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Onchocerca volvulus

March 08, 2023

Onchocerca volvulus is a filarial (arthropod-borne) nematode (roundworm) that causes onchocerciasis (river blindness), and is the second-leading cause of blindness due to infection worldwide after trachoma. It is one of the 20 neglected tropical diseases listed by the World Health Organization, with elimination from certain countries expected by 2020.[1]

Onchocerca volvulus
Onchocerca volvulus, the causative agent of river blindness
Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Class: Chromadorea
Order: Rhabditida
Family: Onchocercidae
Genus: Onchocerca
Species:
O. volvulus
Binomial name
Onchocerca volvulus
Leuckart, 189r

John O’Neill, an Irish surgeon, first described Onchocerca volvulus in 1874, when he found it to be the causative agent of ‘craw-craw’, a skin disease found in West Africa.[2] A Guatemalan doctor, Rodolfo Robles, first linked it to visual impairment in 1917.[3]

O. volvulus is primarily found in sub-Saharan Africa, and humans are the only known definitive host; there is also disease transmission in some South American nations, as well as Yemen (see global map bottom right). It is spread from person to person via female biting blackflies of the genus Simulium.[4]

Morphology

 
Photomicrograph (glycine mount) of several O. volvulus individuals

O. volvulus parasites obtain nutrients from the human host by ingesting blood or by diffusion through their cuticle. They may be able to trigger blood-vessel formation because dense vascular networks are often found surrounding the worms.[5] They are distinguished from other human-infecting filarial nematodes by the presence of deep transverse striations.[6]

It is a dioecious species, containing distinct males and females, which form nodules under the skin in humans. Mature female worms permanently reside in these fibrous nodules, while male worms are free to move around the subcutaneous tissue. The males are smaller than females, with male worms measuring 23 mm in length compared to 230–700 mm in females.[6]

The release of oocytes (eggs) in female worms does not depend upon the presence of a male worm, although they may attract male worms using unidentified pheromones.[7] The first larval stage, microfilariae, are 300 μm in length and unsheathed, meaning that when they mature into microfilariae, they exit from the envelope of the egg.[8]

Lifecycle

The average adult worm lifespan is 15 years, and mature females can produce between 500 and 1,500 microfilariae per day. The normal microfilarial lifespan is 1.0 to 1.5 years; however, their presence in the bloodstream causes little to no immune response until death or degradation of the microfilariae or adult worms.[9]

Blackfly stages

 
The lifecycle of O. volvulus
  1. The microfilariae of O. volvulus are found in the dermis layer of skin in the host.
  2. When a female Simulium blackfly takes a blood meal from an infected host, the microfilariae are also ingested.
  3. From here, the microfilariae penetrate the gut and migrate to the thoracic flight muscles, where they enter the first juvenile phase, J1.
  4. After maturing into J2, the second juvenile phase, they migrate to the proboscis, where they are found in the saliva.
  5. J2 stage juveniles then mature into infectious stage three juveniles, J3, in the saliva. The lifecycle in the blackfly takes between one and three weeks.[10]

Human stages

  1. When the female blackfly takes a blood meal, J3 juveniles pass into the human bloodstream.
  2. From here, the juveniles migrate to the subcutaneous tissue, where they form nodules and mature into adult worms over a period of 6–12 months.
  3. After maturation, the smaller adult males migrate from nodules to subcutaneous tissue, where they mate with the larger adult females.
  4. The eggs mature internally to form stage-one microfilariae, which are released from the female's body one at a time and remain in the subcutaneous tissue.
  5. The microfilariae are taken up by a female blackfly when it takes a blood meal, thus completing the lifecycle of O. volvulus.[4]

Disease

O. volvulus causes onchocerciasis, which causes severe itching. Long-term infection can cause keratitis, an inflammation of the cornea in the eye, and ultimately leads to blindness.[8] Symptoms are caused by the microfilariae and the immune response to infection, rather than the adults themselves. The most effective treatment involves using ivermectin, although resistance to this drug has been reported as developing.[11] Ivermectin prevents female worms from releasing microfilariae for several months, thus relieving symptoms and temporarily preventing transmission. However, this does not kill adult worms, so it must be taken once annually as long as adult worms are present.[12]

