4 EQUINE VETERINARY EDUCATION / AE / JANUARY 2009

Case Report Cutaneous habronemiasis in a 9-year-old Arab gelding in the United Kingdom S. S. Down*, I. Hughes and F. M. D. Henson Queen’s Veterinary School Hospital, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK.

Keywords: horse; ; ; cutaneous habronemiasis; granuloma

Summary appearance and treatment of cutaneous habronemiasis in the pastern region of an adult horse and is presented as Cutaneous habronemiasis causes ulcerative granulating an example of a differential diagnosis that should be lesions in the skin of equids. Dramatic exuberant tissue considered when investigating possible neoplastic lesions may be seen, which becomes traumatised by the horse. of the limbs in horses. To the authors’ knowledge, cutaneous habronemiasis has not previously been documented on the distal limb of Case details horses in the UK. Cutaneous habronemiasis should be considered as a potential differential diagnosis for History ulcerative granulating skin lesions on the distal limb of the horse. A 9-year-old Arabian gelding was presented to the Queen’s Veterinary Hospital, for investigation and Introduction treatment of a ulcerated mass on the dorsum of the right fore pastern, 1 cm proximal to the coronary band (Fig 1). Cutaneous habronemiasis is a well recognised cause of The mass had first been presented to the referring skin lesions of the horse in tropical and temperate veterinary surgeon 10 months previously. At this stage the climates. The disease is caused by infection with the owner reported a small, nonulcerated, nonpainful nodule. larvae of the , , The mass was then seen to increase in size and ulcerate, Habronema microstoma or Draschia megastoma. particularly in the 3 months prior to referral. Intermittent The pathogenesis of the condition has been well haemorrhage had been seen. The gelding was seen to described and it has been shown that infectious bite the heel bulbs of the affected limb on regular nematode larvae are deposited in moist areas of the skin occasions. No treatment had been undertaken. There was and pre-existing wounds. no history of previous disease or illness. The habronema larvae cause non-neoplastic The gelding was turned out to pasture 24 h a day. ulcerative nodules in the skin, which may be multiple or repelling agents had been placed over the nodule, as this solitary, and can induce an excessive granulation tissue was an area of fly aggregation. The gelding had been response at the site of infestation. It is thought that this is treated with anthelmintics on a regular basis, but the field due to a hypersensitivity reaction. Areas of predisposition have been described to include the prepuce, urethral process of the penis and medial canthus of the eye. Infection of the distal extremity has also been noted in the tropics. To our knowledge there has not been a case of cutaneous habronemiasis reported in the UK within the last 20 years, with the only other report being in 1984 (Trees et al. 1984). This Case Report describes the presentation,

*Author to whom correspondence should be addressed. Present address: The Centre for Equine Studies, The Health Trust, Lanwades Park, Kentford, Suffolk CB8 7UU, UK. Fig 1: Ulcerated mass dorsal pastern. EQUINE VETERINARY EDUCATION / AE / JANUARY 2009 5

was not cleaned of faecal material. The gelding had been in the owner’s possession for 5 years, and was not known to have been imported or to have travelled abroad. a)

Fig 4a: Habronema microstoma nematode in longitudinal section (arrow) within area of necrosis. Haematoxylin and eosin.

b)

Fig 4b: Habronema microstoma nematodes seen in longitudinal (white arrow) and transverse sections (black arrow), within area of necrosis. Haematoxylin and eosin. Fig 2: a) Latero-medial and b) Dorso-palmar weightbearing radiographic views revealing radiopaque areas within mass dorsal pastern.

