History

Fact Explanation
Skin nodules Following the bite of a black fly, larvae are injected into the human skin. Larvae develop into adult worms. Over a period of years, adult female worms become enveloped by host tissue, forming characteristic subcutaneous nodules. These nodules occur as response of the host tissue to the constant production of foreign proteins by the organism, which ultimately results in the formation of a granuloma. [1]
Itchy skin rash Fertilized adult female worms produce microfilariae found throughout the body but preferentially reside in the eye and skin. The rash occurs due to the pronounced cellular immune response to microfilariae in the skin [2].
Depigmentation of skin It occurs as part of the changes which occur in chronic infection and is associated with microfilarial death and concomitant inflammatory infiltration of the skin [3].
Itchy, red eyes The death of a microfilaria gives rise to local inflammation in the form of circumscribed oedema and cellular infiltration around the microfilarial body [4].
Loss of vision. Due to sclerosing keratitis as a result of massive invasion of the cornea by microfilariae giving rise to permanent corneal damage [4].
References
  1. BRATTIG N.W.. Pathogenesis and host responses in human onchocerciasis: impact of Onchocerca filariae and Wolbachia endobacteria. Microbes and Infection [online] 2004 January, 6(1):113-128 [viewed 30 June 2014] Available from: doi:10.1016/j.micinf.2003.11.003
  2. CABRERA Z, BUTTNER DW, PARKHOUSE RM. Unique recognition of a low molecular weight Onchocerca volvulus antigen by IgG3 antibodies in chronic hyper-reactive oncho-dermatitis (Sowda). Clin Exp Immunol [online] 1988 Nov, 74(2):223-229 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1541786
  3. OTTESEN E. A.. Immune Responsiveness And The Pathogenesis Of Human Onchocerciasis. Journal of Infectious Diseases [online] 1995 March, 171(3):659-671 [viewed 01 July 2014] Available from: doi:10.1093/infdis/171.3.659
  4. THYLEFORS B. Ocular onchocerciasis Bull World Health Organ [online] 1978, 56(1):63-73 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2395538

Examination

Fact Explanation
Subcutaneous nodules which are firm, non-tender and mobile. Over a period of years, adult female worms become enveloped by host tissue, forming characteristic subcutaneous nodules. These nodules occur as response of the host tissue to the constant production of foreign proteins by the organism, which ultimately results in the formation of a granuloma [1].
Papular rash. Due to the pronounced cellular immune response to microfilariae in the skin [2].
Drooping of skin. Due to degradation of the dermal extracellular matrix and elastic fibres which can be caused by parasite or host proteases [1].
Leopard skin. Due to bilaterally symmetrical depigmentation. It occurs as part of the changes which occur in chronic infection and is associated with microfilarial death and concomitant inflammatory infiltration of the skin [3].
Lymphadenopathy. Onchocerca volvulus infection results in follicular hyperplasia with infiltration of eosinophils and neutrophils and high numbers of plasma cells within lymph nodes [1].
snow flake opacities of the cornea. The death of a microfilaria gives rise to local inflammation in the form of circumscribed oedema and cellular infiltration around the microfilarial body. After some time the microfilariae disintegrates and becomes lysed, leaving only a blurred greyish opacity [4].
Elevated intraocular pressure. Due to the presence of microfilariae in the anterior uveal tissue which induces hypersecretion of aqueous humour [4].
Slit-lamp examination revealing microfilariae in the cornea and anterior chamber. In patients with a high microfilarial load, wandering microfilariae can invade the conjunctiva, cornea and posterior regions of the eye [1].
Pale optic disc. The onchocercal lesions of the posterior segment of the eye involve the optic nerve, the retina, and the choroid. The optic nerve may show acute papillitis, with oedema and congestion, which rapidly progresses to optic atrophy [4].
References
  1. BRATTIG N.W.. Pathogenesis and host responses in human onchocerciasis: impact of Onchocerca filariae and Wolbachia endobacteria. Microbes and Infection [online] 2004 January, 6(1):113-128 [viewed 30 June 2014] Available from: doi:10.1016/j.micinf.2003.11.003
  2. CABRERA Z, BUTTNER DW, PARKHOUSE RM. Unique recognition of a low molecular weight Onchocerca volvulus antigen by IgG3 antibodies in chronic hyper-reactive oncho-dermatitis (Sowda). Clin Exp Immunol [online] 1988 Nov, 74(2):223-229 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1541786
  3. OTTESEN E. A.. Immune Responsiveness And The Pathogenesis Of Human Onchocerciasis. Journal of Infectious Diseases [online] 1995 March, 171(3):659-671 [viewed 01 July 2014] Available from: doi:10.1093/infdis/171.3.659
  4. THYLEFORS B. Ocular onchocerciasis Bull World Health Organ [online] 1978, 56(1):63-73 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2395538

