Liver Fluke (Fasciolosis)
Acute liver fluke disease, caused by large numbers of
immature fluke, can be fatal in sheep. In this scenario, a drug such as Triclabendazole is recommended, as it controls many immature and adult stages of the parasite.
In late winter and early spring, where adult fluke are
present, these can be controlled by higher doses of some Benzimidazole drugs and specific fluke treatments such as Nitroxynil, Closantel and Oxyclozanide. Mixed infections, found in autumn and early
winter, are also best treated with products that are licensed to control both immature and adult fluke.
Seek advice from your vet or prescribing animal health
merchant and always read the product label.
Gut Worm Scours (PGE)
Wormers are widely used to control the adult and larval
gut roundworms that cause ‘Parasitic Gastroenteritis’ (PGE), which usually manifests itself in late summer.
Worms are active in the pasture from early spring
onwards, favouring temperatures above 10 degrees centigrade and high humidity levels. Larval activity drops off during high summer, due to the intense sunlight and drying out of the pasture and
animal faeces; resuming again with the autumn rain.
Products are grouped according to their chemical
structures into three main ‘broad spectrum’ categories:-
Group 1 – The Benzimidazoles (BZ) e.g. Albendazole
Group 2 – The Imidazothiazoles &
Tetrahydropyrimidines (LM) e.g. Levamisole
Group 3 – The Macrocyclic Lactones, Avermectins /
Milbemycins (AV) e.g. Ivermectin
Wormers in the above groups will be active against the
major species of gut worms and lung worms. Some will also be active against tapeworms and liver fluke.
The products in group 3 - Avermectins / Milbemycins -
offer varying degrees of persistent activity against gut worms. They are also active against some external parasites and are therefore termed ‘Endectocides’.
In recent years, there has been increasing anthelmintic
resistance in the gut worms present in UK sheep. In Scotland and the North of England, there is widespread reported resistance to the Group 1 Benzimidazole ‘white drenches’, and some flocks are
also showing resistance to other drugs.
The Benzimidazole products are recommended for use where Nematodiris
battus is a problem, as this particular worm is still largely susceptible to the drug. Benzimidazoles are also effective against tapeworm and, in higher doses, are used against adult liver fluke.
Group 2 products, such as levamisole are active against
many of the intestinal parasites, but have no activity against liver fluke or tapeworms.
The Group 3 Macrocyclic lactones have persistent activity
against the majority of worm species and are used in strategic worming programmes and as treatment for quarantined, replacement stock, before their introduction to the flock.
Most of the wormers on the market will control the
dormant stages of gut worms that cause winter scours in sheep. Consult the product label to ensure that these stages are covered, or repeat treatments may be required.
The advisory booklet ‘Sustainable Control Of Parasites
in Sheep’ (SCOPS) is available from the National Sheep Association. SCOPS promotes effective worming strategies and treatment of newly purchased stock, to limit the causes of worm resistance.
SCOPS also recommends that routine faecal egg counts are
undertaken, to determine whether worming is necessary and whether the wormers selected are actually working correctly in individual flock situations.
Parasitic Pneumonia
During the autumn months, outbreaks of coughing can be
noted in the sheep flock. This is due to damage inflicted by lungworm, Dictyocaulus filaria. Adult worms can be present in the lungs one week after ingestion of the larvae from the pasture. These invading larvae cause bronchitis, which can then lead to pneumonia.
Most of the available wormers are active against the adult form of lungworm.
Sheep Scab
Sheep scab mites are controlled by either plunge dipping
with a Diazinon dip, or by injecting the whole flock with a macrocyclic lactone injection (e.g. Ivermectin, Doramectin or Moxidectin). Plunge dipping will also control all the other major sheep
ectoparasites, whilst the macrocyclic lactone injection will also control gut worms.
When treating scab in the flock, the number of doses of
injection and the frequency between injections varies depending upon the product selected. It is therefore recommended to consult your prescribing animal health merchant or vet about dosing and to
fully read the product instructions..
