Habronemiasis (Equine Summer Sore) in an 8-year-old Arab Horse

hind limbs. The right eye's ocular examination revealed abundant mucopurulent discharge, blepharospasm, and chemosis. The granulomatous tumor had a diameter of 1.8 cm and was evident on the palpebral conjunctiva of the medial canthus. The skin lesion was identified as habronemiasis based on the history, clinical symptoms. Treatment includes prednisolone tab with reducing dosage for 30 days, an oral dose of Ivermectin, topical oxytetracycline ointment for five days, chloramphenicol and triamcinolone eye drop for three days. The diagnosis was confirmed due to the positive reaction of the lesions to treatment protocol. Conclusion: Ocular habronemiasis is the common form of habronemiasis. Deposing of dead larva causes a hypersensitivity reaction. Treatments include corticosteroid to reduce inflammation-association tissue proliferation, antibiotic ointment for prevention of second bacterial infection, an antihistamine for the prevention of histamine-mediated pruritic and allergic conditions, and oral antihelminth for the killing of adult form in the stomach. The current study authors suggest fly control is essential in preventing habronemiasis.


Introduction
Habronemiasis, or equine summer sore, is caused by habronema larvae, commonly in tropical and subtropical climates. Habronema larvae could cause preocular infectious resulting in conjunctivitis, blepharitis, or dermatitis 1 . Habronema microstoma (H. microstoma), Habronema muscae, and Draschia megastoma are three worms known to cause habronemiasis. Habronema's adult stage is usually asymptomatic and lives in the equine stomach. Adult female nematodes produce eggs in horse stomachs, and eggs are passed with feces. Then the eggs in the horse feces are ingested by the maggots of various flies. Mature flies deposit the infective L3 larvae on the horse mucus membrane 2 . Flies mostly deposit their eggs on moist skin area which is attractive to them, like the preocular area. If the horse consumes the parasite's larvae, the adult parasite will complete its life cycle in the horse's stomach. A local hypersensitivity reaction occurs on the cutaneous or mucus membrane if the larvae remain on the cutaneous 3 .
When flies are most active, the spring and summer seasons are also the seasons with the highest incidence of habronemiasis. The medial canthus of the eye is the most common location for finding preocular lesions caused by habronemiasis. These lesions have an inflammatory and granulomatous appearance. These granules are composed of necrotic, caseous, or calcified material that is found surrounding either the dead remnants of the larvae or the larvae themselves 4 . A clinical presentation might be used to make a diagnosis. Sulfur-like granules are also pathognomonic. Histopathologic examination may be used to confirm the diagnosis. In several cases, the histology material showed evidence of an eosinophilic granulomatous inflammation associated with worms. In addition, a polymerase chain reaction (PCR) assay for molecular diagnosis of the two species of Habronema (H. microstoma and H. muscae) has been developed. It was determined with a specificity of one hundred percent and a sensitivity of ninety-seven percent that habronema DNA was present in the feces of horses. In addition, a PCR test was developed to diagnose stomach form of habronema. Validation of a PCR method has been completed to identify habronema species in skin samples from individuals with cutaneous infection 5 .
On cytology, eosinophils are abundant in smears from conjunctival scrapings. The conventional treatment for habronemiasis consists of anthelmintic medicine, removal or surgical debulking, and anti-inflammatory drugs. During the winter, lesions may spontaneously recover 6 . The current article describes a case of habronemiasis and its successful management.

