A model for the assessment of bluetongue virus serotype 1 persistence in Spain.

Bluetongue virus (BTV) is an arbovirus of ruminants that has been circulating in Europe continuously for more than two decades and has become endemic in some countries such as Spain. Spain is ideal for BTV epidemiological studies since BTV outbreaks from different sources and serotypes have occurred continuously there since 2000; BTV-1 has been reported there from 2007 to 2017. Here we develop a model for BTV-1 endemic scenario to estimate the risk of an area becoming endemic, as well as to identify the most influential factors for BTV-1 persistence. We created abundance maps at 1-km2 spatial resolution for the main vectors in Spain, Culicoides imicola and Obsoletus and Pulicaris complexes, by combining environmental satellite data with occurrence models and a random forest machine learning algorithm. The endemic model included vector abundance and host-related variables (farm density). The three most relevant variables in the endemic model were the abundance of C. imicola and Obsoletus complex and density of goat farms (AUC 0.86); this model suggests that BTV-1 is more likely to become endemic in central and southwestern regions of Spain. It only requires host- and vector-related variables to identify areas at greater risk of becoming endemic for bluetongue. Our results highlight the importance of suitable Culicoides spp. prediction maps for bluetongue epidemiological studies and decision-making about control and eradication measures.

Effectiveness and cost-benefit study to encourage herd owners in a cost sharing vaccination programme against bluetongue serotype-8 in Belgium.

Bluetongue (BT) is a ruminant viral infectious disease transmitted by Culicoides spp. midges. In 2006, when bluetongue virus serotype 8 (BTV-8) appeared for the first time in Northern Europe, it rapidly spread and infected a large proportion of animals. BThas a significant economic impact due to a direct effect on animal health and to an indirect effect in disrupting international trade of animals and animal products. In spring 2008, a compulsory subsidized vaccination programme in Europe resulted in a drastic decrease in the number of reported cases. However, due to the turn-over of the population, without a continuous vaccination programme, the animal population was becoming progressively susceptible. Vaccination would enable Belgium to maintain its status of freedom from infection of BTV-8 that could possibly be re-introduced. Subsidizing it could be an incentive to convince more farmers to vaccinate. To finance this programme, both decision-makers and stakeholders need to be persuaded by the effectiveness and the cost-benefit of vaccination. The study evaluated the effectiveness of vaccination against BTV-8 in Belgium. The change in serology which has shown the effectiveness of the vaccine to induce antibody production has been significantly associated with the time between the first injection and the sampling date and the number of injections of the primo-vaccination. This study also clearly confirms the benefit of vaccination by reducing economic impact of treatment and production losses, especially in dairy cattle. Based on a participating epidemiological approach, a national voluntary and subsidized vaccination was accepted, and permitted Belgium to vaccinate more than 9,000 herds in 1 month. Because this mass vaccination occurred before the vector season, it probably helped Belgium remain free from BTV-8.

Epidemiological and Molecular Studies on Lumpy Skin Disease Outbreaks in Turkey during 2014-2015.

This study was carried out to explore epidemiological and molecular features of lumpy skin disease virus (LSDV) in the Aegean, Central Anatolian and Mediterranean regions of Turkey, to evaluate the risk factors associated with LSDV infection and to investigate the financial impact of LSD and potential role of the Culicoides spp. in the transmission of LSDV. Samples were obtained from 611 cattle, each from different farms, and each clinically suspected to be infected with LSDV during the months of July 2014 and June 2015. Culicoides spp. were trapped from April to June 2015. Genetic characterization of the local LSDV field isolates was conducted by sequencing G-protein-coupled chemokine receptor gene segment. Real-time PCR high-resolution melting analysis was used for distinguishing each type of capripoxviruses. Viral DNA was detected in 448 of the 611 animals and Culicoides midges. Three hundred and ninety-three of the 448 affected farms were surveyed. The morbidity and mortality rates detected were 12.3% and 6.4%, respectively. Phylogenetic analysis showed that the field isolates in this study were clustered together with other Africa and Middle East isolates. Genotyping of isolates from infected cattle has revealed the presence of LSDV. A generalized mixed linear model showed that there were positive associations between LSDV infection, European breeds, small-sized family-type farms and nearness of farm to a lake. The financial cost of disease presence in surveyed cattle farms was estimated to be 72.75 GBP per head. The sequence analysis of the mitochondrial cytochrome oxidase subunit I gene showed that the species of Culicoides in LSDV-positive pools was Culicoides punctatus. Detection of LSDV in Culicoides punctatus suggests that it may have played a role in transmitting LSDV. Furthermore, movement of infected animals into disease-free areas increases the risk of the transmission of LSD. Control strategies for LSDV infection should include consideration of the risk factors identified in this study.

