Molecular evidence of ‘Siisa form’, a new genotype related to Onchocerca ochengi in cattle from North Cameroon

Eisenbarth, Albert; Ekale, David; Hildebrandt, Julia; Achukwi, Mbunkah Daniel; Streit, Adrian; Renz, Alfons

doi:10.1016/j.actatropica.2013.05.011

Cited by 20 publications

(26 citation statements)

References 30 publications

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“…denkei and the Siisa-clade of O . ochengi ) [ 46 , 47 , 48 ]. In the field, during the morphological identification and parity dissection, any Onchocerca larvae which emerged were also recorded and transferred to a POL-membrane slide.…”

Section: Methodsmentioning

confidence: 99%

Onchocerciasis Transmission in Ghana: Persistence under Different Control Strategies and the Role of the Simuliid Vectors

et al. 2015

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BackgroundThe World Health Organization (WHO) aims at eliminating onchocerciasis by 2020 in selected African countries. Current control focuses on community-directed treatment with ivermectin (CDTI). In Ghana, persistent transmission has been reported despite long-term control. We present spatial and temporal patterns of onchocerciasis transmission in relation to ivermectin treatment history.Methodology/Principal FindingsHost-seeking and ovipositing blackflies were collected from seven villages in four regions of Ghana with 3–24 years of CDTI at the time of sampling. A total of 16,443 flies was analysed for infection; 5,812 (35.3%) were dissected for parity (26.9% parous). Heads and thoraces of 12,196 flies were dissected for Onchocerca spp. and DNA from 11,122 abdomens was amplified using Onchocerca primers. A total of 463 larvae (0.03 larvae/fly) from 97 (0.6%) infected and 62 (0.4%) infective flies was recorded; 258 abdomens (2.3%) were positive for Onchocerca DNA. Infections (all were O. volvulus) were more likely to be detected in ovipositing flies. Transmission occurred, mostly in the wet season, at Gyankobaa and Bosomase, with transmission potentials of, respectively, 86 and 422 L3/person/month after 3 and 6 years of CDTI. The numbers of L3/1,000 parous flies at these villages were over 100 times the WHO threshold of one L3/1,000 for transmission control. Vector species influenced transmission parameters. At Asubende, the number of L3/1,000 ovipositing flies (1.4, 95% CI = 0–4) also just exceeded the threshold despite extensive vector control and 24 years of ivermectin distribution, but there were no infective larvae in host-seeking flies.Conclusions/SignificanceDespite repeated ivermectin treatment, evidence of O. volvulus transmission was documented in all seven villages and above the WHO threshold in two. Vector species influences transmission through biting and parous rates and vector competence, and should be included in transmission models. Oviposition traps could augment vector collector methods for monitoring and surveillance.

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Section: Methodsmentioning

confidence: 99%

Onchocerciasis Transmission in Ghana: Persistence under Different Control Strategies and the Role of the Simuliid Vectors

et al. 2015

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“…Furthermore, filariae closely-related to O . volvulus might repopulate the human host [ 22 ] posing a potential risk of infection, or they might transfer genes to O . volvulus which negatively affect the effectiveness of ivermectin, presently the sole drug intervention in use [ 23 ].…”

Section: Introductionmentioning

confidence: 99%

“…For this reason we combine microscopic differentiation of infective larvae with a PCR-based molecular approach which allows the detection of yet unknown filarial species and strains in addition to already known Onchocerca spp. [ 22 ].…”

Section: Introductionmentioning

confidence: 99%

Ongoing Transmission of Onchocerca volvulus after 25 Years of Annual Ivermectin Mass Treatments in the Vina du Nord River Valley, in North Cameroon

Eisenbarth¹,

Achukwi²,

Renz³

2016

PLoS Negl Trop Dis

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BackgroundRecent reports of transmission interruption of Onchocerca volvulus, the causing agent of river blindness, in former endemic foci in the Americas, and more recently in West and East Africa, raise the question whether elimination of this debilitating disease is underway after long-term treatment of the population at risk with ivermectin. The situation in Central Africa has not yet been clearly assessed.Methods and findingsEntomologic data from two former endemic river basins in North Cameroon were generated over a period of 43 and 48 months to follow-up transmission levels in areas under prolonged ivermectin control. Moreover, epidemiologic parameters of animal-borne Onchocerca spp. transmitted by the same local black fly vectors of the Simulium damnosum complex were recorded and their impact on O. volvulus transmission success evaluated. With mitochondrial DNA markers we unambiguously confirmed the presence of infective O. volvulus larvae in vectors from the Sudan savannah region (mean Annual Transmission Potential 2009–2012: 98, range 47–221), but not from the Adamawa highland region. Transmission rates of O. ochengi, a parasite of Zebu cattle, were high in both foci.Conclusions/significanceThe high cattle livestock density in conjunction with the high transmission rates of the bovine filaria O. ochengi prevents the transmission of O. volvulus on the Adamawa plateau, whereas transmission in a former hyperendemic focus was markedly reduced, but not completely interrupted after 25 years of ivermectin control. This study may be helpful to gauge the impact of the presence of animal-filariae for O. volvulus transmission in terms of the growing human and livestock populations in sub-Saharan countries.

