Antiparasitics in Animal Health: Quo Vadis?

New paradigms in the prevention of canine vector-borne diseases

The prevention of canine vector-borne diseases (CVBDs) is pivotal for the health and welfare of dogs as well as for reducing their zoonotic risk to humans. Scientific knowledge gained in recent years contributed to the development of new strategies for the control of these diseases in different social and cultural contexts. Here, we discuss recent advances in the prevention of vector-borne pathogens (VBPs) affecting dogs with a focus on those of zoonotic relevance.

Tick-borne diseases in Europe: Current prevention, control tools and the promise of aptamers

In Europe, tick-borne diseases (TBDs) cause significant morbidity and mortality, affecting both human and animal health. Ticks can transmit a wide variety of pathogens (bacteria, viruses, and parasites) and feed on many vertebrate hosts. The incidence and public health burden of TBDs are tending to intensify in Europe due to various factors, mainly anthropogenic and often combined. Early detection of tick-borne pathogens (TBPs), preventive measures and treatment are of great importance to control TBDs and their expansion. However, there are various limitations in terms of the sensitivity and/or specificity of detection and prevention methods, and even in terms of feasibility. Aptamers are single-stranded DNA or RNA that could address these issues as they are able to bind with high affinity and specificity to a wide range of targets (e.g., proteins, small compounds, and cells) due to their unique three-dimensional structure. To date, aptamers have been selected against TBPs such as tick-borne encephalitis virus, Francisella tularensis, and Rickettsia typhi. These studies have demonstrated the benefits of aptamer-based assays for pathogen detection and medical diagnosis. In this review, we address the applications of aptamers to TBDs and discuss their potential for improving prevention measures (use of chemical acaricides, vaccination), diagnosis and therapeutic strategies to control TBDs.

Assessing the efficacy of the ovicidal fungus Mucor circinelloides in reducing coccidia parasitism in peacocks

The biological control of gastrointestinal (GI) parasites using predatory fungi has been recently proposed as an accurate and sustainable approach in birds. The current study aimed to assess for the first time the efficacy of using the native ovicidal fungus Mucor circinelloides (FMV-FR1) in reducing coccidia parasitism in peacocks. For this purpose, an in vivo trial was designed in the resident peacock collection (n = 58 birds) of the São Jorge Castle, at Lisbon, Portugal. These animals presented an initial severe infection by coccidia of the genus Eimeria (20106 ± 8034 oocysts per gram of feces, OPG), and thus received commercial feed enriched with a M. circinelloides suspension (1.01 × 108 spores/kg feed), thrice-weekly. Fresh feces were collected every 15 days to calculate the coccidia shedding, using the Mini-FLOTAC technique. The same bird flock served simultaneously as control (t0 days) and test groups (t15-t90 days). The average Eimeria sp. shedding in peacocks decreased up to 92% following fungal administrations, with significant reduction efficacies of 78% (p = 0.004) and 92% (p = 0.012) after 45 and 60 days, respectively. Results from this study suggest that the administration of M. circinelloides spores to birds is an accurate solution to reduce their coccidia parasitism.

Target-based discovery of a broad-spectrum flukicide

Diseases caused by parasitic flatworms impart a considerable healthcare burden worldwide. Many of these diseases-for example, the parasitic blood fluke infection schistosomiasis-are treated with the drug praziquantel (PZQ). However, PZQ is ineffective against disease caused by liver flukes from the genus Fasciola because of a single amino acid change within the target of PZQ, a transient receptor potential ion channel in the melastatin family (TRPMPZQ), in Fasciola species. Here, we identify benzamidoquinazolinone analogs that are active against Fasciola TRPMPZQ. Structure-activity studies define an optimized ligand (BZQ) that caused protracted paralysis and tegumental damage to these liver flukes. BZQ also retained activity against Schistosoma mansoni comparable to PZQ and was active against TRPMPZQ orthologs in all profiled species of parasitic fluke. This broad-spectrum activity manifests as BZQ adopts a pose within the binding pocket of TRPMPZQ that is dependent on a ubiquitously conserved residue. BZQ therefore acts as a universal activator of trematode TRPMPZQ and a first-in-class, broad-spectrum flukicide.

Faecal egg count reduction tests and nemabiome analysis reveal high frequency of multi-resistant parasites on sheep farms in north-east Germany involving multiple strongyle parasite species

Anthelmintic resistance in sheep parasitic gastrointestinal nematodes is widespread and a severe health and economic issue but prevalence of resistance and involved parasite species are unknown in Germany. Here, the faecal egg count reduction test (FECRT) was performed on eight farms using fenbendazole, ivermectin and moxidectin and on four farms using only moxidectin. A questionnaire was used to obtain data on management practices to potentially identify risk factors for presence of resistance. All requirements of the recently revised WAAVP guideline for diagnosing anthelmintic resistance using the FECRT were applied. Nematode species composition in pre- and post-treatment samples was analysed with the nemabiome approach. Using the eggCounts statistic package, resistance against fenbendazole, ivermectin and moxidectin was found on 7/8, 8/8 and 8/12 farms, respectively. No formal risk factor analysis was conducted since resistance was present on most farms. Comparison with the bayescount R package results revealed substantial agreement between methods (Cohen's κ = 0.774). In contrast, interpretation of data comparing revised and original WAAVP guidelines resulted in moderate agreement (Cohen's κ = 0.444). The FECR for moxidectin was significantly higher than for ivermectin and fenbendazole. Nemabiome data identified 4 to 12 species in pre-treatment samples and treatments caused a small but significant decrease in species diversity (inverse Simpson index). Non-metric multidimensional scaling and k-means clustering were used to identify common patterns in pre- and post-treatment samples. However, post-treatment samples were scattered among the pre-treatment samples. Resistant parasite species differed between farms. In conclusion, the revised FECRT guideline allows robust detection of anthelmintic resistance. Resistance was widespread and involved multiple parasite species. Resistance against both drug classes on the same farm was common. Further studies including additional drugs (levamisole, monepantel, closantel) should combine sensitive FECRTs with nemabiome data to comprehensively characterise the anthelmintic susceptibility status of sheep nematodes in Germany.

Structure-activity relationship and target investigation of 2-aryl quinolines with nematocidal activity

Within the context of our anthelmintic discovery program, we recently identified and evaluated a quinoline derivative, called ABX464 or obefazimod, as a nematocidal candidate; synthesised a series of analogues which were assessed for activity against the free-living nematode Caenorhabditis elegans; and predicted compound-target relationships by thermal proteome profiling (TPP) and in silico docking. Here, we logically extended this work and critically evaluated the anthelmintic activity of ABX464 analogues on Haemonchus contortus (barber's pole worm) - a highly pathogenic nematode of ruminant livestock. First, we tested a series of 44 analogues on H. contortus (larvae and adults) to investigate the nematocidal pharmacophore of ABX464, and identified one compound with greater potency than the parent compound and showed moderate activity against a select number of other parasitic nematodes (including Ancylostoma, Heligmosomoides and Strongyloides species). Using TPP and in silico modelling studies, we predicted protein HCON_00074590 (a predicted aldo-keto reductase) as a target candidate for ABX464 in H. contortus. Future work aims to optimise this compound as a nematocidal candidate and investigate its pharmacokinetic properties. Overall, this study presents a first step toward the development of a new nematocide.