Evaluation of in vitro methods for assessment of infection of Australian Culicoides spp. with bluetongue viruses.

Biting midges from the genus Culicoides (Diptera: Ceratopogonidae) are the vectors of several globally important arboviruses that affect livestock. These include orbiviruses from the bluetongue virus (BTV) and African horse sickness virus (AHSV) groups and members of the Simbu serogroup of orthobunyaviruses, such as the recently emerged Schmallenberg virus. In this article, the authors evaluate several methods for feeding wild­caught Australian Culicoides on BTV infected preparations of blood and sucrose. Feeding Culicoides on the membrane of embryonated chicken eggs was identified as the preferred feeding method. Although, cotton wool pads soaked in either virus­infected blood or virus­sucrose mixtures were also successful. A non­destructive nucleic acid extraction technique for the detection of viral RNA in Culicoides was also evaluated as it allows for readily differentiating infected from non­infected Culicoides.

Bluetongue disease risk assessment based on observed and projected Culicoides obsoletus spp. vector densities.

Bluetongue is an arboviral disease of ruminants causing significant economic losses. Our risk assessment is based on the epidemiological key parameter, the basic reproduction number. It is defined as the number of secondary cases caused by one primary case in a fully susceptible host population, in which values greater than one indicate the possibility, i.e., the risk, for a major disease outbreak. In the course of the Bluetongue virus serotype 8 (BTV-8) outbreak in Europe in 2006 we developed such a risk assessment for the University of Veterinary Medicine Vienna, Austria. Basic reproduction numbers were calculated using a well-known formula for vector-borne diseases considering the population densities of hosts (cattle and small ruminants) and vectors (biting midges of the Culicoides obsoletus spp.) as well as temperature dependent rates. The latter comprise the biting and mortality rate of midges as well as the reciprocal of the extrinsic incubation period. Most important, but generally unknown, is the spatio-temporal distribution of the vector density. Therefore, we established a continuously operating daily monitoring to quantify the seasonal cycle of the vector population by a statistical model. We used cross-correlation maps and Poisson regression to describe vector densities by environmental temperature and precipitation. Our results comprise time series of observed and simulated Culicoides obsoletus spp. counts as well as basic reproduction numbers for the period 2009-2011. For a spatio-temporal risk assessment we projected our results from the location of Vienna to the entire region of Austria. We compiled both daily maps of vector densities and the basic reproduction numbers, respectively. Basic reproduction numbers above one were generally found between June and August except in the mountainous regions of the Alps. The highest values coincide with the locations of confirmed BTV cases.

Assessment of the risk of a bluetongue outbreak in Europe caused by Culicoides midges introduced through intracontinental transport and trade networks.

The importation of infected hosts and the arrival of windborne infected Culicoides (Diptera: Ceratopogonidae) were considered unlikely mechanisms for bluetongue virus (BTV) incursion into a BTV-free area during the recent BTV serotype 8 (BTV-8) epidemic in northern Europe. Therefore, alternative mechanisms need to be considered. Air, sea and land transport networks continue to expand, and an important consequence of this is vector-borne pathogen importation. One important aspect of bluetongue (BT) epidemiology not yet addressed is the potential movement of infected Culicoides via transport and trade networks. Therefore, a risk assessment model was constructed to assess the probability of a BTV outbreak as a consequence of the introduction of Culicoides via these networks. The model was applied to calculate the risk for a BTV-8 epidemic in Spain in 2007 caused by the introduction of Culicoides from affected northern European countries. The mean weighted annual risk for an outbreak caused by transportation of a single vector from an affected northern European country varied from 1.8 × 10(-7) to 3.0 × 10(-13), with the highest risks associated with Culicoides imported from Belgium, the Netherlands, Germany and France. For this mechanism to pose a significant risk to BTV-free countries, a large number of vectors would have to be transported.

Atmospheric dispersion models and their use in the assessment of disease transmission.

Atmospheric dispersion models can be used to assess the likely airborne spread of both plant and animal diseases. These models, often initially developed for other purposes, can be adapted and used to study past outbreaks of disease as well as operationally to provide advice to those responsible for containing or eradicating disease in the event of a specific emergency. The models can be run over short periods of time where emissions and infection periods can be accurately determined or in situations requiring a statistical approach perhaps covering many weeks or even months. They can also be embedded within other simulation models, i.e. models which seekto represent a wider variety of disease transmission mechanisms. Whilst atmospheric dispersion models have been used successfully in a number of instances, they have the potential for wider application in the future. To achieve maximum success in these ventures, close collaboration between the modellers and scientists from the appropriate range of disciplines is required.

Quantitative assessment of the probability of bluetongue virus overwintering by horizontal transmission: application to Germany.