Fig 3: Surgical removal of mass. Note yellow ‘sulphur’ granules deep to the skin surface. Fig 5: Surgical wound 3 weeks post initial cast removal. 6 EQUINE VETERINARY EDUCATION / AE / JANUARY 2009

Clinical findings held in place with a layer of elasticated, nonadhesive bandage (Vetrap)7. Elasticated, adhesive bandage At presentation, the gelding was in good bodily condition. (Tensoplast)8 was used to fix the bandage proximally and All clinical parameters were within normal limits. A large distally to the skin and hoof capsule. The bandage was ulcerated mass, measuring 73 x 53 x 55 mm was present on changed b.i.d. for 3 days following surgery, decreasing to the dorsal pastern of the right foreleg. Palpation of the s.i.d. on Day 4 post surgery. Hydrogel (IntraSite)4 was mass was resented, and the mass was considered to be placed over the granulation bed prior to dressing adherent to the underlying tissue. No lameness was seen placement post surgery. From Day 7 post surgery bandage at the walk or trot. changes were every 2–4 days as necessary. For cost reasons the nonadhesive absorbent dressing (Allevyn) was Further investigation replaced with nappies (Pampers)9 and the secondary and tertiary layers reduced. This was continued until Week 8 Routine haematological examination, including a blood post surgery. smear, was unremarkable. Multiple radiographic views Antimicrobial (3 days of crystalline penicillin 10 Mu were obtained of the pastern region, which revealed no q.i.d., 6.6 mg/kg bwt gentamicin s.i.d.) and nonsteroidal involvement of deeper bony structures. The proximity of anti-inflammatory therapy (1 g b.i.d. for 3 days, followed the mass to the proximal interphalangeal joint (PIP) and by 1 g s.i.d. for 7 days) was continued post surgery. dorsal pouch of the distal interphalangeal joint (DIP) was Antimicrobial therapy was then changed to trimethoprim noted. The soft tissue structure of the mass was readily and sulphadiazine (Trimediazine, 5.2 mg/kg bwt visible, and seen to contain multiple radiopaque trimethoprim and 26 mg/kg bwt sulphadiazine per os)10 ‘granules’ (Fig 2). Ultrasonography of the mass showed for the following 21 days. Oral moxidectin paste areas of hyperechogenicity from 1–3 cm distal to the skin (Equest)11 was given 5 days post surgery at a dose rate of surface. The medial collateral ligament of the distal 0.4 mg/kg bwt. interphalangeal joint, the dorsmedial aspect of the distal The surgical site was skin grafted with punch grafts interphalangeal joint and extensor process of the third taken from the superficial pectoral muscles 17 and 27 days phalanx were visible and appeared uninvolved. The PIP post surgery to enhance healing by secondary intention. joint and associated structures were nonvisible The gelding responded poorly to bandage placement, ultrasonographically due to the position of the mass. resulting in self-mutilation secondary to multiple bandage displacements. The granulation tissue was therefore Differential diagnosis debrided and the foot and pastern cast at Weeks 8, 12 and 16 post surgery to allow epithelialisation. On consideration of the clinical and imaging findings, the principle differential diagnoses included a fibroblastic Histopathology sarcoid, a bacterial/fungal granuloma, exuberant granulation tissue, an eosinophilic granuloma, neoplasia, a The gross appearance was that of an ulcerated, firm foreign body reaction and cutaneous habronemaiasis. mass. Multiple yellow granules were seen within fibrous- type tissue. Histological examination showed a densely Treatment cellular mass within the dermis, extending to the surface of the skin. The mass consisted of sheets of eosinophils In view of the size of the mass, it was decided to attempt and mast cells along with fewer lymphocytes separated complete surgical excision under general anaesthesia into multiple variably sized lobules by prominent rather than biopsy the mass (Fig 3). Antimicrobial therapy trabeculae and organised collagen and fibroblasts. of crystalline penicillin (Crystapen, 10 Mu i.v.)1 and Within the mass were multiple variably sized areas of gentamicin (Gentaject 10%, 6.6 mg/kg bwt i.v.)2 and numerous degenerative neutrophils and eosinophils anti-inflammatory and analgesic therapy of depicting necrosis. Some sections showed single phenylbutazone (Equipalazone, 4.4 mg/kg bwt i.v.)3 was nematode larvae, measuring approximately 50 µm in given prior to surgery. The mass was removed with sharp diameter within the centre of these necrotic areas (Fig 4). excision without damaging any tendinous structures or Where intact, the epidermis was moderately penetration of the underlying PIP joint capsule. The hyperkeratotic and hyperplastic. margins of the surgical site were undermined to ensure removal of associated fibrous material. Primary closure Further diagnostics could not be achieved due to the large size of the defect and the tissue bed was left open for healing by To further classify the nematode larvae found on secondary intention histopathology, formalin fixed and paraffin embedded The granulation bed was dressed with a nonadherent, tissue was sent to a laboratory to undergo a novel semi- dry absorbent dressing (Allevyn)4 followed with a layer of nested PCR assay (Traversa 2004a,b, 2006, 2007). The tissue cotton wool5 and gauze (K Band)6 bandages. This was was PCR positive for H. microstoma. EQUINE VETERINARY EDUCATION / AE / JANUARY 2009 7

