Genetic growth potential interacts with nutrition on the ability of mice to cope with Heligmosomoides bakeri infection

Starving for nutrients: anorexia during infection with parasites in broilers is affected by diet composition

In 2 experiments, we investigated whether diet composition plays a role in pathogen-induced anorexia, the voluntary reduction in ADFI during infection in broilers. We hypothesized that either energy or CP dietary content could influence the extent of anorexia in Ross 308 broilers and infection outcomes with Eimeria maxima. From d 13 of age, half of the birds were infected, and half were uninfected. ADFI was measured daily, and BW every 3 d until d 29. Oocyst excretion was measured daily from d 17 to 23. The impact of parasitism on the small intestine was assessed on d 19 and 25. In Experiment 1, 336 birds were offered diets progressively diluted with lignocellulose, starting from a diet with 3,105 (kcal ME/kg) and 20% CP. There was a significant interaction between infection and diet on ADFI during the acute stage of infection (d 17 to 21): for control birds diet dilution decreased ADFI and consequently reduced energy and CP intake. For infected birds, diet dilution increased ADFI, leading to the same energy and CP intake across diets. Oocyst excretion and villi length to crypt depth ratio (VCR) were constant across infected treatments. In Experiment 2, 432 birds were offered diets with constant ME (3,105 kcal/kg), but different CP contents (24, 20, 26, and 12%). Infection significantly reduced ADFI. Although there was no interaction between infection and diet on ADFI, there was an interaction on CP intake during the acute stage of infection. Infected birds on the 20% CP diet achieved the same CP intake as uninfected birds. There were no differences in the VCR and ADG of the infected birds on 24, 20 and 16% CP treatments, but birds on 12% had the lowest ADG and excreted more oocysts. We suggest that during infection, birds target a nutrient resource intake, which appears to be beneficial for infection outcomes, while at the same time they avoid excess protein intake. We conclude that different mechanisms regulate ADFI in infected and uninfected birds.

Resistance and tolerance to mixed nematode infections in chicken genotypes with extremely different growth rates

Fast growing broilers are less able to cope with fitness related challenges. As the allocation of metabolic resources may be traded off between performance and defence functions in parasitized hosts, we hypothesized that fast growing broilers are more sensitive to mixed nematode infections compared with slower growing genotypes under the same environmental conditions. Therefore, we compared male birds of genotypes selected for either meat production (Ross-308, R) or egg production (Lohmann Brown Plus, LB) or for both purposes (Lohmann Dual, LD), to assess their resistance and tolerance to mixed nematode infections with Ascaridia galli and Heterakis gallinarum. While infections reduced feed intake in all three genotypes, feed conversion efficiency was not affected. Infections impaired growth performance only in R birds, indicating lower tolerance in the fast growing genotype compared with slower growing LB and LD genotypes. Impaired tolerance in R birds was associated with a relative nutrient scarcity due to an infection-induced lower feed intake. Resistance to experimentally induced infections depended on host genotype as well as on the worm species involved. Overall, the A. galli burden was higher in R than LB, whereas the burden of LD was not different from that of R and LB. In contrast, the H. gallinarum burden of first generation worms was similar in the three genotypes. Susceptibility to re-infection with H. gallinarum was higher in LB than in LD, whereas very low levels of re-infection were observed in R birds. Our data collectively suggest that resistance and tolerance to mixed nematode infections are sensitive to growth rate in chickens. These differences amongst genotypes may partly be associated with a mismatch between the actual nutrient supply and genotype-specific nutrient requirements.

Does selection for growth rate in broilers affect their resistance and tolerance to Eimeria maxima?

Chickens exhibit varied responses to infection with Eimeria parasites. We hypothesise that broilers selected for increased growth rate will show lower resistance and tolerance to a coccidian challenge. 288 chickens of fast (F) or slow (S) growing lines were inoculated with 0 (control), 2500 (low-dose), or 7000 (high-dose) sporulated E. maxima oocysts at 13 days of age in two consecutive rounds. Gain and Intake were measured daily and their values relative to BW at the point of infection were calculated over the pre-patent (days 1-4 post-infection), acute (d5-8 pi), and recovery (d9-12 pi) phases of infection to assess the impact of infection. Levels of plasma carotenoids, vitamins E and A, long bone mineralisation, caecal microbiota diversity indices, and histological measurements were assessed at the acute (d6 pi) and recovery stage (d13 pi). In addition, we measured the levels of nitric oxide metabolites and the number of parasite genome copies in the jejunumat d6pi. In absolute terms F birds grew 1.42 times faster than S birds when not infected. Infection significantly reduced relative daily gain and intake (P < 0.001), with the effects being most pronounced during the acute phase (P < 0.001). Levels of all metabolites were significantly decreased, apart from NO which increased (P < 0.001) in response to infection on d6pi, and were accompanied by changes in histomorphometric features and the presence of E. maxima genome copies in infected birds, which persisted to d13pi. Furthermore, infection reduced tibia and femur mineralisation, which also persisted to d13pi. Reductions in measured variables were mostly independent of dose size, as was the level of parasite replication. The impact of infection was similar for S and F-line birds for all measured parameters, and there were no significant interactions between line x dose size on any of these parameters. In conclusion, our results suggest that line differences in productive performance do not influence host responses to coccidiosis when offered nutrient adequate diets.

