Climate Change Modulates Multitrophic Interactions Between Maize, A Root Herbivore, and Its Enemies.

How climate change will modify belowground tritrophic interactions is poorly understood, despite their importance for agricultural productivity. Here, we manipulated the three major abiotic factors associated with climate change (atmospheric CO2, temperature, and soil moisture) and investigated their individual and joint effects on the interaction between maize, the banded cucumber beetle (Diabrotica balteata), and the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora. Changes in individual abiotic parameters had a strong influence on plant biomass, leaf wilting, sugar concentrations, protein levels, and benzoxazinoid contents. Yet, when combined to simulate a predicted climate scenario (Representative Concentration Pathway 8.5, RCP 8.5), their effects mostly counter-balanced each other. Only the sharp negative impact of drought on leaf wilting was not fully compensated. In both current and predicted scenarios, root damage resulted in increased leaf wilting, reduced root biomass, and reconfigured the plant sugar metabolism. Single climatic variables modulated the herbivore performance and survival in an additive manner, although slight interactions were also observed. Increased temperature and CO2 levels both enhanced the performance of the insect, but elevated temperature also decreased its survival. Elevated temperatures and CO2 further directly impeded the EPN infectivity potential, while lower moisture levels improved it through plant- and/or herbivore-mediated changes. In the RCP 8.5 scenario, temperature and CO2 showed interactive effects on EPN infectivity, which was overall decreased by 40%. We conclude that root pest problems may worsen with climate change due to increased herbivore performance and reduced top-down control by biological control agents.

Rhabditophanes diutinus a parthenogenetic clade IV nematode with dauer larvae.

Comparative studies using non-parasitic model species such as Caenorhabditis elegans, have been very helpful in investigating the basic biology and evolution of parasitic nematodes. However, as phylogenetic distance increases, these comparisons become more difficult, particularly when outside of the nematode clade to which C. elegans belongs (V). One of the reasons C. elegans has nevertheless been used for these comparisons, is that closely related well characterized free-living species that can serve as models for parasites of interest are frequently not available. The Clade IV parasitic nematodes Strongyloides are of great research interest due to their life cycle and other unique biological features, as well as their medical and veterinary importance. Rhabditophanes, a closely related free-living genus, forms part of the Strongyloidoidea nematode superfamily. Rhabditophanes diutinus (= R. sp. KR3021) was included in the recent comparative genomic analysis of the Strongyloididae, providing some insight into the genomic nature of parasitism. However, very little is known about this species, limiting its usefulness as a research model. Here we provide a species description, name the species as R. diutinus and investigate its life cycle and subsequently gene expression in multiple life stages. We identified two previously unreported starvation induced life stages: dauer larvae and arrested J2 (J2A) larvae. The dauer larvae are morphologically similar to and are the same developmental stage as dauers in C. elegans and infective larvae in Strongyloides. As in C. elegans and Strongyloides, dauer formation is inhibited by treatment with dafachronic acid, indicating some genetic control mechanisms are conserved. Similarly, the expression patterns of putative dauer/infective larva control genes resemble each other, in particular between R. diutinus and Strongyloides spp. These findings illustrate and increase the usefulness of R. diutinus as a non-parasitic, easy to work with model species for the Strongyloididae for studying the evolution of parasitism as well as many aspects of the biology of Strongyloides spp, in particular the formation of infective larvae.

Environmental tolerance of entomopathogenic nematodes differs among nematodes arising from host cadavers versus aqueous suspension.

Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous suspension. In the heat tolerance bioassays, following exposure to 30 °C, 35 °C and 37. 5 °C, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 °C regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 °C to -2 °C. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.

Preferential infectivity of entomopathogenic nematodes in an envenomed host.

