What is the life cycle and treatment of Strongyloides stercoralis?

From the Guidelines

Strongyloides stercoralis has a complex life cycle involving both free-living and parasitic stages, and the most effective treatment is ivermectin, administered as 200 mcg/kg/day orally for 1-2 days for uncomplicated infections, as recommended by the most recent guidelines 1. The infection begins when filariform larvae in soil penetrate human skin, enter the bloodstream, and migrate to the lungs. They then ascend the respiratory tract, are swallowed, and reach the small intestine where adult females produce eggs that hatch into rhabditiform larvae. These larvae can either be excreted in stool or transform into infectious filariform larvae within the intestine, causing autoinfection that allows the parasite to persist for decades. Some key points to consider in the treatment of strongyloidiasis include:

• For immunocompromised patients or disseminated disease (hyperinfection syndrome), extended therapy with ivermectin 200 mcg/kg/day for 7-14 days is recommended, as stated in the British Society of Gastroenterology consensus guidelines 1.
• Alternative treatments include albendazole 400 mg twice daily for 7 days, though it's less effective than ivermectin, as noted in the UK guidelines for the investigation and management of eosinophilia in returning travellers and migrants 1.
• Post-treatment stool examinations should be performed at 2-4 weeks to confirm cure, and preventive treatment is crucial before initiating immunosuppressive therapy in patients from endemic areas, as immunosuppression can trigger potentially fatal hyperinfection syndrome, as warned by the Infectious Diseases Society of America (IDSA) and the American Society of Tropical Medicine and Hygiene (ASTMH) 1. The parasite's ability to autoinfect makes complete eradication essential, as even low-level infections can persist indefinitely and potentially become life-threatening if the host becomes immunocompromised. It is also important to note that:
• Blood eosinophilia is a common finding in patients with S. stercoralis infection, though it is not present in all patients, as mentioned in the British Society of Gastroenterology consensus guidelines 1.
• S. stercoralis serology is unreliable in immunocompromised individuals, making diagnosis and treatment more challenging in this population, as stated in the same guidelines 1.

From the FDA Drug Label

The patient should be reminded of the need for repeated stool examinations to document clearance of infection with Strongyloides stercoralis. The life cycle of Strongyloides stercoralis is not directly described in the provided drug labels. However, the labels do mention that ivermectin is active against the intestinal stages of Strongyloides stercoralis, and that repeated stool examinations are necessary to document clearance of the infection 2, 2, 2. Treatment of strongyloidiasis typically involves a single dose of ivermectin, but retreatment may be necessary in some cases, especially in immunocompromised patients 2, 2.

From the Research

Life Cycle of Strongyloides stercoralis

• The life cycle of Strongyloides stercoralis is complex and unique among human-infecting nematodes 3
• It involves an internal autoinfective cycle with autoinfective larvae randomly migrating through tissue, parthenogenesis, and the potential for lifelong infection in the host 3
• The parasite also has a limited external cycle with a single generation of free-living adults 3
• The life cycle of S. stercoralis is characterized by its ability to produce both parasitic and bacterial infections at remote organ sites, often resulting in nosocomial infections 4

Treatment of Strongyloides stercoralis

• The treatment of choice for Strongyloides stercoralis infection is ivermectin, which has replaced thiabendazole due to better tolerance 5
• Other treatment options include thiabendazole and albendazole 5
• In cases of hyperinfection or disseminated disease, treatment with antihelminthic drugs such as ivermectin, thiabendazole, or albendazole may be effective, but data are limited to case reports or case series 5
• Concomitant bacterial infections must be treated with appropriate antimicrobial agents 4

Clinical Manifestations and Diagnosis

• Strongyloidiasis can occur without symptoms or as a potentially fatal hyperinfection or disseminated infection 6
• Diagnosis can be difficult and often requires multiple stool samples to identify the larvae 5
• Clinical suspicion remains an important component of the evaluation, especially in immunocompromised patients 7
• Screening tests have limitations, and emphasis must be placed on screening and treatment before transplantation or immunosuppression 7