Onchocerciasis
Disease Details
Family Health Simplified
- Description
- Onchocerciasis, also known as river blindness, is a parasitic disease caused by the filarial worm Onchocerca volvulus, transmitted to humans through the bite of an infected blackfly, leading to severe itching, skin changes, and visual impairment.
- Type
- Onchocerciasis, also known as river blindness, is a parasitic disease caused by the filarial worm Onchocerca volvulus. It is not genetically transmitted; rather, it is spread through the bite of infected blackflies of the Simulium species.
- Signs And Symptoms
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It is possible for the larvae to move through the body without triggering a response from the host's immune system, so some people who are infected with the parasite experience no symptoms; the Global Burden of Disease Study estimated that in 2017 there were at least 20.9 million people infected worldwide, of which 14.6 million had skin disease symptoms and 1.15 million experienced symptoms that impacted vision. After a blackfly bite, it can take 12–18 months for the larvae to develop into mature adult worms that will produce their own larvae, which is what leads to the development of symptoms. Almost all the clinical manifestations of onchocerciasis are due to localized host inflammatory responses to dead or dying microfilariae (larvae). The signs and symptoms of onchocerciasis are usually divided into two categories, skin and eye symptoms.
Skin symptoms will develop years before any vision problems. These symptoms include:
Intense itching
Swelling
Inflammation
Depigmentation
Hyperpigmentation
Rash
Nodules under the skin
Skin atrophy
Hanging groin (folds of inelastic atrophic skin in the groin associated with enlarged lymph nodes)Eye symptoms include:
Vision impairment, low vision, or permanent blindness.
Clouding of the cornea
Light sensitivity
Lesions on eyes
Glaucoma
Eye pain
Eye rednessEye symptoms provides the common name associated with onchocerciasis, river blindness, and may involve any part of the eye from conjunctiva and cornea to uvea and posterior segment, including the retina and optic nerve. The microfilariae migrate to the surface of the cornea. Punctate keratitis occurs in the infected area. This clears up as the inflammation subsides. However, if the infection is chronic, sclerosing keratitis can occur, making the affected area become opaque. Over time, the entire cornea may become opaque, thus leading to blindness. Some evidence suggests the effect on the cornea is caused by an immune response to bacteria present in the worms. - Prognosis
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Onchocerciasis, also known as river blindness, is a chronic parasitic disease caused by the filarial worm Onchocerca volvulus. Prognosis for individuals with onchocerciasis can vary based on the severity of the infection and the timeliness and effectiveness of treatment:
1. **Mild Infection**: With appropriate and timely treatment, the prognosis is generally good. Antiparasitic medications such as ivermectin can kill the microfilariae (the larval stage of the parasite) and reduce symptoms.
2. **Severe Infection**: If left untreated, onchocerciasis can lead to serious complications, including severe itching, skin changes, and significant visual impairment or blindness. Chronic infection can also cause permanent skin changes and damage to lymphatic tissues.
3. **Management**: Continuous treatment and mass drug administration programs in endemic areas have significantly reduced the prevalence and severity of the disease. Regular intake of ivermectin every 6-12 months is recommended to control the infection and prevent transmission.
Overall, while onchocerciasis can have severe and debilitating effects if untreated, effective treatment and management programs greatly improve the long-term prognosis for affected individuals. - Onset
- Onchocerciasis, also known as river blindness, is caused by the parasitic worm *Onchocerca volvulus*. The onset of symptoms is typically gradual and can take months to years after the initial infection, as the adult worms and microfilariae (larvae) gradually accumulate in the body. Early signs may include skin rashes, intense itching, and the formation of nodules under the skin. If left untreated, it can eventually lead to more severe symptoms, such as skin changes (e.g., leopard skin, lizard skin), eye lesions, and blindness.
- Prevalence
- Onchocerciasis, also known as river blindness, primarily affects populations in sub-Saharan Africa. It is caused by the parasitic worm *Onchocerca volvulus*, which is transmitted through the bite of infected blackflies. The World Health Organization estimates that about 21 million people are infected, with 99% of cases occurring in 31 African countries. It remains a significant public health issue in these regions, despite ongoing efforts to control and eliminate the disease.
