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Acta Tropica Apr 2023Female Simulium damnosum s.l. were caught at a site in a savannah zone beside the Mono River in Togo and at varying distances westwards perpendicular to it in an...
Female Simulium damnosum s.l. were caught at a site in a savannah zone beside the Mono River in Togo and at varying distances westwards perpendicular to it in an experiment to investigate short-range dispersal by the flies. The numbers of flies caught and the percentages that were parous decreased with increasing distance from the river, the latter suggesting that nulliparous flies disperse on average further than parous flies. The decreases were quantified using statistically significant multiple regressions involving distances from the river and the days since the start of the experiment because there was much day-to-day variation, probably attributable to the flies' gonotrophic cycles. For future modelling purposes a relationship between numbers caught and distance alone was also estimated for both numbers caught and parous rates. Of the different members of the S. damnosum species complex identified in larval samples, S. damnosum s.str. predominated (66.7%), with S. squamosum accounting for 25.5% and the Beffa form of S. soubrense for 7.8%, proportions that were not significantly different from those of adults identified at the river and 10 km away. A small sub-sample of dissected parous flies showed that transmission was occurring at the riverside and at 10 km away from the river.
Topics: Animals; Female; Simuliidae; Onchocerciasis; Insect Vectors; Togo; Rivers
PubMed: 36781096
DOI: 10.1016/j.actatropica.2023.106863 -
ZooKeys 2022An updated checklist of the family Simuliidae from India is presented. A total of 79 species of belonging to eight different subgenera are listed. Eleven species that...
An updated checklist of the family Simuliidae from India is presented. A total of 79 species of belonging to eight different subgenera are listed. Eleven species that were not reported in the previous checklist are added here. The present list contributes to a better understanding of the diversity of Simuliidae in India, as well as the impact of species on the public health of this mega-diverse country.
PubMed: 36761802
DOI: 10.3897/zookeys.1118.84686 -
Parasites & Vectors Dec 2022Documentation on water mites in Spain is scarce, as is information on the parasite-host relationship between certain water mite species and representatives of the...
BACKGROUND
Documentation on water mites in Spain is scarce, as is information on the parasite-host relationship between certain water mite species and representatives of the dipteran family Simuliidae. The discomfort caused to humans and animals by black flies seems to be increasing in recent years. In this context, an investigation of parasitic water mites is of great importance, not only from the point of view of biodiversity, but also in terms of their potential to control black fly populations.
METHODS
Rivers across a wide region of eastern Spain were sampled to determine the specific richness of simuliid dipterans and to investigate their possible parasites, such as water mites, mermithid nematodes and microsporidia (fungal microbes). Data on environmental variables, abundance, prevalence and intensity of parasitism on the collected specimens were analyzed.
RESULTS
In 10 streams, 15,396 simuliid pupae were collected and checked for the presence of water mite larvae; 426 pupae in seven streams were found to be associated with water mite larvae. Of the 21 simuliid species identified based on morphological characters, eight were found to be associated with water mite larvae. Water mite infection was not equally distributed among black fly species. Also, the prevalence of parasitism was low and differed among simuliid species, ranging from one to 13 water mites per black fly pupa. Variation at the intra- and interspecific levels was detected in terms of the number of water mites inside the black fly cocoons. Free-living deutonymphal and adult water mites representing 15 different species of six genera and five families were morphologically identified. The taxonomic identity of the parasitic mite larvae is unclear at present. Morphologically, they fit descriptions of larval Sperchon (Hispidosperchon) algeriensis Lundblad, 1942, but the possibility cannot be excluded that they represent Sperchon algeriensis, the most abundant species at the adult stage in this study and unknown at the larval stage, or even another species of the genus. A molecular analysis produced for the first time cytochrome oxidase I gene sequences for S. algeriensis.
CONCLUSIONS
Our results contribute to current knowledge on Spanish Hydrachnidia and their relationships with simuliids as hosts. However, further research is needed to evaluate the diversity, distribution, bioecology and prevalence of this parasitism.
Topics: Humans; Animals; Simuliidae; Mites; Parasites; Water; Spain; Pupa; Larva
PubMed: 36528694
DOI: 10.1186/s13071-022-05610-2 -
The American Journal of Tropical... Jan 2023Transmission of Onchocerca volvulus (causing "river blindness") was interrupted in two states of Nigeria (Plateau and Nasarawa) in 2017 in accordance with 2016 WHO...
