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![• Mazzotti skin tests
– Administer a single small dose of DEC (50-100 mg).
– After 2 -24 hrs intense pruritus with or without erythema is elicited
over involved areas, which indicate the death of microfilariae in the
skin
– Steroids may be necessary to control this inflammatory reaction
– The test must be used with caution in individuals who may be heavily
infected because a severe systemic reaction can be provoked. A DEC
patch test that causes a localized skin reaction may be used in such
patients.
• Immunodiagnosis/ Serological tests for detection of filarial
antigen: – ELISA, FAT
– Commercial kits are available to test venous blood and can be
quantitative (enzyme-linked immunoassay [ELISA]) Og4C3
monoclonal antibody–based assay or qualitative
immunochromatographic test (ICT).
• Eosinophilia (non-specific)](https://image.slidesharecdn.com/gv00ictdqpckoteztzm8-18-251125081203-55a50ffb/75/18-ONCHOCERCA-VOLVULUs-power-point-presentation-30-2048.jpg)
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18. ONCHOCERCA VOLVULUs power point presentation
- 1.
- 2. ONCHOCERCA VOLVULUS • Tissuenematode, helminth worm found in subcutaneous tissue • Found in West and central Africa, parts of east Africa (not Kenya), the Middle east, Central and South America • Adults found in subcutaneous nodules • Microfilariae found in the skin, but do sometimes appear in blood, in the eye in heavy infections • May be found in urine, sputum and CSF especially after rx • Causes onchocerciasis (river blindness) the world’s 2nd leading cause of blindness.
- 3. Morphology • Adults –cylindrical worms. Females are 30- 50 cm; males are 20 -40 cm long • Can live in a human body for up to 15 years. • Microfilariae – unsheathed, 300- 320 micrometers in length, tail tapes to a point, nucleus does not extend to the tail end
- 4. • It’s Vector:Simulium damnosum (black fly) spreads Onchocerca volvulus which causes onchocerciasis. • Black fly of genus : Simulium : damnosum, neavei, ethiopiense and woodi.
- 5. Life cycle • Adultsmate, fertilized females produce microfilariae • Microfilariae in skin is taken up by Simulium flies (S.domnosum) –Blackfly lay eggs on fast flowing waters/well oxygenated water where the larvae develop (larvae require high oxygen) (thus found in rivers – river blindness); phoretic relationship with crabs • In the mosquito - microfilariae penetrates stomach wall, migrate to flight muscles then to proboscis, development to infective stage ~ 10 days
- 6. • When themosquito feeds again, Microfilariae deposited in bite and develop to adults in subcutaneous nodules • Worms mature and produce microfilariae; about 9-12 months, adults 10 – 15 yrs • Man is the only definitive host of the parasite. • Other possible modes of transmission – congenital – 1:20 newborns babies in heavily infected areas have mf in their skin soon after birth – Microfilariae in blood transplacental e.g after rx – Adults cross placenta and establish in babies.
- 12. Clinical presentation • Incubationperiod 15 – 18 months, may be asymptomatic • Pruritis of the skin, skin rash, intense itching and lesions • Subcutaneous nodules (onchocercomas) in bony prominences. In Africa normally around the hips, in South & Central America on the head • Lymphadenitis resulting in hanging groins (loss of skin elasticity) • Elephantiasis of the scrotum in males
- 13. • Serious visualimpairment and blindness • Pathological lesions – Subcutaneous fibrous nodules (onchocereomas) • Can be as large as 6 cm • Single or multiple nodules • Painless and non-suppurating • Concentric mass of fibrous tissue with a honeycomb central area – Ocular lesions • In person with nodules on head or face • Due to microfilariae – may be found moving through substantia propria of cornea and in anterior chamber • Manifestations – simple conjunctivitis, small round opacities, pannus in anterior quadrant of cornea, iridocylitis, secondary glaucoma, optic atrophy, blindness • SOWDA – arabic for dark, results from strong immune response by the host; Cells involve upper dermis usually localized to one limb, itchy, swelling, dark with scaling papules, enlarged regional lymph nodes.