Effect of the Combination of Synthetic Anthelmintics with Carvacryl Acetate in Emulsions with and without a Sodium Alginate Matrix on Haemonchus contortus

The present study aimed to evaluate the effect of nanoemulsions using combined synthetic anthelmintics, thiabendazole (TBZ), levamisole (LEV), and ivermectin (IVM), with carvacryl acetate (CA) against Haemonchus contortus, and also tested the presence and absence of alginate (ALG). The anthelmintic effect of the CA/TBZ nanoemulsion was evaluated in the egg hatch test (EHT). The effects of CA/IVM and CA/LEV nanoemulsions were evaluated in the larval development test (LDT). The emulsions CA/TBZ/ALG and CA/TBZ showed a multimodal profile, with most particles on the nanometric scale. The encapsulation efficiency in CA/TBZ/ALG was 80.25%, and that in CA/LEV/ALG was 89.73%. In the EHT, CA/TBZ and CA/TBZ/ALG showed mean combination indices (CIs) of 0.55 and 0.36, respectively, demonstrating synergism in both. In LDT, CA/IVM had an average CI of 0.75, and CA/LEV and CA/LEV/ALG showed CI values of 0.4 and 0.93, respectively. It was concluded that CA/TBZ showed a synergistic interaction, and CA/TBZ/ALG showed an enhanced effect. In addition, the matrix brought stability to the product, encouraging its improvement to obtain higher efficacy.

A phenotypic screen of the Global Health Priority Box identifies an insecticide with anthelmintic activity

BACKGROUND

Infection with parasitic nematodes (helminths), particularly those of the order Strongylida (such as Haemonchus contortus), can cause significant and burdensome diseases in humans and animals. Widespread drug (anthelmintic) resistance in livestock parasites, the absence of vaccines against most of these nematodes, and a lack of new and effective chemical entities on the commercial market demands the discovery of new anthelmintics. In the present study, we searched the Global Health Priority Box (Medicines for Malaria Venture) for new candidates for anthelmintic development.

METHODS

We employed a whole-organism, motility-based phenotypic screening assay to identify compounds from the Global Health Priority Box with activity against larvae of the model parasite H. contortus, and the free-living comparator nematode Caenorhabditis elegans. Hit compounds were further validated via dose-response assays, with lead candidates then assessed for nematocidal activity against H. contortus adult worms, and additionally, for cytotoxic and mitotoxic effects on human hepatoma (HepG2) cells.

RESULTS

The primary screen against H. contortus and C. elegans revealed or reidentified 16 hit compounds; further validation established MMV1794206, otherwise known as 'flufenerim', as a significant inhibitor of H. contortus larval motility (half-maximal inhibitory concentration [IC50] = 18 μM) and development (IC50 = 1.2 μM), H. contortus adult female motility (100% after 12 h of incubation) and C. elegans larval motility (IC50 = 0.22 μM). Further testing on a mammalian cell line (human hepatoma HepG2 cells), however, identified flufenerim to be both cytotoxic (half-maximal cytotoxic concentration [CC50] < 0.7 μM) and mitotoxic (half-maximal mitotoxic concentration [MC50] < 0.7 μM).

CONCLUSIONS

The in vitro efficacy of MMV1794206 against the most pathogenic stages of H. contortus, as well as the free-living C. elegans, suggests the potential for development as a broad-spectrum anthelmintic compound; however, the high toxicity towards mammalian cells presents a significant hindrance. Further work should seek to establish the protein-drug interactions of MMV1794206 in a nematode model, to unravel the mechanism of action, in addition to an advanced structure-activity relationship investigation to optimise anthelmintic activity and eliminate mammalian cell toxicity.

Efficacy of afoxolaner or the combination of afoxolaner with milbemycin oxime against Otodectes cynotis in naturally infested dogs

Otodectes cynotis, commonly known as "the ear mite," is a highly contagious ectoparasite and a significant cause of otitis externa in canines. The objective of the current study was to determine the efficacy of the isoxazoline afoxolaner (Nexgard®), and the combination of afoxolaner with milbemycin oxime (Nexgard Spectra®), in dogs naturally infested with O. cynotis. In total, 32 infested client-owned dogs from two different sites in Greece were included. The animals were randomly divided into four equal groups based on their infestation score. Group 1 served as the negative control, group 2 received one oral administration of Nexgard (Day 0), group 3 received two monthly oral administrations of Nexgard (Days 0, 30), and group 4 received two monthly oral administrations of Nexgard Spectra (Days 0, 30), according to label instructions. Otoscopic examinations for mites and observations on debris/cerumen in the ears were carried out on Days 0, 15, 30, and 45. A quantitative assessment of ear mites by ear duct flushing and live mite counts was performed on Day 45. The results demonstrated that a single oral dose of afoxolaner and two monthly doses of afoxolaner or afoxolaner with milbemycin oxime resulted in a 99.9% reduction in live mite counts compared to the untreated control group by Day 45. Additionally, treated dogs showed improved clinical symptoms, such as ear cerumen/debris decrease, while untreated dogs experienced worsening symptoms over the study duration. No adverse events were reported. Overall, these results support the use of afoxolaner-based products to treat O. cynotis infestation in dogs.

Antidotal Effects of the Antihistamine Diphenhydramine Against Cholinesterase Inhibitor Poisoning: A Meta-Analysis of Median Lethal Doses in Experimental Animals

The H1-antihistamine diphenhydramine antagonizes cholinesterase inhibitor poisoning in various animal species. One aspect of acute antidotal actions of diphenhydramine is increasing the median lethal doses (LD50) of toxicants. The objective of this meta-analysis was to assess the antidotal action of diphenhydramine against short-term toxicity (LD50) of cholinesterase inhibitors in experimental animals. The experimental studies selected were according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. They were conducted in laboratory animals (mice, rats, and chicks) to determine acute LD50 values of cholinesterase inhibitors (organophosphates, carbamates, and imidocarb) under the influence of diphenhydramine vs. controls. Twenty-eight records were selected from 12 studies on mice (n= 242), rats (n= 27), and young chicks (n= 128). The forest plot of randomized two-group meta-analysis assessed effect size, subgroup analysis, drapery prediction, heterogeneity, publication bias-funnel plot as well as one-group proportions meta-analysis of percent protection. Diphenhydramine significantly increased the combined effect size (i.e. increased LD50) in intoxicated experimental animals in comparison to controls (-3.71, standard error (SE) 0.36, 95%CI -4.46, -2.97). The drapery plot proposed a wide range of confidence intervals. The I2 index of heterogeneity of the combined effect size was high at 81.03% (Q= 142.3, p < 0.0001). Galbraith regression also indicated data heterogeneity; however, the normal quantile plot indicated no outliers. Subgroup analysis indicated significantly high heterogeneity with organophosphates (I2 = 63.72%) and carbamates (I2 = 76.41%), but low with imidocarb (I2 = 51.48%). The funnel plot and Egger regression test (t= -13.7, p < 0.0001) revealed publication bias. The median of the diphenhydramine protection ratio was 1.655, and the related forest plot of one group proportion meta-analysis revealed a statistically high level of protection (0.594, SE 0.083, 95%CI 0.432, 0.756), with high heterogeneity (I2= 99.86). The risk of bias assessment was unclear, while the total score (16 out of 20) of each study leaned towards the side of the low risk of bias. In conclusion, the meta-analysis of LD50 values indicated that diphenhydramine unequivocally protected experimental animals from the acute toxicity of cholinesterase inhibitors. The drug could be an additional antidote against acute poisoning induced by cholinesterase inhibitors, but a word of caution: it is not to be considered as a replacement for the standard antidote atropine sulfate. Further studies are needed to examine the action of diphenhydramine on adverse chronic effects of cholinesterase inhibitors.

