Diseases

•Strongyloidiasis

•Cochin-China diarrhea

People are the principal hosts of S. Stercoralis, but dogs and monkeys have a similar parasite. A similar species, S. fullerborni, can infest higher primates and humans.

•no male form has been reliably

identified in the parasitic stage

•female species reproduce in a

parthenogenetic manner

Description

•small colorless, semitransparent filariform nematode with a finely striated cuticle

•has s short buccal cavity and a long, slender, cylindrical esophagus

•paired uteri contain a single a single file of thin-shelled, transparent, sermented eggs

Action

The parasitic females penetrate the mucosa of the intestinal villi, where they burrow in serpentine channels in the mucosa, depositing eggs and securing nourishment.

Eggs

• deposited in the intestinal mucosa

• hatched into rhabditiform larvae that penetrate

the glandular epithelium and pass into the lumen

of the intestine and out in the feces.

1.DIRECT CYCLE, like hookwormAfter a short feeding period of 2 – 3 days in the

soil, the rhabditiform larva about 700 in length. The infective filaform larvae penetrate the human skin, enter the venous circulation, and pass through the right heart to the lungs, where they penetrate into the alveoli. From the lungs, the adolescent parasites ascend to the glottis, are swallowed and reach the upper part of the small intestine, where they develop into adults. Occasionally some larvae pass through the pulmonary barrier into the arterial circulation and reach

various organs of the body. During their migrationin the host the larvae pass through two molts to become adolescent worms. In about 28 days after the initial infectionion, matuer ovipositing females then develop.

2. INDIRECT CYCLEIn this cycle, the rhabdidtiform

larvae develop into sexually mature, free-living males and females in the soil. After fertilization, the free-living female produces eggs that develop into rhabditiform larvae, which may become infective filariform larvae within a few days and enter new hosts, or repeat the free-living generation. The indirect method appears to be associated with the optimal environmental conditions for a free-living existence in tropical countries, while the direct method is more frequently followed in the less favorable, colder regions. Strains may show chiefly one or the other type of development or a mixture of both types.

3. Autoinfection

At times the larvae may

develop rapidly into the filaform

stage in the intestine and, by penetrating the intestinal mucosa or the perinial skin, establish a developmental cycle within the host. Autoinfection explains persistent strongyloidiases in patients living in nonendemic areas. Several studies indicate that a substantial number of British and Australian veterans of World War II who were exposed in Southeast Asia have carries asymptomatic Strongyloides infections for 30 years or more. Autoinfection is also one of the few examples of multiplication of a helminth within the host.

Epidemiology

• runs parallel to that of a hookworm, but its prevalence is lower in temperate zones like the tropical and subtropical areas where warmth, moisture and lack of sanitation favor is free-living

Pathology and Symptomatology • moderate infections may cause a burning, dull or sharp, nonradiating midepigastric pain. Pressure to this area may elicit pain and tenderness. Nausea and vomiting may be present; diarrhea and constipation alternate. The result in weight loss and chronic dynestery accompanied by malabsorption and steatorrhea.

Diseases

•ancylostomiasis

•Uncinariasis

•Necatoriasis

•Hookworm infection

•Necator americanus

•Ancylostoma duodenale

•A. braziliense (rarely)

•A. caninum (rarely)

•A. ceylanicum (rarely)

Species

Morphology•adult hookworms are small, cylindrical, fusiform, grayish white nematodes

• the female are larger than the males

• the worm has a relatively thick cuticle

• there are single male paired female reproductive organs

• the posterior end of the male has a broad, translucent, membranous caudal bursa with riblike rays, which is used for attachment to the female during copulation

The Egg• has bluntly rounded ends and a single thin transparent hyaline shell

• is unsegmented at oviposition and in two to eight cell stages of division in fresh feces

The life cycles of the several species of hookworm are similar. Humanity is almost the exclusive host of A. duodenate and N. americanus, although these species have been reported occasionally in primates and other mammals. The adults of A. braziliense, a parasite of wild domestic felines and canines in the tropics, are infrequently found in humans. A caninum, the common hookworm of dogs and cats, is extremely rare intestinal parasite of humans.

