Parasites in horses: symptoms, treatment and prevention

What are parasites in horses?

Parasites in horses are defined as organisms that colonize on or in the horse's body and feed on their host (the horse). These parasites can include different types of worms, such as strongyles and roundworms, as well as other microorganisms such as lungworms and skin parasites such as mites and fly larvae. These parasites can cause a variety of health problems, from weight loss and dull coat to serious illness. It is therefore important to recognize and treat parasite infestations in horses at an early stage in order to maintain the animal's health and performance.

Types of parasites in horses

The list of parasites in horses is long, yet manageable. A distinction is made here between endoparasites and ectoparasites. The main difference between endoparasites and ectoparasites lies in their habitat inside or outside the host's body. Endoparasites live inside the horse's body, typically in the digestive tract or other organs, while ectoparasites live on the outer surface of the horse or in its immediate environment.

Both types of parasites can cause serious health problems in the horse, so it is important to take both preventative measures and appropriate treatments to minimize the risk of parasite infestation and protect the horse's health. Regular checks for parasite infestations and the use of appropriate preventative measures and treatments can help to maintain the horse's well-being and performance.

What are endoparasites in horses?

Endoparasites are organisms that reside within the body of their host and feed on its tissues or body fluids. In the context of horses, endoparasites mainly include different types of worms that live in the gastrointestinal tract of the horse. These worms include, for example, strongyles, roundworms and tapeworms.

Here you will find an overview of the types of worms that can infect your horse, how horses can become infected, what symptoms can occur and how these parasites are diagnosed:

These parasites can multiply in the horse's digestive system and become established there, which can lead to a number of health problems. If the population of endoparasites in the horse's body multiplies uncontrollably, they can damage the digestive tract, cause digestive disorders, impair nutrient absorption and even lead to serious illnesses.

Some endoparasites can also migrate to other organs of the horse and cause damage there. For example, lungworms can infect the horse's respiratory system and cause breathing problems.

‍3 Endoparasites in horses that you should know and what you can do about them

1. small and large strongyles in horses

Small strongyles

When the pastures open at the end of April, beginning of May, the small strongyles are in season. This is because our horses become infected with the small strongyles by ingesting infectious worm larvae in the pasture. These then pierce the intestinal mucosa in the large intestine, and the larvae can also migrate in the intestinal wall for several months. A special characteristic of these strongylids is their ability to encapsulate in the intestinal wall. This occurs through communication between adult worms and the larvae. When a sufficient number of egg-laying worms are present, they signal this and the larvae encase themselves in a capsule. In this way, the larvae can remain dormant for up to 3 years and only continue their development into adult worms when "necessary". Some signs that your horse may have small strongyles include diarrhea and weight loss, colic and fever may also occur, as well as edema (water retention in the lower abdomen and limbs). Although rare, there is a risk of larval cyathostominosis, which is triggered by the encapsulation of the larvae in the intestinal wall. The greatest risk is in spring, when the small strongyles migrate. This leads to massive damage to the intestinal mucosa, and young horses up to the age of 6 years can be particularly affected by larval cyathostominosis. Unfortunately, this type of worm infestation can also be fatal.
A worm infestation of small strongyles is detected by repeated fecal examinations according to the contemporary selective deworming strategy. Treatment usually starts from a worm infestation level of 200 EpG.
Due to the existing resistance situation with the worming agent Ivermectine in horses up to 6 years of age. 

The encapsulated small strongylids, 90 % of which are found in the intestinal wall, can only be effectively controlled by a single approved active ingredient called moxidectin using a single treatment.

‍Moxidectin is fat-soluble and has the special property of penetrating the connective tissue capsule that surrounds the larvae in the intestinal wall and killing the resting stages. This successfully combats the main worm burden in horses.

All other preparations approved for the treatment of small strongyles only combat the 10 % that are in the intestinal tube and do not reliably prevent the outbreak of larval cyathostominosis.

‍Thelarge strongyles

The large strongyles are also known as bloodworms (Strongylus vulgaris) and pose a serious threat to horses as they can cause serious health problems. The adult worms live in the cecum and large intestine, while the larvae migrate in the walls of the intestinal arteries. Their migration can cause mucosal bleeding and inflammation, which can lead to colic and lameness. In addition, the larvae can lead to vascular congestion and dilatation, which can lead to serious complications if they burst.

