Some relationships between age, immune responsiveness and resistance to parasites in ruminants

Effects of age on differential resistance to duck hepatitis A virus genotype 3 in Pekin ducks by 16 S and transcriptomics

Duck hepatitis A virus genotype 3 (DHAV-3) is the major cause of viral hepatitis in ducks in Asia. Previous studies have shown that ducklings younger than 21 days are more susceptible to DHAV-3. To elucidate the mechanism by which age affects the differential susceptibility of Pekin ducks to DHAV-3, intestinal (n = 520), liver (n = 40) and blood (n = 260) samples were collected from control and DHAV-3-infected ducks at 7, 10, 14, and 21 days of age. Comparisons of plasma markers, mortality rates, and intestinal histopathological data showed that the resistance of Pekin ducks to DHAV-3 varied with age. 16 S sequencing revealed that the ileal microbial composition was influenced by age, and this correlation was greater than that recorded for caecal microbes. Candidatus Arthromitus, Bacteroides, Corynebacterium, Enterococcus, Romboutsia, and Streptococcus were the differntially abundant microbes in the ileum at the genus level after DHAV-3 infection and were significantly correlated with 7 differentially expressed genes (DEGs) in 7- and 21-day-old ducklings. 3 immunity-related pathways were significantly different between 7- and 21-day-old ducklings, especially for IFIH1-mediated induction of the interferon-alpha/beta pathway, which induces differential production of CD8(+) T cells and was influenced by a combination of differentially abundant microbiota and DEGs. We found that microbes in the ileum changed regularly with age. The intestinal microbiota was associated with the expression of genes in the liver through IFIH1-mediated induction of the interferon-alpha/beta pathway, which may partially explain why younger ducklings were more susceptible to DHAV-3 infection.

Prevalence and risk factors for gastrointestinal parasitosis in small ruminant farms in the Sahelian zone of Niger

The general aim of this study is to analyse the risk factors for gastrointestinal parasitosis in small ruminants in order to contribute to the emergence of targeted treatment methods, at herd and agro-climatic zone levels, for the integrated and sustainable management of parasitic diseases in Sahelian livestock systems. The methodology was based on a questionnaire survey conducted in 37 villages and coprological analysis using the McMaster method on faecal samples from 968 small ruminants, including 555 goats and 413 sheep. Multiple logistic regression was used to highlight the risk factors associated with each type of parasitosis encountered. The results showed that the most widespread farming system remained 100% traditional, with feeding based essentially on natural grazing. Coprological results showed the prevalence of nematodosis (70.2%), Cestodosis (4.1%) and Coccidiosis (79.9%), with an average prevalence of coinfection of 56.9%. These parasite loads were significantly higher during the rainy season and in the more arid northern Sahelian zone, with a marked reduction at the end of the season. Average parasitic egg excretions were 1089 EPG of nematodes and 6864 EPG of coccidia. Parasite loads were higher in the wetter southern strip and varied significantly by breed. Of the five breeds of small ruminants studied, the ara-ara sheep had the highest parasitic loads and prevalences for nematodosis (78.6%), coccidiosis (89,3%) and coinfection (70.9%), appears to be the most susceptible to parasitosis. As for risk factors for severe parasite pressure, animals at the end of the rainy season, older animals and those with poor body condition were at risk of nematodiasis or coinfection. On the other hand, animals at the beginning of the rainy season, farms located in less arid southern Sahelian zones and male subjects were the groups at significant risk of coccidiosis. In these extensive Sahelian farming conditions, the control of these parasitoses by selective treatment of animals could be developed, targeting in particular the risk groups highlighted in this study.

Clair CC. Age-dependent relationships among diet, body condition, and Echinococcus multilocularis infection in urban coyotes

Urban coyotes (Canis latrans) in North America increasingly exhibit a high prevalence of Echinococcus multilocularis, a cestode of recent and rising public health concern that uses rodents as intermediate hosts and canids as definitive hosts. However, little is known about the factors that drive the high urban prevalence of this parasite. We hypothesized that the diet of urban coyotes may contribute to their higher E. multilocularis infection prevalence via either (a) greater exposure to the parasite from increased rodent consumption or (b) increased susceptibility to infection due to the negative health effects of consuming anthropogenic food. We tested these hypotheses by comparing the presence and intensity of E. multilocularis infection to physiological data (age, sex, body condition, and spleen mass), short-term diet (stomach contents), and long-term diet (δ13C and δ15N stable isotopes) in 112 coyote carcasses collected for reasons other than this study from Edmonton, Alberta and the surrounding area. Overall, the best predictor of infection status in this population was young age, where the likelihood of infection decreased with age in rural coyotes but not urban ones. Neither short- nor long-term measures of diet could predict infection across our entire sample, but we found support for our initial hypotheses in young, urban coyotes: both rodent and anthropogenic food consumption effectively predicted E. multilocularis infection in this population. The effects of these predictors were more variable in rural coyotes and older coyotes. We suggest that limiting coyote access to areas in which anthropogenic food and rodent habitat overlap (e.g., compost piles or garbage sites) may effectively reduce the risk of infection, deposition, and transmission of this emerging zoonotic parasite in urban areas.

Effect of commercial tannins on parasitic infection and immunity of lambs naturally infected with Haemonchus contortus

This study aimed to evaluate the effects of different doses of quebracho extract tannins (Schinopsis lorenzii) (EQ) included in the basal diet (DB) on the count of eggs per gram of feces (EPG), count of parasites in the abomasum, hematological, and immunological parameters in lambs naturally infected with Haemonchus contortus. Forty-eight lambs were evaluated for 42 days and divided into four groups (n = 12): CONT- lambs that received DB without EQ supplementation; G1%- DB with EQ at 1% of dry matter intake (DMI) level; G3%- DB with EQ at the 3% of DMI level; G6%- DB with EQ at the 6% DMI level. For EPG counts, feces were collected weekly. For counting abomasal parasites, at the end of the experiment (D42) half of the lambs in each group were slaughtered. For hematological and immunological analysis, venous blood samples were collected at D0, D21, and D42 to perform the erythrocyte count, mean cell volume (MCV), hematocrit, differential leukocyte count, total plasma protein dosage, and serum IgA class anti-H. contortus using an indirect enzyme immunoassay (ELISA). In the EPG count, there was no significant difference (p > 0.05) between the groups compared with the control. Analysis of the abomasal parasite count showed Haemonchus contortus in its entirety; however, there was no significant difference (p > 0.05) in the number of males, females, and total parasites. No differences (p > 0.05) were observed in erythrocyte count, MCV, hematocrit, and total plasma protein. The average total leukocyte, monocyte, eosinophil, and basophil counts showed no difference (p > 0.05). However, the averages of segmented neutrophils in the G1% and G3% groups presented a reduction in the percentage of cells (p < 0.05) between D21 and D42. Regarding the lymphocyte count, a difference was observed in the CONT and G3% groups at D21 and D42 (p < 0.05), when compared to D0. The analyses of the average absorbance of anti-Haemonchus contortus serum IgA showed no difference (p > 0.05), when the groups were analyzed over time or when compared between them. It can be concluded that the inclusion of different doses of tannins from EQ did not alter the parasitological, hematological, and immunological parameters of lambs infected with H. contortus.

