Bluetongue Control Research Articles

Анализ рисков распространения катаральной лихорадки овец в Казахстане

Kazakhstan is considered to be free from bluetongue. At the same time, biting midges of the genus Culicoides, which are the main vectors of the bluetongue virus, are widespread in the country. An optimal climate for biting midge breeding, a high density of livestock susceptible to the virus, and a constant influx of imported breeding stock from areas where the infection is endemic in southern Kazakhstan cumulatively constitute favorable conditions for the spread of bluetongue in the case of virus transmission in Kazakhstan from other countries. The uncontrolled spread of this infection on the territory of Kazakhstan can be associated with colossal economic losses since sheep breeding is paramount for domestic animal husbandry. In this case, economic costs will not be limited only by the death of animals; significant damage can be caused to the image of our country as an exporter of lamb. This review provides information highlighting the importance of bluetongue control programs in Kazakhstan and an analysis of the risks of the spread of this infection in the country.

Modelling bluetongue risk in Kazakhstan

BackgroundBluetongue is a serious disease of ruminants caused by the bluetongue virus (BTV). BTV is transmitted by biting midges (Culicoides spp.). Serological evidence from livestock and the presence of at least one competent vector species of Culicoides suggests that transmission of BTV is possible and may have occurred in Kazakhstan.MethodsWe estimated the risk of transmission using a mathematical model of the reproduction number R0 for bluetongue. This model depends on livestock density and climatic factors which affect vector density. Data on climate and livestock numbers from the 2466 local communities were used. This, together with previously published model parameters, was used to estimate R0 for each month of the year. We plotted the results on isopleth maps of Kazakhstan using interpolation to smooth the irregular data. We also mapped the estimated proportion of the population requiring vaccination to prevent outbreaks of bluetongue.ResultsThe results suggest that transmission of bluetongue in Kazakhstan is not possible in the winter from October to March. Assuming there are vector-competent species of Culicoides endemic in Kazakhstan, then low levels of risk first appear in the south of Kazakhstan in April before spreading north and intensifying, reaching maximum levels in northern Kazakhstan in July. The risk declined in September and had disappeared by October.ConclusionThese results should aid in surveillance efforts for the detection and control of bluetongue in Kazakhstan by indicating where and when outbreaks of bluetongue are most likely to occur. The results also indicate where vaccination efforts should be focussed to prevent outbreaks of disease.Graphical abstract

Bayesian optimisation of restriction zones for bluetongue control

We investigate the restriction of animal movements as a method to control the spread of bluetongue, an infectious disease of livestock that is becoming increasingly prevalent due to the onset of climate change. We derive control policies for the UK that minimise the number of infected farms during an outbreak using Bayesian optimisation and a simulation-based model of BT. Two cases are presented: first, where the region of introduction is randomly selected from England and Wales to find a generalised strategy. This “national” model is shown to be just as effective at subduing the spread of bluetongue as the current strategy of the UK government. Our proposed controls are simpler to implement, affect fewer farms in the process and, in so doing, minimise the potential economic implications. Second, we consider policies that are tailored to the specific region in which the first infection was detected. Seven different regions in the UK were explored and improvements in efficiency from the use of specialised policies presented. As a consequence of the increasing temperatures associated with climate change, efficient control measures for vector-borne diseases such as this are expected to become increasingly important. Our work demonstrates the potential value of using Bayesian optimisation in developing cost-effective disease management strategies.

Bluetongue: control, surveillance and safe movement of animals.

The performance of different bluetongue control measures related to both vaccination and protection from bluetongue virus (BTV) vectors was assessed. By means of a mathematical model, it was concluded that when vaccination is applied on 95% of animals even for 3 years, bluetongue cannot be eradicated and is able to re‐emerge. Only after 5 years of vaccination, the infection may be close to the eradication levels. In the absence of vaccination, the disease can persist for several years, reaching an endemic condition with low level of prevalence of infection. Among the mechanisms for bluetongue persistence, the persistence in the wildlife, the transplacental transmission in the host, the duration of viraemia and the possible vertical transmission in vectors were assessed. The criteria of the current surveillance scheme in place in the EU for demonstration of the virus absence need revision, because it was highlighted that under the current surveillance policy bluetongue circulation might occur undetected. For the safe movement of animals, newborn ruminants from vaccinated mothers with neutralising antibodies can be considered protected against infection, although a protective titre threshold cannot be identified. The presence of colostral antibodies interferes with the vaccine immunisation in the newborn for more than 3 months after birth, whereas the minimum time after vaccination of animal to be considered immune can be up to 48 days. The knowledge about vectors ecology, mechanisms of over‐wintering and criteria for the seasonally vector‐free period was updated. Some Culicoides species are active throughout the year and an absolute vector‐free period may not exist at least in some areas in Europe. To date, there is no evidence that the use of insecticides and repellents reduce the transmission of BTV in the field, although this may reduce host/vector contact. By only using pour‐on insecticides, protection of animals is lower than the one provided by vector‐proof establishments.

