What is the diagnosis and treatment for Loa loa infection?

Diagnosis and Treatment of Loa loa Infection

Loa loa infection should be diagnosed through daytime blood microscopy and treated with diethylcarbamazine (DEC) after careful assessment of microfilarial load, with specialist consultation strongly recommended due to potential severe adverse reactions. 1

Diagnosis

Clinical Presentation

• Loa loa (African eye worm) presents with characteristic Calabar swellings (transient, migratory, painless swellings often on extremities) 2
• Visible migration of adult worms across the subconjunctival space of the eye is pathognomonic 2
• Patients may experience pruritus, urticaria, and a sensation of movement under the skin 2
• Eosinophilia is commonly present (often >30% of total white blood cells) 2

Diagnostic Testing

• Daytime blood microscopy (10 am to 2 pm) is the gold standard for diagnosis, using citrated blood samples (20 ml total volume, not refrigerated) 1
• Serological testing with Loa-specific antibody tests has high sensitivity (93.8%) but may cross-react with other filarial infections 3
• Characteristic microfilariae have a sheath and body nuclei extending to the tip of the tail 2

Treatment Algorithm

Step 1: Assess Microfilarial Load

• Determine microfilarial count in peripheral blood 1
• If microfilariae > 1000/ml: High risk of severe adverse reactions with DEC 1
• If microfilariae < 1000/ml or negative: Lower risk with DEC treatment 1

Step 2: Pre-Treatment Assessment

• Rule out co-infection with onchocerciasis through skin snips and slit lamp examination 1
• Screen for strongyloidiasis before using corticosteroids 1
• Consult with tropical medicine or parasitology specialists before initiating treatment 1

Step 3: Treatment Based on Microfilarial Load

For high microfilarial load (>1000/ml):

• Start prednisolone (after screening for strongyloidiasis) 1
• Administer albendazole 200 mg twice daily for 21 days to reduce microfilarial load 1
• Check blood microscopy at day 28 1
• Repeat albendazole course if needed until microfilarial count is <1000/ml 1
• Once microfilarial count is <1000/ml, proceed to DEC treatment with prednisolone cover 1

For low microfilarial load (<1000/ml) or negative blood film:

• DEC can be given without steroid cover 1
• DEC regimen: 50 mg single dose on day 1,50 mg three times daily on day 2,100 mg three times daily on day 3,200 mg three times daily on day 4, then continue 200 mg three times daily for 21 days 1

Step 4: Follow-up

• Repeat blood microscopy at 6 and 12 months after the last negative sample to monitor for relapse 1

Important Cautions

Risk of Severe Adverse Events

• DEC can cause encephalopathy with high mortality in patients with high microfilarial loads 1
• In patients co-infected with onchocerciasis, DEC can cause severe reactions including blindness, hypotension, pruritus, and erythema 1
• A test dose of 50 mg DEC can be used to detect onchocerciasis co-infection (will precipitate mild Mazzotti reaction if present) 1

Alternative Treatment Options

• Ivermectin (200 μg/kg) may be used to reduce microfilarial load but is not the definitive treatment for adult worms 4, 5
• Ivermectin carries risk of severe adverse events in individuals with high L. loa microfilaraemia 5
• Doxycycline has been used in other filarial infections but is not the standard treatment for loiasis 1

Special Considerations

• Loa loa is endemic in Central and West Africa, particularly in forested areas 3, 6
• Occult loiasis (no microfilaremia but with clinical symptoms) can be diagnosed with specific IgG4 serology 7
• Cross-reactivity with lymphatic filariasis rapid diagnostic tests can occur, complicating diagnosis in co-endemic areas 6, 8