Entomopathogenic nematodes and parasitoid wasps are used as biological control agents for management of insect pests such as the Indian meal moth, Plodia interpunctella. The parasitoid wasp Habrobracon hebetor injects a paralytic venom into P. interpunctella larvae before laying eggs. A previous study reported that the entomopathogenic nematode Heterorhabditis indica preferentially infects P. interpunctella that have been envenomed by H. hebetor while results in this study showed a similar preference by the entomopathogenic nematode, Steinernema glaseri. We therefore tested four hypotheses for why nematode infection rates are higher in envenomed hosts: (1) elevated CO2 emission from envenomed hosts attracts nematodes, (2) paralysis prevents hosts from escaping nematodes, (3) volatile chemicals emitted from envenomed hosts attract nematodes and increase infection, and (4) reduced immune defenses in envenomed hosts increase nematode survival. Results showed that envenomed P. interpunctella larvae emitted lower amounts of CO2 than non-envenomed larvae. Physical immobilization of P. interpunctella larvae did not increase infection rates by S. glaseri but did increase infection rates by H. indica. Emissions from envenomed hosts were collected and analyzed by thermal desorption gas chromatography/mass spectrometry. The most abundant compound, 3-methyl-3-buten-1-ol, was found to be an effective cue for S. glaseri attraction and infection but was not an effective stimulus for H. indica. Envenomed P. interpunctella exhibited a stronger immune response toward nematodes than non-envenomed hosts. Altogether, we conclude that different mechanisms underlie preferential infection in the two nematode species: host immobilization for H. indica and chemical cues for S. glaseri.

Modelling the development of anthelmintic resistance in cyathostomin parasites: The importance of genetic and fitness parameters.

Previously described models for the free-living and parasitic phases of the cyathostomin life-cycle were combined into a single model for the complete life-cycle. The model simulates a single free-living population on pasture utilising parasite egg output from the horses and localised temperature and rainfall data to estimate infective larval density on herbage. Multiple horses of different ages are possible, each with an individualised anthelmintic treatment programme. Genotypes for anthelmintic resistance are included allowing for up to three resistance genes with 2 alleles each. Because little is known of the genetics of resistance to anthelmintics in cyathostomins, the first use of this model was to compare the effect of different assumptions regarding the inheritance of resistance on model outputs. Comparisons were made between single and two-gene inheritance, where the heterozygote survival was dominant, intermediate or recessive under treatment, and with or without a fitness disadvantage associated with the resistance mechanism. Resistance developed fastest when the heterozygotes survived anthelmintic treatment (i.e., were dominant) and slowest when they did not (i.e., were recessive). Resistance was slower to develop when inheritance was poly-genic compared to a single gene, and when there was a fitness cost associated with the resistance mechanism, although the latter variable was the least influential. Importantly, while these genetic factors sometimes had a large influence on the rate at which resistant genotypes built up in the model populations, their order of ranking was always the same, when different anthelmintic use strategies were compared. Therefore, the described model is a useful tool for evaluating different treatment and management strategies on their potential to select for resistance.

Isolation and growth inhibition potential of entomopathogenic nematodes against three public health important mosquito vectors.

The prevalence of mosquito vector borne diseases and the resistance of mosquitoes to conventional pesticides have been of important public concern to the mosquito endemic countries. Present study was conducted to identify the native bio-larvicidal potential of the entomopathogenic nematodes; Steinernema siamkayai (KPR-4) Heterohabditis indica (KPR-8), Steinernema glaseri and Steinernema abbasi. The isolated nematodes were subsequently cultured and evaluated their larvicidal potential against the larvae of Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. Among the tested four different nematode species, the S. abassi exerted the highest mortality against A. aegypti (97.33%), the H. indica (KPR-8) against A. stephensi (97.33%) and the S. siamkayai (KPR-4) against C. quinquefasciatus (98.67%). The maximal mosquito-larvicidal property of EPNs was found with the LC50 and LC90 values (IJs/larvae): S. abbasi = 12.47 & 54.35 on A. aegypti; H. indica KPR-8 = 19.88 & 66.81 on A. stephensi and S. siamkayai KPR-4 = 16.69 & 58.97 on C. quinquefasciatus, respectively. The presently generated data on the molecular and larvicidal characteristics of the entomopathogenic nematodes form an important baseline data that upon further research would lead to the development of eco-friendly mosquito-control agent.

Identification of third stage larval types of cyathostomins of equids: An improved perspective.

