Latest bluetongue virus update
This page will be updated regularly with resources and information – for any queries email RuminantHW@ahdb.org.uk
Latest update 12 September 2024
Following a report of clinical suspicion in sheep near Faversham in Kent, BTV-3 has been confirmed. In accordance with the disease control framework, a 20km temporary control zone has been declared.
Three further cases were identified through surveillance testing in Essex in the current Restricted Zone, and one further case was identified through surveillance testing in East Yorkshire in the current Temporary Control Zone. No changes in these zones are necessary.
This brings the total number of premises affected to 46.
Recent BTV-3 updates
Following surveillance within the temporary control zone in North East Lincolnshire, 2 further cases of BTV-3 was detected. In accordance with the disease control framework, the temporary control zone has been further extended.
One further case was identified through surveillance testing in Essex in the current Restricted Zone. No changes in this zone are necessary.
This brings the total number of premises affected to 41.
Following surveillance within the temporary control zone in North East Lincolnshire, a case of BTV-3 was detected. In accordance with the disease control framework, the temporary control zone has been extended.
Following reports of suspicion in cattle and sheep, the chief veterinary officer confirmed the presence of bluetongue serotype 3 (BTV-3) on 2 new premises in the Restricted Zone on 10 September. One further case was identified through surveillance testing in the zone.
Following reports of suspicion in cattle and sheep, the chief veterinary officer confirmed the presence of bluetongue serotype 3 (BTV-3) on 3 new premises in the Restricted Zone on 8 September. One further case was identified through surveillance testing in the zone. This brings the total number of premises affected to 34.
Advice for farmers
RH&W’s advice to farmers and their vets remains three-fold, farmers need to beware when buying animals in, take action to report any signs, and always, remain vigilant:
- Buyer beware, source animals from Europe responsibly and request pre-movement testing.
- Take action, prioritise biosecurity and report any suspicious clinical signs.
- Vigilance is key, monitor livestock closely.
To ‘act’ on BTV-3, be aware of how bluetongue is transmitted as a vector-borne disease, take caution against misinformation, and promote evidence-based tactics on-farm.
- Awareness of how BTV-3 is transmitted as a vector-borne disease
- Caution against any misinformation, but instead view the latest facts
- Tactics on-farm to help with midge control must be evidence-based
BTV-3 detection update – August 2024
Detection of evidence of disease/exposure to a virus usually falls into two categories:
- Looking for the virus itself (antigen testing).
- Looking for an animal’s response to the virus (antibody testing). Both natural infection and vaccination should result in a positive test for antibodies.
There are different samples that can be collected for these tests. Most commonly a blood test, but other samples such as swabs, urine or bulk milk samples from a dairy herd, can also be used to detect both virus and antibody with varying degrees of success. The best sample to take to be certain of infection, and the timing of sample collection, is dependent on the virus we are working with.
There are three main reasons why bulk milk testing is not suitable for early detection of BTV-3 in England.
1.1. The BTV-3 bulk milk ELISA is not very sensitive for early detection application. The sensitivity of the test is 54% when the herd prevalence is <2%. Herd prevalence is likely to be low at the start of an outbreak, so only having a sensitivity of 54% will mean close to half of antibody positive animals will be missed. Even in a more widespread outbreak where the herd prevalence is 4%, the sensitivity is 85%, which is still relatively low. Ideally a test would have a sensitivity of 100% (meaning it would not miss any antibody positive animals). With sensitivity below 100%, animals that have been exposed to the virus may not be detected (false negatives) by the bulk milk sample ELISA test. In early surveillance, this would be detrimental to any control plan.
1.2 There is a risk of vaccinated (but not infected) animals being detected. This would cause significant inconvenience for affected farms.
- Animals imported from a BTV positive country must be vaccinated before entry to the UK. In 2016, a survey showed that there were a significant number of vaccinated cattle in the UK. If these are detected on surveillance testing, a full BTV investigation, together with movement restrictions would potentially be conducted.
- There is a possibility that some animals that were vaccinated or infected during the previous BTV-8 outbreak are still alive. The test cannot distinguish a response to BTV-3 from BTV-8.
1.3 Bulk milk testing is not suitable to detect the BTV-3 itself, the current test is to detect antibodies against it. BTV is associated with red blood cells and hence is very difficult to detect in other samples such as urine or milk where red blood cell content is low. While PCRs tend to be extremely sensitive in detecting BTV (i.e., they will pick up virus if it is there), this is not the case for BTV in milk.
Bulk milk testing is relatively quick, easy and cheap and it does not require blood samples to be taken. The Netherlands did use this method in the early stages of the outbreak to determine whether they had had earlier infections that they had not been detected clinically or by PCR. While this testing did identify some antibody positive bulk milk samples, they could not determine if these were previously infected or vaccinated animals (to other BTV serotypes like BTV-8 or BTV-4) which did result in full investigations. However, it was useful to give an indication of how far the virus had spread throughout the country.
In conclusion, in an early outbreak situation, prevalence is likely to be less than 2% and therefore a sensitive test is required. The current BTV bulk milk ELISA is not sensitive enough (54%) to provide useful data. As the virus is associated with red blood cells , there is little virus, if any, found in milk. Therefore, if we want to detect virus, blood samples need to be collected for PCR.
In England, early detection sampling for BTV-3 will be performed by strategic blood testing for virus detection (by PCR).
Bluetongue is a notifiable animal disease. If you suspect it you must report it immediately by calling the Defra Rural Services Helpline on 03000 200 301. In Wales, contact 0300 303 8268. In Scotland, contact your local Field Services Office. Failure to do so is an offence.
Additional Resources
- APHA – Sign up for disease alerts
- RH&W – Latest bluetongue announcement
- APHA – Interactive Bluetongue Virus Map (arcgis.com)
- APHA – BTV-3 How to be prepared for a possible outbreak
- GOV.UK – Bluetongue: information and guidance for livestock keepers
- GOV.UK – Bluetongue serotype 3 (BTV-3) vaccine permits
- GOV.UK – Bluetongue: how to spot and report it
- GOV.UK – Bluetongue movement licences and designated slaughterhouses
- GOV.UK – Bluetongue guidance for shows and events in England in 2024 26.06.2024
- DEFRA – Bluetongue: disease control framework in England – 23.05.24
- RH&W – ‘ACT’ on BTV-3 campaign – 20.05.24
- RH&W – BTV ACT midge control flyer – 20.05.24
- BCVA – Bluetongue disease control framework set out – an update from BCVA
- GOV.WALES – Bluetongue bilingual information – 15.05.24
- RH&W – Scottish bluetongue leaflet – 28.03.24
- DEFRA – Bluetongue Flyer – 16.02.24
- DEFRA – How to spot and report the disease
- GOV.WALES – Bluetongue
- GOV.SCOTLAND – Bluetongue
- DAERA – Bluetongue
- AHDB – Bluetongue
- NFU – Bluetongue – the latest info and updates
- NADIS – Bluetongue in cattle and sheep
- The Pirbright Institute – Bluetongue virus
- World Organisation for Animal Health –Bluetongue
- NSA – Sheep farmers warned to remain vigilant amid first Bluetongue case in sheep
What is bluetongue?
Bluetongue (BTV) is a viral disease transmitted by biting midges, which affects all ruminants (e.g. sheep, cattle, goats and deer) and camelids (e.g. llama and alpaca).
The latest strain, BTV-3 appear to mimic BTV-8 in its behaviour, however the existing BTV-8 serotype vaccine will not offer cross protection against this new strain.