Liver Fluke…again!

Liver Fluke

You may have received warnings about liver fluke recently from the likes of the NSA, SCOPS or in the farming press. This is especially important this year as conditions are ideal for fluke and its intermediary host the Mud Snail.

 

Here’s a reminder of what you hopefully know already:
Liver fluke disease (fasciolosis) is caused by the parasite Fasciola hepatica. Disease can result from the migration of large numbers of immature flukes through the liver, or from the presence of adult flukes in the bile ducts, or both. Liver fluke can infect all grazing animals (and man) but mainly affects sheep and cattle. It is most pathogenic in sheep. 

Compared to other helminths the life-cycle is complex, involving an intermediate host, the mud snail, and several free-living stages. The role of the snail, which prefers muddy, slightly acidic conditions, means that the incidence of liver fluke is far greater in the wetter areas of the country. With the capacity of the snail to multiply rapidly along with the multiplication of the parasite within the snail, there is potential for very large numbers of parasites.

Adult fluke lay eggs that are passed out onto pasture in the faeces. At suitable temperatures, a larval stage develops within the egg, hatches and migrates in thin films of moisture, actively seeking the snail host. Within the snail they undergo two further developmental stages, including multiplication, eventually becoming infective, and emerge from the snail when the temperature and moisture levels are suitable.

They migrate onto wet herbage, encyst and become the highly resilient infective stage of the liver fluke. Following ingestion, the young flukes migrate to the liver, through which they tunnel, causing considerable damage. The infection is patent about 10–12 weeks after the larvae are ingested. The whole cycle takes 18-20 weeks.

The epidemiology of liver fluke is often viewed as the result of two distinct cycles of snail infection and pasture contamination. 

Summer infection of snails
In wet summers, snail populations multiply rapidly and snails are invaded by hatching larvae from May–July. If wet weather continues, the snails shed massive numbers of infective larvae onto pasture during July–October. Clinical fasciolosis resulting from summer infection of snails arises usually from ingestion of large numbers of larvae over a short period of time in July–October.

Winter infection of snails
Less commonly, snails can become infected in late summer or early autumn and development within infected snails is delayed as the snails become dormant and hibernate. The larvae are then not shed onto the pasture until the following spring. This can produce an initial and significant infection in herds or flocks in the spring.
Fasciolosis
There are three presentations:
Acute:     Sudden death or dullness, anaemia, ascites and abdominal pain in the autumn. Treat with Triclabendazole (e.g. Fasinex).
Subacute:     Rapid weight loss, anaemia, bottlejaw and ascites in some cases in the winter. Treat with product active against late stage larvae e.g. Nitroxynil (Trodax), Oxyclosanide (Zanil).
Chronic:     Progressive weight loss, anaemia, bottlejaw, scour and ascites in early spring. Treat with adulticide e.g. Closantel (Closamectin), Chlorsulon (Ivomec Super).

Control
Fencing off particularly wet areas on farms, even temporarily, will help reduce exposure. If possible, stock should also be moved off high risk fields onto safer grazing at this time of year. Lower risk fields would include those with no or few mud snail habitats, fields not grazed by sheep or cattle earlier in the year, or fields growing stubble or forage crops.

Resistance
There are reports of Triclabendazole resistance in the UK but it’s difficult to prove as Faecal Egg Counts in fluke are unreliable. Anecdotally however, it seems to be increasing which would be expected. Avoid over using Triclabendazole if possible and rotate the different flukicides. Take advice and use management to reduce risks. Liver fluke and the resultant disease Fasciolosis is complex and takes some understanding. More information can be found at: www.scops.org.uk, on the Nadis website or look for links on our Severn Edge website.
Contact the surgery for advice and any Flock/Herd Health Planning.

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Related SEV Branch