Helminth Interaction with the Host Immune System: Short-Term Benefits and Costs in Relation to the Infectious Environment

Chronic infections imply that the parasite and the host immune system closely interact for a long time without a fatal outcome. Environmental changes encountered by hosts and parasites, such as coinfections, can deeply affect the stability of this apparent equilibrium. Our study aimed to determine the effect of the infectious environment on the costs and benefits of chronic infection with the gut nematode Heligmosomoides polygyrus in mice. Heligmosomoides polygyrus is known for its capacity to actively interfere with the host immune response by secreting molecules that can dampen immunity. We simulated bacterial coinfection of H. polygyrus-infected CBA-strain mice during the chronic phase of the infection by injecting them with Escherichia coli lipopolysaccharide. We found that infection by H. polygyrus induced only weak costs for the host (in terms of reproductive investment) and was characterized by the upregulation of both Th1 (interferon-γ) and anti-inflammatory (transforming growth factor-β) cytokines, which is favorable to parasite persistence. However, when co-occurring with the simulated bacterial infection, H. polygyrus infection was associated with a pronounced shift toward a pro-inflammatory status, which was deleterious to both the parasite and the host. Our study highlights the dynamic equilibrium reached during chronic infection, where a rapid environmental change, such as a concomitant bacterial infection, can deeply affect the outcome of the host-parasite interaction.

Tolerance and resistance to a nematode challenge are not always mutually exclusive

The relationship between the manifestations of tolerance (a host's ability to reduce the impact of a given level of pathogens) and resistance (a host's ability to clear pathogens) has been assumed to be an antagonistic one. Here we tested the hypothesis that mice from strains more resistant to intestinal nematodes will experience reduced tolerance compared with less resistant mice. Three inbred strains of mice were used: C57BL/6 mice have been characterised as susceptible, whereas BALB/c and NIH mice have been characterised as resistant to Heligmosomoides bakeri infection. Mice of each strain were either parasitised with a single dose of 250 L3H. bakeri (n=10) in water or were sham-infected with water (n=10). Body weight, food intake and worm egg output were recorded regularly throughout the experiment. Forty-two days p.i. mice were euthanised and organ weights, eggs in colon and worm counts were determined. C57BL/6 mice showed significantly greater worm egg output (P<0.001), eggs in colon (P<0.05) and female worm fecundity (P<0.05) compared with NIH and BALB/c mice. Parasitised BALB/c mice grew more whilst parasitised C57BL/6 mice grew less than their sham-infected counterparts during the first 2 weeks post-challenge (P=0.05). Parasitism significantly increased liver, spleen, small intestine and caecum weights (P<0.001) but reduced carcass weight (P<0.01). Average daily weight gain and worm numbers were positively correlated in NIH mice (P=0.05); however, the relationship was reversed when carcass weight was used as a measure for tolerance. BALB/c mice did not appear to suffer from the consequences of parasitism, with carcass weight similar in all animals. Our hypothesis that strains more resistant to the H. bakeri infection are less tolerant compared with less resistant strains is rejected, as the two resistant strains showed variable tolerance. Thus, tolerance and resistance to an intestinal nematode infection are not always mutually exclusive.

Evaluation of biochemical, hematological and parasitological parameters of protein-deficient hamsters infected with Ancylostoma ceylanicum

BACKGROUND

Hookworms infect millions of people worldwide and can cause severe clinical symptoms in their hosts. Prospective cohort studies in Brazil show high rates of hookworm reinfection in malnourished children compared to well-nourished children, despite previous treatment. Additionally, soil-transmitted helminth (STH) infections can worsen the nutritional status of affected populations. Therefore, this study aims to clarify the effects of host malnutrition during Ancylostoma ceylanicum infection and how this infection affects host physiological parameters using a hamster model.

METHODOLOGY/PRINCIPAL FINDINGS

Hamsters were divided into four experimental groups: normal diet or low-protein diet (also referred to as "malnourished") and A. ceylanicum infection or no infection. More severe pathogenesis was observed in the infected malnourished group, as demonstrated by significant decreases in the hemoglobin concentration, erythrocyte number and packed-cell volume compared to the non-infected malnourished group. Greater numbers of adult parasites and eggs were observed in the malnourished group compared to the control group; however, the oviposition rate was lower in the malnourished group. In general, greater values of total lipids were observed in malnourished animals compared to control animals, including lipids excreted in the stool.

CONCLUSIONS

In this work, we have demonstrated that animals fed an isocaloric low-protein diet presented more severe pathogenesis when infected with A. ceylanicum. The increased lipid concentration in the liver and blood is related to the conversion of the excess carbohydrate into fatty acids that increase the concentration of triglycerides in general. Triglycerides were excreted in the feces, indicating that infection associated with malnutrition caused a greater loss of these molecules for this group of animals and confirming the hypothesis that both nutrition and infection are responsible for the malabsorption syndrome. Taken together, the results found in this work confirm the hypothesis that the nutritional condition of the host greatly influences the course of the infection.