Vaccine-induced time- and age-dependent mucosal immunity to gastrointestinal parasite infection

Individuals vary broadly in their response to vaccination and subsequent challenge infection, with poor vaccine responders causing persistence of both infection and transmission in populations. Yet despite having substantial economic and societal impact, the immune mechanisms that underlie such variability, especially in infected tissues, remain poorly understood. Here, to characterise how antihelminthic immunity at the mucosal site of infection developed in vaccinated lambs, we inserted gastric cannulae into the abomasa of three-month- and six-month-old lambs and longitudinally analysed their local immune response during subsequent challenge infection. The vaccine induced broad changes in pre-challenge abomasal immune profiles and reduced parasite burden and egg output post-challenge, regardless of age. However, age affected how vaccinated lambs responded to infection across multiple immune pathways: adaptive immune pathways were typically age-dependent. Identification of age-dependent and age-independent protective immune pathways may help refine the formulation of vaccines, and indicate specificities of pathogen-specific immunity more generally.

Season, weight, and age, but not transmissible cancer, affect tick loads in the endangered Tasmanian devil

The Tasmanian devil (Sarcophilus harrisii) is a carnivorous marsupial threatened by a transmissible cancer, devil facial tumour disease (DFTD). While we have a good understanding of the effect of the transmissible cancer on its host, little information is available about its potential interactions with ectoparasites. With this study, we aimed to determine the factors driving tick loads in a DFTD affected Tasmanian devil population, using long-term mark-recapture data. We investigated the effect of a range of life history traits (age, weight, sex, body condition) and of DFTD (time since DFTD arrival and presence of tumours) on the ectoparasitic tick load of the devils. Mixed effect models revealed that tick load in Tasmanian devils was primarily driven by season, weight, body condition and age. Young devils had more ticks compared to older or healthier devils. The reduction in Tasmanian devil population size over the past 14 years at the studied site had little effect on tick infestation. We also found that devils infected by DFTD had a similar tick load compared to those free of observable tumours, suggesting no interaction between the transmissible cancer and tick load. Our study highlights seasonality and life cycle as primary drivers of tick infestation in Tasmanian devils and the need for further investigations to integrate devil stress and immune dynamics with ectoparasite counts.

Fleece rot and dermatophilosis (lumpy wool) in sheep: opportunities and challenges for new vaccines

During prolonged wetting of the fleece, proliferation of bacterial flora often dominated by Pseudomonas aeruginosa or Dermatophilus congolensis can induce dermatitis and fleece damage termed fleece rot and dermatophilosis respectively, which predispose sheep to blowfly strike. A large research effort in the 1980s and 1990s on vaccines to control fleece rot and dermatophilosis met with limited success. This review examines theoretical and technological advances in microbial ecology, pathogenesis, immunology, vaccine development and the characterisation of microbial virulence factors that create new opportunities for development of vaccines against these diseases. Genomic technologies have now created new opportunities for examining microbial dynamics and pathogen virulence in dermatitis. An effective vaccine requires the combination of appropriate antigens with an adjuvant that elicits a protective immune response that ideally provides long-lasting protection in the field. A clinical goal informed by epidemiological, economic and animal welfare values is needed as a measure of vaccine efficacy. Due to dependence of fleece rot and dermatophilosis on sporadic wet conditions for their expression, vaccine development would be expedited by in vitro correlates of immune protection. The efficacy of vaccines is influenced by genetic and phenotypic characteristics of the animal. Advances in understanding vaccine responsiveness, immune defence in skin and immune competence in sheep should also inform any renewed efforts to develop new fleece rot and dermatophilosis vaccines. The commercial imperatives for new vaccines are likely to continue to increase as the animal welfare expectations of society intensify and reliance on pharmacotherapeutics decrease due to chemical resistance, market pressures and societal influences. Vaccines should be considered part of an integrated disease control strategy, in combination with genetic selection for general immune competence and resistance to specific diseases, as well as management practices that minimise stress and opportunities for disease transmission. The strategy could help preserve the efficacy of pharmacotherapeutics as tactical interventions to alleviate compromised welfare when adverse environmental conditions lead to a break down in integrated strategic disease control. P. aeruginosa and D. congolensis are formidable pathogens and development of effective vaccines remains a substantial challenge.

Evaluation of protection in grazing lambs immunised with different doses of Haemonchus contortus gut membrane glycoproteins in Southern Brazil

A vaccine containing doses ranging from 2 μg to 50 μg of integral membrane proteins from Haemonchus contortus intestinal cells (H11 and H-gal-GP complex) has been shown to be effective for lambs. A vaccine for H. contortus was tested in two-month old grazing Corriedale lambs during an eight-month trial on the outskirts of Bagé, Rio Grande do Sul, Brazil. The animals were kept in a single paddock and allocated to five similar groups according to weight, sex and faecal egg counts (FEC). Vaccinated lambs received 0, 2, 5, 10 or 50 μg of the same antigen diluted in QuilA adjuvant. Vaccine injections were given at days 0, 21, 49, 91, 133, and 175. Lambs were sampled weekly for FEC, packed cell volume (PCV), and plasma ELISA antibody titre. Lambs with PCVs ≤15 % were drenched with levamisole (7.5 mg/kg body weight) as a salvage treatment. During days 77-98 an artificial challenge was administered to increase parasite transmission. Post-artificial challenge (from day 98-217), the FEC of the vaccinated lambs were 59.3 % lower than those of the control lambs. Antigen dose correlated with changes in PCV (r = 0.387 p-value < 0.001). Vaccinated lambs also had higher PCV than controls (p < 0.001; contrast analysis). Salvage treatment was needed in 16.7 % of vaccinated lambs and 88 % of control lambs.

Feeding selenium-biofortified alfalfa hay during the preconditioning period improves growth, carcass weight, and nasal microbial diversity of beef calves

We previously reported that feeding Se-biofortified alfalfa hay to weaned beef calves in a preconditioning program decreases morbidity and mortality during the feedlot period. To understand the mode of action by which supranutritional Se supplementation supports calf health, we examined the effect of agronomic Se-biofortification on nasal microbiome and fecal parasites. Recently weaned Angus-cross beef calves (n = 30) were randomly assigned to two groups and fed an alfalfa hay-based diet for 9 weeks in a preconditioning program. Alfalfa hay was harvested from fields fertilized with sodium selenate at a rate of 0 or 90 g Se/ha. Calculated Se intake from dietary sources was 1.09 and 27.45 mg Se/calf per day for calves consuming alfalfa hay with Se concentrations of 0.06 and 3.47 mg Se/kg dry matter, respectively. Feeding Se-biofortified alfalfa hay for 9 weeks was effective at increasing whole-blood Se concentrations (556 ± 11 vs 140 ± 11 ng/mL; P < 0.001) and increasing body weight (P_Treatment, = 0.03) in weaned beef calves. Slaughter yield grades were higher for calves that had been fed Se-enriched alfalfa hay during the preconditioning period (P_Treatment = 0.008). No significant differences were observed in fecal parasite load, which remained low. The nasal microbiome and microbiota diversity within calves and across calves expanded from weaning (week 0) to the feedlot period (week 12), which was promoted by feeding Se-biofortified alfalfa hay. Especially concerning was the expansion of nasal Mycoplasmataceae in the feedlot, which reached over 50% of the total microbiota in some calves. In conclusion, we identified dietary Se-biofortified alfalfa hay as a potential promoter of nasal microbiome genome and microbiota diversity, which may explain in part high-Se benefits for prevention of bovine respiratory disease complex in beef calves.

