First Diagnosis of an Imported Human Myiasis Caused by Hypoderma sinense (Diptera: Oestridae), Detected in a European Traveler Returning From India


  • This paper has been presented at the meeting: XI Congreso Iberico De Parasitología that was held in Lisboa, Portugal, from September 15 to 18, 2009.

Maria J. Perteguer, PhD, Servicio de Parasitología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Ctra. Majadahonda-Pozuelo, E-28220 Majadahonda, Madrid. E-mail:


This paper reports a case of myiasis caused by Hypoderma sinense in a European man returning from a journey through northern India. The patient showed eosinophilia, systemic signs of inflammation, and painful swellings in several parts of the body. The diagnosis was confirmed by specific serology and parasite molecular identification.

The genus Hypoderma (Diptera: Oestridae) includes seven species of flies which, at the larval stage, can cause internal myiasis. In domestic and wild ruminants, the disease is characterized by the presence of subcutaneous warbles in the dorsal and lumbar regions.1 Human cases of hypodermosis have been associated with subcutaneous creeping myiasis,2 ophthalmomyiasis,3 and meningitis,4 although the most common symptoms are skin allergies accompanied by eosinophilia.5,6 In China, hypodermosis is one of the most important arthropod infections in cattle and yaks, especially in the northern regions of the country7 where its prevalence can reach 90% to 100%. In some cases, there may be 400 larvae affecting a single animal.8 The highest known prevalences of human hypodermosis (0.4%–7%, in farmers) have been reported in the same areas.9 In several European countries, treatments with injectable or pour-on ivermectin formulations have been used for nationwide control of cattle hypodermosis (reviewed by Boulard et al.10), resulting in the reduction of the prevalence of infection to just 0.5%. Indeed, in the UK, Ireland, and Denmark cattle hypodermosis has been eradicated. Consequently, the number of reports of human infestation by Hypoderma spp. has been greatly reduced.11 However, the increasing movement of people around the world, in particular, to and from developing countries, can expose travelers to these “exotic” pathogens now.

This paper reports a case of imported human hypodermosis in a European man returning from northern India. The patient showed severe symptoms that clinically resembled those of other parasitoses, leading to initial misdiagnoses of lymphatic filariasis, gnathostomiasis, and sparganosis. The surgical extraction of larvae suggested a diagnosis of a probable myiasis although it was not until an anti-Hypoderma enzyme-linked immunosorbent assay (ELISA) test was performed that the diagnosis was confirmed. The causal agent was identified as Hypoderma sinense by molecular methods.

Case Report

The patient was a 34-year-old Spanish man who had traveled to Ladakh, a mountainous area in northern India, as a tourist guide in August 2006. Goats and yaks are raised in the area. In October 2006, the patient started to notice discomfort and abdominal pain. One month later he began suffering from painful inflammation in the right groin and testicular region. The patient was initially treated at a hospital in Madrid, where he was subjected to ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) examinations. These revealed inflammation of the right spermatic cord plus iliac and inguinal adenopathy. The patient also showed notable eosinophilia (5,100 eosinophils/µL, 31.2%). Day and night blood microfilariae level tests returned negative results, as performed by filarial-specific polymerase chain reaction (PCR), tests for faecal and urinary parasites, and parasitic (filariasis, trichinellosis, toxocariasis, anisakiasis, strongyloidosis), bacterial (brucellosis, salmonellosis, tuberculin, urinary mycobacterium), and viral [human immunodeficiency virus (HIV)] serological tests. In spite of the laboratory results, lymphatic filariasis was suspected, and the patient was treated with albendazole (a single dose of 400 mg) and diethylcarbamazine (6 mg/kg/d/15 d) plus prednisone (60 mg/d/5 d). After beginning the prednisone treatment, the eosinophil count decreased significantly to 100/µL (0.4%), only to increase again to 2,590/µL (21.1%) once the treatment was suspended.