O. volvulus has been proposed as one of the causative agents of nodding syndrome, a condition that affects children aged 5 to 15 and is currently only observed in South Sudan, Tanzania, and northern Uganda. Although the cause of the disease is unknown, O. volvulus is being increasingly studied as a possible cause due to its ubiquity in areas where the disease is found.[13]

Epidemiology

 
Geographical distribution of O. volvulus as of March 2017: Endemic countries are shown in red, previous endemic countries in blue, and countries with no local cases in orange.[14]

An estimated 187 million people are at risk of O. volvulus infection, with 17–25 million people infected and 0.8 million showing some impairment of vision. O. volvulus has not directly caused a single death, but has cost 1.1 million disability adjusted life years, which measure the number of years of healthy life lost due to a specific disease and show the burden of a disease.[15]

Simulium blackfly adults require moving water to breed and eggs remain in water until they exit from the pupa and enter the adult stage of their lifecycle. Due to this restriction, O. volvulus is only found around streams or rivers. Artificial water systems, such as hydroelectric power plants, built in Africa, provide ideal conditions all year for blackfly development and make controlling its spread difficult.[16]

About 99% of cases of onchocerciasis are found in 31 countries in sub-Saharan Africa, although areas of limited transmission occur in Brazil, Venezuela, and Yemen.[14] The disease is thought to have been imported into Latin America through the slave trade.[17] Onchocerciasis was eliminated from Colombia in 2013, Ecuador in 2014, Mexico in 2015, and Guatemala in 2016[15] due to control programs that used mass drug administration with ivermectin.[14]

Genome

 
Representation of the possible chromosome fusion seen in O. volvulus

The total genome size of O. volvulus is 1.5x108 base pairs and contains around 4,000 genes, with genes for collagen and cuticular proteins being highly expressed in mature adults.[18] O. volvulus has four chromosome pairs, which include a single pair of sex chromosomes. A large X sex chromosome and a smaller Y sex chromosome determine male worms, while two X chromosomes determine female worms.[19]

One of the three nonsex chromosomes is thought to have formed by a fusion event between two smaller chromosomes.[18]

Evolution

(Simplified phylogenetic tree of the genus Onchocerca.[20])

Dirofilaria

Onchocerca flexuosa

Onchocerca lupi

Onchocerca ochengi

Onchocerca volvulus

O. volvulus has low genetic variation between individuals. This suggests a population bottleneck occurred in the past that caused a rapid decrease in the population size.[18] It also shows high haplotype diversity, which is a measure of how unique a group of linked genes is. This pattern of low genetic variation and high haplotype diversity suggests fast population expansion after a bottleneck and has led to the theory that a host shift event from cattle allowed O. volvulus to infect humans.[21] This is also supported by genetic data that place O. ochengi (a cattle-infecting strain) as the sister group to O. volvulus.[20]

Immune response

Adult worms are found in nodules and are hidden from most components of the human immune system. Microfilariae are more vulnerable to attack by immune cells because they exit nodules to complete their lifecycle. O. volvulus can be detected by the immune system through the release of soluble antigens and antigens found on the surface of microfilariae and infective J3 juveniles. These antigens allow the immune system to detect the presence of a foreign organism in the body and trigger an immune response to clear infection.[22]

The immune response involves raising antibodies (IgG, IgM and IgE type) that can react with soluble antigens released by Onchocerca volvulus.[23] Opsonising antibodies that tag cells for destruction are also found against the infective J3 stage and microfilariae, but there is not enough evidence at the moment to say whether this is protective.[24]

The antigens of O. volvulus are highly complex and show cross-reactivity with several other filarial worms. Little evidence indicates that antibodies made are specific to O. volvulus. However, after the age of 40, the number of parasites carried (the intensity of infection) decreases, suggesting that over time, some sort of protective immune response develops.[22]

