Molecular epidemiology of Foot and Mouth Disease virus (FMD) in Southern Africa.by station k b
Molecular epidemiology of Foot and Mouth Disease virus (FMD) in Southern Africa.
Foot-and-mouth disease virus (FMDV) is the causative agent of a highly contagious and economically devastating disease of cloven-hooved domestic and wild animals. It can cause a high number of deaths among young animals and production losses in adults and is the single most limiting constraint to international trade of live animals and animal products. It is indeed a contagious viral disease of sheep, cattle, pigs, and wild ruminants. The disease causes a high rate of morbidity in multiple species, and is ...view middle of the document...
FMDV SAT 1 was first isolated in Ethiopia . FMDV belongs to the genus Aphthovirus in the family Picornaviridae and possesses a single strand of positive-sense RNA genome. It has a high mutation rate because the viral RNA–dependent RNA polymerase lacks proofreading ability, resulting in 7 immunogenically distinct serotypes (O, A, C, Southern African Territories [SAT] 1, SAT 2, SAT 3, and Asia 1) and numerous and constantly evolving variants showing a spectrum of antigenic diversity. Vaccination is an effective way to control FMD; however, the protection conferred by vaccination or infection is usually serotype specific and sometimes incomplete within a serotype.
FMDV has a genome consisting of a single strand of positive-sense RNA. Consequently, the virus has a high mutation rate and may change, on a random basis, 1–8 nucleotides (nt) per replication cycle. Nucleotide sequencing of part or all of the genome region coding for the outer capsid polypeptide VP1 was first used to study the epidemiology of FMD by Beck and Strohmaier , who investigated the origin of outbreaks of types O and A in Europe over a 20-year period. Since then, genetic variability has been used to individually characterize strains of FMDV and track their movement across international borders, and a large number of epidemiologic studies have been published. Previously, on the basis of comparisons of partial VP1 sequences (≈170 nt at the 3´ end of the gene) of FMD type O viruses, differences between 2 isolates within 4% have been suggested to indicate a recent common origin, whereas differences of >15% signify geographic isolation over many years, similar to the distinctions made between human polioviruses. Isolates with >85% nt sequence identity have been placed within groups or topotypes, which tend to be restricted in their geographic distribution. The 10 topotypes have been named Europe-South America (Euro-SA), Middle East–South Asia (ME-SA), Southeast Asia (SEA), Cathay (CHY), West Africa (WA), East Africa 1 (EA-1), East Africa 2 (EA-2), East Africa 3 (EA-3), Indonesia-1 (ISA-1), and Indonesia-2 (ISA-2). The Indonesian topotypes, which have not been identified since 1983, are considered extinct. (Alfred et al, 2002).
FMD is endemic to sub-Saharan Africa; widespread outbreaks of clinical disease occur during most years. Of the 7 serotypes, 6 have reportedly occurred on the African continent, and disease control becomes more complicated because of marked regional differences in the distribution and prevalence of various serotypes and intratypic variants .FMD remains largely uncontrolled in southern Africa because vaccination for prophylactic purpose is not being practiced except for a few dairy herds containing exotic animals. With no control and preventive measures in place, FMD causes substantial economic loss to farmers and to the nation from embargoes of livestock and livestock product trade . To initiate control measures for FMD, the following must...