Ancylostoma and Necator Hookworms

Causative agents of ancylostomosis and necatorosis (hookworm infection)

Parasites. Ancylostoma duodenale and Necator americanus are common parasites of the human small intestine, causing enteritis and anemia. Infection is mainly by the percutaneous route. The dog parasite Ancylostoma caninum has been identified as the cause of eosinophilic enteritis in humans. Larvae of various hookworm species from dogs and other carnivores can penetrate into human skin, causing the clinical picture of "cutaneous larva migrans" (p. 602).

Occurrence. Human hookworm infections are most frequent in the subtro-pics and tropics (for instance in southern Europe, Africa, Asia, southern US, Central and South America). The number of persons infected worldwide is estimated at about 1.25 billion (WHO, 1998). In central Europe, hookworm infections are seen mainly in travelers returning from the tropics or in guest workers from southern countries.

Morphology, life cycle, and epidemiology (Fig. 10.14). The hookworms that parasitize humans are 0.7-1.8 cm long with the anterior end bent dorsally in a hooklike shape (ankylos: bent, stoma: mouth, necator: killer). The entrance to the large buccal capsule is armed with toothlike structures (Ancylostoma) or cutting plates (Necator). The thin-shelled, oval eggs (about 60 im long) containing only a small number of blastomeres are shed with feces. In one to two days the first-stage larvae leave the eggshells, molt twice, and develop into infective third-stage larvae. Since the shed second-stage cuticle is not entirely removed, the third-stage larva is covered by a special "sheath." Larvae in this stage are sensitive to dryness. In moist soil or water they remain viable for about one month. Higher temperatures (optimum: 20-30 °C) and sufficient moisture favor the development of the parasite stages outside of a host.

Humans are infected mainly by the percutaneous route. Factors favoring infection include working in rice paddies, walking barefoot on contaminated

— Life Cycles of Hookworms

— Life Cycles of Hookworms

Female Hookworm Larvae
Fig.10.14 1 Female and male hookworms; 2 hookworm egg shed in stool with blastomeres; 3 development of first-stage larva (L1) in egg; 4 hatched L1 larva; 5 L2 larva; 6 L3 larva with sheath, infective stage.

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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