Functionalized Core-Shell Yttrium Oxide Nanoparticles as Antioxidants Agents in Heat Stressed Rats

Herein, we assess the antioxidant potential of core-shell yttrium oxide nanoparticles functionalized with ethylene glycol methacrylate phosphate (EGMP). The antioxidant properties of these nanoparticles were investigated in heat stressed models of 21 rats (heat stressed group, group B). Different samples of blood, serum, and tissue homogenate were collected at different time intervals in order to measure oxidative biomarkers such as enzymatic antioxidants (SODs, GPX, GST, GR, and TAC) and oxidative byproducts (MDA, PC, and 8-OHdG). Liver specimens of prophylactic group and heat stressed ones were also histopathologically examined 2 h post NPs injection. The measurements of oxidative biomarkers were complementary with histopathological findings and confirmed the antioxidant properties of poly EGMP yttrium oxide NPs.

A simplified Barbervax® vaccination regimen in lambs to evoke immunological protection to Haemonchus contortus

This study assessed the feasibility of altering the pre-weaning vaccination schedule of the commercially available Barbervax® vaccine directed against Haemonchus contortus, to avoid the 2nd priming vaccination which typically falls between lamb marking and weaning. Merino lambs (n = 175) born to maiden ewes, located in the Northern Tablelands, New South Wales, were randomly allocated to treatment groups (n = 35) and subjected to five different vaccination regimes. One group remained as unvaccinated controls and another had the full set of three priming doses. The other three groups were vaccinated only at marking and weaning receiving a double dose of vaccine at marking and/or weaning. The hypothesis tested was that reducing the interval between lamb marking and weaning to 6 weeks, and providing a double dose of vaccine at marking, weaning or both would remove the need for the second priming vaccination between lamb marking and weaning. This priming vaccination in the vaccination protocol necessitates an additional mustering of ewes with young lambs at foot and is a time consuming and costly exercise which increases the risk of mis-mothering. Blood and faecal samples were collected at frequent intervals for worm egg count (WEC), larval differentiation and H. contortus vaccine specific ELISA antibody analysis. Overall, the results supported the hypothesis, and it was found that antibody titres and WEC reductions equivalent to the registered vaccine regimen were achieved by the alternative regimens. This finding requires further investigation under a wider range of conditions. Deviation from the registered vaccination protocol would constitute off-label usage, and at this time and until further evaluations are done these deviations are not recommended.

Biocompatibility and biodistribution of surface-modified yttrium oxide nanoparticles for potential theranostic applications

The surface of ultrafine yttrium oxide nanoparticles (NPs) with mean size of 7-8 nm was modified with a functional polymer layer to improve their dispersion and impart fluorescent properties for imaging purposes. Surface functionalization was achieved by silanization of yttrium oxide NPs with 3-trimethoxysilylpropyl methacrylate followed by grafting of a co-polymer made of acrylic acid (AA) and ethylene glycol methacrylate phosphate (EGMP). The polymer shell decreases the surface energy of NPs, enhances their polarity, and, as a result, improves their colloidal stability. The synthesized NPs are capable of scavenging free radicals and for this reason have therapeutic potential that warrants further investigations. Furthermore, these stabilized core-shell NPs showed a very low cytotoxicity, confirming that the polymer shell sensibly improves the biocompatibility of bare yttrium oxide NPs, which are otherwise toxic on their own. Poly-EGMP yttrium NPs proved to be safe up to 0.1 mg/g body weight in 1 month old Sprague-Dawley rats, showing also the ability to cross the blood-brain barrier short time after tail injection. The surface modification of yttrium NPs here described allows these NPs to be potentially used in theranostics to reduce neurodegenerative damage due to the heat stress.

Diarrhoea associated with gastrointestinal parasites in grazing sheep

Diarrhoea is a common, widespread and frustrating reality for sheep enterprises in most sheep producing regions globally and of particular concern in Australia as the major risk factor for breech flystrike. Parasitic disease has long been recognised as an important factor in diarrhoea in sheep, particularly the gastrointestinal nematodes (Trichostrongylus and Teladorsagia species). This review focuses on the role of parasitic infections in causing diarrhoea in sheep, with emphasis on the epidemiology of diarrhoea outbreaks related to worms and opportunities to manage the risk of diarrhoea outbreaks in sheep related to parasitic infections. Parasitic nematodes damage the gastrointestinal tract via a complex relationship between direct impacts from worms, such as physical changes to the gut mucosa, and indirect effects largely associated with the host response. Diarrhoea associated with large worm burdens is most efficiently managed through integrated parasite management programs. Despite some limitations, measuring faecal worm egg counts remains a mainstay for assessing the contribution of worms to outbreaks of diarrhoea in sheep. Larval hypersensitivity scouring is emerging as a significant cause of worm-related diarrhoea in sheep without large adult worm burdens in some geographic locations. The syndrome describes a heightened inflammatory response to the ingestion of trichostrongylid infective larvae seen in the gut of sheep with diarrhoea, and is most effectively addressed through selecting sheep for low breech soiling ('dag scores'), as worm resistant sheep may show an increased propensity for diarrhoea, even with low rates of larval challenge. Importantly, dag should be considered as a separate trait to WEC in breeding indexes. Outbreaks of diarrhoea in young sheep are often multifactorial, and co-infections with nematodes and other infectious agents associated with diarrhoea are common. This presents challenges for the field investigation of diarrhoea in grazing sheep.

Four single nucleotide polymorphisms (SNPs) are associated with resistance and resilience to Haemonchus contortus in Brazilian Morada Nova sheep

Gastrointestinal nematodes are a major constraint in sheep production. Breeding for resistance has proven to be an effective and feasible approach to address this problem. The use and investigation of genetic markers for resistance traits could accelerate genetic progress and lead to a better understanding of underlying molecular mechanisms. Thus, the aim of this study was to evaluate if five single nucleotide polymorphisms SNPs OAR2_14765360, OAR6_81718546, OAR11_62887032, OAR12_69606944 and OAR15_59871543 are associated with resistance and resilience traits in a flock of the Morada Nova sheep breed. Lambs were submitted to two consecutive parasite challenges by oral infection with 4000 infective larvae L₃) of Haemonchus contortus. Fecal egg counts (FEC), packed cell volume (PVC) and body weight were measured every one or two weeks for 42 days in each trial. DNA samples from 287 lambs, 131 ewes and 4 rams were amplified by ARMS-PCR or PCR-RFLP and genotypes were determined. Analysis of variance (ANOVA) was used for association analyses between genotypes and phenotypes. In case of significant association, the allele substitution effect was calculated based on a linear model. OAR2_14765360 and OAR12_69606944 were associated with FEC, and OAR12_69606944 also had significant effects on PCV and weight gain, showing favourable associations of the CC genotype with all evaluated traits. Both OAR6_81718546 and OAR11_62887032 were associated with weight gain, and OAR6_81718546 had an additional effect on PCV. OAR15_59871543 was not polymorphic in the population. OAR6_81718546 and OAR12_69606944 presented significant allele substitution effects of -1.06 ± 0.52 kg for the T allele on final body weight and 0.74 ± 0.32 for the C allele in PCV of the same sampling date, respectively. This is the first report of SNPs associated with gastrointestinal nematode resistance in this sheep breed. Our findings support the existence of quantitatice trait loci (QTL) for resistance and resilience in linkage disequilibrium with the polymorphic SNPs and suggest their future use for explorations of these traits in Morada Nova sheep.