Outcome larvae do not complete their life cycle and can only survive up to one month in cutaneous tissue (Waddell The horse responded well to foot casts, which were 1969). The mechanism of stimulation of the exuberant managed at home under the guidance of the referring granulation tissue is unknown, but is thought to be a veterinary surgeon. Each cast was removed 3 weeks post hypersensitivity reaction to dead or dying larvae (von placement. This revealed a markedly decreased area of Tscharner et al. 2000). It is also suggested that the release granulation tissue, which at Week 16 (Fig 5) was smooth, of chemotactic factors from the larvae due to level, nonmalodorous and without discharge. From immunoglobulin E interaction results in a focal eosinophilia Week 16 the granulation tissue was left to heal without (Vasey 1981). Necrotic, caseous or calcified material often further intervention, and the horse was gradually surrounds the nematode larvae, resulting in small yellow reintroduced to pasture and ridden work. granules seen on gross inspection. These are pathognomic for this condition (Scott 1988) and, with hindsight, were Discussion visible on the preoperative radiographs. The disease is sporadic in populations of horses, but Previous reports of cutaneous habronemiasis have come certain individuals are predisposed to yearly recurrences. primarily from temperate and tropical climates including There has been no association with breed, age and sex in Asia, Africa and the southern USA. Cases have also been most studies, although Arabians were over-represented in seen in northern USA and Canada (Vasey 1981). There is one study (Pusterla et al. 2003). Two of 3 horses of the minimal evidence for cutaneous infection in the sample population in a recent study (Traversa 2007) were temperate regions of western Europe. A case of also Arabian. The most recent European case of cutaneous habronemiasis has been previously reported in conjunctival habronemiasis that has been documented the UK in the tear line beneath the anterior canthus of the was also in an Arabian horse. There may therefore be eye (Trees et al. 1984). A case of conjunctival some predilection in this breed. It has been suggested that habronemiasis was reported in a horse in Belgium a greater hypersensitivity to nematode larvae may occur (Gasthuys et al. 2004). This case, as far as the authors are in Arabians with respect to others (Pusterla et al. 2003). aware, is the first reported case of cutaneous Another theory is that the colour of the horse may be habronemiasis of a distal limb in the UK. involved in this predilection. Horses with a light coat colour Adult nematodes inhabit the stomach of horses, and have been over-represented (Pusterla et al. 2003), and are rarely associated with clinical disease. Several surveys grey is a common coat colour in this breed. In the present in Europe have shown the occurrence of gastric case, the horse presented was a light coloured chestnut. habronemiasis, where adult nematodes are found within Light colours may be more attractive to when against the walls of the stomach. Dorny et al. (1999) showed 6 of a darker background, giving a greatest degree of 11 ponies were found to contain gastric Habronema contrast, and may thus be a reason for an over- species at post mortem examination in Belgium. In another representation in this breed (Howard and Wall 1998). study in Normandy, France, 8.5% of horses were found to Definitive diagnosis is made on the discovery of larvae be infected (Collobert-Laugier et al. 2000). Gastric within tissue. This may be done via deep scrapings or habronemiasis has also been surveyed in Germany (62%; biopsy, or histopathology of surgically removed masses as Bauer 1986), Poland (8–16%; Gawor 1995), The Netherlands in this case. Biopsy tissue should be digested in acid pepsin (4.3%; Borgsteede and van Beek 1998) and central Italy, solution for 12–18 h at 37°C. A stereoscopic microscope where 53.6% of the sample population were found using x10 magnification is used to examine the digest for infected using semi-nested PCR assay techniques on larvae. Usually there are only a few larvae present within faecal samples (Traversa 2006). lesions, and combined with exuberant, necrotic or In infected horses, eggs and larvae of the gastric calcified tissue due to the effect of the immune response, nematodes are passed out in the faeces. Maggots of the reliability of obtaining larvae within biopsies, skin scrapes or intermediate host, which includes the ( smears is low. Live larvae can only be found in the very calcitrans) and the (Musca domestica), ingest the early stages of infection (Waddell 1969). larvae and eggs in the faeces of the carrier horse. The The presence of yellowish granules in association with infective larval stage develops in the maggot as it matures sheets of eosinophils and mast cells, along with the and subsequently escapes from the mouth parts of the history and clinical examination is usually diagnostic. Use adult fly as it feeds. Feeding around the mouth of the horse of the novel semi-nested PCR technique, as was used in results in swallowing of larvae and hence completes the this case, allows rapid identification of infective media, parasite’s life cycle (Soulsby 1965). allowing prompt treatment. In this case, the granules The cause of the cutaneous form of habronemiasis is were readily visible on radiographs and ultrasonography, believed to be due to infectious larvae deposited on the as multiple radiopaque and hyperechoic areas within skin of the horse. These areas are usually moist or open the mass respectively. Biopsy of the mass was not wounds where flies may be feeding. The larvae have also performed as the owner wished to proceed straight to been shown to penetrate intact skin (Scott 1988). These surgical excision. 8 EQUINE VETERINARY EDUCATION / AE / JANUARY 2009