- 14. • Lizard skin–Xeroderma due to lichenification and thickening of skin • Presbyderma – loss of skin elasticity, premature aging • Leopard skin – skin depigmentation in patches • Hanging groin (loss of skin elasticity) • Arthritis – may be monoarthritis affecting the large joints e.g hip, pain disappears rapidly on rx
- 15. Maddening itching, depigmentation (leopardskin), and thickened skin
- 17. Destruction of elastictissue, formation of redundant folds and loss of pigmentation
- 19. Lymph glands inpockets of skin : ‘hanging groin’ , in severe cases ‘minor elephantiasis’
- 20. Nodules over bonyprominences
- 21. Pathophysiology: • Inflammatory cellscomprising : Eosinophils, Neutrophils and Macrophages surround the dead microfilariae • IgG antibodies, immune complex formation and complement activation on the surface of microfilariae attract cells, killing of mf. And inf. larvae ( Greene B.M. et. al.,1981; J. Immunology ). Does not confer protective imm. • Microfilariae : antibody dependent cell mediated cytotoxicity reaction (ADCC). • Humoral response is marked in endemic areas ( Greene B.M. et. al.,1985; Rev. Infect Dis ). • Nodules : with thick fibrous wall with cellular infiltrate, formed by granulomatous reaction around adult worm. Calcification of nodules and dead worms can occur. • Macrophages : filled with lipid are found.( Gatrill A.J. et. al., 1987; Histochem J.)
- 22. ■ Lichenified dermatitis (sowda,i.e., a localized form of chronic papular dermatitis usually confined to one extremity) involves edema, hyperpigmented papules and plaques, and intense pruritus that is usually limited to a single limb and associated with regional lymphadenopathy.
- 25.
- 26.
- 27. Nodules containing O.Volvuluson the head.
- 28. Cross section ofworms in Subcutaneous nodules.
- 29. Diagnosis • Search forthe presence of microfilariae in blood, urine and eyes. – Detection of microfilariae of O. volvulus in the cornea or anterior chamber of the eye using slit-lamp examination. • Search for adult worms (macrofilariae) • Skin snips (thighs, buttocks, scapula, iliac crest), place in normal saline to allow m.f to migrate; examine after 12 – 24 hrs for microfilariae in wet preparations then stain (e.g Giemsa) and examine for features (unsheathed, nucleus not reaching tip of tail) • Microfilariae - negative form skin snips in SOWDA
- 30. • Mazzotti skintests – Administer a single small dose of DEC (50-100 mg). – After 2 -24 hrs intense pruritus with or without erythema is elicited over involved areas, which indicate the death of microfilariae in the skin – Steroids may be necessary to control this inflammatory reaction – The test must be used with caution in individuals who may be heavily infected because a severe systemic reaction can be provoked. A DEC patch test that causes a localized skin reaction may be used in such patients. • Immunodiagnosis/ Serological tests for detection of filarial antigen: – ELISA, FAT – Commercial kits are available to test venous blood and can be quantitative (enzyme-linked immunoassay [ELISA]) Og4C3 monoclonal antibody–based assay or qualitative immunochromatographic test (ICT). • Eosinophilia (non-specific)
- 31. 1 & 2) Blood free skin snip. 3) Skin biopsy. 4) Skin fragment.
- 33.
- 34. Microfilariae of O.Volvulusare longer and do not have nuclei to the end of tail. sheath less, sharply pointed and curved tail. Cephalic space
- 35. Microfilariae of Onchocercavolvulus are unsheathed and measure 300-315 µm in length. The tail tapers to a point and is often sharply bent. The nuclei do not extend to the tip of the tail. Microfilariae typically reside in skin but may be found in blood or urine during heavy infections, or invade the eye and cause a condition known as river blindness. Adult males of Onchocerca volvulus measure 15-45 mm in length; females are 30-50 cm. Adults usually reside in nodules (onchocercomas) in subcutaneous tissue.
- 36.
- 38. Treatment • Diethylcarbamazine (DEC)only kills microfilaria. Causes hyperpolarization of nerve membrane and flaccid paralysis of the nematode, worms are removed by normal peristalsis • Ivermectin (Mectizan®)- (150 microgram/kg single dose) only kills microfilaria. Binds to glutamate gated chloride channels in the parasites’ nervous system, causing them to open. • Suramin only kills macrofilaria should be used in extreme cases because of toxicity.
- 39. • Use ofDoxycycline has irreversibly eliminated skin microfilaria through direct effect on endosymbiont. But not suitable for mass treatment (too long • Both benzodiazepines Diazepam and Midazolam had a synergistic effect on the activity of ivermectin • Nodulectomy (surgical removal of nodules) • The blindness is irreversible due to fibrosis.
- 40. Wolbachia and onchocerciasis •Wolbachia bacteria are endosymbionts of Onchcerca • Wolbachia thrive in the filarial worms responsible for river blindness • Wolbachia are killed by antibiotics • Antibiotics interfere with the life cycle of Onchcerca • Wolbachi protein extracts seem to be responsible for keratitis • Antibiotic treatment leads to cure
- 41. Prevention and control •Vector control: Tememphos as larvicide is effective but resistance develops. Aerial spraying of insecticides over breeding sites in fast flowing rivers.
- 42. • Personal prophylaxis:yearly ivermectin • Nodulectomy : been useful in reducing incidence of blindness in Mexico and Guatemala • Migration of communities from endemic areas