Lower Immunocompetence Research Articles

COVID-19 Effects on Geriatric Population and Failures of Aminoquinoline Therapy: Compilation of Studies from EU, USA, and China; Safety and Efficacy of Vaccines in the Prevention and Treatment of COVID-19.

Mortality of the older adult population suffering from COVID-19 has been increasing at an alarming rate, and people older than 76 years of age reported 18% mortality. Mainly, the EU and USA exhibited a greater fatality rate due to lack of selective immunization and anti-SARS Co-V-2 therapeutics. Very limited reports are available to delineate the impact of COVID-19 on the geriatric population and the failures of aminoquinoline therapy. We performed a substantial literature review in the PubMed/Medline databases to extract the information pertaining to the COVID-19 impact on the geriatric population and recent failures of aminoquinoline therapy in COVID-19 patients of EU, China, USA and the requirement of vaccination. Both parental strains and mutant variants of SARS Co-V-2 can induce severe respiratory complications, multiorgan failure, and clotting abnormalities in older adults due to low immunocompetence. Aminoquinoline derivatives, such as chloroquine (CQ) and hydroxychloroquine (HCQ), are preferred primarily for COVID-19 treatment, but several controversies are being reported for its usage worldwide. In this review, we have provided the effects of COVID-19 on the geriatric population of EU and an overview of the mechanism of action of aminoquinolines. Furthermore, CQ and HCQ are not the preferred choice of drugs if the COVID-19 patients already have existing co-morbid conditions viz., diabetes mellitus and hypertension. A new advent of COVID-19 vaccines, such as nucleic acid-based (DNA/mRNA) vaccines, protein subunit vaccines, viral vector vaccines, and inactivated vaccines, have been developed for treating SARS-CoV-2 infection after the failure of aminoquinoline therapy in EU, China, and USA patients. However, some of the vaccines are yet to be examined against mutant strains of SARS CoV-2 that originated in the UK, Nigeria, South Africa, Brazil, and India.

Infection with Batrachochytrium dendrobatidis reduces salamander capacity to mount a cell-mediated immune response.

The vertebrate immune system is a costly defense system that is responsible for preventing and eliminating parasites and pathogens. Theory predicts that hosts experience tradeoffs associated with immune deployment and other physiological functions. Although empirical evidence for immune-physiology tradeoffs are well documented in the literature, fewer studies have examined tradeoffs within the immune system in wild vertebrates. We explored the topic of concomitant immune challenges in amphibians by exposing salamanders (Plethodon cinereus) to a fungal pathogen Batrachochytrium dendrobatidis (hereafter "Bd") and then to phytohemagglutinin (hereafter "PHA"). We measured Bd infection using quantitative PCR and used measurements of the tail thickness at the PHA injection site as an estimate of skin swelling. We tested whether Bd reduced the salamander's capacity to mount an immune response towards PHA or whether Bd would stimulate immune activity and thereby increase the response towards PHA. Salamanders that were infected with Bd had a reduced skin-swelling when injected with PHA compared to noninfected salamanders, a result that is consistent with the hypothesis that Bd-infected salamanders have lower immunocompetence than noninfected salamanders. We also found that PHA-induced swelling response was negatively associated with Bd infection abundance (i.e., the infection burden of all exposed salamanders, including those that were exposed but not infected), indicating that salamanders with a higher infection abundance had the lowest swelling response to PHA. Our results suggest that individuals of P. cinereus might experience an energetic tradeoff between successfully fighting off Bd and mounting an immune response towards PHA.