Multiple treatment regimes for cutaneous 8BSN Medical, Brierfield, Lancashire, UK. 9 habronemiasis are present within the literature suggesting Proctor and Gamble, Trafford Park, Manchester, UK. 10Vétoquinol UK, Great Slade, Buckingham, UK. that there is no successful single treatment routinely used. 11Fort Dodge Animal Health, Hedge End, Southampton, UK. Treatments include use of local and systemic treatments. Treatments are aimed at providing a larvicidal and anti- References inflammatory action. Treatments include ivermectin, moxidectin, organophosphates, corticosteroids, dimethyl Bauer, C. (1986) Infestation with stomach parasites in horses in north sulphoxide, and topical petroleum and antimicrobial Germany. Wochensch, Deutsche Tierärztl. 93, 383-389. therapy. Eighty-six percent of horses treated with a single Borgsteede, F.H. and van Beek, G. (1998) Parasites of stomach and small intestine of 70 horses slaughtered in The Netherlands. Vet. Q. 20, 31-34. i.m. injection of ivermectin showed no evidence of larvae in biopsies taken 5 weeks later in one study (Herd et al. Collobert-Laugier, C., Lamidae, C., Brisseaua, N., Moussu, C. and Hamet, N. (2000) Prevalence of stomach nematodes (Habronema 1981). Of the 24% that were nonresponsive, 100% spp., Draschia megastoma and Trichostrongylus axei) in horses responded to a second i.m. dose. Oral moxidectin was examined post mortem in Normandy. Rev. Méd. Vét. 151, 151-156. chosen in this instance due to its comparable efficacy (S. Dorny, P., Eysker, M., Demeulenenaere, D., Smets, K. and Vercruysse, J. Lloyd, personal communication) and licensing. Smaller (1999) Study on the gastrointestinal metazoan parasite fauna of ponies in Belgium. Vlaams Diergeneeskundig Tijdschrift 68, 173-178. lesions have been seen to resolve with use of oral Fadok, V.A. (1984) Parasitic skin diseases of large . Vet. Clin. N. prednisolone (Fadok 1984; Mathison 1995). Surgical Am.: Large Anim. Pract. 6, 3-26. removal or debulking of large habronemic granulomas is Gasthuys, F.M.R., van Heerden, M. and Vercruysse, J. (2004) Conjunctival also widely accepted (Mohamed et al. 1990; Mathison habronemiasis in a horse in Belgium. Vet. Rec. 154, 757-758. 1995). Due to the large size of lesion in this case surgical Gawor, J.J. (1995) The prevalence and abundance of internal parasites removal was undertaken. Treatment with oral moxidectin in working horses autopsied in Poland. Vet. Parasitol. 58, 99-108. was given to target any larvae left in situ. Corticosteroids Herd, R.P. and Donham, J.C. (1981) Efficacy of ivermectin against were not used due to surgical debulkment of the cutaneous Draschia and Habronema infection in horses. Am. J. vet. Res. 42, 1953-1955. inflammatory nidus, and to decrease the risk of reduction in healing by secondary intention. Moxidectin was then Howard, J.J. and Wall, R. (1998) Effects of contrast on attraction of the housefly, Musca domestica, to visual targets. Med. Vet. Entomol. 