Prevalence and risk factors associated with gastrointestinal parasites in ruminant livestock in the Coastal Savannah zone of Ghana

Gastrointestinal (GIT) parasite infections result in significant economic losses to ruminant livestock production. To determine the prevalence and risk factors associated with GIT parasite infections in livestock from Ghana, a cross-sectional survey was conducted in cattle and small ruminants kept under different management systems in the Coastal Savannah zone from October 2014 to February 2015. Faecal samples were collected from 328 cattle and 502 small ruminants (sheep and goats) and examined by formal ether concentration microscopy. The management systems and environmental conditions of the farm or household were observed, and a questionnaire administered to the livestock owners. Overall, 90.8% (754/830) of livestock were infected with at least one of ten different parasites (Eimeria, Strongylid nematodes, Toxocara, Trichuris, Schistosoma, Dicrocoelium, Paramphistomum, Fasciola, Moniezia and Thysaniezia), with Eimeria the most prevalent (78.4%). Most (64.5%) livestock had coinfections with two to five parasites with parasite intensity mostly light and at least one parasite was found in 98.6% (140/142) of the herds. Binary logistic regression models were generated to assess the risk factors associated with infection. Earthen floor was positively associated with strongylid infection, multiple ruminant species with Paramphistomum infection and flock size (>25 animal) with Thysaniezia, Dicrocoelium and Fasciola infections. Separating young animals from older animals was negatively associated with Strongylid infection, feed supplementation with Thysaniezia infection and small ruminant species with Paramphistomum and Toxocara infections. The findings from this study suggests that good sanitation, proper husbandry practices and improved nutrition can improve livestock health and production in Ghana.

Morada Nova sheep breed: Resistant or resilient to Haemonchus contortus infection?

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Resistance against Haemonchus contortus was assessed in a Morada Nova flock.

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More than 88% of the lambs had PCV ≥ 24% even with high fecal egg counts (FEC).

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Only susceptible lambs had decreased live weight due to parasitism.

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More than 98% of the ewes had FEC below 4000 EPG.

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PCV of the ewes was not affected by H. contortus infection.

Morada Nova is a Brazilian hair sheep breed that is well adapted to the country’s mainly tropical climate and has good potential for meat and leather production. This breed is reported to be resistant to Haemonchus contortus infection, a highly desired characteristic due to the large impact of this parasite on sheep farming. Therefore, the present study aimed to characterize 287 recently weaned Morada Nova lambs and 123 ewes in relation to their resistance against H. contortus. The animals were dewormed and 15 days later artificially infected with 4000 H. contortus L₃ (D0). They were individually monitored by periodic assessment of fecal egg count (FEC), packed cell volume (PCV), and live weight (LW). On D42, the sheep were again dewormed and submitted to a new parasitic challenge, following the same scheme. The animals of each category (lambs and ewes) were ranked according to individual mean FEC values, and classified as resistant (R, 20%), intermediate (I, 60%), or susceptible (S, 20%) to H. contortus infection. At weaning, high FEC were observed in all three phenotypes (P > 0.05). After the artificial infections, there was a significant difference (P < 0.05) among the three lamb phenotypes for the mean FEC (R < I < S), PCV (R > I > S), and LW (R = I > S). The infection levels (FEC) were negatively correlated with PCV (r = -0.66; P < 0.001), and LW (r = -0.30; P < 0.001). Despite this, the lambs were resilient, since more than 88% of these animals maintained the PCV above 24%, even when heavily infected. The importance of selective parasite control before weaning to reduce the negative impact on slaughter weight was evidenced, taking into account the high positive correlation between LW at weaning and final LW (r = 0.73; P < 0.001). The ewes, in turn, were strongly resistant to the parasite. Despite highly significant differences (P < 0.001) for mean FEC between phenotypes (R < I < S), 98% of the ewes maintained FEC below 4000 EPG. Their health was not affected, since PCV and LW did not differ between phenotypes, and these parameters were not significantly correlated with FEC (P > 0.05). With the phenotypic characterization performed here, it is possible to introduce procedures for parasite control in Morada Nova flocks, facilitating the target-selective treatment approach. The results of this study can also support improvement of meat production by the Morada Nova breed.

Helminth Load in Feces of Free-Ranging Blue and Fin Whales from the Gulf of California

INTRODUCTION

This is the first worldwide systematic and quantitative study to count and identify helminth parasites from 100 blue and 44 fin whale fecal samples collected in the Gulf of California during winter (1993-2014).

RESULTS

Blue and fin whale feces had similar prevalence of adult acanthocephalans (Bolbosoma sp.) in feces (18.2% and 14.6%, respectively), but blue whales had significantly higher helminth egg prevalence in feces (100%) and mean intensity (443 ± 318 eggs/g) compared to fin whales (61%, 252 ± 327 eggs/g). Diphyllobothrium sp. eggs were identified in blue whale feces and Diphyllobothridae, Ogmogaster sp. and Crassicauda sp. eggs were identified in fin whale feces. We tested the hypothesis that egg intensity in blue whale's feces varies as a function of age class, reproductive status, sex, preservation and sampling years using a Generalized Linear Model. This model explained 61% of the variance in the helminth egg intensity, but it was not significant. Eighteen blue whale individuals were resampled over time without significant difference between consecutive samples.

CONCLUSIONS

Thus, all individual blue whales that migrate to the Gulf of California during winter are permanently parasitized with helminths, while the resident fin whales showed lower prevalence and intensity. This helminth load difference is likely due to their different diets duringsummer-fall, when blue whales feed on other krill species in the California Current System and fin whales shift to school fish prey types in the Gulf of California.

Influence of the physiological stage of Blackbelly sheep on immunological behaviour against gastrointestinal nematodes

The influence of the physiological stage of a Blackbelly flock against natural infection by gastrointestinal parasitic nematodes (GIN) was investigated. Data on serum and saliva IgA levels and peripheral cellular immune response were recorded in 51 sheep for 6 months. The flock was divided based on their physiological stage as follows: a) pregnant ewes, b) lactating ewes, c) non-pregnant ewes, d) pre-weaning lambs, e) growing lambs and f) replacement sheep. Additionally, sheep were classified based on the parasite infection as stabled or grazing management system as follows: g) non-infected stabled sheep, h) infected and stabled sheep and i) infected grazing sheep. Faeces and blood samples were collected every fifteen days. The percentage of packed cell volume (PCV), plasma protein, (PP) and leucocyte differential counts (LDC) were recorded. Likewise, serum and saliva IgA levels were measured by the indirect ELISA technique. The number of GIN eggs excreted per g of faeces (EPG) was also determined using the McMaster technique. Data were analysed using the SAS program to identify fixed effect of physiological stages, infection time and interactions. Results showed high EPG values in stabled lactating ewes (2764) and in growing lambs (2950-4550 EPG). Pregnant ewes had higher PCV values (27%) than lactating ewes (23.5%). Infected lambs showed low PCV values (28.5%) and high PP values (5.9 g/dL) compared with non-infected lambs (31% PCV and 5.6 g/dL PP). The two most abundant GIN species identified were Haemonchus contortus (91%) and Trichostrongylus colubriformis (81%). Pregnant and non-pregnant ewes showed 29% and <20% of IgA values, respectively. High EPG, low IgA and eosinophils counts were observed until 180 days of age in infected lambs. In conclusion, the group of infected lactating ewes and lambs showed susceptibility to GIN than the other groups, including the pregnant ewes.