Modulation by O. volvulus

Microfilariae can also modulate the immune system to avoid destruction. The complement system is used to enhance the effect of antibodies and phagocytic cells, which engulf and destroy other cells. Microfilariae block this pathway by cleaving C3b—an important protein in this process—to form iC3b. iC3b cannot go on to activate the next step in the pathway and allows microfilariae to remain in the body with little to no attack by the immune system.[25]

Endosymbiotic relationship with Wolbachia

O. volvulus, along with most filarial nematodes, share an endosymbiotic relationship with the bacterium Wolbachia. In the absence of Wolbachia, larval development of O. volvulus is disrupted or ceased.[26] These bacteria have been proposed to enhance the symptoms and severity of onchocerciasis by triggering inflammatory responses in the host.[27]

References

  1. ^ "Neglected tropical diseases". World Health Organization. March 2017. Retrieved 17 March 2017.
  2. ^ O’Neill, J. (1875). "On the presence of a filaria in " craw-craw" (PDF). The Lancet. 105 (2686): 265–266. doi:10.1016/s0140-6736(02)30941-3.
  3. ^ Robles, R. (1917). "Enfermedad nueva en Guatemala". La Juventud Médica.
  4. ^ a b Duke, B.O. (1993). "The population dynamics of Onchocerca volvulus in the human host". Tropical Medicine and Parasitology. 44 (2): 61–68. ISSN 0177-2392. PMID 8367667.
  5. ^ Burnham, G. (1998). "Onchocerciasis". Lancet. 351 (9112): 1341–1346. doi:10.1016/S0140-6736(97)12450-3. ISSN 0140-6736. PMID 9643811. S2CID 208794023.
  6. ^ a b Neafie, R.C. (1972). "Morphology of Onchocerca volvulus". American Journal of Clinical Pathology. 57 (5): 574–586. doi:10.1093/ajcp/57.5.574. ISSN 0002-9173. PMID 5025601.
  7. ^ Schulz-Key, H.; Soboslay, P.T. (1994). "Reproductive biology and population dynamics of Onchocerca volvulus in the vertebrate host". Parasite. 1 (1S): S53–S55. doi:10.1051/parasite/199401s1053. ISSN 1252-607X.
  8. ^ a b Udall, D.N. (2007). "Recent updates on onchocerciasis: diagnosis and treatment". Clinical Infectious Diseases. 44 (1): 53–60. doi:10.1086/509325. ISSN 1537-6591. PMID 17143815.
  9. ^ Schulz-Key, H. (1990). "Observations on the Reproductive Biology of Onchocerca volvulus". Acta Leidensia (in Dutch). 59 (1–2): 27–44. PMID 2378210.
  10. ^ Eichner, M.; Renz, A.; Wahl, G.; Enyong, P. (1991). "Development of Onchocerca volvulus microfilariae injected into Simulium species from Cameroon". Medical and Veterinary Entomology. 5 (3): 293–298. doi:10.1111/j.1365-2915.1991.tb00555.x. ISSN 1365-2915. PMID 1768922. S2CID 2794018.
  11. ^ Lustigman, S.; McCarter, J.P. (2007). "Ivermectin Resistance in Onchocerca volvulus: Toward a Genetic Basis". PLOS Neglected Tropical Diseases. 1 (1): e76. doi:10.1371/journal.pntd.0000076. ISSN 1935-2735. PMC 2041823. PMID 17989789.
  12. ^ Ejere, Henry O. D.; Schwartz, Ellen; Wormald, Richard; Evans, Jennifer R. (15 August 2012). "Ivermectin for onchocercal eye disease (river blindness)". The Cochrane Database of Systematic Reviews (8): CD002219. doi:10.1002/14651858.CD002219.pub2. ISSN 1469-493X. PMC 4425412. PMID 22895928.
  13. ^ Idro, R.; Opar, B.; Wamala, J.; Abbo, C.; Onzivua, S.; Mwaka, D.A.; Kakooza-Mwesige, A.; Mbonye, A.; Aceng, J.R. (2016). "Is nodding syndrome an Onchocerca volvulus-induced neuroinflammatory disorder? Uganda's story of research in understanding the disease". International Journal of Infectious Diseases. 45: 112–117. doi:10.1016/j.ijid.2016.03.002. ISSN 1878-3511. PMID 26987477.
