Desiccation tolerance of gastrointestinal nematode third-stage larvae: exploring the effects on survival and fitness

Haemonchus contortus Adopt Isolate-Specific Life History Strategies to Optimize Fitness and Overcome Obstacles in Their Environment: Experimental Evidence

Gastrointestinal nematodes (GIN) use flexible life history strategies to maintain their fitness under environmental challenges. Costs incurred by a challenge to one life trait can be recouped by increasing the expression of subsequent life traits throughout their life cycle. Anticipating how parasites respond to the challenge of control interventions is critical for the long-term sustainability of the practice and to further ensure that the parasites withstand favourable adaptive responses. There is currently limited information on whether distinct populations of a GIN species respond to the same environmental challenge in a consistent manner, with similar alterations to their life history strategies or comparable fitness outcomes. This study compared the life history traits and experimental fitness of three distinct Haemonchus contortus isolates exposed to environmental challenges at both the parasitic (i.e., passage through resistant or susceptible sheep) and free-living (i.e., exposure to diverse climatic conditions) life stages. The key findings show that H. contortus maintain their fitness under challenge with isolate-specific alterations to their life history strategies. Further, partial exploration of the H. contortus isolates transcriptomes using cDNA-AFLP methods confirmed disparate expression profiles between them. These results bring fresh insights into our understanding of the non-genetic adaptive processes of GIN that may hinder the efficacy of parasite control strategies.

Research progress and limitation analysis of RNA interference in Haemonchus contortus in China

Haemonchus contortus is a highly pathogenic and economically important parasitic nematode that affects small ruminants worldwide. While omics studies hold great promise, there are fewer research tools available for analyzing subsequent gene function studies. RNA interference (RNAi) technology offers a solution to this problem, as it especially allows for the knockout or shutting off of the expression of specific genes. As a result, RNAi technology has been widely used to explore gene function and disease treatment research. In this study, we reviewed the latest advancements in RNAi research on Haemonchus contortus in China, with the aim of providing a reference for the identification of key genes involved in growth and development, anthelmintic resistance, diagnostic markers, and diagnostic drug targets for the treatment of Haemonchus contortus.

Serial passage in resistant sheep drives the infectivity and fitness of Teladorsagia circumcincta in susceptible lambs: Experimental evidence

Gastrointestinal nematodes (GIN) of small ruminants have adapted their life history strategies to thrive in diverse and fluctuating environments. Environments which alter their expression of life traits may also drive changes in the infection or transmission dynamics, particularly if transferred to a foreign setting. This study aimed to explore how repeated exposure to a resistant sheep host environment would alter the life history traits and infection dynamics of Teladorsagia circumcincta when consequently infected in susceptible lambs. Following just three generations of passage in resistant sheep, T. circumcincta significantly increased their infectivity and fitness in susceptible lambs compared to a control population. This is the first evidence to indicate the resistant host environment can drive such rapid changes in the expression of GIN life traits, with potentially undesirable epidemiological outcomes.

Confounding factors affecting faecal egg count reduction as a measure of anthelmintic efficacy

Increasing anthelmintic resistance (AR) in livestock has stimulated growing efforts to monitor anthelmintic effectiveness (AE) on livestock farms. On-farm assessment of AE relies on measuring the reduction in faecal egg count (FEC) following treatment; and if conducted rigorously, qualifies as a formal FEC reduction test (FECRT) for AR. Substantial research effort has been devoted to designing robust protocols for the FECRT and its statistical interpretation; however, a wide range of factors other than AR can affect FEC reduction on farms. These are not always possible to control, and can affect the outcome and repeatability of AE measurements and confound the on-farm classification of AR using FECRT. This review considers confounders of FEC reduction, focusing on gastrointestinal nematodes of ruminants, including host and parasite physiology and demography; pharmacokinetic variation between drugs, parasites and hosts; and technical performance. Drug formulation and delivery, host condition and diet, and seasonal variation in parasite species composition, can all affect AE and hence observed FEC reduction. Causes of variation in FEC reduction should be attenuated, but this is not always possible. Regular monitoring of AE can indicate a need to improve anthelmintic administration practices, and detect AR early in its progression. Careful interpretation of FEC reduction, however, taking into account possible confounders, is essential before attributing reduced FEC reduction to AR. Understanding of confounders of FEC reduction will complement advances in FECRT design and interpretation to provide measures of anthelmintic efficacy that are both rigorous and accessible.

