Investigating the development of diarrhoea through gene expression analysis in sheep genetically resistant to gastrointestinal helminth infection.

Gastrointestinal helminths infect livestock causing health problems including severe diarrhoea. To explore the underlying biological mechanisms relating to development and control of diarrhoea, we compared 4 sheep that were susceptible to development of diarrhoea with 4 sheep that were diarrhoea-resistant. Transcriptomes in the tissues where the parasites were located were analyzed using RNASeq. By considering low-diarrhoea sheep as control, we identified 114 genes that were down-regulated and 552 genes that were up-regulated genes in the high-diarrhoea phenotype. Functional analysis of DEGs and PPI sub-network analysis showed that down-regulated genes in the high-diarrhoea phenotype were linked to biological processes and pathways that include suppression of 'antigen processing and presentation', 'immune response', and a list of biological functional terms related to 'suppression in immune tolerance'. On the other hand, up-regulated genes in the high-diarrhoea phenotype probably contribute to repair processes associated with tissue damage, including 'extracellular matrix organization', 'collagen fibril organization', 'tissue morphogenesis', 'circulatory system development', 'morphogenesis of an epithelium', and 'focal adhesion'. The genes with important roles in the responses to helminth infection could be targeted in breeding programs to prevent diarrhoea.

Single nucleotide polymorphisms from candidate genes associated with nematode resistance and resilience in Corriedale and Pampinta sheep in Argentina.

Selective breeding of genetically resistant animals is considered a promising strategy to face the problem of nematode resistance to anthelmintics and mitigate concerns about the presence of chemical residues in animal food products and the environment. Gastrointestinal nematode resistance is a complex, multifactorial trait related to host immunity. However, the mechanisms underlying host resistance and response to infection remain to be fully elucidated. In this context, the objective of this study was to provide insight into the chromosomal regions determining nematode resistance and resilience in Corriedale and resistance in Pampinta sheep breeds. A total of 170 single nucleotide polymorphisms (SNP) from 76 candidate genes for immune response were studied in 624 Corriedale and 304 Pampinta animals. Lambs underwent artificial or natural challenges with infective larvae mainly from Haemonchus contortus. Fecal egg counts, estimated breeding values for fecal egg counts, and rate of packed cell volume change and FAMACHA© score change over the challenge were used, when available, as indicators of host parasite resistance or resilience. Phenotype-genotype association studies were conducted and significance values obtained were adjusted for multiple testing errors. Eight SNPs, located on OARs 3, 6, 12, and 20, reached significance in Corriedale sheep under artificial challenge. Those SNP represent allelic variants from the MHC-Ovine Lymphocyte Antigen-DRA, two C-type lectin domain families, the Interleukin 2 receptor ß, the Toll-like receptor 10, the Mannan binding lectin serine peptidase 2, and the NLR family, CARD domain containing 4 genes. On Pampinta lambs under natural challenge, we found three significant SNPs, located in the TIMP metallopeptidase inhibitor 3, the FBJ murine osteosarcoma viral oncogene homolog, and the Interleukin 20 receptor alpha genes, on OARs 3, 7, and 8, respectively. The results obtained herein confirm genomic regions previously reported as associated with nematode resistance in other sheep breeds, reinforcing their role in host response to parasites. These findings contribute to gain knowledge on parasite resistance and resilience in Corriedale sheep and report for the first time SNPs associated with resistance to gastrointestinal parasite infections in Pampinta breed.

Prevalence and Genotyping of Echinococcus Species from Livestock in Kajiado County, Kenya.

