Hookworms ( 钩虫 ) Two major species of hookworms can infect human Necator americanus (...

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"

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 cycleLife cycle

Life cycleLife 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

Pathogenesis3. Anemia

Especially in young children hypoproteinemic because of some loss of serum proteins Iron-deficiency Why the small worms can cause anemia?

The pump-like action when worms suck bloodThe worms secrete an anticoagulant, which facilitates bleedingThe worms usually change the sites when suck blood

4. Allotriophagy (Geophagy): due to the iron-deficiency

Edema, ascites and Edema, ascites and loss of labour forceloss of labour force

AllotriophagyAllotriophagy

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

1. Chemotherapy: Albendazole; Mebendazole

2. Sanitary disposal of human feces is the most effective control measure in preventing the spread of infection with the hookworms

3. 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 piperazine 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:

1. Why A. lumbricoides infection distributed so widely?

2. Why hookworms can cause anemia ? What are the characteristics of the anemia?

3. Geo-helminth

4. Bio-helminth