Threadworm infection in pregnancy

• there are no reported cases in which infection with E. vermicularis caused harm to the fetus
  • 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 antihelminthic medications in the second trimester is actually recommended because of the problems related to severe maternal anemia and fetal 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 fetus (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