Treatment of Filariasis
Critical Pre-Treatment Screening is Mandatory
Before initiating any treatment for filariasis, you must screen for co-infections with Loa loa and Onchocerca volvulus to prevent fatal encephalopathy and severe adverse reactions. 1, 2
Screening Algorithm:
Obtain daytime blood microscopy (10 am to 2 pm) using 20 ml citrated blood to screen for Loa loa, as microfilariae circulate during daylight hours and diethylcarbamazine (DEC) can cause fatal encephalopathy in patients with high Loa loa microfilarial loads (>1000/ml) 1, 2
Perform skin snip microscopy and slit lamp examination to exclude onchocerciasis, as DEC can cause severe reactions including blindness, hypotension, pruritus, and erythema in co-infected patients 1, 2
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, 2
If Loa loa microfilariae are detected, determine the exact microfilarial count, as patients with >1000/ml are at highest risk of severe adverse events including encephalitis and death 1
Primary Treatment Regimens for Lymphatic Filariasis
Standard Regimen (Non-Endemic Onchocerciasis Areas):
Diethylcarbamazine (DEC) 6 mg/kg divided into 3 doses daily for 14 days PLUS doxycycline 200 mg once daily for 6 weeks is the recommended treatment after excluding onchocerciasis and loiasis co-infection 1, 2
This combination targets both microfilariae and adult worms through the Wolbachia endosymbiont 3
Doxycycline at 200 mg/day for 4-6 weeks shows 80-90% reduction of adult worms in bancroftian filariasis and also reduces lymph vessel dilation and hydrocele 3
When microfilaraemia is present, prednisolone is usually given alongside DEC to reduce inflammatory reactions 2
Alternative Regimen (Onchocerciasis Co-Endemic Areas):
Ivermectin 200 μg/kg as a single dose PLUS albendazole 400 mg as a single dose is the alternative where DEC is contraindicated 1, 2
This combination is safe and effective, with adverse event profiles not significantly different from placebo in non-microfilaraemic individuals who comprise 80-90% of at-risk populations 4
Ivermectin should be taken with food, as bioavailability increases 2.5-fold with high-fat meals 2, 5
Albendazole should be taken with or after food 2
Treatment for Onchocerciasis
Doxycycline 200 mg once daily for 6 weeks, starting ivermectin 200 μg/kg monthly for 3 months on day one of doxycycline 1
A 6-week regimen of 100 mg doxycycline per day sterilizes adult female Onchocerca volvulus, while 200 mg/day for 4-6 weeks reveals 50-60% macrofilaricidal effects 3
Ivermectin is active against tissue microfilariae of Onchocerca volvulus but not against the adult form 5
Treatment for Loiasis (Loa loa)
High Microfilarial Load (>1000/ml):
Prednisolone PLUS albendazole 200 mg twice daily for 21 days 1
- This approach reduces the risk of encephalopathy associated with rapid microfilarial death 1
Low Microfilarial Load (<1000/ml) or Negative:
DEC escalating regimen is recommended 1
Current treatment recommendations for loiasis show significant inconsistencies with variability in dosage protocols and low-quality evidence 6, 1
The common microfilarial threshold of 8000 microfilariae per milliliter dictates treatment strategy adjustments in some protocols 6
Critical Drug Interactions and Contraindications
Azithromycin significantly increases serum ivermectin concentrations, and caution is advised with co-administration 1, 2
Warfarin: Post-marketing reports of increased INR have been rarely reported when ivermectin was co-administered with warfarin 5
Alcohol may worsen side effects during treatment 2
In areas where lymphatic filariasis co-exists with Loa loa, progressive neurologic decline and encephalopathy within a few days of taking ivermectin have caused great concern 7
Special Populations
Pregnancy:
Ivermectin can be used in second and third trimesters with no observed teratogenicity in limited human data 1, 2
Ivermectin should not be used during pregnancy according to FDA labeling since safety has not been established, though WHO suggests it may be used in second and third trimesters 2, 5
Breastfeeding:
Ivermectin is excreted in very low levels in breast milk and is likely compatible with breastfeeding 1, 2
Treatment of mothers who intend to breast-feed should only be undertaken when the risk of delayed treatment outweighs the possible risk to the newborn 5
Pediatric Patients:
Children aged 12-24 months should be discussed with an expert before treatment 1, 2
Safety and effectiveness in pediatric patients 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
At least three stool examinations should be conducted over three months following treatment for strongyloidiasis to ensure eradication, as recrudescence can occur up to 106 days post-treatment 5
Follow-up serological testing in 3-6 months may be warranted to ensure complete parasite clearance in lymphatic filariasis 1
Common Pitfalls to Avoid
Failure to screen for Loa loa before administering ivermectin or DEC can result in life-threatening encephalitis, particularly in patients who have traveled to endemic regions of West or Central Africa 2, 5
Using DEC in onchocerciasis co-infected patients without proper screening can cause severe reactions including blindness 1, 2
Inadequate follow-up after treatment may miss recrudescence, particularly in strongyloidiasis where concentration techniques (such as Baermann apparatus) should be employed as larvae counts may be very low 5
Assuming single treatment is curative: Current drugs used for mass drug administration only temporarily clear microfilariae without killing all adult worms, and repeated courses may be necessary 7, 8
Treating immunocompromised patients (including HIV-infected) with standard regimens may be inadequate; several treatments at 2-week intervals may be required, and suppressive therapy once per month may be helpful 5