Covers the two hookworm and nematode species Ancylostoma duodenale and Strongyloides stercoralis, starting with the Old World hookworm's morphology, blood-feeding in the small intestine and iron-deficiency anaemia, then its life cycle, skin-penetration migration route through the lungs, diagnosis by stool egg detection, and cutaneous larva migrans from animal hookworms. The Strongyloides section describes its small size, unusual reproduction inside and outside the host, infection route, and symptoms, including severe disease in immunocompromised people. Mnemonics and recap questions accompany each part.
Topic 96 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 9 sections, about 1,069 words (7 min of reading), with 15 flashcards.
In this note
Ancylostoma duodenale.Strongyloides stercoralis.
Ancylostoma duodenale (Commonly known as the Old World hookworm)
Strongyloides stercoralis
Ancylostoma duodenale (Old World Hookworm)
Ancylostoma duodenale – General Characteristics
Ancylostoma Life Cycle & Infection
Cutaneous Larva Migrans
Strongyloides stercoralis – Overview & Life Cycle
Bonus: Strongyloidiasis Symptoms
Ancylostoma duodenale (Commonly known as the Old World hookworm)
General Overview and Characteristics
This is one of the two major hookworms that infect humans
It can also infect animals such as cats and dogs
Adult male worms measure between eight and eleven millimeters, while adult females are slightly larger, around ten to thirteen millimeters
These worms attach to the blood vessels of the small intestine and feed by sucking blood
They are a major cause of chronic blood loss, leading to iron deficiency anemia, particularly in children
In children, chronic infection can also lead to growth delays and developmental problems, especially in tropical areas
Life Cycle and Transmission
The eggs of the worm are passed out in human feces
In favorable conditions like warm moist soil, the eggs hatch within one to two days
The hatched larvae are known as rhabditiform larvae, which live in feces or soil and grow for about five to ten days
These larvae go through two molts and become filariform larvae, which are the infectious stage
Infective larvae can survive in soil for three to four weeks
Infection Process
Humans become infected when the filariform larvae come into contact with bare skin, often through the feet
The larvae penetrate the skin and enter the bloodstream
They travel through the blood to the heart and then to the lungs
From the lungs, they pass into the alveoli, ascend the airways to the throat, and are swallowed
They then reach the small intestine, where they mature into adult worms and begin feeding and reproducing
Lifespan
Adult worms usually live in the host for one to two years
However, in some cases, they may survive for several years
Diagnosis
The most common method of diagnosis is by detecting hookworm eggs in a stool sample
