The Truth About Ticks

Wendy Fox, Chairperson of BADA - UK highlights the serious threat to human health

Whether hill and mountain, upland or lowland, sheep are susceptible to a growing threat, and in turn, so is the wildlife and people in their vicinity.

In the UK the most common tick is the sheep tick (Ixodes ricinus), which is about the size of a sesame seed (2.5 mm). It is oval, with four pairs of legs and a flattened body. It is also known as the deer tick and also the castor bean tick. Studies by The Game Conservancy Trust and Oxford University indicate that the tick population appears to be on the increase and with a rise in numbers comes the threat of bacterial and viral diseases.

During spring and autumn adult ticks may be found "questing" - waiting in ambush on vegetation from ground level to about 18 inches high for a suitable host to pass by. Unfed females are rusty red with a small dark shield on the back, and males are smaller and uniformly dark. After feeding for up to ten days on any mammal including humans, the adult female swells to the size of a small pea. Most people, when asked to describe a tick, refer to something coffee bean sized, and like a grey-blue balloon. This description is how most people observe ticks on dogs, sheep or hedgehogs and describes a fully engorged adult. In this form a tick can be quite clearly seen. However, when newly hatched a fully fed tick is much smaller and less noticeable.

Blood meal
After feeding and mating, females drop off their hosts and deposit eggs on the ground in autumn and early spring. These hatch and produce tiny Larvae (0.5 mm) which have only three pairs of legs. They attach to small and medium-sized mammals and birds and feed for about three to five days. After their first blood meal, they moult to the nymph stage and acquire eight legs. The nymphs then feed again and moult to the final stage - the adult. After a final blood meal, the female lays a single batch of many thousands of eggs, and then dies.

Ticks are relatives of spiders and along with mites belong to the family Acarina. They are designed to bite and feed un-noticed. Their saliva contains a natural anaesthetic, which means that the tick can feed without causing irritation. It is this ability that makes this tiny terror a potential time bomb.

During the bite, when the tick injects its numbing saliva which flows into the bloodstream, a concoction of bacteria and viruses that the tick may be carrying can also enter. For sheep, this can lead to diseases such as Louping ill and tick fever.

When looking at previous studies on the effects of ticks such as The Bowland: Bleasdale Scheme from 1980-1985, tick control with pour on or sheep dip used to coincide with the rise in tick activity was reported to be reasonably successful. Every animal of the 13,000 ewes and shearlings involved had reduced tick loads. Tick counts reduced by 74% in spring and 78% in autumn. Lamb losses reduced from 10.7% to 2.5%. These rates of success were dependent on the range of land, commitment from neighbouring properties and wildlife migration. In 1985 it was shown that tick control could be cost effective by eliminating serious losses but in comparison to recent studies, which show a higher presence of ticks, it would appear that the tick is fighting back.

The Game Conservancy Trust has been studying the impact of sheep ticks and the disease Louping ill on red grouse in Scotland. In 1985 around 4% of grouse chicks encountered by researchers were infested with ticks; by 2003 the figure had risen to 92% and of these up to 80% of infected chicks died. After radio tracking wading birds, scientists reported chicks as young as 3 weeks old with heavy tick infestations.

Studies carried out and published in the Journal of Animal Ecology also show that hares were found to be important hosts for all stages of ticks at two study sites and, where sheep were frequently treated with acaricide, hares then fed the greatest proportion of adult ticks. Hare densities were reduced at the experimental sites between 1993 and 2001 but remained relatively constant at the control site. Both nymph and larvae tick burdens on red grouse chicks declined over this period to very low levels at the treatment site but not at the control site. The estimated size of the tick population at the treatment site decreased by more than 99% by 1999. Studies by scientists at Oxford University have shown that in addition to hares, the common grey squirrel and pheasants also act as suitable hosts to transfer known infections throughout the tick population. Tick sampling has shown that infected ticks populate many parts of the UK from the remote Isles of Scotland to the urban parks.

