Strongyloides stercoralis - Host Immunity, Clinical Manifestation
Host immunity against Strongyloides stercoralis
Since an intact immune system is absolute for the control of Strongyloides stercoralis infection, autoinfection is mostly seen in patients with suppressed cell-mediated immunity (CMI). Hyperinfection syndrome, frequent auto-infection which leads to increased worm load in the intestinal lumen, occurs in immunocompromised people.
Serum antibodies including serum IgG, IgA, IgM and eosinophils are believed to provide host immune protection against the Strongyloides stercoralis infection. The antibody and eosinophil levels are decreased in severe infections.
Clinical Manifestations of Strongyloides stercoralis
Clinical manifestations of strongyloidiasis, caused by Strongyloides stercoralis, vary according to the host immune system.
In an immunocompetent host, the parasite may persist in the host for years without producing any or minimal symptoms.
In an immunocompromised host, the parasite can cause life-threatening infections such as hyperinfection syndrome and disseminated strongyloidiasis.
Cutaneous phase
cutaneous phase involves invasion of the skin by Strongyloides stercoralis filariform larvae
within 24 hours at the site of entry the feet, manifestations such as petechial haemorrhage, congestion, and oedema occur
associated with intense itching
in previously sensitized patients, larva currens occur which is caused by external auto-infection and is a local allergic reaction to the akin penetrating larvae
in larva currens clinical syndromes such as linear pruritic, erythematous, and serpiginous lesions appear around the site of invasion and the route of larval migration
these parasitic lesions start around the perianal area and then extend to the buttocks, upper thighs, and lower abdomen
the spread of these lesions is at the rate of 5 mm to 10 mm per hour
Pulmonary phase
pulmonary phase occurs when the Strongyloides stercoralis larvae migrate through the lungs
common clinical syndromes include dyspnoea, wheezing, low-grade fever, cough production with blood-streaked sputum
other syndromes are Loeffler-like syndromes with pneumonitis, high-grade eosinophilia, and bronchopneumonia, pneumonia, or asthma
in serious cases, disseminated strongyloidiasis occurs
eggs and rhabditiform larvae can be demonstrated in the sputum
Intestinal phase
intestinal phase involves invasion of the intestine by adult Strongyloides stercoralis
in acute cases, clinical syndromes which are common include profuse water and mucoid diarrhoea, abdominal discomfort, indigestion, nausea, vomiting
in chronic cases, clinical syndromes include diffuse abdominal pain, vomiting, nausea, diarrhoea with occasional blood, and hyperactive or hypoactive bowel movement
in children, severe cases of malabsorption of fat and protein may result in steatorrhoea, hypoalbuminaemia, chronic diarrhoea, oedema of the lower and upper limbs, and cachexia
Hyperinfection syndrome
hyperinfection syndrome is a clinical form of strongyloidiasis caused by the infective Strongyloides stercoralis filariform larvae
can be defined as frequent auto-infection which leads to increased worm load in the intestinal lumen
does not include the dissemination to extra-intestinal sites
common in patients taking immunosuppressive drugs such as corticosteroids, tacrolimus, radiation, chemotherapy
also common in organ transplant patients, and in patients with lymphomas, leukaemia, autoimmune disease (lupus), AIDS, HTLV-1
Disseminated strongyloidiasis
disseminated strongyloidiasis is a clinical form caused by the infective Strongyloides stercoralis filariform larvae
the larvae are widely disseminated outside the intestinal tract and on organs such as the heart, central nervous system (CNS), urinary organs, and endocrine organs
clinical syndromes include diffuse pulmonary infiltrates, gram-negative septicemia, oedema, severe diarrhoea, paralytic ileus
CNS invasion leads to meningitis or brain abscess
prognosis is poor and mortality is high