Transmission of Onchocerca volvulus (causing "river blindness") was interrupted in two states of Nigeria (Plateau and Nasarawa) in 2017 in accordance with 2016 WHO guidelines. Ivermectin mass drug administration was halted in January 2018, and posttreatment surveillance activities were conducted over a 3-year period. Vector Simulium damnosum s.l. flies were collected during the 2019 (39 sites) and 2020 (42 sites) transmission seasons. Head pools were tested by polymerase chain reaction for the presence of third-stage O. volvulus larvae; 15,585 flies were all negative, demonstrating an infective rate of < 1/2,000 with 95% confidence. In 2021, the Nigerian Federal Ministry of Health declared the two-state area as having eliminated transmission. Plateau and Nasarawa states are the first of 30 endemic states in Nigeria to have met the WHO criteria for onchocerciasis elimination. Post-elimination surveillance will need to continue given the risk of reintroduction of transmission from neighboring states.
Topics: Animals; Humans; Ivermectin; Onchocerciasis; Mass Drug Administration; Insect Vectors; Onchocerca volvulus; Simuliidae
PubMed: 36450227
DOI: 10.4269/ajtmh.22-0491 -
Parasites & Vectors Nov 2022Despite decades of community-directed treatment with ivermectin (CDTI), onchocerciasis transmission persists in Cameroon and has been associated with increased risk for...
BACKGROUND
Despite decades of community-directed treatment with ivermectin (CDTI), onchocerciasis transmission persists in Cameroon and has been associated with increased risk for epilepsy in endemic communities. We investigated the onchocerciasis situation in the Ntui Health District (a known onchocerciasis focus in Cameroon where the Sanaga River constitutes the main source of black fly vectors) using parasitological, entomological and serological parameters.
METHODS
In July 2021, community-based surveys were conducted in four villages (Essougli, Nachtigal, Ndjame and Ndowe). Onchocerciasis was diagnosed via microscopic examination of skin snips. Using rapid diagnostic tests, we screened children aged 3-6 years for Ov16 antibodies as a proxy for recent onchocerciasis transmission. Monthly black fly biting rates were obtained from the two riverside villages (Nachtigal and Essougli) for 12 consecutive months (July 2021 to June 2022) using the human landing catch technique. Some black flies were dissected each month to check for infection.
RESULTS
Overall, 460 participants were recruited; mean age was 32.1 (range: 3-85) years with 248 (53.9%) being males. Among skin snipped participants (n = 425), onchocerciasis prevalence was 14.6%. Participants with epilepsy (n = 25) were more often skin snip positive (45.8% vs 12.7%; P < 0.001) and had higher microfilarial loads (9.2 ± 22.0 vs 0.7 ± 3.5 microfilariae/skin snip; P < 0.001) compared to their peers without epilepsy. Eight (6.5%) of the 123 tested children were Ov16 seropositive. The breeding sites we investigated along the Sanaga River during the current study harbored fewer vectors (annual biting rates reaching 530,322 vs 606,370 in the Mbam River) and exhibited lower black fly infection rates (annual transmission potentials reaching 1479 vs 4488 in the Mbam River) when compared to recent entomological reports in Cameroon.
CONCLUSION
Despite substantial biting rates, black fly infection rates (by microscopy) in the Ntui Health District were rather low resulting in overall low transmission potentials in study villages. Thanks to CDTI, O. volvulus infection in both humans and insects is on the decrease. However, there is evidence that O. volvulus is still endemic in these communities. Reducing the vector population will further accelerate onchocerciasis elimination prospects.
Topics: Child; Male; Animals; Humans; Adult; Female; Onchocerciasis; Cameroon; Intestinal Volvulus; Simuliidae; Microfilariae; Ivermectin
PubMed: 36443885
DOI: 10.1186/s13071-022-05585-0 -
Mitochondrial DNA. Part B, Resources 2022The complete mitochondrial genome of was sequenced and annotated, and its general features and base composition were analyzed. The mitogenome was 15,896 bp long,...
