Hookworms ( 钩虫 )

1. Hookworms (钩虫) Two major species of hookworms can infect human Necator americanus (美洲板口线虫) Ancylostoma duodenale (十二指肠钩口线虫)

2. General Introduction • Human intestinal nematode of smaller size, inhabit the small intestine • World-wide distribution, about 900 million infections in the world • A. duodenale is prevalent in Southern Europe, North Africa, Northern Asia (North China), and the more pathogenic one • N. americanus is the predominant species in the Western hemisphere and equatorial Africa (South China) • Many areas are endemic for both species • Heavy infection may evoke anemia known as "Yellow Laziness"

3. Morphology:Adults Ancylostoma duodenale • Female is 10-13 mm in length by 0.6 mm in diameter • Males are 8-11 mm by 0.4 mm • Posterior end has an umbrella-shaped bursa with riblike rays • Two pairs of curved teeth on the ventral wall of its buccal capsule

4. Morphology:Adults Necator americanus • Females are 9-11 mm in length by 0.4 mm in diameter • Males are 7-9 mm by 0.3 mm • Smaller than A. duodenale • A pair of semilunar cutting plateson the ventral wall of the buccal capsule

5. Buccal capsule Ancylostoma duodenale Necator americanus

6. Morphology:Egg oval or can-shaped with a thin, hyaline shell, measured 60-75 by 36-40 µm.

8. Life cycle

11. Life cycle • No intermediate host is necessary • Larva takes a free living mode • The filariform larva is the infective stage • Infection routes: skin penetration(mainly); orally swallow; maternal-child • Residing in human upper small intestine: duodenum, jejunum • Blood-Lung migration: skin --- lymphatic system --- right side of the heart --- lung --- respiratory tree --- coughed up and swallowed --- small intestine • Persisting migrans(迁延移行):Ancylostoma duodenale

12. Pathogenesis 1. Hookworm larvae dermatitis: Penetration of the skin by the filariform larvae may be asymptomatic in previously uninfected individuals. However, those experiencing repeated infections develop itching, known as "ground itch" or "dew itch".

13. Pathogenesis 2. Migration of pre-adult cause temporary pulmonary inflammation: In heavily infected individuals (i.e., 500-1000 worms), there can be symptoms of pneumonia during the migratory phase in the developmental cycle of these worms

14. Pathogenesis 3. Abdominal pains, diarrhea, loss of appetite… 4. Anemia • Especially in young children • Hypoproteinemic because of some loss of serum proteins • Iron-deficiency

15. Why the small worms can cause anemia? • The pump-like action when worms suck blood • The worms secrete an anticoagulant, which facilitates bleeding • The worms usually change the sites when suck blood 5. Allotriophagy(Geophagy): due to the iron-deficiency 6. Ancylostomiasis in infant

17. Edema, ascites and loss of labour force

18. Allotriophagy

19. Laboratory diagnosis • Brine floatation is the method of first choice • Hookworm larvae cultivation is used for species identification • Hookworm larvae in sputum

20. Epidemiology • Most prevalent in the tropical and subtropical zones • In China, mostly mixed infected, while A.duodenale is somewhat northward distributed and N. americanus in southward

21. Epidemiology • Moist, shady, sandy, or loamy soil favors persistence of these worms • Larvae can survive for up to 6 weeks • Do not live long in clay, dry, hard packed soils, or where temperatures are freezing, or are higher than 45C

22. Principles of Control • Chemotherapy: Albendazole; Mebendazole • Sanitary disposal of human feces is the most effective control measure in preventing the spread of infection with the hookworms • Protection of the susceptible population