Substandard and falsified ivermectin tablets obtained for self-medication during the COVID-19 pandemic as a source of potential harm

In 2019, a global viral pandemic, due to the SARS-CoV-2 virus, broke out. Soon after, the search for a vaccine and/or antiviral medicine began. One of the candidate antiviral medicines tested was ivermectin. Although several health authorities warned the public against the use of this medicine outside clinical trials, the drug was widely used at the end of 2020 and in 2021. Simultaneously, several reports started to emerge demonstrating serious adverse effects after self-medicating with ivermectin. It stands to reason that the self-administration of substandard or falsified (SF) medicines bearing harmful quality deficiencies have contributed to this phenomenon. In order to have a better view on the nature of these harmful quality deficiencies, SF ivermectin samples, intercepted in large quantities by the Belgian regulatory agencies during the period 2021-2022, were analyzed in our official medicines control laboratory. None of the samples (n = 19) were compliant to the quality criteria applicable to medicinal products. These SF products either suffered from a systematic underdosing of the active pharmaceutical ingredient or were severely contaminated with bacteria, two of which were contaminated with known pathogens that cause gastrointestinal illness upon oral intake. In addition to the direct risks of self-medicating with such a product, the improper usage and dosage of ivermectin medication might also facilitate ivermectin tolerance or resistance in parasites. This may have detrimental consequences on a global scale, certainly as the number of newly developed active pharmaceutical ingredients that can safely be used to combat parasites is rather scarce.

Essential oils and isolated compounds for tick control: advances beyond the laboratory

BACKGROUND

Tick control is a worldwide challenge due to its resistance to acaricides. Essential oils (EOs) and isolated compounds (EOCs) are potential alternatives for tick control technologies.

METHODS

A review with EOs and EOCs, under field and semi-field conditions, was performed based on Scopus, Web of Science and PubMed databases. Thirty-one studies published between 1991 and 2022 were selected. The search was performed using the following keywords: "essential oil" combined with "tick," "Ixodes," "Argas," "Rhipicephalus," "Amblyomma," "Hyalomma," "Dermacentor," "Haemaphysalis" and "Ornithodoros." The words "essential oil" and "tick" were searched in the singular and plural.

RESULTS

The number of studies increased over the years. Brazil stands out with the largest number (51.6%) of publications. The most studied tick species were Rhipicephalus microplus (48.4%), Ixodes scapularis (19.4%), Amblyomma americanum and R. sanguineus sensu lato (9.7% each). Cattle (70%) and dogs (13%) were the main target animal species. Regarding the application of EOs/EOCs formulations, 74% of the studies were conducted with topical application (spray, pour-on, foam, drop) and 26% with environmental treatment (spray). Efficacy results are difficult to evaluate because of the lack of information on the methodology and standardization. The nanotechnology and combination with synthetic acaricides were reported as an alternative to enhance the efficacy of EOs/EOCs. No adverse reactions were observed in 86.6% of the studies evaluating EOs/EOCs clinical safety. Studies regarding toxicity in non-target species and residues are scarce.

CONCLUSIONS

This article provides a comprehensive review on the use of EOs and EOCs to reduce tick infestations, in both the hosts and the environment. As future directions, we recommend the chemical characterization of EOs, methodology standardization, combination of EOs/EOCs with potential synergists, nanotechnology for new formulations and safety studies for target and non-target organisms, also considering the environmental friendliness.

Efficacy of a fixed-dose combination injectable (0.2 mg/kg doramectin + 6.0 mg/kg levamisole hydrochloride) in Australian cattle against naturally acquired gastrointestinal nematode infections

Australian producers have long used macrocyclic lactones (MLs) to successfully control cattle gastrointestinal nematodes (GINs) and consequently improve production parameters. However, the trajectory of ML resistance development in cattle GINs is following that of small ruminant nematode populations, highlighting a need for novel treatment options to provide efficacy in the current environment and interrupt the long-term establishment of ML-resistant GIN populations in Australian cattle. Here, we describe three field studies conducted in Australia to evaluate the efficacy of a single administration of a novel fixed-dose combination injectable (FDCI) endectocide against naturally acquired infections of cattle GINs. The FDCI is administered subcutaneously to deliver 0.2 mg/kg doramectin and 6 mg/kg levamisole hydrochloride (HCl). Study sites consisted of three farms in New South Wales (n = 2) and Victoria (n = 1). At each site, cattle were randomly allocated into one of three treatment groups: (1) untreated control (saline), (2) FDCI (0.2 mg/kg doramectin, 6 mg/kg levamisole HCl) or (3) positive control (0.2 mg/kg ivermectin). All treatments were administered on Day 0. Fecal samples were collected prior to treatment on Days -1 (Study 3) or 0 (Studies 1 and 2) and again on Day 14 (post-treatment) to evaluate efficacy via fecal egg count (FEC) and for coproculture. Adequacy of infection was confirmed at all three study sites, with Day 14 geometric mean (GM) FECs for saline-treated cattle ranging from 32.5 eggs per gram (EPG) to 623.7 EPG. FECs for FDCI-treated cattle were significantly reduced compared to saline-treated cattle (p ≤ 0.0001) on Day 14, with GM-based efficacy ≥ 99.7% at all three study sites. In contrast, ivermectin was 97.4% effective against cattle GINs in Study 1 but was only 47.2% and 39.8% effective at study site 2 and 3, respectively. Genus-specific efficacies suggest the presence of ivermectin-resistant Cooperia spp. (Study 1), Haemonchus spp. (Study 2) and Ostertagia spp. (Study 3) populations in the naturally infected cattle used in these studies. The post-treatment FEC and genus-specific efficacy estimations indicate the doramectin + levamisole HCl FDCI was highly efficacious against cattle GINs even in the face of ivermectin LOE at study sites 2 and 3. The efficacy of the new FDCI against both ML-susceptible and ML-resistant economically important cattle GINs in Australia affirms it is a valuable treatment option for producers operating in an environment of ML loss of efficacy.

Target-based discovery of a broad spectrum flukicide

Diseases caused by parasitic flatworms impart a considerable healthcare burden worldwide. Many of these diseases - for example, the parasitic blood fluke infection, schistosomiasis - are treated with the drug praziquantel (PZQ). However, PZQ is ineffective against disease caused by liver flukes from the genus Fasciola. This is due to a single amino acid change within the target of PZQ, a transient receptor potential ion channel (TRPMPZQ), in Fasciola species. Here we identify benzamidoquinazolinone analogs that are active against Fasciola TRPMPZQ. Structure-activity studies define an optimized ligand (BZQ) that caused protracted paralysis and damage to the protective tegument of these liver flukes. BZQ also retained activity against Schistosoma mansoni comparable to PZQ and was active against TRPMPZQ orthologs in all profiled species of parasitic fluke. This broad spectrum activity was manifest as BZQ adopts a pose within the binding pocket of TRPMPZQ dependent on a ubiquitously conserved residue. BZQ therefore acts as a universal activator of trematode TRPMPZQ and a first-in-class, broad spectrum flukicide.

Diversity and geographic distribution of haplotypes of Dirofilaria immitis across European endemic countries

BACKGROUND

Dirofilaria immitis, also known as heartworm, is one of the most important parasitic nematodes of domestic dogs, causing a potentially serious disease, cardiopulmonary dirofilariosis, which can be lethal. This species seems to be less 'expansive' than its sister species Dirofilaria repens, and it is believed that climate change facilitates the spread of this parasite to new non-endemic regions.

METHODS

In total, 122 heartworm isolates were analysed from nine endemic countries in Europe (Portugal, Spain, Italy, Greece, Hungary, Romania, Slovakia, and Ukraine) and a single isolate from Bangladesh by amplification and sequencing of two mitochondrial (mt) DNA markers: cytochrome c oxidase subunit 1 (COI) and dehydrogenase subunit 1 (NADH). The main aim of the current study was to determine the genetic diversity of D. immitis and compare it with D. repens haplotype diversity and distribution. DNA was extracted from adult heartworms or microfilariae in blood. Most isolates originated from dogs (Canis lupus familiaris) while 10 isolates originated from wildlife species from Romania, including eight isolates from golden jackals (Canis aureus), one isolate from a Eurasian otter (Lutra lutra) and one isolate from a red fox (Vulpes vulpes).

