Filariae helminthes – nematode worms

• Classes
• Onchocerca volvulus Þ adult subcutaneous tissue Þ river blindness
• Loa loa Þ adult subcutaneous tissue Þ eye worm
• Wuchereria bancrofti and Brugia malayi Þ adult lymphatics Þ elephantiasis
• Description: thread-like nematodes (~200microns – 1 to 2 cm)
• Disease results in 1-5% of infected individuals
• The worms do not cause the disease, rather it is the host’s response to the worms
• Chronic infection leads to disease
• General Life Cycle:
• stage L1 – microfilaria – infects arthropod vector
• stage L2 – larva in arthropod
• stage L3 – infective larva – infects human
• stage L4 – larva in human
• adult stage – in human – reproduces to form more microfilaria
• Control and Rx:
• vector control: insecticide, change environment
• chemotherapy:
• DEC Þ kill adults, widely used, not expensive
• Ivermectin Þ kill microfilaria (not adult forms)

• Mostly asymptomatic
• Dermal: calabar swelling (edemetous response around parasite; comes and goes in different spots); dermatitis pruritis
• Ocular: conjuctiva
• Arthropod vector = horse fly
• Worms are actually visible by the naked eye (Can usually see it in your eye if you look in the mirror!)
• Do not cause serious problems because they remain in the subcutaneous tissue
• One can actually bust open a calabar swelling and pull out the worm with tweezers

• Mostly asymptomatic
• Lymphatic: elephantiasis, lymphedema, hydrocele (picture of man with enlarged testicles), chyluria
• Pulmonary: tropical pulmonary eosinophilia; in lungs Þ asthmatic response
• Disease caused mostly by adults
• Adults infect lymphatics Þ blockage of drainage
• Arthropod vector = mosquito (infected by microfilaria which are only active at night)
• Distribution: W and Central Africa, S and Central America, SE Asia

• Mostly asymptomatic
• Dermal: nodules (surgical removal may cut down on disease – controversial), pruritis, papules, lichenification, sowda (rare, affects one limb only Þ not found in Africa)
• Ocular: uveitis, retinitis, interstitial keratitis (corneal inflammation)
• Arthropod vector = black fly (near rivers)
• Distribution: W Africa
• How do you test?
• remove 1-2 mg piece of tissue from patient
• drown tissue sample in water
• if infected, the worms will come out of tissue
• Blindness takes years to develop
• premature wrinkling
• affects young people
• microfilaria (not adult) causes blindness and disease