12, repeated at 13 weeks. 322-324 Regular larvicidal treatment and cooler climates within Mathison, P.T. (1995) Eosinophilic nodular dermatosis. Vet. Clin. N. Am: the UK are thought to be the reason for the lack of clinical Equine Pract. 11, 75-89. cases seen. The somewhat milder temperatures and Mohamed, F.H., Samra, M.T., Ibrihim, K.E and Idris, S.O. (1990) increased rainfall that have been noted over the recent Cutaneous habronemiasis in horses and domestic donkeys (Equus asinus asinus). Rev. Elév. Méd. vét. Pays trop. 42, 535-540. years in the UK may be the cause for further cases to be Pusterla, N., Watson, J.L., Wilson, W.D., Affolter, V.K. and Spier, S.J. (2003) seen in this country. It is possible that due to the Cutaneous and ocular habronemiasis in horses: 63 cases (1988- uncommon presentation of the condition in the UK, such 2002). J. Am. vet. med. Ass. 222, 978-982. ulcerating granulating wounds may be being Scott, D.W. (1988) Habronemiasis. In: Large Animal Dermatology, Ed: misdiagnosed as sarcoids if unbiopsied. This Case Report D.W. Scott, W.B. Saunders, Philadelphia. pp 251-255. highlights the possibility of cutaneous habronemiasis as a Soulsby, E.J.L. (1965) Habronema spp. In: Textbook of Veterinary Clinical cause of an ulcerative lesion on a distal limb and Parasitology. Vol 1. Helminths, Ed: E.J.L. Soulsby, Blackwell Scientific Publications, Oxford. pp 799-805. encourages the inclusion of this condition as a differential Traversa, D., Giangaspero, A., Galli, P., Paoletti, B., Otranto, D. and diagnosis in appropriate cases. Gasser, R.B. (2004a) Specific identification of Habronema microstoma and Habronema muscae (, ) Acknowledgements by PCR using markers in ribosomal DNA. Mol. Cell probes 18, 215-221. Traversa, D., Giangaspero, A., Iorio, R., Otranto, D., Paoletti, B. and The authors acknowledge Jackie House BSc BVMS Cert Gasser, R.B. (2004b) Semi-nested PCR for the specific detection of Habronema microstoma or Habronema muscae DNA in horse LAS MRCVS for undertaking the gross and histopathology faeces. Parasitol. 129, 733-739. of the samples, Dr Donato Traversa DVM, PhD, DipEVPC Traversa, D., Iorio, R., Capelli, G., Paoletti, B., Bartolini, R., Otyranto, D. and the laboratory for undertaking the semi-nested PCR and Giangaspero, A. (2006) Molecular cross-sectional survey of technique on the tissue samples, providing a definitive gastric habronemosis in horses. Vet. Parasitol. 141, 285-290. diagnosis and to the referring veterinary surgeon for Traversa, D., Iorio, R., Petrizzi, L., De Amicis, I., Brandt, S., Meana, A., referring the case to the hospital. Giangaspero, A. and Otranto, D. (2007) Molecular diagnosis of equid summer sores. Vet. Parasitol. 150, 116-121. 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