Deworming debunked
Lack of evidence for the claimed benefits of deworming
There is mounting evidence that helminth eradication does not produce most, if not all, of the benefits that have been claimed for it.
A "worm wars" debate has been raging since the noughties. On one side, are the established global advocacy organizations which continue to raise funds to implement deworming programmes and distribute free deworming medicines to entire continents in pursuit of their goal, with development economists and parasitologists cheer-leading this approach. On the other side, is a substantial and growing body of research showing that not only does deworming not achieve the benefits claimed for it, but that it may even be detrimental to the health and wellbeing of those who are stripped of their helminths.
A systematic review carried out in 2019 by the highly respected Cochrane Database, including a total of over 50 trials with 84,336 participants, plus an additional trial with one million children, found no benefit for height, haemoglobin, cognition, school performance or mortality. And, while studies carried out more than 20 years ago had shown large effects on weight, this has not been seen in more recent, much larger studies.
Based on the findings, the review authors suggest that philanthropists and governments should re-assess policies for mass treatment.
- 2019 Sept 11 Public health deworming programmes for soil-transmitted helminths in children living in endemic areas
Current evidence does not support large public health programmes of deworming in low- and middle-income settings, particularly in terms of wider, societal and educational benefit.
Other recent studies
- Our findings confirm the WHO recommendation that at low levels of prevalence and intensity, interventions to control soil-transmitted helminths are unnecessary.
- 2019 Jan 31 The long run impact of early childhood deworming on numeracy and literacy: Evidence from Uganda
- Mass deworming of preschool aged children in high prevalence communities in Uganda resulted in no statistically significant gains in numeracy or literacy 7-12 years after program completion.
Previous studies
In 2013, a careful reading of all the published evidence that passes the Cochrane organisation's quality test showed “quite strongly” that deworming alone has no effect on growth, cognitive ability, or school attendance.
Cochrane reiterated their findings in 2015, stating that there is substantial evidence that mass deworming of all children in endemic areas does not improve average nutritional status, haemoglobin, cognition, school performance, or survival.
This conclusion was again confirmed by a study in 2016 which reported that mass deworming for soil-transmitted helminths compared with controls led to little to no improvement in weight or height over a period of about 12 months, little to no difference in proportion stunted, cognition measured by short-term attention, school attendance, or mortality.
In early 2017, researchers at the Liverpool School of Tropical Medicine reported substantial methodological problems with three widely cited studies relating to mass deworming in Africa. The original researchers had claimed that their results showed the long-term effectiveness of these mass deworming programs in developing countries, but this latest critical analysis concluded that the findings are unlikely to be as positive as previously reported.
There is a report on this research by Science Daily.
A 2018 meta-analysis found that, while mass deworming probably reduces the prevalence of soil-transmitted helminth infections, it may have little or no effect on anaemia and iron-deficiency in adolescent girls and non-pregnant women.
Where good, general antenatal care is provided, the deworming of pregnant women produces no benefits in respect of anaemia, birth weight, perinatal mortality, infant mortality or infant response to immunisation.
- Treatment with anthelmintics during pregnancy: what gains and what risks for the mother and child?
- Effects of deworming on child and maternal health: a literature review and meta-analysis
- Effects of Deworming during Pregnancy on Maternal and Perinatal Outcomes in Entebbe, Uganda: A Randomized Controlled Trial
- The impact of prenatal exposure to parasitic infections and to anthelmintic treatment on antibody responses to routine immunisations given in infancy: Secondary analysis of a randomised controlled trial
Reevaluation of an influential trial concluded that deworming children may not improve school attendance.
- Re-analysis of health and educational impacts of a school-based deworming programme in western Kenya: a pure replication
- Re-analysis of health and educational impacts of a school-based deworming programme in western Kenya: a statistical replication of a cluster quasi-randomized stepped-wedge trial
This study found no strong evidence for significant improvements in physical fitness and anthropometric indicators due to deworming over a 6-month follow-up period.
Declines in helminth infection as a result of deworming were not accompanied by an impact on outcomes of nutrition, cognition, or school performance.
No statistically significant difference in weight gain was seen in any of the deworming intervention groups compared to the control group.
The largest randomized trial ever performed in human history - involving two million children in India - looked at how helminths affect health in places where humans naturally have them. This study showed that not only did mass treatment with an effective deworming drug not increase body weight or survival, but that the helminths didn’t seem to be doing any harm, since getting rid of them didn’t improve health.
Deworming HIV-positive adults only produces small and short-term favourable effects on disease progression.
For many years experts have recommended treating large groups at risk of helminth infection - but is this mass approach worthwhile?
The stunted growth seen in children in some Third World communities may be due more to bacterial pathogens than helminths.
Evidence of the harmful effects of deworming
Apart from the lack of evidence for any appreciable benefit from deworming, there is growing evidence of a significant downside to this practice.
Deworming before age 5 may increase the risk ulcerative colitis in adulthood.
Deworming increases the prevalence of allergic sensitization.
Deworming may lead to the emergence of inflammatory and metabolic conditions in countries that are not prepared for these new epidemics.
Deworming significantly increases insulin resistance.
Removal of helminths may also increase the risk from infectious agents such as malaria and influenza.
Children who are hosting helminths are less likely to develop malaria.
Hosting hookworms concurrently with one species of malaria can reduce the malaria burden by almost 50 percent.
A systematic review of randomized controlled trials demonstrates that deworming is unlikely to improve overall public health.
This trial shows the capacity of helminths to suppress proinflammatory immune responses in humans, which could anticipate the future rise in inflammatory diseases when helminth infections are increasingly controlled.
Some treatments may increase problems with diseases they were meant to reduce.
- Deworming programs in animal, human populations may have unwanted impacts
- Conservation: why ugly parasites also need saving
Anthelmintic drugs may have an environmental impact.
- The environmental side effects of medication
- Potential environmental consequences of administration of anthelmintics to sheep
This study is investigating both the beneficial and detrimental effects of helminths and their eradication.
After revealing that individuals who are hosting helminths enjoy less dyslipidemia (unhealthy levels of fats in the blood), less metabolic syndrome, less diabetes, and less atherosclerotic cardiovascular disease, this study's authors suggest that, when individuals who are at moderate or high risk for cardiometabolic disease are deprived of their helminths in deworming campaigns, they may require an increase in preventive medical care to compensate for the loss of beneficial helminth-induced immune modulation.
- Effects of helminths and anthelmintic treatment on cardiometabolic diseases and risk factors: A systematic review -- Full text | PDF