RESULTS

Median spanning network analysis was based on the combined sequence (1721 bp) obtained from two mt markers and successfully delineated nine haplotypes (Di1-Di9). Haplotype Di1 was the dominant haplotype encompassing 91 out of the 122 sequences (75%) from all nine countries and four host species. Haplotype Di2 was the second most common haplotype, formed solely by 13 isolates from Italy. The remaining sequences were assigned to Di3-Di9 haplotypes, differing by 1-4 SNPs from the dominant Di1 haplotype. There was evidence for geographical segregation of haplotypes, with three unique haplotypes associated with Italy and four others associated with certain countries (Di4 and Di7 with Slovakia; Di8 with Greece; Di6 with Hungary).

CONCLUSION

Diversity in D. immitis mt haplotypes was lower by half than in D. repens (9 vs. 18 haplotypes in D. immitis and D. repens, respectively), which may be associated with the slower expansion of heartworm in Central and NE Europe. NADH gene appears to be conserved in Dirofilaria sp. by showing lower genetic diversity than the analysed COI gene.

Occurrence, ecology risk assessment and exposure evaluation of 19 anthelmintics in dust and soil from China

In order to fill the blank of domestic research on anthelmintics in dust and soil, 159 paired dust (including indoor and outdoor dust) and soil samples were collected nationwide. All 19 kinds of the anthelmintics were detected in the samples. The total concentration of the target substances in the outdoor dust, indoor dust and soil samples ranged from 1.83 to 1.30 × 10³ ng/g, from 2.99 to 6.00 × 10³ ng/g and from 0.23 to 8.03 × 10² ng/g, respectively. The total concentration of the 19 anthelmintics in northern China were significantly higher than those in southern China in the outdoor dust and soil samples. No significant correlation was found in the total concentration of anthelmintics between the indoor and outdoor dust because of strong human activities interference, however, a significant correlation existed between the outdoor dust and soil samples and between the indoor dust and soil samples. High ecological risk was found at 35% and 28% of all the sampling sites to non-target organisms in the soil respectively for IVE and ABA, and merits further study. The daily anthelmintics intakes were evaluated via ingestion and dermal contact of soil and dust samples for both children and adults. Ingestion was the predominant way for anthelmintics exposure, and the anthelmintics in soil and dust did not pose a health threat to human health at present.

Botanicals: A promising approach for controlling cecal coccidiosis in poultry

Avian species have long struggled with the problem of coccidiosis, a disease that affects various parts of the intestine, including the anterior gut, midgut, and hindgut. Among different types of coccidiosis, cecal coccidiosis is particularly dangerous to avian species. Chickens and turkeys are commercial flocks; thus, their parasites have remained critical due to their economic importance. High rates of mortality and morbidity are observed in both chickens and turkeys due to cecal coccidiosis. Coccidiostats and coccidiocidal chemicals have traditionally been added to feed and water to control coccidiosis. However, after the EU banned their use because of issues of resistance and public health, alternative methods are being explored. Vaccines are also being used, but their efficacy and cost-effectiveness remain as challenges. Researchers are attempting to find alternatives, and among the alternatives, botanicals are a promising choice. Botanicals contain multiple active compounds such as phenolics, saponins, terpenes, sulfur compounds, etc., which can kill sporozoites and oocysts and stop the replication of Eimeria. These botanicals are primarily used as anticoccidials due to their antioxidant and immunomodulatory activities. Because of the medicinal properties of botanicals, some commercial products have also been developed. However, further research is needed to confirm their pharmacological effects, mechanisms of action, and methods of concentrated preparation. In this review, an attempt has been made to summarize the plants that have the potential to act as anticoccidials and to explain the mode of action of different compounds found within them.

Nemacol is a small molecule inhibitor of C. elegans vesicular acetylcholine transporter with anthelmintic potential

Nematode parasites of humans and livestock pose a significant burden to human health, economic development, and food security. Anthelmintic drug resistance is widespread among parasites of livestock and many nematode parasites of humans lack effective treatments. Here, we present a nitrophenyl-piperazine scaffold that induces motor defects rapidly in the model nematode Caenorhabditis elegans. We call this scaffold Nemacol and show that it inhibits the vesicular acetylcholine transporter (VAChT), a target recognized by commercial animal and crop health groups as a viable anthelmintic target. We demonstrate that it is possible to create Nemacol analogs that maintain potent in vivo activity whilst lowering their affinity to the mammalian VAChT 10-fold. We also show that Nemacol enhances the ability of the anthelmintic Ivermectin to paralyze C. elegans and the ruminant nematode parasite Haemonchus contortus. Hence, Nemacol represents a promising new anthelmintic scaffold that acts through a validated anthelmintic target.

Pharmacokinetic and pharmacodynamic considerations for treating sarcoptic mange with cross-relevance to Australian wildlife

Sarcoptes scabiei is the microscopic burrowing mite responsible for sarcoptic mange, which is reported in approximately 150 mammalian species. In Australia, sarcoptic mange affects a number of native and introduced wildlife species, is particularly severe in bare-nosed wombats (Vombatus ursinus) and an emerging issue in koala and quenda. There are a variety of acaricides available for the treatment of sarcoptic mange which are generally effective in eliminating mites from humans and animals in captivity. In wild populations, effective treatment is challenging, and concerns exist regarding safety, efficacy and the potential emergence of acaricide resistance. There are risks where acaricides are used intensively or inadequately, which could adversely affect treatment success rates as well as animal welfare. While reviews on epidemiology, treatment strategies, and pathogenesis of sarcoptic mange in wildlife are available, there is currently no review evaluating the use of specific acaricides in the context of their pharmacokinetic and pharmacodynamic properties, and subsequent likelihood of emerging drug resistance, particularly for Australian wildlife. This review critically evaluates acaricides that have been utilised to treat sarcoptic mange in wildlife, including dosage forms and routes, pharmacokinetics, mode of action and efficacy. We also highlight the reports of resistance of S. scabiei to acaricides, including clinical and in vitro observations.

A rodent model for Dirofilaria immitis, canine heartworm: parasite growth, development, and drug sensitivity in NSG mice

Heartworm disease, caused by Dirofilaria immitis, remains a significant threat to canines and felines. The development of parasites resistant to macrocyclic lactones (ML) has created a significant challenge to the control of the infection. The goal of this study was to determine if mice lacking a functional immune response would be susceptible to D. immitis. Immunodeficient NSG mice were susceptible to the infection, sustaining parasites for at least 15 weeks, with infective third-stage larvae molting and developing into the late fourth-stage larvae. Proteomic analysis of host responses to the infection revealed a complex pattern of changes after infection, with at least some of the responses directed at reducing immune control mechanisms that remain in NSG mice. NSG mice were infected with isolates of D. immitis that were either susceptible or resistant to MLs, as a population. The susceptible isolate was killed by ivermectin whereas the resistant isolate had improved survivability, while both isolates were affected by moxidectin. It was concluded that D. immitis survives in NSG mice for at least 15 weeks. NSG mice provide an ideal model for monitoring host responses to the infection and for testing parasites in vivo for susceptibility to direct chemotherapeutic activity of new agents.

Analysis of the range of drugs registered in the Russian Federation to control parasitic infections in pigs

The purpose of the research is the analysis of the range of antiparasitic drugs for pig breeding as registered in the Russian Federation and included in the State Register of Medicinal Products for Veterinary Use.The control of parasitic diseases is an essential element of veterinary support for animal husbandry, and its constituent part is the use of antiparasitic drugs. The State Register contains more than three hundred drugs to control parasitic infections of animals of various species. Forty-eight drugs are allowed for use in pig breeding. The analysis of drug compositions found that they contained a limited list of compounds as active substances. For example, 17 antiparasitic drugs contained compounds of the avermectin class as active substances (12 of them had ivermectin as the active substance); 8 drugs against endoparasites contained albendazole in their composition. At the same time, the composition of combined drugs lack distinction and is a combination of two or more active substances produced in mono-preparations. To prevent the resistance in parasites, it is advisable to use a minimum required list of drugs which allows the availability of a reserve for drug rotation in the future. Simultaneous or sequential use of different drugs (including insectoacaricides based on neonicotinoids or synthetic pyrethroids to treat premises in the presence of animals) complicates the assessment of the individual drug effect on animal health and can induce immunological stress, which creates favorable conditions for infectious diseases including opportunistic infections.