Cystic Echinococcosis (CE) is a widespread neglected zoonotic disease and is caused by the larval stage of the dog tapeworm Echinococcus granulosus sensu lato. CE is more frequent in livestock-rearing areas and where people live a nomadic or seminomadic lifestyle such as in Kajiado County, Kenya. There is limited data on CE disease situation in the county of Maasailand; the present study, therefore, reports on the prevalence of CE in cattle, sheep, and goats and their relative importance in CE transmission in Kajiado County. In total, 1,486 livestock (388 cattle, 625 sheep, and 473 goats) slaughtered in two abattoirs were examined for the presence of hydatid cysts in various organs. Cyst isolates were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of the NADH dehydrogenase subunit 1 gene (nad1). The overall prevalence of CE was 14.8% (220/1486), while prevalence per livestock species was 15.2% (72/473) in goats, 14.9% (93/625) in sheep, and 14.2% (55/388) in cattle. Out of the 421 cysts isolated, 389 cysts were successfully characterized to be either E. granulosus sensu stricto (s. s.), 356/389 (91.5%), E. canadensis (G6/7), 26/389 (6.7%), or E. ortleppi, 7/389 (1.8%). This record confirms predominance of E. granulosus s. s. in Maasailand and other parts of Kenya, while the importance of E. ortleppi and E. canadensis (G6/7) to the general CE burden in Maasailand might be higher than previously thought. More so, a higher infection pressure for humans by E. granulosus s. s. based on its abundance could be speculated. The study sheds significant light on CE situation in livestock in the nomadic/seminomadic society of the Maasai in Kajiado County and provides good bases to investigate human CE in the area.

Acting locally - affecting globally: RNA sequencing of gilthead sea bream with a mild Sparicotyle chrysophrii infection reveals effects on apoptosis, immune and hypoxia related genes.

BACKGROUND: Monogenean flatworms are the main fish ectoparasites inflicting serious economic losses in aquaculture. The polyopisthocotylean Sparicotyle chrysophrii parasitizes the gills of gilthead sea bream (GSB, Sparus aurata) causing anaemia, lamellae fusion and sloughing of epithelial cells, with the consequent hypoxia, emaciation, lethargy and mortality. Currently no preventive or curative measures against this disease exist and therefore information on the host-parasite interaction is crucial to find mitigation solutions for sparicotylosis. The knowledge about gene regulation in monogenean-host models mostly comes from freshwater monopysthocotyleans and almost nothing is known about polyopisthocotyleans. The current study aims to decipher the host response at local (gills) and systemic (spleen, liver) levels in farmed GSB with a mild natural S. chrysophrii infection by transcriptomic analysis. RESULTS: Using Illumina RNA sequencing and transcriptomic analysis, a total of 2581 differentially expressed transcripts were identified in infected fish when compared to uninfected controls. Gill tissues in contact with the parasite (P gills) displayed regulation of fewer genes (700) than gill portions not in contact with the parasite (NP gills) (1235), most likely due to a local silencing effect of the parasite. The systemic reaction in the spleen was much higher than that at the parasite attachment site (local) (1240), and higher than in liver (334). NP gills displayed a strong enrichment of genes mainly related to immune response and apoptosis. Processes such as apoptosis, inflammation and cell proliferation dominated gills, whereas inhibition of apoptosis, autophagy, platelet activation, signalling and aggregation, and inflammasome were observed in spleen. Proteasome markers were increased in all tissues, whereas hypoxia-related genes were down-regulated in gills and spleen. CONCLUSIONS: Contrasting forces seem to be acting at local and systemic levels. The splenic down-regulation could be part of a hypometabolic response, to counteract the hypoxia induced by the parasite damage to the gills and to concentrate the energy on defence and repair responses. Alternatively, it can be also interpreted as the often observed action of helminths to modify host immunity in its own interest. These results provide the first toolkit for future studies towards understanding and management of this parasitosis.

Genetic gradient of a host-parasite pair along a river persisted ten years against physical mobility: Baltic Salmo salar vs. Gyrodactylus salaris.

