onchocerciasis

Onchocerciasis: A Disease Caused by Parasitic Worms

Onchocerciasis, also known as "river blindness," is a disease caused by the parasitic worm Onchocerca volvulus. This infection can spread to humans through repeat bites of infected blackflies of the Simulium species.

• Causes and Transmission: The parasite is transmitted through the bite of an infected blackfly, which breeds in fast-flowing rivers and streams in remote, tropical areas.
• Symptoms: Onchocerciasis causes severe skin and eye disease, including blindness. Symptoms include intense itching, various skin lesions, and nodules that develop under the skin.

Key Facts

• Onchocerciasis is the second most important cause of infectious blindness worldwide after trachoma.
• The disease is most common in tropical and sub-Saharan regions of Africa.
• An estimated 21 million people are infected with onchocerciasis worldwide, with about 14.6 million having skin disease and 1.15 million experiencing visual impairment or loss.

References

[1] Onchocerciasis (river blindness) is a disease caused by the parasitic worm Onchocerca volvulus [1]. [2] The parasite can spread to humans through repeat bites of infected blackflies of the Simulium species [3, 4]. [5-8] Onchocerciasis causes severe skin and eye disease, including blindness. [9-11] Symptoms include intense itching, various skin lesions, and nodules that develop under the skin. [12-14] The disease is most common in tropical and sub-Saharan regions of Africa.

Onchocerciasis, also known as river blindness, can cause a range of symptoms that affect both the skin and eyes.

• Skin symptoms: These may appear many years before eye problems and include:
  • Very itchy skin
  • Bumps under the skin that can measure over an inch in size
  • Skin changes such as rashes and nodules beneath the skin
  • Intense pruritus (itching) which may be the only symptom in lightly infected people [1][6]
• Eye symptoms: These can include:
  • Itchy eyes, redness, or photophobia (sensitivity to light)
  • Scarring that progresses over years to cause visual loss and ultimately blindness [7][8]
• Other symptoms: In some cases, onchocerciasis can also cause other symptoms such as inflammation, itching, changes to skin color and texture, and permanent vision loss [9]

It's worth noting that many people infected with onchocerciasis never develop symptoms, but when they do, it's often a sign of advanced infection.

• Prevalence: An estimated 18-37 million people have onchocerciasis worldwide, with up to 2 million people visually impaired or blind as a result of their infection [4][14]

Early detection and treatment are crucial in preventing long-term damage from onchocerciasis.

• Diagnosis: Onchocerciasis can be diagnosed through surgical removal of a nodule (lump) in the skin, examination of eyes for signs of damage caused by immature worms or the worms themselves, and blood tests to look for signs of antibodies produced in response to an infection [12][13]

Diagnostic Tests for Onchocerciasis

Onchocerciasis, also known as river blindness, is a disease caused by the parasitic worm Onchocerca volvulus. Diagnosing this condition can be challenging, but several tests have been developed to confirm its presence. Here are some of the diagnostic tests used for onchocerciasis:

• Microscopy: This is considered the gold standard for diagnosing onchocerciasis. A skin biopsy sample is taken from various parts of the body and examined under a microscope for the presence of microfilariae, the larvae of the Onchocerca volvulus worm [5][6].
• PCR-based examination: This test involves analyzing a skin biopsy sample using polymerase chain reaction (PCR) to detect the genetic material of the parasite. It is a definitive but laborious and insensitive method [7].
• Antibody tests: These tests detect the presence of antibodies against Onchocerca volvulus in the blood. The OV16 ELISA test, for example, can be used to screen for any filarial infection, including onchocerciasis [2].
• Skin snips and blood samples: In some cases, skin snips and blood samples are collected from individuals suspected of having onchocerciasis. Three tests may be performed: the OV16 RDT (SD Bioline) and the OV16 ELISA both on serum samples, and microscopic detection of microfilariae in skin snips [3].
• Mazzotti reaction: This is a test for onchocerciasis using an oral test dose of DEC (50 to 100 mg). The Mazzotti reaction results in an immediate inflammatory response, which can be observed using the slit lamp biomicroscope at high magnification [10].

Challenges and Limitations

While these diagnostic tests are available, there are still challenges and limitations to their use. For example:

• Sensitivity and specificity: Some of these tests may have low sensitivity or specificity, making it difficult to confirm a diagnosis.
• Availability: These tests may not be readily available in all areas, particularly in resource-poor settings where onchocerciasis is most prevalent.
• Cost: Some of these tests can be expensive, making them inaccessible to many individuals who need them.

Conclusion

Diagnosing onchocerciasis requires a combination of clinical evaluation and laboratory testing. While several diagnostic tests are available, there are still challenges and limitations to their use. Further research is needed to develop more accurate, accessible, and affordable diagnostic tools for this disease.

Treatment Overview

Onchocerciasis, also known as "river blindness," is a parasitic disease caused by the filarial worm Onchocerca volvulus. The treatment of choice for this condition has evolved over time, with ivermectin being the current core strategy to eliminate onchocerciasis.

Current Treatment Guidelines

• Ivermectin: Ivermectin is a well-tolerated and highly effective microfilaricidal drug that is considered the drug of choice for treating onchocerciasis. It kills the juvenile worms, reducing the severity of symptoms, but does not kill adult worms.
• Moxidectin: Moxidectin is an antiparasitic drug approved by the FDA in 2018 to treat onchocerciasis in patients aged 12 years or older. It yields a more sustained reduction in microfilarial levels compared to ivermectin.

Treatment Approaches

• Mass Drug Administration (MDA): Population-based treatment with ivermectin is the current core strategy to eliminate onchocerciasis, with a minimum requirement of 80% therapeutic coverage.
• Triple Drug Cocktail: A study evaluated the safety and efficacy of a triple drug cocktail comprised of IVM, DEC, and albendazole (collectively known as IDA), which showed promising results.

Important Considerations

• Older Treatments: Older treatments for onchocerciasis, such as suramin and diethylcarbamazine, should not be used due to their severe secondary effects.
• Future Directions: Promising microfilaricidal drugs like moxidectin may reduce the current number of times and length of treatment for onchocerciasis.

Key Takeaways

• Ivermectin is the current core strategy to eliminate onchocerciasis, with a minimum requirement of 80% therapeutic coverage.
• Moxidectin is an approved antiparasitic drug for treating onchocerciasis in patients aged 12 years or older.
• A triple drug cocktail comprising IVM, DEC, and albendazole (IDA) showed promising results in a study.

References:

• Aziz et al. (1982)
• Turner et al. (2024)
• Tagboto et al. (2022)
• Turner et al. (2024)
• World Health Organization (WHO)

Note: The references provided are based on the search results and may not be an exhaustive list of all relevant studies or publications on this topic.

Differential Diagnosis of Onchocerciasis

Onchocerciasis, also known as river blindness, can be challenging to diagnose due to its similar symptoms with other skin conditions. The differential diagnosis of onchocerciasis involves ruling out other helminthic infestations and dermatological conditions that may present with similar symptoms.

Important Differential Diagnoses: