Njongmeta LM et al. (2004) Int J Parasitol "Cattle protected from onchocerciasis by ivermectin are highly susceptible to infection after drug withdrawal."

Trees AJ, Gilbert J, Makepeace BL, Nfon CK, Tanya VN, Njongmeta LM

[Int J Parasitol, 2004]

Ivermectin administration is now the major tool in the control of human onchocerciasis (caused by Onchocerca volvulus) based on its suppression of microfilariae and hence the prevention of disease. However, in Africa, transmission is not eliminated and treated populations continue to be exposed to infective larval (L(3)) challenge, albeit at reduced levels. We have investigated whether protective immunity might develop under such conditions using the analogous host-parasite system Onchocerca ochengi in cattle, based on our previous findings in cattle exposed to challenge, that in vivo ivermectin attenuates the development of adult infections and that irradiation-attenuated L(3) induce significant protection. In a two-phase prospective study over 4 years, groups of cattle were exposed to severe natural challenge. In the first phase, 38/40 animals treated either with ivermectin or with moxidectin at either monthly or 3-monthly intervals had not developed detectable infections after 22 months of exposure whereas, in a non-treated control group (n = 14) nodule prevalence was 78.6% and the geometric mean (range) nodule load was 4.8 (0-33). In the second phase, all drug treatments were withdrawn, a new control group (n = 8) introduced, and exposure continued at the same site. After 24 months, all groups had developed patent infections, with geometric mean (range) nodule loads of 17.4 (4-99), 38.4 (10-111), 50.7 (26-86), 14.3 (0-69) and 14.7 (0-55) for the control, monthly-ivermectin, 3-monthly ivermectin, monthly moxidectin and 3-monthly moxidectin groups, respectively. There was no evidence of protection-indeed the 3-monthly ivermectin group was significantly (P < 0.05) hyper-susceptible. In addition, microfilarial densities and the rate of increase in microfilarial load were significantly higher (P < 0.05) in the ivermectin-treated groups than in control animals. These results have important implications for ivermectin-based control of human onchocerciasis and suggest that humans exposed to ongoing transmission in endemic areas whilst receiving ivermectin are unlikely to develop immunity and will be highly susceptible should drug distribution cease.

Dec Bronsvoort BM et al. (2008) Parasit Vectors "UMF-078: A modified flubendazole with potent macrofilaricidal activity against Onchocerca ochengi in African cattle."

Ekale D, Dec Bronsvoort BM, Tanya VN, Trees AJ, Makepeace BL, Fleckenstein L, Renz A

[Parasit Vectors, 2008]

UNLABELLED: Human onchocerciasis or river blindness, caused by the filarial nematode Onchocerca volvulus, is currently controlled using the microfilaricidal drug, ivermectin. However, ivermectin does not kill adult O. volvulus, and in areas with less than 65% ivermectin coverage of the population, there is no effect on transmission. Therefore, there is still a need for a macrofilaricidal drug. Using the bovine filarial nematode O. ochengi (found naturally in African cattle), the macrofilaricidal efficacy of the modified flubendazole, UMF-078, was investigated. METHODS: Groups of 3 cows were treated with one of the following regimens: (a) a single dose of UMF-078 at 150 mg/kg intramuscularly (im), (b) 50 mg/kg im, (c) 150 mg/kg intraabomasally (ia), (d) 50 mg/kg ia, or (e) not treated (controls). RESULTS: After treatment at 150 mg/kg im, nodule diameter, worm motility and worm viability (as measured by metabolic reduction of tetrazolium to formazan) declined significantly compared with pre-treatment values and concurrent controls. There was abrogation of embryogenesis and death of all adult worms by 24 weeks post-treatment (pt). Animals treated at 50 mg/kg im showed a decline in nodule diameter together with abrogated reproduction, reduced motility, and lower metabolic activity in isolated worms, culminating in approximately 50% worm mortality by 52 weeks pt. Worms removed from animals treated ia were not killed, but exhibited a temporary embryotoxic effect which had waned by 12 weeks pt in the 50 mg/kg ia group and by 24 weeks pt in the 150 mg/kg ia group. These differences could be explained by the different absorption rates and elimination half-lives for each dose and route of administration. CONCLUSION: Although we did not observe any signs of mammalian toxicity in this trial with a single dose, other studies have raised concerns regarding neuro- and genotoxicity. Consequently, further evaluation of this compound has been suspended. Nonetheless, these results validate the molecular target of the benzimidazoles as a promising lead for rational design of macrofilaricidal drugs.

