Publications

Despite the universal importance of vaccines, approaches to human and veterinary vaccine evaluation differ markedly. For human vaccines, vaccine efficacy is the proportion of vaccinated individuals protected by the vaccine against a defined outcome under ideal conditions, whereas for veterinary vaccines the term is used for a range of measures of vaccine protection. The evaluation of vaccine effectiveness, vaccine protection assessed under routine programme conditions, is largely limited to human vaccines. Challenge studies under controlled conditions and sero-conversion studies are widely used when evaluating veterinary vaccines, whereas human vaccines are generally evaluated in terms of protection against natural challenge assessed in trials or post-marketing observational studies. Although challenge studies provide a standardized platform on which to compare different vaccines, they do not capture the variation that occurs under field conditions. Field studies of vaccine effectiveness are needed to assess the performance of a vaccination programme. However, if vaccination is performed without central co-ordination, as is often the case for veterinary vaccines, evaluation will be limited. This paper reviews approaches to veterinary vaccine evaluation in comparison to evaluation methods used for human vaccines. Foot-and-mouth disease has been used to illustrate the veterinary approach. Recommendations are made for standardization of terminology and for rigorous evaluation of veterinary vaccines.

In the past decade, two pathogens transmitted by Culicoides biting midges (Diptera: Ceratopogonidae), bluetongue virus and Schmallenberg virus, have caused serious economic losses to the European livestock industry, most notably affecting sheep and cattle. These outbreaks of arboviral disease have highlighted large knowledge gaps on the biology and ecology of indigenous Culicoides species. With these research gaps in mind, and as a means of assessing what potential disease outbreaks to expect in the future, an international workshop was held in May 2013 at Wageningen University, The Netherlands. It brought together research groups from Belgium, France, Germany, Spain, Switzerland, United Kingdom and The Netherlands, with diverse backgrounds in vector ecology, epidemiology, entomology, virology, animal health, modelling, and genetics. Here, we report on the key findings of this workshop.

Nairobi sheep disease virus (NSDV) of the genus Nairovirus causes a haemorrhagic gastroenteritis in sheep and goats with mortality up to 90%; the virus is found in East and Central Africa, and in India, where the virus is called Ganjam virus. NSDV is closely related to the human pathogen Crimean-Congo haemorrhagic fever virus, which also causes a haemorrhagic disease. As with other nairoviruses, replication of NSDV takes place in the cytoplasm and the new virus particles bud into the Golgi apparatus; however, the effect of viral replication on cellular compartments has not been studied extensively. We have found that the overall structure of the endoplasmic reticulum (ER), the ER-Golgi intermediate compartment and the Golgi were unaffected by infection with NSDV. However, we observed that NSDV infection led to the loss of protein disulphide isomerase (PDI), an oxidoreductase present in the lumen of the endoplasmic reticulum (ER) and which assists during protein folding, from the ER. Further investigation showed that NSDV-infected cells have high levels of PDI at their surface, and PDI is also secreted into the culture medium of infected cells. Another chaperone from the PDI family, ERp57, was found to be similarly affected. Analysis of infected cells and expression of individual viral glycoproteins indicated that the NSDV PreGn glycoprotein is involved in redistribution of these soluble ER oxidoreductases. It has been suggested that extracellular PDI can activate integrins and tissue factor, which are involved respectively in pro-inflammatory responses and disseminated intravascular coagulation, both of which manifest in many viral haemorrhagic fevers. The discovery of enhanced PDI secretion from NSDV-infected cells may be an important finding for understanding the mechanisms underlying the pathogenicity of haemorrhagic nairoviruses.

Deciphering the evolutionary processes driving nucleotide variation in multiallelic genes is limited by the number of genetic systems in which such genes occur. The complementary sex determiner (csd) gene in the honey bee Apis mellifera is an informative example for studying allelic diversity and the underlying evolutionary forces in a well-described model of balancing selection. Acting as the primary signal of sex determination, diploid individuals heterozygous for csd develop into females, whereas csd homozygotes are diploid males that have zero fitness. Examining 77 of the functional heterozygous csd allele pairs, we established a combinatorical criteria that provide insights into the minimum number of amino acid differences among those pairs. Given a data set of 244 csd sequences, we show that the total number of csd alleles found in A. mellifera ranges from 53 (locally) to 87 (worldwide), which is much higher than was previously reported (20). Using a coupon-collector model, we extrapolate the presence of in total 116-145 csd alleles worldwide. The hypervariable region (HVR) is of particular importance in determining csd allele specificity, and we provide for this region evidence of high evolutionary rate for length differences exceeding those of microsatellites. The proportion of amino acids driven by positive selection and the rate of nonsynonymous substitutions in the HVR-flanking regions reach values close to 1 but differ with respect to the HVR length. Using a model of csd coalescence, we identified the high originating rate of csd specificities as a major evolutionary force, leading to an origin of a novel csd allele every 400,000 years. The csd polymorphism frequencies in natural populations indicate an excess of new mutations, whereas signs of ancestral transspecies polymorphism can still be detected. This study provides a comprehensive view of the enormous diversity and the evolutionary forces shaping a multiallelic gene.