Env diversity-dependent protection of the attenuated equine infectious anaemia virus vaccine

ABSTRACT Lentiviruses harbour high genetic variability for efficient evasion from host immunity. An attenuated equine infectious anaemia (EIA) vaccine was developed decades ago in China and presented remarkably robust protection against EIA. The vaccine was recently proven to have high genomic diversity, particular in env. However, how and to what extent the high env diversity relates to immune protection remains unclear. In this study, we compared immune protections and responses of three groups of horses stimulated by the high-diversity vaccine EIAV_HD, a single molecular clone of the vaccine EIAV_LD with low env diversity, as well as a constructed vaccine strain EIAV_MD with moderate env diversity. The disparity of virus-host interactions between three env diversity-varied groups (5 horses in each group) was evaluated using clinical manifestation, pathological scores, and env-specific antibody. We found the highest titres of env antibodies (Abs) or neutralizing Abs (nAbs) in the EIAV_HD group, followed by the EIAV_MD group, and the lowest titres in the EIAV_LD group (P<0.05). The occurrence of disease/death was different between EIAV_HD group (1/0), EIAV_MD (2/2), and EIAV_LD group (4/2). A similar env diversity-related linear relationship was observed in the clinical manifestations and pathological changes. This diversity-dependent disparity in changes between the three groups was more distinct after immunosuppression, suggesting that env diversity plays an important role in protection under low host immunocompetence. In summary, inoculation with vaccines with higher genetic diversity could present broader and more efficient protection. Our findings strongly suggest that an abundance of Env antigens are required for efficient protection against lentiviruses.

Habitat degradation increases stress-hormone levels during the breeding season, and decreases survival and reproduction in adult common lizards.

The allostatic load model describes how individuals maintain homeostasis in challenging environment and posits that costs induced by a chronic perturbation (i.e., allostatic load) are correlated to the secretion of glucocorticoids, such as corticosterone. Habitat perturbations from anthropogenic activities are multiple and functional responses to those are still unclear. Here, we manipulated the habitat quality in 24 semi-natural populations of the common lizard during 1year. We tested the predictions of the allostatic load model that habitat degradation should increase baseline corticosterone levels, and should induce concomitant physiological changes, such as lipid mobilization and lower immunocompetence, and demographic changes, such as lower body growth, survival and/or reproductive performances. Our results highlight stage-dependent effects of habitat degradation on physiological traits during the breeding season: adult lizards had higher baseline corticosterone levels and yearling lizards had a lower inflammatory response than adults, whereas juveniles had higher circulating lipid levels than yearlings and adults without concomitant change in corticosterone levels. In addition, habitat degradation reduced the performances of adults but not of juveniles: in low habitat quality populations, adult males had a lower survival and females had a smaller fecundity. These results are in accordance with the allostatic load model given that allostatic load was detected only during the season and in life stages of maximal energy expenditure. This underlines the importance to account for individual energy requirements to better understand demographic responses to habitat perturbation.

Impact of immunocompetence index based selection on health conditions in broiler chicken

Present investigation was carried out to assess the impact of immunocompetence index based selection on the survivability of Synthetic Dam Line of broiler chicken. The base population (G0) was screened for various immunocompetence traits, which were then combined in to an index, called immunocompetence (IC) index and two generations (G1 and G2) were obtained after selection for high and low IC index values. Significant differences in percent mortality patterns were noticed in the base population (P< 0.05) and G1 generation (P<0.01), whereas, in G2 generation, high index line had comparatively higher per cent mortality (2.07) as compared to the low index lines (1.29). However, the overall mortality rate was reduced substantially over the two generations of divergent IC index based selection in broiler chicken. The present investigation revealed that selective breeding for better immunocompetence status using IC index could lead to better health status in terms of reduced mortality in broiler chicken.

Establishment and Application of an Automated Chiral Two-dimensional High Performance Liquid Chromatography Method for Bio-analysis of D-Acidic Amino Acids