Host specificity and age-dependent resistance to Cryptosporidium avium infection in chickens, ducks and pheasants

Host- and age-specificity of Cryptosporidium avium were studied in 1-, 21- and 365-day-old chickens (Gallus gallus), domestic ducks (Anas platyrhynchos) and ring-necked pheasants (Phasianus colchicus) under experimental conditions. Cryptosporidium avium was not infectious for ring-necked pheasants, but it was infectious for ducks and chickens at all age categories. The course of infection in ducks did not differ among age categories, but 365-day-old chickens had less severe infections than 1- and 21-day-old chickens. The patent period in chickens and ducks was >30 DPI, but ducks started to shed oocysts of C. avium earlier (5-6 DPI) and at a lower intensity (accumulated value of infection intensity of 58,000-65,000 OPG) than chickens (9-11 DPI and accumulated value of infection intensity of 100,000-105,000 OPG). Experimentally infected birds showed no clinical signs of cryptosporidiosis.

Could diet composition modulate pathological outcomes in schistosomiasis mansoni? A systematic review of in vivo preclinical evidence

Schistosomiasis and malnutrition are often overlapped in poor communities, resulting in disproportionately high mortality rates. Currently, fragmented data make it difficult to define the relationship between diet and schistosomiasis. Thus, we systematically review the preclinical evidence on the impact of diet in Schistosoma mansoni infection. From a structured search, we recovered 27 original articles. All studies used mice and most of them investigated hypoproteic (70.37%), hyperlipidic (22.22%) or vitamin-deficient (7.41%) diets. Diets based on carbohydrate, zinc or milk supplementation were investigated at a reduced frequency (3.70% each). Hypoproteic diets attenuated parasitic load and granulomatous inflammation, but also reduced host resistance to S. mansoni infection, determining higher mortality rates. By stimulating steatohepatitis, parasitic load and granulomatous inflammation, hyperlipidic diets increase organ damage and mortality in infected animals. Although a high-sugar diet and vitamin restriction potentiate and zinc supplementation attenuates S. mansoni infection, the current evidence for these diets remains inconclusive. Analysis of methodological quality indicated that the current evidence is at high risk of bias due to incomplete characterization of the experimental design, diet composition and treatment protocols. From the bias analysis, we report methodological limitations that should be considered to avoid systematic reproduction of inconsistent and poorly reproducible experimental designs.

Gastro-intestinal parasite infections of Ankole cattle in an unhealthy landscape: An assessment of ecological predictors

The distribution of gastro-intestinal (GI) parasites across landscapes is closely related to the spatial distribution of hosts. In GI parasites with environmental life stages, the vitality of parasites is also affected by ecological and landscape-related components of the environment. This is particularly relevant for domestic livestock species that are often kept across habitats with varying degrees of degradation, exposing them to a wide range of environmentally robust parasite species. In our study, we examined the effect of environmental and anthropogenic factors on the prevalence and intensity of GI parasites across a free-ranging stock of Ankole cattle in the Mutara rangelands of northeastern Rwanda. Prevalence and intensity of each parasite type (i.e., strongyle-type nematodes, Strongyloides spp., Moniezia spp., and Eimeria spp.) were used as dependent variables. Two fixed factors related to season and conservation-political history, together with three principal components (condensed from nine ecological variables) were used as independent covariates in a univariate General Linear Model (GLM). Major effects on the prevalence and intensity of strongyle-type nematodes and on the intensity of Eimeria spp. were found in that vegetation-related effects such as above-ground grass biomass in conjunction with a high degree of soil compaction had a negative relationship with these parasite types. These unexpected findings suggest that strongyle-type and coccidian infections increase with increasing rangeland degradation. Strongyle-type nematode prevalence and intensity were also negatively related to goat/sheep density, indicating a 'dilution effect' of GI infections between domestic livestock species.

Study of gastrointestinal parasites in water buffalo (Bubalus bubalis) reared under Mexican humid tropical conditions

The objective was to determine the frequency of gastrointestinal parasites (GP) genera affecting water buffalo (Bubalus bubalis) reared under humid tropical conditions of Mexico. Three hundred eighty-three Munrah breed water buffalo were included, 251 adult females and 132 calves. Feces were directly collected form the rectum of the animals and processed by the McMaster technique. Coprocultures were made to identify the genera of the nematodes. The frequency of GP in B. bubalis was 42%, independently of their age, 60% of calves resulted parasitized. Age had a strong association with the presence of GP (Xi² = 77.4014, d.f. = 1, p = 0.001). The family Trichostrongylidae was found in both age groups. The genera identified were Strongyloides sp. (47.2%), Cooperia sp. (33.9%), and Haemonchus sp. (10.4%), as well as Eimeria sp., Moniezia sp., Trichuris sp., and Strongyloides sp. The highest parasite burden corresponded to the genus Strongyloides sp. with 1108.9 EPG. There is a need to carry out further studies in order to know the prevalence and incidence of nematode affecting to B. bubalis as an introduced animal species to Mexican tropics.

Resistance and resilience to gastro-intestinal nematode parasites and relationships with productivity of Red Maasai, Dorper and Red Maasai ✕ Dorper crossbred lambs in the sub-humid tropics

Resistance and resilience to naturally acquired gastro-intestinal (GI) nematode parasite infections (predominantly Haemonchus contortus) were studied in 1785 lambs born over six lambings (1991 to 1996) consisting of 212 Red Maasai, 311 Dorper and 1262 crossbred (Red Maasai-Dorper) lambs in the sub-humid coastal region of Kenya. These lambs were the progeny of 41 Dorper and 35 Red Maasai rams. Live weights (LWT), blood packed cell volume (PCV) and faecal egg counts (FEC) were recorded at 1- to 2-monthly intervals from birth until the lambs were about one year of age. Red Maasai were more resistant and resilient post weaning to infections with GI nematodes than Dorper lambs as shown by their significantly lower FEC and their significantly higher PCV, respectively. An increasing proportion of Red Maasai genes in the crossbred lambs was associated with decreased FEC and higher PCV, but there was no heterosis for logarithm-transformed FEC (LFEC) or PCV. From one month of age Red Maasai lambs were significantly lighter than Dorper lambs by about 1 kg, but Red Maasai lambs had significantly lower lamb mortality rate from birth to 12 months of age (proportionately 0·30 and 0·66, respectively). Heritability estimates from a repeated measures analysis for records taken at 6 and 8 months of age were 0·14 (s.e. 0·05) for PCV from an animal model and 0·12 (s.e. 0·05) for LFEC from a sire model. The heritability estimate for LFEC from a repeated measures analysis including the four measurements recorded between 6 and 12 months of age was significantly higher (P < 0·05) for Dorper-sired lambs (0·15, s.e. 0·05 for an animal model and 0·19, s.e. 0·07 for a sire model) than for Red Maasai-sired lambs (0·00 and 0·01, s.e. 0·02). The phenotypic and genetic correlations between PCV and LFEC were moderately to highly negative and averaged –0·34 and –0·81, respectively. None of the genetic correlation estimates between LWT and PCV and LWT and LFEC for lambs post weaning were significantly different from zero. The heritability estimates for PCV and LFEC have important implications for within-breed genetic improvement programmes: for the Red Maasai, improvement should concentrate on resilience (e.g. selection for high PCV); for the Dorper, selection should be feasible for both improved resistance (low FEC) and resilience (high PCV).