The Atlantic salmon, Salmo salar L., in the Tornio River in the Northern Baltic Sea basin accommodates a monogenean ectoparasite, Gyrodactylus salaris. The aim of the study was to understand the population structure of apparently co-adapted host-parasite system: no parasite-associated mortality has been reported. The parasite burden among salmon juveniles (parr) was monitored along 460km of the river in 2000-2009. Among the parr, 33.0% were infected (nfish=1913). The genetic structure of the parasite population was studied by sequencing an anonymous nuclear DNA marker (ADNAM1, three main genotypes) and mitochondrial CO1 (three clades, six haplotypes). During the ten years, the parasite population was strongly and stably genetically differentiated among up- and downstream nurseries (nADNAM1=411, FST=0.579; nCO1=443, FST=0.534). Infection prevalence among the smolts migrating to sea was higher than in the sedentary parr populations (82.2%, nfish=129). The spatial differentiation observed among the sedentary juveniles was reflected temporally in the smolt run: parasite genotypes dominating the upper part of the river arrived later than downstream dwellers (medians June 4 and June 2) to the trap 7km from the river mouth. The nuclear and mitochondrial markers were in stable disequilibrium which was not relaxed in the contact zone or among the smolts where the parasite clones often met on individual fish. Only five parasite specimens on smolts (nworms=217) were putative recent sexual recombinants. The contribution of extant salmon hatcheries into the infection was negligible. The host salmon population in Tornio River is known to show significant spatial differentiation (FST=0.022). The stable spatial genetic structure of the parasite against the high physical mobility suggested a possibility of local co-adaptation of the host-parasite subpopulations.

Genetic resistance to infections in sheep.

This paper considers genetic resistance to infectious disease in sheep, with appropriate comparison with goats, and explores how such variation may be used to assist in disease control. Many studies have attempted to quantify the extent to which host animals differ genetically in their resistance to infection or in the disease side-effects of infection, using either recorded animal pedigrees or information from genetic markers to quantify the genetic variation. Across all livestock species, whenever studies are sufficiently well powered, then genetic variation in disease resistance is usually seen and such evidence is presented here for three infections or diseases of importance to sheep, namely mastitis, foot rot and scrapie. A further class of diseases of importance in most small ruminant production systems, gastrointestinal nematode infections, is outside the scope of this review. Existence of genetic variation implies the opportunity, at least in principle, to select animals for increased resistance, with such selection ideally used as part of an integrated control strategy. For each of the diseases under consideration, evidence for genetic variation is presented, the role of selection as an aid to disease control is outlined and possible side effects of selection in terms of effects in performance, effects on resistance to other diseases and potential parasite/pathogen coevolution risks are considered. In all cases, the conclusion is drawn that selection should work and it should be beneficial, with the main challenge being to define cost effective selection protocols that are attractive to sheep farmers.

Application of small RNA technology for improved control of parasitic helminths.

Over the last decade microRNAs (miRNAs) and small interfering RNAs (siRNAs) have emerged as important regulators of post-transcriptional gene expression. miRNAs are short, non-coding RNAs that regulate a variety of processes including cancer, organ development and immune function. This class of small RNAs bind with partial complementarity to their target mRNA sequences, most often in the 3'UTR, to negatively regulate gene expression. In parasitic helminths, miRNAs are being increasingly studied for their potential roles in development and host-parasite interactions. The availability of genome data, combined with small RNA sequencing, has paved the way to profile miRNAs expressed at particular developmental stages for many parasitic helminths. While some miRNAs are conserved across species, others appear to be unique to specific parasites, suggesting important roles in adaptation and survival in the host environment. Some miRNAs are released from parasites, in exosomes or in protein complexes, and the potential effects of these on host immune function are being increasingly studied. In addition, release of miRNAs from schistosome and filarial parasites into host plasma can be exploited for the development of specific and sensitive diagnostic biomarkers of infection. Interfering with miRNA function, as well as silencing key components of the pathways they regulate, will progress our understanding of parasite development and provide a novel approach to therapeutic control. RNA interference (RNAi) by siRNAs has proven to be inconsistent in parasitic nematodes. However, the recent successes reported for schistosome and liver fluke RNAi, encourage further efforts to enhance delivery of RNA and improve in vitro culture systems and assays to monitor phenotypic effects in nematodes. These improvements are important for the establishment of reliable functional genomic platforms for novel drug and vaccine development. In this review we focus on the important roles of miRNAs and siRNAs in post-transcriptional gene regulation in veterinary parasitic helminths and the potential value of these in parasite diagnosis and control.

