Ear mites are tiny, wingless, external parasites that live in the ears of horses and cause psoroptic mange. They are round with eight legs and are sometimes visible to the naked eye. They do not burrow into the horse but rather feed on the skin’s secretions.

Ear mites favor cool, humid environments. They are more likely to infect horses that have a pre-existing health condition, are immunosuppressed, or are otherwise stressed.

Mites are directly contagious between infected animals and spread easily between horses living in close contact. The ear mite can survive for a long time in the environment without a host, so transmission is equally likely through contact with infected equipment or premises.

The main symptom of ear mites in horses is itchiness of the ears, which can vary from mild to intense. Depending on severity, other symptoms may include crusty, swollen, smelly ears, damaged skin, extensive scabbing in the ear canal, brown discharge, and hair loss.

Diagnosis is typically based on physical and otoscopic examination and sometimes skin scrapings or swabs. Treatments include topical or oral parasiticides.

Prevention is possible with consistent grooming, adequate hygiene, and appropriate biosecurity and quarantine measures when a case is identified and when introducing new horses to the herd.

Ear Mites in Horses

Ear mites are wingless, light colored, parasitic arachnids from the family Psoroptes that live in the ears of horses and other animals and cause psoroptic mange. [1][2][3] An infestation of ear mites is called otoacariasis. [1]

The ear mite is tiny, measuring 0.4 to 0.8 mm from head to tail. [1][4] It is considerably larger than its cousins, the Chorioptes and Sarcoptes mites, as it can sometimes be seen by the naked eye. [1]

The ear mite has piercing mouth parts, with a round abdomen and eight legs, two sets of which point backwards from the body and two sets of which point forwards. [2] Females are differentiated from males by which set of legs carry the suckers they use to adhere to their host. [2]

Unlike other external parasites, such as lice or ticks, ear mites do not burrow into the skin but rather feed on skin secretions. [1]

Ear mites are not host-specific, which means that they can move from one type of animal to another. [1]

Psoroptes Mites

Previously, different types of Psoroptes mites were categorized as different biological classes based on which area of the body they infest. This classification has now been revised and all of the subspecies are now considered a single genus. [2]

The different genera of mites making up Psorpotes are all genetically consistent with each other, but typically live on different parts of the body. [1][2]

The species of mite that is usually found in the ears is P. cuniculi (also known as P. Hippotis). [3]

P. (equi) ovis is more likely to be found on the mane, axillae (the area that corresponds with the armpits on a human), base of the tail, or between the hind legs. [2] In extreme cases, these mites may spread over the horse’s back and sides. [4]

It is also possible for ear mites to live on other parts of the body if the ears are heavily infested. Conversely, body mites can make their way to the ears in rare cases. [1]

Ear Mite Life Cycle

The ear mite’s life cycle takes 10 to 16 days and has four stages: adult, egg, larva, and nymph. [2] All stages occur on the host (i.e. horse). [1][2]

The female lays eggs in the skin debris and they hatch within 2 or 3 days. [5] Egg production increases in winter as ear mites prefer cool, moist conditions and horses are typically kept together in close quarters at this time of year. [2][6]

How are Ear Mites Transmitted?

Ear mites do not fly and therefore cannot travel far. [1] They are transmitted through direct contact with an infected animal or indirectly by contact with infected premises or equipment such as blankets, brushes, buckets, tack, and grooming equipment. [1][6]

The survival time of a mite that is off its host is generally about 2 to 3 weeks but varies depending on the temperature and humidity of the local environment. [1] High humidity and low temperatures favour long survival times. [1]

Protected areas such as the corners of stalls, bedding, or organic debris are cool and hold onto moisture which can result in extended off-host survival times. [1] In very favorable conditions, ear mites can live without a host for up to 84 days. [1]

Ear mites are not host-specific, therefore horses can acquire an infection through contact with other animals such as goats, rabbits, and cattle. [1]

Are Ear Mites Harmful to Humans?

