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International Journal of Infectious... Mar 2021Nodding syndrome is one of several forms of onchocerciasis-associated epilepsy (OAE) seen among children in areas formerly hyperendemic for the transmission of... (Review)
Review
Nodding syndrome is one of several forms of onchocerciasis-associated epilepsy (OAE) seen among children in areas formerly hyperendemic for the transmission of Onchocerca volvulus. These forms of epilepsy are highly prevalent and clustered in certain villages located close to blackfly (Diptera: Simuliidae) breeding sites. OAE presents with a wide spectrum of seizures, including generalized tonic-clonic and head nodding seizures, impaired cognitive function, growth stunting and delayed puberty. In 2014, the present authors published a perspective paper in this journal which hypothesized that nodding syndrome may be caused by either a neurotropic virus transmitted by blackflies or an endosymbiont present within the O. volvulus parasite. Seven years later, this critical review presents progress in nodding syndrome research, and assesses whether it is still plausible that a neurotropic virus or endosymbiont could be the cause.
Topics: Animals; Biomedical Research; Humans; Nodding Syndrome; Onchocerca volvulus; Onchocerciasis; Prevalence
PubMed: 33556614
DOI: 10.1016/j.ijid.2021.02.006 -
Current Neurology and Neuroscience... Apr 2022Neurocysticercosis (NCC) has been well recognized as a leading cause of epilepsy. More recently, studies of other parasitic diseases such as cerebral malaria (CM)... (Review)
Review
PURPOSE OF THE REVIEW
Neurocysticercosis (NCC) has been well recognized as a leading cause of epilepsy. More recently, studies of other parasitic diseases such as cerebral malaria (CM) and onchocerciasis are yielding novel insights into the pathogenesis of parasite-associated epilepsy. We compare the clinical and electrophysiological findings in epilepsy associated with these highly prevalent parasites and discuss the mechanisms involved in epileptogenesis.
RECENT FINDINGS
Electrophysiological and imaging biomarkers continue to emerge, and individuals who are at-risk of developing parasite-associated epilepsies are being identified with greater reliability. While both Taenia solium and Plasmodium falciparum directly affect the brain parenchyma, Onchocerca volvulus is not known to invade the central nervous system. Thus, the causal association between O. volvulus and epilepsy remains controversial. Both NCC and CM have a well-defined acute phase when the parasites directly or indirectly invade the brain parenchyma and lead to local inflammatory changes. This is followed by a chronic phase marked by recurrent seizures. However, these stages of epileptogenic process have not been identified in the case of O. volvulus.
Topics: Epilepsy; Humans; Intestinal Volvulus; Neurocysticercosis; Parasitic Diseases; Reproducibility of Results
PubMed: 35332514
DOI: 10.1007/s11910-022-01187-6 -
Research and Reports in Tropical... 2020Onchocerciasis is a parasitic infection caused by the filarial nematode and transmitted through the bites of black flies of the genus that breed in rivers and streams.... (Review)
Review
Onchocerciasis is a parasitic infection caused by the filarial nematode and transmitted through the bites of black flies of the genus that breed in rivers and streams. The impact of mass treatment with ivermectin and supplemented by vector control in some countries has changed the global scene of onchocerciasis. There has been reported progress made in elimination of onchocerciasis in central and southern American countries and in some localities in Africa. The target for elimination in the Americas has been set at 2022 while for 12 countries in Africa this is expected in 2030. This review was conducted to examine the current status of onchocerciasis elimination at the global level and report on progress made. Literature searches were made through PubMed, articles in English or English abstracts, reports and any other relevant articles related to the subject. The global burden of onchocerciasis is progressively reducing and is no longer a public health problem in some regions. However, programs are challenged with a range of issues: cross-border transmission, diagnostic tools, co-endemicity, limited workforce in entomology and maintaining enthusiasm among community drug distributors. More concerted effort using appropriate tools is required to overcome the challenges.
PubMed: 33117052
DOI: 10.2147/RRTM.S224364 -
Current Opinion in Infectious Diseases Oct 2018With increasing international travel and mass global population migration, clinicians in nonendemic countries must be familiar with imported neglected tropical diseases... (Review)
Review
PURPOSE OF REVIEW
With increasing international travel and mass global population migration, clinicians in nonendemic countries must be familiar with imported neglected tropical diseases including onchocerciasis, which is commonly known as 'river blindness'.