Relative maturity and the development of immunity to gastrointestinal nematodes in sheep: an overlooked paradigm?

Sheep display considerable variation in both the timing and magnitude of development of immunity to gastrointestinal nematodes (GIN). Onset of immunity is dependent on a number of factors, including antigenic stimulus, nutrition supply, age and size of the animals, the latter of which are confounded. Here, we review the factors associated with the development of immunity to GIN in sheep, particularly in the context of the role that relative maturity may have through applying the rules of genetic size scaling based on examples from published literature. Comparing animals based on their metabolic age, rather than chronological age, may provide an explanation for the timing of immune development and may reduce the variation in immune development that frequently is observed both between and within breeds. Further, this approach may help explain the phenotypic differences in animal performance between animals of varying immunological capacity to GIN through influences on mature body weight. As such, when considering factors influencing immune development to GIN, physiological age or relative maturity may be considered an overlooked paradigm. We propose it may be worthwhile to consider metabolic age when comparing the immune competence of animals to ensure the subjects are at an analogous stage of physiological development.

Anthelmintic Treatment Does Not Change Foraging Strategies of Female Eastern Grey Kangaroos, Macropus giganteus

Large mammalian herbivores are commonly infected with gastrointestinal helminths. Heavily parasitised hosts are likely to have increased nutritional requirements and would be predicted to increase their food intake to compensate for costs of being parasitised, but experimental tests of the impacts of these parasites on the foraging efficiency of hosts are lacking, particularly in free-ranging wildlife. We conducted a field experiment on a population of free-ranging eastern grey kangaroos (Macropus giganteus) to test this prediction, removing nematodes from one group of adult females using an anthelmintic treatment. We then carried out observations before and following treatment to assess the influence of parasites on foraging behaviour. Contrary to our predictions, the manipulation of parasite burdens did not result in changes in any of the key foraging variables we measured. Our results suggest that despite carrying large burdens of gastrointestinal parasites, the foraging strategy of female kangaroos is likely be driven by factors unrelated to parasitism, and that kangaroos in high nutritional environments may be able acquire sufficient nutrients to offset the costs of parasitism. We conclude that the drivers of forage intake likely differ between domesticated and free-ranging herbivores, and that free-ranging hosts are likely more resilient to parasitism.

Impact of the post-weaning parasitism history on an experimental Haemonchus contortus infection in Creole goat kids

Gastrointestinal nematode (GIN) infections have an important negative impact on small ruminant production. The selection of genotypes resistant to these parasitic infections is a promising alternative control strategy. Thus, resistance against GIN is an important component of small ruminant breeding schemes, based on phenotypic measurements of resistance in immune mature infected animals. In this study we evaluated both the impact of the post-weaning parasitism history on the response to an experimental Haemonchus contortus infection of resistant and susceptible Creole kids chosen on the basis of their estimated breeding value, and the interaction with the kid's genetic status. During the post-weaning period (from 3 months until 7 months of age) Creole kids were reared at pasture according to four different levels of a mixed rotational stocking system with Creole cattle: 100% (control), 75% (GG75), 50% (GG50), and 25% (GG25) of the total stocking rate of the pasture. The level of infection of the kids decreased significantly at 50% and 25% of the total stocking rate. After the post-weaning period at pasture, at 11 months of age kids were experimentally infected with H. contortus. The faecal egg counts (FEC) were significantly lower in the groups showing the highest FEC at pasture. This result suggests that a degree of protection against an experimental H. contortus infection occurred during the post-weaning period and was dependant on the level of parasitism. Interestingly, no interaction was observed between this level of protection and the genetic status. In conclusion, the level of post-weaning natural parasitism history at pasture would not influence the genetic status evaluation. More generally our results suggest that it would be better to expose kids to a high level of gastrointestinal parasitism during the post-weaning period in order to increase the basal level of resistance thereafter.

The heritability of abortion in pedigree Charollais flocks

Foetal death, or abortion at term, in sheep is of major significance to the livestock industry, accounting for more than £24million lost per annum. We have investigated whether there is a genetic component to abortion within two flocks of pedigree Charollais sheep, one followed from 1989 to 2006, the other from 1992 to 2006. Abortion occurred at a rate of 5.74-8.78% per annum against a total mortality rate of 14-24%. By model covariate analysis we have shown that 15.5% aborting ewes went on to have one or more abortions and that this risk increased with parity (p=0.006). Heritability estimates were approximately 0.08 as calculated by SOLAR, pedigreemm and ASReml3, with sire and dam components of 0.046 and 0.048, respectively. Where the lamb was aborted, heritability estimates were highly variable according to the method employed, 0.046-0.378, with sex of the lamb being a significant covariate. This variability indicated one or more underlying, significant factors that were not measured in these analyses, potentially including infectious agents that may be involved. Nevertheless, the ASReml3 estimate (0.179) resolved to 0.074 variance attributable to the sire and 0.092 attributable to the dam, which, while not significant, was suggestive that genetic variants passed by the dam to the lamb may be of more weight than that from the sire in determining whether a lamb will abort.

Age at weaning, immunocompetence and ectoparasite performance in a precocial desert rodent

We studied the effects of early weaning on immunocompetence and parasite resistance in a precocial rodent Acomys cahirinus. We hypothesized that if parasite resistance is energetically expensive and nutritional and immunological support from mothers are necessary for the long-term health of offspring, then early weaned animals would be immunologically weaker and less able to defend themselves against parasites than later weaned animals. We weaned pups at 14, 21, or 28 d after birth and assessed their immunocompetence and resistance against fleas Parapulex chephrenis when they attained adulthood. Immunocompetence was assessed using leukocyte concentrations (LC) and a phytohaemagglutinin injection assay (PHA test). To estimate resistance against fleas, we measured performance of fleas via the number of produced eggs and duration of development and resistance to starvation of the flea offspring. We found a significant positive effect of weaning age on the PHA response but not on LC. The effect of age at weaning on flea egg production was manifested in male but not female hosts, with egg production being higher if a host was weaned at 14 than at 28 d. Weaning age of the host did not affect either duration of development or resistance to starvation of fleas produced by mothers fed on these hosts. We concluded that even in relatively precocial mammals, weaning age is an important indicator of future immunological responses and the ability of an animal to resist parasite infestations. Hosts weaned at an earlier age make easier, less-resistant targets for parasite infestations than hosts weaned later in life.

