Diagnosis and Treatment of Filariasis
Diagnostic Approach
For lymphatic filariasis, diagnosis relies on nocturnal blood microscopy (10 pm to 2 am) using Giemsa-stained thick and thin films, with examination of concentrated blood specimens (Knott, Nuclepore filtered blood, or buffy coat) to increase sensitivity in cases of low parasitemia. 1
Lymphatic Filariasis (Wuchereria bancrofti, Brugia malayi)
- Blood collection timing is critical: Microfilariae circulate nocturnally for W. bancrofti and B. malayi, requiring blood draws between 10 pm and 2 am 1
- Repeat examinations may be necessary due to low parasitemia, with up to 3 exams over 12-24 hour intervals before ruling out infection 1
- Serology is available but does not differentiate between filarial species 1
- Antigen detection tests using finger-prick blood can be performed during daytime hours, offering practical advantages in endemic settings 2
- Ultrasound imaging can visualize adult worms in lymphatic vessels, detecting early infections before symptoms appear 2
Onchocerciasis (Onchocerca volvulus)
- Skin snip microscopy is the primary diagnostic method: incubate razor-thin skin samples (with no visible blood) from areas near nodules in normal saline at 37°C and examine microscopically for microfilariae 1
- Slit lamp examination can identify microfilariae in the eye, though this is rarely positive in travelers 1
- Histopathologic examination of resected nodules (onchocercomas) or skin biopsies can identify microfilariae and adult worms 1
- Serology is available from reference laboratories but does not differentiate between filarial species 1
Loiasis (Loa loa)
- Daytime blood microscopy (10 am to 2 pm) using 20 ml citrated blood samples is the gold standard, as microfilariae circulate during daylight hours 3
- Microfilarial count determination is essential for risk stratification before treatment 3
Critical Pre-Treatment Screening Algorithm
Before initiating any treatment for filariasis, you must exclude co-infections with Loa loa and onchocerciasis to prevent life-threatening complications including fatal encephalopathy and severe neurological adverse events. 4, 3
Mandatory Screening Steps:
Screen for Loa loa co-infection: Obtain daytime blood microscopy (10 am to 2 pm) using 20 ml citrated blood; if positive, determine microfilarial count 4, 3
- High microfilarial load (>1000/ml) contraindicates ivermectin and DEC due to risk of fatal encephalopathy 3
Screen for onchocerciasis co-infection: Obtain skin snips for microscopy and perform slit lamp examination 4, 3
Screen for strongyloidiasis before using corticosteroids in any treatment regimen 3
Treatment Regimens
Lymphatic Filariasis (W. bancrofti, Brugia spp.)
The primary treatment is diethylcarbamazine (DEC) 6 mg/kg in 3 divided doses for 14 days plus doxycycline 200 mg daily for 6 weeks, after excluding onchocerciasis and loiasis co-infection. 4
Alternative Regimen (in onchocerciasis co-endemic areas):
- Ivermectin 200 μg/kg single dose plus albendazole 400 mg single dose when DEC is contraindicated 4
- This combination is FDA-approved for onchocerciasis but used off-label for lymphatic filariasis in co-endemic regions 5
Doxycycline Mechanism:
- Targets Wolbachia endosymbionts: 200 mg daily for 4-6 weeks achieves 80-90% reduction of adult worms in bancroftian filariasis 6
- Improves disease outcomes: Reduces lymph vessel dilation, hydrocele, and can halt or reverse early-stage lymphedema 6
Administration Details:
- Ivermectin should be taken with food as bioavailability increases 2.5-fold with high-fat meals 4
- Albendazole should be taken with or after food 4
- Prednisolone is usually given alongside DEC when microfilaraemia is present to reduce inflammatory reactions 4
Onchocerciasis (O. volvulus)
Treat with doxycycline 200 mg once daily for 6 weeks to target Wolbachia, starting ivermectin 200 μg/kg monthly for 3 months on day one of doxycycline. 1
- Repeat ivermectin every 3-6 months until asymptomatic, then annually if necessary for several years 1
- Seek urgent ophthalmology assessment before treatment 1
- Exclude loiasis prior to treatment and seek expert advice in co-infection 1
- Note: Ivermectin has no activity against adult Onchocerca volvulus parasites; it targets microfilariae only 5
Loiasis (Loa loa)
Treatment depends on microfilarial load:
High Load (>1000/ml):
- Start prednisolone (after screening for strongyloidiasis) 3
- Albendazole 200 mg twice daily for 21 days to reduce microfilarial load 3
Low Load (<1000/ml) or Negative:
- DEC escalating regimen: 50 mg single dose day 1,50 mg three times daily day 2,100 mg three times daily day 3,200 mg three times daily day 4, then continue 200 mg three times daily for 21 days 3
Special Populations
Pregnancy:
- Avoid DEC in pregnancy and seek expert consultation 4
- Ivermectin can be used in second and third trimesters with no observed teratogenicity in limited human data 4
Breastfeeding:
- Ivermectin is excreted in very low levels in breast milk and is likely compatible with breastfeeding 4
Pediatrics:
- Children aged 12-24 months should be discussed with an expert before treatment 4
- Children over 24 months can receive standard dosing 4
Monitoring Requirements
- FBC/LFTs every 2 weeks for 3 months, then monthly if within normal range for prolonged courses 4
- Monitor for adverse reactions including fever, lymphadenitis, and lymphangitis during DEC and doxycycline treatment 4
- Repeat blood microscopy at 6 and 12 months after last negative sample to monitor for relapse in loiasis 3
- Follow-up serological testing in 3-6 months may be warranted to ensure complete parasite clearance in lymphatic filariasis 7