RECENT FINDINGS
Imported onchocerciasis manifests differently in travelers compared with migrants from endemic areas and is likely underdiagnosed in both groups. Recent clinical studies confirm that eosinophilia is not a sensitive marker for Onchocerca volvulus, with one-third of patients having a normal eosinophil count. Novel diagnostics measuring antibodies to multiple recombinant O. volvulus antigens maintain a high sensitivity while improving specificity compared with conventional pan-filarial serologic testing. A 6-week course of doxycycline has macrofilaricidal activity through Wolbachia depletion and may be useful in nonendemic areas in addition to standard serial ivermectin.
SUMMARY
Recent studies characterizing distinct clinical presentations in travelers and migrants may enable clinicians to better recognize imported onchocerciasis. Although novel diagnostics have improved specificity, most remain restricted to tropical disease reference laboratories and to date there is no marker of cure. Prolonged doxycycline treatment may reduce the need for serial ivermectin, though more potent short-course macrofilaricidal drugs are being developed.
Topics: Animals; Antibodies, Helminth; Communicable Diseases, Imported; Diagnostic Tests, Routine; Disease Management; Doxycycline; Filaricides; Human Migration; Humans; Onchocerca volvulus; Onchocerciasis; Transients and Migrants; Travel
PubMed: 30113326
DOI: 10.1097/QCO.0000000000000483 -
Nature Microbiology Nov 2016Ongoing elimination efforts have altered the global distribution of Onchocerca volvulus, the agent of river blindness, and further population restructuring is expected...
Ongoing elimination efforts have altered the global distribution of Onchocerca volvulus, the agent of river blindness, and further population restructuring is expected as efforts continue. Therefore, a better understanding of population genetic processes and their effect on biogeography is needed to support elimination goals. We describe O. volvulus genome variation in 27 isolates from the early 1990s (before widespread mass treatment) from four distinct locales: Ecuador, Uganda, the West African forest and the West African savanna. We observed genetic substructuring between Ecuador and West Africa and between the West African forest and savanna bioclimes, with evidence of unidirectional gene flow from savanna to forest strains. We identified forest:savanna-discriminatory genomic regions and report a set of ancestry informative loci that can be used to differentiate between forest, savanna and admixed isolates, which has not previously been possible. We observed mito-nuclear discordance possibly stemming from incomplete lineage sorting. The catalogue of the nuclear, mitochondrial and endosymbiont DNA variants generated in this study will support future basic and translational onchocerciasis research, with particular relevance for ongoing control programmes, and boost efforts to characterize drug, vaccine and diagnostic targets.
Topics: Africa, Western; Animals; Ecuador; Gene Flow; Genetic Variation; Genotype; Onchocerca volvulus; Phylogeography; Uganda; Wolbachia
PubMed: 27869792
DOI: 10.1038/nmicrobiol.2016.207 -
Brain Research Bulletin Feb 2019Human onchocerciasis, caused by infection by the filarial nematode Onchocerca volvulus, is a major neglected public health problem that affects millions of people in the... (Review)
Review
Human onchocerciasis, caused by infection by the filarial nematode Onchocerca volvulus, is a major neglected public health problem that affects millions of people in the endemic regions of sub-Saharan Africa and Latin America. Onchocerciasis is known to be associated with skin and eye disease and more recently, neurological features have been recognized as a major manifestation. Especially the latter poses a severe burden on affected individuals and their families. Although definite studies are awaited, preliminary evidence suggests that neurological disease may include the nodding syndrome, Nakalanga syndrome and epilepsy but to date, the exact pathophysiological mechanisms remain unclear. Currently, the only way to prevent Onchocera volvulus associated disease is through interventions that target the elimination of onchocerciasis through community distribution of ivermectin and larviciding the breeding sites of the Similium or blackfly vector in rivers. In this review, we discuss the epidemiology, potential pathological mechanisms as well as prevention and treatment strategies of onchocerciasis, focusing on the neurological disease.
