Introduction - Filarial worms reside in the subcutaneous tissues, lymphatic system, or body cavities of humans. - Female worms are longer than the males. - The
Introduction - Filarial worms reside in the subcutaneous tissues, lymphatic system, or body cavities of humans. - Female worms are longer than the males. - The male worm has perianal papillae and unequal spicules but lacks a caudal bursa. - Female worms are viviparous , giving birth to larvae known as microfilariae . - Microfilariae are detected in peripheral blood or cutaneous tissues , depending on the species. - Some species have sheathed microfilariae , where the larvae retain their egg membranes. Periodicity of Microfilariae - Nocturnal periodicity : Peak circulation at night, e.g., Wuchereria bancrofti . - Diurnal periodicity : Peak circulation during the day, e.g., Loa loa . - Non-periodic : Microfilariae circulate consistently throughout the day and night, e.g., Onchocerca volvulus . - Sub-periodic : Microfilariae are present all day but peak in the late afternoon or night. Life Cycle - Definitive host : Humans. - Intermediate host : Blood-sucking arthropods (mosquitoes, blackflies, etc.). - Microfilariae develop in the arthropod , reaching the infective larval stage. - During the arthropod’s next bite, larvae are transmitted to humans. - Adult worms live for many years , while microfilariae survive for 3–36 months. Species of Filarial Worms and Their Diseases - Wolbachia spp. , an endosymbiotic bacterium in filarial worms, contributes to pathogenesis by inducing inflammatory responses. Life Cycle of Wuchereria bancrofti Development in Mosquito - Mosquito ingests microfilariae from an infected human. - Microfilariae reach the mosquito’s stomach, shed their sheaths, and migrate to thoracic muscles . - They develop into: First-stage larvae (sausage-shaped). - Second-stage larvae (after 1 week). - Third-stage (L3) filariform larvae (infective form) in another week. - L3 larvae migrate to the mosquito’s proboscis , ready for transmission. Development in Humans - Mosquito bites a human and deposits L3 larvae near the skin. - L3 larvae enter through the puncture wound and migrate to lymphatic vessels . - They mature into adults in the lymph nodes, mate, and produce microfilariae . - Microfilariae circulate in the peripheral blood , awaiting uptake by another mosquito. - The cycle repeats. - Prepatent period : 8–12 months (time from infection to detectable microfilariae). - Clinical incubation period : 8–16 months (time from infection to symptoms). Pathogenesis Classical Filariasis - Blockage of lymphatic vessels by adult worms leads to: Lymphangitis (inflammation of lymphatic vessels). - Lymphadenitis (inflamed, swollen lymph nodes). - Lymphedema (fluid accumulation in limbs and other tissues). - Elephantiasis (severe tissue swelling and fibrosis). - Hydrocele (fluid accumulation in the scrotum due to lymphatic obstruction). - Lymphoangiovarix (dilation of lymphatic vessels). - Chyluria (rupture of lymphatics leading to chyle in urine). - Secondary bacterial infections exacerbate symptoms. Occult Filariasis - Hypersensitivity reaction to filarial antigens. - No microfilariae in blood (destroyed in tissues). - Clinical features : Massive eosinophilia (30–80%) . - Pulmonary eosinophilia (dry cough, dyspnea, asthma-like symptoms). - Hepatosplenomegaly . - Immune-mediated complications (arthritis, glomerulonephritis, thrombophlebitis). - Tropical Pulmonary Eosinophilia (TPE) :Chronic cough, breathlessness, fever. - Chest X-ray: Mottled shadows (similar to miliary TB) . - High IgE and filarial antibodies . - Responds well to DEC treatment . Diagnosis Demonstration of Microfilariae - Specimens : Peripheral blood, chylous urine, lymphatic fluid, hydrocele fluid. - Techniques : Thick and thin blood smears (stained with Giemsa, Leishman, or Methylene blue). - Knott’s concentration technique : Formalin-centrifugation method. - Nucleopore filtration : Blood filtered through microporous membranes. - DEC provocation test : Diethylcarbamazine induces microfilariae in blood. Other Diagnostic Methods - Ultrasound : Detects filarial dance sign (movement of adult worms in lymphatics). - X-ray : Shows calcified worms . - Serology : ELISA, IFAT, IHA for filarial antigen detection. - Molecular tests : PCR for filarial DNA. Treatment 1. Diethylcarbamazine (DEC) - Drug of choice : Kills both microfilariae and adult worms . - Dosage : 6 mg/kg/day for 12 days (total 72 mg/kg). - Side effects : Allergic Mazzotti reaction due to dying microfilariae. 2. Ivermectin - 200 µg/kg dose. - Effective against microfilariae but not adult worms . 3. Tetracyclines (Doxycycline) - Targets Wolbachia spp. , reducing worm fertility and inflammation. Other Management - Surgery : For hydrocele and severe lymphedema. - Supportive care : Compression therapy, physiotherapy for lymphedema. Prevention and Control 1. Vector Control - Eradication of mosquito breeding sites . - Larvicidal measures :Chemical control ( temephos, fenthion ). - Mosquito larvicidal oils. - Removal of aquatic plants ( Pistia ) to control Mansonia mosquitoes. - Adult mosquito control :Use of DDT, pyrethroids, insecticides . - Personal protection (mosquito nets, repellents). 2. Mass Drug Administration (MDA) - DEC mass therapy :Given to entire communities except pregnant women, young children (<2 years), and severely ill patients . - Often combined with Albendazole or Ivermectin . - Repeated every 2 years in endemic areas. - DEC-medicated salt :Common salt fortified with 1–4 g DEC/kg used in some areas. - Selective treatment :Only those positive for microfilariae receive treatment. Summary - Filarial worms cause lymphatic filariasis, loiasis, onchocerciasis , and mansonelliasis . - Transmission is via mosquitoes or biting flies . - Disease presents as lymphedema, elephantiasis, hydrocele, dermatitis, and eye lesions . - Diagnosis includes blood smears, ultrasound, serology, and PCR . - DEC, Ivermectin, and Doxycycline are key drugs. - Vector control and mass drug administration are crucial for prevention.