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Hookworms

Necator americanus and Ancylostomaduodenale most common human hookworms

Ancylostoma ceylanicum, Ancylostoma braziliense, Ancylostoma caninum

Soil-transmitted helminths

Adults of the human hookworms are blood-sucking nematodes.

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Morphology

N. americanus have a cervical curvature w/c appears like a HOOK

Females: 9 to 13 mm, with a blunt posterior end

Males: 7 to 11 mm, with expanded posterior end (fan-like bursa copulatrix)

Buccal capsule semi-lunar cutting plates

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Morphology

Ancylostoma duodenale body contour tends to follow the general curvature of the body (C).

Buccal capsule: two pairs of ventral teeth, similar in size

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Morphology

A. ceylanicum: two pairs of ventral teeth, the outer pair larger than inner

A. braziliense: two pairs of ventral teeth, a pair of small, very inconspicuous median teeth and a pair of larger outer teeth

A. caninum: has three pairs of ventral teeth

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Morphology

Hookworm eggs

56 to 60 by 34 to 40 m

are ovoidal, thin-shelled and colorless

4 to 8 celled stage

Differentiation of Necator egg from Ancylostoma egg is difficult and impractical

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Morphology

Rhabditiform larva Hatches within 24 to 48 hours

short and stout, with a long and narrow buccal chamber

They feed on bacteria and organic matter

Filariform larvaMouth is closed, the esophagus

elongates

Non feeding stage infective stage to man

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Pathology and Clinical Manifestations

Due to larva:

Ground itch

Creeping eruption or cutaneous larva migrans

Pulmonary lesions

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Pathology and Clinical Manifestations

Due to adult worm:

Anemia

Hypoalbuminemia

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Diagnosis

Recovery of eggs in the stool DFS or concentration techniques

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Strongyloides stercoralis

Threadworm

Fecally-transmitted and soil-transmitted helminth

Can survive in the human body for many years autoinfection

Course of strongyloidiasis is usually chronic with irregular periods of exacerbation

Cochin-china diarrhea

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Morphology

Parasitic female Delicate filiform worms, measuring up to

2 mm in length

Parthenogenetic

Free-living female Shorter but stouter than the parasitic

female

Double bulbed muscular esophageal pharynx

There is no parasitic male

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Morphology

Rhabditiform larva

Muscular elongated esophagus with a pyriform posterior bulb

Short buccal cavity

conspicuous genital premordium

Filariform larva

Long esophagus occupying half the length of the larva

Forked or notched tail

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Filaria

Debilitating tropical disease (lymphedema, elephantiasis, or hydrocoele)

Wuchereria bancrofti and Brugiamalayi

Vector Aedes, Culex and Anopheles (bancrofti); Mansonia (malayi)

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Parasite Biology

Wuchereria

Male: 2 to 4 cm in length; Female: 8 to 10 cm

Microfilaria: 270 to 290 m, enclosed in a hyaline sheath which is much longer than the microfilaria

Two to three rows of distinctly conspicuous nuclei

Graceful curvatures

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Parasite Biology

Brugia

Male: 13 to 23 mm in length; Female: 43 to 55 mm

Microfilaria: 177 to 230 m in length

2 rows of indistinct nuclei

Angular with secondary kinks

2 nuclei at the tip of the tail

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Parasite Biology

Adult females of B. malayi and W.bancrofti are indistinguishable

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Diagnosis

Finding of characteristic microfilariae in thick blood smears taken between 8pm and 4am. nocturnal periodicity

Microfilariae may not be demonstrable during:

Low intensity infection

Dead worms

Obstructed lymphatics