Overview
Hookworms are small parasitic worms that live in the small intestine and feed on blood. People usually become infected by walking barefoot on soil contaminated with human faeces, where the larvae wait to penetrate the skin.
A light infection may cause nothing at all. A heavy one causes iron deficiency anaemia and protein loss, and in children it slows growth and learning. Treatment is a short course of tablets, but reinfection follows quickly unless sanitation improves.
Disease Summary
- Category
- Infectious Disease
- Cause
- Hookworm parasites
- Transmission
- Larvae in contaminated soil entering through the skin
- Body System
- Digestive System
- Preventable
- Yes
- Curable
- Yes
Symptoms
Common Symptoms
Light infections often cause no symptoms. The symptoms below belong mostly to heavier infections, which are what cause harm.
Itching and a Rash Where the Larvae Entered
Often on the feet, this is the skin reaction to larvae penetrating. It is sometimes called ground itch.
Abdominal Pain
Listed by both WHO and CDC as a feature of heavier infections.
Diarrhoea
Listed by WHO among the intestinal effects of heavier infection.
Loss of Appetite and Nausea
Both are listed by CDC and contribute to the weight loss that follows.
Weight Loss and Malnutrition
The worms take both blood and nutrients, so heavier infections cause measurable malnutrition.
Tiredness and Weakness
These follow from the anaemia caused by continuous blood loss into the gut.
Anaemia
WHO states hookworms cause chronic intestinal blood loss resulting in anaemia, especially in adolescent girls and women of reproductive age.
Slowed Growth and Learning in Children
Both WHO and CDC state that heavy infection impairs children’s physical and cognitive development.
Danger Signs
Seek urgent medical attention immediately if any of the following symptoms develop.
Severe Pallor, Breathlessness or a Racing Heart
These indicate severe iron deficiency anaemia from continuous blood loss, and need treatment on their own as well as deworming.
Swelling of the Face, Legs or Abdomen
This reflects the loss of protein that heavy infection causes.
Intestinal Obstruction
WHO states that severe infections may cause intestinal blockage requiring surgery.
Wheeze or Breathing Difficulty in Early Infection
The larvae pass through the lungs, which can cause a temporary cough and wheeze.
Anaemia in Pregnancy
WHO identifies pregnant women as a priority group, because blood loss on top of pregnancy is dangerous for both mother and baby.
Diagnosis
Examining Stool Under the Microscope
CDC states that identifying the eggs in stool is the usual method of diagnosis, and the only definitive one.
Concentrating the Sample
Treating the stool sample to concentrate the eggs before looking makes light infections much easier to find.
Counting the Eggs
Counting eggs establishes how heavy the infection is, which is what determines whether harm is being done and guides community treatment programmes.
Repeating the Sample
CDC advises multiple samples collected on separate days, because eggs may not appear in stool for several months after exposure.
Checking for Anaemia
A blood count alongside the stool test shows whether the infection is causing harm.
Laboratory Tests
Stool Examination for Eggs
Finding the characteristic eggs confirms the infection. CDC notes that the eggs of the two main hookworm species cannot be told apart under the microscope.
Quantitative Egg Count
Gives the number of eggs per gram of stool, which is the measure of infection intensity used in treatment programmes and in judging the risk of anaemia.
Full Blood Count
A low haemoglobin with small, pale red cells indicates the iron deficiency anaemia that heavy hookworm infection causes.
Eosinophil Count
A raised level of this white cell type suggests a worm infection and often prompts the stool test in the first place.
Molecular Stool Test
Detects worm DNA in stool. Used mainly in research and surveillance rather than routine care.
Treatment
Albendazole
One of the two medicines WHO recommends for soil-transmitted worms. It kills the adult worms in the intestine.
Mebendazole
The other WHO-recommended medicine. Both are safe, inexpensive and widely available.
Iron Treatment
CDC states iron supplements address the anaemia. Deworming alone does not replace the iron already lost.
Community Deworming Programmes
WHO recommends periodic treatment of at-risk groups without individual diagnosis. CDC describes these programmes as delivering safe, inexpensive medicines to whole communities.
Treating the Cause of Reinfection
WHO states that treatment must be integrated with health education and sanitation improvements to prevent reinfection, otherwise the benefit is temporary.
Prevention
Wear shoes
This directly blocks the route by which the larvae enter the body, and it is the single most effective individual measure.
Use a latrine and avoid open defecation
Soil becomes infectious only when contaminated with human faeces. WHO’s targets include universal access to basic sanitation in affected areas.
Do not use untreated human waste as fertiliser
CDC names this among the ways soil becomes contaminated.
Wash hands and wash, peel or cook produce
CDC lists handwashing before handling food, and washing, peeling and cooking vegetables.
Periodic deworming of at-risk groups
WHO reports that over 500 million children were treated in a single recent year, covering 62% of children at risk.
