Orsel K, de Jong M C M, Bouma A, Stegeman J A, Dekker A
Faculty of Veterinary Medicine, Department of Farm Animal Health, Utrecht University, P.O. Box 80.151, 3508 TD Utrecht, The Netherlands.
Vaccine. 2007 Aug 21;25(34):6381-91. doi: 10.1016/j.vaccine.2007.06.010. Epub 2007 Jun 28.
The aim of this study was to design a transmission experiment that enabled quantification of the effectiveness of vaccination against foot and mouth disease (FMD) virus in groups of pigs. Previous experiments showed that intradermal injection of pigs with FMD virus 14 days after vaccination was not suitable to start an infection chain, as inoculated vaccinated pigs resisted challenge. Therefore, we carried out two experiments in which we used direct contact to a non-vaccinated pig as route of infection. In the first experiment only the vaccine effect on susceptibility was quantified by exposing pigs, either vaccinated 14 days before or not vaccinated, each to a non-vaccinated seeder pig inoculated with FMD virus O/NET/2001. Since no significant differences were observed between contact infections in vaccinated or non-vaccinated pigs, we performed a second experiment in which both susceptibility and infectivity were subject to vaccination. We quantified virus transmission in homogenous groups of vaccinated or non-vaccinated pigs in which the infection chain was started by exposure to a third group of non-vaccinated infected pigs. Transmission occurred to all contact-exposed pigs in the non-vaccinated groups and to 9 out of 10 contact-exposed pigs in the vaccinated groups. The rate of transmission (beta) was significantly reduced in the vaccine group. Yet, the estimated reproduction ratio in both groups was still above 1. In conclusion, by adjusting our transmission study design and challenge method, we were able to quantify transmission of FMDV among vaccinated pigs. According to this study a single vaccination was not sufficient to stop pig to pig virus transmission. With these results major outbreaks may still be expected, even in groups of vaccinated pigs.
本研究的目的是设计一种传播实验，以量化猪群中口蹄疫（FMD）病毒疫苗接种的有效性。先前的实验表明，在接种疫苗14天后对猪进行皮内注射FMD病毒不适于引发感染链，因为接种疫苗的猪能够抵抗攻击。因此，我们进行了两项实验，其中我们将与未接种疫苗的猪直接接触作为感染途径。在第一个实验中，通过将在14天前接种疫苗或未接种疫苗的猪分别暴露于接种了FMD病毒O/NET/2001的未接种疫苗的接种源猪，仅对疫苗对易感性的影响进行了量化。由于在接种疫苗的猪和未接种疫苗的猪的接触感染之间未观察到显著差异，我们进行了第二个实验，其中易感性和传染性均受疫苗接种的影响。我们在接种疫苗或未接种疫苗的猪的同质组中量化了病毒传播，其中感染链是通过暴露于第三组未接种疫苗的感染猪而开始的。在未接种疫苗的组中，所有接触暴露的猪都发生了传播，在接种疫苗的组中，10头接触暴露的猪中有9头发病。疫苗组的传播率（β）显著降低。然而，两组的估计繁殖率仍高于1。总之，通过调整我们的传播研究设计和攻击方法，我们能够量化FMDV在接种疫苗的猪之间的传播。根据这项研究，单次接种不足以阻止猪与猪之间的病毒传播。即使在接种疫苗的猪群中，仍可能预期会发生重大疫情。