The physiological and bio-marker function of D-acidic amino acids is now becoming the focus in metabolomics study and new drug discovery. A fully automated two-dimensional high performance liquid chromatography (2D-HPLC) was established by using silica-based monolithic ODS column as the first dimension column with acetonitrile-trifluoro acetic acid-water (9:0.05:91, V/V) as the mobile phase, micro Chiralpak QD-1-AX column as the enantiomer separation column with 10 mM citric acid in methanol- acetonitrile (50:50, V/V) as the mobile phase for the second dimension separation, and 4-fluoro-7-nitro-2,1,3- benzoxadiazole (NBD-F) as the fluorometrical derivative reagent. The method has a higher separation efficiency (Rs > 2.5) and a higher detection sensitivity (LOD = 1 fmol) than that of existing methods in the determination of acidic amino acids enantiomers, meanwhile, an online confirmation of the enantiomers amounts were achieved by this method. The recoveries were around 97%–104%, and the RSDs of intra-day and inter-day were less than 5%. Furthermore, by analyzing the aging model senescence accelerated mouse prone 1 (SAMP1) mice which have low immunocompetence, the amounts of D-aspartic acid in thymus and spleen were determined as (206 ± 18) nmol g−1 and (264 ± 21) nmol g−1, respectively. In the experiment, it was found for the first time that there was an obvious increasing trend of D-aspartic acid (p < 0.01) in thymus and spleen of SAMP1 mice compared to senescence accelerated mouse resistant 1 (SAMR1) mice.

Nestling use of alternative acoustic antipredator responses is related to immune condition and social context

Birds present a variety of antipredator responses, including the use of acoustic signals that may be directed to other individuals or to the predator. We tested competing hypotheses regarding antipredator responses by analysing patterns of variation in the use of distress calls in campo flicker, Colaptes campestris campestris, nestlings. More specifically, we tested whether immune response and social context (presence or absence of other individuals of the social group) were associated with variation in use of acoustic signals in response to human handling. Individuals with higher immunocompetence used proportionally more harsh, low-pitched calls (‘scream’ notes) than individuals with lower immunocompetence, while the latter used mostly tonal, high-pitched calls (‘week’ notes); in both cases there was no influence of the social context on call type. Individuals responded to the social context by giving fewer scream notes and week notes in the presence of adults of the social group than when the adults were absent. Although playbacks are necessary to determine the function of the calls, our results indicate that campo flicker nestling antipredator calls could be used to attract other individuals of the group to help defend the nestling. Also, the use of proportionally more scream notes by healthier individuals suggests that these notes could act as an honest signal of the nestlings’ physiological condition.

Immunocompetence index selection of broiler chicken lines for disease resistance and their impact on survival rate

Aim: This study was aimed to develop the disease resistance broiler chicken lines over two generations (G , G and G ) of 0 1 2 selection for immunocompetence (IC) index by targeting all the facets of immune response traits viz., humoral response (HR) to Sheep red blood cells (SRBC), cell mediated immune response (CMI) to phytohaeagglutinationP mitogen (PHA-P), levels of serum serum immunoglobinG (IgG) and serum lysozyme (LZM) level. Materials and Methods: The SDL Synthetic Dam Line (SDL) broiler line consisting of 303, 204 and 300 birds in G , G and 0 1 G generations, respectively were screened for immunocompetence traits such as humoral response to SRBCs, cell mediated 2 immune response to PHA-P and levels of serum lysozyme by Lysoplate assay and IgG by SRID method, and ranked based on their IC index values. Results: The percent survival rate up to 6 weeks of age in SDL broiler chicken lines were selected for high immunocompetence index (HIC) and low immunocompetence index values (LIC) over two generations (G , G and G ) of selection 0 1 2 and observed that significant differences (P< 0.05) in percent survival pattern in the base population (n= 303) with the highest survivability of 100.00% was observed in 5-6 weeks of age followed by 99.37% and 97.23% in 4-5 and 0-4 weeks of age respectively. In the G generation, significant differences ( P<0.01) was noticed in the selected high and low index lines up to 6 1 weeks of age with the overall survival rate lower in high index lines (93.10% ) as compared to the low index lines (97.62%). Whereas the reverse trend was observed in the G generation that the high index line had significantly (P<0.05) higher survival 2 percent (98.62%) as compared to the low index lines (97.93%). Moreover, the overall survival rate was better substantially over the two generations of divergent immunocompetent index selection of SDL broiler chicken lines. The present investigation revealed that breeding for better immunocompetence status by selection index could lead to better health status in term of improved survival rate in broiler chicken over the generation of selection and further suggested that index selection for more number of generations coupled with economic traits would seem to be a viable option for development of disease resistant chicken lines. Conclusion: Breeding for overall genetic improvement of immunocompetence status by index selection with all the facets of immune system could lead to better survival rate and development of disease resistant chicken.