- Epidemiology
- About 21 million people were infected with this parasite in 2017; about 1.2 million of those had vision loss. As of 2017, about 99% of onchocerciasis cases occurred in Africa. Onchocerciasis is currently relatively common in 31 African countries, Yemen, and isolated regions of South America. Over 85 million people live in endemic areas, and half of these reside in Nigeria. Another 120 million people are at risk for contracting the disease. The Onchocerca volvulus main habitat is fast flowing rivers, Onchocerciasis is more commonly found along the large rivers in northern and central regions of Africa, with cases decreasing with distance from the rivers. Multiple exposure to Simulium blackflies raise the number of adult worms and microfilariae that are present in the host. Risk of contracting Onchocerciasis for casual travelers is low, since it often takes several exposures, while travelers that stay for longer visits such as missionaries or long-term volunteers have a greater risk of contracting Onchocerciasis. Onchocerciasis was eliminated in the northern focus in Chiapas, Mexico, and the focus in Oaxaca, Mexico, where Onchocerca volvulus existed, was determined, after several years of treatment with ivermectin, as free of the transmission of the parasite. In April 2013, Colombia became the first country to achieve elimination of Onchocerciasis, verified by the World Health Organization. In the following three years, Ecuador and Guatemala, along with Mexico have been verified to have eliminated Onchocerciasis, with the use of ivermectin.Cities in Nigeria, Cameroon, Ethiopia, Uganda, and the Congo by far have had the largest amount of infected individuals.The efforts of CDTI (Community-Directed Treatment with Ivermectin) was conducted to study Onchocerciasis associations with epilepsy. The results do not go unnoticed as they were able to decrease the number of microfilariae (larvae) loads. This was able to decrease the number of blind people due to onchocerciasis dramatically. However, another issue that arises is the fact that onchocerciasis is able to cause epilepsy, most likely because the level of microfilariae load required to develop epilepsy is much lower than to develop blindness.According to a 2002 WHO report, onchocerciasis has not caused a single death, but its global burden is 987,000 disability adjusted life years (DALYs). The severe pruritus alone accounts for 60% of the DALYs. Infection reduces the host's immunity and resistance to other diseases, which results in an estimated reduction in life expectancy of 13 years. In 2017, the Global Burden of Disease study said that an estimated 220 million people needed preventive chemotherapy for onchocerciasis. Of those infected, 14.6 million had skin disease and 1.15 million experienced vision loss.Onchocerciasis is the second leading cause of blindness from infectious causes. Main disease symptoms, such as blindness and itching, contribute to disease burden by limiting the infected individuals ability to live and work. Individuals most at risk are those who live or work in areas where Simulium blackflies are most common, mostly near rivers and streams. Rural agricultural areas in sub-Saharan Africa see the most disease burden by blackfly bites. Onchocerciasis common to tropical environments, like that of sub-Saharan Africa, where more than 99% percent of infected individuals occupy the 31 countries. Onchocerciasis can be linked to impoverished remote areas, as residents who experience symptoms can no longer tend to land or navigate the area. Areas with high infection rates may experience up to one-third of residents affected by onchocerciasis symptoms. The age group most impacted by the disease are individuals age 61+ years.
- Intractability
- Onchocerciasis, also known as river blindness, is not entirely intractable. While it is a severe and chronic disease, it can be managed and controlled with effective treatments. The primary treatment involves the use of the antiparasitic drug ivermectin, which kills the microfilariae (larvae) but not the adult worms. Repeated doses of ivermectin are often required to keep the microfilariae levels low because adult worms can live for many years. Additionally, vector control measures, such as reducing the population of blackflies that transmit the disease, also play a crucial role in managing onchocerciasis. Although complete eradication of the disease is challenging, significant progress has been made in reducing its prevalence and impact.
- Disease Severity
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Onchocerciasis, also known as river blindness, is a chronic parasitic disease that primarily affects the skin, eyes, and other tissues. Infection is caused by the filarial worm Onchocerca volvulus, which is transmitted through the bites of infected blackflies. Disease severity varies depending on the intensity and duration of infection:
1. **Skin:** Itching, rashes, and skin changes like depigmentation and thickening.
2. **Eyes:** Progressive loss of vision leading to blindness; damage to the cornea and optic nerve.
3. **Systemic:** Potential for long-term disability and significant impairment of quality of life.
Early detection and treatment with antiparasitic medications (e.g., ivermectin) are crucial in mitigating severity and preventing complications. - Healthcare Professionals
- Disease Ontology ID - DOID:11678
- Pathophysiology
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Onchocerciasis, also known as river blindness, is caused by the parasitic worm Onchocerca volvulus. The disease is transmitted through the bite of an infected blackfly (Simulium species). When the fly bites a human, it deposits larvae (microfilariae) into the skin. These larvae mature into adult worms, which can live in subcutaneous nodules for up to 15 years. The adult worms produce millions of microfilariae that migrate through the skin, eyes, and other tissues.