Infection with bloodworms mainly occurs by ingesting contaminated larvae in the pasture or in the stable. Foals are particularly at risk during their first grazing period. The development cycle of the worms begins in the intestine, where the females lay eggs, which are then excreted with the feces. Within a few days, the eggs develop into larvae, which are ingested by the horse. These larvae go through various stages of development before they grow back into sexually mature worms in the intestine.

Symptoms of infection with bloodworms are fever, loss of appetite, shaggy coat and colic. The diagnosis can be made through a fecal examination, although migratory larvae are not detectable. Regular worming and hygiene measures in the stable and on the pasture are essential to combat the infection. These include the removal of droppings, keeping the stable walls dry and avoiding ground feeding in the stable, as well as regular pasture management practices such as changing paddocks, intermediate mowing and draining swampy areas.

2. awl tail (Oxyrius equi) 

Awlworms (Oxyrius Equi), also known as anus worms, pose a serious threat to horses, especially those kept in stables. The adult worms parasitize in the blind and large intestine and feed by causing mucosal bleeding, which can lead to colic. Older horses are particularly susceptible to this infestation. Female awl tails migrate from the horse's intestines to the anal area to lay their eggs. This leads to severe itching and behavioral changes as the horses try to relieve the itching by rubbing themselves against objects. This can lead to skin lesions that are susceptible to bacterial infection and can cause further complications.

The development cycle of the awl tails is complex. The females lay their eggs in a viscous liquid known as"ice cords". These fall into the bedding and are ingested by the horses. The larvae then develop into sexually mature worms inside the horse. The diagnosis of an awl tail infestation is made by examining the anal area for the presence of egg strings. It can be difficult to detect eggs in the feces, necessitating microscopic examination of anal swabs.
Control of awlworm infestations requires a comprehensive strategy. This includes regular treatment with dewormers, professional treatment of skin lesions and strict stall hygiene. It is also important to remove ice cords by washing the anal area thoroughly with soapy water. These measures can minimize the risk of infection and maintain the health and well-being of the horses.
The choice of the appropriate worming treatment for awl infestation is crucial. Benzimidazoles such as pyrantel and fenbendazole have been shown to be effective against oxyurine infestations. However, it should be noted that pyrantel varies in its effectiveness against awl tails.

3. stomach bug - the botfly

What are stomach bugs in horses?

Stomach flies, also known as stomach flies, are parasites belonging to the botfly genus. The species Gasterophilus intestinalis is most commonly found in horses. The females lay their eggs in the horse's coat, which are then ingested by the larvae and can cause damage in the horse's stomach.

What do stomach bugs do to horses?

The larvae of the stomach woodlouse can cause inflammation of the stomach lining in the horse's stomach, which can lead to symptoms such as listlessness, weight loss, dull coat and digestive disorders. A serious infestation can lead to severe damage to the stomach lining and even stomach ulcers.

Which active ingredient against stomach bugs in horses?

Worming treatments with active ingredients such as ivermectin or similar substances are used to control stomach worms in horses. These active ingredients are effective against the larvae of the stomach worms and can help to reduce an infestation.

Which worming treatment for stomach worms in horses?

Choosing the right worming treatment for stomach worms in horses is crucial for effective treatment. Vets can help you choose the right product to suit your horse's individual needs.

When do you give worming treatment to a horse with stomach worms?

Deworming against stomach worms in horses is usually carried out in the fall-winter period, preferably between November and December. This is the time when parasite activity is at its highest and horses are at increased risk of infection. Some experts also recommend a second deworming in January to ensure that the last stomach lice are removed.

What are ectoparasites in horses?

Ectoparasites in horses are organisms that live outside the host's body and feed on its external tissues or body fluids. Unlike endoparasites, which reside inside the body, ectoparasites live on the surface of the horse's body or in its immediate environment. These ectoparasites can take various forms, including fleas, mites, ticks and certain types of fly larvae. They can settle in various parts of the horse's body, including the skin, coat, mane and tail. Some ectoparasites can also live in open wounds or skin lesions.