Antibody-mediated trapping of helminth larvae requires CD11b and Fcγ receptor I.

Infections with intestinal helminths severely impact on human and veterinary health, particularly through the damage that these large parasites inflict when migrating through host tissues. Host immunity often targets the motility of tissue-migrating helminth larvae, which ideally should be mimicked by anti-helminth vaccines. However, the mechanisms of larval trapping are still poorly defined. We have recently reported an important role for Abs in the rapid trapping of tissue-migrating larvae of the murine parasite Heligmosomoides polygyrus bakeri. Trapping was mediated by macrophages (MΦ) and involved complement, activating FcRs, and Arginase-1 (Arg1) activity. However, the receptors and Ab isotypes responsible for MΦ adherence and Arg1 induction remained unclear. Using an in vitro coculture assay of H. polygyrus bakeri larvae and bone marrow-derived MΦ, we now identify CD11b as the major complement receptor mediating MΦ adherence to the larval surface. However, larval immobilization was largely independent of CD11b and instead required the activating IgG receptor FcγRI (CD64) both in vitro and during challenge H. polygyrus bakeri infection in vivo. FcγRI signaling also contributed to the upregulation of MΦ Arg1 expression in vitro and in vivo. Finally, IgG2a/c was the major IgG subtype from early immune serum bound by FcγRI on the MΦ surface, and purified IgG2c could trigger larval immobilization and Arg1 expression in MΦ in vitro. Our findings reveal a novel role for IgG2a/c-FcγRI-driven MΦ activation in the efficient trapping of tissue-migrating helminth larvae and thus provide important mechanistic insights vital for anti-helminth vaccine development.

Selection methods for resistance to and tolerance of helminths in livestock.

Helminthiases are among the most important livestock diseases worldwide, in particular for small ruminants, which are the focus of this review. Resource Allocation Theory implies that high-productivity farm animals proportionate insufficient resources for adequate coping with stressful conditions. Significant differences between breeds and within breeds are seen, as well as genotype vs. environment interactions. With improvement of genetic host resistance to infection, transmission of infection will be impacted. On the other hand, genetic improvement of resilience can lead to a reduction in clinical signs of disease, but not necessarily reduce transmission of infection to other animals. Faecal egg count (FEC) is the main measurement used to evaluate helminthiasis load, despite the fact that the protocols and analytical methods can affect the results, and the FEC data frequently shows aggregative, negative skewed distribution, and a high coefficient of variation. Mass selection where heritability is generally medium to low generally produces slow results and low economic returns. Many studies have been published linking resistance to nematodes in livestock to Quantitative Trait Loci and most studies have concentrated on chromosomes where the major histocompatibility complex region is located. Nevertheless, these complex traits have been seen to be affected by thousands of variants that each has a small effect. More recent studies have shown that genome-wide selection strategies can be useful in selecting animals for improved production and resistance traits in this case.

Transcriptomics identified a critical role for Th2 cell-intrinsic miR-155 in mediating allergy and antihelminth immunity.

Allergic diseases, orchestrated by hyperactive CD4(+) Th2 cells, are some of the most common global chronic diseases. Therapeutic intervention relies upon broad-scale corticosteroids with indiscriminate impact. To identify targets in pathogenic Th2 cells, we took a comprehensive approach to identify the microRNA (miRNA) and mRNA transcriptome of highly purified cytokine-expressing Th1, Th2, Th9, Th17, and Treg cells both generated in vitro and isolated ex vivo from allergy, infection, and autoimmune disease models. We report here that distinct regulatory miRNA networks operate to regulate Th2 cells in house dust mite-allergic or helminth-infected animals and in vitro Th2 cells, which are distinguishable from other T cells. We validated several miRNA (miR) candidates (miR-15a, miR-20b, miR-146a, miR-155, and miR-200c), which targeted a suite of dynamically regulated genes in Th2 cells. Through in-depth studies using miR-155(-/-) or miR-146a(-/-) T cells, we identified that T-cell-intrinsic miR-155 was required for type-2 immunity, in part through regulation of S1pr1, whereas T-cell-intrinsic miR-146a was required to prevent overt Th1/Th17 skewing. These data identify miR-155, but not miR-146a, as a potential therapeutic target to alleviate Th2-medited inflammation and allergy.

