Enemies and turncoats: bovine tuberculosis exposes pathogenic potential of Rift Valley fever virus in a common host,African buffalo (Syncerus caffer)

The ubiquity and importance of parasite co-infections in populations of free-living animals is beginning to be recognized, but few studies have demonstrated differential fitness effects of single infection versus co-infection in free-living populations. We investigated interactions between the emerging bacterial disease bovine tuberculosis (BTB) and the previously existing viral disease Rift Valley fever (RVF) in a competent reservoir host, African buffalo, combining data from a natural outbreak of RVF in captive buffalo at a buffalo breeding facility in 2008 with data collected from a neighbouring free-living herd of African buffalo in Kruger National Park. RVF infection was twice as likely in individual BTB+ buffalo as in BTB− buffalo, which, according to a mathematical model, may increase RVF outbreak size at the population level. In addition, co-infection was associated with a far higher rate of fetal abortion than other infection states. Immune interactions between BTB and RVF may underlie both of these interactions, since animals with BTB had decreased innate immunity and increased pro-inflammatory immune responses. This study is one of the first to demonstrate how the consequences of emerging infections extend beyond direct effects on host health, potentially altering the dynamics and fitness effects of infectious diseases that had previously existed in the ecosystem on free-ranging wildlife populations.     

Hematologic and biochemical values for Spanish ibex (Capra pyrenaica) captured via drive-net and box-trap

Between October 2002 and September 2004, 70 free-ranging Spanish ibex (Capra pyrenaica) were captured in Catalonia, northeastern Spain, using two different physical methods, drive-net (n=26) and box-trap (n=44). Blood samples were taken to determine 20 hematologic and 23 biochemical variables. Values obtained fell within already published reference intervals, with the following exceptions: higher values for red blood cells (RBC), packed cell volume (PCV), white blood cells (WBC), eosinophil count, triglyceride concentration, creatine kinase (CK; in box-trap), chloride, sodium, alpha-1, alpha-2, and gamma electrophoretic fractions of serum proteins; and lower values for hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), urea concentration, CK (in drive-net), albumin, and albumin:globulins ratio (A:G). Published values for aspartate aminotransferase (AST) concentration are both higher and lower than observed in this study. In our study, monocyte and eosinophil counts, as well as triglyceride and potassium concentrations, were lower in animals captured via box-trap than those captured via drive-net. Conversely, MCHC, neutrophil count, total bilirubin concentration, urea, and AST were higher in animals captured via box-trap. Hematologic and biochemical values obtained from Spanish ibexes show that the drive-net is a newer, less-stressful method of capture than the box-trap.     

Dilution effect in bovine tuberculosis: risk factors for regional disease occurrence in Africa

Changes in host diversity have been postulated to influence the risk of infectious diseases, including both dilution and amplification effects. The dilution effect refers to a negative relationship between biodiversity and disease risk, whereas the amplification effect occurs when biodiversity increases disease risk. We tested these effects with an influential disease, bovine tuberculosis (BTB), which is widespread in many countries, causing severe economic losses. Based on the BTB outbreak data in cattle from 2005 to 2010, we also tested, using generalized linear mixed models, which other factors were associated with the regional BTB presence in cattle in Africa. The interdependencies of predictors and their correlations with BTB presence were examined using path analysis. Our results suggested a dilution effect, where increased mammal species richness was associated with reduced probability of BTB presence after adjustment for cattle density. In addition, our results also suggested that areas with BTB infection in the preceding year, higher cattle density and larger percentage of area occupied by African buffalo were more likely to report BTB outbreaks. Climatic variables only indirectly influenced the risk of BTB presence through their effects on cattle density and wildlife distribution. Since most studies investigating the role of wildlife species on BTB transmission only involve single-species analysis, more efforts are needed to better understand the effect of the structure of wildlife communities on BTB dynamics.     

Prevalence of bovine tuberculosis in African buffalo at Kruger National Park

Bovine tuberculosis (BTB) was first detected in Kruger National Park (KNP) in a single African buffalo (Syncerus caffer) in 1990. In 1991/1992, 2,071 African buffalo were examined for BTB as part of a culling program that removed animals from all known herds in KNP. The prevalence of BTB in 1991/1992 was estimated to be 0%, 4.4% (+/-0.6%), and 27.1% (+/-1.4%), in the north, central, and south zones of KNP, respectively. In 1998, a stratified, two-stage cluster sampling method was used to estimate that the prevalence of BTB was 1.5% (+/-2.5%), 16% (+/-5.3%), and 38.2% (+/-6.3%), in the north, central, and south zones, respectively. This represented a significant increase in prevalence (P < or = 0.05) in the south and central zones, but not in the north zone. Continued monitoring of BTB in KNP is important for understanding disease transmission risks, potential population effects, and the efficacy of disease management strategies. The methodology and sample sizes used in 1998 are appropriate for future BTB monitoring in KNP.     

