Human dicrocoeliasis presenting as a subcutaneous mass

Abstract

Human infection by Dicrocoelium dendriticum, a zoonotic liver fluke, is uncommon and soft tissue manifestation is extremely rare. The infection has no specific clinical signs or symptoms and diagnosis may be missed completely, thus treatment may be delayed. Diagnosis in humans is by identification of the eggs in the stool, while a living or dead fluke is rarely seen. The present report concerns the case of a 7-year-old child who presented with recurrent right flank subcutaneous nodules containing a live fluke on excision, and tissue histology showed characteristic brown operculated ova of D dendriticum. This is the first extraintestinal soft tissue presentation in such a setting. It is important to know the life cycle and natural habitat of this rare human parasite in order to make a correct diagnosis and institute early treatment in patients who have become infected.

BACKGROUND

Dicrocoeliasis is a zoonotic infection of herbivorous mammals such as cattle, sheep, rabbits and goats caused by Dicrocoelium dendriticum (lancet/liver fluke) or Dicrocoelium hospes with widespread distribution in Europe, Asia, North America and Africa.^1–4 The adult parasites are hermaphrodites and can be readily differentiated from each other.^1,2 D dendriticum is elongate and tapered anteriorly and posteroirly, while D hospes is narrower, with a uniform body width and a tapered anterior end. However, the eggs of both are morphologically indistinguishable and are operculate with a thick dark brown cuticle.^1,4 The parasite also utilises land snails (eg, Cionella lubrica, Achantinidae and Streptaxidae) and ants (Formica spp.) as first and second intermediate hosts in its life cycle.⁴ Parasitic infection and infestation are often seen in Humans, however, human dicrocoeliasis is uncommon and may be due to inadvertent ingestion of ants containing ova or undercooked infected liver from the aforementioned mammals.^5–7 Digenetic flukes such as D dendriticum may localise in ectopic extraintestinal sites within the peritoneal and pleural cavities.¹ Soft tissue infestation with this parasite is extremely rare, and to the best of our knowledge this is the first extraintestinal subcutaneous presentation in our setting. The patient was a child with an 8-month history of recurrent right flank subcutaneous nodules containing a live fluke on excision; tissue histology showed characteristic brown operculated ova of D dendriticum.

CASE PRESENTATION

A 7-year-old Fulani child presented to the paediatric outpatient clinic with a history of recurrent anterior abdominal wall mass. She had presented 8 months earlier with jaundice, fever and a similar mass at a peripheral hospital where she received treatment and excision of the mass, which was discarded without histopathological analysis. The father, a nomadic pastoralist, could not remember the drugs administered to the child but she improved and was subsequently discharged.

The current mass was not associated with any symptoms such as diarrhoea, vomiting, fever or jaundice, but had been gradually increasing in size. There were also no urinary symptoms of haematuria or dysuria. Examination revealed a rather ill looking, pale, malnourished child who was not jaundiced. Her liver and spleen were not palpably enlarged. At the right flank were multiple firm subcutaneous nodules measuring 8×5 cm, firmly adherent to the underlying structures, while the overlying skin was free and shiny. Excision of the nodular mass revealed a live, curved, leaf-like worm that was identified as D dendriticum; the tissue specimen was sent to the pathology laboratory for analysis.

We analysed a 17 g grey multinodular tissue measuring 6×3.5×2 cm with grey and yellow solid cut surfaces. The tissue was fixed in formalin and processed in paraffin wax while histology sections were stained with H&E. Histology revealed subcutaneous tissue with areas of granulomatous inflammation including numerous eosinophils and focal fibrosis. Within the granulomata were characteristic operculated ova of D dendriticum with a brownish cuticle (figs 1 and 2). The patient was given praziquantel and is yet to be seen at follow-up.

Figure 1.

Granuloma containing brown operculate ova of Dicrocoelium dendriticum.

Figure 2.

Brown-cuticled egg of Dicrocoelium dendriticum.

DISCUSSION

Human dicrocoeliasis is often undiagnosed due to the absence of specific clinical features, and patients who have become infected are usually asymptomatic.¹ However, symptoms such as nausea, vomiting, constipation, diarrhoea, headache, dizziness, abdominal and epigastric pain and biliary obstruction may be present in individual patients, thus simulating a hepatitis-like infection.^1,8,9 The adult worm replicates mainly in the livers of infected cattle and sheep, and passes its eggs into the intestines via the bile duct; there is no clinical illness in these animals,^2,4 though prolonged untreated infection may cause progressive hepatic cirrhosis and depressed liver function that ultimately shortens the reproductive life of the infected animals.^2,4 Other symptoms are hepatosplenomegaly, fever and jaundice. Our patient had jaundice and fever in her first presentation, which may not necessarily be attributable to dicrocoeliasis.

The eggs deposited in faeces are first ingested by land snails and released as slime balls, which are then ingested by formica ants found in vegetation. These ants cling to top vegetation in extreme cold temperatures and are thus eaten by grazing animals.² Human infection occurs with ingestion of undercooked liver from heavily infected sheep or cattle that often have as many as 50 000 to 100 000 parasites, and by accidental or deliberate ingestion of ants.^2,5–7,10 Our patient’s father is a nomadic pastoralist and the entire family is involved in the care and breeding of the animal herds. She was malnourished and could have deliberately eaten ants, containing ova, when out with grazing animal herds (pica disorder is a feature of malnutrition), or inadvertently while chewing blades of grass as commonly occurs with pastoralists. True human infection occurs by ingestion of ants and prolonged egg shedding.^1,5 The eggs or flukes, which are often dead, may also be recovered in surgical or duodenal aspirates¹ as seen in this young child, who had recurrence and a live fluke with eggs in the subcutaneous nodules. Definitive diagnosis is by identification of eggs passed in the stool.¹¹

The egg of D dendriticum is diagnostic and readily differentiated from the eggs of other liver flukes such as Schistosoma spp. and Fasciola gigantica. Also, the rare presence of a live fluke in this child aided positive identification of D dendriticum. It is important to have a detailed patient history and know the life cycle and natural habitat of this parasite in order to make an early diagnosis and institute adequate treatment, especially in pastoralists and individuals who favour consumption of the uncooked liver of cattle, sheep and goats.

LEARNING POINTS

• We present a rare case of true human infection by Dicrocoelium dendriticum, with identification of the fluke and its eggs.

• The tissue presentation may be misdiagnosed as a tumour.

• An adequate history of any contact with livestock may aid diagnosis.

• There is an absence of clinical symptoms, thus a high index of suspicion is needed in diagnosis.