The endosymbiont Wolbachia rebounds following antibiotic treatment

Reduction of Wolbachia in Diaphorina citri (Hemiptera: Liviidae) increases phytopathogen acquisition and decreases fitness

Wolbachia pipientis is a maternally inherited intracellular bacterium that infects a wide range of arthropods. Wolbachia can have a significant impact on host biology and development, often due to its effects on reproduction. We investigated Wolbachia-mediated effects in the Asian citrus psyllid, Diaphorina citri Kuwayama, which transmits Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening disease. Diaphorina citri are naturally infected with Wolbachia; therefore, investigating Wolbachia-mediated effects on D. citri fitness and CLas transmission required artificial reduction of this endosymbiont with the application of doxycycline. Doxycycline treatment of psyllids reduced Wolbachia infection by approximately 60% in both male and female D. citri. Psyllids treated with doxycycline exhibited higher CLas acquisition in both adults and nymphs as compared with negative controls. In addition, doxycycline-treated psyllids exhibited decreased fitness as measured by reduced egg and nymph production as well as adult emergence as compared with control lines without the doxycycline treatment. Our results indicate that Wolbachia benefits D. citri by improving fitness and potentially competes with CLas by interfering with phytopathogen acquisition. Targeted manipulation of endosymbionts in this phytopathogen vector may yield disease management tools.

Overcoming Limitations to Deep Learning in Domesticated Animals with TrioTrain

Variant calling across diverse species remains challenging as most bioinformatics tools default to assumptions based on human genomes. DeepVariant (DV) excels without joint genotyping while offering fewer implementation barriers. However, the growing appeal of a "universal" algorithm has magnified the unknown impacts when used with non-human genomes. Here, we use bovine genomes to assess the limits of human-genome-trained models in other species. We introduce the first multi-species DV model that achieves a lower Mendelian Inheritance Error (MIE) rate during single-sample genotyping. Our novel approach, TrioTrain, automates extending DV for species without Genome In A Bottle (GIAB) resources and uses region shuffling to mitigate barriers for SLURM-based clusters. To offset imperfect truth labels for animal genomes, we remove Mendelian discordant variants before training, where models are tuned to genotype the offspring correctly. With TrioTrain, we use cattle, yak, and bison trios to build 30 model iterations across five phases. We observe remarkable performance across phases when testing the GIAB human trios with a mean SNP F1 score >0.990. In HG002, our phase 4 bovine model identifies more variants at a lower MIE rate than DeepTrio. In bovine F1-hybrid genomes, our model substantially reduces inheritance errors with a mean MIE rate of 0.03 percent. Although constrained by imperfect labels, we find that multi-species, trio-based training produces a robust variant calling model. Our research demonstrates that exclusively training with human genomes restricts the application of deep-learning approaches for comparative genomics.

Combinations of the azaquinazoline anti-Wolbachia agent, AWZ1066S, with benzimidazole anthelmintics synergise to mediate sub-seven-day sterilising and curative efficacies in experimental models of filariasis

Lymphatic filariasis and onchocerciasis are two major neglected tropical diseases that are responsible for causing severe disability in 50 million people worldwide, whilst veterinary filariasis (heartworm) is a potentially lethal parasitic infection of companion animals. There is an urgent need for safe, short-course curative (macrofilaricidal) drugs to eliminate these debilitating parasite infections. We investigated combination treatments of the novel anti-Wolbachia azaquinazoline small molecule, AWZ1066S, with benzimidazole drugs (albendazole or oxfendazole) in up to four different rodent filariasis infection models: Brugia malayi-CB.17 SCID mice, B. malayi-Mongolian gerbils, B. pahangi-Mongolian gerbils, and Litomosoides sigmodontis-Mongolian gerbils. Combination treatments synergised to elicit threshold (>90%) Wolbachia depletion from female worms in 5 days of treatment, using 2-fold lower dose-exposures of AWZ1066S than monotherapy. Short-course lowered dose AWZ1066S-albendazole combination treatments also delivered partial adulticidal activities and/or long-lasting inhibition of embryogenesis, resulting in complete transmission blockade in B. pahangi and L. sigmodontis gerbil models. We determined that short-course AWZ1066S-albendazole co-treatment significantly augmented the depletion of Wolbachia populations within both germline and hypodermal tissues of B. malayi female worms and in hypodermal tissues in male worms, indicating that anti-Wolbachia synergy is not limited to targeting female embryonic tissues. Our data provides pre-clinical proof-of-concept that sub-seven-day combinations of rapid-acting novel anti-Wolbachia agents with benzimidazole anthelmintics are a promising curative and transmission-blocking drug treatment strategy for filarial diseases of medical and veterinary importance.

