Hookworm Disease

Clinical Description

Identification

A common chronic parasitic infection with a variety of symptoms, usually in proportion to the degree of anemia. In heavy infections, the bloodletting activity of the nematode leads to iron deficiency and hypochromic, microcytic anemia, the major cause of disability. Children with heavy long-term infection may have hypoproteinemia and may be retarded in mental and physical development. Occasionally, severe acute pulmonary and GI reactions follow exposure to infective larvae. Death is infrequent and usually can be attributed to other infections.

Infectious Agents

Ancylostoma duodenale, A. ceylanicum, A. braziliense, A. caninum and Necator americanus.


Diagnosis

Light hookworm infections generally produce few or no clinical effects. Infection is confirmed by finding hookworm eggs in feces; early stool examinations may be negative until worms mature. Species differentiation requires microscopic examination of larvae cultured from the feces, or examination of adult worms expelled by purgation following a vermifuge. PCR-RFLP techniques allow species differentiation.


Epidemiology

Mode of Transmission

Eggs in feces are deposited on the ground, embryonate, and hatch; under favorable conditions of moisture, temperature and soil type, larvae develop and become infective in 7–10 days. Human infection occurs when infective larvae penetrate the skin, usually of the foot; in so doing, they produce a characteristic dermatitis (ground itch). The larvae of A. caninum and A. braziliense die within the skin, having produced cutaneous larva migrans. Normally, the larvae of Necator, A. duodenale, A. ceylanicum and other Ancylostoma enter the skin and pass via lymphatics and bloodstream to the lungs, enter the alveoli, migrate up the trachea to the pharynx, are swallowed and reach the small intestine, where they attach to the intestinal wall, developing to maturity in 6–7 weeks (3–4 weeks in the case of A. ceylanicum), and typically producing thousands of eggs per day. Infection withAncylostoma may also be acquired by ingesting infective larvae; possible vertical transmission through breastmilk has been reported.

Incubation Period

Symptoms may develop after a few weeks to many months, depending on intensity of infection and iron intake of the host. Pulmonary infiltration, cough and tracheitis may occur during the lung migration phase of infection, particularly in Necator infections. After entering the body, A. duodenale may become dormant for up to 8 months, after which development resumes, with a patent infection (stools containing eggs) a month later.

Period of Communicability

No person-to-person transmission, but infected people can contaminate soil for several years in the absence of treatment. Under favorable conditions, larvae remain infective in soil for several weeks.

Reservoir

Humans for A. duodenale and N. americanus; cats and dogs for A. ceylanicum, A. braziliense and A. caninum.

Susceptibility

Universal; no evidence that immunity develops with infection.

Occurrence

Endemic in tropical and subtropical countries where sanitary disposal of human feces is not practiced and soil, moisture and temperature conditions favor development of infective larvae. Also occurs in temperate climates under similar environmental conditions (e.g. mines). Both Necator and Ancylostoma occur in many parts of Asia (particularly southeastern Asia), the South Pacific and eastern Africa. N. americanus is the prevailing species throughout southeastern Asia, most of tropical Africa and America; A. duodenale prevails in North Africa, including the Nile Valley, northern India, northern parts of eastern Asia and the Andean areas of South America. A. ceylanicum occurs in southeastern Asia but is less common than either N. americanus or A. duodenale. A. caninum has been described in Australia as a cause of eosinophilic enteritis syndrome.


Prevention and Control

1)    Preventive measures:

a)    Educate the public to the dangers of soil contamination by human, cat or dog feces, and in preventive measures, including wearing shoes in endemic areas.

b)    Prevent soil contamination by installation of sanitary disposal systems for human feces, especially sanitary latrines in rural areas. Night soil and sewage effluents are hazardous, especially where used as fertilizer.

c)    Examine and treat people migrating from endemic to receptive nonendemic areas, especially those who work barefoot in mines, construct dams, or work in the agricultural sector.

d)    WHO recommends a “preventive chemotherapy” strategy focused on treatment of high-risk groups at regular intervals, for the control of morbidity due to soil-transmitted helminth (STH) infections, including ascariasis, trichuriasis and hookworm disease. Recommended drugs and dosages are single-dose mebendazole (500 mg) or albendazole (400 mg, half dose for children 12–24 months). Action to be taken is differentiated according to prevalence of any STH infection (infection with at least one STH) among school-age children (aged 6–15 years):

Category Prevalence of infection among school-aged children Action to be taken
High-risk community ≥50%

a) Treat all school-age children (enrolled and not enrolled) twice each year

b) Also treat with the same frequency:

i)    Preschool children (aged 1–5)

ii)    Women of childbearing age, including women in the 2nd and 3rd trimesters and lactating women

iii)    Adults at high risk in certain occupations (e.g. tea pickers and miners)
Low-risk community ≥20% and <50% Treat all school-age children (enrolled and not enrolled) once each year

Extensive monitoring has shown no significant ill effects of administration to pregnant women, but as a precautionary measure, women in the 1st trimester of pregnancy should not be treated. Administration of anthelminthics to very young children (1–2 years old) is safe, but some key recommendations should be followed:

i) children should never be forced to swallow tablets;

ii) tablets should be crushed and mixed with water;

iii) treatment should be supervised by trained personnel.

2)    Control of patient, contacts and the immediate environment:

a)    Report to local health authority: Official report not ordinarily justifiable, Class 5.

b)    Isolation: Not applicable.

c)    Concurrent disinfection: Safe disposal of feces to prevent contamination of soil.

d)    Quarantine: Not applicable.

e)    Immunization of contacts: Not applicable.

f)    Investigate contacts and source of infection: Each infected contact and carrier is a potential or actual indirect spreader of infection.

g)    Specific treatment: Single dose oral mebendazole (500 mg), or albendazole (400 mg, half dose for children 12–24 months); on theoretical grounds, both are contraindicated during the first trimester of pregnancy unless there are specific medical or public health indications. Single-dose pyrantel pamoate (10 mg/kg) or levamisole (2.5 mg/kg) are also effective. Adverse reactions are infrequent. Follow-up stool examination is indicated after 2 weeks, and treatment must be repeated if a heavy worm burden persists. Iron supplementation will correct the anemia and should be used in conjunction with de-worming. Transfusion may be necessary for severe anemia.

3)    Epidemic measures:

Prevalence survey in highly endemic areas: provide periodic mass treatment. Health education in environmental sanitation and personal hygiene, and provide facilities for excreta disposal.

4)    Disaster implications:

None.

5)    International measures:

None

Source: Heymann (Ed.). (2008). Control of Communicable Diseases Manual, 19th edition. Washington, DC: American Public Health Association.

Common Disease Taxonomy: