The par­a­site steal­ing the Lyme light

In­fec­tion-spread­ing ticks are on the in­crease, which has se­ri­ous im­pli­ca­tions for man and game

The Field - - CONTENT - WRIT­TEN BY JOHN & MATT HOL­LAND

Ticks are on the in­crease; John and Matt Hol­land look at the im­pli­ca­tions

When it comes to dan­ger­ous wildlife, and com­pared to many other coun­tries around the world, the Bri­tish coun­try­side can be re­garded as rea­son­ably safe. How­ever, there is one lit­tle beast lurk­ing in the un­der­growth that can cause a de­bil­i­tat­ing dis­ease and it’s on the in­crease. The crea­ture in ques­tion is the ixo­did tick. It has the po­ten­tial to trans­mit Lyme dis­ease, a bac­te­rial in­fec­tion that, left un­treated in hu­mans, can af­fect the heart, joints and ner­vous sys­tem.

Lyme dis­ease can be caused by three species of bac­te­ria, Bor­re­lia burgdor­feri,

Bor­re­lia garinii and Bor­re­lia afzelii, which are car­ried by the ticks and passed on to their host dur­ing blood feed­ing. In the UK, Bor­re­lia is usu­ally trans­mit­ted by the deer or sheep tick, Ix­odes rici­nus. It can be dif­fi­cult to di­ag­nose Lyme dis­ease, not only be­cause of the va­ri­ety of symp­toms but be­cause ticks can trans­mit other bac­te­ria, viruses, pro­to­zoa and ne­ma­todes that cause sim­i­lar symp­toms and can be present in the same tick.

Un­for­tu­nately, in­ci­dences of Lyme dis­ease are on the in­crease. From 1997 to 2000, there were 0.38 cases for ev­ery 100,000 peo­ple per year be­ing re­ported in England and Wales; by 2011, this was up to 1.73 (Pub­lic Health England [PHE], 2013). Many cases may, how­ever, go un­re­ported and PHE es­ti­mates that there could be al­most three times as many cases each year (NHS Choices, Lyme dis­ease). In Scot­land, the fig­ure is much higher, be­ing around 5.53 cases per 100,000 but reached 56 cases per 100,000 in 2009/10 (Slack et al, 2011).

THE BI­OL­OGY OF TICKS

There are more than 20 species of tick in the UK, many of which are spe­cial­ist par­a­sites of wildlife. The sheep and deer tick, Ix­odes rici­nus, is most abun­dant in south­ern England,

par­tic­u­larly the New For­est and the south­ern coun­ties from Devon to Kent, and also the Lake Dis­trict and Scot­tish High­lands. Ix­odes

rici­nus feeds on a range of an­i­mals, from small mam­mals to deer, birds (in­clud­ing gamebirds) and also do­mes­ti­cated an­i­mals such as dogs, horses, sheep and cat­tle. This species of tick is most com­monly found in woods, heaths and moors but it can oc­cur in parks or gar­dens. They tend to be in long grass, bracken or other un­der­growth that pro­vides the high hu­mid­ity es­sen­tial for their sur­vival. They can be par­tic­u­larly abun­dant in ar­eas where there are many deer be­cause they are hosts for the adult stage.

Ticks have com­plex life­cy­cles that last about two to three years. Start­ing from an egg laid on soil, they de­velop into lar­vae, nymphs and fi­nally adults. Typ­i­cally, they will only feed once dur­ing each of the fi­nal three life stages.

They in­crease from larva the size of a speck of soot to adults that are ap­prox­i­mately 2mm long, reach­ing up to 10mm when fully gorged. The lar­vae typ­i­cally feed on small mam­mals or birds, from which they can ac­quire the in­fec­tive bac­te­ria. Hav­ing fed, they then drop to the ground, moult into nymphs and seek out (known as quest­ing) an­other small ver­te­brate host, pass­ing on Bor­re­lia in the process. Once they have fed, the nymphs again drop to the ground and moult into adults and again quest for a new host. In the case of the sheep tick, th­ese are usu­ally larger mam­mals such as sheep or deer and again the bac­te­ria may be passed. Dogs are also a com­mon host. Ticks will mate at this stage so the large mam­mals are im­por­tant for sur­vival. Once gorged, the adults drop to the ground to lay their eggs.

The adult stage is usu­ally found on dogs whereas on hu­mans it is the minute lar­val and slightly larger nymphal stage, which is why they can go un­no­ticed.

Ticks can be af­fected by en­vi­ron­men­tal con­di­tions be­cause they spend most of their time in the veg­e­ta­tion, only quest­ing when the tem­per­a­ture and hu­mid­ity are right. If it’s too hot or too dry they will die, so wet­ter au­tumns and springs al­low them to be ac­tive for longer.

