What causes lungworms in horses?
Lungworms are internal parasites that affect the respiratory tract in horses. They are part of the same parasitic family that cause the condition known as “Hoose” pneumonia in calves.
The lungworm in horses is scientifically known as Dictyocaulus Arnfeldi.
They are white in colour and are quite a large parasite, ranging from 6-10 cms in length. It is therefore not surprising that they can cause problems in the lungs.
How do horses get lungworms?
Horses ingest the eggs when they graze on infested lands.The eggs mature into larvae within approximately two and a half to three weeks. They then migrate to the horse’s lungs in less than a week and will be laying eggs within a month.In many horses the larvae remain in the lungs as a chronic irritant.The irritating cough that this generates in the infected horse helps them up the windpipe to the animal’s throat. From the throat, they are swallowed and migrate through the intestines before exiting on to pasture.They can re-infect horses in as little as five days if conditions are suitable for them.As with most parasites, serious problems are possible if the burden gets heavy, but this would be very rare in horses.Do horses generally carry lungworms?
No. Donkeys are the carriers of this worm and when they are at pasture with horses the transfer of the problem occurs. If horses are grazing in the same field as donkeys or if the field was used by donkeys before the horse arrived, then they can be infected.Horses grazed without donkeys rarely have the problem of lungworms.Does the land remain contaminated for a long period?
Yes, land previously grazed by infected donkeys could remain infected from year to year in some cases depending on conditions and level of infestation. The lungworm larvae survive low temperatures in winter by hibernating until spring when they become infective again.
Does the carrier donkey show symptoms?
No. While this parasite can cause severe coughing in horses and ponies that contract it, donkeys can tolerate a fairly large infestation of lungworms without showing apparent signs.
Are all donkeys carriers of lungworms?
A significant percentage of donkeys carry lungworms, with figures ranging from as low as 4% to as high as almost 100% depending on circumstances. On a general basis approximately 50% of donkeys carry lungworms. It is in the donkey that this parasite reaches full maturity. Horses can host them also, though much less commonly. However the lungworm is unlikely to reproduce in horses as it needs the donkey to complete its life cycle to maturity.Do lungworms that cause “Hoose” in calves affect horses?
No, there is no cross infection with cattle in this case as the calf lungworm is host specific i.e. it is not transferable from calves to horses or donkeys.
What are the symptoms in horses?
A deep cough is usually present in the affected horse. (This can persist for over a year.) However, it is important to note that there are many other causes of cough in horses that would be far more likely than a lungworm problem.The animal may be “wheezy” or may have pneumonia.There may be an elevated temperature due to secondary infection.A horse that has had lungworms may be more susceptible to developing COPD (Chronic Obstructive Pulmonary Disease) or allergy, at a later stage.How is the condition diagnosed?
History- the horse usually is or has been grazed with donkeys.Failure to respond to antibiotic etc treatments for cough.Laboratory examination of a faeces sample taken from the affected animal to confirm diagnosis. (Baermann Technique used for this purpose at the laboratory).Blood tests may indicate lungworm presence.Deep endoscopic examination of lungs (broncheoles) may show mature larvae present.A ‘lung wash’, known in veterinary terms as Broncheolar Alveolar Lavage (BAL) may also be used in diagnosis to identify specific cellular changes.Will the regular routine egg counts on faeces show presence of lungworms?
No, not usually.
What treatment is used?
After confirming the diagnosis, the treating veterinary surgeon will recommend dosing of all horses and donkeys present on the farm with a product that includes lungworms on its target list. (The majority of the commonly used pastes will do this). These chemicals will remove both the migrating larvae and adult worms.
What are the recommended preventative methods used?
Where horses are grazed alongside donkeys, particular care must be taken to routinely treat both for lungworms, with particular attention to foals as they can sustain permanent lung damage if infected. Pasture management (as described below), is important to prevent carry-over of the infection; otherwise lungworm larvae can live on pasture for extended periods causing re infection.What method of pasture management is used?
If possible, collect all manure at least twice weekly and dispose of the manure appropriately, ensuring that it will not cause further pasture contamination. Composting kills parasites so manure collected from pasture or from stables can be composted. It is advisable to add layers of agricultural lime between the layers of faeces in the compost heap to hasten decomposition and destroy the worm larvae.If manure cannot be picked up from the pasture, harrowing the pasture, preferably on a hot dry sunny day, will disperse the manure and facilitate the death of the parasite larvae.However, it is important to note that harrowing is only useful during dry spells with hot temperatures. Harrowing at any other time of year is not advisable as there is a risk that it will cause spread of the infective larvae across the land.
Should horses not be grazed with donkeys?
Some owners incorrectly believe that donkeys and horses cannot live together due to the risk from lungworm. But the fact is that horses and donkeys can live together quite healthily provided a regular de-worming programme is in place and followed, as advised by your veterinary surgeon.