A seasonal survey of gastrointestinal parasites in captive wild impala antelope on a game facility south of Lusaka, Zambia

Faecal samples (n = 1947) from captive wild impala (Aepyceros melampus melampus) were examined over a period of 14 months to determine quantitative seasonal helminth egg excretion patterns and qualitative protozoan oocyst excretion patterns. Geometric mean monthly faecal egg counts (FECs) ranged from 20 to 575 and coprocultures revealed three parasite genera, namely Trichostrongylus, Haemonchus and Strongyloides. Larvae of the Trichostrongylus spp. were most predominant from faecal cultures. No trematode eggs or lungworms were detected and eggs of the cestode Monezia were only seen in two samples during the entire study period. The nematode FECs showed a marked seasonal variation, being higher during the rainy season, moderate during the cool dry season and low during the hot dry season. The rainy season had significantly higher FECs than the dry season (P < 0.01). The percentage of helminth-egg positive faecal samples ranged from 90.6 to 100% in the rainy season and 72.4 to 85.6% in the dry season. Overall mean FECs in unpelleted faeces were significantly higher than in pelleted faeces (P < 0.01). However, the FECs were not significantly different among seasons in unpelleted faeces (P>0.05), but were significantly higher in pelleted faeces in the rainy season than the dry season (P < 0.05). Pellet size had a significant effect on FEC, with smaller pellets having higher FEC (P < 0.05). Strongyloides eggs and coccidia oocysts were only seen during the rainy season. This represents the first documentation of seasonal parasitic infestation in captive wild antelopes in Zambia. Treatment and control strategies for helminths in these captive wild impala are also suggested based on the findings from this study.

Kinetics of the local immune response in the gastric lymph of lambs after primary and challenge infection with Teladorsagia circumcincta

Groups of 5-month-old lambs which had been trickle infected with Teladorsagia circumcincta for 8 weeks then drenched, and worm-free control lambs were challenged with 50 000 T. circumcincta L3s. From 10 days later fewer parasites were recovered from the previously infected sheep, and secondary cellular and humoral responses were observed in the gastric lymph. Increases in CD4+ and CD25+ T lymphoblast traffic on day 3, followed by CD21+ and IgA+ lymphoblasts on day 5, and an increase in total and parasite specific IgA concentrations peaking on day 6 were observed in previously infected lambs. Similar peaks in lymphoblast output were not observed until days 10-12 in the control lambs. This data was highly comparable with that obtained recently from yearling sheep subjected to an identical infection-challenge regime, and contrasted with that obtained from similar experiments in the 1980s when 4(1/2)-month-old previously infected lambs were more susceptible to and had much weaker immune responses to challenge than 10-month-old sheep. The fact that 40% fewer larvae were given during the trickle infection regime in the four recent trials is offered as an explanation for this difference.

The impact of concomitant infections by Trypanosoma cruzi and intestinal helminths on the health of wild golden and golden-headed lion tamarins

A 4-year longitudinal epidemiological study was carried out to evaluate the effect of infection by Trypanosoma cruzi and three intestinal helminth species on the health of golden and golden-headed lion tamarins. We evaluated health using analysis of blood counts, serum proteins, electrophoretograms, electrocardiograms and a health ranking based on physiological parameters. Among the helminths, Trichostrongylidae was demonstrated as the most pathogenic, followed by Prosthenorchis sp.; concomitant infection by Spiruridae may exacerbate the negative effects of the other two helminths. T. cruzi infection was not highly detrimental to the health of the study animals and was correlated with increased resilience to helminths. Tamarins younger than 1-year of age or older than 4-years had lower health condition. Golden-headed lion tamarins were in lower health condition because of higher parasitic prevalence. Our data suggest that when parasite community pathogenicity and prevalence are high, natural selection will allow survival only of lion tamarins in the best health condition.

Selenium supplementation increases wool growth and reduces faecal egg counts of Merino weaners in a selenium-deficient area

This paper reports on the effects of selenium supplementation on liveweight (LW), greasy fleece weight (GFW), fibre diameter (FD), impact of parasite infection and plasma glutathione peroxidase (GSH-Px) activity in weaned Merino sheep reared in a selenium-deficient area (blood GSH-Px <40 U/g Hb). At weaning, 208 Merino wethers were assigned to two groups: control (CTRL) and treatment (SEL). The SEL group was injected with 0.5 mL of Deposel, a slow release selenium injection. LW, blood and faecal samples were taken at 6-week intervals over a 24-week period. At the end of the trial the animals were shorn and GFW and FD measurements were taken. The SEL group had significantly higher (P < 0.01) LW compared with the CTRL group at Weeks 6, 12, 18 and 24. There was a significant difference (P < 0.05) in GFW between the SEL and CTRL group, 2.93 and 2.75 kg, respectively. There was no difference in FD between the two groups. A trend (P < 0.06) towards lower faecal egg counts in the SEL group was seen but the difference between the two groups was not significant. As expected, the SEL group had significantly (P < 0.001) higher plasma GSH-Px activity compared with the CTRL group. In conclusion, selenium supplementation in weaned Merino sheep reared in a selenium-deficient area could increase the LW and GFW of the young sheep while perhaps reducing the level of parasitic infection.

Effects of Teladorsagia (Ostertagia) circumcincta infection on lambs selected for high fleece weight

The physiological processes leading to the expression of the resilient phenotype, which allow animals to maintain a relatively higher production level during infection, have been investigated in lambs from a closed flock selected for 40 generations for high fleece weight (HFW), but with higher FEC and worm burdens than their unselected control (C) flock run in parallel. After recovery from surgery to implant abomasal cannulae, eight parasite-naive lambs from each flock were infected intraruminally at 4.5 months-of-age with 50,000 Teladorsagia circumcincta L3. Blood, abomasal fluid and faecal samples were collected daily for measurement of serum gastrin and pepsinogen concentrations, blood eosinophils, abomasal pH and FEC. Four lambs from each flock were euthanased on Day 8 post-infection and the other four on Day 28 post-infection. At necropsy, abomasal contents and tissues were collected for worm counts, abomasal lymph nodes and fundic tissue for cytokine gene expression and fundic tissue for histopathology. Expression of resilience appeared to be age-dependent as there were no significant differences in either FEC or worm burden between lambs from the two flocks, unlike older HFW lambs in a previous study. Abomasal secretion did not differ between flocks. Histopathological changes were typical of parasitism: inflammatory cells, mainly eosinophils and lymphocytes, were numerous in nodular areas and there were fewer TGF-alpha positive parietal cells, many of which were vacuolated. By Day 28 p.i., globule leucocytes were present. Mucosal thickness was significantly greater on Day 8 than Day 28 p.i. (p=0.000) and in C than HFW lambs. There were fewer parietal cells on Day 28 than on Day 8 p.i. (p=0.003) for pooled data. Circulating eosinophil counts increased moderately in both groups, significantly less in the HFW lambs. Fewer tissue and blood eosinophils in the HFW than C group on Day 8 p.i. were consistent with cytokine gene expression patterns, particularly lower IL-5 levels. Worm count decreased by 90% by Day 28 p.i., along with declining tissue eosinophil counts and IL-13 gene expression and increasing IL-10 and IL-4 gene expression. Food intake was depressed less in the HFW lambs, suggesting that maintenance of appetite could be an important aspect of the physiological basis for resilience. Although the resilient phenotype was not apparent at the younger age, lesser effects on food intake, differences in ALN cytokine profiles and lower blood and tissue eosinophil numbers in the HFW lambs may lead to the expression of resilience when older.

