Helminth Prevention and Control

What are Helminths?

 

Helminths or parasites, often called "worms", are widespread throughout the world. It is estimated that half of the world’s population is infected with at least one helminth (Hall et al, 2008). Helminth prevention and control is an effective intervention to reduce anemia and should be integrated with other anemia control programs including iron-folic acid supplementation and malaria prevention and control.

There are over 340 species of helminths; most are rare in humans but may infect animals that can serve as a resevoir for infection. Click here for more information on common helminths affecting humans and the diseases they cause. The four main species of helminths that infect people are Ascaris lumbricoides (roundworm); Trichuris triciura (whipworm); and Necator americanus  and Ancylostoma duodenale (hookworm) (WHO, 2013). These four helminths also are commonly associated with malnutrition, including anemia, and disease in children (Hall et al, 2008). These worms are often called “soil-transmitted helminths” which refers to their mode of transmission. Although they are not intestinal helminths, schistosomes (commonly called blood flukes and bilharzia) also are prevalent and cause anemia in some geographic locations close to bodies of water.

Helminth Transmission

 

Helminths can be contracted by humans in various ways. Ingestion of contaminated feces through soil, water or food is a main mode of transmission. Hookworm is most commonly contracted directly through the soles of the feet, usually around open areas of defecation and latrines, when people do not wear shoes or food coverings. Schistosomiasis is contracted by swimming or wading in contaminated water.

Morbidity from helminth infections, including anemia, is determined by the intensity of the infection (number of worms in the gut) and the duration of the infection (Hall, 2008; Crompton et al, 1993). Moderate to heavy infections with hookworm are strongly associated with anemia (Hall, 2008; Roche et al, 1966).

The Most Vulnerable Groups 

Preschool-aged children (ages 1-4) and pregnant women are the most affected by the consequences of helminth infections even though prevalence may be higher in other groups such as school-aged and all adults.  Consequences of helminth infections include: 

  • Preschool children are at-risk of nutritional deficiencies caused by helminth infections .Helminths cause vitamin A malabsorption (Mahalanabis, 1976). In fact, deworming improves iron status in children and has improved growth in some studies.
  • Pregnant women are at risk of nutritional deficiencies caused by helminth infections. Several large-scale studies have demonstrated that deworming and iron supplementation reduced anemia among pregnant women and have led to postive birth outcomes (Brooker, 2008Smith, 2010). 

School-aged children are mentioned here because school deworming programs have been an initiative globally. This group is particularly at risk of helminth infections because they are active and may be more inclined to play in the dirt and water. If a child is infected with helminths, their growth can be impaired, learning capacities diminished, and they are more susceptible to other infections. Making school-age children a target for deworming programs also may have may benefits for the entire population by reducing transmission in untreated students and other groups. For example, one study in Kenya found that when school-age children were dewormed in one school, untreated children in that school and in neighboring schools also benefited (Miguel et al, 2002).

Helminth Treatment

 

WHO recommends preventive doses of anthelminthic medication, treatment, and mass treatment depending on the prevalence of helminths. Click here for the drug doses for helminth prevention and treatment.  

 

Complementary Interventions

 

Long-term solutions to controlling helminth infections are improving the quality of the water supply, sanitation, and hygiene (WASH). Education to ensure the safe and hygienic handling of human feces and wearing shoes in areas designated for defecation are effective measures in controlling transmission. Sanitation is key to the elimination of helminth infections. Soil transmitted helminths are common among school-aged children, with an estimated 50% of children five to nine years of age infected with helminths in developing countries. Much of this burden is due to poor sanitation and open defecation. Children can be treated for helminths but unless their living environments are clean, they will be reinfected. Improvements to WASH are essential for achieving sustained control of helminths in the medium- and long-terms.

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