Ecological drivers of helminth infection patterns in the Virunga Massif mountain gorilla population

The Virunga Massif mountain gorilla population has been periodically monitored since the early 1970s, with gradually increasing effort. The population declined drastically in the 1970s, but the numbers stabilized in the 1980s. Since then, the population has been steadily increasing within their limited habitat fragment that is surrounded by a dense human population. We examined fecal samples collected during the Virunga 2015-2016 surveys in monitored and unmonitored gorilla groups and quantified strongylid and tapeworm infections using egg counts per gram to determine environmental and host factors that shape these helminth infections. We showed that higher strongylid infections were present in gorilla groups with smaller size of the 500-m buffered minimum-convex polygon (MCP) of detected nest sites per gorilla group, but in higher gorilla densities and inhabiting vegetation types occurring at higher elevations with higher precipitation and lower temperatures. On the contrary, the impact of monitoring (habituation) was minor, detected in tapeworms and only when in the interaction with environmental variables and MCP area. Our results suggest that the Virunga mountain gorilla population may be partially regulated by strongylid nematodes at higher gorilla densities. New health challenges are probably emerging among mountain gorillas because of the success of conservation efforts, as manifested by significant increases in gorilla numbers in recent decades, but few possibilities for the population expansion due to limited amounts of habitat.

Seasonal epidemiology of gastrointestinal nematodes of cattle in the northern continental climate zone of western Canada as revealed by internal transcribed spacer-2 ribosomal DNA nemabiome barcoding

Background

Gastrointestinal nematode (GIN) epidemiology is changing in many regions of the world due to factors such as global warming and emerging anthelmintic resistance. However, the dynamics of these changes in northern continental climate zones are poorly understood due to a lack of empirical data.

Methods

We studied the accumulation on pasture of free-living infective third-stage larvae (L3) of different GIN species from fecal pats deposited by naturally infected grazing cattle. The field study was conducted on three organic farms in Alberta, western Canada. Grass samples adjacent to 24 fecal pats were collected from each of three different pastures on each farm. Internal transcribed spacer-2 nemabiome metabarcoding was used to determine the GIN species composition of the harvested larvae. The rotational grazing patterns of the cattle ensured that each pasture was contaminated only once by fecal pat deposition. This design allowed us to monitor the accumulation of L3 of specific GIN species on pastures under natural climatic conditions without the confounding effects of pasture recontamination or anthelmintic treatments.

Results

In seven out of the nine pastures, grass L3 counts peaked approximately 9 weeks after fecal deposition and then gradually declined. However, a relatively large number of L3 remained in the fecal pats at the end of the grazing season. Nemabiome metabarcoding revealed that Cooperia oncophora and Ostertagia ostertagi were the two most abundant species on all of the pastures and that the dynamics of larval accumulation on grass were similar for both species. Daily precipitation and temperature across the whole sampling period were similar for most of the pastures, and multiple linear regression showed that accumulated rainfall 1 week prior to sample collection had a significant impact on the pasture L3 population, but accumulated rainfall 3 weeks prior to sample collection did not.

Conclusions

The results suggest that the pasture L3 population was altered by short-term microclimatic conditions conducive for horizontal migration onto grass. Overall, the results show the importance of the fecal pat as a refuge and reservoir for L3 of cattle GIN on western Canadian pastures, and provide an evidence base for the risk assessment of rotational grazing management in the region.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05101-w.

