A rare illness in Belgium that affected nine people was likely spread after the initial patient ate pork while abroad several years earlier.
Human cysticercosis results from ingesting Taenia solium eggs shed by a tapeworm carrier, forming cystic larvae in tissues. Upon consumption by humans, they develop into a new intestinal tapeworm. Affecting the brain, neurocysticercosis is responsible for a third of epilepsy cases in endemic tropical and subtropical regions.
Between March and June 2023, neurocysticercosis was diagnosed in three boys from different classes and years at a primary school in Belgium, a non-endemic country. The first patient presented with ptosis for a year, and the other two had new-onset focal seizures. Department Zorg (the Department of Care) in the Flemish Ministry of Welfare, Public Health and Family provided several updates on the incident at Het Molentje primary school.
According to a study recently published in The Lancet, one patient was confirmed as having neurocysticercosis by brain-biopsy PCR, and the other two by imaging and treatment response. No tapeworm was detected in the patients or their relatives with negative fecal exams and no travel abroad was reported.
Searching for source
Scientists initially suspected food contamination and searched for the tapeworm carrier by testing feces of 70 school catering staff, volunteers who peeled fruit, teachers, and parents who cooked for festivities. They tested pupils who visited endemic countries based on a questionnaire, and sampled school wastewater in mid-March 2024. The team also conducted serology and brain MRIs for two families with multiple risk factors to find signs of past exposure. All tests were negative.
Because of information sessions and national television coverage on the spread of cysticercosis, some parents arranged brain MRIs privately, uncovering two more asymptomatic boys at the primary school with neurocysticercosis in October and December 2023.
Epidemiological investigations revealed that a single exposure event likely happened between September 2021, when one of the patients was newly admitted to the school, and January, 2022, when the first patient had already developed ptosis.
During the academic year 2021 to 2022, there were 229 primary school and 149 kindergarten students. These pupils were offered a brain MRI between February and June 2024. This revealed two more boys with asymptomatic neurocysticercosis and one with a calcified cerebral lesion.
Consumption of pork abroad
When the last patient was invited for history taking, his father described pulling a 1 m-long, ribbon-like worm from his son’s bottom; the boy then received a dose of mebendazole in August 2022. When abroad in an area endemic with Taenia solium before 2021, he consumed pork from pigs raised in uncontrolled housing conditions. The father became the ninth patient when he was diagnosed with asymptomatic neurocysticercosis, with a second lesion in his right temporal muscle.
All but one of the other family members tested positive. This suggests the boy carried the pork tapeworm causing the outbreak. Although beef tapeworm is endemic in Belgium, it does not cause human cysticercosis. As repeated fecal tests remained clear, transmission had probably ceased; household members also tested negative.
Identification of three symptomatic Belgian children with cysticercosis prompted the outbreak response, revealing six more asymptomatic patients, including the likely source. Most patients were treated with a favorable outcome. At the time of the study, all patients were seizure-free.
Transmission could have occurred through hand contact or indirect fecal–oral contact during boys’ activities or in the boys’ bathroom, explaining why only males appeared to be affected and why half of the children were in one class and year.
Researchers thanked colleagues from the Neurocysticercosis Expert Group at the European Centre for Disease Prevention and Control (ECDC) for their assistance in addressing the outbreak.
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