The cellular lives of Wolbachia

Wolbachia are successful Gram-negative bacterial endosymbionts, globally infecting a large fraction of arthropod species and filarial nematodes. Efficient vertical transmission, the capacity for horizontal transmission, manipulation of host reproduction and enhancement of host fitness can promote the spread both within and between species. Wolbachia are abundant and can occupy extraordinary diverse and evolutionary distant host species, suggesting that they have evolved to engage and manipulate highly conserved core cellular processes. Here, we review recent studies identifying Wolbachia-host interactions at the molecular and cellular levels. We explore how Wolbachia interact with a wide array of host cytoplasmic and nuclear components in order to thrive in a diversity of cell types and cellular environments. This endosymbiont has also evolved the ability to precisely target and manipulate specific phases of the host cell cycle. The remarkable diversity of cellular interactions distinguishes Wolbachia from other endosymbionts and is largely responsible for facilitating its global propagation through host populations. Finally, we describe how insights into Wolbachia-host cellular interactions have led to promising applications in controlling insect-borne and filarial nematode-based diseases.

Bacterial Community Survey of Wolbachia-Infected Parthenogenetic Parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) Treated with Antibiotics and High Temperature

Wolbachia has been shown to induce thelytokous parthenogenesis in Trichogramma species, which have been widely used as biological control agents around the world. Little is known about the changes of bacterial community after restoring arrhenotokous or bisexual reproduction in the T. pretiosum. Here, we investigate the emergence of males of T. pretiosum through curing experiments (antibiotics and high temperature), crossing experiments, and high-throughput 16S ribosomal RNA sequencing (rRNA-seq). The results of curing experiments showed that both antibiotics and high temperatures could cause the thelytokous T. pretiosum to produce male offspring. Wolbachia was dominant in the thelytokous T. pretiosum bacterial community with 99.01% relative abundance. With the relative abundance of Wolbachia being depleted by antibiotics, the diversity and relative content of other endosymbiotic bacteria increased, and the reproductive mode reverted from thelytoky to arrhenotoky in T. pretiosum. Although antibiotics did not eliminate Wolbachia in T. pretiosum, sulfadiazine showed an advantage in restoring entirely arrhenotokous and successive bisexual reproduction. This study was the first to demonstrate the bacterial communities in parthenogenetic Trichogramma before and after antibiotics or high-temperature treatment. Our findings supported the hypothesis that Wolbachia titer-dependence drives a reproduction switch in T. pretiosum between thelytoky and arrhenotoky.

Aspartyl Protease Inhibitors as Anti-Filarial Drugs

The current treatments for lymphatic filariasis and onchocerciasis do not effectively kill the adult parasitic nematodes, allowing these chronic and debilitating diseases to persist in millions of people. Thus, the discovery of new drugs with macrofilaricidal potential to treat these filarial diseases is critical. To facilitate this need, we first investigated the effects of three aspartyl protease inhibitors (APIs) that are FDA-approved as HIV antiretroviral drugs on the adult filarial nematode, Brugia malayi and the endosymbiotic bacteria, Wolbachia. From the three hits, nelfinavir had the best potency with an IC₅₀ value of 7.78 µM, followed by ritonavir and lopinavir with IC₅₀ values of 14.3 µM and 16.9 µM, respectively. The three APIs have a direct effect on killing adult B. malayi after 6 days of exposure in vitro and did not affect the Wolbachia titers. Sequence conservation and stage-specific gene expression analysis identified Bm8660 as the most likely primary aspartic protease target for these drug(s). Immunolocalization using antibodies raised against the Bm8660 ortholog of Onchocerca volvulus showed it is strongly expressed in female B. malayi, especially in metabolically active tissues such as lateral and dorsal/ventral chords, hypodermis, and uterus tissue. Global transcriptional response analysis using adult female B. pahangi treated with APIs identified four additional aspartic proteases differentially regulated by the three effective drugs, as well as significant enrichment of various pathways including ubiquitin mediated proteolysis, protein kinases, and MAPK/AMPK/FoxO signaling. In vitro testing against the adult gastro-intestinal nematode Trichuris muris suggested broad-spectrum potential for these APIs. This study suggests that APIs may serve as new leads to be further explored for drug discovery to treat parasitic nematode infections.

