+

Ancylostoma duodenale andNecator americanus

Kallie McGettigan

+Hookworms

http://animal.discovery.com/videos/monsters-inside-me-flesh-eating-hookworm.html

+Facts:

Commonly known as the hookworm

576-740 million people in the world are infected

Necator americanus was widespread in the Southeastern United States until 20th century and was known as the “American killer”

Second most common human helminthic infection

+Taxonomy:

Kingdom: Animalia

Phylum: Nematoda

Class: Chromadorea

Order: Rhabditida

Family: Ancylostomidae

Genus: Ancylostoma Necator

Species: duodenale americanus

+Geographic Range

Worldwide, most common in areas with warm, moist climates and soil N. americanus commonly found in the Americas, Africa,

India, Southeast Asia, China and the Pacific Islands A. 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

+Hosts

Definitive Host: Humans

Intermediate Host: None

+Morphology

Necator americanus

The anterior end is curved dorsally giving them their “hook” appearance

Has 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 capsule

Males: 7 to 9 mm long have a copulatory bursa that’s diagnostic for the genus The needle like spicules have minute barbs at their tips and are fused distally

Females: 9 to 11 mm long Vulva is located in middle of their body Produce 5,000 to 10,000 eggs a day Live for 3 to 5 years

+Morphology

Ancylostoma duodenale

The anterior end is curved dorsally giving them their “hook” appearance

Has 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 capsule

Males: 8 to 11 mm long Have a copulatory bursa characteristic to the species Needle like spicules have simple tips and are not fused distally

Females: 10 to 13 mm long Vulva is located about a third of the body length from the posterior end Can lay 10,000 to 30,000 eggs a day Can live up to a year

+Life Cycle

+Life Cycle

Eggs 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.

+Pathology

Small infections typically asymptomatic, less than 25 worms Localized skin manifestations (“ground itch”) can occur

during penetration of the L3 larvae Severe infections

Anemia due to blood loss, can eventually lead to cardiac complications In children, the lack of iron and protein can lead to

growth and developmental problems Gastrointestinal and nutritional symptoms can occur Respiratory symptoms can occur during the migration of

the larvae through the pulmonary system

+Diagnosis

Identification of eggs in a fecal sample

In light infections, a more concentrated sample is used by performing a formalin-ethyl acetate sedimentation technique

Use larvae to distinguish between the two worms, cannot tell them apart by the eggs

+Treatment

In countries where the infection is common and reinfection is high, light infections are not treated

In the U.S. mebendazole and albendazole are typically used Pyrantel pamoate is also used

Iron supplements are also given if infected person has anemia

+Control and Prevention

Avoid walking barefoot in areas where infection is common and where night soil is used

Avoid ingesting soil from these areas

Effective prevention includes not defecating outdoors and using effective sewage disposal systems

+References

http://www.cdc.gov/parasites/hookworm/

http://dpd.cdc.gov/dpdx/HTML/Hookworm.htm

http://animal.discovery.com/videos/monsters-inside-me-flesh-eating-hookworm.html

Roberts, L. Janovy, J. Foundations of Parasitology, 8th ed. New York: McGraw-Hill, 2009.

+Quiz:Which of these is a host?

+Which hookworm is able to cause more damage with a few number of worms present ?

Necator americanus

Ancylostoma duodenale

+Which order does the hookworm belong to?

Piroplasmida

Rhabditida

Trichurida

Cyclophylidea

+Where do you find the adult hookworms?

+Which stage of the life cycle is infective?

Rhabditiform Larvae

Adult Worm

Eggs

Filariform Larvae