However, in addition to the typical symptoms by which we can recognize ectoparasites in horses, there are also serious secondary diseases that can be transmitted to the horse through the parasites' saliva, for example.

Which parasite transmits which secondary disease to our beloved horses?

Ectoparasites often cause a range of problems in horses. They can cause itching and skin irritation, leading to excessive scratching, rubbing or biting. This can lead to skin lesions, wounds and infections. In addition, some ectoparasites can transmit diseases, such as ticks, which can transmit Lyme disease.

4 common ectoparasites in horses: What you need to know!

1. ticks, horseflies and co

Ticks, horseflies and other pests can also be a nuisance, especially in the summer months. A nice ride through woods, meadows or to the lake can quickly turn into an ordeal when the bloodsuckers are on the hunt. But you can quickly remedy this. Fly blankets and fly sprays can help you and your horse enormously to keep the horseflies and flies at bay. Fly repellents are available as a spray or as a gel, which is used especially for horses that are afraid of spray bottles. Nevertheless, the sprays are often more effective, here we have a type for you so that your horse is no longer afraid of spray bottles:

2. the deer louse fly - a small parasite on horses

The deer louse fly, also known by the Latin name Lipoptena cervi, is an ectoparasite that can infest horses. This fly species is particularly active from July to October and is often found in rural areas with lots of vegetation and forests. The deer louse fly looks similar to a housefly and is often called a "flying tick". During a ride or walk with the horse, the pests fall onto the horse and make their way to the mane crest and anus region of the horse. Many horses react very nervously and excitedly to the deer louse, even if it is only in the vicinity and not yet on the horse.

The bite of the deer louse fly can be painful for horses and lead to skin irritation. Some horses can have an allergic reaction to the fly's saliva, which can lead to severe itching and skin rashes. Scientists are still unsure whether deer louse flies transmit diseases, the fact is that they carry the bacterium Bartonella schoenbuchensis , it is unclear whether the bacterium can also be transmitted to humans or horses in the event of a bite/sting.

Various measures can be taken to protect horses from deer louse flies. These include the use of insect repellents and fly blankets to protect the horses from being bitten. In addition, you can spray the horse with a hose to flush the deer louse fly from the horse's coat if you suspect it.

3. mites in horses: sucking mite, burrowing mite & co

Scabies in horses? What is it and what do sucking mites, scaly mites and burrowing mites have to do with it? How can you tell if a horse is infested with these mites? Burrowing mites and other mite species are ectoparasites that can infest horses and belong to the mite family. These tiny, wingless parasites feed on dander and can live in the horse's coat or on its skin. The three most common types of mites in horses are Chorioptes equi (dandruff-eating mites), Sarcoptes scabiei (burrowing mites) and Psoroptes equi (sucking mites).

The sucking mite

This mite feeds on the horse's blood and tissue fluids, forming small barks on the skin and retreating between them. This type of mite leads to body mange in horses, which occurs on hairy areas such as the mane and mop of hair and can spread to the horse's hocks. This mite infestation is very annoying and can also promote secondary infections, which can then lead to smelly, purulent skin lesions. 

The grave mite

In the case of the burrowing mite, the first symptoms usually begin in the area of the horse's head, where the mites bore up to 1 cm deep into the skin and feed on the host's tissue fluid and skin cells. As the mange of the burrowing mite progresses, lumps and nodules form on the neck and saddle area. As the infestation progresses, hair loss occurs and thick crusts can form all over the horse's body. The lower limbs are not affected by the burrowing mite. The Sarcoptes mite can seriously weaken a horse and can be fatal. 

The autumn grass mite (grass mites)

As the name suggests, this type of mite is more likely to be found in late summer/autumn. It feeds on the cap cells on the thin-skinned parts of the horse's body. You can recognize an infestation by the small, oozing and pus-filled sores in the fetlock bend of your horse, which are often mistaken for mauke. In some cases, however, the infestation also extends to the nostrils and inner thighs as well as the hose in stallions and geldings or the udder in mares. 