Descriptive statistics of data: understanding the data set and phenotypes of interest.

A good understanding of the design of an experiment and the observational data that have been collected as part of the experiment is a key pre-requisite for correct and meaningful preparation of field data for further analysis. In this chapter, I provide a guideline of how an understanding of the field data can be gained, preparation steps that arise as a consequence of the experimental or data structure, and how to fit a linear model to extract data for further analysis.

Genetic resistance to natural helminth infections in two chicken layer lines.

Groups of Lohmann Brown (LB) and Lohmann Selected Leghorn (LSL) hens were reared under helminth-free conditions and kept afterwards together in a free range system. Mortality rate, body weight development, laying performance and faecal egg counts (FEC) were recorded during a 12 month laying period. At the end of the laying period, 246 LSL and 197 LB hens were necropsied and worms counted following the World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guidelines. In addition adult Heterakis gallinarum and Ascaridia galli were sexed and measured for length. Significant (P<0.01) differences were observed in mortality rates between LSL and LB animals (12.9 vs. 5.7%). LSL hens showed significantly (P<0.05) higher FEC when compared with LB hens at almost all dates of monitoring. Almost all animals became infected with at least one helminth species. The most prevalent species were H. gallinarum, Capillaria spp. and A. galli. LB hens showed a significantly (P<0.05) higher average number of adult H. gallinarum, Capillaria spp. and tapeworms when compared with LSL animals. However, number of adult A. galli was in tendency lower in these animals. In total, LB had a significantly (P<0.05) higher worm burden than LSL (192.3 vs. 94.3). The estimated heritabilities for total worm burden were 0.23 (SE±0.12) in LSL and 0.75 (SE±0.21) in LB, respectively. The number of all different helminth species were positively correlated. The sex ratio of H. gallinarum and A. galli and the average worm lengths were not significantly (P>0.05) different between the genotypes. There was no significant phenotypic correlation between body weight and worm burden in LSL, whereas it was the case in LB (r=0.17, P<0.05). Based on the estimated heritabilities it is possible to select for helminth resistance in both genotypes.

Increased production through parasite control: can ancient breeds of sheep teach us new lessons?

With a rising world population and economic development, the global demand for meat, milk and other animal products is increasing dramatically. Controlling parasitic diseases in livestock, in particular helminth infections, could rapidly improve productivity and resource utilization. There is a growing interest in indigenous ruminant breeds because these animals have adapted to survive with minimal maintenance in the presence of high exposure to parasite infection. Recent findings on the mechanisms of parasite resistance in indigenous breeds are discussed, and the possibility that such studies may lead to new insight into the immunity and control of parasites proposed. These findings have important implications for the preservation of poorly characterized local indigenous breeds.

Common carp have two subclasses of bonyfish specific antibody IgZ showing differential expression in response to infection.

Immunoglobulin heavy chains identified in bony fish are broadly classified into three classes namely IgM, IgD and IgZ. The most recently described isotype is IgZ, a teleosts-fish specific isotype that shows variations in gene structure across teleosts. In this study we have identified two IgZ subclasses in common carp. IgZ1 is a four constant heavy chain domains containing antibody isolated across teleosts and IgZ2 is a two constant domains containing heavy chain chimera with a µ1 and ζ4 domain. Sequence analyses suggest that these subtypes are expressed from two separate genomic loci. Expression analyses show that IgZ1 is more abundant in systemic organs and IgZ2 chimera is preferentially expressed at mucosal sites. The basal expression level of IgM in fish is much higher than of the other isotypes. We show that IgZ1 expression in systemic and mucosal organs is responsive to blood parasites, while mucosal parasite infection induces IgM and IgZ2 gene expression. This report is the first to show differential expression of the IgZ variants in response to pathogens and suggests that the IgZ subtypes in carps may have mutually exclusive humoral functions.