Fleece rot and dermatophilosis in sheep

Fleece rot and dermatophilosis reduce health and production of sheep and predispose them to blow fly strike. This paper reviews aetiology, prevalence, pathogenesis, resistance, attempts to develop vaccines and prospects for new control strategies to these important skin diseases. Although the severity of fleece rot is associated with the abundance of Pseudomonas aeruginosa on skin, microbial ecology studies are providing new insights into the contribution of other bacteria to the disease. Wool traits and body conformation traits that predispose sheep to fleece rot and dermatophilosis are heritable and have been used as indirect selection criteria for resistance for many years. Selection against BoLA-DRB3-DQB class II haplotype in cattle can substantially reduce the prevalence of dermatophilosis and holds promise for identification of gene markers for resistance to these bacterial diseases in sheep. Immune responses in skin and systemic antibody responses to bacterial antigens are acquired through natural infection and contribute to resistance; however, prototype antibacterial vaccines have to date failed to provide protection against the diversity of isolates of Dermatophilus congolensis and Pseudomonas species present in the field. Opportunities for future control through breeding for resistance, vaccines and non-vaccine strategies for controlling the microbial ecology of fleece are discussed. In combination, control strategies need to reduce the risk of transmission, minimise exposure of animals to stressors that enhance the risk of infection, and enhance resistance though genetics or vaccines.

Age-influenced population kinetics and immunological responses of Leishmania donovani in hamsters

Susceptibility of animals to infections depends upon various factors including sex and age of the host, which plays a pivotal role. In this communication, we have investigated the "intake" of Leishmania donovani infection in young (3-4 weeks old) and adult (15-16 weeks old) golden hamsters. The splenic parasite load in young hamsters on day 15 post infection (p.i.) was 54 +/- 4 amastigotes/100 macrophage nuclei and increased to 106.3 +/- 3.5 on day 30 p.i. However, adult group showed 2.2-(P < 0.001) and 1.75-fold (P < 0.001) lesser parasite burden on these days, respectively. But as the disease progresses further, differences in parasite burden become less significant, as revealed by comparable levels of parasite loads at 2 months p.i. Spleen weight measurements correspond to the above observations. In the young group, the levels of antileishmanial antibody rise two and 4.5 times on days 15 and 30 p.i., respectively, as compared to only 1.3 and 2.3 times increase in their respective adult counterparts. However, after 2 months of infection both groups recorded analogous (12-fold) rise in antibody levels. Both mitogenic and antigenic responses in adult hamsters were less suppressed compared to young hamsters on days 15 and 30 p.i. However, both groups exhibited highly suppressed cell-mediated immune (CMI) responses after 2 months of infection. These findings implicate that age of the host may influence the susceptibility and resistance to Leishmania infection.

Performance and nematode infection of ewe lambs on intensive rotational grazing with two different cultivars of Panicum maximum

The daily live weight gain (DLWG), faecal nematode egg counts (FEC), and packed cell volume (PCV) of Suffolk, Ile de France and Santa Inês ewe lambs were evaluated fortnightly for 56 days in the dry season (winter) and 64 days in the rainy season (summer) of 2001-2002. The animals were distributed in two similar groups, one located on Aruana and the other on Tanzania grass (Panicum maximum), in rotational grazing system at the Instituto de Zootecnia, in Nova Odessa city (SP), Brazil. In the dry season, 24 one-year-old ewe lambs were used, eight of each breed, and there was no difference (p > 0.05) between grasses for DLWG (100 g/day), although the Suffolk had higher values (p < 0.05) than the other breeds. In the rainy season, with 33 six-month-old ewe lambs, nine Suffolk, eight Ile de France and 16 Santa Inês, the DLWG was not affected by breed, but it was twice as great (71 g/day, p < 0.05) on Aruana as on Tanzânia grass (30 g/day). The Santa Inês ewe lambs had the lowest FEC (p < 0.05) and the highest PCV (p < 0.05), confirming their higher resistance to Haemonchus contortus, the prevalent nematode in the rainy season. It was concluded that the best performance of ewe lambs on Aruana pastures in the rainy season is probably explained by their lower nematode infection owing to the better protein content of this grass (mean contents 11.2% crude protein in Aruana grass and 8.7% in Tanzania grass, p < 0.05) which may have improved the immunological system with the consequence that the highest PCV (p < 0.05) observed in those animals.

Biochemical differences in Merino sheep selected for resistance against gastro-intestinal nematodes and genetic and nutritional effects on faecal worm egg output

The faecal egg count (FEC) and total egg output is reduced in parasite-resistant sheep and breeding sheep for resistance should reduce infective larval contamination of pastures. This research compares lambs and rams from the parasite-resistant flock, Rylington Merinos, with unselected controls at the same level of larval challenge and the same level of food supply in an animal-house environment. The sheep were penned individually. The parasite resistant sheep excreted 0·85-fold less eggs than the control animals after infection with Trichostrongylus colubriformis and Ostertagia circumcincta for 12 or 18 weeks. During the infection period the parasite resistant lambs had higher plasma immunoglobulin concentration and higher ratio of globulin to albumin than the control animals. In the mature rams these genotype differences diminished. They also had lighter mass of the small intestine with a higher proportion of mucosa, but heavier mass of the large intestine. Parasite infection caused a depletion of blood glutathione in the lambs given food at maintenance or 1·5 × maintenance, and the parasite-resistant sheep (both lambs and rams) also had lower glutathione concentration. Maintaining good body nutrient reserve before the infection reduced the egg output in the early stage of the infection. Food intake had little effect on worm egg production in young sheep given food at maintenance or above. It is suggested that an improvement of nutrition, sulphur-containing amino acids in particular, is required to recover the loss of productive performance caused by the infection.

Epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep in a semi-arid region of eastern Ethiopia

A study on the epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep was carried out in a semi-arid region of eastern Ethiopia for 2.5 years (May 2003 to September 2005). The experimental flock comprised a total of 60 Black Head Ogaden sheep, consisting of four equal groups of young male and female and old male and female sheep. These grazed on communal pastures together with a larger university flock, as well as with animals owned by neighbouring small-holder farmers. A new experimental flock was established each year of the study. Parasitological data (EPG, faecal culture L3, PCV and FAMACHA estimates) and animal performance (weight change) were recorded each month on all experimental animals. In addition, four tracer lambs were assigned each month to the flock to determine the seasonal patterns of infective larvae acquired from pasture. Results showed distinct seasonal patterns associated with the bi-modal annual rainfall. High levels of infection occurred during the short and long rain seasons with peaks occurring in May and September of each year. Haemonchus contortus was the most prevalent parasite, followed by Trichostrongylus spp., with a number of other nematode species being occasionally recorded. H. contortus showed and increased propensity to undergo arrested development during the dry seasons. Correlations between EPG and PCV, EPG and FAMACHA eye scores, and PCV and FAMACHA eye scores were all highly significant (P<0.001). However, there was no significant association between the EPG and LW of the study animals during each study year. This information will provide a basis for developing epidemiologically based control strategies for gastrointestinal nematode parasites that are appropriate for flocks owned by small-holder farmers of semi-arid areas of eastern Ethiopia.