Bots Infection in Horses

Bots infection or Gasterophilus spp. infection is the  most widespread, even though rarely diagnosed is a gastrointestinal endoparasite in horses of all ages and foals

  • “Bots,” the bot fly larval stage, is the phase found in the equine stomach.
  • Gasterophilus intestinalis and Gasterophilus nasals are most usually observed in horses; other less commonly identified organisms include Gasterophilus haemorrhoidalis and Gasterophilus pecorum.
  • Horse bots are the parasitic larvae of the botflies, Gasterophilus spp. Adult females lay their fertilized eggs onto the hair hairs of horses. Bot larvae are eventually ingested by cleaning and can induce inflammatory reactions during migration within the mouth cavity and by adhesion to the stomach wall. In general, bot larvae are considered benign, even when some disease is found. Bot larvae can be discovered by oral inspection or gastroscopy.


The botfly is the same responsible for Gasterophilus intestinalis, Gasterophilus nasalis, and Gasterophilus haemorrhoidalis. If you are located in a region where botflies are common, the only way to avoid this is to medicate horses for the parasitic infection every year.

The life cycle of Gasterophilus-spp:

Direct life cycle:

  • The adult bot fly deposits eggs on the horse’s hairy coating (legs or head) during temperate months. The eggs hatch on the hairy coat, producing first-stage larvae, which then enter the cavity in the mouth by moving there or are ingested by the horse throughout grooming behavior.
  • First- as well as second-stage larvae grow in the oral cavity in the gingival tissue (G. nasalis) or mouth (G. intestinalis).
  • Late second-stage larvae are ingested and develop into third-stage caterpillars in the gut. The third-stage larvae then adhere to the gastric (G. intestinalis) or proximal duodenal (G. nasalis) mucosa and then overwinter.
  • Third-stage larvae disengage from the gastric mucosa in the new season and are excreted in the feces and pupate. Adult bot flies appear during the warmer months and continue the cycle.
  • In a broader sense, Gasterophilus species are not harmful, and associated clinical illness is uncommon until considerable numbers of larvae are present in the intestines, leading to gastric mucosal discomfort or in the duodenal resulting in gastric outflow obstruction. as is rare unless significant numbers of larvae are present in the intestines, resulting in gastric mucosal pain or inflammatory or in the duodenal resulting in gastric outflow obstruction.

Clinical Signs and Symptoms:

Some things to check for if you suspect your horse may have Gasterophilus are:

  • Whitish-yellow ova on the sides of the legs and shoulders (Gasterophilus intestinal)
  • Yellow eggs across neck and jaw (Gasterophilus nasalis)
  • Black eggs surround their mouths and lip (Gasterophilus haemorrhoidalis)
  • Agitation
  • Itching of the mouth and lips
  • Watery stool/ Dysentery Diarrhea
  • Painful lesions in the mouth
  • No appetite
  • Infection with bacteria (watery stool, fever, and lack of appetite)


  1. Gasterophilus intestinalis deposits eggs on the extremities and shoulders
  2. nasalis deliver eggs on the chin and neck
  3. Gasterophilus haemorrhoidalis deposit eggs on lips and mouth


It should be simple to detect whether the eggs are still on your horse’s skin by observing the color and position of the eggs or by giving your veterinarian a sample to look at. To inspect your horse for infection or invasion of the intestines and stomach, it is advised that you see a veterinarian who specializes in equestrian care. Your horse’s medical history, including vaccination records and any indications of unusual behavior, will be questioned by your veterinarian. If larvae are discovered in your horse’s feces, the veterinarian may be able to identify them and provide a conclusive diagnosis. If not, a thorough examination will be required to rule out other conditions. The next step is to conduct a complete physical examination that includes measurements of the patient’s weight, height, body condition score, temperature, behavior, breath sounds, heart rate, and blood pressure. The veterinarian should be able to identify any eggs in your horse immediately soon. The doctor will next observe how your pet moves while walking and trotting to check for lameness. After that, a flexion test, conformation check, and foot test will be performed. Before observing your horse walk and trot once again, the veterinarian will momentarily apply pressure to the joints and administer a numbing drug.


A fecal examination, a urinalysis, a complete blood count, a bacterial and fungal culture, a blood chemistry panel, a packed cell volume (PCV), and a glucose level are among the diagnostic procedures that will also be carried out. To look for any damage or obstructions in the intestines or stomach, abdominal X-rays and ultrasounds will be performed.

Control and Prevention

  • Mechanical control:

    Since here is where the fly’s final stage of development takes place before it emerges feces should be cleaned up and removed. There are various ways to get the bot eggs off the horse. The bot eggs may be removed with a scraper or an instrument with a sharp edge. The larvae may be killed and the eggs can be made to hatch using warm water and the proper pesticide. If they do not get it to the mouth, the first-stage larvae perish shortly after hatching. Larvae may be kept out of the handler by using protection, such as rubber gloves.

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  • Chemical control:

    Areas of the body coated with bot eggs may also get a weekly application of a pesticide during the peak egg-laying season. To limit the amount of larvae in the stomach, oral medicines might be employed. Avermectins, which are often prescribed drugs, are available in a variety of forms, including liquids, gels, boluses, and feed additives. The adult and larval phases of the fly are managed by avermectins. When eggs are first seen in the horse during the early summer, it should be addressed within a month. To manage the second and third-stage larvae, a second treatment should be applied in the autumn.


The removal of the eggs, treatment of the internal bots, and removal of the bots from your horse’s surroundings are the three steps of the therapy for Gasterophilus.


  • Taking the Eggs Out

Although removing the eggs is a time-consuming task, it is vital to manage the infestation. There are a variety of methods to handle this, including applying pesticides from the veterinarian or scraping them off with an instrument with a sharp edge.

  • Care for the Bots

Giving your horse Ivermectins or moxidectin at the end of the summer can kill the internal bugs, and you should administer it again the following year in the early summer to avoid further infestations.

  • Taking the Bots out

Since the larvae are discharged with fecal matter, it is crucial to regularly clean up the feces.

Ivermectin (The treatment of choice is ivermectin (0.2 mg/kg), which has shown efficacy against both oral and stomach stages)

15 thoughts on “Bots Infection in Horses”

  1. It is very clearly Explained and very easy to understand and very informative for Veterinary Doctor’s.


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