Immune response from a resource allocation perspective

The immune system is a life history trait that can be expected to trade off against other life history traits. Whether or not a trait is considered to be a life history trait has consequences for the expectation on how it responds to natural selection and evolution; in addition, it may have consequences for the outcome of artificial selection when it is included in the breeding objective. The immune system involved in pathogen resistance comprises multiple mechanisms that define a host's defensive capacity. Immune resistance involves employing mechanisms that either prevent pathogens from invading or eliminate the pathogens when they do invade. On the other hand, tolerance involves limiting the damage that is caused by the infection. Both tolerance and resistance traits require (re)allocation of resources and carry physiological costs. Examples of trade-offs between immune function and growth, reproduction and stress response are provided in this review, in addition to consequences of selection for increased production on immune function and vice versa. Reaction norms are used to deal with questions of immune resistance vs. tolerance to pathogens that relate host health to infection intensity. In essence, selection for immune tolerance in livestock is a particular case of selection for animal robustness. Since breeding goals that include robustness traits are required in the implementation of more sustainable agricultural production systems, it is of interest to investigate whether immune tolerance is a robustness trait that is positively correlated with overall animal robustness. Considerably more research is needed to estimate the shapes of the cost functions of different immune strategies, and investigate trade-offs and cross-over benefits of selection for disease resistance and/or disease tolerance in livestock production.

Interactive effects of protein nutrition, genetic growth potential and Heligmosomoides bakeri infection pressure on resilience and resistance in mice

The ability of animals to cope with an increasing parasite load, in terms of resilience and resistance, may be affected by both nutrient supply and demand. Here, we hypothesized that host nutrition and growth potential interact and influence the ability of mice to cope with different parasite doses. Mice selected for high (ROH) or low (ROL) body weight were fed a low (40 g/kg; LP) or high (230 g/kg; HP) protein diet and infected with 0, 50, 100, 150, 200 or 250 L3 infective Heligmosomoides bakeri larvae. ROH-LP mice grew less at doses of 150 L3 and above, whilst growth of ROH-HP and of ROL mice was not affected by infection pressure. Total worm burdens reached a plateau at doses of 150L3, whilst ROH mice excreted fewer worm eggs than ROL mice. Serum antibodies increased with infection dose and ROH mice were found to have higher parasite-specific IgG1 titres than ROL mice. In contrast, ROL had higher total IgE titres than ROH mice, only on HP diets. The interaction between host nutrition and growth potential appears to differentially affect resilience and resistance in mice. However, the results support the view that parasitism penalises performance in animals selected for higher growth.

Dietary protein and energy supplies differentially affect resistance to parasites in lactating mammals

Periparturient relaxation of immunity (PPRI) to parasites in mammals results in higher worm burden and worm egg excretion and may have a nutritional basis. Nippostrongylus brasiliensis re-infected lactating rats fed low-crude protein (CP) diets show an augmented degree of PPRI compared with their high CP-fed counterparts. However, such effects of CP scarcity have been confounded by metabolisable energy (ME) scarcity due to increased intake of the high-CP foods. Here, we independently assessed the effects of dietary CP and ME scarcity on the degree of PPRI. Second, parity rats were infected with N. brasiliensis larvae before mating. Upon parturition, dams were allocated to one of six feeding treatments (1-6), consisting of two levels of dietary ME supply, each with three levels of CP supply. On day 2 of lactation, dams were either re-infected with 1600 N. brasiliensis larvae or sham-infected with PBS, while litter size was standardised at ten pups. Dams and litters were weighed daily until either day 8 or 11 of lactation, when worm burdens were assessed as a proxy for PPRI. Increased CP and ME supply independently improved lactational performance. While ME supply did not affect parasitism, increasing CP supply reduced worm burden and the percentage of female worms in the small intestine; the latter was especially pronounced at the lower level of ME supply. The present results support the view that PPRI to parasites may be sensitive to CP scarcity, but not to moderate ME scarcity.

Effectiveness analysis of resistance and tolerance to infection

Background

Tolerance and resistance provide animals with two distinct strategies to fight infectious pathogens and may exhibit different evolutionary dynamics. However, few studies have investigated these mechanisms in the case of animal diseases under commercial constraints.

Methods

The paper proposes a method to simultaneously describe (1) the dynamics of transmission of a contagious pathogen between animals, (2) the growth and death of the pathogen within infected hosts and (3) the effects on their performances. The effectiveness of increasing individual levels of tolerance and resistance is evaluated by the number of infected animals and the performance at the population level.

Results

The model is applied to a particular set of parameters and different combinations of values. Given these imputed values, it is shown that higher levels of individual tolerance should be more effective than increased levels of resistance in commercial populations. As a practical example, a method is proposed to measure levels of animal tolerance to bovine mastitis.

Conclusions

The model provides a general framework and some tools to maximize health and performances of a population under infection. Limits and assumptions of the model are clearly identified so it can be improved for different epidemiological settings.