The Chorioptes mite (scale-eating mite)

This scale-eating mite feeds mainly on skin scales and secretions and lives on the surface of the horse's skin. This type of mite is particularly tenacious, as it can survive for up to 10 weeks without a host. This parasite feels most at home in a warm, damp environment, which is why they can be found in the stables during the cold winter months and make their way to the horse's fetlock. The infestation of the Chorioptes mite is also known as foot mange, due to the region of the infestation, which affects the area of the fetlock bend and the cannon bone.

Mite infestation is a serious problem that can affect the health and well-being of our horses. To minimize this risk and provide a healthy environment for our beloved four-legged friends, cleanliness and hygiene in the stables are crucial.
Regular grooming and cleaning of the horses are essential to prevent mite infestation. This includes regular brushing and washing of horses to remove dirt and potential mites. Particular attention should be paid to the areas around the ears, under the mane and on the legs, as mites like to settle there.
As soon as a mite infestation is detected, quick action is required, as mites can multiply quickly. It is important to consult a vet to obtain the appropriate treatment. Various medications are available on the market that are effective against mites. In addition, some home remedies have also proven to be effective.
To prevent re-infestation with mites, it is important to treat the entire horse population, even if only one horse is affected. In addition, all equipment such as saddles, bridles and blankets should be thoroughly cleaned and disinfected to prevent the mites from spreading.

4. hair lice in horses

What are hair lice and what do hair lice look like on horses?

Hair lice (Wereckiella equi) are ectoparasites that occur frequently in horses. Especially in warm and humid climates in fall and spring , they multiply rapidly and can infest entire herds of horses. It is normal for horses to carry a small amount of hair lice, but if there is severe itching and they are visible to the naked eye, this indicates an infestation that is too severe and needs to be treated. Hair lice are about 1.5 mm long, sometimes slightly larger, and have a rice grain shaped body with yellow and brown stripes.

The lifespan of a hair louse is around 40 to 60 days, during which it can produce up to 100 eggs. These eggs are laid in nests that form small, whitish piles, usually at the root of the hair. After about 10 days, young nymphs hatch from the eggs, which already look like adult hair lice, but are smaller. They are able to reproduce after a short time, which can lead to a rapid spread of the infection.

Hair lice feed on skin flakes and hair, which leads to hair loss that often looks particularly chewed up. They bite and chew off the hair just above the skin, resulting in a patchy coat. Hair lice can also be transmitted to humans through contact with infected horses, although this is rare. Infected horses can also transmit the hair lice to other stable animals such as dogs and cats, so it is important to contain an infestation as soon as possible.

Does my horse have hair lice?

Symptoms of a hair lice infestation in horses include severe itching and a patchy coat as well as restlessness and unhappiness. Some horses react aggressively under the rider , bucking or rubbing themselves bloody, which can lead to further skin problems, such as sores and moulting. Treating a hair lice infestation is therefore essential to ensure the horse's well-being and prevent the infection from spreading further.

What kills hair lice in horses?

To combat hair lice, you should make the parasites' habitat unpleasant. If the infestation is severe, it is necessary to shear the horse and cut off the legs. A vet should be consulted. Ivermectin can be effective, but the hygieneconcept must also be adapted. Alternatively, spray or wash lotions can be used, but with caution due to substances that are toxic to water.

Home remedies for hair lice

The use of coconut oil, neem oil, tea tree oil and black cumin oil is possible, but irritating and without confirmed effect. Diatomaceous earth can attack hair lice, but should not be inhaled. Thorough cleaning of the stable environment and changing the bedding are important. Blankets, grooming materials and equipment should be removed and cleaned if infested. Repeated treatments are required every 14 days to prevent re-infestation.

Worming treatment: the panacea for all worms in horses?

To minimize the risk of endoparasite infestation in horses, regular deworming is crucial. Veterinarians can recommend deworming programs that are tailored to the individual needs of the horse. It is important to strictly adhere to these programs to ensure effective control of the endoparasite population and maintain the horse's health.

