A 10-year-old previously healthy boy had a sudden seizure at home in November 2017. He had a few seconds of fixed gaze, unresponsiveness and then a generalized tonic-clonic seizure with cyanotic lips and frothing at the mouth. The entire episode lasted 2 minutes and was followed by post-ictal fatigue. Within 15 minutes, he arrived at the hospital emergency department, and a general physical examination was performed. He was tired but responded adequately to verbal and physical stimuli, and had a Glasgow coma scale of 15 (maximum score). Tender enlarged, approximately 1 cm in diameter, submandibular lymph nodes were found bilaterally, and he was tender for palpation on a point in the right occipital region of the skull. His oxygen saturation was 100%, blood pressure 125/55 mm Hg, axillar temperature 35.8°C, respiratory rate 22/min, heart rate 93/min, he had no abdominal tumors or pain, no petechia, no neck stiffness and a neurologic examination without remarks. The week before admission, the boy had complained on diffuse throat pain and localized right-sided occipital headache. In the same period, the boy’s mother had also had throat pain and a younger sister had gastroenteritis. The parents had noted an episode of periorbital and cheek dermal swellings with redness bilaterally, but most prominent on the right side, 4 weeks before and recurring bilaterally 2–3 days before the seizure. His medical history was otherwise unremarkable.
Initial laboratory values for complete blood count, blood glucose, serum electrolytes, C-reactive protein and erythrocyte sedimentation rate were normal. An electroencephalogram was normal, and the following day, he was discharged in good condition. A brain magnetic resonance imaging (MRI) 2 days later showed an 8-mm circular lesion in the left frontotemporal lobe with intermediate T2 signal, punctate focus of signal loss (Fig. 1), contrast enhancement and surrounding perifocal edema. Susceptibility-weighted imaging demonstrated loss of signal in the periphery of the lesion. Five days after discharge, a new blood sample and cerebrospinal fluid (CSF) were collected. A complete blood count showed hemoglobin 14.0 [reference value (ref) 11.0–14.8] g/dL, thrombocytes 255 (ref 250–460) × 109/L (L), leucocytes 4.1 (ref 4.4–12.5) × 109/L, and the differential count revealed neutrophils 1.3 (1.5–8.3) × 109/L, lymphocytes 1.4 (1.0–4.3) × 109/L, monocytes 0.3 (ref 0.2–0.9) × 109/L, basophils 0.1 (ref <0.1) × 109/L and eosinophils 1.0 (ref <0.5) × 109/L. The CSF showed a cell count of <3 (ref <5) × 106/L, glucose 3.1 (ref 2.5–4.4) mmol/L, protein 209 (ref 100–500) mg/L, albumin 107 (ref 100–300) mg/L, immunoglobulin (Ig) G level 0.013 (ref 0.004–0.051) g/L, and isoelectric focusing revealed identical IgG bands in serum and spinal fluid. Further specific anamnestic information was gathered and a subsequent result confirmed the diagnosis.
For Denouement see P. 1064.
Continued from P. 1063.
Based on the episodic facial swellings preceding the sudden seizure and the finding of a circular small brain lesion, an intracerebral infestation was suspected. On further history, the mother recalled that the boy had touched a reindeer carrion while hiking 6 weeks before the seizure, in the midst of the egg-laying period of the reindeer warble fly (Hypoderma tarandi). Serologic testing detected IgG antibodies against hypodermin C (HyC) by enzyme-linked immunosorbent assay percentage (positive control = 100, negative = 0, assaying at dilution 1/50). HyC is an enzyme secreted by H. tarandi larvae during migration in the host, in our case with an initial increase in antibody levels followed by a decline over the following year. Blood eosinophil counts fluctuated 4–6 weeks before normalizing. The CSF sample showed no detectable level of anti-HyC antibodies.
