3Facts: Commonly known as the hookworm million people in the world are infectedNecator americanus was widespread in the Southeastern United States until 20th century and was known as the “American killer”Second most common human helminthic infection
4Taxonomy:Kingdom: Animalia Phylum: Nematoda Class: Chromadorea Order: Rhabditida Family: Ancylostomidae Genus: Ancylostoma Necator Species: duodenale americanus
5Geographic RangeWorldwide, most common in areas with warm, moist climates and soilN. americanus commonly found in the Americas, Africa, India, Southeast Asia, China and the Pacific IslandsA. duodenale commonly found in Southeastern Europe, Northern Africa, India, China, and Southeast Asia, also in small areas of the U.S., Caribbean Islands, and South America
7Morphology Necator americanus The anterior end is curved dorsally giving them their “hook” appearanceHas a pair of dorsal and a pair of ventral cutting plates surrounding the anterior margin of the buccal capsule. Also has a pair of subdorsal and subventral teeth near the rear of the buccal capsuleMales:7 to 9 mm longhave a copulatory bursa that’s diagnostic for the genusThe needle like spicules have minute barbs at their tips and are fused distallyFemales:9 to 11 mm longVulva is located in middle of their bodyProduce 5,000 to 10,000 eggs a dayLive for 3 to 5 years
8Morphology Ancylostoma duodenale The anterior end is curved dorsally giving them their “hook” appearanceHas two ventral plates on the anterior margin of the buccal capsule that each have two large teeth. They also have a pair of smaller teeth further back in the capsuleMales:8 to 11 mm longHave a copulatory bursa characteristic to the speciesNeedle like spicules have simple tips and are not fused distallyFemales:10 to 13 mm longVulva is located about a third of the body length from the posterior endCan lay 10,000 to 30,000 eggs a dayCan live up to a year
10Life CycleEggs are passed in the stool, and hatch in 1 to 2 days when in warm moist conditions.The released rhabditiform larvae grow in the feces and soil.After 5 to 10 days and two molts they become filariform larvae that are infective.The infective larvae can survive 3 to 4 weeks in favorable environmental conditions.When contact occurs with a human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs.Then they penetrate into the pulmonary alveoli, up the bronchial trees to the pharynx and then are swallowed.They end up in the small intestine, where they attach to the intestinal wall, where they ingest blood.Most adult worms are eliminated in 1 to 2 years, but can survive for several years.Adult females release eggs which are then excreted in the feces.
11Pathology Small infections typically asymptomatic, less than 25 worms Localized skin manifestations (“ground itch”) can occur during penetration of the L3 larvaeSevere infectionsAnemia due to blood loss, can eventually lead to cardiac complicationsIn children, the lack of iron and protein can lead to growth and developmental problemsGastrointestinal and nutritional symptoms can occurRespiratory symptoms can occur during the migration of the larvae through the pulmonary system
12Diagnosis Identification of eggs in a fecal sample In light infections, a more concentrated sample is used by performing a formalin-ethyl acetate sedimentation techniqueUse larvae to distinguish between the two worms, cannot tell them apart by the eggs
13TreatmentIn countries where the infection is common and reinfection is high, light infections are not treatedIn the U.S. mebendazole and albendazole are typically usedPyrantel pamoate is also usedIron supplements are also given if infected person has anemia
14Control and Prevention Avoid walking barefoot in areas where infection is common and where night soil is usedAvoid ingesting soil from these areasEffective prevention includes not defecating outdoors and using effective sewage disposal systems
15References http://www.cdc.gov/parasites/hookworm/ me-flesh-eating-hookworm.htmlRoberts, L. Janovy, J. Foundations of Parasitology, 8th ed. New York: McGraw-Hill, 2009.