Technology Readiness Levels for vaccine and drug development in animal health: From discovery to life cycle management

Public research and innovation initiatives in animal health aim to deliver key knowledge, services and products that improve the control of animal infectious diseases and animal welfare to deliver on global challenges including public health threats, environmental concerns and food security. The Technology Readiness Level (TRL) is a popular innovation policy instrument to monitor the maturity of upcoming new technologies in publicly funded research projects. However, while general definition of the 9 levels on the TRL-scale enable uniform discussions of technical maturity across different types of technology, these definitions are very generic which hampers concrete interpretation and application. Here, we aligned innovation pipeline stages as used in the animal health industry for the development of new vaccines or drugs with the TRL scale, resulting in TRL for animal health (TRLAH). This more bespoke scale can help to rationally allocate funding for animal health research from basic to applied research, map innovation processes, monitor progress and develop realistic progress expectations across the time span of a research and innovation project. The TRLAH thus become an interesting instrument to enhance the translation of public research results into industrial and societal innovation and foster public-private partnerships in animal health.

Thermal proteome profiling reveals Haemonchus orphan protein HCO_011565 as a target of the nematocidal small molecule UMW-868

Parasitic roundworms (nematodes) cause destructive diseases, and immense suffering in humans and other animals around the world. The control of these parasites relies heavily on anthelmintic therapy, but treatment failures and resistance to these drugs are widespread. As efforts to develop vaccines against parasitic nematodes have been largely unsuccessful, there is an increased focus on discovering new anthelmintic entities to combat drug resistant worms. Here, we employed thermal proteome profiling (TPP) to explore hit pharmacology and to support optimisation of a hit compound (UMW-868), identified in a high-throughput whole-worm, phenotypic screen. Using advanced structural prediction and docking tools, we inferred an entirely novel, parasite-specific target (HCO_011565) of this anthelmintic small molecule in the highly pathogenic, blood-feeding barber’s pole worm, and in other socioeconomically important parasitic nematodes. The “hit-to-target” workflow constructed here provides a unique prospect of accelerating the simultaneous discovery of novel anthelmintics and associated parasite-specific targets.

Identification of antiparasitic drug targets using a multi-omics workflow in the acanthocephalan model

Background

With the expansion of animal production, parasitic helminths are gaining increasing economic importance. However, application of several established deworming agents can harm treated hosts and environment due to their low specificity. Furthermore, the number of parasite strains showing resistance is growing, while hardly any new anthelminthics are being developed. Here, we present a bioinformatics workflow designed to reduce the time and cost in the development of new strategies against parasites. The workflow includes quantitative transcriptomics and proteomics, 3D structure modeling, binding site prediction, and virtual ligand screening. Its use is demonstrated for Acanthocephala (thorny-headed worms) which are an emerging pest in fish aquaculture. We included three acanthocephalans (Pomphorhynchus laevis, Neoechinorhynchus agilis, Neoechinorhynchus buttnerae) from four fish species (common barbel, European eel, thinlip mullet, tambaqui).

Results

The workflow led to eleven highly specific candidate targets in acanthocephalans. The candidate targets showed constant and elevated transcript abundances across definitive and accidental hosts, suggestive of constitutive expression and functional importance. Hence, the impairment of the corresponding proteins should enable specific and effective killing of acanthocephalans. Candidate targets were also highly abundant in the acanthocephalan body wall, through which these gutless parasites take up nutrients. Thus, the candidate targets are likely to be accessible to compounds that are orally administered to fish. Virtual ligand screening led to ten compounds, of which five appeared to be especially promising according to ADMET, GHS, and RO5 criteria: tadalafil, pranazepide, piketoprofen, heliomycin, and the nematicide derquantel.

Conclusions

The combination of genomics, transcriptomics, and proteomics led to a broadly applicable procedure for the cost- and time-saving identification of candidate target proteins in parasites. The ligands predicted to bind can now be further evaluated for their suitability in the control of acanthocephalans. The workflow has been deposited at the Galaxy workflow server under the URL tinyurl.com/yx72rda7.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08882-1.

How can reasonable and repeatable acaricidal tests of natural products against Sarcoptes and Psoroptes mites be carried out?

Sarcoptic and psoroptic mange threaten the health of both animals and humans worldwide and result in enormous socioeconomic loss. Discovery of new lead compounds is a major goal for controlling this kind of disease. However, the methodological shortcomings of acaricidal tests against Sarcoptes and Psoroptes mites for screening active compounds in vitro troubles colleagues and should be given more attention.

Molecular targets for the development of new acaricides against Rhipicephalus microplus: a review

The cattle tick Rhipicephalus microplus is an ectoparasite with high economic importance to bovine culture, mainly in tropical and subtropical regions. The resistance of the tick from the commercial acaricides has hindered its control, thus motivating the search for new strategies. The purpose of this study was to perform a critical review about the main molecular targets of R. microplus that are useful for the discovery of new acaricides. Bibliographic search was conducted in the databases PubMed, ScienceDirect and CAB Direct, using the following descriptors: ‘Rhipicephalus microplus’, ‘Boophilus microplus’, ‘molecular targets’ and ‘action’, published between 2010 and 2021. Out of the 212 publications identified, 17 articles were selected for study inclusion. This review described 14 molecular targets and among these 4 are targets from commercial acaricides. Most of them are enzymes to catalyse important reactions to tick survival, related to energetic metabolism, mechanisms of biotransformation and neurotransmission. The data will be helpful in the development of new more effective and selective acaricides.

Nematode microRNAs can Individually Regulate Interferon Regulatory Factor 4 and mTOR in Differentiating T Helper 2 Lymphocytes and Modulate Cytokine Production in Macrophages

Parasitic nematodes are masterful immunomodulators. This class of pathogens has evolved a spectrum of sophisticated strategies to regulate and evade host immune responses, mediated through the release of various molecules. In this context, the release of microRNAs (miRNAs), short post-transcriptional regulators of gene expression, has been of particular interest in the host-parasite interplay. Evidence that parasite-derived miRNAs modulate host innate and adaptive immune responses has become increasingly compelling. However, since miRNAs are usually contained in extracellular vesicles containing other mediators, it is difficult to assign an observed effect on host cells to miRNAs specifically. Here, the effects of some abundantly secreted miRNAs by nematodes used as models of gastrointestinal infections (Heligmosomoides polygyrus bakeri, Trichuris muris and Ascaris suum) were evaluated, addressing the potential of parasite miRNAs to impair in vitro differentiation of two important types of immune cells in the context of helminth infections, Th2 lymphocytes and macrophages. Mimicking a continuous exposure to low concentrations of nematode miRNAs, the interferon gamma signaling, the IL-2/STAT5 signaling, and the mTOR signaling pathways were identified as downregulated by Hpo-miR-71-5p. Interferon regulatory factor 4 (Irf4) was validated as a target of Hpo-miR-71-5p, while Mtor is targeted by Asu-miR-791-3p, abundant in the T. muris secretions. By trend, Hpo-miR-71-5p impacts mildly but consistently on the amounts of inflammatory cytokines in unpolarized macrophages but leads to slightly increased IL-10 level in alternatively activated cells. In addition, our data suggests that transfected miRNAs remain for days in recipient cells, and that Hpo-miR-71-5p can incorporate into mouse Argonaute protein complexes. Nematode miRNAs can impair both innate and adaptive arms of host immunity. Hpo-miR-71-5p in particular, absent in mammals, interacts with host genes and pathways with crucial involvement in anthelmintic immune responses. This report brings new insights into the dynamics of miRNA-driven immunomodulation and highlights putative targeted pathways. Although the absolute repression is subtle, it is expected that the dozens of different miRNAs released by nematodes may have a synergistic effect on surrounding host cells.

