ELISA based techniques for the identification of foot-and-mouth disease virus and vaccine evaluation in Bangladesh

Epidemiology of FMD infection was studied at farm and field levels. The rate of outbreaks increases following the monsoons and remained throughout the winter (until March). Cattle were found to be more susceptible (96.43%) than buffalo (1.01%), goat (2.27%) and sheep (0.27%). Exotic and their cross-bred animals were more susceptible than local breeds of animals (69.89% and 30.11% respectively). Dynamic FMD infection was also studied at the farm level and it was found that infection was directly related with herd immunity, season of the year and climatic conditions. Outbreaks of FMD at rural area were found to be associated with the introduction of new animals from the market in a herd (75.21%) or transportation of infected animals by road or boats. A total of 956 FMD suspected samples from 257 different field outbreaks were collected during the last five years (1995-1999). At the same time, 367 convalescent sera were collected for the analysis FMD antibodies and the virus involved in infection. FMD suspected epithelial samples were tested using indirect ELISA and 875 samples (85.36%) were found positive either against O, A or Asia I. Throughout the last five years, FMD virus type O predominated (54.07%) over FMD virus types Asia I (19%), and virus type A (16.8%) and 6.48% were found to be negative. None of the epithelial samples was found positive against FMD type C. However, five convalescence sera collected from the northern part of Bangladesh showed very strong reaction (>1:240) against FMD virus type C in LPB-ELISA. Vaccination failure was found one of the major constraints towards the control of FMD using vaccine and factors like lack of potent vaccine, inadequate vaccination coverage, poor cold chain, lack of vaccine evaluation and poor health conditions played an important role in this area. Three FMD vaccine candidates were tested using LPB-ELISA both at laboratory and field conditions. Locally produced bi-valent vaccine (O and A) developed a satisfactory levels of antibody following vaccination among the adult stock, while young calves failed to develop protective levels of antibody and disease developed following natural exposure. Two imported vaccine candidates developed protective level of antibody (>1;80) following vaccination. Ring vaccination around the infected foci was conducted and both the vaccine candidates successfully protected the vaccinated herd. Sero-conversion was studied using LBP-ELISA and 90% of the cattle developed antibody higher than 1:80. Economic losses incurred due to FMD infection were also studied. A survey was conducted on 7757 animals and losses due to loss of draft power, reduced milk production and calf mortality were estimated. Of 7757 animals examined, 4750 animals (61.23%) showed the lesions of FMD infection and loss was estimated at US $0.4 million (US $21.93 per animal). Annual loss due to FMD was estimated at about US $125 million per year. In this study, cost-benefit analysis was also made with regard to the control of FMD using vaccination programme. It was found from our study, that in an average year the loss is US $5.0 per animal (US $125 million/year) due to FMD while cost for the vaccination is not more than US $1.5 per animal (US $37.5 million/year). So the control of FMD using a vaccination programme will save at least US $87.5 million per year. (author)