Are you having problems getting your horse to take the de-worming treatment? In the following video we show you how giving worming treatment or medication by mouth can be as easy as scraping out hooves:

Deworming strategy 1: The flat-rate worming treatment

The blanket quarterly worming treatment is still common practice in some stables. Until ten years ago, this approach was very well established and aimed to combat the large strongyles, but today these are hardly ever found in horse herds. It was very easy to set up a worming schedule for the quarterly method, as the horses were wormed every three months without any diagnosis as to whether there was a worm infestation at all.

However, there is a major problem with this method: resistance. Regular worming without prior diagnostics means that there is no evidence of worm infestation in the horse or, in many cases, no evidence at all. If worming is then carried out too frequently, resistance can develop, meaning that the parasites survive the worming treatment and can cause considerable damage to the horse without the worming treatment being able to do anything about it. Therefore, if you want to protect your horse effectively against worms, do not worm every 3 months.

Deworming strategy 2: Strategic deworming

Strategic worming is an advanced method for maintaining the health of horses. In contrast to conventional blanket deworming, it offers a customized solution based on individual needs. Strategic worming is a middle ground between blanket worming and selective worming. In other words, it combines regular examination of the faeces with targeted deworming as required. An important aspect of this strategy is the avoidance of resistance, as the regular change of active ingredients in consultation with the vet reduces the development of resistance.
Strategic worming offers numerous advantages for the health of horses, including better control of parasite infestation, the avoidance of resistance and a contribution to environmental protection. Although slightly more expensive and time-consuming, the benefits clearly outweigh the costs and make it a recommended method of worming horses.

Deworming strategy 3: Selective deworming

Selective deworming is recommended for adult horses, particularly to control small strongyles that can infect them, especially on pasture. A structured monitoring program, which includes faecal sample testing, forms the basis for the decision to deworm. Targeted treatment only in cases of proven infestation avoids the excessive use of worming treatments, which in turn reduces the risk of resistance. 

But how do you switch from blanket deworming to selective deworming and is this the best way for the horse?
In the first year, faecal samples should be examined four times a year for parasites such as gastrointestinal strongyles (MDS), roundworms, awlworms and tapeworms. This process begins in April/May and continues until the end in October/November. The fecal samples are examined for the number of eggs per gram (EPG) of MDS. If the value exceeds 200 EPG or other intestinal parasites are detected, appropriate deworming is carried out. If the risk of infection remains stable, the frequency of fecal examinations can be reduced to three times a year in the following years. Nevertheless, deworming at least once a year is recommended regardless of the fecal sample test results. In addition to selective deworming, careful quarantine and hygiene measures in stables and on pastures are crucial. These measures help to reduce the spread of parasites and protect the health of the horses.

The great advantage of selective deworming is that deworming is only carried out when a certain amount of worm eggs is detected in the faeces. This gives horse owners and vets regular, clear information about which parasites are affecting the animals and the extent to which small strongyles in particular are present. The costs for the four or three fecal examinations per year vary depending on the provider, but the price range is between €9 and €40 per fecal examination. In some cases, the worming treatment is considerably cheaper, but here too the price is between €10 and €50, depending on the preparation and active ingredient. 

One limitation of selective deworming is that the number of worm eggs found in the faeces does not necessarily correspond exactly to the actual number of worms in the intestines of the horse in question. It is therefore possible that a horse with few or even no worm eggs in its feces still has a considerable number of worms in its digestive tract.

Deworming strategy 4: Modern selective deworming

The difference between selective deworming and modern selective deworming lies mainly in the diagnosis and treatment strategy.

Selective deworming focuses on carrying out deworming only in cases of proven parasite infestation, based on fecal sample examinations. This reduces the risk of drug resistance and enables targeted treatment for each horse. Regular fecal sample examinations are carried out to monitor the parasite infestation and adjust the deworming frequency accordingly.

In contrast, modern selective deworming uses a more advanced approach based on more comprehensive diagnostics. In addition to fecal sample examinations, other parameters such as the presence of certain parasite species in the herd are also taken into account. The decision to deworm is made not only on the basis of fecal sample results, but also taking into account other relevant factors.

Another difference lies in the development and implementation of the method. Contemporary selective deworming was pioneered by a group of dedicated parasitologists and is based on a large number of scientific studies and practical experience. It offers an effective and sustainable solution for the control of endoparasites in horses by combining customized treatments, efficacy monitoring and a reduction in the use of medication.

