Keep watch this summer

Checking stock regularly for symptoms that can look similar to foot and mouth this summer will be the key to spotting bluetongue. Regular inspection around the nose, mouth, and the coronary band (where the hoof stops and skin starts) should catch signs early enough for appropriate action, says Intervet’s large animal veterinary manager Alasdair King.

However, he reminds producers that they must watch out for a range of symptoms in livestock because BTV isn’t easy to detect. “It can take a very alert farmer to detect the mildest of signs,” he says. “And because eradication is virtually impossible, it’s important to focus on the best possible prevention. This includes vaccination with Bovilis® BTV8, managing habitats and using insecticides proven to kill midges (and therefore reduce the risk of infection), as well as being extra vigilant.”

Information gathered from Dutch vets, and countries such as Germany, France and Belgium, show that BTV8 is more severe in its second year, not just in terms of spread (see table 1), but also symptoms and long-term consequences.

“In The Netherlands, up to 20% of infected adult sheep died in 2007, while in beef and dairy herds, in 50% of cases, cattle had crusts and lesions on the nose. Plus they showed excess salivation (38% of cases) fever (31%) and conjunctivitis (31%). Yet despite its name, one Dutch vet said a blue tongue was only reported in about 15% of cases in sheep.”

Although sheep experience the most severe symptoms, and are highly likely to die, cattle may suffer secondary infections such as pneumonia and can act as reservoirs of infection. Even when they show no obvious signs, they keep the virus in circulation. Unfortunately, Mr King points out that as well as foot and mouth, many symptoms of BTV8 in sheep are similar to orf, liver damage, sunburn and the acute form of cobalt and vitamin B12 deficiency. Sheep have difficultly breathing and swallowing and are severely lame; many die or have to be culled.

Mr King suggests producers look out for signs of what looks like a burnt muzzle with stock cooling their noses in troughs.  Abortions or stillbirths without other symptoms are common in cows; and weak calves born up to 14 days early will be more common. Cows may be unable to walk or swallow and have a high fever.  They may be lethargic and can’t get up. It may be that only a few animals show signs in one herd, or that many cows are ill.

“Look out for diarrhoea, lameness, conjunctivitis, crusts on the nose and/or teats, swollen throat, producing a lot of saliva, swollen lower legs, milk drop and increased susceptibility to other diseases.

“Losses of more than 80 million euros were reported by the Dutch livestock sector last year. These include costs associated with weight loss, falling milk yields and vet costs. Plus there were restrictions on live exports and animal products. In the long-term bluetongue disease caused by BTV8 can also result in fertility problems, abortion and abnormalities, and lameness. Of course all of this affects calving pattern or lambing season, replacements and growth rates, which shows we can’t underestimate the damage that this virus can do,” Mr King concludes.

TABLE 1.

SPREAD OF BLUETONGUE VIRUS INFECTION