In January 2007, the patient was referred to the Hospital Carlos III, Madrid, by this time with a swollen left thigh. At anamnesis, he referred to having noticed slightly painful, transient (lasting 2–7 d), erythematous cutaneous swellings in different locations during his summer journey. On examination, swellings were detected in the right spermatic cord, in the upper third of the left thigh, and in the left flank (Figure 1). The patient never suffered from fever. At the time of consultation, the prednisone treatment had been suspended for 2 weeks, and the eosinophil count had reached 7,000/µL (41%). Direct (ie, blood microfilariae levels and faecal parasites), serological (ie, anisakiasis, filariasis, schistosomiasis, trichinellosis, toxocariasis, fasciolasis, echinoccocosis, and gnathostomiasis), and parasitological tests were performed. For the last of these tests, the sample was sent to the Gnathostomiasis International Reference Centre in Thailand. Since gnathostomiasis was suspected, the patient was hospitalized and treated with albendazole (400 mg/12 h/3 wk). To avoid masking eosinophilia, no corticoids were administered. The patient was informed that deworming treatment might mobilize parasites toward the body surface, allowing them to be surgically removed and identified, thus permitting an appropriate course of treatment to be determined. Five days after the treatment, the patient's cutaneous swellings became extremely painful and two nodular lesions appeared, one in the gluteal region and another on the back. Ultrasound scanning revealed a worm-like parasite inside each swelling. These two whitish, oval-shaped parasites (10 × 3 mm and 6 × 2 mm, respectively) were surgically removed. Morphological analysis of a fragment of one of the parasites suggested it might be a fly larva (Figure 1). The other specimen was subjected to histological examination, but this provided no useful results. Five days after beginning the albendazole treatment the eosinophil count reached 29,800/µL (78%), coinciding with the onset of extreme pain from the cutaneous swellings. At the end of the albendazole treatment, the eosinophil count decreased to 18,897/µL (67%). Ivermectin treatment (12 mg/d/2 d) was therefore administered, beginning on February 8, 2007. The eosinophil count decreased to 2,900/µL (30%), and the patient remained asymptomatic for some days, after which another painful swelling appeared on his right leg and the eosinophil count rose to 3,100/µL (34%). The ivermectin treatment was repeated on March 3, 2007, and a few days later the eosinophil count had decreased to 1,600/µL (20.6%). In the meantime, negative serology for Gnathostoma was confirmed. Five days after the second ivermectin treatment, highly painful cutaneous swellings reappeared in various parts of the body that hindered the patient carrying out his normal routine. It was therefore decided to administer an empirical treatment for a potential sparganosis based on similar clinical cases described in the literature.12 Treatment with praziquantel started on March 22, 2007 at a dose of 75 mg/kg/day/3 days, but no significant clinical changes were seen nor was the eosinophil count reduced. Several days after this treatment was begun, a negative serology result for sparganosis was received. Since the patient continued to suffer from severe painful cutaneous swellings and hypereosinophilia, a third round of ivermectin (12 mg/d/3 d) was administered. After this last treatment, the patient quickly became asymptomatic. No cutaneous swellings reappeared and the eosinophil count rapidly normalized. The patient has remained asymptomatic to the present day, 2 years later.

Figure 1.

View of a swelling in the patient's left flank (hip).

Detection of Anti-Hypoderma spp. Igg Antibodies

Since neither the multiple serological nor microscopy tests performed were conclusive, and because the morphological analysis of the larval fragment suggested myiasis (Figure 2), immunodiagnostic tests for hypodermosis were performed using retrospective and tracking sera from the patient. Three consecutive serum samples were sent to the Lugo Veterinary School Laboratory. Anti-Hypoderma antibodies were sought by indirect ELISA using a crude extract obtained from the first instars of Hypoderma lineatum, as described by Panadero et al.13 Different dilutions of the antigen, sera, and immunoconjugate were tested following a previously described protocol.14 The specificity of the procedure was assessed by testing three human sera positive for Gnathostoma. High titers of anti-Hypoderma antibodies were detected during the course of disease (OD 4.359 on November 24, 2006), at 3 months post-infection (p.i.) (on November 24, 2006), and after the treatment (OD 3.977 at 7 months p.i. and 4.044 at 15 months p.i.). These high levels of antibodies against H lineatum antigens confirmed the diagnosis of an infestation by oestrid larvae.

Figure 2.

Microscopic view of the front part (first segment) of a larval fragment extracted from a traveler returning from India identified as Hypoderma sinense by polymerase chain reaction (PCR). (a) General view; (b) detail of the superficial denticles.

Parasite Molecular Identification

Genomic DNA was extracted from the larval parasite tissues using the Quantum Prep AquaPure Genomic DNA Kit (BioRad, Hercules, CA, USA). The hypervariable sequence of the cytochrome oxidase I (cox1) gene coding for the region from the external loop 4 (E4) to the carboxy-terminal (COOH) of the protein (688 bp) was amplified by PCR as previously described.15 The PCR products were detected on 1.6% agarose-Tris-acetate-EDTA (TAE) gel, purified using Ultrafree–DA columns (Amicon, Billerica, MA, USA), and then directly sequenced in an ABI-PRISM 377 sequencer using the Taq DyeDeoxyTerminator Cycle Sequencing Kit (Applied Biosystems, Foster City, CA, USA). The mitochondrial fragments were sequenced in both directions. The sequences were aligned using the ClustalX program and examined by eye. Pairwise comparison of the sequences obtained showed them to be identical to the H sinense cox1 sequence available in the GenBank™ database (Accession number: AY350769).