Case report
An eight-year-old male Arabian horse with a history of wounds on the preocular area ( Figure 1) and hind limbs( Figure 3) was referred to the Large Animal Medicine Unit, Veterinary Clinical Hospital, Shiraz University, Shiraz, Iran. An extensive amount of mucopurulent discharge, blepharospasm, and chemosis were seen during the ocular examination of the right eye. The granulomatous growth  was discernible on the palpebral conjunctiva of the medial canthus and had a diameter of 1.8 centimeters. The mucous membrane was pink, and the rectal temperature was 37.5 degrees Celsius, all of which were seen during the clinical examination of the horse. During the clinical and ophthalmic evaluations, no further abnormalities were discovered. The research horse was dewormed with Albendazole (orally once at a dosing rate of 10 mg/kg) 5 6 months before of clinical signs of habronemiasis. The skin lesion was identified as habronemiasis based on the history and clinical symptoms. After therapy, the lesions were completely cured (30 days, Figure 2 and 4). Treatment includes prednisolone (2 mg/kg) tab with reducing dosage for 30 days. A single dosage of Ivermectin (200 µg/kg, Zoetis, Netherlands) was given orally, and an antibiotic ointment containing 0.5% oxytetracycline (Pfizer, Netherlands) was administered topically every six hours for five days to prevent secondary bacterial infection. Triamcinolone eye drop (corticosteroid, 0.1%, Netherlands) inhibits inflammation-related tissue growth. To avoid histamine-mediated pruritic and allergic symptoms, chlorphenamine eye drops (antihistamine, 0.4 to 0.5 mg/kg BW/day for three days) were used 6,7 .

Discussion
Habronemiasis is a complex parasitic disease of horses, donkeys, mules, zebras, and dogs that commonly occurs in tropical and subtropical areas. The disease caused by three nematodes includes H. microstoma, H. muscae, and Draschia megastoma. House flies, face flies, and stable flies transmit the pathogenic nematode larvae 1 . Cutaneous habronemiais is the most common form of habronemiasis in horses. Cutaneous habronemiais is associated with the deposition of larvae in areas where they cannot complete their life cycle. Deposition of larvae is related to local hypersensitivity 3 . Squamous cell carcinoma, foreign body granulomas, and phycomycosis are the differential diagnosis for ocular habronemiasis. Tests, including histology or PCR, could confirm the diagnosis. Many different options have been indicated for habronemiasis treatment. Treatment options should focus on eliminating the infection, reducing inflammation, and decreasing the size of the lesion 8 .
There is debate over the usefulness of anthelmintic medications because the deposition of dead larvae on the skin brings on a hypersensitive reaction. It is possible for the administration of ivermectin to occasionally worsen pruritus symptoms 7 . Although anthelmintic medications significantly prevent habronemia by eliminating the adult stages of the parasite in the stomach, the disease can still occur. If there are fewer parasite eggs, then there are fewer flies that are infected with the condition. The use of moxidectin therapy 6 has shown evidence of this effect. Based on the findings of several studies, local anthelminthic treatment with solutions of ivermectin, echothiophate, and trichlorfon may be beneficial in treating lesions. On the other hand, there is no evidence to suggest that it can be utilized to treat the lesion itself [6][7][8] .
Infection prevention is a critical component of habronemia care. Controlling flies is critical because they act as intermediate hosts, especially throughout the spring and summer. The removal of their nesting habitat will reduce the quantity of flies. As a result, adequate cleaning and manure management, frequent paddock cleaning, and waste stability are critical in fly control. Certain equipment items, such as fly nets and blankets, can protect certain areas, and face masks might be helpful in the treatment of (peri)ocular habronemia. Stabling horses during peak fly hours is one management method, but fly repellents may also be useful in some situations 9 .

Conclusion
Habronemiasis is a complex parasitic disease commonly found in horses, primarily in tropical and subtropical regions. The most prevalent form of habronemiasis is ocular habronemiasis. When the larvae die, their deposition causes a hypersensitivity reaction. A diagnosis can be made based on clinical presentation, and the presence of sulfur-like granules is a characteristic sign. Histopathologic examination can be used to confirm the diagnosis, often revealing eosinophilic granulomatous inflammation along with nematodes. Treatment options include the use of corticosteroids to reduce inflammationrelated tissue proliferation, antibiotic ointment to prevent secondary bacterial infections, antihistamines to prevent histamine-mediated itching and allergic reactions, and oral anthelminthics to eliminate adult parasites in the stomach.