Health education alongside treatment
WHO states that treatment works best combined with education and sanitation improvement, because otherwise reinfection follows.
Risk Factors
Children
WHO identifies hundreds of millions of preschool and school-age children as at risk.
- Children who play barefoot on contaminated soil
- Children in communities without latrines
- Heavy infection impairs both physical growth and learning
- WHO’s targets include ending illness from these worms in children
Adolescent Girls and Women of Reproductive Age
WHO singles out this group because blood loss compounds existing iron deficiency.
- Adolescent girls, who already lose iron through menstruation
- Pregnant women in the second and third trimesters
- Breastfeeding mothers
- Anaemia in pregnancy affects both the mother and the baby
Communities Without Sanitation
CDC states that risk is highest in warm, moist climates with poor sanitation.
- Households without a latrine
- Communities where open defecation is common
- Farming communities using untreated human waste on crops
- Anyone who works or walks barefoot on contaminated ground
Complications
Iron Deficiency Anaemia
The central complication. WHO states hookworms cause chronic intestinal blood loss resulting in anaemia.
Protein Loss and Swelling
Heavy infection causes loss of protein, which leads to swelling of the face, legs or abdomen.
Impaired Growth and Learning in Children
Both WHO and CDC state that heavy infection affects children’s physical and cognitive development.
Intestinal Obstruction
WHO states that severe infections may cause blockage of the intestine requiring surgery.
Complications in Pregnancy
Anaemia in pregnancy increases risks for both mother and baby, which is why pregnant women are a priority group for treatment.
Temporary Lung Symptoms
The larvae pass through the lungs on their way to the intestine, which can cause a cough and wheeze in early infection.
When to Seek Medical Care
Tiredness, Pallor or Breathlessness
These suggest anaemia, which needs both treating and explaining.
An Itchy Rash on the Feet After Walking on Soil
This may be where the larvae entered, and it is a reason to have stool tested.
Persistent Abdominal Pain or Diarrhoea
Particularly in a child in an endemic area.
A Child Who Is Not Growing Well
Poor growth and poor school performance in an endemic area are reasons to test for worms.
During Pregnancy in an Endemic Area
WHO identifies pregnant women as a priority group for treatment because of the risk of anaemia.
Prognosis
Treatment Clears the Worms Quickly
CDC states that the prescribed medicines eliminate infections within one to three days of oral treatment.
Anaemia Takes Longer to Correct
Iron stores have to be rebuilt after the worms are gone, which takes weeks to months of iron treatment.
Reinfection Is Common
Where the soil remains contaminated, people become reinfected within months. This is why deworming rounds are repeated.
Community Programmes Work
WHO reports a reduction of more than half in the burden of illness from these worms over a recent decade.
Differential Diagnosis
Iron Deficiency Anaemia From Other Causes
Poor diet, heavy periods and bleeding from the gut all cause the same anaemia. This is why the cause is sought rather than assumed.
Other Intestinal Worms
Roundworm and whipworm share the same route and the same communities, and often occur together with hookworm.
Schistosomiasis
Another parasitic infection causing anaemia and abdominal symptoms, identified by finding different eggs in stool or urine.
Malaria
Also causes anaemia and is far more common. Both can be present at once.
Peptic Ulcer Disease
Causes abdominal pain and can cause anaemia through slow bleeding, separated by endoscopy and by the pattern of pain.
References
World Health Organization: Soil-transmitted helminth infections
WHO fact sheet on hookworm and the other soil-transmitted worms, burden, treatment and control targets.
CDC: About Hookworm
How hookworm spreads, its symptoms, who is at risk and how it is prevented.
CDC: DPDx, Intestinal Hookworm
Life cycle, clinical features and the laboratory methods used for diagnosis.
CDC: Clinical Care of Soil-transmitted Helminths
Treatment options, routes and durations, and the place of iron supplementation.
Frequently Asked Questions
How do people catch hookworm?
WHO states that hookworm eggs hatch in soil, releasing larvae that can penetrate skin, and that people mainly become infected by walking barefoot on contaminated soil. Soil becomes contaminated when human faeces is deposited on it or used as fertiliser.
Will one dose of tablets cure it?
It will clear the worms. CDC states that the prescribed medicines eliminate infections within one to three days. It will not prevent reinfection, which follows within months where the soil is still contaminated.
Why does hookworm cause anaemia?
Because the worms attach to the lining of the intestine and feed on blood. WHO describes this as chronic intestinal blood loss, and states it causes anaemia especially in adolescent girls and women of reproductive age.
Should children be dewormed even without symptoms?
In endemic areas, yes. WHO recommends periodic treatment of at-risk groups without individual diagnosis, because the medicines are safe and inexpensive and because infection harms growth and learning before it causes obvious symptoms.
What stops reinfection?
Wearing shoes, using a latrine, not using untreated human waste as fertiliser, and handwashing. WHO is explicit that treatment works best combined with health education and sanitation improvements.