5-(4-Pyridinyl)-3-isothiazolols as Competitive Antagonists of Insect GABA Receptors: Design, Synthesis, and a New Mechanism Leading to Insecticidal Effects

Ionotropic γ-aminobutyric acid (GABA) receptors (iGABARs) are validated targets of drugs and insecticides. Our previous studies showed that the competitive antagonists of insect iGABARs exhibit insecticidal activities and that the 3-isothiazolol scaffold is used as a lead for developing novel iGABAR antagonists. Here, we designed a novel series of 4-aryl-5-(4-pyridinyl)-3-isothiazolol (4-API) analogs that have various aromatic substituents at the 4-position. Two-electrode voltage clamp experiments showed that all synthesized 4-APIs exhibited antagonistic activity against Musca domestica and Spodoptera litura iGABARs (RDL) expressed in oocytes of Xenopus laevis at 100 μM. Of the 4-APIs, the 4-(1,1'-biphenylyl) analog was the most potent antagonist with IC₅₀s of 7.1 and 9.9 μM against M. domestica and S. litura RDL receptors, respectively. This analog also showed a certain insecticidal activity against S. litura larvae, with >75% mortality at 100 μg/g diet. Molecular docking studies with a M. domestica iGABAR model indicated that the π-π stacking interactions formed between the pyridinyl ring and Y252 and between the 4-substituted aromatic group and Y107 might be important for antagonism by the 4-(1,1'-biphenylyl) analog. Our studies provide important information for designing novel iGABAR antagonists and suggest that the 4-APIs acting on iGABARs are promising insecticide leads for further studies.

Safety of oral afoxolaner formulated with or without milbemycin oxime in homozygous MDR1-deficient collie dogs

Afoxolaner, an insecticide and acaricide compound of the isoxazoline class, is available for dogs as an oral ectoparasiticide medicine (NexGard®) and as an oral endectoparasiticide medicine in combination with milbemycin oxime (MO), a macrocyclic lactone (NexGard® Spectra). The safety of these two compounds, alone or in combination, was investigated in homozygous MDR1‐deficient collie dogs, in two studies. Overall, 30 adult collie dogs were treated once orally, 9 with a placebo, 9 with afoxolaner, 6 with MO, and 6 with a combination of afoxolaner and MO. For afoxolaner, the mean investigated dosage corresponded to 3.8 and 4.7 multiples of the maximum recommended therapeutic doses (RTD) in NexGard® and NexGard® Spectra, respectively. For MO, the mean investigated dosage corresponded to 4.7 multiples of the maximum RTD in NexGard® Spectra. Dogs were closely monitored for adverse reactions on the day of treatment and for the following two days. No significant adverse reaction was observed in any dog from the afoxolaner or the afoxolaner + MO groups; in the MO‐only treated group, mild and transient neurological signs were observed during the 4–8 h post‐treatment window. These studies demonstrated a high level of safety of oral afoxolaner, alone or in combination with milbemycin oxime, in homozygous MDR1‐deficient dogs.

Mechanism of praziquantel action at a parasitic flatworm ion channel

[Figure: see text].

Occurrence and Effects of Antimicrobials Drugs in Aquatic Ecosystems

Currently, thanks to the development of sensitive analytical techniques, the presence of different emerging pollutants in aquatic ecosystems has been evidenced; however, most of them have not been submitted to any regulation so far. Among emerging contaminants, antimicrobials have received particular attention in recent decades, mainly due to the concerning development of antibiotic resistance observed in bacteria, but little is known about the toxicological and ecological impact that antimicrobials can have on aquatic ecosystems. Their high consumption in human and veterinary medicine, food-producing animals and aquaculture, as well as persistence and poor absorption have caused antimicrobials to be discharged into receiving waters, with or without prior treatment, where they have been detected at ng-mg L−1 levels with the potential to cause effects on the various organisms living within aquatic systems. This review presents the current knowledge on the occurrence of antimicrobials in aquatic ecosystems, emphasizing their occurrence in different environmental matrixes and the effects on aquatic organisms (cyanobacteria, microalgae, invertebrates and vertebrates).

Antileishmanial Drug Discovery and Development: Time to Reset the Model?

Leishmaniasis is a vector-borne parasitic disease caused by Leishmania species. The disease affects humans and animals, particularly dogs, provoking cutaneous, mucocutaneous, or visceral processes depending on the Leishmania sp. and the host immune response. No vaccine for humans is available, and the control relies mainly on chemotherapy. However, currently used drugs are old, some are toxic, and the safer presentations are largely unaffordable by the most severely affected human populations. Moreover, its efficacy has shortcomings, and it has been challenged by the growing reports of resistance and therapeutic failure. This manuscript presents an overview of the currently used drugs, the prevailing model to develop new antileishmanial drugs and its low efficiency, and the impact of deconstruction of the drug pipeline on the high failure rate of potential drugs. To improve the predictive value of preclinical research in the chemotherapy of leishmaniasis, several proposals are presented to circumvent critical hurdles-namely, lack of common goals of collaborative research, particularly in public-private partnership; fragmented efforts; use of inadequate surrogate models, especially for in vivo trials; shortcomings of target product profile (TPP) guides.

Combination of cypermethrin and thymol for control of Rhipicephalus microplus: Efficacy evaluation and description of an action mechanism

The cattle tick Rhipicephalus microplus is one of the most important ectoparasites in the tropical and subtropical regions of the world. Synthetic pyrethroids are widely used to control this tick, and the selection of resistant populations is a huge problem worldwide. The activity of thymol, a natural monoterpene, free or in combination with other compounds, has been demonstrated against different species of ticks. However, the mode of action is not fully understood. The present study aimed to evaluate the efficacy and the potential mode of action of the combination of cypermethrin and thymol on ticks from two populations with different levels of susceptibility to cypermethrin (low and high susceptibility). The isolated acaricidal activity of cypermethrin and thymol on larvae was carried out in different concentrations. The combination with different concentrations of cypermethrin and fixed concentrations of thymol (1300 µg/mL for the low susceptibility population; 690 µg/mL for the high susceptibility population) were performed. Adult engorged females were divided into five experimental groups (n = 20): 1) Control group untreated; 2) Control group: 2.0% (v/v) DMSO; 3) Thymol group: 1300 µg/mL thymol; 4) Cypermethrin group: 3700 µg/mL cypermethrin; 5) Association of cypermethrin (3700 µg/mL) + thymol (1300 µg/mL). A subgroup was used to study the efficacy of the reproductive parameters and another subgroup, with ten adults from each treatment, was used to quantify thymol and cypermethrin by HPLC chromatographic analysis. All compounds tested were effective on larvae from both populations, and the combination with thymol decreased the LC₅₀ of cypermethrin (232.4 to 52.7 µg/mL) on the low-susceptibility population. The combination of thymol and cypermethrin was effective in both populations of R. microplus (reproductive performance of engorged females) when compared to the untreated control group, even with higher percent control values (pop. 1: 93.5 ± 5.6% and pop. 2: 92.7 ± 1.1%) than the group treated only with cypermethrin (pop. 1: 87.3 ± 7.3% and pop. 2: 83.5 ± 1.2%). From the HPLC analyzes, a higher concentration of cypermethrin (pop. 1: 30.3 ± 6.9 and pop. 2: 45.4 ± 17.7 ng/mg) was detected in the tissues of engorged females treated with the combination compared to analyte concentrations in groups treated with cypermethrin only (pop. 1: 12.4 ± 4.4 pop. 2: 25.5 ± 9.4 ng/mg). This was the first study to investigate the acaricidal efficacy of the combination of thymol + cypermethrin on R. microplus and demonstrate that the presence of thymol increases the concentration of cypermethrin in the internal tissues of engorged females through a possible mechanism for increasing the penetration of cypermethrin at the cuticular level.

