. This review describes the reemergence of FMD in developed countries that had been disease free for many years and the effect that this has had on disease control strategies. The etiologic agent, FMD virus (FMDV), a member of the Picornaviridae family, is examined in detail at the genetic, structural, and biochemical levels and in terms of its antigenic diversity. The virus replication cycle, including virus-receptor interactions as well as unique aspects of virus translation and shutoff of host macromolecular synthesis, is discussed. This information has been the basis for the development of improved protocols to rapidly identify disease outbreaks, to differentiate vaccinated from infected animals, and to begin to identify and test novel vaccine candidates. Furthermore, this knowledge, coupled with the ability to manipulate FMDV genomes at the molecular level, has provided the framework for examination of disease pathogenesis and the development of a more complete understanding of the virus and host factors involved.

Foot-and-Mouth Disease

We report the first atomic resolution structure of an animal virus, human rhinovirus 14. It is strikingly similar to known icosahedral plant RNA viruses. Four neutralizing immunogenic regions have been identified. These, and corresponding antigenic sequences of polio and foot-and-mouth disease viruses, reside on external protrusions. A large cleft on each icosahedral face is probably the host cell receptor binding site.

Structure of a human common cold virus and functional relationship to other picornaviruses

The structure of foot-and-mouth disease virus has been determined at close to atomic resolution by X-ray diffraction without experimental phase information. The virus shows similarities with other picornaviruses but also several unique features. The canyon or pit found in other picornaviruses is absent; this has important implications for cell attachment. The most immunogenic portion of the capsid, which acts as a potent peptide vaccine, forms a disordered protrusion on the virus surface.

The three-dimensional structure of foot-and-mouth disease virus at 2.9 A resolution.

Chemically synthesized peptides corresponding to two different regions of the VP1 polypeptide of foot-and-mouth disease virus (FMDV) produced high levels of serotype-specific virus neutralizing antibody in cattle, guinea pigs and rabbits. A single inoculation of one of these peptides protected guinea pigs against subsequent challenge with the virulent virus.

Protection against foot-and-mouth disease by immunization with a chemically synthesized peptide predicted from the viral nucleotide sequence

The amino acid sequence RGD (arginine-glycine-aspartic acid) is highly conserved in the VP1 protein of foot-and-mouth disease virus (FMDV), despite being situated in the immunodominant hypervariable region between amino acids 135 and 160. RGD-containing proteins are known to be important in promoting cell attachment in several different systems, and we report here that synthetic peptides containing this sequence are able to inhibit attachment of the virus to baby hamster kidney (BHK) cells. Inhibition was dose-dependent and could be reversed on removal of the peptide. A synthetic peptide corresponding to a portion of the same hypervariable region but not containing the RGD sequence did not inhibit virus attachment under the same conditions. Antibody against the RGD region of VP1 blocked attachment of the virus to BHK cells, and neutralizing monoclonal antibodies, which neutralize virus by preventing cell attachment, were blocked by RGD-containing peptides from binding virus in an ELISA test. Cleavage of the C-terminal region of virus VP1 in situ with proteolytic enzymes reduced cell attachment, and antiserum against a peptide corresponding to this region was also able to inhibit attachment of virus to BHK cells. These results indicate that the amino acid sequence RGD at positions 145 to 147 and amino acids from the C-terminal region of VP1 (positions 203 to 213) contribute to the cell attachment site on FMDV for BHK cells.

The cell attachment site on foot-and-mouth disease virus includes the amino acid sequence RGD (arginine-glycine-aspartic acid)

Purified foot-and-mouth disease virus (FMDV) to type O1K was treated with several endopeptidases of differing specificity. The immunizing protein VPThr was cleaved into two detectable fragments by all enzymes except for glutamic acid-specific Staphylococcus aureus V8 protease. The longest fragments were generated by mouse submaxillary gland protease and the shortest by trypsin treatment of the intact virion. Several fragments, including the peptides resulting from the cyanogen bromide (CNBr) cleavage of the isolated protein VPThr were characterized in terms of their molecular weights N- and C-terminal amino acids, and ability to induce virus-specific antibodies. The order of the fragments along the protein was determined, and then located on the amino acid sequence of the protein. Two enzyme-sensitive areas of the protein were found on the surface of the virion: between sequence positions 138 and 154 and between portion 200 and the C terminus. Peptides containing these sections were able to induce neutralizing antibodies against the homologous FMDV. When the virus was treated with trypsin or with chymotrypsin, several amino acids between the detectable fragments were lost and the infectivity of the virus was reduced. The infectivity was retained, however, when the enzyme treatment resulted in cleavage of protein with no loss of amino acids or only the cutting away of the C-terminal section. These results suggest that the property of cell attachment is restricted to small regions of the surface of the virus particle.

R. Franze

Papers

Location and characterization of the antigenic portion of the FMDV immunizing protein