B74.3 Loiasis

Name of the Condition

• Loiasis

Summary

Loiasis is a parasitic infection caused by the nematode Loa loa, a thread-like worm. The condition is transmitted through the bite of infected deer flies (Chrysops species) and primarily affects subcutaneous tissues and the eyes. It is endemic in parts of Central and West Africa and may present with acute or chronic symptoms depending on the host response and parasite load.

Causes

Loiasis is caused by infection with the nematode Loa loa. Transmission occurs when an infected deer fly bites a human, introducing larval parasites into the bloodstream. The larvae mature into adult worms, which migrate through subcutaneous tissues and can cross the conjunctiva, producing microfilariae that circulate in the blood and are ingested by subsequent fly vectors, perpetuating the cycle.

Risk Factors

• Residence in or travel to endemic regions of Central/West Africa where Loa loa-carrying deer flies are prevalent.
• Prolonged exposure to deer fly bites, particularly in forested or rural areas.
• Lack of access to preventive measures such as insect repellent or protective clothing.
• Immunocompromised states, which may increase susceptibility to severe disease.

Symptoms

• Transient, localized swelling (Calabar swellings) that may be painful or pruritic.
• Eye involvement, including subconjunctival migration of adult worms, causing irritation or foreign body sensation.
• Asymptomatic infection in some cases, especially with low parasite loads.
• Peripheral eosinophilia (elevated eosinophil count) is common.

Diagnosis

Diagnosis is typically based on clinical presentation, including characteristic Calabar swellings or eye symptoms, and confirmed by detecting microfilariae in blood smears (often requiring concentration techniques due to low parasite density). Serologic tests or molecular assays may be used in atypical cases. Imaging or tissue biopsy is rarely needed but may be considered if other conditions are suspected.

Treatment Options

Treatment may include antiparasitic medications such as diethylcarbamazine (DEC) or ivermectin, which target microfilariae and adult worms. Corticosteroids may be used to manage inflammatory reactions (e.g., encephalopathy) in heavy infections. Management of symptoms, such as antihistamines for Calabar swellings, may also be necessary. Consultation with an infectious disease specialist is recommended for severe or complicated cases.

Prognosis and Follow-Up

Prognosis is generally good with appropriate treatment, though chronic symptoms (e.g., subcutaneous nodules) may persist. Follow-up may involve monitoring for treatment response, managing complications, and assessing for re-infection in endemic areas. Regular blood smears or serologic testing may be used to confirm clearance of microfilariae.

Complications

• Encephalopathy or neurologic symptoms in heavy infections (rare but serious).
• Chronic subcutaneous nodules or fibrosis.
• Eye damage from repeated worm migration (e.g., corneal scarring).
• Allergic reactions or hypersensitivity to dying parasites.

Lifestyle & Prevention

• Use insect repellent and wear protective clothing to reduce deer fly bites.
• Avoid outdoor activities during peak fly activity (daytime) in endemic areas.
• Sleep under bed nets if exposure is unavoidable.
• Seek prompt medical evaluation for symptoms after travel to endemic regions.

When to Seek Professional Help

Seek medical attention if you experience sudden swelling, eye irritation, or unexplained eosinophilia after travel to endemic areas. Immediate care is needed for severe symptoms like neurologic changes or vision problems.

Tips for Medical Coders

Code B74.3 is specific to loiasis and should be used when the condition is documented. Ensure documentation supports the diagnosis, including clinical findings (e.g., Calabar swellings, eye symptoms) or laboratory confirmation (e.g., microfilariae detection). Avoid coding for asymptomatic carriers unless explicitly documented. Follow guidelines for reporting parasitic infections and associated complications.