  14. ^ a b c "Onchocerciasis Fact sheet N°374". World Health Organization. March 2017. Retrieved 16 March 2017.
  15. ^ a b . World Health Organization. March 2017. Archived from the original on 23 March 2017. Retrieved 17 March 2017.
  16. ^ Myburgh, E.; Nevill, E.M. (2003). "Review of blackfly (Diptera: Simuliidae) control in South Africa". The Onderstepoort Journal of Veterinary Research. 70 (4): 307–316. doi:10.4102/ojvr.v70i4.295. ISSN 0030-2465. PMID 14971733.
  17. ^ Gustavsen, K.; Hopkins, A.; Sauerbrey, M. (2011). "Onchocerciasis in the Americas: from arrival to (near) elimination". Parasites & Vectors. 4: 205. doi:10.1186/1756-3305-4-205. ISSN 1756-3305. PMC 3214172. PMID 22024050.
  18. ^ a b c Unnasch, Thomas R; Williams, S.A. (2000). "The genomes of Onchocerca volvulus". International Journal for Parasitology. 30 (4): 543–552. doi:10.1016/S0020-7519(99)00184-8. PMID 10731575.
  19. ^ Post, R. (2005). "The chromosomes of the Filariae". Filaria Journal. 4: 10. doi:10.1186/1475-2883-4-10. ISSN 1475-2883. PMC 1282586. PMID 16266430.
  20. ^ a b team, European Centre for Disease Prevention and Control (ECDC)—Health Communication Unit—Eurosurveillance editorial (23 April 2015). "Human case of Onchocerca lupi infection, Germany, August 2014". Eurosurveillance. 20 (16). doi:10.2807/1560-7917.es2015.20.16.21099. PMID 25953271.
  21. ^ Morales-Hojas, R.; Cheke, R.A.; Post, R.J. (2007). "A preliminary analysis of the population genetics and molecular phylogenetics of Onchocerca volvulus (Nematoda: Filarioidea) using nuclear ribosomal second internal transcribed spacer sequences". Memórias do Instituto Oswaldo Cruz. 102 (7): 879–882. doi:10.1590/S0074-02762007005000114. ISSN 0074-0276. PMID 17992364.
  22. ^ a b Greene, B.M.; Gbakima, A.A.; Albiez, E.J.; Taylor, H.R. (1985). "Humoral and cellular immune responses to Onchocerca volvulus infection in humans". Reviews of Infectious Diseases. 7 (6): 789–795. doi:10.1093/clinids/7.6.789. ISSN 0162-0886. PMID 4070916.
  23. ^ Ngu, J.L.; Blackett, K. (1976). "Immunological studies in onchocerciasis in Cameroon". Tropical and Geographical Medicine. 28 (2): 111–120. ISSN 0041-3232. PMID 788262.
  24. ^ Greene, B.M.; Taylor, H.R.; Aikawa, M. (1981). "Cellular killing of microfilariae of Onchocerca volvulus: eosinophil and neutrophil-mediated immune serum-dependent destruction". Journal of Immunology. 127 (4): 1611–1618. ISSN 0022-1767. PMID 7276574.
  25. ^ Meri, T.; Jokiranta, T.S.; Hellwage, J.; Bialonski, A.; Zipfel, P.F.; Meri, S. (2002). "Onchocerca volvulus microfilariae avoid complement attack by direct binding of factor H". The Journal of Infectious Diseases. 185 (12): 1786–1793. doi:10.1086/340649. ISSN 0022-1899. PMID 12085326.
  26. ^ Saint André, A.V.; Blackwell, N.M.; Hall, L.R.; Hoerauf, A.; Brattig, N.W.; Volkmann, L.; Taylor, M.J.; Ford, L.; Hise, A.G. (2002). "The Role of Endosymbiotic Wolbachia Bacteria in the Pathogenesis of River Blindness" (PDF). Science. 295 (5561): 1892–1895. Bibcode:2002Sci...295.1892S. doi:10.1126/science.1068732. ISSN 0036-8075. PMID 11884755. S2CID 22130066.
  27. ^ Tamarozzi, F.; Halliday, A.; Gentil, K.; Hoerauf, A.; Pearlman, E.; Taylor, M.J. (2011). "Onchocerciasis: the Role of Wolbachia Bacterial Endosymbionts in Parasite Biology, Disease Pathogenesis, and Treatment". Clinical Microbiology Reviews. 24 (3): 459–468. doi:10.1128/CMR.00057-10. ISSN 0893-8512. PMC 3131055. PMID 21734243.

