In Sri Lanka, filariasis is managed by infectious diseases. Lymphatic filariasis is a chronic mosquito-borne parasitic infection caused by thread-like nematodes (Wuchereria bancrofti, Brugia malayi, and Brugia timori) that lodge in human lymphatic vessels, where adult worm pairs live for 5-7 years and release millions of microfilariae into the bloodstream. WHO estimates that 859 million people across 50 countries remain at risk and roughly 51 million are infected, with India accounting for nearly 40% of the global burden.
Filariasis (ICD-10: B74) is a group of parasitic infections caused by filarial nematode worms transmitted by blood-feeding arthropods. Lymphatic filariasis — the dominant clinical syndrome — is caused by three species: Wuchereria bancrofti (responsible for around 90% of cases globally, transmitted predominantly by Culex quinquefasciatus and Anopheles mosquitoes), Brugia malayi (Southeast Asia, parts of India, transmitted by Mansonia and Anopheles), and Brugia timori (Lesser Sunda islands of Indonesia). Adult worms 5-10 cm long inhabit lymphatic vessels and lymph nodes, where mating pairs produce microfilariae 200-300 micrometers long that circulate in peripheral blood — generally with strict nocturnal periodicity for with. bancrofti and B.
The key symptoms of Filariasis are: Painless rubbery enlargement of inguinal, axillary, or epitrochlear lymph nodes from adult worm nesting in draining lymphatic vessels., Episodes of high fever (39-40 °C), rigors, and exquisitely tender red streaks tracking from a limb into a swollen lymph node — acute dermatolymphangioadenitis (ADL), typically lasting 3-7 days and recurring every few weeks to months., Painless, progressive scrotal swelling that transilluminates — hydrocele caused by lymphatic obstruction at the spermatic cord; bilateral in roughly one-third of severely affected men., Non-pitting swelling of one or both legs that progresses from soft, reversible edema (Stage 1) to hyperkeratotic, fibrotic, fissured skin with deep skinfolds and mossy lesions (Stage 4 elephantiasis)., Milky-white urine, particularly after fatty meals, with or without microscopic hematuria — chyluria from rupture of dilated lymphatics into the urinary tract., Nocturnal paroxysmal cough, wheeze, and breathlessness in a young adult from an endemic region — tropical pulmonary eosinophilia, often misdiagnosed as asthma., Acute funiculitis, epididymitis, or orchitis with painful scrotal swelling separate from hydrocele..
Diagnosis combines clinical pattern recognition with parasitological or antigen tests. In active microfilaremia, a thick blood film stained with Giemsa and collected during the species-specific peak periodicity (typically between 10 p.m. and 2 a.m. for W. bancrofti) reveals microfilariae and identifies the species by sheath, tail, and nuclear features. Concentration techniques (Knott's method, membrane filtration) improve sensitivity in light infections. The rapid Filariasis Test Strip and circulating filarial antigen (CFA) assay (ICT card and Og4C3 ELISA) detect Wuchereria bancrofti antigen at any time of day without nocturnal sampling and are now standard for both diagnosis and population-level mapping; they do not, however, detect Brugia species. Anti-filarial antibody serology (IgG4 to BmR1 or BmA antigens) is useful for Brugia and for low-burden infections in travelers. Scrotal ultrasound demonstrates the pathognomonic filarial dance sign — characteristic chaotic motion of adult worms inside dilated lymphatic vessels — and is useful for confirming live worms before treatment. PCR can detect parasite DNA in blood, urine, and tissue when microscopy and antigen tests are negative. In suspected tropical pulmonary eosinophilia, the diagnostic triad is residence in or travel from an endemic area, peripheral eosinophilia above 3,000/µL with elevated IgE, and dramatic clinical response to DEC.
Outlook depends mainly on how early the infection is detected and treated. With one or two annual rounds of preventive chemotherapy (DEC + albendazole or IDA), more than 95% of microfilaremic individuals clear circulating microfilariae and no longer transmit infection. Adult worms can take 2-4 years to die without doxycycline; with doxycycline 4-6 weeks, sterility and death of adult worms occur within 12-18 months. Early lymphedema (Stage 1-2) often regresses with combined antifilarial treatment and rigorous limb hygiene; Stage 3-4 elephantiasis is largely irreversible, but acute attacks fall by 80% and quality of life improves substantially with structured morbidity-management programmes. Hydrocele responds dramatically to surgery, with restoration of function in over 90%. Tropical pulmonary eosinophilia has an excellent prognosis if treated early — over 90% recover full pulmonary function with DEC — but delayed treatment leaves a fixed restrictive pattern in roughly 20%. Population-level elimination is feasible: 19 countries have been verified by WHO as having eliminated lymphatic filariasis as a public-health problem (2024 data), and India is on track for verification in several states.
Tropical medicine and infectious disease physicians confirm species, choose the safest treatment combination in regions where onchocerciasis or Loa loa coexist, and arrange follow-up parasitology. Lymphology, vascular surgery, urology, and physiotherapy services are essential for established hydrocele, advanced lymphedema, and disability rehabilitation.
Find specialists →Microfilariae cleared within 1-2 weeks of DEC or IDA. ADL attacks decrease in frequency from monthly to once or twice yearly after 3-6 months of consistent skin hygiene. Early-stage lymphedema improves within 6-12 months. Adult worms killed by doxycycline die over 12-24 months. Tropical pulmonary eosinophilia resolves within 2-3 weeks of DEC. Hydrocelectomy recovery: return to work in 1-2 weeks, full healing in 6 weeks.
Daily walking, swimming in clean water, yoga, and gentle resistance training all improve lymphatic flow and reduce limb volume. Avoid heavy weight-bearing exercise during acute ADL attacks. Limb-specific exercises taught by a lymphedema therapist (toe-flexion, ankle-pumping, calf-pumping) used while wearing compression are particularly effective.
Look for a clinician based in or trained at a centre involved in WHO-endorsed elimination programmes — for example, ICMR-VCRC in India, Liverpool School of Tropical Medicine, or US CDC parasitic disease branch. For chronic disease, a multidisciplinary clinic with lymphology, urology, dermatology, and physiotherapy outperforms single-specialty care.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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