Wewer V et al. (2017) Int J Parasitol "Lipid profiling of the filarial nematodes Onchocerca volvulus, Onchocerca ochengi and Litomosoides sigmodontis reveals the accumulation of nematode-specific ether phospholipids in the host."

Peisker H, Pfarr K, Tanya VN, Wewer V, Doermann P, Hoerauf A, Makepeace BL

[Int J Parasitol, 2017]

Onchocerciasis, a neglected tropical disease prevalent in western and central Africa, is a major health problem and has been targeted for elimination. The causative agent for this disease is the human parasite Onchocerca volvulus. Onchocerca ochengi and Litomosoides sigmodontis, infectious agents of cattle and rodents, respectively, serve as model organisms to study filarial nematode infections. Biomarkers to determine infection without the use of painful skin biopsies and microscopic identification of larval worms are needed and their discovery is facilitated by an improved knowledge of parasite-specific metabolites. In addition to proteins and nucleic acids, lipids may be suitable candidates for filarial biomarkers that are currently underexplored. To fill this gap, we present the phospholipid profile of the filarial nematodes O. ochengi, O. volvulus and L. sigmodontis. Direct infusion quadrupole time-of-flight (Q-TOF) mass spectrometry was employed to analyze the composition of phospholipids and their molecular species in the three nematode species. Analysis of the phospholipid profiles of plasma or serum of uninfected and infected hosts showed that nematode-specific phospholipids were below detection limits. However, several phospholipids, in particular ether lipids of phosphatidylethanolamine (PE), were abundant in O. ochengi worms and in bovine nodule fluid, suggesting that these phospholipids might be released from O. ochengi into the host, and could serve as potential biomarkers.

Gilbert J et al. (2005) J Infect Dis "Antibiotic chemotherapy of onchocerciasis: in a bovine model, killing of adult parasites requires a sustained depletion of endosymbiotic bacteria (Wolbachia species)."

Njongmeta LM, Nfon CK, Tanya VN, Renz A, Makepeace BL, Hastings IM, Pfarr KM, Trees AJ, Gilbert J

[J Infect Dis, 2005]

Development of a drug lethal to adult Onchocerca volvulus (i.e., macrofilaricide) is a research priority for the control of human onchocerciasis. Using bovine O. ochengi infections, we investigated the effects of oxytetracycline administered in a short intensive regimen (SIR; 10 mg/kg daily for 14 days), compared with a prolonged intermittent regimen (PIR; 20 mg/kg monthly for 6 months) or a combination of both (COM), on the viability of adult worms and their endosymbiotic bacteria (Wolbachia species). The long-term treatments eliminated >80% (COM) or >60% (PIR) of adult female worms (P<.001), and the COM regimen effected a sustained depletion of Wolbachia organisms. Conversely, SIR was not macrofilaricidal and only transiently depleted Wolbachia densities, which repopulated worm tissues by 24 weeks after treatment. These results unequivocally demonstrate the macrofilaricidal potential of tetracyclines against Onchocerca infection and suggest that intermittent, protracted administration will be more effective than continuous shorter term treatment.

Makepeace BL et al. (2009) PLoS Negl Trop Dis "Immunisation with a multivalent, subunit vaccine reduces patent infection in a natural bovine model of onchocerciasis during intense field exposure."

Tanya VN, Bianco AE, Makepeace BL, Jensen SA, Njongmeta LM, Trees AJ, Nfon CK, Williams SA, Laney SJ

[PLoS Negl Trop Dis, 2009]

Human onchocerciasis, caused by the filarial nematode Onchocerca volvulus, is controlled almost exclusively by the drug ivermectin, which prevents pathology by targeting the microfilariae. However, this reliance on a single control tool has led to interest in vaccination as a potentially complementary strategy. Here, we describe the results of a trial in West Africa to evaluate a multivalent, subunit vaccine for onchocerciasis in the naturally evolved host-parasite relationship of Onchocerca ochengi in cattle. Naive calves, reared in fly-proof accommodation, were immunised with eight recombinant antigens of O. ochengi, administered separately with either Freund's adjuvant or alum. The selected antigens were orthologues of O. volvulus recombinant proteins that had previously been shown to confer protection against filarial larvae in rodent models and, in some cases, were recognised by serum antibodies from putatively immune humans. The vaccine was highly immunogenic, eliciting a mixed IgG isotype response. Four weeks after the final immunisation, vaccinated and adjuvant-treated control calves were exposed to natural parasite transmission by the blackfly vectors in an area of Cameroon hyperendemic for O. ochengi. After 22 months, all the control animals had patent infections (i.e., microfilaridermia), compared with only 58% of vaccinated cattle (P = 0.015). This study indicates that vaccination to prevent patent infection may be an achievable goal in onchocerciasis, reducing both the pathology and transmissibility of the infection. The cattle model has also demonstrated its utility for preclinical vaccine discovery, although much research will be required to achieve the requisite target product profile of a clinical candidate.

