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)
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" It can profoundly affect entire populations by gradually sapping the victims’ strength, vitality, and overall well-being
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
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 plates on the ventral wall of the buccal capsule
Buccal capsule Ancylostoma duodenale Necator americanus
Morphology: Egg oval or can-shaped with a thin, hyaline shell, measured 60-75 by 36-40 µm.
Life cycle
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
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".
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
Pathogenesis 3. Anemia Especially in young children hypoproteinemic because of some loss of serum proteins Iron-deficiency Why can the small worms 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 4. Allotriophagy (Geophagy): due to the iron-deficiency
Edema, ascites and loss of labour force Allotriophagy
Laboratory diagnosis Brine floatation is the method of first choice Hookworm larvae cultivation is used for species identification Hookworm larvae in sputum
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
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 45C
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
HYPERACTIVE CHILD SYNDROME HISTORY A mother brought her 7-year-old son to the psychiatrist because he had some behavioral problems in school and at home. She stated that he was very irritable and inattentive and that his attention span was very short. In addition, he begun to experience insomnia and had episodes of enuresis. He was unable to sit still, had lost some weight, and his appetite was not as good as usual. His birth and development were normal. The astute psychiatrist inquired further and learned that the child was also experiencing perianal itching. He performed a swab of the perianal area. The results confirmed his suspicion. The child was treated with albendazole and all his symptoms disappeared.
The child gets infected with: A. ascaris B. whipworm C. pinworm D. hookworm He may acquire the infection from: The plan of treatment should include:
Questions: Why A. lumbricoides infection distributed so widely? Why hookworms can cause anemia ? What are the characteristics of the anemia? Geo-helminth Bio-helminth