Straw Itch Mite in Horses

There are close to 50 species of mites that can cause mange in horses, causing itchiness and rash. Horses that are infested with straw itch mites are constantly scratching and stomping their feet due to the itchiness these bugs can cause. It is relatively difficult for you to find the mites because they are so small so it is essential that your horse is seen by a veterinary professional. In fact, the pyemotes ventricosus mite is so small it actually feeds on nymphs and larvae such as furniture beetles, which are less than a centimeter long and the mites are about 0.2 millimeters long.

Straw itch mite mange is caused by the pyemotes ventricosus mite which comes from infested grain or hay. These tiny bugs live on other bugs that live in hay, grain, and oats until they get the opportunity to feed off your horse or another pet (or you). The symptoms of straw itch mites are similar to other itchy pests such as scabies mites or leg mites. These symptoms may include itchiness, lesions, rash, and inflammation. While they are not serious in nature, these bugs can be extremely aggravating for your horse as well as for you. Because these mites do not usually reside on horses, the veterinarian will most likely not be able to find any live bugs from samples taken. Instead, the veterinarian will rely on your recollection of symptoms and history of your horse.

Straw itch mites have been responsible for many dermatitis outbreaks in the United States in both animals and people. Since first reported in the 19th century, these infestations have found their way into homes all over the world by way of certain wheat, hay, and grains sold in various farm supply and ranch stores. Some of the common signs of straw itch mite infestations are:

• Itchy red rash on the affected areas (usually face and muzzle or legs) depending on where you feed them.
• Stomping feet
• Biting at legs and feet
• Hair loss
• Crusty scabs
• Anxiety
• Loss of appetite (due to the bites received when eating hay)
• Weight loss (due to the appetite loss)

 Types

There is only one type of straw itch mite, but these bugs are commonly referred to by other names such as:

• Forage mite
• Pyemotes herfsi
• Pyemotes tritici
• Pyemotes ventricosus mite
• Straw itch mite
• Trombiculid mite

The bite of the pyemotes ventricosus mite is what causes the straw itch mite mange (dermatitis). This type of mite, due to the minute size, can cause aggravation to your horse that is difficult to diagnose.

It is important that your horse sees a veterinarian (preferably one that specializes in horses) to get a definitive diagnosis of straw itch mite and rule out other illnesses. There are many causes of dermatitis besides mites and some of them can be serious such as equine cutaneous pythiosis or severe bacterial infection. The veterinarian will first need to know your companion’s medical history including immunizations, illnesses, injuries, abnormal eating habits, strange behavior, and the side effects seen that brought you to contact the veterinarian. You also need to provide your veterinarian with a list of any medications you have given your horse recently because this could confuse the diagnosis and alter the treatment plan.

A complete physical examination is performed next, which will include weight, height, reflexes, body condition score, temperature, blood pressure, heart rate, breath sounds, and respiration rate. The veterinarian will then take skin scrapings from several of the affected areas with a scalpel for microscopic evaluation. This can help to verify a mite infestation and find out whether it is a straw itch mite or a different type of mite. In addition, laboratory tests needed will include a urinalysis, fecal exam, blood culture, biochemical profile, and complete blood count (CBC). Finally, some radiographs (x-rays) may be done to check for underlying illnesses or diseases.

As with many other mange and mite infestations, treating your horse for straw itch mite  consists of several steps such as trimming hair, cleaning and sanitizing, medicated shampoos, and medications.

Trimming Hair

The first thing your veterinarian will do is clip the hair away from the affected areas. Also, the feathers on the legs will be trimmed to prevent further infestation.

Cleaning and Sanitizing

Next, the area will need to be thoroughly cleaned with warm water and disinfected with antibacterial soap. This will prevent infections, prepare the area for treatment, and ease the itchiness and inflammation a bit. 

Medicated Shampoos

The most common medicated shampoos used in treating horses for straw itch mite mange are organophosphates, rotenone liquids, and lime sulphur mixtures.

Topical and Oral Medication

Some of the recommended medications include moxidectin, bromo cyclen, milbemycin oxime, amitraz, ivermectin, fipronil, diazinon, sulfiram, and benzyl benzoate lotion. In addition, your veterinarian will probably prescribe corticosteroids and anti-inflammatory medication for itching, and inflammation and antibiotics to prevent infection.

The prognosis for straw itch mite mange is excellent once you get treatment. You also have to be vigilant about getting rid of the straw, grain, and other feed and bedding that may be infested. Unfortunately, it may take several treatments to get rid of the mites completely. Be proactive, being certain to obtain your feed and bedding from a reputable supplier that is known to be safe.