Clinical observations from a study comparing two different treatments for bluetongue in sheep

In September 2023, the official national reference laboratory confirmed the presence of BTV serotype 3 in The Netherlands. In the following weeks, it appeared that the infection caused very severe clinical signs in sheep, but it was challenging for the involved veterinary clinicians to select appropriate labeled drugs to treat them. The objective of this study was therefore to document the clinical presentation and survival outcomes of sheep affected by bluetongue and to evaluate the effects of a treatment protocol with and without antihistamines. From a group of 83 sheep with acute and clear clinical signs of bluetongue, one group of 41 sheep received a single injection of meloxicam (1 mg/kg) followed by oral paracetamol tablets (10-20 mg/kg, 3dd for 3d). Another group with 42 sheep received the same treatment with the addition of an antihistamine injection (chlorphenamine maleate, 1 mg/kg, 1dd for 3d). Clinical signs and survival rates were monitored for all sheep. Logistic regression and survival analyses were performed to evaluate the data. An overall case fatality rate of 57% was observed, which illustrates the challenge in treating infected naïve animals with BTV-3. The most commonly encountered clinical signs were excessive salivation, dyspnea, depression, and lameness. Severe salivation was associated with significantly reduced survival time. The mean survival time for the group treated with antihistamines was 0.8 days, whereas it was 2.5 days for the group without antihistamines. The results of this study may not be representative of bluetongue infections caused by other serotypes or under different conditions. Based on our findings, however, we cannot recommend the use of antihistamines for treating bluetongue-affected sheep, as they did not improve survival. We would like to emphasize the importance of timely decision-making regarding the continuation or cessation of treatment, given the typically low survival rates in clinically affected sheep.