Treatment of Filariasis
Critical Pre-Treatment Screening is Mandatory
Before initiating any treatment for filariasis, you must screen for Loa loa and onchocerciasis co-infections, as failure to do so can result in fatal encephalopathy or severe neurological complications including blindness. 1, 2
Screening Algorithm:
- Obtain daytime blood microscopy (10 am to 2 pm) using 20 ml citrated blood samples to screen for Loa loa, as microfilariae circulate during daylight hours 1, 3
- Perform skin snip microscopy by incubating razor-thin skin samples in normal saline at 37°C to exclude onchocerciasis 1
- Conduct slit lamp examination to identify microfilariae in the eye for onchocerciasis screening 1
- If skin snips and slit lamp are unavailable, administer a test dose of DEC 50 mg to precipitate a mild Mazzotti reaction if onchocerciasis is present 1
Treatment for Lymphatic Filariasis (W. bancrofti, B. malayi)
Primary Regimen (After Excluding Co-Infections):
The CDC recommends diethylcarbamazine (DEC) 6 mg/kg divided into 3 doses daily for 14 days PLUS doxycycline 200 mg daily for 6 weeks. 1
- This combination targets both microfilariae and adult worms through the Wolbachia endosymbiont 4
- Doxycycline at 200 mg/day for 6 weeks achieves 80-90% reduction of adult worms in bancroftian filariasis 4
- When microfilaraemia is present, prednisolone should be given alongside DEC to reduce inflammatory reactions 2
Alternative Regimen (In Onchocerciasis Co-Endemic Areas):
Use ivermectin 200 μg/kg single dose PLUS albendazole 400 mg single dose if DEC is contraindicated due to onchocerciasis co-infection risk 1, 2
- Ivermectin should be taken with food, as bioavailability increases 2.5 times with high-fat meals 2, 5
- Albendazole should be taken with or after food 2
- This combination reduces microfilariae by 85-100% at 12-24 months 6
Critical caveat: Ivermectin has no activity against adult Onchocerca parasites and limited activity against adult lymphatic filariasis worms 5, 6
Treatment for Onchocerciasis (O. volvulus)
Start doxycycline 200 mg once daily for 6 weeks, beginning ivermectin 200 μg/kg monthly for 3 months on day one of doxycycline. 1
- Doxycycline 200 mg/day for 4-6 weeks shows 50-60% macrofilaricidal effects against adult worms 4
- Ivermectin alone achieves 83.2% reduction in skin microfilariae at 3 days and 99.5% at 3 months 5
- Never use DEC in onchocerciasis as it causes severe Mazzotti reactions including blindness, hypotension, pruritus, and erythema 1, 3
Treatment for Loiasis (Loa loa)
Treatment Algorithm Based on Microfilarial Count:
The exact microfilarial count must be determined before any treatment, as this is the single most important factor in preventing fatal encephalopathy. 1, 3
High Microfilarial Load (>1000/ml):
- Screen for strongyloidiasis before using corticosteroids 3
- Start prednisolone (exact dosing not standardized across guidelines, but mandatory specialist consultation required) 3
- Administer albendazole 200 mg twice daily for 21 days to reduce microfilarial load before definitive treatment 1, 3
- Albendazole can be dosed from 400 mg daily up to 800 mg daily for 10-28 days depending on microfilarial burden 3
Low Microfilarial Load (<1000/ml) or Negative:
Use escalating DEC regimen: 3
- Day 1: 50 mg single dose
- Day 2: 50 mg three times daily
- Day 3: 100 mg three times daily
- Day 4: 200 mg three times daily
- Days 5-21: Continue 200 mg three times daily
Critical warning: DEC can cause encephalopathy with high mortality in patients with high Loa loa microfilarial loads 1, 3, 5
Special Populations
Pregnancy:
- Avoid DEC in pregnancy and seek expert consultation 1, 2
- Ivermectin can be used in second and third trimesters with no observed teratogenicity in limited human data 1, 2, 5
Breastfeeding:
- Ivermectin is excreted in very low levels in breast milk and is likely compatible with breastfeeding 1, 2, 5
Pediatrics:
- Children aged 12-24 months require expert consultation before treatment 1, 2
- Children over 24 months can receive standard dosing 1, 2
- Safety and effectiveness in children weighing less than 15 kg have not been established 5
Monitoring Requirements
Monitor full blood counts and liver function tests every 2 weeks for 3 months, then monthly if within normal range for prolonged courses. 1, 2
- Monitor for adverse reactions including fever, lymphadenitis, and lymphangitis during DEC and doxycycline treatment 1, 2
- Repeat blood microscopy at 6 and 12 months after last negative sample to monitor for relapse in loiasis 1, 3
- At least three stool examinations should be conducted over three months following treatment for strongyloidiasis to ensure eradication 5
- Follow-up serological testing in 3-6 months may be warranted to ensure complete parasite clearance in lymphatic filariasis 1
Critical Drug Interactions and Warnings
- Azithromycin significantly increases serum ivermectin concentrations—use caution with co-administration 1, 2
- Post-marketing reports of increased INR have been rarely reported when ivermectin was co-administered with warfarin 5
- Alcohol may worsen side effects 1, 2
- Patients with hyperreactive onchodermatitis (sowda) may experience severe adverse reactions, especially edema and aggravation of onchodermatitis 5
Common Pitfalls to Avoid
- Never initiate DEC or ivermectin without first determining Loa loa microfilarial count—this is the most critical step to prevent fatal encephalopathy 3
- Never use DEC in patients with onchocerciasis co-infection without proper screening, as it causes severe Mazzotti reactions including blindness 1, 2
- In non-endemic areas where reinfection is impossible, recrudescence of Strongyloides larvae can occur up to 106 days following ivermectin therapy—repeat stool examinations are essential 5
- Consider apheresis for extremely high Loa loa loads (>8,000-30,000 mf/ml) as an adjunct to reduce microfilarial burden 3
- Mandatory specialist consultation with tropical medicine or parasitology is required before treating any patient with confirmed or suspected Loa loa infection 3