Liver fluke disease or fasciolosis can occur in three forms: acute, sub-acute and chronic. The signs of the disease vary accordingly. In the acute form, the signs are: weakness, anaemia, shortness of breath and sudden death.
In the sub-acute and chronic form, the signs are a progressive loss of condition, pale mucous membranes, anaemia and emaciation.
Signs of fasciolosis
- The acute form
This is associated with immature flukes, and usually occurs in autumn and early winter, two to six weeks after the animal has ingested large numbers of metacercariae (larvae). Immature flukes move through the liver, resulting in dark to yellowish-white lesions in the organ. This can cause severe bleeding leading to anaemia.
- The sub-acute form
This is usually seen in late autumn and winter, six to 10 weeks after the animal has ingested metacercariae, but in smaller numbers than with the acute form.
- Chronic fasciolosis
This is associated with mature flukes, and seen mainly in late winter and early spring, four to five months after the animal has ingested metacercariae. Mature flukes are present in the bile ducts, where they cause necrosis (cell death) and ulcers in the lining of the bile ducts.
Flukes can also harm the body in other ways: they can produce poisons and irritants, and their scales and suckers can cause lesions (injuries). Anaemia usually follows; more than 0,5ml blood per fluke can be lost per day. On post mortem, the liver may have an irregular outline and be pale and firm. The ventral lobe will be smaller.
Fasciolosis can be controlled in two ways:
- Reduce the population of the intermediate snail host;
- Use a registered anthelmintic.
To achieve long-term snail control, you could drain the habitat, but you should at all costs avoid destroying it. This is environmentally very undesirable, apart from being expensive. When snail habitats are small and localised, it is more feasible to fence such areas or use a molluscicide (snail bait).
A registered fluke anthelmintic can be used as a preventative to reduce contamination of pastures by fluke eggs. This must be applied at the right time, however. Alternatively, reduce fluke populations when they are large.
To treat the sub-acute or acute forms of the disease, use one of the liver fluke product groups shown in the table above.
Note: the foregoing is intended merely as an overview; speak to your vet about control measures.
- Anthelmintics Drugs that expel parasitic worms.
- Metacercaria In infected snails the young parasite goes through three stages: sporocyst (an elongated sac); redial (a larval form with an oral sucker); and cercaria. The latter has a tapering head with large penetration glands and is passed on when the snail attaches itself to plant material. Here it encysts (forms a capsule) and become the infective metacercaria. This is ingested by the animal in large numbers.