External links

  • "Onchocerca volvulus". NCBI Taxonomy Browser. 6282.

March 08, 2023
onchocerca, volvulus, filarial, arthropod, borne, nematode, roundworm, that, causes, onchocerciasis, river, blindness, second, leading, cause, blindness, infection, worldwide, after, trachoma, neglected, tropical, diseases, listed, world, health, organization,. Onchocerca volvulus is a filarial arthropod borne nematode roundworm that causes onchocerciasis river blindness and is the second leading cause of blindness due to infection worldwide after trachoma It is one of the 20 neglected tropical diseases listed by the World Health Organization with elimination from certain countries expected by 2020 1 Onchocerca volvulusOnchocerca volvulus the causative agent of river blindnessScientific classificationKingdom AnimaliaPhylum NematodaClass ChromadoreaOrder RhabditidaFamily OnchocercidaeGenus OnchocercaSpecies O volvulusBinomial nameOnchocerca volvulusLeuckart 189rJohn O Neill an Irish surgeon first described Onchocerca volvulus in 1874 when he found it to be the causative agent of craw craw a skin disease found in West Africa 2 A Guatemalan doctor Rodolfo Robles first linked it to visual impairment in 1917 3 O volvulus is primarily found in sub Saharan Africa and humans are the only known definitive host there is also disease transmission in some South American nations as well as Yemen see global map bottom right It is spread from person to person via female biting blackflies of the genus Simulium 4 Contents 1 Morphology 2 Lifecycle 2 1 Blackfly stages 2 2 Human stages 3 Disease 4 Epidemiology 5 Genome 6 Evolution 7 Immune response 7 1 Modulation by O volvulus 8 Endosymbiotic relationship with Wolbachia 9 References 10 External linksMorphology Edit Photomicrograph glycine mount of several O volvulus individuals O volvulus parasites obtain nutrients from the human host by ingesting blood or by diffusion through their cuticle They may be able to trigger blood vessel formation because dense vascular networks are often found surrounding the worms 5 They are distinguished from other human infecting filarial nematodes by the presence of deep transverse striations 6 It is a dioecious species containing distinct males and females which form nodules under the skin in humans Mature female worms permanently reside in these fibrous nodules while male worms are free to move around the subcutaneous tissue The males are smaller than females with male worms measuring 23 mm in length compared to 230 700 mm in females 6 The release of oocytes eggs in female worms does not depend upon the presence of a male worm although they may attract male worms using unidentified pheromones 7 The first larval stage microfilariae are 300 mm in length and unsheathed meaning that when they mature into microfilariae they exit from the envelope of the egg 8 Lifecycle EditThe average adult worm lifespan is 15 years and mature females can produce between 500 and 1 500 microfilariae per day The normal microfilarial lifespan is 1 0 to 1 5 years however their presence in the bloodstream causes little to no immune response until death or degradation of the microfilariae or adult worms 9 Blackfly stages Edit The lifecycle of O volvulus The microfilariae of O volvulus are found in the dermis layer of skin in the host When a female Simulium blackfly takes a blood meal from an infected host the microfilariae are also ingested From here the microfilariae penetrate the gut and migrate to the thoracic flight muscles where they enter the first juvenile phase J1 After maturing into J2 the second juvenile phase they migrate to the proboscis where they are found in the saliva J2 stage juveniles then mature into infectious stage three juveniles J3 in the saliva The lifecycle in the blackfly takes between one and three weeks 10 