Infective
Any infective tick population can pose a problem even with harsh winters to help lower the numbers. Pathogens can survive in infected ticks for long periods and because the sheep tick (Ixodes ricinus) can survive unfed up to a year while waiting for a new host, ticks infected during their previous phase can still be infective after long periods of hibernation. This increase in the tick population is probably due in part to the milder climate and the warmer winters which allow not only a higher survival rate of individual ticks but also an early start to the 'questing' season. The mild and wet spring and summers make the perfect climate for ticks who, with the benefit of warm autumns, will continue activity for much longer. Ticks are indiscriminate feeders. Any passing warm blooded host will make a suitable meal. Mice, voles, migrating birds, foxes, badgers, deer, cattle, sheep and people will equally be latched on to by the hooked front legs of a tick in waiting.

Flocks and the surrounding wildlife can act as reservoirs for bacteria and viruses without individuals necessarily showing symptoms. In one UK study, blood samples from a flock of sheep were tested by PCR (Polymerase Chain Reaction) finding that 100% of the flock was carrying Louping ill and 80% tick fever. The presence of these diseases in flocks across the UK spreads the infections far and wide within the surrounding wildlife as ticks feed from multiple hosts throughout their entire life cycle. Studies show that migratory birds and sea birds also act as reservoirs for tick-borne pathogens and so their distribution lacks any boundaries set out by animal trafficking rules and regulations.

Costly problems
The cost of not controlling ticks on sheep can be huge. Problems resulting from tick infestations can be low ewe milk production, reduced thriftiness of livestock, poor lambing or abortion, fleece quality deterioration, poorly finished lambs (which can result in selling as stores rather than as finished lambs), poorly developed ewe lambs (affecting oestrus if less than 60% of mature body weight is reached resulting in unsuccessful tupping), higher mortality resulting in flock replacement costs and vaccination of diseases such as Louping ill. The cost to the human can barely be quantified when infection can lead to a life-time of ill health, physical disability and loss of earnings. Every agricultural worker or indeed anyone enjoying the great outdoors plays a game of Russian roulette with the tick.

It is recognised that Borrelia burgdorferi (Bb) the cause of Lyme disease and the most commonly found bacterial infection amongst ticks, can be passed from animal to human and from mother to child during pregnancy. It is a 'spirochaetal' form of bacteria, similar to, but much more advanced than, syphilis. It is also recognised that many people can become asymptomatic carriers of the disease. Just like chicken pox, which can later develop into shingles, or glandular fever (Epstein-Barr virus), such infections are merely suppressed by the immune system and never truly eradicated. Joseph Burrascano, Jr., M.D., one of the world's leading Lyme disease specialists, believes this cumulative effect of multiple bites can be different for each individual. Dr. Burrascano calls it 'the one bite too many theory' as some people can be infected but remain symptom-free until bitten 'once too often' which activates the latent infection. There are many hundreds of types and sub-types of Borrelia and only a very few have been studied. Along with other previously considered 'exotic' diseases now known to be endemic in the UK, Borrelia bacteria can make the result of a tick bite disastrous. Because of these risks, English Nature in conjunction with DEFRA still advise "If a tick does attach, go to a doctor to have it removed, and to be prescribed preventive drugs (antibiotics) against Lyme disease."

With thanks to NSA Sheep Farmer, September/October 2005

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Tick Control Programme

Sheep pour on is arresting mounting tick populations

Milder winters coupled with an increase in areas of unmanaged moorland are encouraging the tick population to soar according to The Heather Trust. The trend has resulted in a rise in Louping-ill and other tick transmitted diseases among sheep. Grouse chicks are also affected and this can lead to the cancellation of shoots and loss of substantial sums of money to the rural infrastructure. Landowners across the UK are responding by establishing tick control programmes, which are encouraging farmers to treat their flocks with the persistent alphacypermethrin pour on.

Tick pyaemia
Tick pyaemia incidences have fallen dramatically within the last 12 months on one 800 ewe Perthshire hill unit since adopting a tick control initiative led by The Heather Trust and involving co-operation between four estates and seven farms. "We had used a cypermethrin-based product to counter ticks, but it was obviously lacking impact since we had an average of 26 lambs affected per season due to tick pyaemia infection," explains Iain Wilkinson, farms manager to Murthly Estate. "In 2004 we adopted a new approach to tick treatment which reduced the number of infected cases to a nominal four lambs. We introduced Dysect Sheep Pour On, an alphacypermethrin which provides the longest available tick control. We made a total of five treatments throughout the season to the ewes, and four to the lambs.
"Changing product not only brought a massive reduction to the number of tick pyaemia incidences, but the longer persistence gave us greater flexibility of up to seven weeks between treatments. In comparison, the previous pour-on product we used provided four weeks protection," says Mr. Wilkinson. "That flexibility means a lot; up to five people are involved in the day long gather which can easily be delayed for one week due to poor weather.
"In fact we plan to use Dysect again in 2005, and this year to reduce the number of treatments by one, to both ewes and lambs, which will bring cost savings in product and time, and for us that time saving is money."

