Hookworms

Strongylid Nematodes - Hookworms - Chap. 25

Hookworm disease is one of the most important parasitic diseases of humans.

Number of humans infected is estimated at 1.2 billion with 50,000 to 60,000 deaths each year.

Hookworms occur Wisconsin - 4.9% prevalence in 1987 survey – but are not endemic here

• cases in WI?

2 species of hookworms infect humans

1. Ancylostoma duodenale - Old World Hookworm

Distribution –

2 species of hookworms infect humans

2. Necator americanus - New World Hookworm

Distribution –

Also occurs in Africa and Asia - probably introduced into the U.S. with the slave trade.

Stereotyped rural southerner as lazy, shiftless, and good-for-nothing (poor white trash) is partly due to the high prevalence of this parasite in southern U.S.

Hookworm Distribution

Females:

9-13 mm long with egg-filled uterus

Male hookworms:

7-11 mm long

Posterior end forms a __________________

Morphology of Ancylostoma duodenale

Buccal capsule contains 2 pairs of large ventral (anterior) teeth

Copulatory bursa is at posterior end and contains 2 thin spicules that separate distally.

Morphology of Necator americanus

Buccal capsule contains a pair of ventral and dorsal cutting plates.

Copulatory bursa contains spicules that are fused distally.

Life Cycle of 2 Hookworms is similar

1. Adults occur in the human __________________ Male and female are commonly found in copula. Both are well attached to the intestinal mucosa with the buccal capsule.

2. Female releases eggs which are passed in the feces.

Both species show high fecundity:

A. duodenale produces 25,000 to 30,000 eggs/day.

N. americanus produces 9,000 eggs/day.


3. Eggs embryonate in warm, moist shady soil.

4. In 1-2 days, the __________ (also called the rhabditiform larva) hatches and feeds on bacteria and debris in the feces & soil.

5. L1 molts twice to the ______ stage (called the filariform larva) in a week. 6. L3 are infective and migrate to the surface of the soil and upon contact with human skin will______________________ Larvae typically penetrate skin of the feet when one walks barefooted through warm soil.


7. After penetrating the skin, the L3 enter the circulation, are carried to the heart, and follow the pulmonary circulation to the ______________________

Here, they break out of the lung capillaries, enter the alveoli, migrate up the respiratory tree, and are swallowed. 8. Arriving in the small intestine, the L3 molts twice to the adult stage.It takes 5 weeks from the time of skin penetration until the adults are mature.

Pathology

Extent of pathology is associated with the numbers of adults

Symptoms appear in infections of 100 or more worms.

A heavy infection involves 500 or more worms.

• Symptoms are severe and the infection may be life-threatening.

1. _____________________________ - penetration of L3 into the skin, usually the feet; itching and reddish rash occurs.

2. ______________________________- pneumonia-like symptoms occur as L3 break out of the capillaries and enter the alveoli (symptoms are not as severe as Ascaris migration)

3 Phases of Pathology

3. __________________________ - adults attach to the mucosal wall and may penetrate into the submucosa where they voraciously suck blood - up to 200 ml of blood may be lost/day

• A. duodenale takes 0.26 ml/day; N. americanus 0.03 ml/day

• Hookworms are very wasteful, as most of the blood taken simply passes through its intestine but is lost to the host.

3. Anemia cont.

Blood loss is associated with _________________________________________

_________________________________________

• Infected adults become tired and rundown

• Mental and physical retardation commonly occurs in children.

Recent findings indicate that there is a reduction in gamma globulins which results in _____________________________ to other infections.

Combination of these factors can be fatal.

Diagnosis DIAGNOSIS - identify the eggs in the feces

All hookworm eggs look the same so can’t ID species

Eggs are ovoid with thin, smooth eggshell.

Internally, eggs are always early in mitosis - contain 2 to 16 cells.

Size: 55-75 µm x 35-40 µm

Treatment and Prevention

TREATMENT - ______________________________ is effective in treating both species

PREVENTION:

1. ___________________________________ - stop pollution of soil with infected feces

- this has eliminated much of the problem in southern U.S.

