Vet’s View

Liver fluke can be fa­tal. Char­lotte Mouland out­lines the key facts about this canny par­a­site, what dis­ease it causes in ru­mi­nants and how best to con­trol it

Country Smallholding - - Inside This - with Char­lotte Mouland

Liver fluke, by Char­lotte Mouland

LIVER FLUKE used to be thought of as a dis­ease only af­fect­ing par­tic­u­larly wet farms, but with warmer, wet­ter weather pat­terns and in­creased move­ment of live­stock around the coun­try it is now wide­spread.

The life­cy­cle

Ma­ture liver fluke par­a­sites re­side in the bile ducts of cat­tle and sheep and re­lease their eggs into the bile, which are even­tu­ally ex­creted in the host an­i­mal’s fae­ces. Adult liver fluke can grow up to 3.5cm in length and take a very dis­tinc­tive flat, leaf shape. The liver fluke eggs are in­fec­tive to other ru­mi­nants, but only af­ter a num­ber of key steps in their life­cy­cle. Know­ing this helps to ex­plain the sea­son­al­ity and ge­o­graph­i­cal spread of liver fluke. At tem­per­a­tures above 10°C, liver fluke eggs de­velop and hatch into a motile lar­val stage called a miracidia; Miracidia have a very short life­span of just three hours and their sole in­ten­tion in this time is to find a host wa­ter snail. If suc­cess­ful, within the snail a fur­ther three lar­val stages de­velop to form a cer­caria; Cer­caria are shed from the snail and at­tach to grass blades, de­vel­op­ing into the fi­nal and in­fec­tive lar­val stage, the metac­er­cariae; In­fec­tive lar­vae are eaten by ru­mi­nants and mi­grate through the liver, caus­ing ex­ten­sive dam­age on their way to the bile duct. The liver fluke life­cy­cle is there­fore a very long and de­tailed process and de­pends both on the cor­rect tem­per­a­tures and the avail­abil­ity of wa­ter snails.

What dis­ease does liver fluke cause?

There are two stages in the life­cy­cle where liver fluke causes dis­ease to the in­fected an­i­mal. Firstly, when the lar­vae mi­grate through the liver of the sheep or cow which can cause se­vere tis­sue dam­age; the ex­tent of this in­jury de­pends on how many lar­vae are eaten.

The sec­ond stage of dis­ease oc­curs when the ma­ture fluke take res­i­dence in the bile ducts. Be­cause sheep have much smaller liv­ers than cat­tle, the dam­age caused by im­ma­ture fluke track­ing across the liver is more prom­i­nent in sheep and may cause sud­den death. Longer-term dis­ease caused by adult fluke dam­ag­ing the bile ducts is more com­monly seen in cat­tle and can cause weight loss, di­ar­rhoea and oc­ca­sion­ally ‘bot­tle jaw’ (fluid swelling un­der the jaw).

Con­trol on your hold­ing

There are two ways to con­trol fluke on your farm: a) re­duc­ing the wa­ter snail pop­u­la­tions on the land or b) us­ing flu­ki­cides to treat in­fected an­i­mals. Re­duc­ing wa­ter snail pop­u­la­tions isn’t as sim­ple as it sounds, but fenc­ing off wet ar­eas or wa­ter­ways can help.

Strate­gic use of flu­ki­cides should be con­sid­ered in hold­ings that host liver fluke par­a­sites. Un­like with gut worms, adult ru­mi­nants don’t de­velop an im­mu­nity to liver fluke, so all ages are sus­cep­ti­ble to dis­ease. Work with your vet to de­ter­mine if liver fluke are present on your hold­ing and de­vise a spe­cific liver fluke con­trol plan. The long dry weather this sum­mer will prob­a­bly have pushed stock closer to nat­u­ral wa­ter­ways to graze, so we will have to wait and see how this af­fects the liver fluke pic­ture this au­tumn and win­ter.

A liver show­ing acute dam­age from liver fluke

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