Autochthonous ascariasis in Aotearoa

The intestinal nematode Ascaris had an estimated global prevalence of 731.8 million people in 2020.¹ The highest prevalence was in Oceania (28.77%), from four studies in Melanesia.¹

Ascaris is acquired via the faeco-oral route when fertilised eggs, shed in faeces and embryonated in soil (requires 10 to 15 days), are ingested through contaminated soil, food or water. Eggs hatch in the small intestine releasing larvae, which penetrate the mucosa, migrate haematogenously to the lungs to mature, are coughed and swallowed thus returning to the small intestine to reside as adult worms. The prepatent period is 2 to 3 months.²

Human infections are often asymptomatic, though may present with non-specific gastrointestinal symptoms or, uncommonly, as Löffler’s syndrome. High worm burdens may result in intestinal obstruction or malnutrition.²

Ascaris lumbricoides (A. lumbricoides) primarily infects humans, whereas Ascaris suum (A. summ) infects pigs. Human infections with A. suum occur, though the distinction between the two species is debated.^2–4 In Aotearoa, A. suum is endemic in pigs, whereas A. lumbricoides is associated with overseas exposure in endemic areas.^3,4

Autochthonous (locally acquired) cases are rare; here we report two such cases that we postulate were A. suum infections.

Cases

A 14-month-old girl presented with diarrhoea, having been conservatively managed for verotoxin-producing Escherichia coli detected via a faeces polymerase chain reaction (PCR) test. One month later, her mother noted the presence of a worm in her nappy.

A 3-year-old girl presented with abdominal pain and diarrhoea. She subsequently passed a worm per rectum. No faeces examination for bacteria or other parasites was performed.

Both children were treated with mebendazole.

Both children lived in Northland, on farms housing cows and pigs. Neither child had direct contact with pigs, but both had contact with soil around the farm. Neither child had travelled overseas.

Worm specimens from both children were preserved in formalin and submitted for identification. Microscopy revealed tricuspid mouth parts, corporal striations, a lateral white line and tapered tail, consistent with Ascaris spp (Figure 1). DNA extraction and sequencing was attempted at a referral laboratory but was unsuccessful.

View Figure 1.

Discussion

We report two cases of Ascaris infection that occurred without overseas travel exposure. We postulate that these locally acquired infections were caused by A. suum due to exposure to soil contaminated with pig faeces. Eggs can survive in soil for several years.²

Diagnosis requires faeces specimens collected prior to anti-parasitic treatment and transported promptly under appropriate conditions for microscopic examination of eggs. Collecting multiple specimens can improve diagnostic sensitivity. Infrequently, adult worms may be submitted for diagnostic confirmation.

Treatment with mebendazole or albendazole is highly effective.⁵ Follow-up testing may be performed after 2 weeks and again 2 months later. Infection prevention measures include effective sanitation, hand hygiene and safe food handling. A One Health approach is essential to reduce zoonotic transmission.⁶

There is extensive debate regarding whether A. suum and A. lumbricoides are distinct species. Species identification is difficult because morphologic differences are subtle and variable results are reported using PCR and sequencing assays to speciate.^2,7,8 Some studies report high genetic similarity between species, with some authors concluding they are the same, or a hybrid, species.^7,9 In contrast, some studies report entirely distinct genomic clustering of human and pig specimens.¹⁰

While the issue of speciation is far from resolved, both A. lumbricoides and A. suum cause human infections.^7,9 Given A. suum is endemic in pigs in Aotearoa, the potential for human infection is clear.^3,9

The two cases described here raise the possibility of under-recognised autochthonous ascariasis in Aotearoa. This report serves as a reminder to clinicians to consider ascariasis, even in cases without overseas travel, particularly if there is exposure to pigs or contaminated soil.