What is Trombiculosis (Chiggers)?
Trombiculosis can affect horses during the trombicula autumnalis’ larval stage, which only lasts four or five days, but then they drop off and develop into nymphal stage. Because of this, you may not even notice any change in your horse unless they injure themselves scratching or if the area becomes infected, which is rare. The harvest mites do not suck the blood of their hosts like previously thought. Instead, they inject a cytolytic enzyme into the skin and then sucks up the dissolved tissue. It is the enzyme that creates the itchiness and the bite that creates the scabs and rash.
Trombiculosis in horses is caused by what are commonly known as chiggers or harvest mites, but are scientifically referred to as Trombicula autumnalis. The larvae of these mites actually break down tissues with their saliva so they can eat the dissolved tissue (fluids). This process is what usually causes the itchiness and lesions which are found on the extremities, neck, and muzzle of infected equines. These tiny orange-red larvae are usually found in hay, grass, and wooded areas.
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Symptoms of Trombiculosis (Chiggers) in Horses
Since the harvest mite only stays on the horse during the larval stage, which only lasts four or five days, you may not see any signs of infestation. The most often reported symptoms of trombiculosis include:
- Scratching or biting at skin on legs
- Foot stamping
- Rubbing on sturdy objects like walls and fences
- Patches of orange or brown on face, fetlocks, tail, and mane
- Head shaking
- Lesions with crusty scabs
- Flakes in the hair similar to dandruff
- Inflamed areas of skin
Although there is only one type of harvest mite (trombicula autumnalis), there are many other names they are commonly known by. Some of these are:
- Berry bug
- Black soil itch mite
- Duck shooters itch mite
- Heel bug
- Mower’s mite
- Orange tawny
- Red bug
- Scrub-itch mite
- Trombiculid mite
- Velvet mite
Causes of Trombiculosis (Chiggers) in Horses
The cause of trombiculosis is the harvest mite larvae. However, there are certain risks that can lead to the infestation of the harvest mite larvae, which include:
- Crowded living conditions
- Lack of daily grooming
- Living in areas where harvest mites are known to be prevalent
- Access to thick vegetation
Diagnosis of Trombiculosis (Chiggers) in Horses
To diagnose harvest mite infestation, your veterinarian will need to do a thorough medical history and examination first. To assess your horse’s medical history the veterinarian will need to know of any previous illnesses or injuries, immunization records, strange behavior, or abnormal appetite. You should also be sure to mention any type of medication you have given your horse. The physical examination will start with the veterinarian watching your horse from a distance to check attitude, stature, behavior, and conformation. The veterinarian may have you walk your horse around while watching the muscles and joints in motion to see if there is any lameness or other abnormalities.
The veterinarian will check your horse from head to tail looking for any skin lesions, itchy spots, rashes, redness, inflammation, or other irregularities. During the physical examination the veterinarian will palpate various areas of your horse and listen to breath sounds and heartbeat. In addition, the veterinarian will check your horse’s reflexes, weight, height, body condition score, respirations, blood pressure, and body temperature.
Skin tissue samples will be taken from various areas by trimming the hair and using a sterile instrument to scrape the skin. These will be examined under a microscope to look for larvae. However, even if the veterinarian does not find any larvae, it does not mean your horse does not have trombiculosis. They are present only for a few days so may have already fallen off. Other tests needed include complete blood count (CBC), blood cultures, fungal and bacterial cultures, chemical profile, urinalysis, and fecal examination. Radiographs will be done next to look for any underlying illnesses.
Treatment of Trombiculosis (Chiggers) in Horses
To treat trombiculosis, the veterinarian will shave or clip the areas where the larvae are suspected to be and treat with a shampoo, cream, ointment, or powder. There are certain types of medicated shampoos and medications specially marked for horses that can be used. The areas have to be clean and dry before applying any treatment.
There are many medicated shampoos sold on the market that you can use to treat your horse for trombicula autumnalis infestations. Some of the shampoos that are safe for your equine are keratolytic or sulphide and you may be able to get your veterinarian to do this for you if you ask. If you do it yourself, you should talk to the veterinarian about getting a sedative for this.
Permethrin 10% spray or pyrethrin .20% are both good choices for treating your horse. Acaricide is another chemical that works well for getting rid of trombicula autumnalis larvae. However, these medications only work to kill the larvae and it does nothing for the itching or lesions. The veterinarian can give your horse an injection of corticosteroids and topical cream to help with the itch.
Recovery of Trombiculosis (Chiggers) in Horses
Fortunately, these larvae do not remain in place for long so you should have no trouble getting rid of them. In fact, they may already be gone by the time your horse is seen by the veterinarian. Prognosis is excellent and even if your horse has a rash or lesions, these should heal within a few days.