Human stages Edit When the female blackfly takes a blood meal J3 juveniles pass into the human bloodstream From here the juveniles migrate to the subcutaneous tissue where they form nodules and mature into adult worms over a period of 6 12 months After maturation the smaller adult males migrate from nodules to subcutaneous tissue where they mate with the larger adult females The eggs mature internally to form stage one microfilariae which are released from the female s body one at a time and remain in the subcutaneous tissue The microfilariae are taken up by a female blackfly when it takes a blood meal thus completing the lifecycle of O volvulus 4 Disease EditO volvulus causes onchocerciasis which causes severe itching Long term infection can cause keratitis an inflammation of the cornea in the eye and ultimately leads to blindness 8 Symptoms are caused by the microfilariae and the immune response to infection rather than the adults themselves The most effective treatment involves using ivermectin although resistance to this drug has been reported as developing 11 Ivermectin prevents female worms from releasing microfilariae for several months thus relieving symptoms and temporarily preventing transmission However this does not kill adult worms so it must be taken once annually as long as adult worms are present 12 O volvulus has been proposed as one of the causative agents of nodding syndrome a condition that affects children aged 5 to 15 and is currently only observed in South Sudan Tanzania and northern Uganda Although the cause of the disease is unknown O volvulus is being increasingly studied as a possible cause due to its ubiquity in areas where the disease is found 13 Epidemiology Edit Geographical distribution of O volvulus as of March 2017 Endemic countries are shown in red previous endemic countries in blue and countries with no local cases in orange 14 An estimated 187 million people are at risk of O volvulus infection with 17 25 million people infected and 0 8 million showing some impairment of vision O volvulus has not directly caused a single death but has cost 1 1 million disability adjusted life years which measure the number of years of healthy life lost due to a specific disease and show the burden of a disease 15 Simulium blackfly adults require moving water to breed and eggs remain in water until they exit from the pupa and enter the adult stage of their lifecycle Due to this restriction O volvulus is only found around streams or rivers Artificial water systems such as hydroelectric power plants built in Africa provide ideal conditions all year for blackfly development and make controlling its spread difficult 16 About 99 of cases of onchocerciasis are found in 31 countries in sub Saharan Africa although areas of limited transmission occur in Brazil Venezuela and Yemen 14 The disease is thought to have been imported into Latin America through the slave trade 17 Onchocerciasis was eliminated from Colombia in 2013 Ecuador in 2014 Mexico in 2015 and Guatemala in 2016 15 due to control programs that used mass drug administration with ivermectin 14 Genome Edit Representation of the possible chromosome fusion seen in O volvulus The total genome size of O volvulus is 1 5x108 base pairs and contains around 4 000 genes with genes for collagen and cuticular proteins being highly expressed in mature adults 18 O volvulus has four chromosome pairs which include a single pair of sex chromosomes A large X sex chromosome and a smaller Y sex chromosome determine male worms while two X chromosomes determine female worms 19 One of the three nonsex chromosomes is thought to have formed by a fusion event between two smaller chromosomes 18 Evolution Edit Simplified phylogenetic tree of the genus Onchocerca 20 DirofilariaOnchocerca flexuosaOnchocerca lupiOnchocerca