To date, there have been no reports of ear mites in humans. [1] It is theoretically possible that ear mites could be transmitted from a horse to a human host under very specific conditions, but there is no known case of this happening. [1]

Therefore, ear mites are not considered a risk to human health.

Risk factors

Ear mite infestations in horses are more likely in the winter months because mites prefer cool, moist environments. [6]

Mites are more likely to affect horses that are undernourished, undergroomed, stressed, or have reduced immune system function from other causes, including pre-existing conditions and use of certain medications. [6]

Pregnant mares, ill horses, and those with thick or long hair are also more likely to be infected. [6]

Horses that are kept close together or that share equipment or premises with other horses are at greater risk. [6]

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Symptoms

Ear mites cause a variety of symptoms with variable severity. [1] In some horses, there are few or no symptoms. [1] In others, ear mites cause severe disease and extreme discomfort. [1]

The main symptom is itchiness, which may be mild or intense. [1]

Horses who have itchy ears typically show it by: [1]

  • Head shaking
  • Ear scratching or rubbing
  • Head shyness
  • Lopsided ears

Other symptoms of ear mite infestation in horses include:[1][2]

  • Bumpy, crusty, thick, or swollen skin on the tips of the ear
  • Damaged skin due to rubbing
  • Damaged skin from the direct effect of the mites
  • Extensive scabbing inside the ear canal
  • Brown discharge
  • Visible white mites on the surface of the skin or in the discharge
  • Foul odor from the skin/ears
  • Hair loss

In severe cases, ear mites cause an allergic or hypersensitivity reaction which results in extreme symptoms and a rapid, more exaggerated response to future infestation. [1]

Secondary Infections

Horses with damaged skin due to ear mites are at risk of developing infections. [5]

Signs of secondary skin infections may include: [1]

In cases where the infestation is large, ear mites sometimes infect and inflame other parts of the horse’s body including the mane or the tail. [1] In extremely severe cases, the horse’s entire topline is affected. [1]

Diagnosis

Diagnosis is based on the presence of mites in the ears upon physical and otoscopic examination (examination using a scope to see into the ear canal). [1]

Otoscopic examination of horses can be challenging for two reasons: [1]

  • The affected horse’s ears may be very sensitive and sore
  • Ear mites are small and may live deep in the ear canal.

As such, some horses must be sedated for this procedure. [1][4]

In cases where no mites are found, diagnosis is based on characteristic tissue damage. [1] Other diagnostic tools used to determine the presence of ear mites include: [1][2]

  • Skin scrapings or swabs
  • Skin biopsy

Treatment

Treatment for ear mites starts with a thorough ear cleaning, typically performed while the horse is still under sedation. [1] Cleaning helps remove many of the living adults and larvae, but anti-parasitic treatment is still required to eliminate microscopic eggs and mites to fully clear the infestation.

There are two anti-parasitic treatment options: topical or oral parasiticides. [1]

Topical Treatment

Topical parasiticides are applied twice weekly for three weeks. [1] Horses with severely sore ears may not be difficult to handle and resistant to topical treatment. [1] Some experts warn against topical treatment of the ears to avoid pain and discomfort for the horse. [4]

Horses with especially heavy infestations sometimes carry ear mites on other parts of their bodies. [1] For this reason, if the treatment of choice is topical parasiticides, it is necessary to treat the horse’s whole body at the same time as their ears. [1]

Topical parasiticides are available in spray and dip formulations to facilitate whole body coverage. Most types must be applied every week or two for three or four weeks to effectively break the mite life cycle and clear the infestation. [1]

Systemic Treatment

Oral parasiticides such as ivermectin or eprinomectin are effective at controlling ear mites. [1] These medications do not kill the ear mite eggs, so a second dose is required 14 days after the first treatment. [1]

Hygiene and Secondary Infections

All horses in close contact or that share equipment or premises must be treated at the same time or the risk of re-infestation is high. [5] Premises and equipment must be disinfected simultaneously. [5]

In cases where secondary skin infections are present, antibiotics and/or anti-fungal medications may be required. Anti-inflammatories may be prescribed to aid healing and provide pain relief.