Detoxification-related gene expression accompanies anhydrobiosis in the foliar nematode (Aphelenchoides fragariae)

The foliar nematode (Aphelenchoides fragariae) is a quarantined pest that infects a broad range of herbaceous and woody plants. Previous work has demonstrated its remarkable ability to survive rapid and extreme desiccation, although the specific molecular mechanisms underlying its anhydrobiotic response have not been characterized. The authors used RNA sequencing and de novo transcriptome assembly to compare patterns of gene expression between hydrated and 24-hr desiccated nematodes. In total, 2,083 and 953 genes were significantly up- and downregulated, respectively, in desiccated nematodes. Of the 100 annotated genes with the largest positive fold-changes, more than one third encoded putative detoxification-related proteins. Genes encoding enzymes of Phase I and Phase II detoxification systems were among the most strongly upregulated in the transcriptome, including 35 cytochrome p450s, 23 short chain dehydrogenase/reductases, 5 glutathione-S-transferases, and 22 UDP-glucuronosyltransferases. Genes encoding heat shock proteins, unfolded protein response enzymes, and intrinsically disordered proteins were also upregulated. Anhydrobiosis in A. fragariae appears to involve both strategies to minimize protein misfolding and aggregation, and wholesale induction of the cellular detoxification machinery. These processes may be controlled in part through the activity of forkhead transcription factors similar to Caenorhabditis elegans’ daf-16, a number of which were differentially expressed under desiccation.

Cell grazing and Haemonchus contortus control in sheep: lessons from a two-year study in temperate Western Europe

Managing infections of sheep with anthelmintic resistant gastrointestinal nematodes (GIN) is a major challenge for sheep producers in Western Europe. New methods of grazing management have been poorly explored as a component of an integrated and sustainable control of these parasites. Therefore, the purpose of this study was to evaluate the effect of two different types of grazing systems of sheep (intensive cell grazing versus conventional rotational grazing) on GIN infections over two years in a farm located in a temperate environment of Western France. When considering the whole study, the type of grazing system did not influence significantly the intensity of egg excretions of adult ewes even if the proportion of ewes excreting high numbers of GIN eggs was higher in cell grazing system than in rotational grazing system. The most striking result of this survey was the effect of grazing system on the GIN species composition harbored by ewes and by their lambs: with time, the proportions of H. contortus infections were lower in cell grazing system than in rotational grazing system. In conclusion, the cell grazing system, as implemented in this study, could limit the importance of this highly pathogenic nematode species in sheep.

Storage of gastrointestinal nematode infective larvae for species preservation and experimental infections

Techniques to preserve the infective third-stage larvae (L3) of gastrointestinal nematodes are of considerable interest to preserve rare species and to maintain a stable source for routine experimental infections. This study compares the relative pros and cons of the two most common techniques, cryopreservation and refrigeration by comparing how they influence consequent infection outcome parameters in terms of life-history traits and fitness as a function of time using the gastrointestinal nematode of sheep Haemonchus contortus as a study species. Establishment capacity was found to be significantly reduced in cryopreserved stocks of L3 compared to refrigerated stocks, but this was followed by significant increases in their fecundity. Refrigeration did not affect L3 stocks consequent fitness by 16 months (the maximum examined) although they did incur a significant reduction in establishment, followed once again by an augmentation in fecundity. The study highlights potential areas for bias in comparing studies using L3 larvae maintained for different periods of time under different techniques.

Assessment of the impact of plant species composition and drought stress on survival of strongylid third-stage larvae in a greenhouse experiment

Grazing livestock is always exposed to infective parasite stages. Depending on the general health status of the animal, the farm management, environmental conditions and pasture exposure, the impact ranges from non-affected to almost moribund animals. The greenhouse experiment was performed to investigate how climatic changes and plant composition influence the occurrence/survival of strongylid third-stage larvae (L3) on pasture. Ten different types of plant species compositions (eight replicates for each) were inoculated with approximately 10,000 Cooperia oncophora L3. The different plant compositions can be assorted to two groups: without legume content and with legume content (52-62% legume content). Half of the replicates were watered adequately, while the other half was hold under drought stress (DS), mimicking longer dry periods. During the DS cycles, the respective containers were not watered until they reached the wilting point. Grass samples were taken 1, 4 and 6 weeks after inoculation, soil samples were taken only once after 6 weeks and all samples were examined for occurrence of L3. After the second DS cycle, the number of L3 present on herbage samples was reduced significantly. The higher the legume content of the pasture composition, the higher is the L3 occurrence on pasture. Independent of the watering scheme, the soil served as the most important reservoir with consistently higher numbers of L3 in the soil compared to herbage.