Cyathostomins comprise around 50 parasite species of equids, offering a great challenge regarding their individual identification. The objective of our work was to improve identification of infective third stage larvae (L3) with a morphological key supplemented with detailed scientific illustrations based on our research and available literature. The highlighted features were; the number, arrangement, and shape of intestinal cells (IC), general features and the total body length of the eight different Cyathostomin sensu latum types (Type A, B, C, D, E, F, G, H), Gyalocephalus capitatus, and Posteriostomum spp. Due to variability, we were unable to define final body length measurements to differentiate L3 of cyathostomins. However, IC characteristics displayed a higher difference between L3 types than total body length. Through the number and arrangement of IC, 14 species were classified within three larval types. The classification of L3 into distinct larval types sensu latum gives us the advantage of reducing the number of probable species presented in equine faecal samples using a low-cost technique when monitoring the parasite fauna present in individual horses or on the farm level. The present improved identification key shall increase the diagnostic capabilities of classical equine parasitology techniques, using general L3 morphology thereby pragmatically improving regional and transnational epidemiological and biodiversity studies. The present key may also assist in defining the cyathostomin community in cyathostominosis clinical cases and within drug resistant populations across different management systems and geographical locations.

Equine strongyle communities are constrained by horse sex and species dipersal-fecundity trade-off.

BACKGROUND: Equine strongyles are a major health issue. Large strongyles can cause death of horses while cyathostomins (small strongyles) have shown increased resistance to anthelmintics worldwide. Description of strongyle communities have accumulated but little is known about the diversity of these communities and underpinning environmental factors. METHODS: Strongyles were recovered after ivermectin treatment from 48 horses located in six premises in Poland. Correlation between previously published species fecundity and the observed relative abundance and prevalence were estimated. Significance of horse sex was determined at the species level (prevalence, relative abundance) and at the community level (species richness and dissimilarity between communities). RESULTS: Strongyle species fell into two groups, contrasted by their prevalence and relative abundance. Six to nine horses were necessary to sample at least 90% of strongyle community diversity, providing a minimal cut-off to implement sampling trial in the field. Strongyle communities entertained a network of mostly positive interactions and species co-occurrence was found more often than expected by chance. In addition, species fecundity and prevalence were negatively correlated (Pearson's r = -0.71), suggesting functional trade-offs between species dispersal abilities and fecundity. This functional trade-off may underpin species coexistence. Horse sex was also a significant constraint shaping strongyle communities. Indeed, mares generally displayed more similar strongyle communities than stallions (P = 0.003) and Cylicostephanus calicatus was more abundant in stallions suggesting sex-specific interactions (P = 0.006). CONCLUSIONS: While niche partitioning is likely to explain some of the positive interactions between equine strongyle species, coexistence may also result from a functional trade-off between dispersal ability and fecundity. There is significant evidence that horse sex drives strongylid community structure, which may require differential control strategies between mares and stallions.

The behaviour of the nematode, Steinernema feltiae (Nematoda: Steinernematidae) in sand contaminated with the industrial pollutant chromium VI.

This study set out to determine the suitability of the nematode Steinernema feltiae as a bioindicator for heavy metal pollution, specifically chromium VI. Nematodes were introduced into sand contaminated with concentrations of Cr VI+, in a range between 10 and 100 ppm, in increments of 10. Reproductive potential, development times and infectivity vs exposure times to Cr VI were employed as endpoints. It was observed that infective juveniles (IJ) from this nematode can survive and successfully infect host insects in the presence of Cr VI for as much as 13 days, and that the nematode increases its reproductive potential at concentrations up to 100 ppm Cr VI+. Conversely, development times (time in days taken for progeny to emerge after larval host death) and IJ infectivity rates were observed to reduce with increasing concentrations of Cr VI. The ability of this nematode to survive in the presence of high concentrations of Cr VI, and its ability to increase progeny numbers at the early stages of Cr VI exposure may provide a survival advantage for this nematode at contaminated sites. It may also demonstrate potential for development as a model species for toxicological assessment in in-situ field sampling.

A combined effort to avoid strongyle infection in horses in an oceanic climate region: rotational grazing and parasiticidal fungi.