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“…Finally, cloned amplicons derived from both the adult control samples and 10 larvae (5 from each melt curve group) were analysed by Sanger sequencing, confirming the discriminating variants and concordance with the reference whole mitochondrial genome sequences for the 2 species. This result does not, however, exclude the possibility that additional genetic variation may exist within the HRMamplicon in either or both species of Onchocerca examined (or other potential Onchocerca species endemic to onchocerciasis regions [21][22][23] ochengi control sequences used. Although a single base change is unlikely to confound the interpretation between the melt profiles of the O. volvulus and O. ochengi control samples described here, this assay does offer further opportunity beyond conventional O150 assays to explore genetic variation among and within species.…”

Section: Resultsmentioning

confidence: 99%

“…By exploiting the multicopy nature of the mitochondrial genome (in the same way that O150 assays target a highly abundant repetitive element in the genome), this assay is very sensitive, requiring only 1/ 100th of a single larva, thus leaving sufficient material for further genetic epidemiological analysis. Although O. volvulus and O. ochengi samples could be distinguished easily via HRM or RFLP assays, no effort was made to identify other described Onchocerca species that may coexist in onchocerciasis endemic regions [21][22][23]; further work is required to characterise melt profiles and/or restriction sites from additional Onchocerca spp. voucher specimens or sequences as they become available.…”

Section: Discussionmentioning

confidence: 99%

Discrimination betweenOnchocerca volvulusandO. ochengifilarial larvae inSimulium damnosum(s.l.) and their distribution throughout central Ghana using a versatile high-resolution speciation assay

Doyle

Armoo

Renz

et al. 2016

Preprint

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Background: Genetic surveillance of the human filarial parasite, Onchocerca volvulus, from onchocerciasis endemic regions will ideally focus on genotyping individual infective larval stages collected from their intermediate host, Simuliid blackflies. However, blackflies also transmit other Onchocerca species, including the cattle parasite O. ochengi, which are difficult to distinguish from the human parasite based on morphological characteristics alone. This study describes a versatile approach to discriminate between O. volvulus and O. ochengi that is demonstrated using parasite infective larvae dissected from blackflies.Results: A speciation assay was designed based on genetic differentiation between O. volvulus and O. ochengi mitochondrial genome sequences that can be performed in high-throughput high-resolution melt (HRM)-or lower throughput conventional restriction fragment length polymorphism (RFLP) analyses. This assay was validated on 185 Onchocerca larvae dissected from blackflies captured from 14 communities in Ghana throughout 2011−2013. The frequency of O. ochengi was approximately 67 % of all larvae analysed, which is significantly higher than previously reported in this region. Furthermore, the species distribution was not uniform throughout the study region, with 25 %, 47 % and 93 % of O. volvulus being found in the western-most (Black Volta, Tain and Tombe), the central (Pru) and eastern-most (Daka) river basins, respectively. Conclusions: This tool provides a simple and cost-effective approach to determine the identity and distribution of two Onchocerca species, and will be valuable for future genetic studies that focus on parasites collected from blackflies. The results presented highlight the need to discriminate Onchocerca species in transmission studies, as the frequency of each species varied significantly between the communities studied.

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Molecular evidence of ‘Siisa form’, a new genotype related to Onchocerca ochengi in cattle from North Cameroon

Cited by 20 publications

References 30 publications

Onchocerciasis Transmission in Ghana: Persistence under Different Control Strategies and the Role of the Simuliid Vectors

Onchocerciasis Transmission in Ghana: Persistence under Different Control Strategies and the Role of the Simuliid Vectors

Ongoing Transmission of Onchocerca volvulus after 25 Years of Annual Ivermectin Mass Treatments in the Vina du Nord River Valley, in North Cameroon

Discrimination betweenOnchocerca volvulusandO. ochengifilarial larvae inSimulium damnosum(s.l.) and their distribution throughout central Ghana using a versatile high-resolution speciation assay

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