Maternal corticosterone elevation during egg formation in chickens (Gallus gallus domesticus) influences offspring traits, partly via prenatal undernutrition

The relationship between maternal stress during pregnancy in humans and the subsequent physical and mental health disorders in their children has inspired a wide array of studies on animal models. Almost all of these studies have used mammalian species, but more recently oviparous species in which the embryo develops outside the mother’s body have received more attention. These new models facilitate disentangling of the underlying mechanism due to the accessibility of the prenatal environment, the egg. Studies in birds have found that maternal stress during egg formation induces phenotypic alterations in the offspring that hatch from these eggs. However, different offspring traits have been measured in different studies and potential underlying mechanisms are barely addressed. In this study we experimentally manipulated maternal corticosterone levels in laying hens. We found that mothers with experimentally elevated plasma corticosterone levels produced offspring that are smaller at hatching, less competitive, less fearful, have lower immunocompetence and higher plasma testosterone levels, as well as an alteration of visually guided behavioural lateralization. Earlier we have showed that eggs produced by these corticosterone treated mothers were lighter and contained lower concentrations of testosterone and progesterone in the yolk. While yolk hormones showed no correlation with any offspring traits, egg mass correlated positively with offspring’s body mass from hatching until 10days of age and hatching mass correlated positively with the offspring’s ability to compete for food, indicating that prenatal under nutrition might mediate some effects of maternal stress.

Immunocompetence potential of Tinospora cordifolia on selected postmenopausal women

Postmenopausal age is such a special stage in the life of women. It has been further estimated that postmenopausal women in India would constitute about 14.1% of the total population by 2025. Several irritable symptoms attributed to menopause are often encountered during these later years of life and freedom from related symptoms and comfort could add life to years. Increasing the immunocompetence in the selected low immunocompetent postmenopausal women is the urgent need to prevent secondary infection and the main aim of the present study was to evaluate the effect of Tinospora cordifolia on low immunocompetent postmenopausal women. A group of 200 postmenopausal women was selected and divided into two groups A and B of 100 each. 100 women served as the experimental group and the remaining 100 served as the control group. The experimental group A consisted of postmenopausal women with low immunocompetence and was treated with 525 mg/day of water extract of T. cordifolia. The control group was placed on placebo treatment. The impact was studied in terms of weight changes and biochemical parameters representing the symptoms in question over a period of six months. Findings as related to low immunocompetence revealed that T. cordifoliaproved to be excellent booster of immunocompetence. Key words: Water extract of Tinospora cordifolia, postmenopausal women, immunoglobulin A, G, M, complementary C3, C4, nutritional counseling.

Animals in translation: why there is meaning (but probably no message) in animal communication

Birds present a variety of antipredator responses, including the use of acoustic signals that may be directed to other individuals or to the predator. We tested competing hypotheses regarding antipredator responses by analysing patterns of variation in the use of distress calls in campo flicker, Colaptes campestris campestris, nestlings. More specifically, we tested whether immune response and social context (presence or absence of other individuals of the social group) were associated with variation in use of acoustic signals in response to human handling. Individuals with higher immunocompetence used proportionally more harsh, low-pitched calls (‘scream’ notes) than individuals with lower immunocompetence, while the latter used mostly tonal, high-pitched calls (‘week’ notes); in both cases there was no influence of the social context on call type. Individuals responded to the social context by giving fewer scream notes and week notes in the presence of adults of the social group than when the adults were absent. Although playbacks are necessary to determine the function of the calls, our results indicate that campo flicker nestling antipredator calls could be used to attract other individuals of the group to help defend the nestling. Also, the use of proportionally more scream notes by healthier individuals suggests that these notes could act as an honest signal of the nestlings' physiological condition.