Parasitology and One Health-Perspectives on Africa and Beyond

This concept paper reviews issues pertaining to parasitic and vector-borne infections, of humans, animals, or both, of topical relevance to the African continent as well as to neighbouring and interconnected geographies. This analysis is carried out through the "One Health" lens, being mindful of the central role of agriculture and livestock keeping in Africa's sustainable development. The possible agricultural transformation that the continent may undergo to fulfil the rising demand for animal protein of its growing population, coupled with the ongoing climate changes, may lead to potentially enhanced interactions among humans, domesticated and wild animals, in a fast-changing environment. In this view, tackling parasitic conditions of livestock can prove being multidimensionally beneficial by improving animal health as well as communities' food security, livelihood and public health. Accordingly, the value of applying the One Health approach to drug discovery and development in the fight against parasitic neglected tropical diseases and zoonoses, is also underscored. Overall, this article upholds the adoption of a holistic, global, interdisciplinary, multisectoral, harmonised and forward-looking outlook, encompassing both life and social sciences, when dealing with parasitic conditions of humans and animals, in Africa and beyond, in COVID-19 times and further.

Assessment of lipid profile in fat body and eggs of Rhipicephalus microplus engorged females exposed to (E)-cinnamaldehyde and α-bisabolol, potential acaricide compounds

In the present study, the lipid profile from the fat body and eggs of Rhipicephalus microplus was evaluated after exposure of engorged females to (E)-cinnamaldehyde and α-bisabolol, substances which have acaricide potential according to the literature. Engorged females collected from artificially infested cattle were immersed in a concentration of 10.0 mg/mL of each substance. Dissection of the female fat bodies was performed at different times (72 h and 120 h), for subsequent lipid extraction. In addition, on the fifth day of oviposition, were collected 50.0 ml50.0 mL aliquots of the egg mass of each treatment to perform the same lipid extraction procedure. To assess the lipid profiles, the samples were submitted to the thin layer chromatography (TLC) and gas chromatography-mass spectrometry (GCMS) analysis. Furthermore, an in silico analysis was performed using PASS online® software to predict the possible molecular targets of (E)-cinnamaldehyde and α-bisabolol. As result, the main lipids identified from the fat body were triacylglycerides, fatty acids, and cholesterol, whereas, triacylglycerides (TAG), fatty acids (FA), and cholesterol (CHO) and cholesterol esters (CHOE), were identified in the eggs. The results also showed a significant increase (p < 0.05) of CHO in the fat body in the group exposed to (E)-cinnamaldehyde at 72 h (0.12 μg/fat body) and 120 h (0.46 μg/fat body), in the eggs from females treated with this same substance, there was a significant reduction (p < 0.05) in the amount of CHO (0.21 μg), compared to the water control group (0.45 μg). In the GCMS technique, 5 chemical classes were found, and variations were observed between these substances, mainly hydrocarbons and steroids, in the different groups, and (E)-cinnamaldehyde promoted the greatest changes. From the predictions of the in silico study, 38 and 20 targets were selected, respectively, which are mainly related to alterations in lipid metabolism, immune system and nervous system. This study provides the first report of changes in lipid metabolism of R. microplus exposed to (E)-cinnamaldehyde and α-bisabolol, as well as presenting possible activity on the molecular targets of these substances, expanding knowledge for the potential use of these compounds in the development of botanical acaricides.

Onchocerciasis drug development: from preclinical models to humans

Twenty diseases are recognized as neglected tropical diseases (NTDs) by World Health Assembly resolutions, including human filarial diseases. The end of NTDs is embedded within the Sustainable Development Goals for 2030, under target 3.3. Onchocerciasis afflicts approximately 20.9 million people worldwide with > 90% of those infected residing in Africa. Control programs have made tremendous efforts in the management of onchocerciasis by mass drug administration and aerial larviciding; however, disease elimination is not yet achieved. In the new WHO roadmap, it is recognized that new drugs or drug regimens that kill or permanently sterilize adult filarial worms would significantly improve elimination timelines and accelerate the achievement of the program goal of disease elimination. Drug development is, however, handicapped by high attrition rates, and many promising molecules fail in preclinical development or in subsequent toxicological, safety and efficacy testing; thus, research and development (R&D) costs are, in aggregate, very high. Drug discovery and development for NTDs is largely driven by unmet medical needs put forward by the global health community; the area is underfunded and since no high return on investment is possible, there is no dedicated drug development pipeline for human filariasis. Repurposing existing drugs is one approach to filling the drug development pipeline for human filariasis. The high cost and slow pace of discovery and development of new drugs has led to the repurposing of “old” drugs, as this is more cost-effective and allows development timelines to be shortened. However, even if a drug is marketed for a human or veterinary indication, the safety margin and dosing regimen will need to be re-evaluated to determine the risk in humans. Drug repurposing is a promising approach to enlarging the pool of active molecules in the drug development pipeline. Another consideration when providing new treatment options is the use of combinations, which is not addressed in this review. We here summarize recent advances in the late preclinical or early clinical stage in the search for a potent macrofilaricide, including drugs against the nematode and against its endosymbiont, Wolbachia pipientis.

Rational Pharmacotherapy in Infectious Diseases: Issues Related to Drug Residues in Edible Animal Tissues

Simple Summary

Drug use is essential to treat diseases in food-producing animals. The most widely used drugs are antiparasitics and antimicrobials. They contribute to guaranteeing good-quality food in sufficient quantity for human consumption. When using veterinary medicines, it is essential to follow the instructions on the package label. Administering the correct dose by the indicated route in the animal species for which the drug is labeled is critical. After a pharmacological treatment is administered to livestock, a period (indicated on the label) must often elapse before the tissues from the treated animals can be consumed by humans. Veterinary drug residues are controlled by taking food samples to verify that drug concentrations do not exceed the permitted limits. This allows authorities to know if the medicine use is correct or if suitable corrective measures should be taken. When label’s directions are not followed, drug residues may appear in food. The residues exceeding the permitted limits established by the authorities can produce unfavorable consequences, mainly on the consumer’s health. The food trade and even the environment can be affected by drug residues in animal tissues. Therefore, the correct use of drugs in livestock is critical, which includes respecting the rules to avoid residues in food for human consumption.

Abstract

Drugs are used in veterinary medicine to prevent or treat animal diseases. When rationally administered to livestock following Good Veterinary Practices (GVP), they greatly contribute to improving the production of food of animal origin. Since humans can be exposed chronically to veterinary drugs through the diet, residues in food are evaluated for effects following chronic exposures. Parameters such as an acceptable daily intake (ADI), the no-observed-adverse-effect level (NOAEL), maximum residue limits (MRLs), and the withdrawal periods (WPs) are determined for each drug used in livestock. Drug residues in food exceeding the MRLs usually appear when failing the GVP application. Different factors related either to the treated animal or to the type of drug administration, and even the type of cooking can affect the level of residues in edible tissues. Residues above the MRLs can have a diverse negative impact, mainly on the consumer’s health, and favor antimicrobial resistance (AMR). Drug residue monitoring programmes are crucial to ensure that prohibited or authorized substances do not exceed MRLs. This comprehensive review article addresses different aspects of drug residues in edible tissues produced as food for human consumption and provides relevant information contributing to rational pharmacotherapy in food-producing animals.