Selective Elimination of Wolbachia from the Leafhopper Yamatotettix flavovittatus Matsumura

Wolbachia infections affect the reproductive system and various biological traits of the host insect. There is a high frequency of Wolbachia infection in the leafhopper Yamatotettix flavovittatus Matsumura. To investigate the potential roles of Wolbachia in the host, it is important to generate a non-Wolbachia-infected line. The efficacy of antibiotics in eliminating Wolbachia from Y. flavovittatus remains unknown. This leafhopper harbors the mutualistic bacterium Candidatus Sulcia muelleri, which has an important function in the biological traits. The presence of Ca. S. muelleri raises a major concern regarding the use of antibiotics. We selectively eliminated Wolbachia, considering the influence of antibiotics on leafhopper survival and Ca. S. muelleri prevalence. The effect of artificial diets containing different doses of tetracycline and rifampicin on survival was optimized; high dose (0.5 mg/ml) of antibiotics induces a high mortality. A concentration of 0.2 mg/ml was chosen for the subsequent experiments. Antibiotic treatments significantly reduced the Wolbachia infection, and the Wolbachia density in the treated leafhoppers sharply declined. Wolbachia recurred in tetracycline-treated offspring, regardless of antibiotic exposure. However, Wolbachia is unable to be transmitted and restored in rifampicin-treated offspring. The dose and treatment duration had no significant effect on the infection and density of Ca. S. muelleri in the antibiotic-treated offspring. In conclusion, Wolbachia in Y. flavovittatus was stably eliminated using rifampicin, and the Wolbachia-free line was generated at least two generations after treatment. This report provides additional experimental procedures for removing Wolbachia from insects, particularly in host species with the coexistence of Ca. S. muelleri.

Pyrvinium Pamoate and Structural Analogs Are Early Macrofilaricide Leads

Onchocerciasis and lymphatic filariasis are neglected tropical diseases caused by infection with filarial worms. Annual or biannual mass drug administration with microfilaricidal drugs that kill the microfilarial stages of the parasites has helped reduce infection rates and thus prevent transmission of both infections. However, success depends on high population coverage that is maintained for the duration of the adult worm's lifespan. Given that these filarial worms can live up to 14 years in their human hosts, a macrofilaricidal drug would vastly accelerate elimination efforts. Here, we have evaluated the repurposed drug pyrvinium pamoate as well as newly synthesized analogs of pyrvinium for their efficacy against filarial worms in vitro and in vivo. We found that pyrvinium pamoate, tetrahydropyrvinium and one of the analogs were highly potent in inhibiting worms in in vitro whole-worm screening assays, and that all three compounds reduced female worm fecundity and inhibited embryogenesis in the Brugia pahangi-gerbil in vivo model of infection.

High-content approaches to anthelmintic drug screening

Most anthelmintics were discovered through in vivo screens using animal models of infection. Developing in vitro assays for parasitic worms presents several challenges. The lack of in vitro life cycle culture protocols requires harvesting worms from vertebrate hosts or vectors, limiting assay throughput. Once worms are removed from the host environment, established anthelmintics often show no obvious phenotype - raising concerns about the predictive value of many in vitro assays. However, with recent progress in understanding how anthelmintics subvert host-parasite interactions, and breakthroughs in high-content imaging and machine learning, in vitro assays have the potential to discern subtle cryptic parasite phenotypes. These may prove better endpoints than conventional in vitro viability assays.