The complete mitochondrial genome of was sequenced and annotated, and its general features and base composition were analyzed. The mitogenome was 15,896 bp long, comprising 13 protein-coding genes, 22 transport RNA genes, 2 ribosomal RNA genes, and 1 control region. The phylogenetic relationships based on the concatenated nucleotide sequences of 17 metagenomes from families Chironomidae, Ceratopogonidae, and Simuliidae were reconstructed. According to the phylogenetic topologies, was closely related to ( + ) in the maximum likelihood tree.
PubMed: 36386026
DOI: 10.1080/23802359.2022.2122746 -
PLoS Neglected Tropical Diseases Nov 2022The objective of this study was to characterise the vector in a small hyper-endemic focus of onchocerciasis (the Kakoi-Koda focus) which has recently been discovered on...
BACKGROUND
The objective of this study was to characterise the vector in a small hyper-endemic focus of onchocerciasis (the Kakoi-Koda focus) which has recently been discovered on the western slopes of the rift valley above Lake Albert.
METHODOLOGY/PRINCIPAL FINDINGS
Aquatic stages of blackflies were collected by hand from streams and rivers, and anthropophilic adult females were collected by human landing catches. Using a combination of morphotaxonomy and DNA barcoding, the blackflies collected biting humans within the focus were identified as Simulium dentulosum and Simulium vorax, which were also found breeding in local streams and rivers. Simulium damnosum s.l., Simulium neavei and Simulium albivirgulatum were not found (except for a single site in 2009 where crabs were carrying S. neavei). Anthropophilic specimens from the focus were screened for Onchocerca DNA using discriminant qualitative real-time triplex PCR. One specimen of S. vorax was positive for Onchocerca volvulus in the body, and out of 155 S. dentulosum, 30% and 11% were infected and infective (respectively).
CONCLUSIONS/SIGNIFICANCE
Simulium dentulosum currently appears to be the main vector of human onchocerciasis within the Kakoi-Koda focus, and S. vorax may be a secondary vector. It remains possible that S. neavei was the main (or only) vector in the past having now become rare as a result of the removal of tree-cover and land-use changes. Simulium vorax has previously been shown to support the development of O. volvulus in the laboratory, but this is the first time that S. dentulosum has been implicated as a probable vector of onchocerciasis, and this raises the possibility that other blackfly species which are not generally considered to be anthropophilic vectors might become vectors under suitable conditions. Because S. dentulosum is not a vector in endemic areas surrounding the Kakoi-Koda focus, it is probable that the Kakoi-Koda focus is significantly isolated.
Topics: Adult; Animals; Female; Humans; Onchocerciasis; Democratic Republic of the Congo; Insect Vectors; Plant Breeding; Onchocerca volvulus; Simuliidae
PubMed: 36331979
DOI: 10.1371/journal.pntd.0010684 -
Insects Oct 2022One of the most popular tools for species discovery and resolution is the DNA barcode, typically based on the cytochrome oxidase I (COI) gene. However, other non-genic...
One of the most popular tools for species discovery and resolution is the DNA barcode, typically based on the cytochrome oxidase I (COI) gene. However, other non-genic barcodes are available for Diptera. The banding sequence of polytene chromosomes in some dipteran cells, particularly of the larval silk glands, can provide a unique species barcode. We used the sequence of bands to reveal a new species of black fly in the () species group from California, USA. To further characterize the species and provide more integrated taxonomy, we morphologically described all life stages above the egg, formally named the species n. sp., and provided a conventional COI barcode. The COI barcode confirmed the chromosomal and morphological evidence that the species is a new member of the group, and enabled identification of the larva and female, which are structurally similar to those of other species. The chromosomal barcode shows that this species has the most rearranged complement, compared with the eight other North American members of its species group, with up to 12 times the number of fixed rearrangements. Up to six chromosomal rearrangements, including autosomal polymorphisms and sex-linked phenomena, are shared with other members of the group. The most unique and conspicuous chromosomal feature of this new species is a large, pale-staining chromocenter from which the six chromosomal arms radiate. The distribution of this univoltine species in lowland rivers of California's Central Valley could make it vulnerable, given climate change and increasing land development.
PubMed: 36292851
DOI: 10.3390/insects13100903 -
Parasites & Vectors Oct 2022The presence of breeding sites and distribution of species of Simulium damnosum sensu lato are critical in understanding the epidemiology of onchocerciasis and...