Tungiasis in domestic, wild, and synanthropic animals in Brazil

Tungiasis is an ectoparasitic skin disease of humans and warm-blooded animals caused by fleas of the genus Tunga (Jarocki, 1938). Dogs, cats, pigs, and synanthropic rodents are the main animal reservoirs. Of the 14 known species, 12 are found in Latin America and, among these, eight are found in Brazil, including the two zoonotic species Tunga penetrans and Tunga trimamillata. Tunga penetrans predominates among humans and Brazilian pets, where the dog is the most affected species, and its presence is a risk factor associated with the disease in humans. Tunga spp. are widely distributed throughout the national territory, with T. penetrans being the most dispersed and the most frequent in animals from endemic areas, especially in underprivileged communities. Infections in animals, associated with inadequate management, favor the spread and perpetuation of the disease. Intense injuries can result in sequelae and serious clinical conditions, compromising the health, welfare, and productivity of animals, as well as leading to death. Health precariousness, lack of control and neglect in the management of populations of domestic and synanthropic animals, poor hygiene habits of individuals, lack of information from both the population and related professionals, lack of effective treatment, and of perception of tungiasis as a disease are among the main challenges for the control of this parasitosis. As recommended for other zoonotic Neglected Tropical Diseases, strategies based on the concept of One Health can guarantee more effective results in the fight against human and animal tungiasis.

Heartworm disease - Overview, intervention, and industry perspective

Dirofilaria immitis, also known as heartworm, is a major parasitic threat for dogs and cats around the world. Because of its impact on the health and welfare of companion animals, heartworm disease is of huge veterinary and economic importance especially in North America, Europe, Asia and Australia. Within the animal health market many different heartworm preventive products are available, all of which contain active components of the same drug class, the macrocyclic lactones. In addition to compliance issues, such as under-dosing or irregular treatment intervals, the occurrence of drug-resistant heartworms within the populations in the Mississippi River areas adds to the failure of preventive treatments. The objective of this review is to provide an overview of the disease, summarize the current disease control measures and highlight potential new avenues and best practices for treatment and prevention.

Clinical implications and treatment options of tungiasis in domestic animals

Tunga penetrans, Tunga trimamillata and Tunga hexalobulata are the three species of sand fleas which cause tungiasis in domestic animals. Tunga penetrans and T. trimamillata are zoonotic in the tropical and sub-tropical endemic communities of Latin America and Africa. Tungiasis in animals frequently occurs alongside human tungiasis. Currently, most of the attention given to tungiasis is focusing on the human disease, and animal tungiasis is extremely neglected despite its public health and animal health significance. This review highlights recent findings concerning the clinical implications and treatment options but also summarises the occurrence, major features, public health and economic significance of tungiasis in domestic animals. Pigs, dogs, cats and domestic ruminants have been reported to harbour high intensities of sand fleas in endemic communities. High infection intensities cause significant animal morbidity which is often exacerbated by excoriations and secondary bacterial infections which are potentially fatal. In addition to the potential economic losses accruing from tungiasis-related morbidity, infected domestic animals contribute to transmission and persistence of sand fleas and eventually also to severe human disease. Although control of animal tungiasis is possible by adoption of proper husbandry practices, affected communities may not afford the resources required to implement them. Also, there are no widely acceptable and affordable insecticides for treatment of tungiasis in animals. Extension services aiming at increasing awareness on tungiasis and its control should be intensified. Also, available commercial insecticides should be evaluated for therapeutic and prophylactic properties against animal tungiasis.

The molecular targets of ivermectin and lotilaner in the human louse Pediculus humanus humanus: New prospects for the treatment of pediculosis

Control of infestation by cosmopolitan lice (Pediculus humanus) is increasingly difficult due to the transmission of parasites resistant to pediculicides. However, since the targets for pediculicides have no been identified in human lice so far, their mechanisms of action remain largely unknown. The macrocyclic lactone ivermectin is active against a broad range of insects including human lice. Isoxazolines are a new chemical class exhibiting a strong insecticidal potential. They preferentially act on the γ-aminobutyric acid (GABA) receptor made of the resistant to dieldrin (RDL) subunit and, to a lesser extent on glutamate-gated chloride channels (GluCls) in some species. Here, we addressed the pediculicidal potential of isoxazolines and deciphered the molecular targets of ivermectin and the ectoparasiticide lotilaner in the human body louse species Pediculus humanus humanus. Using toxicity bioassays, we showed that fipronil, ivermectin and lotilaner are efficient pediculicides on adult lice. The RDL (Phh-RDL) and GluCl (Phh-GluCl) subunits were cloned and characterized by two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes. Phh-RDL and Phh-GluCl formed functional homomeric receptors respectively gated by GABA and L-glutamate with EC₅₀ values of 16.0 μM and 9.3 μM. Importantly, ivermectin displayed a super agonist action on Phh-GluCl, whereas Phh-RDL receptors were weakly affected. Reversally, lotilaner strongly inhibited the GABA-evoked currents in Phh-RDL with an IC₅₀ value of 40.7 nM, whereas it had no effect on Phh-GluCl. We report here for the first time the insecticidal activity of isoxazolines on human ectoparasites and reveal the mode of action of ivermectin and lotilaner on GluCl and RDL channels from human lice. These results emphasize an expected extension of the use of the isoxazoline drug class as new pediculicidal agents to tackle resistant-louse infestations in humans.

Human cosmopolitan lice are responsible for pediculosis, which represent a significant public health concern. Resistant lice against insecticides and lack of safety of the treatments for human and environment is a growing issue worldwide. Here we investigated the efficacy on lice of the classical macrocyclic lactone drug, ivermectin, and of the isoxazoline drug, lotilaner. This study was done to decipher their mode of action at the molecular and functional levels in order to propose new strategies to control lice infestation. Our bioassay results indicate that ivermectin and lotilaner were potent at killing human adult lice, with lotilaner showing a higher efficacy than ivermectin. Furthermore, we identified and pharmacologically characterized the first glutamate- and GABA-gated chloride channels ever described in human lice yet. Mechanistically, our molecular biology and electrophysiology findings demonstrate that ivermectin acted preferentially at glutamate channels, while lotilaner specifically targeted GABA channels. These results provide new insights in the understanding of the insecticide mode of action and highlight the potential of isoxazolines as a new alternative for the treatment of human lice.

When Secretomes Meet Anthelmintics: Lessons for Therapeutic Interventions

Helminth secretomes comprise many potential immunomodulators. The molecular and functional diversity of these entities and their importance at the host-parasite interface have been increasingly recognized. It is now common to hypothesize that parasite-derived molecules (PDMs) are essential mediators used by parasites to establish and remain in their hosts. Suppression of PDM release has been reported for two anthelmintic drug classes, the benzimidazoles and macrocyclic lactones, the mechanisms of action of which remain incompletely resolved. We propose that bringing together recent insights from different streams of parasitology research, for example, immunoparasitology and pharmacology, will stimulate the development of new ways to alter the host-parasite interface in the search for novel anthelmintic strategies.

Protecting dogs and cats against the Australian paralysis tick, Ixodes holocyclus (Acari: Ixodidae): A review of the Australian acaricide registration process

Tick control is mainly achieved through the use of effective ectoparasiticides that can be either dermally or systemically distributed in/on the host. Before any acaricide can be legally made available to veterinarians and pet owners, it must demonstrate efficacy in a series of well-designed dose confirmation studies. The data generated during these studies are then reviewed by government regulators and used for the registration of the acaricide. In Australia, the most significant tick species is the Australian paralysis tick, Ixodes holocyclus. This three-host tick produces a potent neurotoxin (holocyclotoxin) that induces a rapidly ascending flaccid paralysis that can be fatal to companion animals and larger mammals such as cattle and horses. The Australian Pesticides and Veterinary Medicines Authority (APVMA) is the national Australian regulator which sets the data requirements for the registration of acaricides. This paper reviews the requirements set by the APVMA and puts them in direct context with the biology, distribution and reported acaricide susceptibility of I. holocyclus. An overview of acaricides currently registered in Australia for the control of I. holocyclus in dogs and cats, their reported efficacy data and the conduct of I. holocyclus efficacy trials are also provided.

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A review of the requirements for the conduct of acaricide efficacy trials for Ixodes holocyclus was undertaken.

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The requirements of the Australian government regulator were put in direct context with the biology of the species.

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The need for the inclusion of Far North Queensland ticks into tick studies needs to be further assessed.

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At present, there is no evidence of acaricide resistance in Ixodes holocyclus.