NEMATODES 4

• Lymphatic filariasis is one of the most debilitating diseases in tropical countries
• Two most common mosquito-borne causative agents: Wuchereria bancrofti and Brugia malayi
• Infective Stage: Third stage larvae
• Species and Anatomic Location of filarial nematodes

  • Lymphatic filariasis: Wuchereria bancrofti, Brugia malayi, Brugia timori
  • Subcutaneous filariasis: Loa loa, Onchocerca volvulus, Mansonella streptocerca, Mansonella ozzardi
  • Serous cavity filariasis: Mansonella perstans
• Diagnostic Stage: Microfilariae
• Lymphatic filariasis is the second leading cause of permanent and long-term disability, affecting both physical and psychological aspects
• Biology of filarial nematodes

  • Long, slender, thread-like nematodes
  • Adults of all species are parasites of vertebrate hosts including humans
  • Adult female filarial worm is viviparous (larviparous)
• Epidemiology: Cosmopolitan parasitic infection affecting 120 million people worldwide in 83 endemic countries
• Characteristics of Wuchereria and Brugia nematodes
• Objectives of the lecture

  • Discuss the biology of filarial nematodes
  • Discuss the life cycle of filarial nematodes
  • Describe the clinical manifestations of filarial nematodes
  • Enumerate management and prevention and control of filarial nematodes
• Transmission and Diseases

  1. Spread by bite of an arthropod

  2. Mosquitoes, Black flies, Midges

  3. NOT by feco-oral route

  4. Disease caused by allergic reaction to the filaria
• Pathogenesis and Clinical Manifestations: Infection usually acquired during childhood and takes years to manifest. Adult worms in the lymph nodes cause inflammation that obstructs lymphatic vessels leading to lymphedema
• Lymphangiectasis and Lymphangiogenesis


  Predispose to secondary bacterial infections and inflammatory response to skin and subcutaneous tissue leading to LYMPHEDEMA and ELEPHANTIASIS
• Acute Stage


  Asymptomatic Microfilaremia is the main reservoir for mosquito vectors, "Endemic Normals" have suppressive immunoregulatory mechanism, Expatriate Syndrome occurs in non-endemic persons transferred to endemic regions, Acute Dermatolymphangioadenitis is the most common acute manifestation of LF, Acute Filarial Lymphangitis is directly caused by adult worms that died spontaneously or following treatment
• Why in the Lymphatic System?

  Lymphatic Localization: For parasitic survival, Lymph is less aggressive than blood (no platelet, no complement system, incomplete coagulation system, no granulocytes, slow flow), Adult worm causes lymphangiectasis (parasite-induced lymphatic dilatation), Lymphangiogenesis: parasite induced endothelial cell proliferation and differentiation leading to collateralization
• Clinical Spectrum of Lymphatic Filariasis

  • Asymptomatic Microfilaremia
  • Acute Dermatolymphangioadenitis
  • Acute Filarial Lymphangitis
  • Lymphedema and Elephantiasis
  • Genitourinary Lesion such as hydrocoele
  • Tropical Pulmonary Eosinophilia
• Pathogenesis and Clinical Manifestations

  1. Infection usually acquired during childhood

  2. Takes years to manifest

  3. Adult worms in the lymph nodes cause inflammation that obstructs lymphatic vessels leading to LYMPHEDEMA

  4. Microfilariae DO NOT cause symptoms

  5. Clinical course: 1. Asymptomatic, 2. Acute Stage, 3. Chronic Stage
• Chronic Stage

  Lymphedema and Elephantiasis have characteristic features of fibrosis and cellular hyperplasia in and around the lymphatic walls, Dead calcified adult worms elicit immune response leading to lymphatic blockage and subsequent Lymphedema and Elephantiasis
• Chronic Stage

  Hydrocoele results in the obstruction of lymphatics of tunica vaginalis, Chyluria is manifested as milky urine due to rupture of lymphatics in the kidney
• Diagnosis: Thick Blood Smear
• Occult Filariasis

  Tropical Pulmonary Eosinophilia is caused by immunologic hyperresponsiveness to filarial infection, may be misdiagnosed as bronchial asthma or TB
• Knott Concentration Method

  1. Collect 1 mL of blood + 10mL formalin. Shake. (Formalin lyses RBC)

  2. Centrifuge. (If no centrifuge, allow the tube to stand in upright position for 12 hours)

  3. Decant the supernatant fluid.

  4. Examine a drop of sediment on slide and cover slip.

  5. A portion of sediment may be spread on a slide as thick smear and stain with Giemsa or Hematoxylin
• Small epithelioid granuloma (Meyers-Kouwenaar bodies)
• Diagnosis

  1. Thick Blood Smear

  2. Curved microfilaria: W. bancrofti

  3. Kinky microfilaria: B. malayi

  4. Specimen collection best done at night 8pm to 4am

  5. Nocturnal periodicity of the parasite

  6. DEC Provocative Test

  7. Circulating Filarial Antigens (CFA) Detection

  8. Knott Concentration Method
• Misdiagnosed as bronchial asthma or TB
• Caused by immunologic hyperresponsiveness to filarial infection
• Paroxysmal nocturnal cough, hypereosinophilia, diffuse miliary lesions
• Microfilaria not found in blood but may be found in tissues
• Doxycycline


  • Anti-Wolbachia (bacteria inside filaria that is essential for growth, development, embryogenesis, and survival of filaria)
• Diethylcarbamazine (DEC)


  • Drug of choice
  • Effective against adult and microfilaria
  • Adverse events: fever, myalgia, headache, sore throat or cough lasting 24-48 hours; self-limited à symptomatic treatment
• Treatment
• Albendazole


  • Has added benefit of clearing intestinal helminths
• Ivermectin


  • Not effective against adult worms and TPE
• Prevention and Control

  1. Interrupt transmission of parasite via preventive chemotherapy

  2. Annual Diethylcarbamazine (DEC) plus Albendazole or Ivermectin in endemic areas

  3. Hygiene education program for those with clinical manifestations

  4. Personal Protective Measure against mosquito
• Onchocerca volvulus
• Biology: Adult
• Introduction
• Wolbachia causes symptoms of Onchocerciasis
• Epidemiology
• Biology: Microfilaria