Ticks and their effect on sheep health

The threat from tick-borne fever, for instance, is increasing year-on-year – though the dry spell last year did lessen the scale of the problem somewhat – according to Inverness-based SRUC's Eilidh Corr. At the launch of the new lab, she highlighted the various diseases caused by ticks.

"But, we fear that the infection rates that we know about are very much the tip of the iceberg," she told an audience at Moredun last week. "There are, undoubtedly, a lot more cases which will not have been recorded."

Research work is centering on the success of a new molecular diagnostic test which replaced a defunct and unwieldy test in 2014 after a two-year gap following the dropping of that old test. Ms Corr revealed that the new, more accurate testing procedure had shown in its first year of 1000 tests that 40% of them had a tick-borne disease, or had been challenged by it.

The new test has since been available from all SRUC VIOs since 2016 and has a week-long turnaround. It was adopted by the Animal and Plant Health Agency as the 'go to' test in 2017 after proving itself in the field.

The results from recent and ongoing tests will now be put to use to identify high risk areas – ticks are also tested for their disease carrying capability – and allow specific intervention or management to be carried out to mitigate any potential threats to livestock, or humans.

The new test also has a wide range of use, with everything from blood and lesion samples, to post-mortem brain and spinal cord evaluation. It is also being used to evaluate the threat to wildlife from ticks and the new surveillance lab has come up with an easy to use 'sample bag' for gamekeepers and the Game and Wildlife Conservation Trust to use.

The main disease caused by ticks is tick-borne fever, however it is also thought that the immuno-suppression caused by TBF is a factor in escalating infection into many other areas of concern for sheep farmers, like louping ill, plus other infections not necessarily caused by the tick's influence, but by the sheep's reduced ability to fight other diseases.

There is also the major threat to human health caused by ticks, Lyme disease. Dr Mara Rocchi, an expert in immuno response from the Moredun, highlighted a map which clearly showed the geographical range of infection in humans.

This was not just confined to the West Coast of Scotland, where ticks cause serious issues in livestock, but also to the central Highlands and Perthshire. For some reason, the far south coast of England is also a Lyme disease hotspot identified by the mapping process.

The two main sheep infections are:

* Louping ill virus (LIV), which is mainly detected in sheep, cattle, red grouse and ticks in upland areas, particularly in Scotland, Cumbria, Wales, Devon and Ireland. It has also been detected in a range of other animal species, including goats, dogs, pigs, horses, deer, llamas, alpacas and mountain hares.

There is currently no vaccine available and treatment by antibiotics is not thought to be very effective.

* Tick pyemia affects lambs at two to 12 weeks old and is characteriaed by debility, crippling lameness, and paralysis. Pyemic abscesses are common in joints but may be found in virtually any organ and it causes significant economic loss through debilitation and death. The disease is enzootic in many regions of the UK and Ireland where ticks are common.

Treatment of clinical cases of tick pyemia with penicillin or tetracycline can be effective, provided the lesions are not too advanced.

In both diseases, control of tick infestation is the most effective prevention. This can be achieved either by restricting lambs and ewes to low-ground, tick-free pastures for the first few weeks of life, or by dipping ewes before lambing and administering acaricides as dips or smears on lambs.

In young lambs, pour-on preparations of cypermethrin or smears applied before lambs are moved from lambing fields to hill pastures reportedly control ticks effectively.