Ophthalmologic Manifestations of Onchocerciasis Workup

  • Author: Deborah R Eezzuduemhoi, MD; Chief Editor: Hampton Roy Sr, MD   more...
 
Updated: Apr 26, 2010
 

Laboratory Studies

  • Skin snips has been the standard diagnostic technique. A scleral punch is the tool of choice to obtain samples of epidermis and dermis. Standardized techniques allow for relatively precise quantification of microfilarial load per milligram of tissue. However, this method is insensitive in low transmission areas and in areas where long-term use of the microfilaricidal ivermectin has resulted in the significant reduction of individual and community microfilariae loads. Also, the procedure is painful and involves a high risk of blood-borne infections (eg, HIV).
  • The oncho-dipstick assay is a more reliable and patient friendly alternative to the skin snip technique in establishing a diagnosis of human onchocerciasis. A positive result may indicate active infection by the parasite. In one study, the sensitivity of the oncho-dipstick assay was 100% in urine and 92% in tears; its specificity was 100% in both urine and tears.
  • Enzyme-linked immunosorbent assay (ELISA) and immunochromatographic test (ICT): ELISA, the ubiquitous biological technique, uses multiple recombinant antigens. ELISA is useful to differentiate O volvulus from its cousins but requires a specialized laboratory. ICT, a rapid format antibody card test, uses an individual antigen.
    • The sensitivity of ELISA and ICT has been estimated as 97% and 86%, respectively.
    • Both ELISA and ICT are more sensitive than the skin snip technique and the patch test using topical diethylcarbamazine (DEC).
    • ICT compares with ELISA and is inexpensive.
  • Polymerase chain reaction (PCR): An advanced molecular technique using DNA or RNA probes specific to O volvulus can assay the blackfly vector and human host infection using PCR technology. These probes are sensitive very early in the disease. Although highly specific, PCR requires meticulous laboratory technique to avoid contamination and false-positive results. In addition to requiring specialized skills and being expensive, PCR-based diagnostic methods of onchocerciasis still depend on skin snips.
  • Older techniques
    • Nodulectomy: Adult worms can be identified after surgical nodulectomy.
    • Mazzotti test: This test relied on the intense pruritic response induced by microfilariae after treatment with DEC. Used in a minute quantity, it can be associated with untoward effects, ranging from mild discomfort, fever, headaches, and itching to tachypnea, tachycardia, and even pulmonary edema. Antihistamines and corticosteroids pretreatment may lessen the discomfort.
    • Microfilariuria: This test requires a small dose of DEC as it mobilizes the microfilariae into the urine.
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Histologic Findings

O volvulus can be identified using special stains. The adult form is a threadlike, coiled, white worm. The female measures about 50-100 cm, and the male measures 2.5-5.0 cm. The microfilariae are only 0.3 µm in length. The living microfilariae are coiled, whereas the dead worms are straight and opacified. Each living or dead filaria is surrounded by granulation tissue, fibrin, polymorphonuclear neutrophils, eosinophils, plasma cells, and giant cells.

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Contributor Information and Disclosures
Author

Deborah R Eezzuduemhoi, MD  Assistant Professor, Department of Ophthalmology and Visual Sciences, Texas Tech University, Health Sciences Center School of Medicine

Deborah R Eezzuduemhoi, MD is a member of the following medical societies: American Academy of Ophthalmology, American Academy of Pediatrics, and Women in Ophthalmology, Inc

Disclosure: Nothing to disclose.

Coauthor(s)

Deborah Wilson, MD  Director of Glaucoma Service, Assistant Professor, Department of Ophthalmology, Georgetown University Medical Center

Deborah Wilson, MD is a member of the following medical societies: American Academy of Ophthalmology and American College of Physicians

Disclosure: Nothing to disclose.

Specialty Editor Board

John D Sheppard Jr, MD, MMSc  Professor of Ophthalmology, Microbiology and Molecular Biology, Clinical Director, Thomas R Lee Center for Ocular Pharmacology, Ophthalmology Residency Research Program Director, Eastern Virginia Medical School; President, Virginia Eye Consultants

John D Sheppard Jr, MD, MMSc is a member of the following medical societies: American Academy of Ophthalmology, American Society for Microbiology, American Society of Cataract and Refractive Surgery, American Uveitis Society, and Association for Research in Vision and Ophthalmology

Disclosure: Nothing to disclose.

Simon K Law, MD, PharmD  Assistant Professor of Ophthalmology, Jules Stein Eye Institute; Chief of Section of Ophthalmology Surgical Services, Department of Veterans Affairs Healthcare Center, West Los Angeles

Simon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, American Glaucoma Society, and Association for Research in Vision and Ophthalmology

Disclosure: Nothing to disclose.

R Christopher Walton, MD  Professor, Director of Uveitis and Ocular Inflammatory Disease Service, Department of Ophthalmology, Assistant Dean for Graduate Medical Education, University of Tennessee College of Medicine; Consulting Staff, Regional Medical Center, Memphis Veterans Affairs Medical Center, St Jude Children's Research Hospital

R Christopher Walton, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Healthcare Executives, American Uveitis Society, Association for Research in Vision and Ophthalmology, and Retina Society

Disclosure: Nothing to disclose.

Lance L Brown, OD, MD  Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri

Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy Sr, MD  Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Hampton Roy Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, and Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

References

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  7. Nguyen JC, Murphy ME, Nutman TB, et al. Cutaneous onchocerciasis in an American traveler. Int J Dermatol. Feb 2005;44(2):125-8. [Medline].

  8. Pearlman E, Hall LR, Higgins AW, et al. The role of eosinophils and neutrophils in helminth-induced keratitis. Invest Ophthalmol Vis Sci. Jun 1998;39(7):1176-82. [Medline].

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