The pathophysiology of onchocerciasis involves both the mechanical damage caused by the microfilariae and the host's immune response to the worms. The migrating microfilariae can cause severe itching, skin changes, and eye damage. Dead microfilariae provoke intense inflammatory responses, leading to skin depigmentation, atrophy, and severe eye lesions, which can result in vision impairment or blindness. - Carrier Status
- Carrier status for onchocerciasis involves being infected with the parasitic worm Onchocerca volvulus. Humans serve as the definitive hosts, where the worms mature and reproduce. The disease is primarily spread through the bites of infected blackflies, which serve as vectors. There is no asymptomatic carrier state in onchocerciasis; individuals infected with the parasite will eventually exhibit symptoms ranging from mild itching to severe skin and eye conditions, potentially leading to blindness.
- Mechanism
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Onchocerciasis, also known as river blindness, is caused by the parasitic worm *Onchocerca volvulus*. The disease mechanism involves the following key stages and molecular mechanisms:
1. **Transmission**: The disease is transmitted to humans through the bite of an infected blackfly (*Simulium* species), which introduces *O. volvulus* larvae into the skin.
2. **Development**: The larvae mature into adult worms within the human host. Adult worms typically reside in subcutaneous nodules (onchocercomas).
3. **Reproduction and Microfilariae**: Adult female worms produce thousands of microfilariae daily. These microfilariae migrate through the skin, eyes, and other tissues.
4. **Immune Response and Tissue Damage**:
- **Skin**: Microfilariae provoke immune responses, causing intense itching, rash, and depigmentation, often leading to a condition known as "leopard skin."
- **Eyes**: In the ocular tissues, microfilariae can lead to inflammation and sclerosing keratitis, eventually resulting in blindness.
5. **Molecular Mechanisms**:
- **Immune Evasion**: *O. volvulus* can modulate the host's immune system to evade detection. The parasite secretes proteins that interfere with normal immune signaling.
- **Inflammatory Response**: Dead and dying microfilariae release antigens that trigger inflammatory responses. This involves pathways such as Toll-like receptors (TLRs) and other innate immune mechanisms that recognize parasitic molecules.
- **Oxidative Stress and Tissue Damage**: The inflammation results in the generation of reactive oxygen species (ROS) and nitric oxide (NO), contributing to tissue damage and scarring.
- **Endosymbiont Bacteria**: *O. volvulus* harbors endosymbiotic Wolbachia bacteria, which are essential for the worm's fertility and survival. Wolbachia also contribute to the inflammatory response when the worms die.
Understanding these mechanisms is crucial for developing targeted therapies and effective disease management strategies. - Treatment
- In mass drug administration (MDA) programmes, the treatment for onchocerciasis is ivermectin (trade name: Mectizan). Ivermectin is administered four times a year and will be continually administered for 10–14 years due to the lifespan of the adult worm. Intense skin itching is eventually relieved, and the progression towards blindness is halted. The drug works by reducing the release of larvae from the adult worm but the drug does not kill it. However the drug does not prevent transmission of Onchocerciasis. It however reduces morbidity and has shown promising results to eliminate in some endemic areas of AfricaIvermectin treatment is particularly effective because it only needs to be taken once or twice a year, needs no refrigeration, and has a wide margin of safety, with the result that it has been widely given by minimally trained community health workers. Patients taking the drug for the treatment of onchocerciasis may have adverse effects within 1–2 days after the drug is administered. Symptoms of urticaria, pruritus, fever, dermatitis, myalgia, urticaria, swelling of face and limbs, or postural hypotension.
- Compassionate Use Treatment
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For onchocerciasis, also known as "river blindness," treatment primarily focuses on the use of ivermectin, which is effective in killing the microfilariae (larval stage of the parasite).
**Compassionate Use Treatment**:
- **Ivermectin**: This remains the primary drug used under compassionate use programs, particularly in regions where it is not readily available through regular channels.
**Off-label or Experimental Treatments**:
- **Doxycycline**: Used off-label to target the endosymbiotic bacteria Wolbachia within the adult worms. This antibiotic has shown promise in sterilizing female worms and reducing microfilariae levels.
- **Moxidectin**: Currently being evaluated, moxidectin is an anthelmintic that may offer longer-lasting suppression of microfilariae compared to ivermectin.
- **Minocycline and Rifampicin**: Though less common, these antibiotics are also being explored for their potential effects on Wolbachia.