ochengiOnchocerca volvulusOnchocerca gibsoniOnchocerca gutturosaOnchocerca jakutensisO volvulus has low genetic variation between individuals This suggests a population bottleneck occurred in the past that caused a rapid decrease in the population size 18 It also shows high haplotype diversity which is a measure of how unique a group of linked genes is This pattern of low genetic variation and high haplotype diversity suggests fast population expansion after a bottleneck and has led to the theory that a host shift event from cattle allowed O volvulus to infect humans 21 This is also supported by genetic data that place O ochengi a cattle infecting strain as the sister group to O volvulus 20 Immune response EditAdult worms are found in nodules and are hidden from most components of the human immune system Microfilariae are more vulnerable to attack by immune cells because they exit nodules to complete their lifecycle O volvulus can be detected by the immune system through the release of soluble antigens and antigens found on the surface of microfilariae and infective J3 juveniles These antigens allow the immune system to detect the presence of a foreign organism in the body and trigger an immune response to clear infection 22 The immune response involves raising antibodies IgG IgM and IgE type that can react with soluble antigens released by Onchocerca volvulus 23 Opsonising antibodies that tag cells for destruction are also found against the infective J3 stage and microfilariae but there is not enough evidence at the moment to say whether this is protective 24 The antigens of O volvulus are highly complex and show cross reactivity with several other filarial worms Little evidence indicates that antibodies made are specific to O volvulus However after the age of 40 the number of parasites carried the intensity of infection decreases suggesting that over time some sort of protective immune response develops 22 Modulation by O volvulus Edit Microfilariae can also modulate the immune system to avoid destruction The complement system is used to enhance the effect of antibodies and phagocytic cells which engulf and destroy other cells Microfilariae block this pathway by cleaving C3b an important protein in this process to form iC3b iC3b cannot go on to activate the next step in the pathway and allows microfilariae to remain in the body with little to no attack by the immune system 25 Endosymbiotic relationship with Wolbachia EditO volvulus along with most filarial nematodes share an endosymbiotic relationship with the bacterium Wolbachia In the absence of Wolbachia larval development of O volvulus is disrupted or ceased 26 These bacteria have been proposed to enhance the symptoms and severity of onchocerciasis by triggering inflammatory responses in the host 27 References Edit Neglected tropical diseases World Health Organization March 2017 Retrieved 17 March 2017 O Neill J 1875 On the presence of a filaria in craw craw PDF The Lancet 105 2686 265 266 doi 10 1016 s0140 6736 02 30941 3 Robles R 1917 Enfermedad nueva en Guatemala La Juventud Medica a b Duke B O 1993 The population dynamics of Onchocerca volvulus in the human host Tropical Medicine and Parasitology 44 2 61 68 ISSN 0177 2392 PMID 8367667 Burnham G 1998 Onchocerciasis Lancet 351 9112 1341 1346 doi 10 1016 S0140 6736 97 12450 3 ISSN 0140 6736 PMID 9643811 S2CID 208794023 a b Neafie R C 1972 Morphology of Onchocerca volvulus American Journal of Clinical Pathology 57 5 574 586 doi 10 1093 ajcp 57 5 574 ISSN 0002 9173 PMID 5025601 Schulz Key H Soboslay P T 1994 Reproductive biology and population dynamics of Onchocerca volvulus in the vertebrate host Parasite 1 1S S53 S55 doi 10 1051 parasite 199401s1053 ISSN 1252 607X a b Udall D N 2007 Recent updates on onchocerciasis diagnosis and treatment Clinical