Oozing skin may require wound care until the infection is resolved. [5]

Prognosis

As with any type of parasite, the infestation will persist until the parasite’s life cycle is broken. Due to this, it’s important for horse owners and care takers to ensure affected horses receive the entire course of parasiticides on time, as prescribed by the attending veterinarian.

With treatment, ear mites in horses have an excellent prognosis. Infestations should fully resolve with diligent treatment of the environment and entire herd in 3 – 6 weeks. [5] Secondary skin infections are also expected to fully resolve with treatment in otherwise healthy horses.

Prevention

In order to prevent the spread of ear mite infestations, infected horses must be isolated until successfully treated. [5] All new horses coming to the premises must be isolated and treated before being added to the group. [6]

Due to the ear mite’s ability to live for a long time without a host, extended stable quarantine periods are necessary to prevent infection. [1] For the ear mite (Psoroptes cuniculi), a period of 12 weeks is recommended. [1] For other Psoroptes mites that live on the body, shorter stable quarantine period of 7 weeks is sufficient. [1]

Checking for mites or their characteristic symptoms, trimming or thinning long or thick hair, keeping horses in good health and well fed, grooming regularly, and bathing the horse periodically are recommended. [6]

Practicing excellent hygiene to eradicate mites that are living off the host is also crucial to preventing infection and especially re-infection. [6]

The use of insect repellants is effective in preventing infestation. [2]

Pest Resistance

The widespread use of antiparasitic protocols including ivermectin and eprinomectin has been successful in lowering the incidence of ear mite infestation. [2]

This practice does raise the question of pest resistance. [6] Using chemicals to kill pests results in the eradication of the weaker members of the population, leaving the stronger ones to reproduce, potentially creating offspring that are more likely to survive that chemical in the future. [6] This can eventually lead to the need for stronger pesticides to eliminate the same pest species, which has the potential to become an environmental hazard. [6]

Using parasiticides only when necessary and ensuring that treatment is continued until the whole infestation is eradicated are recommended to offset the potential negative effects of pest resistance. [6]

Always inform your veterinarian of all animals that may come into contact with insecticides before treating your horse. Some animals are highly sensitive to these chemicals, particularly cats.

Summary

Ear mites are tiny, wingless parasites that infect the ears of horses and other animals, resulting in psoroptic mange. They cause mild to severe itching as well as crusty, swollen, odorous and uncomfortable ears.

  • Horses that are ill, under-conditioned, stressed, pregnant, have thick or long hair, or are kept in close contact with other horses are at greater risk of infection.
  • Transmission occurs through direct contact with an infected animal, equipment, or premises. Animals other than horses are also carriers of ear mites.
  • Ear mites can survive for a few weeks off the host.
  • Diagnosis is based on physical and otoscopic examination as well as skin scrapings and swabs.
  • Treatment is oral or topical parasiticides.
  • Prevention requires the isolation of (potential) infected animals and excellent hygiene for equipment and premises.

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References

  1. Parasitic Diseases.
  2. Mites.Pdf. External Parasite and Vector Control Guidelines. American Association of Equine Practitioners.
  3. Ural. K. et al., Eprinomectin Treatment of Psoroptic Mange in Hunter/Jumper and Dressage Horses: A Prospective, Randomized, Double-Blinded, Placebo-Controlled Clinical Trial. Veterinary Parasitology. 2008.View Summary
  4. Bergvall. K., Advances in Acquisition, Identification, and Treatment of Equine Ectoparasites. Clinical Techniques in Equine Practice. 2005.
  5. Barbet. J. L., Ectoparasites of Horses. Equine Infectious Diseases. Elsevier. 2014.
  6. Machtinger. E. T. et al., Pests and Parasites of Horses. Brill | Wageningen Academic. 2022.