EPIDEMIOLOGY

-Nomand (1876) observed minute cylindrical worms in the diarrhoiec feces and intestinal walls of some French soldiers in Cochin-China.

-these were named Strongyloides stercolaris (strongylus-round; eidos-resembling ; stercoralis-feces)

-found mainly in warm moist tropics, but may also occur in the temperate regions.

-it is common in Brazil,Columbia and in the Far East-Myanmar,Thailand, Vietnam ,Malaysia and Philippines.

LIFE CYCLE

Life Cycle:

The Strongyloides life cycle is more complex than that of most nematodes with its alternation between free-living and parasitic cycles, and its potential for autoinfection and multiplication within the host.  Two types of cycles exist:

Free-living cycle:
1)The rhabditiform larvae passed in the stool (see "Parasitic cycle" below) can either molt twice and become infective filariform larvae (direct development) or molt four times and become free living adult males and females that mate and produce eggs from which rhabditiform larvae hatch . 
2)The latter in turn can either develop into a new generation of free-living adults (as represented in ), or into infective filariform larvae .  The filariform larvae penetrate the human host skin to initiate the parasitic cycle (see below) .



Parasitic cycle:
1)Filariform larvae in contaminated soil penetrate the human skin , and are transported to the lungs where they penetrate the alveolar spaces; they are carried through the bronchial tree to the pharynx, are swallowed and then reach the small intestine . 
2)In the small intestine they molt twice and become adult female worms . 
3)The females live threaded in the epithelium of the small intestine and by parthenogenesis produce eggs , which yield rhabditiform larvae. 
4)Therhabditiform larvae can either be passed in the stool (see "Free-living cycle" above), or can cause autoinfection . 
5)In autoinfection, the rhabditiform larvae become infective filariform larvae, which can penetrate either the intestinal mucosa (internal autoinfection) or the skin of the perianal area (external autoinfection); in either case, the filariform larvae may follow the previously described route, being carried successively to the lungs, the bronchial tree, the pharynx, and the small intestine where they mature into adults; or they may disseminate widely in the body. 

mORphoLOGy

1.      Rhabditiform  (first stage larvae)

                    I.            About 0. 25 mm long

                  II.            Relatively short muscular eosophagus ending in an enlarged bulb.

2.      Female Filariform  (third stage)

                                I.            About 2.5mm long and 0.55mm in breadth

                              II.            Thin and transperant

                            III.            Long osephagus of uniform width.

                            IV.            Notched tail tip

3.      In free living phase

                                I.            Female is 1mm long

                              II.            Male is 0.7mm long

CLINICAL MANIFESTATION

Cutaneous

·         there maybe dermatitis, with erythema and itching at site of penetration

·         particularly when large number of larvae penetrate the skin

·         those sensitized by prior infection ,there maybe allergy respond

·         this may prevent larvae from entering the blood circulation , which instead migrate in skin

·         this lead to the formation of creeping eruption or larvae migrans/larvae currens

·         larvea currens=rapidly progressing linear urticarial tracks caused by migrating strongyloides larvae

Intestinal (Gastrointestinal)

·         Resemble as the peptic ulcer and malabsorption syndrome

·         Mucus diarrhea normally without blood

·         In heavy infection, the mucosa of intestine maybe combed with worm

·         -May lead to extensive sloughing, causing dysenteric stools

      .     Bloating , distension
      .    Diffuse abdominal pain

DIAGNOSIS

1.      Demonstration of the rhabditiform larvae in freshly passed stool

·         This is the most important method of specific diagnosis

·         Larvae found in stale stools have to be differentiated from larvae hatched from hookworm eggs.

·         Larvae may sometimes be present in sputum and gastric aspirates

2.      Stool culture

·         When larvae are scanty in stool

·         The larvae develop into free-living forms and multiply in charcoal culture set up with stool

·         Large number of free-living larvae and adults can be seen after 7-10 days

3.       Serological test

·         Use strongyloides or filarial antigen

·         Complement fixation, indirect haemagglutination  and ELISA

·         But the antigens are not freely available, and extensive cross reactions limit the utility of these test

4.      Radiological

·         Radiological appearances in intestinal infections are said to be characteristic

·         Helpful in diagnosis

·         Obtain a chest radiograph to reveal possible patchy alveolar infiltrates in acute strongyloidiasis

·          In severe strongyloidiasis, findings are diverse; the chest radiograph may depict diffuse interstitial infiltrates, segmental or diffuse alveolar infiltrates, or pleural effusions.

5.      Full Blood Count

·         Peripheral eosinophilia is a constant finding

·         In severe hyperinfection eosinophilia may sometimes absent