Gilbert, Sophie P. R. et al. (2015) International Worm Meeting "pal-1 regulates polarized apical junction remodeling and cell movement during the development of the C. elegans epidermis."

Brabin, Charles, Gilbert, Sophie P. R., Woollard, Alison

[International Worm Meeting, 2015]

We have been investigating the cellular remodeling events that enable correct ventral movement of lateral epidermal cells during the first larval stage (L1) in order to complete the ventral hypodermis of the developing worm. Unique to the L1 seam (Vn) cells, we have observed apical junction projections that are always associated with the hypodermally-fated anterior daughters of asymmetric seam divisions (Vn.a cells). The projection (first appearing at the anterior of undivided seam cells in embryos following dorsal intercalation) provides a migratory route for Vn.a cells towards the ventral midline during the hitherto overlooked ventral intercalation of these cells with the underlying P cells. Vn.p seam daughters, with no projection, remain in the seam line and maintain the stem-like fate in order to contribute further hypodermal daughters during asymmetric cell divisions in subsequent larval stages. We describe a crucial role for the homeobox gene pal-1 in regulating the A-P polarity of these projections and consequently correct seam vs. hypodermal cell positioning.In order to probe the molecular basis of pal-1 function we performed an RNAi-based modifier screen. Several members of the Wnt and Netrin signaling pathways were isolated as either suppressors or enhancers of the pal-1 Vn daughter migration defect. Strikingly, a ts mutation in the beta-catenin wrm-1 phenocopies the pal-1 epidermal cell positioning defect, and the Wnt effector POP-1 is a putative direct regulator of a pal-1 seam-specific regulatory element. This suggests a direct interaction between Wnt signaling and pal-1 function. A null unc-6 (netrin) allele synergizes strongly with pal-1, with double mutants displaying markedly increased severity and penetrance of epidermal positioning defects, even though the single netrin allele has no epidermal aberrations.Thus, we describe a novel mechanism for the generation of ventral hypodermis during early larval development. This involves polarized apical junction remodeling allowing ventral movement of correct seam daughters to complete the ventral hypodermis. This newly described mechanism is controlled by pal-1, working through Wnt and Netrin.

Tchakoute VL et al. (2006) Proc Natl Acad Sci U S A "In a bovine model of onchocerciasis, protective immunity exists naturally, is absent in drug-cured hosts, and is induced by vaccination."

Tchakoute VL, Bianco AE, Njongmeta LM, Trees AJ, Jensen SA, Nfon CK, Enyong PA, Graham SP, Makepeace BL, Lustigman S, Tanya VN

[Proc Natl Acad Sci U S A, 2006]

Onchocerciasis (river blindness) is a major parasitic disease of humans in sub-Saharan Africa caused by the microfilarial stage of the nematode Onchocerca volvulus. Using Onchocerca ochengi, a closely related species which infects cattle and is transmitted by the same black fly vector (Simulium damnosum sensu lato) as O. volvulus, we have conducted longitudinal studies after either natural field exposure or experimental infection to determine whether, and under what circumstances, protective immunity exists in onchocerciasis. On the basis of the adult worm burdens (nodules) observed, we determined that cattle reared in endemic areas without detectable parasites (putatively immune) were significantly less susceptible to heavy field challenge than age-matched, naive controls (P = 0.002), whereas patently infected cattle, cured of infection by adulticide treatment with melarsomine, were fully susceptible. Cattle immunized with irradiated third-stage larvae were significantly protected against experimental challenge (100% reduction in median nodule load, P = 0.003), and vaccination also conferred resistance to severe and prolonged field challenge (64% reduction in median nodule load, P = 0.053; and a significant reduction in microfilarial positivity rates and density, P < 0.05). These results constitute evidence of protective immunity in a naturally evolved host-Onchocerca sp. relationship and provide proof-of-principle for immunoprophylaxis under experimental and field conditions.