BACKGROUND
The presence of breeding sites and distribution of species of Simulium damnosum sensu lato are critical in understanding the epidemiology of onchocerciasis and evaluating the impact of elimination interventions. Reports on breeding sites and species distribution of members of S. damnosum s.l. in Cameroon are scarce and the few ones available date back to more than three decades. The aim of this study is to provide information on S. damnosum breeding sites across the rainy (RS) and dry (DS) seasons and the species composition in three different regions in Cameroon: Southwest (SW), Northwest (NW) and North (N).
METHODS
A cross-sectional two-season study was carried out in three regions with different ecological characteristics (SW-rainforest; NW-mixed forest-Guinea savanna; N-Sudan savanna). Pre-control onchocerciasis endemicity, relief maps and historical entomological information were used to identify potential rivers for purposive sampling. Sampled larvae were fixed in Carnoy's solution and sorted, and S. damnosum s.l. larvae were stored until identification by cytotaxonomy. Geographical coordinates of potential breeding sites were recorded to produce maps using ArcGIS, while Chi-square tests in SPSS were used to test for any differences between black fly seasonal breeding rates.
RESULTS
A total of 237 potential breeding sites were sampled (RS = 81; DS = 156) and 72 were found positive for S. damnosum s.l. The SW had the most positive sites [67 (RS = 24; DS = 43)], with a significant difference in the rate of breeding between the seasons (P < 0.05). Among 68 sites visited in both seasons, 16 (23.5%) were positive in one of the two seasons with more sites positive in DS(11) than RS(05), 14 (20.6%) and 38 (55.9%) respectively positive and negative in both seasons. Simulium damnosum sensu stricto and S. sirbanum were the main species in the N, while S. squamosum and S. mengense were the predominant species in the NW and SW. Simulium soubrense and S. yahense were uniquely recorded in the SW.
CONCLUSIONS
A comprehensive mapping of breeding sites requires rainy and dry seasons sampling. This study demonstrates that a breeding site survey of S. damnosum s.l. is achievable in forest as well as savanna zones. Not all potential breeding sites are actual breeding sites. Observation of S. soubrense in the SW indicates changes in species composition over time and could affect onchocerciasis epidemiology in this area.
Topics: Animals; Simuliidae; Onchocerciasis; Cross-Sectional Studies; Rainforest; Cameroon; Sudan; Grassland; Insect Vectors; Forests; Breeding
PubMed: 36271434
DOI: 10.1186/s13071-022-05462-w -
International Health Sep 2022More than 40 million people live in onchocerciasis-endemic areas in Nigeria. For at least 19 y, mass drug administration (MDA) with ivermectin was implemented with at...
BACKGROUND
More than 40 million people live in onchocerciasis-endemic areas in Nigeria. For at least 19 y, mass drug administration (MDA) with ivermectin was implemented with at least 65% total population coverage in Kaduna, Kebbi and Zamfara states. Impact surveys done using skin biopsies yielded no infections. Serological and entomological assessments were undertaken to determine if onchocerciasis transmission had been interrupted and MDA could be stopped.
METHODS
The presence of onchocerciasis-specific immunoglobulin G4 antibody was measured by enzyme=linked immunosorbent assay conducted on dried blood spots collected from 5- to 9-year-old children resident in each state. O-150 polymerase chain reaction testing of Simulium damnosum s.l. heads for Onchocerca volvulus DNA was done on black flies collected by human landing capture and Esperanza window traps.
RESULTS
A total of 9078 children were surveyed across the three states. A total of 6139 vectors were collected from Kaduna state, 129 from Kebbi state and 2 from Zamfara state; all were negative. Kebbi and Zamfara states did thousands of hours of black fly catching and intensive river prospecting. The resulting low fly catch was due to a low fly population incapable of sustaining transmission.
CONCLUSION
Onchocerciasis transmission has been interrupted and the three states meet World Health Organization thresholds: seropositivity in children <0.1% and <1/2000 infective black flies with 95% confidence. The 2.2 million people in Kaduna state and 4 million in Kebbi and Zamfara states no longer need ivermectin for onchocerciasis.
Topics: Animals; Child; Child, Preschool; Humans; Immunoglobulins; Immunosorbents; Ivermectin; Nigeria; Onchocerciasis; Simuliidae
PubMed: 36130252
DOI: 10.1093/inthealth/ihac036