BACKGROUND: An approach to preventing strongyle infection in horses was tested, comprising rotational pasturing and the administration of spores of two parasiticidal fungi, Mucor circinelloides and Duddingtonia flagrans. METHODS: Twenty-two adult Spanish Sport Horses were dewormed with ivermectin (1 mg pour-on/kg body weight) and then randomly divided into three groups. G-1 was maintained with continuous grazing, and G-2 and G-3 were kept on a four-paddock rotation system. Commercial pelleted feed (2.5 kg/horse) was supplied to G-1 and G-2 twice a week; horses in G-3 received pellets containing 2 × 106 spores/kg of each fungus. Fecal samples were analyzed by the flotation method to estimate the reduction in the fecal egg counts (FECR), the percentage of horses shedding eggs (PHR), and the egg reappearance period (ERP). RESULTS: Third-stage larvae were identified in fecal pats as Cyathostomum (sensu lato) types A, C and D, Gyalocephalus capitatus, Triodontophorus serratus, Poteriosthomum spp., Strongylus vulgaris and S. edentatus. Two weeks after treatment, the FECR values were 100% in G-1, 96% in G-2 and 99% in G-3; the PHR values were 100% in G-1, 75% in G-2 and 88% in G-3. A strongyle ERP of 6 weeks was observed in G-1, ERP of 10 weeks was observed in G-2, and ERP of 16 weeks was observed in G-3. The counts of eggs per gram of feces (EPG) were > 300 EPG in G-1 and G-2 but remained below 250 EPG in G-3 throughout the observation period of 12 months. CONCLUSIONS: These results suggest that horse strongyle infection could be decreased by combining rotational pasturing with feeding pellets containing the spores of parasiticidal fungi.

[Laboratory susceptibility tests of Aedes aegypti and Culex quinquefasciatus larvae to the entomopathogenic nematode Heterorhabditis bacteriophora].

INTRODUCTION: Aedes aegypti is the vector of dengue, yellow fever, Zika and Chikungunya viruses, and Culex quinquefasciatus is the vector of St. Louis and West Nile encephalitis viruses. OBJECTIVE: To evaluate infectivity of Heterorhabditis bacteriophora N4 in C. quinquefasciatus and A. aegypti larvae under laboratory conditions. MATERIALS AND METHODS: Thirty second-instar larvae of the two mosquito species were exposed each to different doses (0:1, 1:1, 5:1, 15:1, 100:1, 500:1, 750:1 and 1,500:1) of nematode infective juveniles. Four replications per dose were performed. RESULTS: Parasitism varied between 2.5 and 80 % in C. quinquefasciatus, and between 4.2 and 92.5 % in A. aegypti, with significant differences between doses (p<0.0001). DL50 were: 160.8 infective juveniles per larva for C. quinquefasciatus and 113.6 infective juveniles per larva for A. aegypti. In C. quinquefasciatus, 4 to 6 % of the infective juveniles developed to adults and in A. aegypti, 12- 61 %. In A. aegypti the emergence of new infective juveniles occurred with 100:1, 500:1, 750:1 and 1,500:1 infective juveniles per larva, and in C. quinquefasciatus, with 1,500:1 infective juveniles per larva. Melanization of infective juveniles was observed in both mosquito species. CONCLUSION: The susceptibility of these mosquito species to parasitism of an indigenous isolate of H. bacteriophora in the laboratory was demonstrated. Heterorhabditis bacteriophora N4 could be an efficient biological control agent.

Life history adjustments to intestinal inflammation in a gut nematode.

Many parasitic nematodes establish chronic infections. This implies a finely tuned interaction with the host immune response in order to avoid infection clearance. Although a number of immune interference mechanisms have been described in nematodes, how parasites adapt to the immune environment provided by their hosts remains largely unexplored. Here, we used the gastrointestinal nematode Heligmosomoides polygyrus to investigate the plasticity of life history traits and immunomodulatory mechanisms in response to intestinal inflammation. We adopted an experimental model of induced colitis and exposed worms to intestinal inflammation at two different developmental stages (larvae and adults). We found that H. polygyrus responded to intestinal inflammation by up-regulating the expression of a candidate gene involved in the interference with the host immune response. Worms infecting mice with colitis also had better infectivity (earlier adult emergence in the intestinal lumen and higher survival) compared with worms infecting control hosts, suggesting that H. polygyrus adjusted its life history schedule in response to intestinal inflammation.