Condition, innate immunity and disease mortality of inbred crows

Cooperatively breeding American crows (Corvus brachyrhynchos) suffer a severe disease-mediated survival cost from inbreeding, but the proximate mechanisms linking inbreeding to disease are unknown. Here, we examine indices of nestling body condition and innate immunocompetence in relationship to inbreeding and disease mortality. Using an estimate of microsatellite heterozygosity that predicts inbreeding in this population, we show that inbred crows were in relatively poor condition as nestlings, and that body condition index measured in the first 2-33 days after hatching, in addition to inbreeding index, predicted disease probability in the first 34 months of life. Inbred nestlings also mounted a weaker response along one axis of innate immunity: the proportion of bacteria killed in a microbiocidal assay increased as heterozygosity index increased. Relatively poor body condition and low innate immunocompetence are two mechanisms that might predispose inbred crows to ultimate disease mortality. A better understanding of condition-mediated inbreeding depression can guide efforts to minimize disease costs of inbreeding in small populations.

PCR-RFLP Analysis of IL-2Rγ and IL-15Rα Genes in Kadakanath Native Chicken

Jaiswal, G., Kumar, S., Prasad, Y. and Singh, D.P. 2009. PCR-RFLP analysis of IL-2Rγ and IL-15Rα genes in Kadakanath native chicken. J. Appl. Anim. Res., 36: 239–242. DNA polymorphism, at Interleukin-2R γ-chain (IL-2Rγ) and Interleukin-15R α-chain (IL-15Rα) genes were studied by PCR-RFLP technique in 48 random bred Kadakanath native chicken, 24 in high and 24 in low immunocompetence (IC) index groups. Amplification of these regions yielded products of 600 and 1120 bp, respectively. Hph I digestion of IL-2Rγ PCR product generated fragments of 465 and 454 bp sizes. Two types of homozygotes (465bp and 454 bp fragments) and heterozygotes (both 465 and 454 bp fragments) were observed. The gene and genotypic frequencies of A and B alleles and AA, BB and AB genotypes were 0.19 and 0.81 and 2.33, 65.12 and 32.56, respectively. PCR-RFLP analysis ofIL-2Rygene with Pst 1, Dde 1 and Taq 1 showed monomorphic pattern in all the individuals. High IC-index group demonstrated higher magnitude of all IC-traits. BB genotype demonstrated higher HA titre than the AB genotype in both the lines. Hinf I PCR-RFLP of IL-15Rα revealed monomorphic banding pattern in all the samples analyzed. Hph I PCR-RFLP of IL-2Rγ region may lead to development of molecular marker for high humoral immune response in chicken.

The Polistes war: weak immune function in the invasive P. dominulus relative to the native P. fuscatus

Invasive species are of growing ecological concern, in part because of conflicts arising with native congeners. The European paper wasp Polistes dominulus was first introduced to North America in the 1970s, and may be displacing at least one native species, P. fuscatus. Previous reports indicate that in native territories over half of P. dominulus colonies are infected by Strepsipteran parasites, which decrease host fitness. In North America, P. fuscatus are parasitized to a lesser degree (approximately one-third), but no infected colonies of invasive P. dominulus have been reported. Because immune function is an indicator of susceptibility to parasitism, we quantified activated levels of immune function by measuring the encapsulation response and phenoloxidase activity and then compared these levels between species. Counterintuitively, our results indicate that P. dominulus has lower levels of both mechanisms of immunity. Additionally, P. dominulus displayed less self-grooming activity than P. fuscatus. We briefly discuss possible immunological explanations for this invasion success, including the selective expression of low immunocompetence.

