What Does the Vet Say? - January 2025

Dr Eoin Ryan and Aisling Tracey from the National Disease Control Centre (NDCC) at the Department of Agriculture, Food and the Marine (DAFM) recently published a paper titled Bluetongue: What are the risks for Irish cattle farmers and what can we do about it?  The details of this paper were presented at at recent conference by Dr Ryan who is senior superintending veterinary inspector at the DAFM and head of the NDCC.

The clinical signs of bluetongue, as outlined in the paper, may include some or all of the following:

• Fever, inappetence (loss or lack of appetite), drop in milk yield, reddening of the mucus membranes, sores on the nose, gum and dental pads, swelling of the face, lips and tongue (i.e. blue tongue), breathing difficulties if the tongue swells, drooling, discharge from the eyes and/or nose, lameness due to coronitis (inflammation and swelling at the top of the hoof) and abortion or deformities in offspring/foetuses.
• In severe cases, death can result.
• Sheep are more likely to show obvious and more severe clinical signs of bluetongue than cattle if they become infected, and mortality rates can reach 30-70 per cent.

Resembling other conditions

• The clinical signs of bluetongue can resemble other conditions commonly seen in sheep and cattle, the paper reveals, such as infectious bovine rhinotracheitis (IBR), photosensitisation, malignant catarrhal fever (MCF), or anaphylaxis.

Huge production losses

• Cases of bluetongue serotype-3 in the Netherlands in autumn 2023 and into 2024 resulted in huge production losses, significant welfare issues and high mortality (up to 60 per cent) in some outbreaks.
  Due to the similarities between the deformities caused by Schmallenberg virus and bluetongue virus in offspring/aborted foetuses, foetal carcasses submitted for post-mortem to regional veterinary laboratories are routinely tested for bluetongue and Schmallenberg viruses. Similarly, because bluetongue is only one of a number of conditions which can cause severe milk drop in dairy cattle, samples from such disease investigations are routinely tested for bluetongue as part of the overall diagnostic testing.

Vaccination

The paper advises that vaccination against bluetongue virus is a key control measures and is necessary for disease eradication. Licensed bluetongue vaccines are commercially available for bluetongue serotypes 1, 4 and 8 which can help to facilitate intra-EU movement.
Animals from certain countries require vaccination against bluetongue to meet certification requirements, prior to movement. Proof of vaccination status for the bluetongue virus strains recently circulating in those countries or regions should be obtained.
The recent emergency use of BTV3 vaccines in EU Member States and in Great Britain have been authorised under emergency circumstances as a disease-control measure, where BTV3 is circulating, according to the paper. These BTV3 vaccines do not guarantee that animals will not become infected; however, they do reduce the severity of the disease and the amount of the virus in the blood of infected animals, and so they are of great benefit to livestock farmers in reducing the impact of an outbreak of bluetongue.
According to the paper, BTV3 vaccines have not yet obtained European Marketing Authorisation, nor have they determined an immunity period guaranteed in the specifications of the vaccine. So, for this reason, animals vaccinated using these BTV3 vaccines do not meet the certification requirements for intra-community trade. This means that livestock vaccinated using BTV3 vaccines cannot enter Ireland. In autumn 2024, an outbreak of serotype 12 (BTV12) was detected in the Netherlands. BTV12 had not previously ever been detected in Europe. No vaccine is available at all for this new strain. This means that if it spreads widely in spring 2025, control will be very challenging. This poses an additional risk for Ireland, in addition to the existing risk of BTV3.