Use of the scan statistic on disaggregated province-based data: foot-and-mouth disease in Iran

The spatial scan statistic was applied to density-smoothed data that approximated the spatial distribution within the area and reduced the potential bias produced when location data have been aggregated for large areas. The method is illustrated, using data on the location of foot-and-mouth disease (FMD) outbreaks in Iran. Data examined were 4477 FMD outbreaks reported on a per province basis between June 1996 and September 2003. A kernel density of the outbreak locations was estimated, using a fixed radius and the centroid of each province as the designated location of all cases reported for the province. The radius that produced a density map with the highest correlation with expert opinion was 4° (latitude/longitude). Livestock density was used as a proxy for the underlying population at risk of acquiring FMD. Livestock and outbreak density maps were overlain to obtain the number of outbreaks and livestock in each of 15,599 cells covering the mapped surface of the country. A spatial scan statistic was applied to the density-smoothed data assuming that the outbreaks had a Poisson distribution. Results were compared with those obtained using a spatial scan statistic on provincially aggregated data. Application of the spatial scan statistic on the density-smoothed data allowed identification of clusters (P < 0.01) related more to the actual geographic distribution of cases (expert opinion) and of animals at risk, than to the distribution of the provinces. Significant clusters of FMD were identified that coincided with roads, neighboring countries, and high-density population areas, suggesting that the region may represent a route for cross-continent transmission of FMD.     

口蹄疫病毒VP1基因的克隆及结构蛋白VP1的原核表达

根据Genbank中的O型口蹄疫病毒全基因序列设计了一对扩增口蹄疫病毒VP1基因的引物，用该特异性表达引物从口蹄疫阳性质粒pMD—P1中扩增得到目的基因VP1（639bp）。用相同的限制性内切酶酶切目的基因和表达载体PET32a后构建重组表达载体．转化宿主菌BL21（DE3），经酶切及PCR鉴定筛选出阳性克隆．测序证明目的基因正确插入了表达载体，用不同浓度的IPTG诱导VP1基因的表达，收集菌液进行SDS—PAGE电泳，Westerll—blotting分析蛋白免疫原性。结果表明，VP1结构蛋白在大肠杆菌中表达量较高，表达产物的分子量约为41Ku，并能被口蹄疫阳性血清所识别，经分析表达蛋白约占菌体蛋白的34％。口蹄疫病毒VP1蛋白在大肠杆菌中高效表达且表达产物具有免疫原性。     

The duration of the foot-and-mouth disease virus carrier state in African buffalo (i) in the individual animal and (ii) in a free-living herd

The maintenance of a virus depends on a number of factors, including the duration of infectivity and the size of the available host population. In this work, foot-and-mouth disease virus was shown to persist in individual African buffalo (Syncerus caffer) for up to at least five years; thus, the duration of infectivity is more than adequate to cover the normal periods between calving peaks. In a small isolated free-living population which varied from 30 to 100 buffalo, two immunological types of foot-and-mouth disease virus were maintained for at least 24 years and through several generations.     

Assessment using ELISA of the herd immunity levels induced in cattle by foot-and-mouth disease oil vaccines

The development of a liquid-phase blocking sandwich ELISA (LPBE) to measure antibodies (Ab) produced in cattle with the O, A and C foot-and-mouth disease virus (FMDV) types of commercial vaccines used in Argentina is described. The test was specific: 99% of naïve cattle sera (n = 130) gave titres below log₁₀ = 1.2, and none had a titre above log₁₀ = 1.5. Comparative studies with serum neutralization test (SNT) using sera from cattle which received one or more vaccine doses is reported. The overall rank correlation coefficient (Spearman's , r_s) between SNT and LPBE were highly significant (r_s > 0.67, P < 0.0001) for all vaccine strains. LBPE Ab titres on sera collected 90 days post vaccination were compared with results of cattle protection tests by applying a logistic regression. The minimum Ab titres at which 85% and 75% of the cattle were protected for each FMDV type were determined in order to interpret field Ab data in terms of protection. Application of this method allows large scale serological examinations to monitor antibody levels in vaccinated animals as an indirect indicator of the FMD control program status in the field. Its use in the evaluation of commercial batches of FMD vaccine is discussed.     