The Eagle effect in the Wolbachia-worm symbiosis

Background

Onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis) are two human neglected tropical diseases that cause major disabilities. Mass administration of drugs targeting the microfilarial stage has reduced transmission and eliminated these diseases in several countries but a macrofilaricidal drug that kills or sterilizes the adult worms is critically needed to eradicate the diseases. The causative agents of onchocerciasis and lymphatic filariasis are filarial worms that harbor the endosymbiotic bacterium Wolbachia. Because filarial worms depend on Wolbachia for reproduction and survival, drugs targeting Wolbachia hold great promise as a means to eliminate these diseases.

Methods

To better understand the relationship between Wolbachia and its worm host, adult Brugia pahangi were exposed to varying concentrations of doxycycline, minocycline, tetracycline and rifampicin in vitro and assessed for Wolbachia numbers and worm motility. Worm motility was monitored using the Worminator system, and Wolbachia titers were assessed by qPCR of the single copy gene wsp from Wolbachia and gst from Brugia to calculate IC₅₀s and in time course experiments. Confocal microscopy was also used to quantify Wolbachia located at the distal tip region of worm ovaries to assess the effects of antibiotic treatment in this region of the worm where Wolbachia are transmitted vertically to the microfilarial stage.

Results

Worms treated with higher concentrations of antibiotics had higher Wolbachia titers, i.e. as antibiotic concentrations increased there was a corresponding increase in Wolbachia titers. As the concentration of antibiotic increased, worms stopped moving and never recovered despite maintaining Wolbachia titers comparable to controls. Thus, worms were rendered moribund by the higher concentrations of antibiotics but Wolbachia persisted suggesting that these antibiotics may act directly on the worms at high concentration. Surprisingly, in contrast to these results, antibiotics given at low concentrations reduced Wolbachia titers.

Conclusion

Wolbachia in B. pahangi display a counterintuitive dose response known as the “Eagle effect.” This effect in Wolbachia suggests a common underlying mechanism that allows diverse bacterial and fungal species to persist despite exposure to high concentrations of antimicrobial compounds. To our knowledge this is the first report of this phenomenon occurring in an intracellular endosymbiont, Wolbachia, in its filarial host.

Transcriptomic Analysis Reveals the Sexually Divergent Host-Wolbachia Interaction Patterns in a Fig Wasp

Wolbachia are widely distributed in arthropods and nematodes, acquiring nutrients from the hosts, and inducing remarkable reproductive modulations on the hosts. To investigate the interaction of Wolbachia and insects, Wolbachia are often artificially eliminated from Wolbachia-infected hosts, which may produce negative effects of antibiotics. In the present study, based on the transcriptomic data of a fig wasp species Ceratosolen solmsi with two sibling lineages, one natively infected and the other noninfected with Wolbachia, we investigated the expression patterns of genes. The comparison results of differently expressed genes (DEGs) between Wolbachia infected and noninfected samples show that males have many more DEGs than females. The male unique upregulated genes are enriched in biological processes mainly related to biosynthesis, transport, positive regulation of I-kappaB kinase/NF-kappaB signaling, MAPK cascade, and pathogenesis; the male unique downregulated genes are enriched in biological processes mainly related to transport, oxidation–reduction, cellular responses to oxidative stress, lipid oxidation, cytoskeleton organization, actin filament-based process, and localization. In addition, for the Wolbachia’s gene expression, the number of genes up-regulated in males is higher than that in females. The results revealed divergent patterns of the host–Wolbachia interactions between males and females in the fig wasp species.

Computational Design and Preliminary Serological Analysis of a Novel Multi-Epitope Vaccine Candidate against Onchocerciasis and Related Filarial Diseases