Seasonal Dynamics, Parity Rate, and Composition of Culicoides (Diptera: Ceratopogonidae) Occurring in the Vicinity of Wild and Domestic Ruminants in the Czech Republic.

In the light of the emergence of bluetongue and Schmallenberg viruses in northern and central Europe, an extensive entomological survey within the framework of a bluetongue control program was undertaken from 2008 to 2013 in the Czech Republic to investigate Culicoides biting midges (Diptera: Ceratopogonidae) collected in close proximity of domestic livestock and semiwild ruminants. Insects were sampled using CDC black-light suction traps placed overnight near ruminants in farms or in forest game preserves to provide data on Culicoides fauna collected near these two groups of hosts inhabiting different environments. From almost a half million biting midge specimens collected at 41 sampling sites, 34 species were identified including three species newly recorded for the Czech Republic: Culicoides (Oecacta) clastrieri Callot, Kremer & Deduit, Culicoides (Oecacta) odiatus Austen, and Culicoides (Pontoculicoides) saevus Kieffer. The Culicoides obsoletus species group, incriminated as a bluetongue virus vector, was predominant in both domestic livestock (91%) and semiwild game (52%). A relatively high proportion (around 30%) of C. obsoletus Meigen females with pigmented abdomen (= more likely parous) was observed from spring till autumn. In contrast, adult biting midges were found to be largely absent during at least three winter months, approximately December till March, which could be considered as the biting midge vector-free period.

Control of bluetongue in Europe

Since 1998, bluetongue virus (BTV) serotypes 1, 2, 4, 6, 8, 9, 11 and 16 have spread throughout Europe. In 2006, BTV serotype 8 (BTV-8) emerged unexpectedly in northern Europe throughout a region including Belgium, France, Germany, Luxembourg and the Netherlands. In the following year, it spread rapidly throughout the rest of Europe. In 2008, two more BTV serotypes were detected in northern Europe: BTV-6 in the Netherlands and Germany and BTV-11 in Belgium. The European incursion of BTV has caused considerable economic losses, comprising not only direct losses from mortality and reduced production but also indirect losses because of ensuing bans on trade of ruminants between BTV-infected and non-infected areas. Given the significance of the disease, all affected countries have established control and eradication measures, which have evolved with the availability of detection and prevention tools such as vaccines. Before 2005, BTV vaccination campaigns in affected countries used only modified live virus vaccines and only sheep were vaccinated, except in Italy, where all susceptible domestic ruminant species were included. After 2005, inactivated vaccines became available and cattle and goats were included in the vaccination campaigns. This review looks at how bluetongue disease has evolved in Europe and how effective vaccination strategies have been.

Developing vaccines against foot-and-mouth disease and some other exotic viral diseases of livestock

Vaccines remain the main tool for the control of livestock viral diseases that pose a serious threat to animal and occasionally human health, reduce food security, distort trade in animals and their products, and undermine agricultural development in poor countries. Globalization and climate change increase the likelihood for new patterns of emergence and spread of livestock viruses. Conventionally attenuated and killed virus products have had spectacular success, and recent examples include the global eradication of rinderpest and the control of bluetongue in the UK and northern Europe. However, in many cases, livestock vaccines could benefit from improvement in some properties (e.g. stability, speed of onset and duration of immunity, and breadth of cross-protection to different serotypes or strains) and in some cases are not available at all. Compared with human vaccines, uptake of livestock products is highly cost-sensitive and their use may also need to be compatible with post-vaccination screening methods to determine whether or not animals continue to be infected. Requirements and prospects for new or improved vaccines are described for some priority viral diseases with potential for transboundary spread, particularly for foot-and-mouth disease.

Seasonal spread and control of Bluetongue in cattle

Bluetongue is a seasonal midge-borne disease of ruminants with economic consequences on herd productivity and animal trade. Recently, two new modes of transmission have been demonstrated in cattle for Bluetongue virus serotype 8 (BTV8): vertical and pseudo-vertical transmission. Our objective was to model the seasonal spread of BTV8 over several years in a homogeneous population of cattle, and to evaluate the effectiveness of vaccination strategies. We built a deterministic mathematical model accounting for the seasonality in vector abundance and all the modes of transmission. We proposed a counterpart of the basic reproduction number ( R 0) in a seasonal context ( R S ). Set A( t) is the number of secondary cases produced by a primary case introduced at time t. R S is the average of A( t). It is a function of midge abundance and vaccination strategy. We also used A ⁎, the maximum of A( t), as an indicator of the risk of an epidemic. Without vaccination, the model predicted a large first epidemic peak followed by smaller annual peaks if R S >1. When R S <1, small epidemics could occur if A ⁎ >1. Vaccination reduced R S and A ⁎ to less than one, but almost perfect vaccine efficacy and coverage were required to ensure no epidemics occurred. However, a lower coverage resulting in R S>1 could decrease infection prevalence. A further step would be to optimize vaccination strategies by targeting an appropriate period of the year to implement the vaccination.