口蹄疫转基因植物可饲疫苗研究进展

口蹄疫是由口蹄疫病毒引起的一种急性热性高度接触性传染病,给畜牧业造成极大的经济损失,疫苗是预防和控制该病的有效方法。近年来,转基因植物可饲疫苗由于其易于生产、成本低廉、使用方便和安全等诸多的优点成为口蹄疫新型疫苗的研究热点。文章综述了口蹄疫转基因植物可饲疫苗的研究现状,介绍了其原理和方法,分析了其优缺点和改进方法,并对其应用前景进行了展望。     

Foot-and-mouth disease: measurements of aerosol emission from pigs as a function of virus strain and initial dose

Measurements of airborne foot-and-mouth disease virus have been made using 20 pigs that had either O UKG or C Noville injected into their heel-pads to determine if the kinetics of virus emission are related to the virus strain and dose administered in the challenge inoculum. Viable virus was detected in aerosol emissions for 3 days regardless of the strain or dose of virus given. No correlation was found between the peak level of virus emission and dose, but pigs infected with a lower dose of virus had a delayed onset of aerosol emission and emitted a greater total amount of aerosolised virus. Irrespective of the dose, both the total amount and the peak level of virus emission were higher from pigs infected with C Noville compared to those infected with O UKG. The results suggest that care should be taken when extrapolating from laboratory derived data to the field; this is particularly the case in the early days of an outbreak when the aerosol characteristics of the virus involved may be unknown and the amount of virus that an individual animal has been challenged with remains uncertain.     

Sequence analysis of the protein-coding regions of foot-and-mouth disease virus O/HK/2001

The nucleotide sequence of the protein-coding region of foot-mouth-disease virus (FMDV) strain O/HK/2001 was determined and compared with the sequences of other FMDVs that were registered in GenBank. The protein-coding region was 6966 nucleotides in length and encoded a protein of 2322 amino acid residues. Comparison of the nucleotide sequence and its deduced amino acid sequence with those of other isolates indicated that O/HK/2001 belonged to the Cathay topotype. A genomic coding region nucleotide sequence phylogenetic tree of several FMDV-O isolates showed that O/HK/2001 was most closely related to FMDV isolates found in Taiwan during 1997, and especially shared significant similarity to HKN/2002, suggesting that the virus causing outbreaks in Hong Kong was genetically most-closely related to that causing an outbreak of type O in Taiwan. Mutations in O/HK/2001 were revealed, including frequent substitutions in the VP1 and L proteins, and deletions involving 10 amino acid residues in the 3A protein. This study was undertaken to assess the regional variation of prevalent FMDV type O viruses and to establish a sequence database for FMDV molecular epidemiological investigation.     

Effectiveness of movement-prevention regulations to reduce the spread of foot-and-mouth disease in The Netherlands

After the foot-and-mouth disease (FMD) outbreak in 2001 the Dutch government implemented movement-prevention regulations to reduce the number of contacts between farms and consequently the risk of spread of highly contagious animal infections in the future. We studied the efficacy of these regulations by comparing registered cattle-movement data from 2000 to those from 2002. We also used the spatial and stochastic simulation model InterFMD to evaluate the consequences of the observed alterations in cattle-contact structure on the spread and control of a FMD epidemic.

There was a significant decrease in the number of cattle movements “for live use”, no difference in the number of group movements “for live use” and a distinct change in the overall contact structure. The most important structure changes were a decrease in the number of group movements from dairy farms to cattle-collection centres (−44%), and an increase in the number of group movements from dairy farms to beef farms (111%).

Our simulations demonstrated that the implemented regulations result in a concentration of the FMD-affected area and therefore in a reduction in size of the epidemics. Based on the intended Dutch strategy to control future FMD outbreaks, the decrease in extreme epidemics (95th percentiles) went from 31 infected farms in an epidemic-length of 65 days to 8 infected farms in an epidemic-length of 53 days in sparsely populated areas. In densely populated areas this decrease went from 135 infected farms to 103, while the duration reduced from 88 days to 81.     

O型口蹄疫病毒VP1基因的克隆及原核表达载体构建

用Trizol提取O型口蹄疫病毒RNA,根据已经公布的O型口蹄疫病毒核苷酸序列,设计合成1对VP1基因的引物,通过RT-PCR扩增出VP1基因,将其克隆至表达载体pET-32a中。经测序表明,目的基因VP1已正确地整合至表达质粒中。