Abstract
Foot-and-mouth disease (FMD) is a highly contagious viral disease of all cloven hoofed
animals and is characterized by fever, formation of vesicles usually in, and around, the
mouth and on the feet. Out of seven antigenically diverse serotypes (O, A, C, Asia 1, SAT 1,
SAT 2 and SAT 3), serotype O, A and Asia 1 are endemic in ruminants in Bangladesh. FMD
in buffalo showed overt clinical signs, while it is generally subclinical in small ruminants.
The morbidity rate is usually too high but mortality is generally low. FMD causes
significant economic losses through death of young calves, reduction in milk production,
loss of draught power and loss of access to profitable international livestock and livestock
product markets. Successful prevention and control of FMD in livestock is mostly
dependent upon the early detection, detection of specific serotypes and warning systems.
This study was, therefore, aimed to investigate epidemiology and pathology of FMD,
serotyping and genomics of the viruses in Bangladesh. A total of 89 outbreaks from 16
districts (eight divisions) of Bangladesh were investigated during the period from
February, 2011 to December, 2013. Results of outbreak investigation revealed higher rate of
infectivity during post monsoon (N=29) followed by pre monsoon (N=24), winter (N=19)
and monsoon (N=17). Highest rate of infectivity was seen during Eid festival (Eid-ul-adha)
irrespective of seasons. Gross and microscopic investigation of the dead calves (N=07)
revealed myocardial necrosis and severe bronchopneumonia. FMD viral antigens were
detected in skin and heart muscle of infected dead calves using immunohistochemistry.
Out of 270 samples collected from natural outbreaks and tested in RT-PCR, FMD viruses
were identified in 220 cases. The viral serotypes confirmed were serotype O (N=139), Asia
1 (N=29) and A (N=05) from field cases. The VP1 gene of FMD viral Serotype O (N=10),
Asia 1 (N=08) and A (N=03) were sequenced, translational and phylogenetic analysis were
carried out to know the level of mutation and topotypes of the viruses involved. Highest
rate of mutation was seen in the VP1 gene of FMD viral serotype A and a total of 13
substitution of aa was seen in an isolate. Three local isolates (BD_AH_09_2012,
BD_AH_10_2013 and BD_AH_11_2011) of FMD viral serotype A showed substitution of aa
in 13, 9 and 6 points respectively. Moderate level of mutation was noted in a local isolate
(BD_AH_14_2011) of FMD viral serotype O, where substitution of five amino acids (aa)
was seen. The FMD viral serotype Asia 1 showed aa substitutions at positions 108 and 210.
The studied FMD viral serotype O (N=10) belonged to India-2001 lineage of ME-SA
topotype, Asia 1 (N=08) to Lineage C of Asia topotype and A (N=03) to Genotype VII (18)
of A topotype. Results of sequencing and translational analysis of the VP1 gene of FMD
viruses revealed intra serotypic and intratopotypic variation at nucleotide and aa level.
This study isolated a total of 12 FMD viruses in culture and made a safe repository. The
genetic and antigenic properties of the isolated viruses require further evaluation before
selecting the isolates as vaccine candidate.