Hookworm disease (ancylostomiasis) refers to an intestinal parasitic infection caused by hookworms of the family Ancylostomatidae that inhabit the human small intestine. Mild infections are asymptomatic and only detectable through the presence of eggs in stool, which is termed hookworm infection. Typical clinical manifestations include anemia, malnutrition, and gastrointestinal dysfunction. Severe cases may lead to heart failure and growth and developmental disorders.
Etiology and Epidemiology
The two most common species of hookworms parasitizing humans are Ancylostoma duodenale and Necator americanus. Adult worms are semi-transparent, grayish-white or pale yellow in color, and measure about 1 cm in length. They are dioecious, with males and females living in the upper segment of the small intestine. Using their buccal cavity, they attach to the intestinal mucosa, feeding on blood and tissue fluid. A mature female Ancylostoma duodenale produces 10,000–30,000 eggs per day, while a female Necator americanus produces 5,000–10,000 eggs daily. Eggs are excreted in feces, and in warm, moist, and loose soil, they hatch into rhabditiform larvae. After 1–2 weeks and two molts, they develop into filariform larvae, the infective stage.
Filariform larvae penetrate human skin through hair follicles, sweat gland openings, or damaged skin when in contact with contaminated soil, entering blood vessels and lymphatics. They are carried to the right heart and then to the lungs, where they break through capillaries into alveoli. From there, they migrate upward to the pharynx, are swallowed, and finally reach the small intestine, where they mature into adult worms. Adult worms typically survive in the human body for about 3 years, but their lifespan may extend up to 15 years.
Patients with hookworm disease are the primary source of infection. Skin contact with contaminated soil is the main route of infection, but ingestion of food contaminated with infective larvae is also a potential route. Infants and toddlers may become infected through contaminated diapers or clothing, especially those placed on soil harboring larvae, as well as through activities such as crawling or sitting on the ground. The general population is susceptible to infection. Hookworm disease is globally prevalent and widely distributed, with mixed infections of Ancylostoma duodenale and Necator americanus being common in many regions.
Clinical Manifestations
Symptoms Caused by Larvae
Larval Dermatitis
Larvae often invade thin skin on the toes, fingers, or other exposed areas. This invasion may result in red papules or small vesicles, accompanied by a burning or prickling sensation and severe itching, which typically resolves within a few days. Scratching and ulceration can lead to secondary bacterial infections, pustule formation, fever, and lymphadenitis.
Respiratory Symptoms
Within 3–7 days of infection, the migration of larvae to the lungs may cause throat irritation, cough, fever, shortness of breath, wheezing, and blood-tinged sputum, or even massive hemoptysis. Chest X-rays may show transient pulmonary infiltrates. Eosinophilia is often observed in the blood. Symptoms typically last from several days to weeks.
Symptoms Caused by Adult Worms
Anemia
Blood-loss-induced anemia is the primary symptom, presenting as varying degrees of anemia, pallor of the skin and mucous membranes, fatigue, and dizziness. In children, this can impair physical and intellectual development. Severe cases may result in anemia-related heart disease.
Gastrointestinal Symptoms
In the early stages of infection, symptoms include increased appetite, excessive hunger, and weight loss. As the disease progresses, appetite may decrease, accompanied by gastrointestinal dysfunction, abdominal distension, pica, malnutrition, and in severe cases, melena.
Hookworm Disease in Infants
In infants, clinical manifestations often include acute hemorrhagic diarrhea, characterized by black or tarry stools, gastrointestinal dysfunction, pallor, fever, systolic heart murmurs at the apex, hepatosplenomegaly, growth retardation, severe anemia, and hemoglobin levels below 50 g/L. Leukocytosis and significant eosinophilia are observed in most cases, occasionally resembling a leukemoid reaction. Onset is common between 5–12 months of age, although cases in newborns have also been reported.
Laboratory Examinations
General Examinations
Complete blood count typically shows microcytic hypochromic anemia. Reticulocyte counts may be normal or mildly elevated. In early stages, leukocyte counts, especially eosinophil counts, may be elevated; however, in later stages, especially in severe anemia, leukocyte counts may decline. Stool tests frequently show positive occult blood results. Serum iron levels are significantly reduced. Bone marrow examination reveals hyperplasia.
Pathogen Detection
Hookworm ova can be identified in fresh stool samples using direct smears or the saturated saline flotation method. Stool cultures after 5–6 days may reveal hookworm larvae, and larvae may also be identified in sputum samples. Adult worms can sometimes be located through stool washing or via intestinal endoscopy.
Diagnosis and Differential Diagnosis
In endemic areas, the possibility of hookworm disease should be considered in children with symptoms such as anemia, gastrointestinal dysfunction, pica, malnutrition, and growth and developmental delays. The detection of hookworm eggs or the hatching of larvae from stool specimens serves as a definitive diagnostic criterion. In cases with a cough, the identification of larvae in sputum also confirms the diagnosis. Intradermal testing using hookworm antigens may yield positive results, and in conjunction with epidemiological data and clinical features, an early diagnosis may be established. Anemia should be differentiated from iron-deficiency anemia caused by other factors, while melena should be distinguished from peptic ulcers.
Treatment
Anthelmintic Therapy
Benzimidazoles
This class of broad-spectrum anthelmintics is effective against adult worms and eggs. The anthelmintic effect occurs gradually, with hookworms being expelled 3–4 days after treatment. Commonly used formulations include:
- Mebendazole: A dose of 100 mg is administered twice daily for 3 consecutive days, regardless of age. The cure rate exceeds 90%. Side effects are minimal and transient, with headache, nausea, and abdominal pain observed in rare cases. It should be used cautiously in patients with severe liver or kidney diseases and in children under 2 years of age.
- Albendazole: A single-dose treatment is effective, with a dosage of 200 mg for children, which can be repeated after 10 days. It should be used with caution in children with severe cardiac dysfunction or active peptic ulcers.
Pyrantel Pamoate
This is another broad-spectrum anthelmintic with rapid action, expelling worms within 1–2 days of administration. The typical dose is 11 mg/kg (maximum dose 1 g) taken once daily before bedtime for 2–3 consecutive days. Side effects are mild and may include nausea, abdominal pain, and diarrhea. Treatment should be postponed in cases of acute hepatitis or nephritis.
Levamisole
This is a broad-spectrum anthelmintic administered at a dosage of 1.5–2.5 mg/kg as a single dose before bedtime for 3 consecutive days, constituting one treatment course. Side effects are mild and may include headache, vomiting, nausea, and abdominal pain. Rare cases of leukopenia, liver function impairment, or rash have been reported. It should be used cautiously in patients with liver or kidney dysfunction.
Combination Therapy
Combining levamisole with pyrantel pamoate can enhance therapeutic efficacy.
Symptomatic Treatment
Anemia should be corrected with the administration of iron supplements and adequate nutrition. Severe anemia may require repeated small-volume blood transfusions.
Prevention
Efforts to improve health education, reinforce food hygiene practices, and manage human waste through sanitary practices are key measures. Regular mass screening and treatment programs in endemic areas, as well as enhanced personal protective measures, are essential to curb the risk of infection. The prognosis is generally favorable.