Abstract
Foot-and-mouth disease (FMD) in Turkey is controlled using biannual mass vaccination of cattle. However, vaccine protection is undermined by population turnover and declining immunity. A dynamic model of the Turkish cattle population was created. Assuming biannual mass vaccination with a single-dose primary course, vaccine history was calculated for the simulated population (number of doses and time since last vaccination). This was used to estimate population immunity. Six months after the last round of vaccination almost half the cattle aged <24 months remain unvaccinated. Only 50% of all cattle would have received >1 vaccine dose in their life with the last dose given ≤6 months ago. Five months after the last round of vaccination two-thirds of cattle would have low antibody titres (<70% protection threshold). Giving a two-dose primary vaccination course reduces the proportion of 6–12 month old cattle with low titres by 20–30%. Biannual mass vaccination of cattle leaves significant immunity gaps and over-reliance on vaccine protection should be avoided. Using more effective vaccines and vaccination strategies will increase population immunity, however, the extent to which FMD can be controlled by vaccination alone without effective biosecurity remains uncertain.
Highlights
Foot-and-mouth disease (FMD) in Turkey is controlled using biannual mass vaccination of cattle
Whilst foot-and-mouth disease (FMD) has been eradicated in Turkish Thrace, mass vaccination has failed to control the disease in the rest of the country (Anatolia, Fig. 1)
A single dose of a ≥ 3PD50 vaccine contains at least three times the dose required to prevent clinical FMD in 50% of cattle that have FMD virus injected into the tongue three weeks after vaccination
Summary
Foot-and-mouth disease (FMD) in Turkey is controlled using biannual mass vaccination of cattle. Assuming biannual mass vaccination with a singledose primary course, vaccine history was calculated for the simulated population (number of doses and time since last vaccination). This was used to estimate population immunity. This results in differences in the seasonality of livestock births and population age structure These demographic factors determine the proportion of cattle eligible for routine FMD vaccination (≥ 2 months old), the proportion recently vaccinated and the proportion that have received multiple doses. These proportions change with time as animals are born, age and die. To save resources, a single-dose primary course is used in many countries, including Turkey at the time of this study
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