Contrary to the expected benefits of routine treatment of worms (helminths) during pregnancy, a single-dose of this widely used intervention is not associated with improved infant survival, or with any effect on the occurrence of infectious diseases, or on growth and anaemia at 1 year of age. These findings, published Online First in The Lancet, contrast with the strongly advocated WHO policy of routine antenatal deworming in developing countries to combat the expected negative effects of worms in pregnancy on maternal health, birth outcomes, and subsequent child health, and suggest that the value of this intervention should be re-examined.

There is evidence that maternal exposure to parasitic worm infections might reduce an infant’s immune responses to vaccination and increase susceptibility to other diseases. This is a major concern in developing countries where parasitic worms are endemic and could explain why vaccines appear to be less effective in these countries. Because vaccination is the most cost-effective means of reducing child mortality in developing countries, any intervention that may improve vaccine efficacy should be considered. But the benefits of deworming during pregnancy for this purpose have not been fully assessed.

In this study, Emily Webb from the London School of Hygiene and Tropical Medicine, London, UK, and Ugandan colleagues examined the effects of deworming during pregnancy on immune responses to vaccination and infectious disease incidence in infants.

2507 women in the second or third trimester of pregnancy who were due to deliver in Entebbe General Hospital in Uganda were recruited between April 2003 and November 2005. At enrolment, 1693 women were infected with at least one worm species.

To compare the effects of deworming treatment with no treatment, women were randomly assigned to either one-dose of albendazole plus praziquantel (628 women), albendazole and a praziquantel-matching placebo (625), praziquantel and an albendazole-matching placebo (626), or an albendazole-matching placebo plus a praziquantel-matching placebo (628).

Newborns were followed up until age 12 months to assess immune response to BCG, tetanus, and measles after immunisation at birth, and incidence of infectious diseases (malaria, diarrhoea, pneumonia, measles, and tuberculosis) and vertical HIV transmission.

Findings showed similar infant immune response to BCG, tetanus, and measles immunisation regardless of maternal treatment, and no effect was recorded for either anti-worming treatment on the incidence of infectious diseases during the first year of life or on vertical HIV transmission.

The authors say: “Our findings suggest that one effective anthelmintic intervention given in the second or third trimester of pregnancy is insufficient to alter any effect of maternal worms on vaccine and infectious disease outcomes in infancy.”

They conclude: “These results contrast with the expected benefits of routine anthelmintic treatment recently advocated, and the value of such a policy should be reviewed.”

In a Comment, Maria Yazdanbakhsh and Adrian Luty from Leiden University Medical Center, Leiden, The Netherlands, say:“This trial seems to resolve speculation about whether helminth infections in the second and third trimester of pregnancy could affect immune responses of newborns to vaccines, and are thereby associated with detrimental health indicators. This finding has serious implications for policy makers who advocate the use of anthelmintic treatment during pregnancy.”

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Source: The Lancet