Overall, contemporary selective deworming offers a more progressive and holistic approach to managing parasite infestations in horses, resulting in better animal health and a reduced environmental impact.

FAQ: Worms and parasites in horses

1. How long does a horse shed worms after worming?

After a successful worming treatment, it is important to know that your horse may shed more worms over the next three days. Deworming always takes place on a fixed date and it is crucial that the horses can excrete an increased amount of larvae, eggs and adult worms in the following days after treatment. It is therefore advisable not to let the horses out to pasture together after deworming and the stalls should be thoroughly cleaned to minimize the spread of parasites.

2. Are the worms killed after the worming treatment?

The effect of a worming treatment on all worms in the horse depends on various factors. As described in the section on worming treatment: the panacea for all worms in horses?

 resistant worms can survive deworming, while sensitive worms are killed. Complete eradication of all worms is therefore not guaranteed, especially if resistant worms are present.

To maximize the effectiveness of deworming and prevent the development of resistance, various measures are required. These include selective deworming based on fecal sample testing to treat only horses with a high worm infestation, as well as avoiding excessive deworming to maintain a refuge for non-resistant worms.

It is important to follow the vet's instructions carefully and to monitor the horse regularly for parasites in order to develop appropriate deworming strategies and avoid resistance.

3. Can worms cause itching in horses?

Yes, worms can cause itching in horses. When a horse is infested with worms, various symptoms can occur, including itching. This itching can be caused by the movement of worms in the gut, eggs in the anus area or allergic reactions to worm larvae or dying worms. It is important to carry out regular worming programs and have the horse's health checked regularly by a vet to prevent or treat worm infestations.

4. How can I tell if my horse has worms?

There are several signs that can indicate that a horse is infested with worms. Here are some common symptoms:

• Weight loss or poor coat condition despite adequate feeding.
• Loss of appetite or sudden changes in eating behavior.
• Abdominal pain or colic.
• Diarrhea or altered consistency of the feces.
• Anemia can lead to fatigue and poor performance.
• Itching at the anus or base of the tail.
• Cough, especially in the case of infections with lungworms.

It is important to regularly examine your horse's feces and consult a veterinarian if worm infestation is suspected. Your veterinarian can perform a fecal examination to determine if and what type of worms are present and give you appropriate deworming recommendations.

5. What can you feed your horse against worms?

There are no specific foods that can directly help a horse against worm infestation. The best way to control worm infestations is regular worming and good management to reduce the likelihood of infection.

Here are some general management practices that can help reduce the risk of worm infestation:

• Regular deworming according to your vet's recommendations.
• ‍Pasture hygiene: Keep pastures clean and remove droppings regularly to reduce the spread of worm eggs.
• Rotational grazing: Avoid overgrazing by regularly rotating horses between different grazing areas.
• Remove horse droppings regularly, both in the pasture and in stables or paddocks.
• Avoid feeding hay or straw on a dirty floor to minimize contamination with worm eggs.
• Observe hygiene practices when handling and feeding horses to reduce the transmission of worm eggs.

However, a healthy diet rich in fiber and nutrients can help support the horse's overall health, which in turn can improve its ability to fight off worm infections. Talk to your vet about the best way to feed your horse to ensure it is getting all the nutrients it needs.

6. What helps against the deer louse fly?

It can be helpful to remove this annoying parasite with a fine-toothed comb. The most effective and quickest way, however, is to wash the horse or dog with water. The water causes the deer louse fly to lose its grip and is flushed out of the coat. It is also recommended that humans take a shower as quickly as possible, as the bite of the deer louse fly can also be very unpleasant or even painful for humans.

7. Why does a horse get mites?

A horse can get mites for various reasons. Mites are natural inhabitants of the horse's environment and are often omnipresent. They feed on the horse's dander and blood. However, under certain conditions, such as a weakened horse's immune system or humid, warm environments, mites can proliferate and lead to an infestation. Factors such as luxuriant coats and long manes, which offer ideal hiding places, as well as a lack of hygiene, immunodeficiency, infections or malnutrition can also increase the horse's susceptibility to mite infestation.