2. ___________________________________ - prevent penetration of L3

Dog and Cat Hookworms

Dog hookworm - Ancylostoma caninum - is easily recognized by its 3 pairs of teeth in the buccal capsule.

Cat hookworm - Ancylostoma braziliense - has a pair of long teeth.

Dog and Cat Hookworms

Both species inhabit the small intestine of their hosts.

Life cycles and pathology are similar to human species.

HUMANS may serve as accidental hosts of these hookworms when the filariform larvae (L3) penetrate human skin.

L3 penetrates human skin

2 Pathological Problems in Humans:

1. __________________________________________(= Creeping Eruption)

L3 of dog or cat hookworms enter human skin and wander about in epidermis

L3 are unable to penetrate into the dermis and are eventually killed by our immune system

Wandering L3 cause a red, itchy irritation

Treated with thiabendazole ointment

Present in the U.S.; another reason to clean up dog and cat feces!

2 Pathological Problems in Humans:

2. _______________________caused by Ancylostoma caninum

Recent finding only in ____________________- over 200 cases reported

A few L3 are able to penetrate skin to enter circulation and are carried to small intestine.

Cause severe swelling and bleeding in region of small intestine where they attach (called enteritis).

Method of Infection: Dog defecates on lawn and then person mows lawn barefooted and L3 penetrate skin.

Probably just a matter of time before cases appear in the U.S.

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Rhabditid Nematodes - Chapter 24Strongyloides stercoralis

This tiny nematode occurs in the small intestine of ___________________________________________________ Parasite is cosmopolitan in distribution but is most common in warm, moist climates.

Only ____________________________ occur as parasites in the small intestine of their hosts.

- These worms are very small; only 2 mm in length.

- Recognized by their elongate esophagus and single row of eggs within the uterus.

Both males and females are found in part of the life cycle as free-living soil organisms.

Life Cycle of Strongyloides stercoralis

LIFE CYCLE involves the ability to undergo either a free-living existence or a parasitic existence depending on conditions.


1. Parasitic female lives in the small intestine of humans and other mammals.

- Females produce eggs by __________________________- unfertilized eggs give rise to offspring.

-Parasitic females burrow into the mucosa to release their ova.

2. By the time the eggs reach the lumen of the small intestine, the eggs hatch and the ______ (= rhabditiform larvae) are released into the lumen.


3. At this point, there are 3 possible pathways that can be followed in the life cycle:

(1) _______________________ - L1 molt twice to the L3 stage (= filariform larvae) as they pass through the large intestine.

They penetrate the wall of the large intestine, enter the circulation, migrate through the lungs, enter respiratory tree, and are swallowed.

Larvae molt twice in small intestine and become parasitic females.


(2) _______________________ - L1 are passed in the feces onto warm, moist soil.

In the soil, the L1 molt 2x to L3

(filariform larvae)

L3 penetrate the skin (like hookworm larvae) and enter the circulation. Go through lung migration, are swallowed, and molt to parasitic females in the small intestine.


(3) ________________________ - L1 rhabditiform larvae are passed in the feces and develop directly into free-living males and females.

These adults copulate and eggs are released in the soil.

L1 (rhabditiform larvae) hatch from the eggs and may again develop into free-living adults - OR - may instead molt 2x to become infective L3 that penetrate skin to start a new parasitic cycle.

Pathology of Strongyloides stercoralis

Infection is long-lasting (up to 40 years in WWII POW's) and is generally asymptomatic. 3 stages of pathology: 1. ______________________________- skin penetration of L3

- cause itching and reddening of skin at penetration sites 2. ______________________________ - due to lung migration of L3

- pneumonia-like symptoms similar to Ascaris & hookworms


3. ______________________________________________ - parasitic females burrow into the mucosa and submucosa of the small intestine causing ulceration of tissue and sloughing of intestinal cells. - ulceration causes secondary bacterial infections


Small intestinal damage in immunocompetent persons causes intestinal pain -AIDS patients:

(this is the only helminth that causes greater pathology in AIDS patients)

Strongyloides stercoralis

DIAGNOSIS – (1) (2) TREATMENT - __________________________________ is the drug of choice but has serious side effects PREVENTION -

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Hookworms