Ensayos de sensibilidad de larvas de Aedes aegypti y Culex quinquefasciatus frente al nematodo Heterorhabditis bacteriophora en condiciones de laboratorio / Laboratory susceptibility tests of Aedes aegypti and Culex quinquefasciatus larvae to the entomopathogenic nematode Heterorhabditis bacteriophora

Resumen Introducción. Aedes aegypti es el vector de los virus del dengue, la fiebre amarilla, el Zika y el chikungunya, y Culex quinquefasciatus, de los virus de la encefalitis de Saint Louis y de la del Oeste del Nilo. Objetivo. Evaluar la capacidad infecciosa de Heterorhabditis bacteriophora N4 en larvas de C. quinquefasciatus y A. aegypti en el laboratorio. Materiales y métodos. Treinta larvas de segundo estadio de cada especie de mosquito se expusieron a diferentes dosis (0:1, 1:1, 5:1, 15:1, 100:1, 500:1, 750:1 y 1.500:1) de ejemplares juveniles infectivos del nematodo. Se hicieron cuatro réplicas por dosis. Resultados. El parasitismo varió entre 2,5 y 80 % en C. quinquefasciatus y entre 4,2 y 92,5 % en A. aegypti, con diferencias significativas entre las dosis (p<0,0001). Las DL50 fueron de 160,8 ejemplares juveniles infectivos por larva de C. quinquefasciatus y 113,6 por larva de A. aegypti; 4 a 6 % de los ejemplares juveniles infectivos llegaron a la fase adulta en C. quinquefasciatus, y 12 a 61 % en A. aegypti. Nuevos ejemplares juveniles infectivos aparecieron a partir de la dosis de 100:1. En A. aegypti aparecieron solo con dosis superiores a esta y, en C. quinquefasciatus, con una dosis de 1500:1. Se observó melanización de los ejemplares juveniles infectivos en las dos especies de mosquitos. Conclusión. Se estableció la sensibilidad de estas especies de mosquitos al parasitismo producido por un aislamiento autóctono de H. bacteriophora en condiciones de laboratorio y su potencial efecto como agente de control biológico.

Abstract Introduction: Aedes aegypti is the vector of dengue, yellow fever, Zika and Chikungunya viruses, and Culex quinquefasciatus is the vector of St. Louis and West Nile encephalitis viruses. Objective: To evaluate infectivity of Heterorhabditis bacteriophora N4 in C. quinquefasciatus and A. aegypti larvae under laboratory conditions. Materials and methods: Thirty second-instar larvae of the two mosquito species were exposed each to different doses (0:1, 1:1, 5:1, 15:1, 100:1, 500:1, 750:1 and 1,500:1) of nematode infective juveniles. Four replications per dose were performed. Results: Parasitism varied between 2.5 and 80 % in C. quinquefasciatus, and between 4.2 and 92.5 % in A. aegypti, with significant differences between doses (p<0.0001). DL50 were: 160.8 infective juveniles per larva for C. quinquefasciatus and 113.6 infective juveniles per larva for A. aegypti. In C. quinquefasciatus, 4 to 6 % of the infective juveniles developed to adults and in A. aegypti, 12- 61 %. In A. aegypti the emergence of new infective juveniles occurred with 100:1, 500:1, 750:1 and 1,500:1 infective juveniles per larva, and in C. quinquefasciatus, with 1,500:1 infective juveniles per larva. Melanization of infective juveniles was observed in both mosquito species. Conclusion: The susceptibility of these mosquito species to parasitism of an indigenous isolate of H. bacteriophora in the laboratory was demonstrated. Heterorhabditis bacteriophora N4 could be an efficient biological control agent.

The influence of organic matter content and media compaction on the dispersal of entomopathogenic nematodes with different foraging strategies.

In laboratory experiments, we investigated how media with varying ratio of peat:sand and two levels of compaction influence dispersal success of entomopathogenic nematode (EPN) species with different foraging strategies: Steinernema carpocapsae (ambusher), Heterorhabditis downesi (cruiser) and Steinernema feltiae (intermediate). Success was measured by the numbers of nematodes moving through a 4 cm column and invading a wax moth larva. We found that both compaction and increasing peat content generally decreased EPN infective juvenile (IJ) success for all three species. Of the three species, H. downesi was the least affected by peat content, and S. carpocapsae was the most adversely influenced by compaction. In addition, sex ratios of the invading IJs of the two Steinernema species were differentially influenced by peat content, and in the case of S. feltiae, sex ratio was also affected by compaction. This indicates that dispersal of male and female IJs is differentially affected by soil parameters and that this differentiation is species-specific. In conclusion, our study shows that organic matter: sand ratio and soil compaction have a marked influence on EPN foraging behaviour with implications for harnessing them as biological pest control agents.

