Pfarr, K. | Search bioRxiv

bioRxiv2025

Fexinidazole and Corallopyronin A target Wolbachia-infected sheath cells present in filarial nematodes

The discovery of the endosymbiotic bacteria Wolbachia as an obligate symbiont of filarial nematodes has led to antibiotic-based treatments for filarial diseases. While lab and clinical studies have yielded promising results, recent animal studies reveal that Wolbachia levels may rebound following treatment with suboptimal doses of the antibiotic rifampicin. Previous work showed that a likely source of the bacterial rebound in females were dense clusters of Wolbachia in ovarian tissue. The number, size, and density of these Wolbachia clusters were not diminished despite antibiotic treatment. Here we define the cellular characteristics of the Wolbachia clusters in Brugia pahangi (wBp) and identify drugs that also target them. We have evidence that the Wolbachia clusters originate from newly formed sheath cells adjacent to the ovarian Distal Tip Cells. The dramatically enlarged volume of an infected sheath cell is strikingly similar to endosymbiont-induced bacteriocytes found in many insect species. Ultrastructural analysis reveals that the clustered Wolbachia present within the sheath cells exhibit a distinct morphology and form direct connections with the oocyte membrane and possibly the cytoplasm. This includes membrane-based channels providing a connection between Wolbachia-infected sheath cells and oocytes. We also determined that the Wolbachia within the sheath cells are either quiescent or replicating at a very low rate. Screens of known antibiotics and other drugs revealed that two drugs, Fexinidazole and Corallopyronin A, significantly reduced the number of clustered Wolbachia located within the sheath cells.

pathology↗

bioRxiv2023

Estimating the number of breeders from helminth larvae with genomic data.

Effective control of helminth infections requires the application of mathematical models to inform control efforts and policy, the development of product profiles for new drugs, and the monitoring of existing drugs for resistance. Key to the success of these approaches is accurately estimating the number of worms within a host, as well as distinguishing, in drug efficacy trials and monitoring, between adults surviving treatment and adults who have reinfected a host following drug treatment. In practice, observing adult worms is often extremely challenging in a patient, as many adult helminths are embedded deep in host tissues. Genetic approaches to infer kinship between larvae or eggs offer a solution to establish adult worm burdens, and to distinguish between treatment failure or treatment success followed by reinfection. Here, we use low-coverage whole-genome, and mitochondrial sequencing, of Onchocerca volvulus larvae to estimate the number of adults contributing to pools of offspring of known and unknown parentage. lcWGS reconstructs full-sibling relationships, resolving the number of unique adult worms contributing to a pool of offspring. Mitochondrial genotyping reconstructs maternal sib-ship, thus estimating the minimum number of adult females within a patient. Further development will improve these techniques for evaluating adult worm burden and trial outcome.

genomics↗

bioRxiv2022

Identification of the onchocerciasis vector in the Kakoi-Koda focus of the Democratic Republic of Congo

BackgroundThe 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 FindingsAquatic 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 S. vorax, which were also found breeding in local streams and rivers. Simulium damnosum s.l., S. neavei and S. 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/SignificanceSimulium 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 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. AUTHOR SUMMARYRiver blindness (=onchocerciasis) is a severely debilitating disease caused by the nematode parasite Onchocerca volvulus, and in Africa it is known to be transmitted from person to person by blood-sucking blackflies (Diptera: Simuliidae) of the Simulium damnosum complex, the S. neavei group and (rarely) by S. albivirgulatum. Using classical morphological characteristics and DNA analysis we have unexpectedly identified the vector blackfly as S. dentulosum (and possibly S. vorax) in a small endemic area (the Kakoi-Koda focus) which has been recently discovered on the western slopes of the rift valley in the Democratic Republic of Congo above Lake Albert. In the surrounding endemic areas, the vectors are S. damnosum complex and/or S. neavei (as normally expected), and because S. dentulosum is not a vector in these surrounding areas, it follows that this focus is entomologically isolated from immigrant blackfly species which might otherwise have carried new infections into the Kakoi-Koda focus (and vice-versa). This is of local importance, because it makes elimination of the parasite easier, but our findings have wider significance across Africa, because they raise the possibility that under the right conditions, other common and widely-distributed blackfly species might unexpectedly become man-biters and significant vectors.

ecology↗