SPREAD­ING BOR­RE­LIA

The re­la­tion­ships be­tween ticks, their mam­malian hosts and Bor­re­lia are com­plex. The Bor­re­lia mul­ti­plies within the smaller ver­te­brates such as ro­dents and birds (known as reser­voir hosts) and not larger ones such

Tick bites can be pre­vented by keep­ing legs cov­ered, wear­ing long-sleeved shirts and us­ing in­sect re­pel­lent

as deer, sheep, dogs and hu­mans. How­ever, Bor­re­lia, once within hu­mans and dogs, can start to at­tack the cen­tral ner­vous sys­tem caus­ing the symp­toms of Lyme dis­ease. On a more pos­i­tive note, the pro­por­tion of ticks car­ry­ing Bor­re­lia is typ­i­cally very low in the UK (0% to 10%) but be­ware in the hotspots where it can be high; it is also on the in­crease in some ur­ban ar­eas.

lyme dis­ease

While still rare, the risk of con­tract­ing Lyme dis­ease is on the in­crease in the UK. Once in­fected, there are three stages of the dis­ease. The first oc­curs be­tween three and 36 days and usu­ally re­sults in a sin­gle cir­cu­lar red rash that does not itch but spreads out­wards, giv­ing the ap­pear­ance of a bulls­eye. Mild, flu-like symp­toms can also oc­cur. The sec­ond stage, which not all cases progress to, oc­curs over weeks or months. Symp­toms can in­clude joint pains, neu­ro­log­i­cal prob­lems, in­flam­ma­tion around the brain, heart prob­lems and rashes. Stage three is per­sis­tent Lyme dis­ease, which has mul­ti­ple symp­toms af­fect­ing the joints, skin, nerves, heart and brain. In the lat­ter it can cause dis­rup­tion of bal­ance, mem­ory and per­son­al­ity. Chronic fa­tigue is also de­scribed.

Di­ag­no­sis in stage one is from the rash or flu-like ill­ness, es­pe­cially if as­so­ci­ated with a tick bite, and for­tu­nately an­tibi­otics are usu­ally an ef­fec­tive treat­ment with no per­sis­tent ef­fects. How­ever, symp­toms can vary be­tween in­di­vid­u­als and for other species of Bor­re­lia a rash may not al­ways oc­cur. Stages two and three are more dif­fi­cult to di­ag­nose but blood tests may help.

Fur­ther in­for­ma­tion is avail­able on­line. How­ever, if you be­lieve you have been in­fected then you should con­sult with your doc­tor and let them know you have spent time where ticks oc­cur. Tick bites can be pre­vented by keep­ing legs cov­ered and wear­ing long-sleeved shirts, us­ing in­sect re­pel­lent on ex­posed skin and not ly­ing down in long veg­e­ta­tion. All parts of the body and head, es­pe­cially the armpits, waist and groin, should be checked for ticks im­me­di­ately af­ter vis­it­ing ar­eas where they oc­cur, and any at­tached ticks should be re­moved quickly and cor­rectly.

in game wildlife

Al­though greater move­ment and abun­dance of deer aids the spread and in­creases the pro­fu­sion of ticks, their higher num­bers also help to di­lute the in­fec­tion rates. An­other un­cer­tainty is whether the in­crease in the num­ber of re­leased pheas­ants is ex­ac­er­bat­ing the spread of Lyme dis­ease. Pheas­ants are a reser­voir host for Bor­re­lia so have the po­ten­tial to main­tain or spread the dis­ease. Those work­ing with game should there­fore be es­pe­cially vig­i­lant for tick bites and take pre­cau­tions to pre­vent be­ing bit­ten.

Be­sides trans­mit­ting dis­eases, heavy tick in­fes­ta­tion would ap­pear to be harm­ful, par­tic­u­larly to chicks where it can cause mor­tal­ity. This is most likely to oc­cur in ar­eas where tick bur­dens are high and with ground-nest­ing birds, which is why red grouse are vul­ner­a­ble.

In rough, hill-graz­ing ar­eas an­other se­ri­ous dis­ease, loup­ing ill, can also be trans­mit­ted by the sheep tick. This usu­ally poses a threat to red grouse but can cause high mor­tal­i­ties (60%) in newly in­tro­duced sheep flocks; even ac­cli­ma­tised flocks can suf­fer 5% to 10% mor­tal­ity (Sar­gi­son, 2008).

There is still much to learn about ticks, their hosts and dis­ease trans­mis­sion. In ad­di­tion, how the man­age­ment of wildlife and its move­ment around the coun­try­side in­flu­ences the risk of ticks car­ry­ing Lyme and other pathogens needs fur­ther in­ves­ti­ga­tion. You can help with this by send­ing ticks to the tick sur­veil­lance scheme run by PHE. Mean­while, it is best to be vig­i­lant and take pre­cau­tions to avoid tick bites, es­pe­cially if, un­for­tu­nately, you are one of those peo­ple they seem to find more at­trac­tive.

Top: Ix­odes rici­nus, the sheep and deer tick

Left: you are most at risk in woods, heath and moor

Above: one of the sneaky places ticks hide on dogs Be­low: a cir­cu­lar rash is a symp­tom of Lyme dis­ease

Greater move­ment and abun­dance of deer has aided the spread and in­crease of ticks

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