Effects of Chemical Immobilization on Survival of African Buffalo in the Kruger National Park

ABSTRACT Capturing, immobilizing, and fitting radiocollars are common practices in studies of large mammals, but success is based on the assumptions that captured animals are representative of the rest of the population and that the capture procedure has negligible effects. We estimated effects of chemical immobilization on mortality rates of African buffalo (Syncerus caffer) in the Kruger National Park, South Africa. We used a Cox proportional hazards approach to test for differences in mortality among age, sex, and capture classes of repeatedly captured radiocollared buffalo. Capture variables did not improve model fit and the Cox regression did not indicate increased risk of death for captured individuals up to 90 days postcapture [exp (β) = 1.07]. Estimated confidence intervals, however, span from a halving to a doubling of the mortality rate (95% CI = 0.56–2.02). Therefore, capture did not influence survival of captured individuals using data on 875 captures over a 5-year period. Consequently, long-term research projects on African buffalo involving immobilization, such as associated with research on bovine tuberculosis, should result in minimal capture mortality, but monitoring of possible effects should continue.     

Evaluation of the association of parasitism with mortality of wild European rabbits Oryctolagus cuniculus (L.) in southwestern Australia

Abundances of the parasitic nematodes Trichostrongylus retortaeformis and Passalurus ambiguus, and 8 Eimeria species were estimated by fecal egg and oocyst output in 12 discrete free-ranging populations of wild rabbits (Oryctolagus cuniculus) in southwestern Australia. Comparisons of parasite egg and oocyst counts were made between those rabbits known to have survived at least 2 mo after fecal samples were collected and those rabbits that did not survive. There were significant negative relationships between parasite egg and oocyst counts and survival when all age groups and collection periods were pooled for several species of coccidia and for T. retortaeformis. However, when the same comparisons were made within rabbit age groups and within collection periods, there were very few significant differences even where sample sizes were quite large. The differences indicated by the pooled analysis for coccidia were most likely due to an uneven host age distribution with respect to survival, combined with an uneven distribution of the oocyst counts with rabbit age. The result for T. retortaeformis was similarly affected but by a seasonal pattern. Parasitism by nematodes and coccidia did not appear to be an important mortality factor in these rabbit populations, at least at the range of host densities we examined. This suggests that other factors must have been responsible for the observed pattern of density-dependent regulation in these rabbits.     

A recombinant Mycobacterium smegmatis induces potent bactericidal immunity against Mycobacterium tuberculosis

We report the involvement of an evolutionarily conserved set of mycobacterial genes, the esx-3 region, in evasion of bacterial killing by innate immunity. Whereas high-dose intravenous infections of mice with the rapidly growing mycobacterial species Mycobacterium smegmatis bearing an intact esx-3 locus were rapidly lethal, infection with an M. smegmatis Δesx-3 mutant (here designated as the IKE strain) was controlled and cleared by a MyD88-dependent bactericidal immune response. Introduction of the orthologous Mycobacterium tuberculosis esx-3 genes into the IKE strain resulted in a strain, designated IKEPLUS, that remained susceptible to innate immune killing and was highly attenuated in mice but had a marked ability to stimulate bactericidal immunity against challenge with virulent M. tuberculosis. Analysis of these adaptive immune responses indicated that the highly protective bactericidal immunity elicited by IKEPLUS was dependent on CD4(+) memory T cells and involved a distinct shift in the pattern of cytokine responses by CD4(+) cells. Our results establish a role for the esx-3 locus in promoting mycobacterial virulence and also identify the IKE strain as a potentially powerful candidate vaccine vector for eliciting protective immunity to M. tuberculosis.     