The current rules on bluetongue vaccination in EU: from the origin to date

The Council Directive 2000/75/EC lays down controlling rules and measures to contrast and to eradicate bluetongue disease, including rules on the establishment of protection and surveillance zones and the use of vaccines against bluetongue. In the past years, only sporadic incursions of certain serotypes of the bluetongue virus were recorded in EU. However, after the adoption of the Directive, and particularly after the introduction into the Union of bluetongue viruses serotypes 1 and 8 in the years 2006-2007,the infection has become more widespread in EU, with the potential of becoming endemic in certain areas. The rules of vaccination against bluetongue laid down in Directive 2000/75/EC are based on the experience of the use of so-called “modified live vaccines”, or “live attenuated vaccines” that were the only available vaccines when the Directive was adopted. The use of those vaccines may lead to an undesired local circulation of the vaccine virus, also in unvaccinated animals. In recent years inactivated vaccines against bluetongue, which does not pose a risk for unvaccinated animals, have been introduced. The widespread use of these vaccines, during a vaccination campaign, led to a significant improvement in the disease situation. It’s now widely accepted that vaccination with inactivated vaccines is the preferred tool for the control of bluetongue and prevention of this clinical disease in EU. In order to ensure the better control of the bluetongue virus spread, the Authors underline the necessity to amend the current rules on vaccination to take account of recent technological developments in vaccine production.

Bluetongue control strategy, including recourse to vaccine: a critical review

The bluetongue (BT) epidemic that has prevailed in Europe since 2000 is the first example of continental spread of the BT virus (BTV) in large naive populations of susceptible animals. Based on the results of intensive surveillance and research in countries of the southern Mediterranean that were affected by the infection early on in the epidemic, a new strategy for prevention and control of the disease was developed to limit direct losses and to reduce the consequences due to movement restrictions. The basic innovations that were introduced were the use of mass vaccination of all domestic ruminant species to limit the spread of BTV and the use of intensive active surveillance to limit, as far as possible, the zone where movement restrictions must be applied. The novel strategy that was adopted dramatically reduced the number of clinical outbreaks in southern Europe and the Mediterranean Basin and ensured safer animal trade. In 2006, the first BTV-8 epidemic occurred, this time in north-western Europe. During this epidemic, affected countries adopted a 'wait and see' approach. No vaccination was implemented until 2008 and, in many instances, the movement of animals was authorised within restricted areas, thereby facilitating the spread of infection. The delay in administering vaccination was due to the decision to avoid the use of modified live virus vaccines, although this type of vaccine performed satisfactorily in the previous BT epidemics in southern Europe. Bluetongue has demonstrated that the infectious agents present in southern Africa can easily spread to the Mediterranean Basin, which should be considered a single entity as far as the epidemiology of animal diseases is concerned. Therefore, any effective strategy for the prevention and control of animal disease in Europe must take into account this reality and recognise the need for regional surveillance networks that include all the countries that border the Mediterranean.

A DIVA system based on the detection of antibodies to non-structural protein 3 (NS3) of bluetongue virus

Vaccination programs for the control of bluetongue (BT) in ruminants have limitations due to difficulties in differentiating infected from vaccinated animals (DIVA). To overcome this problem a DIVA test that looks at a differential immune response to bluetongue virus (BTV) non-structural protein 3 (NS3) was developed. The NS3 encoding gene of strain BTV4/22045/PT04 was inserted into expression vector pET-28a and expressed in Escherichia coli strain JM109. Recombinant NS3 protein was used as an antigen in an indirect ELISA (NS3-ELISA) to measure the serologic response to NS3 protein in cattle and sheep. Following a cattle vaccination/challenge experiment with a bivalent inactivated BTV 2–4 vaccine, NS3 antibodies were detected at approximately 15 days post-infection in control unvaccinated animal, while vaccinated animals did not develop detectable NS3 antibodies and, with exception of one, remained negative even after virus challenge. The inactivated vaccine induced antibodies against the major core structural protein (VP7) of BTV as well as neutralizing antibodies in all animals. To evaluate the applicability of NS3-ELISA in field scenario, a total of 562 serum samples collected from uninfected, BTV-infected and vaccinated animals were tested for NS3 antibodies. Taken together, the results confirm that NS3 antibodies were induced to the greatest levels in animals infected with BTV in comparison to the levels induced in animals immunized with inactivated BTV vaccines, implying that antibody response to NS3 allows the differentiation between infected and vaccinated animals.