Higher order taxa
Viruses; ssRNA positive-strand viruses, no DNA stage; Picornaviridae; Aphthovirus
Equine rhinitis A virus, Foot-and-mouth disease virus
Description and Significance
Aphthoviruses are responsible for foot-and-mouth disease (FMD) - a major economic pest worldwide. The disease is endemic in parts of Asia, Africa, the Middle East and South America. Sporadic outbreaks in other areas have also been witnessed. A pandemic of type O has been raging in many countries for the past few years. The virus is controlled largely in the European Union by vaccination or slaughter of infected animals.
Unfortunately, the inactivated vaccines presently available are not entirely effective. Vaccination blocks disease symptoms but does not always block transmission of the virus to other animals. This only makes the detection of infection more difficult. Sheep can harbor the virus for several months while cows can do the same for up to a year or even longer. Occasional vaccine-linked disease outbreaks occur as a result.
The genome of the aphthovirus is not segmented and contains a single molecule of linear positive-sense, single-stranded RNA. The complete genome is 7500 nucleotides long. The 5'-end of the genome has a genome-linked protein (VPG) held by a phosphodiester bond through tryosine. The 5'-end terminus has a poly (C) tract while the 3'-terminus has a poly (A) tract. (source: ICTV dB Descriptions)
Virion Structure of an Aphthovirus
The virions of an apthovirus consist of a non-enveloped capsid that is round with icosahedral symmetry. The isometric capsid has a diameter of 27-30 nm. The capsid appears round and consists of 12 capsomers. (source: ICTV dB Descriptions)
Reproduction Cycle of an Aphthovirus in a Host Cell
The single-step growth curve type experiments performed at high multiplicity of infection has lead to a great understanding of the Picornavirus replication process. Replication occurs entirely in the cytoplasm and can even occur in enucleated cells and is not inhibited by actinomycin D.
The virus attaches and enters into the cell via a membrane receptor. There is an assembly of virions in the cytoplasm followed by the aggregation of the new virus. Cell lysis takes place, after which the new virus is released. (source: BIORES)
Viral Ecology & Pathology
Foot and Mouth Disease (FMD) appears to have been first observed in 1514 in Italy. The US has been free of FMD since 1929. The A, O and C types of FMD virus were first isolated in Europe, but have aso been identified in South America. The SAT types are limited to the southern African teritories while the ASIA type is observed only in Asia.
The aphthovirys affects swine, sheep, goats, deer, water buffalo, and other cloven-hooved ruminants. Although the virus is widespread, 57 countries were considered FMD-free zones without vaccination by the World Organization for Animal Health (OIE), four countries were FMD-free with vaccination, eight countries had FMD_free zones without vaccination, and four countries had FMD_free zones with vaccination. The virus can persist in contaminated feed and the environment for up to one month. The virus is endemic in regions of Arica, Asia, South America and Europe. Persistence in wildlife reservoirs contributes to the difficulty in eradicating and controlling FMD. (sources: OiE and AVMA)