Great Britain is now in a ‘seasonally vector low period’ for BTV 3 and this has led to changes in the control measures adopted and the temporary easing of BTV control restrictions within the Kent and Norfolk Temporary Control Zones (TCZ).
The ‘vector low period’ is when biting midge activity is reduced due to current weather conditions. This makes transmission of the virus between midge and livestock much less likely.
The midge vector is most active during the summer months but usually dies off during the winter. Midge do not actively bite at temperatures below 4 degrees celsius.
This reduction in transmission risk has led to the decision not to cull infected animals where results indicate older infection and the presence of BTV antibodies is detected. However, other measures, such as restricting infected animals to their current location may well continue. Animals testing negative from TCZs may be allowed to move under licence if certain conditions are met. Some restrictions on the movements of animals within the TCZ have also been eased. However, the temporary easing of restrictions will need to be revised when vector activity increases; usually in the warmer March and April climate.
As of the 4th of February 2024, there were 83 cases of BTV 3 in England on 44 premises. There is still no evidence that the disease is actively circulating in Great Britain.
Symptoms of BTV-3 can vary across ruminants, with clinical signs in sheep generally being more overt than in cattle. In sheep, clinical signs include ulcers in the mouth, discharge of mucus, drooling from the mouth and nose, oedema (swelling of the mouth, head and neck) and sudden death.
Reports in cattle suggest that they are less severely infected. Symptoms include mouth ulcers, nasal discharge, crusty erosions around the nostrils, lethargy and milk drop.
Calves can become infected with bluetongue virus before birth, if the mother is infected while pregnant. Signs of infection include calves born small, weak, deformed or blind, death of calves within a few days of birth and abortions
There is currently no vaccine against BTV 3. The current strategy centres around quick reporting and heightened surveillance for the disease. For other Bluetongue virus stains (1, 2, 4 and 8) vaccination remains the most effective way to protect a herd or flock. Members should also discuss the risks of importing stock from BTV affected countries with their vet. Farmers should also take particular care when importing germinal products and should make sure that they know where the animals or donors originated from and that they meet all the export health certificate requirements. Requesting a pre-export test should be considered.
BTV is a notifiable disease. The FUW continues to urge members to be vigilant for signs of infection and to report any suspect cases to APHA.