Even though bluetongue virus (BTV) transmission is apparently interrupted during winter, bluetongue outbreaks often reappear in the next season (overwintering). Several mechanisms for BTV overwintering have been proposed, but to date, their relative importance remain unclear. In order to assess the probability of BTV overwintering by persistence in adult vectors, ruminants (through prolonged viraemia) or a combination of both, a quantitative risk assessment model was developed. Furthermore, the model allowed the role played by the residual number of vectors present during winter to be examined, and the effect of a proportion of Culicoides living inside buildings (endophilic behaviour) to be explored. The model was then applied to a real scenario: overwintering in Germany between 2006 and 2007. The results showed that the limited number of vectors active during winter seemed to allow the transmission of BTV during this period, and that while transmission was favoured by the endophilic behaviour of some Culicoides, its effect was limited. Even though transmission was possible, the likelihood of BTV overwintering by the mechanisms studied seemed too low to explain the observed re-emergence of the disease. Therefore, other overwintering mechanisms not considered in the model are likely to have played a significant role in BTV overwintering in Germany between 2006 and 2007.

[Risk assessment of bluetongue disease incursion into Germany using geographic information system (GIS)]. / Risikoabschätzung zur Einschleppung der Bluetongue Disease nach Deutschland mit Hilfe eines Geographischen Informationssystems (GIS).

Using a geographic information system (GIS), by analysis of the relationship between the spatial distribution of cattle density and the risk factors temperature, altitude and rainfall, we defined geographical habitats enabling optimal development and competence of Culicoides spp. to transmit Bluetongue-Virus (BTV): Risk zones (low, high, highest risk) were identified mainly in Baden-Württemberg, Hessen and Rheinland-Pfalz if persistently infected ruminants are imported into these zones in summer (June to August mainly), based on the current climatic conditions, BTD outbreaks are considered a real possibility. Overwintering of the virus seems unlikely. However, global warming will lead to a steady increase of the size of the risk zones. In addition, the possibility of primary outbreaks increases. The reason for this is not only the expected northern shift of Culicoides imicola, but in addition an increasing vector competence of domestic Culicoides species. We therefore recommend the storage of vaccines as well as conducting ecological studies analysing the presence of Culicoides vectors. Using the data from these studies, it will be possible to produce updated quantitative risk assessment via GIS.

Epizootics of bovine ephemeral fever on dairy farms in Saudi Arabia.

In 1990 and 1996, field veterinarians suspected the clinical occurrence of bovine ephemeral fever among dairy and conventional cattle in different regions of Saudi Arabia. The disease has a seasonal occurrence; it begins in early summer (May) and ends in late autumn (November). The mortality rate is low: 0.3% to 0.6%. The morbidity rate ranged from 5% to 61% within the different age groups of one affected herd in the 1996 outbreaks and from 3.4% to 19% among four affected herds in the 1990 outbreaks. A sudden sharp drop in milk production occurred in lactating animals, some of which had become dry by the end of the outbreaks. Trials to isolate the causative virus in cell culture and in baby mice were unsuccessful. Serum neutralisation tests, which used a cell culture-adapted vaccine strain of bovine ephemeral fever virus as an antigen, revealed the presence of specific antibodies with significantly increased titres in the convalescent sera of affected animals. In addition, the testing of paired sera from non-affected heifers and from both dry and milking cows, performed twice, with an interval of 21 days, revealed the presence of neutralising antibodies. In the 1990 outbreaks, comparative serological studies indicated a high percentage (67.5%; 27/40) of seropositive animals in herds in which bovine ephemeral fever had been previously suspected. No antibodies were detected in animals of herds which had no recorded clinical history of bovine ephemeral fever. Following serological confirmation of the prevalence of bovine ephemeral fever in Saudi Arabia, some dairy farms started using a live imported vaccine to control the disease. This study discusses the epizootiological findings in regard to bovine ephemeral fever, as well as its economic impact on four affected dairy farms in 1990. In addition, the authors evaluate the efficacy of immunoprophylaxis in another dairy herd during the same outbreaks.

Bluetongue virus in laboratory-reared Culicoides variipennis sonorensis: applications of dot-blot, ELISA, and immunoelectron microscopy.

An avidin-biotin complex (ABC) dot-blot, an antigen capture enzyme-linked immunosorbent assay (ELISA), and immunoelectron microscopy (IEM) were used to detect bluetongue (BLU) virus or viral antigen or both in adult Culicoides variipennis sonorensis Wirth & Jones. The dot-blot and ELISA procedures detected viral antigen in 10-22% (depending on serotype) of the biting midges infected with BLU-2, BLU-10, BLU-13, and BLU-17 and approximately 68% of the midges infected with BLU-11. IEM analyses revealed BLU virus in salivary glands, fat body, and thoracic muscle tissue from infected insects. There appeared to be selective growth of the virus in salivary gland tissue.