Infectious Diseases 44 1 53 60 doi 10 1086 509325 ISSN 1537 6591 PMID 17143815 Schulz Key H 1990 Observations on the Reproductive Biology of Onchocerca volvulus Acta Leidensia in Dutch 59 1 2 27 44 PMID 2378210 Eichner M Renz A Wahl G Enyong P 1991 Development of Onchocerca volvulus microfilariae injected into Simulium species from Cameroon Medical and Veterinary Entomology 5 3 293 298 doi 10 1111 j 1365 2915 1991 tb00555 x ISSN 1365 2915 PMID 1768922 S2CID 2794018 Lustigman S McCarter J P 2007 Ivermectin Resistance in Onchocerca volvulus Toward a Genetic Basis PLOS Neglected Tropical Diseases 1 1 e76 doi 10 1371 journal pntd 0000076 ISSN 1935 2735 PMC 2041823 PMID 17989789 Ejere Henry O D Schwartz Ellen Wormald Richard Evans Jennifer R 15 August 2012 Ivermectin for onchocercal eye disease river blindness The Cochrane Database of Systematic Reviews 8 CD002219 doi 10 1002 14651858 CD002219 pub2 ISSN 1469 493X PMC 4425412 PMID 22895928 Idro R Opar B Wamala J Abbo C Onzivua S Mwaka D A Kakooza Mwesige A Mbonye A Aceng J R 2016 Is nodding syndrome an Onchocerca volvulus induced neuroinflammatory disorder Uganda s story of research in understanding the disease International Journal of Infectious Diseases 45 112 117 doi 10 1016 j ijid 2016 03 002 ISSN 1878 3511 PMID 26987477 a b c Onchocerciasis Fact sheet N 374 World Health Organization March 2017 Retrieved 16 March 2017 a b Progress towards eliminiating onchocerciasis in the WHO region of the Americas Verification of elimination of transmission in Guatemala and progress report on the elimination of human onchocerciasis 2015 2016 World Health Organization March 2017 Archived from the original on 23 March 2017 Retrieved 17 March 2017 Myburgh E Nevill E M 2003 Review of blackfly Diptera Simuliidae control in South Africa The Onderstepoort Journal of Veterinary Research 70 4 307 316 doi 10 4102 ojvr v70i4 295 ISSN 0030 2465 PMID 14971733 Gustavsen K Hopkins A Sauerbrey M 2011 Onchocerciasis in the Americas from arrival to near elimination Parasites amp Vectors 4 205 doi 10 1186 1756 3305 4 205 ISSN 1756 3305 PMC 3214172 PMID 22024050 a b c Unnasch Thomas R Williams S A 2000 The genomes of Onchocerca volvulus International Journal for Parasitology 30 4 543 552 doi 10 1016 S0020 7519 99 00184 8 PMID 10731575 Post R 2005 The chromosomes of the Filariae Filaria Journal 4 10 doi 10 1186 1475 2883 4 10 ISSN 1475 2883 PMC 1282586 PMID 16266430 a b team European Centre for Disease Prevention and Control ECDC Health Communication Unit Eurosurveillance editorial 23 April 2015 Human case of Onchocerca lupi infection Germany August 2014 Eurosurveillance 20 16 doi 10 2807 1560 7917 es2015 20 16 21099 PMID 25953271 Morales Hojas R Cheke R A Post R J 2007 A preliminary analysis of the population genetics and molecular phylogenetics of Onchocerca volvulus 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Diseases 185 12 1786 1793 doi 10 1086 340649 ISSN 0022 1899 PMID 12085326 Saint Andre A V Blackwell N M Hall L R Hoerauf A Brattig N W Volkmann L Taylor M J Ford L Hise A G 2002 The Role of Endosymbiotic Wolbachia Bacteria in the Pathogenesis of River Blindness PDF Science 295 5561 1892 1895 Bibcode 2002Sci 295 1892S doi 10 1126 science 1068732 ISSN 0036 8075 PMID 11884755 S2CID 22130066 Tamarozzi F Halliday A Gentil K Hoerauf A Pearlman E Taylor M J 2011 Onchocerciasis the Role of Wolbachia Bacterial Endosymbionts in Parasite Biology Disease Pathogenesis and Treatment Clinical Microbiology Reviews 24 3 459 468 doi 10 1128 CMR 00057 10 ISSN 0893 8512 PMC 3131055 PMID 21734243 External links Edit Onchocerca volvulus NCBI Taxonomy Browser 6282 Retrieved from https en wikipedia org w index php title Onchocerca volvulus amp oldid 1139186161, wikipedia, wiki, book, books, library,

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