Diagnosis
 

Palpating
Combined with a travel history in an endemic area, a presumptive diagnosis of Onchocerciasis can be make using this simple technique in which the physician feels the areas of the patient’s body that are most likely to contain subcutaneous nodules.  While this technique does not definitively demonstrate Onchocerciasis, it is an good indication that further tests should be run to confirm this diagnosis. (5)

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Skin Snips
In this common diagnostic test, the skin is prepared with an antiseptic and then a fold is squeezed between the physician’s thumb and forefinger.  A tiny slice (3-5 mg) of the skin is then removed with a small razorblade.  To observe the microfilariae, the skin snip is placed in saline or incubated for 4 hours in a cultured medium.  The microfilarial load can be estimated with this method by counting the emerging microfilariae.  If the infection is light, the microfilarial load may be low, meaning that multiple skin snips must be taken to secure a diagnosis.  This method is specific, but it is becoming increasingly unpopular with patients in endemic areas due to its invasiveness. (7)

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Slit Lamp Exam
A microscope with a light is used to examine the eye under high magnification.  The physician can then look for free floating intraocular microfilaria. (5)

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Mazzotti Test
If the skin snip is negative for microfilariae, an oral test dose of 5 mg DEC is administered.  DEC inhibits neuromuscular transmission in nematodes.  If the patient has onchocerciasis, intense pruritus results within 2 hours due to dying microfilariae.  Although the itching can be alleviated with corticosteroids and will subside within a few days, severe systemic reactions and ocular complications are risks with this diagnostic method. (7)

 
 

DEC Patch Test
A local application of 10% DEC anhydrous lanolin is applied to the skin and covered with a dressing.  The patch is then checked for local dermatitis caused by the dying microfilariae.  This is safer than the Mazzotti test because there is no risk of provoking a systemic reaction, but is not as sensitive as a skin snip.  The easy application and low risk of this test make it ideal for testing for the re-emergence of the disease in a treatment area.(7)

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Nodulectomy
This technique is very invasive and therefore is impossible to use on a population level.  The surgery leads to a positive diagnosis of Onchocerciasis if the adult worms can be observed in the nodule.  In addition to use as a diagnostic, this technique has therapeutic purposes because removal of the adult worms eliminates the nodule and reduces the microfilarial load. (7)

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ELISA test
A drop of blood from a pricked finger is collected on filter paper in this serological test.  An enzyme-linked immunosorbent assay (ELISA) can then detect the presence of the O. volvulus antigens.  This test is 70-80% sensitive and 96-100% specific.  This test is not more widely used because it requires expensive lab equipment and cannot distinguish between current and past infections, which is a major problem in endemic areas. (5)

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PCR (Polymerase Chain Reaction)
This technology uses a machine to amplify parasite DNA sequences in skin-snip specimens.  This method is highly sensitive and can be used to diagnose patients with low-level infections.  This high sensitivity also means that a return infection could be cause more quickly.  Because the machine amplifies the DNA to such a great extent, very little original sample is needed.  Therefore, the specimen could be collected with a skin scratch, in which the superficial layer of the epidermis is carefully removed with a lancet.  Patients much prefer this less invasive method.  The major disadvantage of the PCR technique is its high cost and need for complicated technology. (14)

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Rapid-Format Antibody card tests
A drop of blood onto a card from a finger can be tested for antibodies (IgG4) to the O. Volvulus antigen.  A color change on the card surface indicates a positive test.  This is a similar technique to the ELISA test, but is more useful in the field because it is faster and less expensive.  Promising initial studies have shown good sensitivity and specificity, but further studies are needed to determine how valuable this technique is in diagnosing Onchocerciasis. (5)