Mass vaccination programs lasting at least five years in combination with improved, continuous surveillance systems would be the only effective measures for eradicating bluetongue in Europe, according to recent conclusions reached by the European Food Safety Authority (EFSA).
Bluetongue is not a threat to humans but it has a high mortality rate among animals. It is a vector-borne viral disease of domestic and wild ruminants such as sheep, goats, cattle and deer. It is transmitted through the bites of certain species of Culicoides midges, one of many insects commonly referred to as flies.
Bluetongue originated in Africa more than a century ago, and was long thought to be confined there. In the past decade it has emerged in Europe, first in the Netherlands and then Belgium, Germany and Luxembourg. Next came outbreaks in the Czech Republic and Scandinavia, Switzerland and Denmark.
Quarantine, inoculation and live modified virus vaccine, along with attempts to control the midge vector, have been used as prevention measures.
EFSA’s experts have reviewed control measures for bluetongue and options for safe trade of animals from infected to disease-free areas, following a request from the European Commission. They have also updated their scientific advice on epidemiological aspects of the disease, particularly its transmission patterns.
Eradication of bluetongue is very difficult – at least five consecutive years of vaccination covering 95 percent of susceptible cattle and sheep would be needed, the experts concluded. Such mass vaccination campaigns would have to be followed by sensitive surveillance systems capable of detecting low levels of virus prevalence – lower than 1 percent of animals in a monitored area. The disease could otherwise re-appear some years after completion of the vaccination campaign.
Surveillance systems should be defined on a case-by-case basis taking into account aspects such as the geographical area monitored and the epidemiological phase of the disease.
Immunization and transmission
Experts also highlighted that:
- New-born animals receive antibodies from their mothers that protect them from the disease for about three months. However, these antibodies may interfere with vaccination, thus making vaccination ineffective during this period. Immunity starts in most cases 21 days after the second dose of the basic vaccination scheme.
- Some species of the midges that transmit the disease are active throughout the year – especially in mild-winter areas such as the Mediterranean basin. In these areas, transmission of the virus may occur at any time. In colder areas, such as in northern Europe, midges are inactive for about three winter months, during which transmission is halted.
In line with EFSA’s “Promoting Methods for Evidence Use” approach, EFSA’s Panel on Animal Health and Welfare captured the strategy for performing this risk assessment in a protocol that documents all the steps taken in reaching its final conclusions. This new approach enhances the robustness and transparency of the scientific process.
EFSA’s scientific advice will assist policy-makers as they review legislation on bluetongue.
The next step for now is for EFSA to classify different types of bluetongue according to their characteristics. That work is scheduled to conclude by the end of June. This will help identify specific protection and control measures.
(To sign up for a free subscription to Food Safety News, click here.)