Adaptive Host-Abandonment of Ectoparasites Before Fledging? Within-Brood Distribution of Nest Mites in House Sparrow Broods

We studied the within-brood distribution of a haematophagous mite Pellonyssus reedi living on nestling house sparrows (Passer domesticus) near the time of fledging. We measured the natural level of infestation of individual nestlings, and determined the feeding efficiency of mites, by scoring their feeding status. Within-brood distribution of mite loads was unrelated to nestling body mass, tarsus length, or immunocompetence. These results did not support parasite preference for large or susceptible hosts. Mite feeding-efficiency was also unrelated to these nestling characteristics, confirming that large nestlings or nestlings with less-developed immunocompetence did not provide superior feeding conditions for mites. Therefore, our results do not support the hypothesis that within-brood distribution of avian ectoparasites is explained by the parasites' preferences for characteristics, such as large body size or low immunocompetence, that make nestlings suitable hosts. On the other hand, we found that mite loads were negatively correlated with nestling age and feather length, suggesting that nestlings closer to fledging harbored fewer mites then their less-developed nestmates. Furthermore, feather length had a stronger relationship with parasite distribution than did nestling age. We presume, therefore, that feather characteristics, i.e., length, may serve as a signal for mites to perceive the ready-to-fledge state of nestlings, inducing abandonment behavior. These results support another, largely neglected hypothesis, i.e., that the avoidance or abandonment of those nestlings that are close to fledging may also explain the parasites' distribution in a brood. This hypothesis is based on the argument that many nest-dwelling ectoparasites breed in the nest material and emerge only periodically to feed on nestlings. In such parasites, the ability to recognize and avoid mature fledglings can be adaptive because this may help the parasites to avoid their removal from the nest so they can continue to reproduce by feeding on unfledged chicks of the current or later broods. Our results suggest that adaptive host-abandonment by nest-dwelling ectoparasites can influence within-brood parasite distributions around the time of fledging.

Physiological responses of juvenile and adult shore crabs Carcinus maenas (Crustacea: Decapoda) to pyrene exposure

This study measured aspects of the physiology of juvenile [(<35 mm carapace width (CW)] and adult (>60 mm CW) Carcinus maenas to test the hypothesis that these different life-history stages exhibit different sensitivities to environmental contamination. Newly-collected juveniles had significantly ( P < 0.05) lower immunocompetence (phagocytosis and cellular integrity), lower metabolic energy (haemolymph glucose) and increased scope for growth compared with adults. Seven day exposure to a sub-lethal concentration (200 μg L −1) of pyrene significantly ( P < 0.01) reduced immunocompetence, elevated basal heart rate and decreased respiration (at rest) for juveniles but had no overall impact on adult crab physiology. Results confirm that physiological differences exist between juvenile and adult shore crabs, and cause juveniles to be more susceptible to the effects of pyrene exposure than adults. Such differences in sensitivity to contamination between life-cycle stages of the same species have to be taken into account during the risk assessment process.

Within‐brood size differences affect innate and acquired immunity in rollerCoracias garrulusnestlings

The immune system has a crucial importance determining animal health and survival. Its maintenance and activation are costly and usually trade with other physiologically costly functions. In birds, number and size of siblings in a nest are likely to determine the development of immunity. Indeed lower immunocompetence is expected in large than in small broods. Moreover, in asynchronous breeders, siblings are expected to differ in immunocompetence because asynchrony produces marked size hierarchy within‐broods. Here we studied the effect of environmental conditions at the nest, chick sex and size, and natural mass differences among siblings due to hatching asynchrony on the development of the innate and acquired immune systems in the threatened non‐size dimorphic asynchronous breeder European rollerCoracias garrulus. Constitutive innate immune function was estimated by using a new technique proposed byMatson et al. (2005). Natural Antibody (NAb) and Complement levels, innate immunity, varied with the mass difference between each chick and its heaviest sibling. NAb levels were higher in late‐hatched siblings compared to early‐hatched ones, indicating that the smallest offspring in each brood has the most developed innate immune system. This relationship was independent of the nest environment. The heterophil/lymphocyte (H/L) ratio, which may indicate the level of stress, was higher in the heaviest siblings of each brood. In addition, the H/L ratio and white blood cell count (WBC) of nestlings, measures belonging to both the innate and acquired arms of the immune system, were related to conditions suffered in the nest. Our results may be explained by differential allocation of resources by female rollers as a way to improve the survival of the whole brood.