Speciation in the genus Cloacina (Nematoda: Strongylida): species flocks and intra-host speciation.

Sequences of the first and second internal transcribed spacers (ITS1 + ITS2) of nuclear ribosomal DNA were employed to determine whether the congeneric assemblages of species of the strongyloid nematode genus Cloacina, found in the forestomachs of individual species of kangaroos and wallabies (Marsupialia: Macropodidae), considered to represent species flocks, were monophyletic. Nematode assemblages examined in the black-striped wallaby, Macropus (Notamacropus) dorsalis, the wallaroos, Macropus (Osphranter) antilopinus/robustus, rock wallabies, Petrogale spp., the quokka, Setonix brachyurus, and the swamp wallaby, Wallabia bicolor, were not monophyletic and appeared to have arisen by host colonization. However, a number of instances of within-host speciation were detected, suggesting that a variety of methods of speciation have contributed to the evolution of the complex assemblages of species present in this genus.

Encysted cyathostomin larvae in foals - progression of stages and the effect of seasonality.

Cyathostomins (small strongyles) are ubiquitous in grazing horses and are known pathogens as cause of larval cyathostominosis. As part of their life cycle, cyathostomin larvae invade the mucosal walls of the large intestines and undergo encystment. Newly ingested third stage larvae are known to undergo arrested development and this can lead to an accumulation of encysted burdens over the course of a grazing season. It is believed that the host immune system plays a significant role in triggering this arrestment. Little is known about the development and progression of larval stages in foals that are not expected to mount a pronounced immune response to ingested cyathostomin larvae. This study evaluated counts of encysted larvae measured in 37 foals. The foals were born in 2013, 2014, and 2015 into a parasitology research herd kept without anthelmintic intervention and were humanely euthanatized between 50 and 293days of age as part of an ongoing parasite transmission study. A mucosal digestion technique was performed to enumerate encysted early third stage (EL3) and late third stage/fourth stage (LL3/L4) larvae in the cecum, ventral colon and dorsal colon. Counts were analyzed statistically to evaluate the influence of foal age, sex, and seasonality on the counts. Total counts as well as LL3/L4 counts were significantly higher during the grazing season (March-November). Three defined age groups (>100, 100-200, >200days) did not have statistically different counts. Male foals had significantly higher total counts compared to females, and this has not been reported before. The study found that 41% of the recovered larvae were EL3s, but no indication of arrested development of these was observed. This indicates that cyathostomin infection in foals progresses in a manner substantially different from mature horses.

The route of administration drastically affects ivermectin activity against small strongyles in horses.

The goal of the current study was to evaluate the comparative efficacy of ivermectin (IVM) against small strongyles (cyathostomins) following its oral and intramuscular (IM) administration, in naturally parasitized horses. The parasitological data were complemented with the assessment of the plasma disposition kinetics of IVM. The trial included two different experiments. In experiment I, 40 horses naturally infected with small strongyles were randomly allocated into four experimental groups (n=10) and treated with IVM (0.2mg/kg) as follows: IVM oral paste, animals were orally treated with Eqvalan® (IVM 1.87% paste, as the reference formulation) by the oral route; IVM oral solution, animals were orally treated with Remonta® (IVM 2% solution, as a test formulation); IVM IM solution, animals were IM treated with the test product (Remonta® IVM 2% solution); and control, animals were kept without treatment as untreated controls. In experiment II, 24 horses naturally parasitized with small strongyles were randomly allocated into the same four experimental groups (n=6) described for experiment I. Faecal samples were individually collected directly from the rectum of each horse prior (day -1) and at 7 and 15 (Experiment I) or 7, 15 and 21 (Experiment II) days after-treatment, to assess the eggs per gram (epg) counts and estimate the efficacy of the treatments. Additionally, the comparative plasma disposition kinetics of IVM in treated animals was assessed in experiment II. In both experiments, an excellent (100%) IVM efficacy was observed after its oral administration (test and reference formulations). However, the IM administration of IVM resulted in a low efficacy (36-64%). Similar IVM plasma concentration was observed after its oral administration as a paste or as a solution. The higher IVM plasma profiles observed after the IM administration accounted for an enhanced systemic availability. The improved IVM efficacy observed against adult cyathostomins after its oral administration can be explained by an enhanced drug exposure of the worms located at the lumen of the large intestine. These findings may have a direct impact on the practical use of macrocyclic lactones in horses.