Topics: Africa; Africa South of the Sahara; Animals; Epilepsy; Humans; Ivermectin; Onchocerca volvulus; Onchocerciasis
PubMed: 30458251
DOI: 10.1016/j.brainresbull.2018.08.024 -
Trends in Parasitology Jan 2018Human onchocerciasis - commonly known as river blindness - is one of the most devastating yet neglected tropical diseases, leaving many millions in sub-Saharan Africa... (Review)
Review
Human onchocerciasis - commonly known as river blindness - is one of the most devastating yet neglected tropical diseases, leaving many millions in sub-Saharan Africa blind and/or with chronic disabilities. Attempts to eliminate onchocerciasis, primarily through the mass drug administration of ivermectin, remains challenging and has been heightened by the recent news that drug-resistant parasites are developing in some populations after years of drug treatment. Needed, and needed now, in the fight to eliminate onchocerciasis are new tools, such as preventive and therapeutic vaccines. This review summarizes the progress made to advance the onchocerciasis vaccine from the research laboratory into the clinic.
Topics: Animals; Antiparasitic Agents; Drug Resistance; Humans; Onchocerca volvulus; Onchocerciasis, Ocular; Vaccines
PubMed: 28958602
DOI: 10.1016/j.pt.2017.08.011 -
PLoS Neglected Tropical Diseases Jan 2021The possibility that onchocerciasis may cause epilepsy has been suggested for a long time, but thus far, an etiological link has not been universally accepted. The... (Review)
Review
BACKGROUND
The possibility that onchocerciasis may cause epilepsy has been suggested for a long time, but thus far, an etiological link has not been universally accepted. The objective of this review is to critically appraise the relationship between Onchocerca volvulus and epilepsy and subsequently apply the Bradford Hill criteria to further evaluate the likelihood of a causal association.
METHODS
PubMed and gray literature published until September 15, 2020, were searched and findings from original research were synthesized. Adherence to the 9 Bradford Hill criteria in the context of onchocerciasis and epilepsy was determined to assess whether the criteria are met to strengthen the evidence base for a causal link between infection with O. volvulus and epilepsy, including the nodding syndrome.
RESULTS
Onchocerciasis as a risk factor for epilepsy meets the following Bradford Hill criteria for causality: strength of the association, consistency, temporality, and biological gradient. There is weaker evidence supporting causality based on the specificity, plausibility, coherence, and analogy criteria. There is little experimental evidence. Considering the Bradford Hill criteria, available data suggest that under certain conditions (high microfilarial load, timing of infection, and perhaps genetic predisposition), onchocerciasis is likely to cause epilepsy including nodding and Nakalanga syndromes.
CONCLUSION
Applying the Bradford Hill criteria suggests consistent epidemiological evidence that O. volvulus infection is a trigger of epilepsy. However, the pathophysiological mechanisms responsible for seizure induction still need to be elucidated.
Topics: Animals; Causality; Child; Databases, Factual; Epilepsy; Humans; Microfilariae; Nodding Syndrome; Onchocerca volvulus; Onchocerciasis; Risk Factors; Seizures
PubMed: 33411705
DOI: 10.1371/journal.pntd.0008965 -
The Korean Journal of Parasitology Feb 2015Serine proteases form one of the most important families of enzymes and perform significant functions in a broad range of biological processes, such as intra- and... (Review)
Review
Serine proteases form one of the most important families of enzymes and perform significant functions in a broad range of biological processes, such as intra- and extracellular protein metabolism, digestion, blood coagulation, regulation of development, and fertilization. A number of serine proteases have been identified in parasitic helminths that have putative roles in parasite development and nutrition, host tissues and cell invasion, anticoagulation, and immune evasion. In this review, we described the serine proteases that have been identified in parasitic helminths, including nematodes (Trichinella spiralis, T. pseudospiralis, Trichuris muris, Anisakis simplex, Ascaris suum, Onchocerca volvulus, O. lienalis, Brugia malayi, Ancylostoma caninum, and Steinernema carpocapsae), cestodes (Spirometra mansoni, Echinococcus granulosus, and Schistocephalus solidus), and trematodes (Fasciola hepatica, F. gigantica, and Schistosoma mansoni). Moreover, the possible biological functions of these serine proteases in the endogenous biological phenomena of these parasites and in the host-parasite interaction were also discussed.
Topics: Animals; Cestoda; Host-Parasite Interactions; Life Cycle Stages; Nematoda; Serine Proteases; Trematoda
PubMed: 25748703
DOI: 10.3347/kjp.2015.53.1.1