Parasitic infections affect millions of people globally, particularly in tropical and subtropical regions. Three significant parasitic diseases — onchocerciasis (commonly known as river blindness), strongyloidiasis, and scabies — vary in their causative agents, modes of transmission, clinical manifestations, and treatment protocols. Addressing these infections requires targeted therapeutic strategies to eliminate the parasites, manage symptoms, and prevent reinfection.
Onchocerciasis (River Blindness)
Cause and Transmission:
Onchocerciasis is caused by Onchocerca volvulus, a filarial nematode transmitted to humans through the bites of infected blackflies (genus Simulium). The larvae (microfilariae) migrate through the skin and eyes, causing intense itching, skin changes, and visual impairment, including blindness.
Treatment:
The primary treatment for onchocerciasis is ivermectin, which is administered orally, typically in single doses of 150–200 µg/kg every 6–12 months. Ivermectin does not kill adult worms but is highly effective at reducing microfilariae, alleviating symptoms, and decreasing transmission.
In regions where onchocerciasis is endemic, mass drug administration (MDA) of ivermectin is often implemented. Doxycycline (100 mg daily for 4–6 weeks) is also used as a complementary treatment. It targets Wolbachia, an endosymbiotic bacteria essential to the worm’s survival, gradually sterilizing and killing adult worms.
Prevention and Control:
Vector control (blackfly population reduction) and MDA programs remain crucial for disease control and potential elimination in endemic areas.
Strongyloidiasis
Cause and Transmission:
Strongyloidiasis is caused by the nematode Strongyloides stercoralis. It infects humans through skin contact with soil contaminated with infectious larvae. The parasite can cause long-term infections due to its ability to replicate within the host, leading to autoinfection. This can result in chronic symptoms or, in immunocompromised individuals, life-threatening disseminated strongyloidiasis.
Treatment:
The drug of choice for strongyloidiasis is ivermectin. The standard dosage is 200 µg/kg orally once daily for 1–2 days. In disseminated infections, treatment is extended until larvae are no longer detectable.
An alternative is albendazole, administered as 400 mg twice daily for 7 days. However, ivermectin is generally more effective and better tolerated.
Special Considerations:
In patients undergoing immunosuppressive therapy or infected with HTLV-1, strongyloidiasis should be screened and treated proactively to prevent hyperinfection syndrome.
Scabies
Cause and Transmission:
Scabies is an infestation of the skin by the mite Sarcoptes scabiei var. hominis. It spreads through prolonged skin-to-skin contact and is common in overcrowded living conditions. The mites burrow into the skin, causing intense itching, especially at night, and a characteristic rash.
Treatment:
The first-line treatment for scabies is topical permethrin 5% cream, applied over the entire body (from neck down in adults) and left on for 8–14 hours before washing off. A second application is usually recommended after 7–14 days to kill newly hatched mites.
Oral ivermectin (200 µg/kg) is an effective alternative, especially for crusted (Norwegian) scabies or in institutional outbreaks. It is typically given as two doses, one week apart. Crusted scabies may require multiple doses and combined topical and oral therapy.
Additional Measures:
All close contacts should be treated simultaneously, regardless of symptoms, to prevent reinfestation. Clothes, bedding, and towels should be washed in hot water or sealed in plastic bags for at least 72 hours.
Conclusion
Effective treatment of parasitic infections such as onchocerciasis, strongyloidiasis, and scabies hinges on accurate diagnosis, timely intervention, and community-wide strategies to prevent recurrence. Ivermectin plays a central role in the treatment of all three conditions, highlighting its broad antiparasitic activity. Public health measures such as improved sanitation, vector control, mass drug administration, and health education are essential to reduce the burden of these diseases, especially in endemic and resource-limited settings.