Pronounced phenotype in activated regulatory T cells during a chronic helminth infection.

Although several markers have been associated with the characterization of regulatory T cells (Tregs) and their function, no studies have investigated the dynamics of their phenotype during infection. Since the necessity of Tregs to control immunopathology has been demonstrated, we used the chronic helminth infection model Schistosoma mansoni to address the impact on the Treg gene repertoire. Before gene expression profiling, we first studied the localization and Ag-specific suppressive nature of classically defined Tregs during infection. The presence of Foxp3+ cells was predominantly found in the periphery of granulomas and isolated CD4+CD25(hi)Foxp3+ Tregs from infected mice and blocked IFN-gamma and IL-10 cytokine secretion from infected CD4+CD25- effector T cells. Furthermore, the gene expression patterns of Tregs and effector T cells showed that 474 genes were significantly regulated during schistosomiasis. After k-means clustering, we identified genes exclusively regulated in all four populations, including Foxp3, CD103, GITR, OX40, and CTLA-4--classic Treg markers. During infection, however, several nonclassical genes were upregulated solely within the Treg population, such as Slpi, Gzmb, Mt1, Fabp5, Nfil3, Socs2, Gpr177, and Klrg1. Using RT-PCR, we confirmed aspects of the microarray data and also showed that the expression profile of Tregs from S. mansoni-infected mice is simultaneously unique and comparable with Tregs derived from other infections.

Increasing accuracy in estimation of economic values for resistance to gastrointestinal helminths in meat sheep.

The impact of utilising different indices and numbers of index traits in estimation of economic values (EVs) for resistance to gastrointestinal (GI) helminths were investigated. Seven indices based on yearling weight (YW), litter size (LS) and ewe live weight (ELW) were evaluated under a scheme that considered individual records (Scheme 1) and one that utilised extra information from individual's relatives (Scheme 2). Under an objective where index response in YW was maximum (R(IYW) = max) economic values were US$ 0.00, 0.41, 0.35 and 1.58 in scheme 1 and -0.07, 0.25, -1.10 and -0.02 in scheme 2 for indexes 1, 2, 3 and 4 respectively. In the determining the effect of the number of index traits on the estimates of EVs, calculations were done for five breeding objectives. Eight scenarios (indices) under each objective that differed in the number of traits considered were evaluated. In all scenarios, EVs under R(IYW) = max were positive and were US$ 0.00, 0.79, 2.68, 2.66, 2.66, 2.62, 2.44 and 2.62 for scenarios 1-8 respectively. Generally, economic value estimates varied across breeding schemes and objectives.

Genetic factors of sheep affecting gastrointestinal parasite infections in the Distrito Federal, Brazil.

Three sheep farms were used in the Distrito Federal, Central Brazil, to study the occurrence of parasites in the feces. A total of 1798 collections were taken over the period of a year. A total of 1205 were taken in Santa Inês breed (SI) in all three farms, 323 in Bergamasca (Berg), 54 in Ile de France, 49 in IlexSI, 103 in Morada Nova (MN) and 64 in TexelxSI, these last five groups being on a single farm. The animals were drenched soon after weaning and feces collected every 3 weeks to calculate fecal egg count (FEC), at least on two occasions on each animal. In some cases, blood was collected to determine packed cell volume (PCV) at fecal collection. Fixed effects included farm, breed/genetic group within farm, animal age (months), birth type (simple, twin) and sex. (Co)variance components were estimated for Santa Inês sheep using restricted maximum likelihood under an animal model. FECs were affected by month and farm showing that climate and management are important sources of variation for the parasites studied. While age and birth type of the lambs did not affect infection level, their genetic group was important, showing that breeding strategies can help control these parasites. Heritabilities for infection level in the sheep varied between 0.09 for Strongyloides and 0.31 for Moniezia expansa. Genetic selection strategies for sheep aimed at reducing these infections should result in more resistant animals.