REPRODUCTIVE CONFLICTS AFFECT LABOR AND IMMUNE DEFENSE IN THE QUEENLESS ANT DIACAMMA SP. “NILGIRI”

In many species of social Hymenoptera, totipotency of workers induces potential conflicts over reproduction. However, actual conflicts remain rare despite the existence of a high reproductive skew. One of the current hypotheses assumes that conflicts are costly and thus selected against. We studied the costs of conflicts in 20 colonies of the queenless ant Diacamma sp. "nilgiri" by testing the effects of conflicts on labor and worker immunocompetence, two parameters closely linked to the indirect fitness of workers. In this species, the dominant female is the only mated worker (gamergate) and monopolizes reproduction. We experimentally induced conflicts by splitting each colony into two groups, a control group containing the gamergate and an orphaned group displaying aggressions until a new dominant worker arises. Immunocompetence was assessed by the clearance of Escherichia coli bacteria that we injected into the ants. Time budget analysis revealed a lower rate of labor and especially brood care in orphaned groups, supporting the existence of a cost of conflicts on labor. Fifteen days after splitting, a lower immunocompetence was also found in orphaned groups, which concerned workers involved and not involved in conflicts. We propose that this immunosuppression induced by conflicts could stem from stress and not directly from aggression.

Responses to Cohn's Discussion on the Zinkernagel-Hengartner 'Credo 2004'

Responses to Cohn's Discussion on the Zinkernagel-Hengartner 'Credo 2004'

REGULAR ARTICLES / ARTICLES RÉGULIERSFactors affecting the distribution and transmission ofElaphostrongylus rangiferi(Protostrongylidae) in caribou (Rangifer tarandus caribou) of Newfoundland, Canada

Elaphostrongylus rangiferi was introduced to caribou (Rangifer tarandus caribou) of Newfoundland by infected reindeer (R. t. tarandus) from Norway and has caused at least two epizootics of cerebrospinal elaphostrongylosis (CSE), a debilitating neurologic disease. In an attempt to understand the conditions necessary for such outbreaks, we examined the effects of herd density and climatic factors on parasite abundance. The abundance of E. rangiferi was represented by counts of first-stage larvae in feces collected from young caribou (calves and yearlings) in 7 distinct caribou herds in Newfoundland. Abundance of E. rangiferi was highest in February and in the Avalon (632 ± 14 (mean ± SE)) and St. Anthony (526 ± 145) herds, the 2 herds in which CSE was most frequently reported. Mean abundance in February samples from young animals correlated positively with mean annual minimum temperature (rS= 0.829, df = 6, P = 0.04) and the number of days per year above 0°C (rS= 0.812, df = 6, P = 0.05) and negatively with mean summer temperatures (rS= –0.830, df = 6, P = 0.04). Results suggest that abundance of E. rangiferi and the likelihood of cases of CSE are increased by moderate summer temperatures suitable for the activity and infection of gastropod intermediate hosts and by mild winters with little snow that extend the transmission period. Abundance of larvae was not correlated with herd density. Animals in all 7 herds also had the muscle worm Parelaphostrongylus andersoni, a related nematode with similar dorsal-spined larvae. In 2 additional herds (Cape Shore and Bay de Verde), P. andersoni occurred alone and larvae were passed only by young caribou. In herds with dual infections, numbers of P. andersoni larvae were depressed, declined more quickly in young animals, and were considered to be present in only low numbers in February samples used for E. rangiferi analysis. Upon initial infection, young caribou develop a resistance to E. rangiferi that prevents or reduces reinfection later in life. This was demonstrated by examining the brains of caribou for recently acquired worms, which must develop there for up to 90 days before continuing their tissue migration into the skeletal muscles. Recent infections were detected in only calves and yearlings in all herds with E. rangiferi except the Avalon herd, where developing worms were also found on the brains of older caribou. The infection of older animals in the Avalon herd may reflect a lower immunocompetence of a naive herd that has only recently been exposed to E. rangiferi.