Neglected Tropical Diseases

The NTD Initiative

Onchocerciasis

Diagnosis

Clinical examination

• A physical examination of the patient is necessary to detect the localized dermatitis or the subcutaneous nodules.
  
  
• However, due to the geographic overlap with other filarial diseases, such as O. volvulus, Loa loa (L. loa), Mansonella perstans (M. perstans), Mansonella ozzardi (M. ozzardi), and Mansonella streptocerca (M. streptocerca), overlapping clinical syndromes is not an exception and may add complexity in diagnosing onchocerciasis.^1,5
  
  
• It is imperative, however, to ascertain which individuals or communities are heavily infected with L. loa before applying treatment for onchocerciasis since the treatment options could cause severe adverse effects.

Laboratory diagnostic

• Demonstration of microfilariae: In the field, a definitive diagnostic is generally reliant on simple demonstration of O. volvulus microfilariae in skin snips.⁵
  
  
• Demonstration of adult worms: Biopsy or ultrasound demonstration of adult worms in nodules is also possible. In an excised intramuscular or subcutaneous nodule, adult worms can be seen visually as hair-like white worms that are shaped like coils. Most nodules have three to five worms. But up to 50 worms could be found in one nodule.
  
  
• Blood examination: Due to the geographic overlap in the distribution of filarial disease and the resulting overlap of clinical symptoms, examination for circulating microfilaremia is often necessary to rule out any differential diagnoses.⁵
  • Sensitivity and/or specificity of eosinophil count in infected temporary residents or infected residents is poor. Additionally, IgE levels are non-specific of O. volvulus infection.
  • PCR to detect the DNA of parasites using skin snips is recognized as the most sensitive available test to detect even low levels of infection in individual patients.^2,3,5
  • A localized Mazzoti reaction test is a patch test where topical diethylcarbamazine is applied to a small area of skin in order to provoke a localized Mazzoti reaction. This is a very sensitive and specific diagnostic test tool for children under 15 years of age in endemic areas.⁴

Learn more about onchocerciasis:

• Epidemiology
• Life Cycle
• Symptoms
• Treatment and Control
• Back to Onchocerciasis Overview

 

---

References

1. McCarthy JS, Ottesen EA, Nutman TB: Onchocerciasis in endemic and non endemic populations: differences in clinical presentation and immunologic findings. J Infect Dis 170:736, 1994.
2. Toe L, Boatin BA, Adjami A, et al:Detection of Onchocerca volvulus infection by o-150 polymerase chain reaction analysis of skin scratches. J Infect Dis 178:282, 1998.
3. Boatin BA, Toe L, Alley ES, et al: Detection of Onchocerca volvulus infection in low prevalence areas: A comparison of three diagnostic methods. Parasitology 125:545, 2002.
4. Kilian HD: The use of a topical Mazzotti test in the diagnostic of onchocerciasis. Trop Med Parasitol 39:235, 1988.
5. Vincent JA, Lustigman S, Zhang S, et al: A comparison of newer tests for the diagnosis of Onchocerciasis. Ann Trop Med Parasitol 94:253, 2000.