Treatment of Filariasis
Critical Pre-Treatment Screening Required
Before initiating any treatment for filariasis, you must exclude co-infections with onchocerciasis and loiasis, as failure to do so can result in fatal encephalopathy, blindness, and severe neurological complications. 1, 2, 3
Mandatory Screening Steps:
Obtain skin snips for microscopy and perform slit lamp examination to exclude onchocerciasis, as diethylcarbamazine (DEC) can cause severe reactions including blindness, hypotension, pruritus, and erythema in co-infected patients 2, 3
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 2, 3
Obtain daytime blood microscopy (10 am to 2 pm) using 20 ml citrated blood samples to screen for Loa loa, as DEC can cause fatal encephalopathy in patients with high Loa loa microfilarial loads (>1000/ml) 1, 2, 4
If Loa loa is detected, determine the exact microfilarial count to stratify risk, as patients with >1000/ml are at highest risk of severe adverse events including encephalitis and death 2, 4
Primary Treatment Regimen for Lymphatic Filariasis
For lymphatic filariasis (Wuchereria bancrofti, Brugia malayi, Brugia timori) after excluding co-infections, treat with diethylcarbamazine (DEC) 6 mg/kg orally in 3 divided doses for 14 days PLUS doxycycline 200 mg orally daily for 6 weeks. 1, 2, 3
Rationale for Combination Therapy:
DEC targets microfilariae but has limited macrofilaricidal activity, while doxycycline eliminates the Wolbachia endosymbiont from adult worms, providing superior antiparasitic efficacy 2, 5
Doxycycline 200 mg daily for 6 weeks showed 50-60% macrofilaricidal effects and 80-90% reduction of adult worms in bancroftian filariasis, with additional benefits of reducing lymph vessel dilation and halting lymphoedema progression 5
Multi-dose DEC regimens are significantly more effective than single-dose therapy, achieving 99.6% reduction in microfilaremia versus 85.7% with complete clearance in 75% versus 23.1% at 12 months 6
Alternative Regimen in Onchocerciasis Co-Endemic Areas
In areas where onchocerciasis is co-endemic and DEC is contraindicated, use ivermectin 200 μg/kg as a single oral dose PLUS albendazole 400 mg as a single oral dose. 2, 3, 7
Important Limitations:
Ivermectin has no activity against adult Onchocerca volvulus parasites, which reside in subcutaneous nodules 7
This regimen is less effective than DEC/doxycycline for lymphatic filariasis but prevents severe adverse reactions in onchocerciasis co-infection 2, 8
Ivermectin should be taken with food, as bioavailability increases 2.5-fold with high-fat meals 3
Special Treatment Algorithm for Loiasis Co-Infection
If Loa loa microfilariae are detected, treatment depends on microfilarial load: 1, 4
High Microfilarial Load (>1000/ml):
First screen for strongyloidiasis before using corticosteroids 1, 4
Start prednisolone and administer albendazole 200 mg orally twice daily for 21 days 1, 4
Check daytime blood microscopy at day 28, repeat albendazole course as needed until microfilarial load decreases to <1000/ml 1
Then treat with DEC using escalating regimen with prednisolone cover 1, 4
Low Microfilarial Load (<1000/ml) or Negative:
DEC can be given without steroid cover using the following escalating regimen: 1, 4
- 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
Repeat daytime blood microscopy at 6 and 12 months after the last negative sample to monitor for relapse 1, 4
Special Populations and Contraindications
Pregnancy:
Ivermectin can be used in second and third trimesters with no observed teratogenicity in limited human data 2, 3
Breastfeeding:
- Ivermectin is excreted in very low levels in breast milk and is likely compatible with breastfeeding 2, 3
Pediatric Patients:
Monitoring Requirements During Treatment
Monitor full blood counts and liver function tests every 2 weeks for 3 months, then monthly if within normal range for prolonged courses. 2, 3
Adverse Reaction Monitoring:
Watch for fever, lymphadenitis, and lymphangitis during DEC and doxycycline treatment 2, 3
Prednisolone is usually given alongside DEC when microfilaraemia is present to reduce inflammatory reactions 3
Follow-Up Testing:
Repeat blood microscopy at 6 and 12 months after last negative sample for loiasis 1, 4
Follow-up serological testing in 3-6 months may be warranted to ensure complete parasite clearance in lymphatic filariasis 2
Critical Drug Interactions
Azithromycin significantly increases serum ivermectin concentrations, and caution is advised with co-administration 2, 3
Common Pitfalls to Avoid
Never use DEC without first excluding onchocerciasis and loiasis, as this can cause fatal complications 1, 2, 3, 4
Do not rely solely on single-dose therapy, as most treated subjects fail to completely clear microfilariae after a single dose 6, 9
Do not refrigerate blood samples for nocturnal microscopy (10 pm to 2 am), as this can affect microfilarial viability 1
Remember that blood collection timing is critical: nocturnal (10 pm to 2 am) for W. bancrofti and B. malayi, but daytime (10 am to 2 pm) for Loa loa 2, 4