: Onchocerciasis is a skin and eye disease that exerts a heavy socio-economic burden, particularly in sub-Saharan Africa, a region which harbours greater than 96% of either infected or at-risk populations. The elimination plan for the disease is currently challenged by many factors including amongst others; the potential emergence of resistance to the main chemotherapeutic agent, ivermectin (IVM). Novel tools, including preventative and therapeutic vaccines, could provide additional impetus to the disease elimination tool portfolio. Several observations in both humans and animals have provided evidence for the development of both natural and artificial acquired immunity. In this study, immuno-informatics tools were applied to design a filarial-conserved multi-epitope subunit vaccine candidate, (designated Ov-DKR-2) consisting of B-and T-lymphocyte epitopes of eight immunogenic antigens previously assessed in pre-clinical studies. The high-percentage conservation of the selected proteins and epitopes predicted in related nematode parasitic species hints that the generated chimera may be instrumental for cross-protection. Bioinformatics analyses were employed for the prediction, refinement, and validation of the 3D structure of the Ov-DKR-2 chimera. In-silico immune simulation projected significantly high levels of IgG1, T-helper, T-cytotoxic cells, INF-γ, and IL-2 responses. Preliminary immunological analyses revealed that the multi-epitope vaccine candidate reacted with antibodies in sera from both onchocerciasis-infected individuals, endemic normals as well as loiasis-infected persons but not with the control sera from European individuals. These results support the premise for further characterisation of the engineered protein as a vaccine candidate for onchocerciasis.

Corallopyronin A for short-course anti-wolbachial, macrofilaricidal treatment of filarial infections

Current efforts to eliminate the neglected tropical diseases onchocerciasis and lymphatic filariasis, caused by the filarial nematodes Onchocerca volvulus and Wuchereria bancrofti or Brugia spp., respectively, are hampered by lack of a short-course macrofilaricidal–adult-worm killing–treatment. Anti-wolbachial antibiotics, e.g. doxycycline, target the essential Wolbachia endosymbionts of filariae and are a safe prototype adult-worm-sterilizing and macrofilaricidal regimen, in contrast to standard treatments with ivermectin or diethylcarbamazine, which mainly target the microfilariae. However, treatment regimens of 4–5 weeks necessary for doxycycline and contraindications limit its use. Therefore, we tested the preclinical anti-Wolbachia drug candidate Corallopyronin A (CorA) for in vivo efficacy during initial and chronic filarial infections in the Litomosoides sigmodontis rodent model. CorA treatment for 14 days beginning immediately after infection cleared >90% of Wolbachia endosymbionts from filariae and prevented development into adult worms. CorA treatment of patently infected microfilaremic gerbils for 14 days with 30 mg/kg twice a day (BID) achieved a sustained reduction of >99% of Wolbachia endosymbionts from adult filariae and microfilariae, followed by complete inhibition of filarial embryogenesis resulting in clearance of microfilariae. Combined treatment of CorA and albendazole, a drug currently co-administered during mass drug administrations and previously shown to enhance efficacy of anti-Wolbachia drugs, achieved microfilarial clearance after 7 days of treatment at a lower BID dose of 10 mg/kg CorA, a Human Equivalent Dose of 1.4 mg/kg. Importantly, this combination led to a significant reduction in the adult worm burden, which has not yet been published with other anti-Wolbachia candidates tested in this model. In summary, CorA is a preclinical candidate for filariasis, which significantly reduces treatment times required to achieve sustained Wolbachia depletion, clearance of microfilariae, and inhibition of embryogenesis. In combination with albendazole, CorA is robustly macrofilaricidal after 7 days of treatment and fulfills the Target Product Profile for a macrofilaricidal drug.

Infections with filarial roundworms can cause the disfiguring human neglected tropical diseases onchocerciasis and lymphatic filariasis. Treatment of these diseases is limited, as there is no well-tolerated treatment available that kills the adult worms after a short-term regimen. Thus, mass drug administrations (MDA) are performed with drugs that temporarily clear the microfilariae, the filarial offspring, to inhibit the transmission of the disease. As these MDA treatments have to be given 1–2 times per year for many years, the goal to eliminate onchocerciasis and lymphatic filariasis is hampered. In the present study we investigated a novel preclinical candidate for the treatment of filariasis. Corallopyronin A (CorA) is a natural compound that clears the essential Wolbachia endobacteria of filariae. Using the Litomosoides sigmodontis rodent model of filariasis we demonstrated that 2 weeks of CorA treatment clears Wolbachia endosymbionts in vivo, leading to a maintained clearance of microfilariae by inhibition of filarial embryogenesis. Combination therapy of CorA with the MDA drug albendazole allowed lower CorA doses and shortened treatment to 7 days. More importantly, it also led to the death of the adult filariae. Portfolios (Target Product Profiles) of new drugs against filariae should show adult killing efficacy like CorA.