Filarial Worms

### **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** - *