The eggs passed in the feces, mature rapidly and produce the rhabditiform larvae in 1 to 2 days under favorable conditions and an optimal temperature of 23 to 33C.

Hookworm larvae remain within a few inches of where they are deposited unless carried by floods or animals to other locations.

The following factors favor hookworm maintenance and dispersal:

1. Infected individuals who defecate on the soil in areas frequented by others, fecal concentration in secluded areas near the house. Return to this restricted area by members of the family leads to family infection. The one-room school without sanitary facilities is an excellent source of infection.

2. A shaded sandy or loam soil, which is a favorable culture medium for hookworm larvae. Clay soil which packs tightly, is unsuitable for the larvae.

3. A warm climate, which favors the development of the eggs and larvae and promiscuous defecation. Cold, snowy climes force people into shelter; hence the widespread use of the privy in such areas.

4. Moisture, 30 – 50 inches of rain, especially during the warm season of the year when egg and larval development are possible.

5. A poor, ignorant population that does not wear shoes. The population of half of the world does not wear shoes, nor can they afford them.

Pathology and Symptomatology

When the larvae penetrate the skin they produce maculopapules and localized erythema. Itching is often severe, and as it is related to contact with the soil, especially o the dewy mornings when the moisture prmits the larvae to beat the surface.

Hookworm is essentially a chronic infection, and the infected individual often shows no acute symptoms.

The hookworms attached to the mucosa of the small intestine by their buccal capsules. The favorite site is the upper small intestine, but in heavy infections the worms may be present as far as the lower ileum. They suck the host’s blood and mucosal substances by the tractile pull of the contracting and expanding esophagus.

DiseaseCreeping eruption is a dermatitis

characterized by serpiginous intracutaneous lesions caused by migration of nematode larvae that normally do not infect the human host.

Like the cerceriae of bird schistosomes, can produce annoying skin eruptions known as “swimmer’s itch” by allergic sensitization.

Epidemiology

Creeping eruption, which is prevalent in many tropical and subtropical countries of the world is caused by the filariform larvae of A. braziliense, which lives as an adult in the intestine of humanity’s two close animal friends, the dog and the cat. Hence, their feces are ever available to pollute the human environment. Sea and fresh-water batehrs who bask in the sun on the beach while their dogs pollute it.

Pathology and Symptomatology

• indurated, reddish, itchy papules develop

• linear, slightly elevated, erythematous, serpiginous, intracutaneous tunnels are produced by the larvae

• vesicles form along the course of the tunnels, and the surface becomes dry and crusty

• itching is intense and scratching may lead to secondary infection

Diseases

• Enterobiasis

• Oxyuriasis

• Pinworm

• Seatworm

Infection of the same or another person may be affected by (1) the important hand-to-mouth transmission from scratching the perianal areas of from handling contaminated Fomites, (2) inhalation of airborne eggs in dust, (3)

rarely, retroinfection through the anus. Eggs hatch in the perianal region and the larvae migrate back into the large intestine. Heavy infections are affected by the transference of eggs from perianal region to the hands and thence to the mouth directly or through contaminated food.

Pathology and Symptomatology

E. vermicularis is relatively innocuous and rarely produces serioous lesions. The clinical symptoms are due largely to the perianal, perineal, and vaginal irritation caused by the migrations of the gravid female worm, and less frequently to the intestinal activities of the parasite. The local pruritus and discomfort produce a cahin of secondary reflex symptoms that tend to debilitate the patient – this debilitation is due to disturbed sleep.

Diagnosis

Pinworm infection is suspected in children who show perianal itching, insomnia, and restlessness. Diagnosis is made by finding the adult worms or eggs. Often the first evidence of infection is the discovery of the adult worms on the feces or in the perianal region.