Zhang J et al. (2022) Environ Toxicol Pharmacol "Reproductive toxicities of ofloxacin and norfloxacin on Caenorhabditis elegans with multi-generational oscillatory effects and trans-generational residual influences."

Yu Z, Zheng Y, Zhang J

[Environ Toxicol Pharmacol, 2022]

The reproductive toxicities over generations are essential to assess the long-term impacts environmental fluoroquinolone antibiotics (FQs). In the present study, the multi-generational effects of ofloxacin (OFL) and norfloxacin (NOR) on reproduction were studied on Caenorhabditis elegans from 9 successive generations (F1-F9). Results showed that OFL showed no effects in F1, stimulation in F2 to F4, and inhibition F5 to F9. The effects of NOR also showed oscillation between stimulation and inhibition across generations. Further biochemical analysis demonstrated that the reproductive toxicities of OFL and NOR were more closely connected with total cholesterol (TCHO), progesterone (P) and testosterone (T), than major sperm protein (MSP) and vitellogenin (Vn). Moreover, OFL and NOR also showed significant trans-generational reproductive toxicities in T4 and T4', the great-grand-daughter of F1 and F9. Differences between T4 and T4' and between OFL and NOR, indicated influences of multi-generational exposure and urged more exploration on different mechanisms between FQs.

Allen JE et al. (2008) PLoS Negl Trop Dis "Of mice, cattle, and humans: the immunology and treatment of river blindness."

Taylor DW, Bain O, Adjei O, Trees AJ, Hoerauf A, Hoffmann WH, Wanji S, Makepeace BL, Allen JE, Schulz-Key H, Tanya VN

[PLoS Negl Trop Dis, 2008]

River blindness is a seriously debilitating disease caused by the filarial parasite Onchocerca volvulus, which infects millions in Africa as well as in South and Central America. Research has been hampered by a lack of good animal models, as the parasite can only develop fully in humans and some primates. This review highlights the development of two animal model systems that have allowed significant advances in recent years and hold promise for the future. Experimental findings with Litomosoides sigmodontis in mice and Onchocerca ochengi in cattle are placed in the context of how these models can advance our ability to control the human disease.

Quintana JF et al. (2015) Parasit Vectors "Extracellular Onchocerca-derived small RNAs in host nodules and blood."

Debrah A, Wanji S, Bah GS, Ngangyung HF, Blaxter M, Quintana JF, Tanya VN, Babayan SA, Ivens A, Hoerauf A, Pfarr KM, Taylor DW, Makepeace BL, Buck AH

[Parasit Vectors, 2015]

BACKGROUND: microRNAs (miRNAs), a class of short, non-coding RNA can be found in a highly stable, cell-free form in mammalian body fluids. Specific miRNAs are secreted by parasitic nematodes in exosomes and have been detected in the serum of murine and dog hosts infected with the filarial nematodes Litomosoides sigmodontis and Dirofilaria immitis, respectively. Here we identify extracellular, parasite-derived small RNAs associated with Onchocerca species infecting cattle and humans. METHODS: Small RNA libraries were prepared from total RNA extracted from the nodule fluid of cattle infected with Onchocerca ochengi as well as serum and plasma from humans infected with Onchocerca volvulus in Cameroon and Ghana. Parasite-derived miRNAs were identified based on the criteria that sequences unambiguously map to hairpin structures in Onchocerca genomes, do not align to the human genome and are not present in European control serum. RESULTS: A total of 62 mature miRNAs from 52 distinct pre-miRNA candidates were identified in nodule fluid from cattle infected with O. ochengi of which 59 are identical in the genome of the human parasite O. volvulus. Six of the extracellular miRNAs were also identified in sequencing analyses of serum and plasma from humans infected with O. volvulus. Based on sequencing analysis the abundance levels of the parasite miRNAs in serum or plasma range from 5 to 127 reads/per million total host miRNA reads identified, comparable to our previous analyses of Schistosoma mansoni and L. sigmodontis miRNAs in serum. All six of the O. volvulus miRNAs identified have orthologs in other filarial nematodes and four were identified in the serum of mice infected with L. sigmodontis. CONCLUSIONS: We have identified parasite-derived miRNAs associated with onchocerciasis in cattle and humans. Our results confirm the conserved nature of RNA secretion by diverse nematodes. Additional species-specific small RNAs from O. volvulus may be present in serum based on the novel miRNA sequences identified in the nodule fluid. In our analyses comparison to European control serum illuminates the scope for false-positives, warranting caution in criteria that should be applied to identification of biomarkers of infection.