Differential Diagnoses

Fact Explanation
Scabies. It presents with pruritic papules, but the presence of burrows is characteristic [1].
Leprosy. It also presents with hypopigmented lesions in the skin but is also associated with anaesthesia of the area of the skin lesion [2].
vitamin A deficiency. It also presents with lesions in the eye known as bitot spots but presents as night blindness [3].
References
  1. CHOSIDOW OLIVIER. Scabies. N Engl J Med [online] 2006 April, 354(16):1718-1727 [viewed 01 July 2014] Available from: doi:10.1056/NEJMcp052784
  2. LOCKWOOD D.N.J.. The diagnosis of leprosy is delayed in the United Kingdom. [online] 2001 April, 94(4):207-212 [viewed 01 July 2014] Available from: doi:10.1093/qjmed/94.4.207
  3. MAHALANABIS D. Breast feeding and vitamin A deficiency among children attending a diarrhoea treatment centre in Bangladesh: a case-control study. BMJ [online] 1991 Aug 31, 303(6801):493-496 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1670801

Investigations - for Diagnosis

Fact Explanation
Skin-snip biopsy and the use of Polymerase Chain Reaction (a razor blade is used to remove tiny skin samples (3-5 mg) from multiple sites. They are then placed in saline to observe for microfilariae emerging from the samples). O. volvulus microfilariae reside in the upper layers of the dermis [1].
Antibody tests (eg: to Ov16 antigen). It has been shown that antibodies to Ov16 often developed long before the first appearance of microfilariae in skin snips [2].
Antigen detection tests. Specific parasite antigens (oncho-C27) circulate in body fluids during infection [3].
Diethylcarbamazine (DEC) patch test. (topical application of diethylcarbamazine cream) Examination of the skin 48 hours later reveals a localized papular reaction which occurs due to the death of microfilariae in the skin as a result of DEC [2].
References
  1. TOé LAURENT, BOATIN BOAKYE A., ADJAMI AIME, BACK CHRISTIAN, MERRIWEATHER ANTHONY, UNNASCH THOMAS R.. Detection of Infection by O‐150 Polymerase Chain Reaction Analysis of Skin Scratches . J INFECT DIS [online] 1998 July, 178(1):282-285 [viewed 01 July 2014] Available from: doi:10.1086/517454
  2. WEIL GARY J., STEEL CATHY, LIFTIS FANYA, LI BEN‐WEN, MEARNS GILLIAN, LOBOS EDGAR, NUTMAN THOMAS B.. A Rapid‐Format Antibody Card Test for Diagnosis of Onchocerciasis. J INFECT DIS [online] 2000 December, 182(6):1796-1799 [viewed 01 July 2014] Available from: doi:10.1086/317629
  3. AYONG L. S., TUME C. B., WEMBE F. E., SIMO G., ASONGANYI T., LANDO G., NGU J. L.. Development and evaluation of an antigen detection dipstick assay for the diagnosis of human onchocerciasis. Trop Med Int Health [online] 2005 March, 10(3):228-233 [viewed 01 July 2014] Available from: doi:10.1111/j.1365-3156.2004.01384.x

Management - General Measures

Fact Explanation
Avoid vector contact in endemic areas with the use of protective clothing and repellants. The infection is transmitted through the bites of black flies carrying infective third-stage larvae [1].
References
  1. HOERAUF ACHIM, SPECHT SABINE, BüTTNER MARCELLE, PFARR KENNETH, MAND SABINE, FIMMERS ROLF, MARFO-DEBREKYEI YEBOAH, KONADU PETER, DEBRAH ALEXANDER YAW, BANDI CLAUDIO, BRATTIG NORBERT, ALBERS ANNA, LARBI JOHN, BATSA LINDA, ADJEI OHENE, BüTTNER DIETRICH W.. Wolbachia endobacteria depletion by doxycycline as antifilarial therapy has macrofilaricidal activity in onchocerciasis: a randomized placebo-controlled study. Med Microbiol Immunol [online] December, 197(3):295-311 [viewed 01 July 2014] Available from: doi:10.1007/s00430-007-0062-1

Management - Specific Treatments

Fact Explanation
Ivermectin. Dose- 150 mcg every 3-6 months. It is a microfilaricide and also plays a role in suppression of reproduction in adult worms [1].
Doxycycline. Dose- 100-200 mg/day for 6 weeks. It interrupts embryogenesis in the long-term and also has macrofilaricidal activity [2].
References
  1. OSEI-ATWENEBOANA MIKE Y, ENG JEFFREY KL, BOAKYE DANIEL A, GYAPONG JOHN O, PRICHARD ROGER K. Prevalence and intensity of Onchocerca volvulus infection and efficacy of ivermectin in endemic communities in Ghana: a two-phase epidemiological study. The Lancet [online] 2007 June, 369(9578):2021-2029 [viewed 01 July 2014] Available from: doi:10.1016/S0140-6736(07)60942-8
  2. HOERAUF ACHIM, SPECHT SABINE, BüTTNER MARCELLE, PFARR KENNETH, MAND SABINE, FIMMERS ROLF, MARFO-DEBREKYEI YEBOAH, KONADU PETER, DEBRAH ALEXANDER YAW, BANDI CLAUDIO, BRATTIG NORBERT, ALBERS ANNA, LARBI JOHN, BATSA LINDA, ADJEI OHENE, BüTTNER DIETRICH W.. Wolbachia endobacteria depletion by doxycycline as antifilarial therapy has macrofilaricidal activity in onchocerciasis: a randomized placebo-controlled study. Med Microbiol Immunol [online] December, 197(3):295-311 [viewed 01 July 2014] Available from: doi:10.1007/s00430-007-0062-1