O/IND/R2/75 vaccine strain was received from the virus seed laboratory, IIL, Hyderabad. O/HAS/34/05 virus was used for experimental infection of buffalo. O/HAS/34/05 virus is homologous to O/IND/R2/75 (r1 value > 1.00) [11]; and was

isolated from epithelial tissue of a suspected FMD case in a non-vaccinated buffalo from Sirsa District, Haryana U0126 State. Challenge virus O/HAS/34/05 was prepared by passaging in the tongues of buffalo calves as described for cattle by Nagendrakumar et al. [12]. Briefly, one buffalo calf was inoculated intradermolingually with BHK 21 monolayer adapted O/HAS/34/05 virus (105 TCID50). The tongue epithelium was collected 48 h post inoculation. For a second passage, epithelial tissue was collected from vesicles SP600125 nmr and after trituration in 0.04 M phosphate buffer followed by centrifugation at 3000 rpm; the clear supernatant was used

to inoculate (intradermolingually) the 2nd buffalo. The same procedure was followed for third buffalo passage. Then the tongue epithelium was collected from third passage buffalo and 20% W/V virus suspension was prepared. To make the glycerol stock 50% of sterile glycerol was added to the virus suspension and stored at −20 °C. The virus was then titrated in buffalo calves to establish the buffalo infective dose 50 values (BID50). Murrah male buffalo calves (n = 24; 6–12 months of age) and crossbred male cattle calves (n = 12; 6–12 months of age) were obtained from the holding farm PDK4 of IIL, Hyderabad. These animals were reared in the farm from one month of age and were screened by 3 rounds of testing for FMDV-non-structural protein (NSP) antibodies using PrioCHECK® FMDV NS kit (Prionics Lelystad B.V., The Netherlands)

and structural antibodies [13]. All the animals were negative against both NSP and structural antibodies in all the three rounds of testing. In addition, the animals were tested for the absence of virus in the oesophago-pharyngeal fluids (Probang samples) by inoculation of primary bovine thyroid cells [14] followed by antigen ELISA [15] and RT-PCR [16]. Monovalent FMD vaccine incorporating O/IND/R2/75 (7 μg/dose) FMDV inactivated antigen was formulated with Montanide ISA 206 (Seppic, France) as a water-in-oil-in-water (W/O/W) emulsion. One group of buffalo calves (GrI; n = 6) and a second group of cattle calves (GrII; n = 6) were administered with 2.0 ml of formulated vaccine by intra-muscular route whereas a third and a fourth group of buffalo (GrIII; n = 6) and cattle (GrIV; n = 6) calves remained unvaccinated. Donor buffalo (n = 12) were inoculated with 105 BID50 of buffalo passaged O/HAS/34/05 FMDV by the intradermolingual route at 24 h before contact challenge.