5 September 1997

WORMS A THREAT IN EVERY SYSTEM

Both indoor and outdoor pigs suffer from worm infections. Mike Taylor head of parasitology at MAFFs Central Veterinary Laboratory, Weybridge, outlines control strategies to minimise economic losses

WORM infestation has been highlighted with the return to more extensive systems which carry a greater risk of infection.

But producers must be aware that worms can also occur in indoor pigs. Wherever possible consult a vet for advice on identifying species involved, the anthelmintic to use for a particular farming system and the frequency and method of application.

A number of effective anthelmintics are available for pigs. Flubendazole, fenbendazole, oxibendazole, thiophanate, febantel, and ivermectin are highly effective against the adult and developing larvae of gastrointestinal nematodes of pigs.

Where lungworm infections are a concern flubendazole, febantel, or ivermectin are the drugs of choice. Fenbendazole must be given at increased dose rates to control lungworm.

In outdoor pigs on permanent pasture all sows in a herd may need regular anthelmintic treatment according to the parasite species and levels of infection present.

Again consult a vet for identification of species involved and the frequency of treatment required.

Effective worm control of the major parasite species of pigs can be achieved by a combination of anthelmintic dosing following a move to clean pasture.

Autumn anthelmintic treatment of the whole herd is vital before a move to clean grassland. This should be followed with a treatment again six months later in the spring which limits the level of infection on the pasture effectively.

Eradication of existing nematodes in intensive units is unrealistic due to the long survival times of Ascaris and Trichuris eggs. Modern cost-effective control programmes should, therefore, aim to reduce infection to levels that have no economic effect on performance.

Removal of faecal debris and steam cleaning of floors, crates and equipment will help reduce much of the contamination. To prevent immediate re-contamination all animals in the unit should be treated with a broad spectrum anthelmintic within one to two weeks before clean-up. Sows should also be treated with an anthelmintic before introduction to the farrowing crates. Washing sows with soap before farrowing helps to remove worm eggs.

Detergents do not kill eggs but are useful in removing adhering dirt and manure containing eggs.

An effective monitoring programme includes periodic screening of the herd using faecal egg counts and post mortem examination of pigs that die. Information from the abattoir provides another useful monitor of the effectiveness of worm control on the unit.

Pigs brought into fattening units may harbour worm burdens. Anthelmintic treatment of pigs on arrival should be considered as a way of controlling worm populations and their effects. And batch depopulation and steam cleaning of buildings should be practised wherever possible. &#42

CONTROL STRATEGIES

&#8226 Both indoor and outdoor pigs affected.

&#8226 Consult vet for treatment strategy.

&#8226 Begin treatment in autumn.

Autumn anthelmintics treatment for outdoor pigs is vital before a move to fresh paddocks, according to CVLs Mike Taylor.

FIRST – KNOW YOUR ENEMY

Ascarid worms

(Large round worms )

Adult worms may be up to 40cm (16in) long and occur in the small intestine. Eggs passed out in the faeces develop into second stage larvae and develop rqpidly in warm moist weather. Eggs are extremely hardy and can survive for 10 years only hatching when ingested by the pig.

Larvae are then released and burrow through the wall of the liver and from the liver to the lungs where they become fourth stage larvae. These are coughed up, swallowed and return to the small intestine to mature into adult worms about seven weeks after eggs are ingested.

The main impact is economic, for lesions caused by migrating larval stages cause condemnation of livers, heart and lungs. Clinical signs are not usually seen, although heavy infections can cause enteritis. Larvae migrating through liver and lungs also provide entry sites for pneumonia causing pathogens. Severe infections may cause verminous pneumonia.

Hyostrongylus rubidus

(red stomach worm)

Adult worms are 1cm (0.4in) long, slender and reddish. Eggs passed out in faeces hatch and larvae undergo development to the third stage infective larvae.

Egg development is dependent on the climate. Warm wet weather favours development but cold and dry weather kills many eggs. But larvae which reach the infective third stage can survive a wide range of weather and may live for a year on pasture. These migrate from faeces and when ingested by pigs, pass to the stomach where they enter glands lining the wall, emerging as adult worms on stomach lining surface.

Clinical disease is seen in the lactating sow where marked weight loss occurs despite adequate feeding. The weight loss continues after the litter is weaned.

Typically the sow is thin, shows pallor of mucous membranes and skin. Diarrhoea is not usually present but faeces may be intermittently dark. Disease often appears when sows and gilts have been turned on to permanent pig paddocks with the boar between litters. Inhibition of larvae in the mucosa is a common phenomenon, with development resuming after farrowing.

Oesophagostomum species (nodular worms)

Adult worms are 1.5cm (0.6in) long and found in parts of the large intestine.

Eggs are passed in the faeces where they develop into third stage infective larvae. After ingestion larvae pass to the large intestine entering the wall where the fourth stage develops. These larvae remain in the intestine wall before developing into fifth stage larvae which mature into adult worms seven to eight weeks after infection.

Clinical disease is typified by diarrhoea with the main effect subclinical usually associated with reductions in weight gain.

Metastrongylus species

(lungworms)

Infection is usually confined to pigs kept outdoors because the worm requires an intermediate host, the earthworm, to complete its life cycle.

First stage larvae develop in eggs, which hatch after ingestion by the earthworm where further development occurs.

When the worm is eaten, larvae are released and burrow into the intestine wall where they migrate through the bloodstream to the lungs. These larvae migrate through the lung tissue and develop into adult worms within the bronchioles, three to four weeks after ingestion.

Pigs on pasture land are most frequently infested as intermediate hosts – earthworms – are readily available but indoor pigs may also be infected. Lung damage then causes characteristic coughing mostly in young pigs.