Transmission characteristics and optimal diagnostic samples to detect an FMDV infection in vaccinated and non-vaccinated sheep

- R0 of transmission of FMDV Asia-1 in non-vaccinated sheep is 1.14.
- Rv of transmission of FMDV Asia-1 in vaccinated sheep is significantly <1.
- Viral excretion of FMDV infected sheep is long, but contact transmission occurs mainly in the first week after infection.
- Mouth swabs used for virus detection are the best samples for detection of an FMDV infection in sheep.

We wanted to quantify transmission of FMDV Asia-1 in sheep and to evaluate which samples would be optimal for detection of an FMDV infection in sheep.For this, we used 6 groups of 4 non-vaccinated and 6 groups of 4 vaccinated sheep. In each group 2 sheep were inoculated and contact exposed to 2 pen-mates. Viral excretion was detected for a long period (>21 days post-inoculation, dpi). Transmission of FMDV occurred in the non-vaccinated groups (R0 = 1.14) but only in the first week after infection, when virus shedding was highest. In the vaccinated groups no transmission occurred (Rv < 1, p = 0.013). The viral excretion of the vaccinated sheep and the viral load in their pens was significantly lower than that of the non-vaccinated sheep.FMDV could be detected in plasma samples from 12 of 17 infected non-vaccinated sheep, for an average of 2.1 days, but in none of the 10 infected vaccinated sheep. In contrast, FMDV could readily be isolated from mouth swab samples from both non-vaccinated and vaccinated infected sheep starting at 1-3 dpi and in 16 of 27 infected sheep up till 21 dpi. Serologically, after 3-4 weeks, all but one of the infected sheep were detected using the NS-ELISA. We conclude that vaccination of a sheep population would likely stop an epidemic of FMDV and that the use of mouth swab samples would be a good alternative (instead of using vesicular lesions or blood samples) to detect an FMD infection in a sheep population both early and prolonged after infection.