Infected donkeys can share lungworms with horses. Today, many donkeys have found homes at horse barns

Donkeys are asses. They have some similar and different problems from horses. Donkeys have a propensity to be easy keepers.

While donkeys with lungworms generally won’t show any clinical signs of disease, horses that graze with donkeys can pick up the parasite. Lungworms can cause respiratory problems in horses.

Species Specific

We asked Dr. Nathan Voris, a field veterinarian with Zoetis, to give us some basic facts about lungworms in donkeys and horses.

The lungworm found in donkeys is Dictyocaulus arnfieldi. Cattle have a different species (Dictyocaulus viviparous). In cattle, that worm causes severe lung damage. These two lungworms do not cross animal species (cattle lungworms don’t infect horses and donkeys), but horses can get lungworms from infected donkeys.

Lungworm Life Cycle and Description

Lungworms are up to 80 mm long (3 inches) and are a white worm.

These parasites (Dictyocaulus spp.) are host-adapted. Horse infection rarely occurs unless they graze with donkeys, according to Voris.

“D. arnfieldi cannot reach adult, reproductive stages in the horse, so an infected horse cannot infect other horses,” he noted. “Infected donkeys are clinically unaffected by lungworm infections.”

Horses can suffer respiratory irritation/bronchitis. Voris explained that adult worms live in the donkey’s terminal bronchioles and can be found in the major airways. Immature lungworms (larvae) are coughed up, swallowed, then passed in the feces. This infects the pasture.

This means that while these parasites can infect horses, they cannot reproduce in horse. That makes horses a ‘dead-end host.’

“Since horses are not definitive hosts, reproductive stages will not be found in horses,” emphasized Voris. “Therefore, eggs and larvae of Dictyocaulus arnfieldi will not be present in feces, making them difficult to identify as the definitive cause of respiratory disease in the horse.”

Larval culture of donkey feces is the definitive diagnostic tool.

Problems in Horses

In horses that show clinical signs of coughing or respiratory disease, it can be difficult to diagnose lungworms as the culprit. Horses that graze with donkeys and develop respiratory issues, veterinarians might test the donkeys. Taking a fecal sample from a donkey can reveal lungworm larvae. A veterinarian can perform other diagnostic tests. These tests can further define the type of inflammatory airway disease (IAD) affecting the horse.

Equine lungworm infection is restricted to the bronchial tree. This is the part of the windpipe just before and after it branches to go to each lung. This is different from cattle lungworm.

“So, lung damage, per se, should not occur,” noted Voris. “However, lungworms can cause Inflammatory airway disease, which can be difficult to manage. Unfortunately, lungworm infection can be difficult to definitively diagnose as the cause of the problem. Diagnoses is often via ‘guilt by association’ when there is a history of the horse grazing with a donkey.”

Prevention and Treatment

Voris said horses grazing with donkeys are at risk for lungworm infections. Deworm horses and donkeys appropriately. “Grazing horses and donkeys in separate pastures will prevent exposure,” he said.

Your veterinarian can help advise you on how to best protect your horses and donkeys against parasite infections.

Further Reading

  • Kimberly S. Brown
    Kimberly S. Brown is an award-winning writer and publisher. She is the Editorial Director for My Senior Horse. Brown spent 10 years at Equine Network, parent company of My Senior Horse. Prior to that she worked for three years in equine nutrition after she retired from nearly 30 years working at The Blood-Horse. Brown spent the last 15 years of her time at that organization creating and developing The Horse and TheHorse.com.
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