Be on the look out

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 to reduce the midge population (and therefore 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.

“Vets tell us they see a range of clinical signs from nothing, to mild, severe, or even death. In The Netherlands, up to 20% of 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 had 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. High fever, lethargy, swollen lips and throat can also be seen. Sheep have difficultly breathing and swallowing and are severely lame; many die or have to be culled.

“Last year, the Dutch reported more clinical signs in sheep – about four times as high as 2006. There were also more long-term effects. For instance, more rams were infected and the high fever caused a rapid drop in semen quality which took 2-4 months to recover. Some even became sterile.”

Mr King suggests producers look out for signs of what looks like a burnt muzzle with stock cooling their noses in troughs.  Visible signs such as swollen heads or bottle jaw may also be seen. In addition, wool breaks can occur due to temporary damage to the follicles, he adds. 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 all 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.”

According to Mr King, milk yields in Dutch dairy herds fell by 2-4 litres/cow/day for up to three months; similarly in Germany yields fell by up to 40% and 3-7% in France. There were reports of lower intakes leading to cows losing weight or drying off.  The Dutch goat industry was also affected for the first time last year and suffered a drop in milk output. Its 400 commercial units saw up to 40% morbidity. Again, typically a high fever (up to 42^oC), plus less obvious clinical symptoms were seen such as erythema of the udder skin and small subcutaneous haemorrhages.

“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.”

TABLE 1.

SPREAD OF BLUETONGUE VIRUS INFECTION

SYMPTOMS OF BLUETONGUE VIRUS

• Fever (temperatures up to 40-42C)
• Lethargy
• Loss appetite
• Milk drop
• Crusts on nose
• Nasal discharge
• Conjunctivitis
• Drooling saliva
• Ulcers in mouth
• Lameness
• Lying down
• Swollen lower legs, red swollen coronary band
• Swelling of head and neck
• Swollen ulcerated teats