This is the first report of human infestation diagnosis caused by H sinense larvae in Europe, in a patient returning from India. It is very likely that the infestation resulted from contact with infested cattle or yaks in the region—which is endemic for hypodermosis—where the patient had been traveling. Human cases of myiasis might occur when newly hatched larvae on the coat of infected animals come into contact with the hands or bare arms.2

On the basis of the patient's clinical symptoms during the early stage of infestation, and taking into account the results obtained from the different diagnostic tests, a presumptive diagnosis of gnathostomiasis was initially reached, followed by one of sparganosis. Since these diseases are very rare in Spain, serological tests were not immediately available, but empirical treatments were administered. The morphological features of the fragment of a surgically extracted larva suggested an infestation by Hypoderma spp. The identification of the different species of Hypoderma relies on the examination of larval morphological features,16,17 but the small size of the fragment hindered complete identification. However, the presence of high anti-H lineatum antibody titers in the patient's serum (detected by ELISA at different times) was indicative of infestation by Hypoderma larvae, supporting the previous morphological suspicion of myiasis. The assessment of cross-reactivity with antigens of other members of the Hypodermatinae subfamily, ie, Hypoderma bovis, Hypoderma tarandi, Hypoderma diana, and Przhevalskiana silenus (see Monfray and Boulard18; Boulard et al.19) is useful when performing ELISA prepared with H lineatum antigens, even though they may not be endemic in the patient's country of origin.

Repeated treatment with ivermectin seemed to be effective since the patient quickly became asymptomatic and the eosinophil count normalized. Ivermectin is effective in the treatment of several myiases, and it is a good alternative when surgical removal is unfeasible.20 This is important since Hypoderma larvae can migrate within the body to involve in the central nervous system21 or, more often, to the eyes, where they cause ophthalmomyiasis.22 In our case, two parasite larvae were surgically removed. Considering that the swellings did not have any breath hole and the larval size, a diagnosis of fly first instars (LI), ready to moult to second instars (LII) was made. Furthermore, after the first and second round of ivermectin treatment, new painful swellings appeared probably due to other undetected parasites, and it was not until the third ivermectin round that the patient became asymptomatic. Although cases of human myiasis are uncommon in Europe, if symptoms are indicative this disease should be kept in mind by physicians examining immigrants and travelers returning from endemic areas such as Ladakh. While serological analysis is useful in the diagnosis of myiasis-causing Hypoderminae larvae in travelers not previously exposed to larval infestation, molecular identification is important. In this work, the sequencing of a partial mitochondrial cox1 gene sequence confirmed H sinense to be the causal agent.

Human cases of infestation by Hypoderma spp. have previously been reported, with H bovis and H lineatum or H tarandi as the agents most frequently identified.2,22 Reports of human myiasis associated with H diana or Hypoderma actaeon are exceptional.23H sinense (Pleske 192624), has long been considered synonymous with H lineatum.25–27 Recently, the validity of H sinense as a species in its own right infecting cattle and yaks in China was demonstrated by molecular and morphological methods.28 Its endogenous life cycle has also been described.29 This is the first report, however, of H sinense as a causal agent of human hypodermosis. Nevertheless, given the difficulty to establish a correct diagnosis of the present case, and the paucity of the literature, it seems possible that diagnosis may have been easily missed in previous similar cases. Unlike other myiasis-causing larvae (eg, Gasterophilus spp.) Hypoderma spp. can simulate their larval development (although without reaching the fully mature third instars) in human hosts often with serious consequences. Migration through the oesophagus29 may have accounted for the discomfort and abdominal pain initially described by the patient in the present report.

Human cases caused by Hypoderma species often show a seasonal distribution associated with contact with cattle in the previous autumn or summer. Miller et al.30 listed three clinical features to aid in the diagnosis of Hypoderma spp. infestation in humans: (1) seasonal occurrence, (2) transient migratory areas of inflammation, and (3) high eosinophilia. Serological methods are useful in the diagnosis of imported cases of human myiasis in travelers returning from endemic areas. Nevertheless, confirmation is required by the morphological examination of recovered larvae and their molecular identification.


The authors thank Professor Dr Luis Zapatero of the Universidad Complutense de Madrid for his invaluable help in the morphological characterization of the extracted parasite fragment. Thanks are also due to the Gnathostomiasis International Reference Centre of Thailand (University of Mahidol, Bangkok) for undertaking the Gnathostoma serological analysis. This work was supported by the Spanish Ministry of Science and Innovation and the Instituto de Salud Carlos III within the Network of Tropical Diseases Research (RICET RD06/0021/0019).

Declaration of Interests

The authors state that they have no conflicts of interest to declare.