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Managing disease risk with the trade of small ruminants in Europe

01 September 2017, at 12:00am

Paul Roger offers his expert view on the growing threats involved in the mass transportation of animals – and what can be done to minimise them.

The European trade in small ruminants poses threats – both to individual animals and to whole populations. Factors that may influence disease threats include: travel time, geographical and meteorological changes and exposure to diseases, which might be exotic to the country of origin or destination. The risk varies according to changes in management practice and changes in vector populations, among other variables that can influence epidemiology. These risks are often reported on a six-point scale (see Table 1).

Such threats are sometimes difficult to quantify and can cause catastrophic losses even when identified relatively early in the outbreak of disease (e.g. footand-mouth disease (FMD), Schmallenberg virus (SBV) and Zika virus).

Disease threats include, most obviously, the spread of infection through animals incubating or carrying disease where no clinical signs are shown. But transporting animals also increases the potential for transferring resistant bacterial populations from one location to another, and for the movement of helminth populations that are resistant to anthelminthic treatments.

The diseases that tend to raise the most interest are those that are exotic to the UK. This is particularly true of those new and emerging diseases that we have seen in recent years, which have leapt from areas where the disease is endemic into new vector populations and naive livestock populations. These diseases can cause high losses and test the resourcefulness of veterinary scientists in not only identifying the threats, but also devising and delivering effective means of control. Examples include bluetongue virus (BTV) – where a new midge vector has become involved in spread and a previously unknown serotype arrived in northern Europe, and, more recently, the emergence of a completely novel pathogen, SBV. Both of these viruses adapted to regional vectors.

The response of the pharmaceutical industry to these challenges has been incredible; an effective killed vaccine has been provided from scratch in a very short period of time. However, the use of these new tools has been variable in uptake and, because of the effectiveness of the drug companies’ responses, the threats have been somehow diminished in the eyes of many livestock producers. This makes the balance between the availability of protection and the utilisation of this technology critical. This balance needs careful management in considering where the responsibility lies in the protection of individual flocks. It is no use calling for a vaccine if the product is not used when it is available.

Surveillance of new and emerging threats

Disease risks need to be identified. In the UK, we are lucky to have a natural sea barrier separating us from the European mainland, but this natural defence needs to be backed up by surveillance so new and emerging threats can be readily identified. Unfortunately, this barrier has the potential to be breached through the airborne spread of disease either as fomites through carriers; by mechanical spread; or by illegal, unregulated or even regulated movement of humans and animals (85 percent of new and emerging threats are likely to have zoonotic implications). This means that, as well as quarantine regulations and import controls, what constitutes our natural baseline for disease needs to be understood so that variations and changes in these patterns can be easily flagged up. This syndromic surveillance requires a wide base operating in real-time with data collection from the widest possible sources of information – sources that can be ranked and incorporated into deliverable information on national, regional and more local epidemiology of disease.

At present, the UK has a system of surveillance that has served the livestock industry and its advisers well, but the database this provides is biased as it relies on independent submission to APHA laboratories and its partners. There is no proper link with the data that could be gleaned from the abattoirs or from fallen stock even at a gross level, though this is gradually changing. The poultry, pig and fish industries have the potential to lead the way in providing the type of analysis and information base needed across the whole livestock sector. This should include equine and companion animals, as well as the ruminants, where presently the dairy sector is responding to this challenge.

Protecting against the main threats

The main threats are listed in Table 2. These threats may first appear on farm but be missed, and the role of the OV in identifying potential problems at ante-mortem inspection is a vital part of our protective armoury. Indeed, suspicion of disease when it occurs may give rise to complex differentials (see Table 3) and confirmation of disease is needed rapidly and rigorously to high levels of sensitivity and specificity.

Controls depend on the identification and risk analysis followed by containment of disease, which may include movement restriction, culling strategy, the use of vaccines, vector controls and an understanding of endemic disease and how that may affect the necessary controls.

At present, we have a useful shared intelligence network with surveillance colleagues in other European countries, providing information on disease threats. Information is also shared on websites, such as ProMED.mail, and the use of digital technologies allows relevant information to be rapidly distributed when new disease outbreaks occur.

Within our veterinary services in government and its agencies, there presently exists a unit (the Surveillance Intelligence Unit) coordinating and reviewing these surveillance processes and providing a vital service to allow government to carry out its statutory duties. Funding cuts could threaten the effectiveness of this delivery, which could have adverse influence on areas of animal health and welfare, food safety and security, public health and, in turn, trade. This is an area where investment in the proper and effective use of information technology could provide marked gains in both the private and public sectors and which could help to ensure that the UK continues to have a useful lead in global livestock production and its associated technologies.

OVs fill a critical position in the protection of both our animal and human populations and contribute to the available data sources daily, as well as providing an essential safety net in the identification of emerging disease. The delivery of information on animal disease is developing with new ideas on the collection of abattoir data, and the opportunities fallen stock centres offer, to provide a better information base. This, coupled with the changing structure of veterinary practice in the UK, must open doors to the gathering and analysis of this data, which is vital for the protection of the future of our livestock industry.

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