Main » Infectious diseases » Soil-mediated Helminthiases » Ankylostoma duodenale and necator americanus
Photo 1. The eggs of helminths.Schistosoma haematobium
Photo 2. The eggs of helminths (S. mansoni).
Photo 3. The eggs of helminths (S. japonicum).
Photo 4. The eggs of helminths (Fasciola hepatica).
Photo 5. The eggs of helminths (Ascaris lumbricoides).
Photo 6. The eggs of helminths — Ascaris (infertile).
Photo 7. The eggs of helminths (Paragonimus westermani).
Photo 8. The eggs of helminths (Diphyllobothrium latum).
Photo 9. The eggs of helminths (Hookworm).
Photo 10. The eggs of helminths (Trichuris trichiura).
Photo 11. The eggs of helminths (Enterobius vermicularis).
Photo 12. The eggs of helminths (Hymenolepis nana).
Photo 13. The eggs of helminths (H. diminuta)
Photo 14. The eggs of helminths (Taenia).
Photo 15. The eggs of helminths (Clonorchis sinensis, Opisthorchis felineus, Heterophyes heterophyes).
The common hookworms of man are A. duodenale and N. americanus. It is estimated that 1000 million persons are infected with hookworm (about a quarter of the world's population). Usually one species predominates in any one locality. The map shows the approximate areas in which one or other species dominates. Since the larvae can only develop in warm moist soil the distribution of the parasite is limited by climatic conditions.
Distribution map of hookworm infection
Photo 16. Comparative size of nematodes.
||N. americanus ♀ ♂
||A. duodenale ♀ ♂
||E. vermicularis ♀
||T. spiralis ♀ and ♂
||T. trichiura ♀
||T. trichiura ♂
Photo 17. Filariform larva of hookworm. Eggs (9) passed in the faeces hatch into rhabditiform larvae in damp soil; they feed and undergo two moults to produce an infective sheathed filariform larva, (x 350)
Photo 18. Larvae of hookworm in lung of dog. These penetrate bare skin, usually of feet or legs and enter the blood stream, to reach the lungs. The larvae then penetrate into the bronchioles, pass into the pharynx and are swallowed. They become attached to the small intestine and mature to adults. (x 100)
Photo 19. Adult hookworms in situ. The worms are about one cm long and characteristically curved. They are attached by their buccal capsules to the villi of the small intestine. (Natural size)
Photo 20. Indentification of adult hookworms. A. caninum (x470) The different species may be distinguished by the characteristic morphology of the head capsule (313-316) and male bursa (317), seen here in scanning electromicrographs. The male bursae are distinguished by the numbers and pattern of the Tays'.
Photo 21. Indentification of adult hookworms (A. duodenale). (x630)
Photo 22. Indentification of adult hookworms (A. ceylanicum). (x670)
Photo 23. Indentification of adult hookworms (N. americanus) (x 470).
Photo 24. Indentification of adult hookworms (A. duodenale) (x 470).
Photo 25. Section of adult A. deodunale in situ. The hookworm feeds by sucking blood from the intestinal mucosa. It has been estimated that a single A. duodenale can withdraw as much as 0.2 ml a day while N. americanus withdraws 0.05 ml. (x 20)
Photo 26. Clinical picture of gross hookworm disease. Severe anaemia is the classical feature of hookworm disease. This results from high hookworm loads and low daily iron intake. The patients usually complain of lassitude, shortness of breath, while oedema and ascites also occur.
Photo 27. Blood film from a patient with hookworm anaemia. The typical anaemia resulting from severe hookworm infection is of the iron deficiency type with a low serum iron, (x 900)
Photo 28. Creeping eruption due to larvae of dog hookworms. Infective larvae of various species of animal hookworms (eg A. braziliense, A. caninum, A. ceylanicum) frequently fail to penetrate the dermis. They migrate through the epidermis leaving typical serpiginous tracks known also as 'creeping eruption'.
Photo 29. Necator americanus and ankylostoma duodenale.
Adults are attached to the walls of the jejunum (A) by the buccal capsule. Females lay large numbers of eggs which are passed out with the faeces (B). They mature through 4- and 8-segmented stages (C) to larvae which hatch in the soil (D). There they feed on bacteria and undergo two moults to produce filariform, infective larvae (E). These penetrate the skin of a new host (F) usually on the feet. They migrate into venules, entering the right heart (G) and lungs (H). Here they grow before penetrating from the capillaries into the alveoli. They enter the trachea (I), then the pharynx, are swallowed and pass into the small intestine (A) where they mature.
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