Host specificity and basic ecology of Mammomonogamus (Nematoda, Syngamidae) from lowland gorillas and forest elephants in Central African Republic.

Syngamid strongylids of the genus Mammomonogamus undoubtedly belong among the least known nematodes with apparent zoonotic potential and the real diversity of the genus remains hard to evaluate without extensive molecular data. Eggs of Mammomonogamus sp. are frequently found in feces of African forest elephants (Loxodonta cyclotis) and western lowland gorillas (Gorilla gorilla gorilla) in Dzanga-Sangha Protected Areas. Using sedimentation-based coproscopic techniques, we found the eggs of Mammomonogamus in 19·7% elephant and 54·1% gorilla fecal samples with 8-55 and 1-24 eggs per gram of fecal sediment for elephants and gorillas, respectively. We used a combination of light microscopy, scanning electron microscopy and analysis of cytochrome c oxidase subunit I (cox1) and a partial sequence of 18S rDNA isolated from single eggs to test the hypothesis of possible Mammomonogamus conspecificity in gorillas and elephants. Whereas 18S rDNA sequences were identical in both gorillas and elephants, we distinguished seven different haplotypes within the cox1. Two haplotypes were found in both gorillas and elephants suggesting sharing of Mammomonogamus. Assignment of the parasite to M. loxodontis is proposed. Provided sequences represent the first genomic data on Mammomonogamus spp.

Shortened egg reappearance after ivermectin or moxidectin use in horses in the UK.

This study reports ivermectin and moxidectin egg reappearance periods (ERP) from UK horses with persistently positive faecal egg counts (FEC), defined as positive FEC within the ERP of an anthelmintic post-treatment, or with FECs that remained positive after the normal ERP post-anthelmintic treatment. A selected population of UK pleasure horses deemed at high risk of strongyle infection was studied. The earliest ERP recorded after ivermectin or moxidectin, using first positive FEC, was 5 weeks. From 16 premises where moxidectin was used, five had ERP ≥12 weeks using two further metrics. For premises where moxidectin was administered to only one animal (present or tested), and evaluated as one group (n = 61), ERP was ≥10 weeks. For premises where ivermectin was used, the ERP was ≥5 weeks. Premises with only one horse (present or tested), dosed with ivermectin (n = 31), analysed as one group, demonstrated egg reappearance ≥6 weeks. These field data suggest shortened ERPs following macrocyclic lactone treatment compared to previously published values (8-10 and >13 weeks respectively) when these drugs were first marketed.

Body condition is negatively associated with infection with Syngamus trachea in the ring-necked pheasant (Phasianus colchicus).

The role that parasites play in regulating animal populations is debated, however recent research hints at their pervasiveness among free-living animal populations. Parasites exert both direct and indirect effects on host populations, and can act to regulate populations. The Ring-necked pheasant is an important game-bird species in the UK, and large numbers of birds are released annually. The impact of the ubiquitous tracheal nematode, Syngamus trachea on pheasant populations through effects on host condition was assessed on two pheasant estates in the south west of England. Pheasants infected with S. trachea demonstrated a significant reduction in host condition compared with uninfected controls, with as few as one pair of worms per bird. Although there was no difference in worm burden between sexes, analysis of regression slopes revealed there was a significant difference between sexes in the magnitude of the effect of increasing worm burden on host condition, with detectable effects observed in hosts with one and three pairs of worms for males and females respectively. The observed reductions in host condition in birds with even sub-clinical infections could be the cause of poor reproductive success and survival of pheasants post-release.