The patient was diagnosed with intracerebral myiasis caused by the larva of H. tarandi and was treated with a standard dose (200 µg/kg body weight) of the antiparasitic drug ivermectin, which is a registered drug for parasitic infections but is not labeled for use in myiasis. The treatment was repeated twice during the following 4 weeks because of 2 relapses of scalp dermal swellings. The lymph node enlargement, head ache and regional skull tenderness disappeared. Brain MRI was repeated 2 weeks and then 4 months after the first MRI: showing marked regression of the intracerebral lesion. Over a 2.5-year follow-up, the boy has had normal clinical and laboratory findings and no recurrent seizures. He is now an active football player with no health complaints.
Myiasis is the condition where fly larvae have infested a mammal and feed on its tissues. The history of visiting a reindeer area during the H. tarandi egg-laying period, with subsequent episodic facial dermal swellings before and shortly after the seizure, serology results, peripheral eosinophilia and clinical response to treatment were all compatible with a diagnosis of myiasis caused by H. tarandi. Furthermore, the history of a seizure in a time period with the presence of facial dermal swellings, together with the brain MRI findings, strongly indicated an intracerebral infestation.
The reindeer warble fly is a member of the family Oestridae and remains common in most regions where reindeer and caribou live, including Alaska, Canada, Greenland, Scandinavia, Finland, and Russia.1 Female H. tarandi normally lay eggs on reindeer hair, and occasionally on human hair.2 The major period for egg-laying in Northern Norway is early July to late September. Following egg hatching, the larva penetrates the skin and migrate in the host tissues. Common infestation findings in humans are migrating dermal swellings in the head region, lymph node swelling, periorbital edema, and in some cases, ophthalmomyiasis, including ophthalmomyiasis interna (OMI) where the larva invade the eye globe.3,4 Most reported human cases of myiasis caused by H. tarandi involve OMI,4,5 and there has, to our knowledge, not been reported any case with cerebral manifestation. Three cases of intracerebral myiasis caused by larvae of Hypoderma bovis, the common cattle grub, have been reported6–8: an 8-year-old Turkish child with a 10-day history of convulsions and 2 similar cases in 6- and 7-year-old boys in France. In all 3 cases, computed tomography scans showed intracerebral hematomas, and H. bovis larvae were found during neurosurgery. The common cattle grub is a close relative to H. tarandi and was relatively common decades ago, but are now extinct in Norway and most other European countries following intensive eradication programs using antiparasitic drugs.2
Among 22 human cases of myiasis caused by H. tarandi reported between 1982 and 2016, most were complicated by OMI. The 22 cases comprised 16 children, and 18 were residents in or visited northern parts of Norway or Sweden, 1 was a visitor to a reindeer area of southern Norway, 2 were reported from northern Canada and 1 from Greenland.1 Additionally, 39 cases were reported from Norway between 2011 and 2016.5 Of these, 32 were children, and no serious complications such as eye involvement developed, maybe because of increasing awareness, early diagnosis and antiparasitic treatment.
Clinicians should be aware of the typical clinical manifestations of myiasis caused by H. tarandi, such as migrating dermal swellings, periorbital edema and tender enlarged lymph nodes. Notably, lymphadenopathy and eosinophilia are not always present. A detailed exposure and travel history is essential, although in most cases, the infested person cannot recall any contact with a bumblebee-sized fly compatible with a female H. tarandi. Direct or visual contact with reindeer is not a prerequisite for acquiring the infestation because H. tarandi can stay in an area long time after the reindeer have left and can fly up to 900 km.9 It takes weeks for the adult flies to develop from the mature larval stage dropping from the reindeer in May/June, and female H. tarandi can get unnoticed onto the reindeer or human host by flying or jumping up from the ground.2
The many reports of myiasis caused by H. tarandi involving serious eye complications, and our case reported here that H. tarandi, like H. bovis, may cause severe intracerebral infestations in children, show the importance of awareness and early diagnosis of human myiasis caused by H. tarandi. Suspicion of the infestation should be evoked by migrating dermal swellings, lymphadenopathy, periorbital edema, and now also cerebral symptoms, following visit or stay in an area with reindeer in the egg-laying season for H. tarandi.
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