An example of another larger scale tick control programme is the Angus Glens Moorland Health Project, a co-operation of five vet practices, 11 proprietors, 30 farmers, 30 gamekeepers and 30,000 ewes. Co-ordinated by Ian Gill of the Kirriemuir-based Thrums Veterinary Group and Ian McCall of the Game Conservancy's Advisory Services, the venture was originally instigated by one of the landowners involved in the project who had expressed concern over the increasing incidence of Louping-ill not only among sheep and lambs, but also grouse chicks in which mortality due to Louping ill can reach 80%.

The venture, which is jointly funded by the proprietors and Tayside Leader+, was further inspired by the success of earlier control programmes in Morayshire, the North York Moors, the Forest of Bowland and the Northern Uplands of England. "The earlier ventures were designed to reduce the death rates among lambs and grouse chicks caused largely by tick-related diseases," says Mr. Gill.

Year-round protection
"Tick control programmes pose a major challenge in that ticks feed on sheep for only two weeks, however they can be any two weeks of the year, therefore the sheep require protection throughout the year, but particularly from March through to October," says Mr. Gill.

One year on and he reports the large scale project to be progressing 'reasonably well' with co-operation from all those concerned. A range of sheep treatment options is being offered to the project members, including Dysect, OP dip and deltamethrin products, says Mr. Gill. "Product effectiveness is carefully monitored. All stock including ewes, lambs, hares, grouse and deer are checked for tick, and a watch is made for Louping-ill, and other tick borne diseases in sheep by analysing blood samples taken from sheep and grouse. So far, we have found that Dysect offered longer persistency with full protection for eight weeks, while both OP dips and deltamethrin gave up to six weeks protection and therefore necessitated additional costly gathers."

It is hoped that ventures like the Angus Glens Moorland Health Project will achieve their ultimate objective to reduce the tick population and levels of tick borne disease in sheep and cattle and this should favour a return to higher grouse populations.

Cooperation
Simon Thorp of the Heather Trust explains: "There is no quick fix and great attention to detail is required using the best treatments available if the required level of tick reduction is to be achieved. Co-operation between neighbouring landowners and farmers is also essential if the measures are to be effective," he says. "We are advising on establishing and co-ordinating similar schemes throughout the country and we are campaigning for this work to be included within the scope of agri-environment schemes in the hope that this will serve to combat the spread of Louping-ill among sheep and grouse."

He adds: "A grouse moor's annual bag of, for example, 500 brace is worth £50,000 to the local economy. However, this income is threatened if sheep ticks reduce grouse numbers, and it not only affects the landowner but also the entire rural infrastructure, from keepers to hotel proprietors. Furthermore, the issue stretches beyond heather moorland and grouse moors to vast areas of other moorland managed by sheep. In fact, sheep ticks proliferate on the moors of southwest England, through Wales and the length of the Pennines.
"So it's hardly surprising that the presence of ticks and the associated diseases can greatly reduce the attraction to farmers of turning grazing livestock out onto the hills," says Mr. Thorp. "Therefore, an active tick control programme using a persistent alphacypermethrin pour-on treatment will make a major contribution towards more sustainable and profitable sheep flocks in these areas and improve the level of moorland management of grazing livestock."

With thanks to NSA Sheep Farmer, September/October 2005

For more information on Louping-ill, see the article Louping Ill in Sheep by Dr. Hugh Read, Moredun and
http://www.vet.uga.edu/vpp/gray_book/FAD/LOI.htm

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Coccidiosis

The Nadis Sheep Disease Focus article on coccidiosis in sheep

Janssen Animal Health launches free coccidiosis testing scheme for UK's lambs - Murray Farmcare of Dumfries Newsletter, May 2007

Tel: 01494 567555; Email: ahealth@jacgb.jnj.com

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