Abstract
Foot and mouth disease (FMD) is the most economically important disease of ruminants affecting seventy seven percent of the world's livestock population. Among all other ruminants, cattle are the most susceptible to foot and mouth disease virus and it brings significant economic loss to the farmers throughout the world. It is utmost important to contain the spread of virus and control the disease. The study was aimed to detect the duration of post infection antibody and post vaccination antibody against foot and mouth disease virus in cattle. Simultaneously, to determine the duration of maternally derived antibody in calves born to FMD vaccinated dams. To confirm natural infection, clinical samples were collected from FMD suspected cattle to detect foot and mouth disease virus (FMDV) by uniplex RT-PCR (URT-PCR) and to identify the circulating serotypes by multiplex RT-PCR (mRT-PCR). Among the 25 clinical samples; sixteen (64%) were found positive and 9 (36%) samples were found negative for FMDV by uRT-PCR. FMD positive samples were further subjected to mRT-PCR for detection of serotypes. The highest number of samples i.e. 7 samples (43.75%) was found positive for FMDV O type, followed by 5 samples (31.25%) positive for A type, and 2 samples (12.5%) positive for Asia-1 type. There were 2 cases (12.5%) of mixed infection with concurrent presence of O and Asia-1 serotypes. No isolates were found positive for FMDV C type. The antibody titers were determined by performing Liquid Phase Blocking Enzyme Linked Immunosorbent Assay (LPB-ELISA) using sera samples collected from naturally infected cattle, vaccinated cattle and from calves born to vaccinated dams. Post infection peak antibody titers were recorded on the 11 weeks post infection and after that a steep fall of antibody titer was observed for all serotypes. Nevertheless, it remained above the protective value (PI value >50) up to 21 weeks post infection (wpi). To study the duration of post vaccination antibody, noninfected cattle (n=120) were selected by performing a specialized (Differentiation of Infected from Vaccinated Animal-DIVA) ELISA and vaccinated with contemporary trivalent FMD vaccines. Post vaccination antibody determined by LPB-ELISA revealed that, the farming system (subsistence/organized) significantly (Significant at p≤0.05 and p≤0.01) affects the response of cattle to FMD vaccination. The peak rise of post vaccination antibody was detected at 3 wpv and 94.4% cattle were found seropositive (PI value more than 50%) in organized farms and 88.9% cattle were found seropositive in subsistence farms. The antibody titers remained within the protective value up to 27 weeks post vaccination in organized farms and 19 weeks post vaccination in subsistence farms under studies. The highly significant variation was observed among the effect of three types of vaccines used for immunization of cattle. The DLS (Department of Livestock Services) FMD vaccine induced significantly higher antibody titer compared to Bangla FMD vac and Aftovaxpur. Although PI values were found higher in Aftovaxpur than Bangla FMD vac, only few values were found statistically significant. The maternally derived antibody was found to persist up to the age of 22 to 23 weeks (five months) for both vaccines (DLS FMD vaccine, Aftovaxpur) and both farms (two organized farms) used in the study. Calves born to dams vaccinated with DLS FMD vaccine possessed comparatively higher antibody titer than calves born to dams vaccinated with Aftovaxpur at the same age level. From these findings about the duration of post infection antibody, post vaccination antibody and maternal antibody; it could be concluded that by practicing vaccination regularly using locally produced vaccines in cattle can limit the spread of disease and contribute to the control of FMD infection in Bangladesh.