A field trial of production and financial consequences of helminthosis control in sheep production in Ethiopia.

We used a partial-budget analysis to evaluate profitability of different management strategies of three genotypes of sheep in a 2 x 2 x 3 factorial experiment conducted at Debre Berhan research station in the central highlands of Ethiopia. This involved two anthelmintic-treatment levels (treated vs. non-treated), two supplementary nutrition levels (protein-energy supplementation yes/no) and three genotypes: indigenous Menz (n=40), 50% Awassi x 50% Menz crosses (n=38) and 75% Awassi x 25% Menz crosses (n=31). All sheep were exposed to natural sub-clinical helminthosis challenge. Supplemented sheep were offered a concentrate mix daily on an individual basis. Anthelmintic-treated sheep were drenched with fenbendazole against nematodes and with triclabendazole against trematodes. Data were collected during the experimental period (for 10 months from approximately 1 year of age) on feed intake, live weight, eggs per gram (EPG) of faeces, packed-cell volume (PCV), wool weight, and adult-worm burden. Actual market input and output prices were recorded. Supplemented sheep had significantly higher marginal profit (MP) per sheep than non-supplemented sheep (ETB 33 vs. 4). Likewise, anthelmintic treated sheep performed significantly better than their non-treated contemporaries (MP=ETB 28 vs. 8). The 75% Awassi crosses were least profitable.

Phenotypic differences on the outcome of the host-parasite relationship: behavior of mice of the CBi stock in natural and experimental infections.

Investigation of defined animal models may help to elucidate the role of the host genetic background in the development and establishment of a parasitic infection. Four lines of mice obtained by disruptive selection for body conformation (CBi+, CBi-, CBi/C and CBi/L) and the unselected control line CBi were examined in their response to different parasites to assess whether these distinct genotypes showed differences in their resistance to natural and experimental parasitosis. Protozoans (Trichomonas muris and Spironucleus muris) and nemathelminths (Syphacia obvelata and Aspiculurus tetraptera) were found naturally parasitizing the mice's intestines. CBi/C and CBi were the only genotypes in which T. muris was found. CBi- was least resistant to S. muris. The helminth parasitic burden showed differences between sexes within genotypes (males had a higher burden than females) and among genotypes (CBi/L males had the lowest burden). CBi/L animals were also most resistant to experimental challenge with Heligmosomoides polygyrus and Trypanosoma cruzi. Since all the animals examined shared a common habitat throughout the study and were equally exposed to infection, the phenotypic differences in the natural enteroparasitism herein described evince genetic differences among lines in the host-parasite relationship. This interpretation is further supported by the differences in the response to the experimental challenge to H. polygyrus and T. cruzi.

Immunocompetence does not correlate with resistance to helminth parasites in house mouse subspecies and their hybrids.

A central point not yet elucidated in immuno-ecological studies is whether the different ways to assess the immune status of individuals are good indicators of parasite resistance of the host. We investigate the relationship between immunocompetence and the resistance/susceptibility phenotype of five strains of two European subspecies of the house mouse and their hybrids derived from natural populations. The assessment of immunocompetence was measured indirectly by the mass of the spleen and directly by the phytohaemagglutinin (PHA) test. The resistance of each mouse strain to common helminths was previously determined by the distribution of parasite burdens obtained after experimental infection. We found no relationship between the resistance/susceptibility phenotype of strains and the level of PHA response or the size of the spleen. A significant negative correlation was found between residuals of log spleen mass (controlled for body mass) and PHA response, suggesting that these two components of immune function are not independent measures of defence against parasitism. We discuss the validity of these two techniques of measuring immunocompetence and emphasize the importance of taking into account the complexity of the immune system at structural and functional levels in understanding the component of selection attributable to parasitism in the evolution of immunocompetence.