Threadworm infection in pregnancy

• there are no reported cases in which infection with E. vermicularis caused harm to the foetus
  • there has been a case published where two adult threadworms were found within an embryo on histologic examination of tissue after dilation and curettage for embryonic death (1)
  • ova from the helminths were recovered from the vagina and endometrium of the patient
  • this most unusual case provides further evidence for the invading capacity of E vermicularis
  • the authors believed that the cause of death was unrelated to the threadworm infection - they suggested that the threadworm infestation most likely occurred after the fetal demise
• threadworm infection has not been linked to poor pregnancy outcome
• the use of mebendazole in pregnancy has been investigated in a study by de Silva et al (2):
  • the study investigation was performed in a country where treatment with anti-helminthic medications in the second trimester is actually recommended because of the problems related to severe maternal anaemia and foetal injury that may occur with certain helminthic infections
  • the study found that the rate of major congenital defects was not significantly higher in the mebendazole group than in the control group (97 [1·8%] of 5275 vs 26 [1·5%] of 1737; odds ratio 1·24 [95% CI 0·8-1·91], p=0·39)
    • however among 407 women who had taken mebendazole in the first trimester (contrary to medical advice), 10 (2·5%) had major congenital defects (odds ratio vs controls 1·66 [0·81-3·56], p=0·23).
    • the study authors suggested that mebendazole therapy during pregnancy was not associated with a significant increase in major congenital defects, but their results indicated that mebendazoe should be avoided during the first trimester
  • note though that some authors advocate no treatment until after delivery unless the potential benefit greatly outweighs the risk to the foetus (3)
  • note that a MeReC Bulletin stated "..Adoption of strict hygiene measures for at least 6 weeks is the only alternative for those who cannot have or do not want anthelmintic treatment (e.g. pregnant women)..." (4)
  • Public Health England guidance (5) notes if threadworm in pregnancy (at least in first trimester)
    • then only hygiene measures for 6 weeks is the treatment indicated

Reference:

• (1) Mendoza E et al. Invasion of human embryo by Enterobius vermicularis. Arch Pathol Lab Med 1987;111: 761-762.
• (2) de Silva NR et al. Effect of mebendazole therapy during pregnancy and birth outcome. Lancet 1999;353:145-1149.
• (3) Hamblin J, Connor PD. Pinworms in pregnancy. JABFP 1995; 8: 321-324
• (4) MeReC Bulletin (2008); 18 (4)
• (5) Public Health England (June 2021). Managing common infections: guidance for primary care