Tissue Parasites
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Direct answer
Microfilariae of Wuchereria bancrofti circulate in peripheral blood with nocturnal periodicity — highest between 10 pm and 2 am, matching the biting habit of the Culex quinquefasciatus vector — so the classical diagnostic is a night blood smear or, in daylight, a provoking dose of diethylcarbamazine. It causes most Indian lymphatic filariasis (Brugia malayi contributes a smaller southern and north-eastern share), its recurrent adenolymphangitis hardening into lymphoedema, elephantiasis and hydrocele; the national response is annual mass drug administration with diethylcarbamazine, with the World Health Organization's triple-drug ivermectin–diethylcarbamazine–albendazole regimen recommended to accelerate elimination. Around it live the other tissue parasites the exam keeps: Brugia malayi with its two-caudal-nuclei microfilaria, tropical pulmonary eosinophilia, guinea worm (eradicated from India), and the tissue-migrating larval and helminthic syndromes of Trichinella, Toxocara, hydatid and schistosome cousins.
What you must remember
- Microfilaria bench card: bancrofti — sheathed, tail free of nuclei; Brugia malayi — sheathed with two discrete nuclei at the tail tip; both spotted on thick night films, or by the membrane filtration and antigen-based immunochromatographic tests now preferred for surveys.
- Clinical ladder: acute adenolymphangitis with fever along a lymphatic vessel; chronic lymphoedema of limb or scrotum, hydrocele (the commonest chronic manifestation in Indian men), chyluria; bacterial superinfection accelerates elephantiasis, so hygiene and entry-lesion care are part of management alongside elevation and exercise.
- Treatment: diethylcarbamazine kills microfilariae and some adult worms; doxycycline (against Wolbachia) serves special settings; chronic lymphoedema needs limb care, not more drug courses — hydrocele goes to surgery.
- Tropical pulmonary eosinophilia (Weingarten syndrome): paroxysmal nocturnal cough, wheeze, extreme eosinophilia and high immunoglobulin E with barely detectable microfilaraemia — a hypersensitivity to microfilariae in the lung, classically responsive to diethylcarbamazine.
- Mass drug administration under India's lymphatic filariasis elimination programme: annual single-dose diethylcarbamazine (with albendazole in various campaign formats), moving toward the World Health Organization's triple-drug ivermectin–diethylcarbamazine–albendazole regimens in eligible districts.
- Dracunculus medinensis (guinea worm): emerges through a painful skin blister, transmitted via cyclops in step-wells; India has reported no indigenous cases since the late 1990s.
- Tissue migrants for contrast: Trichinella spiralis from pork — myalgia, periorbital oedema, eosinophilia, larvae coiled in striated muscle; Toxocara causing visceral and ocular larva migrans in children with pica; Echinococcus granulosus forming hydatid cysts in liver and lung in sheep-rearing tracts, treated with albendazole plus careful surgery (spillage risks anaphylaxis).
- Schistosomiasis is not endemic in India — a stem with haematuria plus freshwater swimming is asking for a travel history.
A leg that keeps swelling, read properly
A man from eastern Uttar Pradesh reports two decades of recurrent fever with red, painful cords along his groin, and now a woody swelling of the left leg with thickened skin. The examination maps the lymphatic failure: non-pitting oedema, skin folds deepened, and interdigital entry lesions that matter more than any microfilaria at this stage, because acute bacterial lymphangitis drives the progression. A night smear or antigen test confirms past or current infection where needed, ultrasound may show live adult worms (the filarial dance sign); management divides honestly: drugs for active infection, and limb care — washing, drying, entry-lesion treatment, elevation, exercise, footwear — for the lymphoedema drugs cannot reverse. Hydrocele goes to surgery. His village receives mass drug administration regardless of individual status, because elimination arithmetic is done at district level, not the bedside.
Where students slip
Periodicity gets wasted: "nocturnal periodic" is the phrase that explains both the night smear and the Culex vector's habits, and candidates forget that a daytime negative smear does not exclude infection — the diethylcarbamazine provocation test or antigen assay answers it. Second, Brugia microfilariae are identified by their two terminal nuclei; every sheathed microfilaria gets labelled bancrofti by tired examinees. Third, tropical pulmonary eosinophilia is misfiled as asthma with a high eosinophil count — the specific treatable answer is diethylcarbamazine, and the viva probes the mechanism of pulmonary hypersensitivity with amicrofilaraemic blood. Fourth, guinea-worm and filariasis programmes are confused: India interrupted dracunculiasis transmission by the late 1990s, while lymphatic filariasis elimination through mass drug administration continues — the two national stories belong to different decades and different drugs.
Frequently asked questions
Why is a night blood smear used for Wuchereria bancrofti?
The microfilariae show nocturnal periodicity, peaking between about 10 pm and 2 am in synchrony with the night-biting Culex quinquefasciatus vector; daytime sampling needs a diethylcarbamazine provocation test or antigen detection.
How is chronic filarial lymphoedema managed?
Limb hygiene including washing, drying and treating interdigital entry lesions, elevation, exercises and footwear — drug courses address active infection but do not reverse lymphoedema, and hydrocele requires surgery.
What is tropical pulmonary eosinophilia?
A hypersensitivity to microfilariae trapped in the pulmonary circulation — paroxysmal nocturnal cough and wheeze with marked eosinophilia and high immunoglobulin E but scanty microfilaraemia — classically responding to diethylcarbamazine.
What is the mass drug administration strategy for filariasis in India?
Annual single-dose diethylcarbamazine to entire endemic communities (with albendazole in campaign formats), with movement toward the World Health Organization's triple-drug ivermectin–diethylcarbamazine–albendazole combination in eligible districts.