These treatments are part of ongoing research to improve outcomes for individuals affected by onchocerciasis. - Lifestyle Recommendations
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For onchocerciasis, also known as river blindness:
**Lifestyle Recommendations:**
1. **Avoid Insect Bites:**
- **Use Insect Repellents:** Apply repellents containing DEET to exposed skin.
- **Wear Protective Clothing:** Long-sleeved shirts and pants can help shield your skin.
- **Use Bed Nets:** Sleep under insecticide-treated bed nets, especially in endemic areas.
2. **Stay Indoors During Peak Hours:**
- **Avoid Dusk and Dawn Outdoors:** Blackflies, which transmit the parasite, are most active during these times.
3. **Environmental Control:**
- **Reduce Breeding Sites:** Avoid areas near rivers and streams where blackflies breed.
- **Community-wide Efforts:** Support programs aimed at reducing blackfly populations and promoting environmental management.
4. **Personal Hygiene and Cleanliness:**
- **Regular Cleaning:** Maintain personal hygiene to reduce the chances of secondary infections in the skin affected by the disease.
5. **Health Monitoring and Medical Follow-up:**
- **Regular Check-ups:** Consult healthcare providers regularly if you're in or have traveled to endemic regions.
- **Treatment Adherence:** Follow prescribed treatments strictly, such as ivermectin, to manage the disease and prevent complications.
Implementing these recommendations can help mitigate the risk of contracting and dealing with onchocerciasis. - Medication
- Onchocerciasis, also known as river blindness, is primarily treated with ivermectin. This medication is typically administered as an oral dose every six months to kill the microfilariae (larval worms) of Onchocerca volvulus, the parasite responsible for the disease. Ivermectin does not kill the adult worms but helps reduce symptoms and transmission. Doxycycline is sometimes used as an adjunct treatment because it can target Wolbachia bacteria, which are symbiotic with the adult worms, thereby indirectly affecting the adult worms' viability.
- Repurposable Drugs
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There are several drugs that have been explored for repurposing in the treatment of onchocerciasis. Among the prominent ones are:
1. **Doxycycline**: This antibiotic targets the Wolbachia bacteria, which are endosymbionts essential for the survival and fertility of the Onchocerca volvulus worms.
2. **Minocycline**: Similar to doxycycline, minocycline is another antibiotic that targets Wolbachia bacteria.
3. **Rifampicin**: This antibiotic has also been investigated for its potential to deplete Wolbachia.
These drugs can be used alongside the standard treatment, ivermectin, to potentially enhance efficacy and manage infections in areas with high transmission rates or where ivermectin resistance may be a concern. - Metabolites
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Onchocerciasis, also known as river blindness, is caused by the parasitic worm *Onchocerca volvulus*. As the disease is primarily associated with the infection of this parasite, there are no specific metabolites unique to onchocerciasis itself. However, the metabolic products of the parasite and the immune response they trigger in the human host, such as the release of inflammatory mediators and eosinophilic activity, play crucial roles in the disease's pathology.
Nanotechnological approaches are being explored for onchocerciasis, including the development of nanocarriers for targeted drug delivery. These nanocarriers can enhance the effectiveness and reduce the side effects of antiparasitic medications, such as ivermectin and doxycycline, which are used to treat and manage the infection. - Nutraceuticals
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Onchocerciasis, also known as river blindness, is primarily treated through antiparasitic medications like ivermectin. There is limited evidence to suggest that nutraceuticals (dietary supplements and food derived products) play a significant role in the treatment or prevention of onchocerciasis. Treatment typically focuses on medication to kill the microfilariae and managing symptoms.
In the context of nanotechnology, research is still in its early stages. Nanomedicine may hold potential for improved drug delivery systems or novel treatments in the future, but current standard treatment protocols do not include nanotechnology-based therapies. - Peptides
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Onchocerciasis, also known as river blindness, is caused by the parasitic worm Onchocerca volvulus. The adult worms live in subcutaneous nodules in the human host and produce microfilariae. These microfilariae cause significant morbidity when they migrate through the skin and eyes.
Peptides: Research has shown that certain peptides can play roles in the immune response against Onchocerca volvulus. For example, synthetic peptides derived from the parasite's proteins have been studied and used to better understand the host’s immune response and, potentially, to develop diagnostic tools and vaccines.
Nan: Nanotechnology applications in onchocerciasis are relatively nascent. However, there is potential for nanoparticles to be used in drug delivery systems to improve the treatment of onchocerciasis. Nanoparticles could help in targeting the parasitic worms more effectively and potentially reducing the side effects of existing medications.