Relationship between pace of life and immune responses in wild rodents

Life histories of animals tend to vary along a slow to fast continuum. Those with fast life histories have shorter life spans, faster development, and higher reproductive rates relative to animals with slower life histories. These differences in life histories have been linked to differences in investment in immunological defenses. Animals with faster life histories are predicted to invest relatively more in innate immune responses, which include rapidly‐deployed, non‐specific defenses against a broad spectrum of invaders. On the other hand, animals with slower life histories are predicted to invest relatively more in adaptive immune responses, which are more slowly‐deployed and are highly pathogen‐specific. These predictions have been confirmed in some taxa, but other studies have not found this association. We tested this prediction by measuring innate and adaptive immunity of white‐footed mice Peromyscus leucopus, chipmunks Tamias striatus, and gray squirrels Sciurus carolinensis, three species of rodents that inhabit deciduous forests in the northeastern US. These species exhibit a range of life histories, with mice having a relatively fast life history, squirrels a relatively slow one, and chipmunks an intermediate one. We found mice to have the greatest ‘bacterial killing capacity’, a common measure of innate immunity, and squirrels the lowest, consistent with the pace‐of‐life immune‐defense hypothesis. We also found squirrels to mount the most pronounced antibody response when challenged with lipopolysaccharide (LPS), an immunogenic component of bacteria, while mice had the lowest, again consistent with predictions based on their life histories. These results have implications beyond ecoimmunology because the probability that a host species will transmit an infection – its ‘reservoir competence’ – has been linked to its immune strategy. Understanding the relationship between immunology and reservoir competence is a critical frontier in the ecology of infectious diseases.     

Hematology and serum chemistry values in captive and wild pichis, Zaedyus pichiy (Mammalia, Dasypodidae)

As part of an ongoing study on the health status of pichis, Zaedyus pichiy (Mammalia, Dasypodidae), blood was collected under manual restraint from 72 free-ranging pichis captured in Mendoza Province, Argentina, between November 2001 and December 2006, and from 22 captive-kept pichis in January 2007. Reference values were established for hematology and serum chemistry. Pichis had lower leukocyte counts and higher mean corpuscular volumes than most other mammals. Blood values were similar for captive and wild pichis, and only a few significant differences were found among genders or age classes.     

NOD2-deficient mice have impaired resistance to Mycobacterium tuberculosis infection through defective innate and adaptive immunity

NOD2/CARD15 mediates innate immune responses to mycobacterial infection. However, its role in the regulation of adaptive immunity has remained unknown. In this study, we examined host defense, T cell responses, and tissue pathology in two models of pulmonary mycobacterial infection, using wild-type and Nod2-deficient mice. During the early phase of aerosol infection with Mycobacterium tuberculosis, Nod2(-/-) mice had similar bacterial counts but reduced inflammatory response on histopathology at 4 and 8 wk postchallenge compared with wild-type animals. These findings were confirmed upon intratracheal infection of mice with attenuated Mycobacterium bovis bacillus Calmette-Guérin. Analysis of the lungs 4 wk after bacillus Calmette-Guérin infection demonstrated that Nod2(-/-) mice had decreased production of type 1 cytokines and reduced recruitment of CD8(+) and CD4(+) T cells. Ag-specific T cell responses in both the spleens and thoracic lymph nodes were diminished in Nod2(-/-) mice, indicating impaired adaptive antimycobacterial immunity. The immune regulatory role of NOD2 was not restricted to the lung since Nod2 disruption also led to reduced type 1 T cell activation following i.m. bacillus Calmette-Guérin infection. To determine the importance of diminished innate and adaptive immunity, we measured bacterial burden 6 mo after aerosol infection with M. tuberculosis and followed a second infected group for assessment of survival. Nod2(-/-) mice had a higher bacterial burden in the lungs 6 mo after infection and succumbed sooner than did wild-type controls. Taken together, these data indicate that NOD2 mediates resistance to mycobacterial infection via both innate and adaptive immunity.     

Observations on the epidemiology and interactions between myxomatosis, coccidiosis and helminth parasites in a wild rabbit population in Scotland

A study of the epidemiology of myxomatosis and the protozoan liver parasite, Eimeria stiedae, in a population of wild rabbits in Scotland from 1977 to 2010 is reported. Rabbits were collected on a monthly basis resulting in a total of 5,337 animals examined for the infections. The investigation showed that within any 1 year over the 34 years of the investigation the percentage of rabbits with myxomatosis varied between 0 and 24 %, while for E. stiedae infections fluctuated between 3 and 42 %. There were strong seasonal trends in the prevalence of myxomatosis with over 16 % being infected in September and October, and for E. stiedae, peaks of over 40 % of livers infected were recorded in July. From 2007 to 2010, faeces were also examined for coccidia oocysts and parasitic nematode eggs. Rabbits infected with the myxoma virus had mean oocyst counts of 73,665 per gram faeces, while rabbits not infected with the myxoma virus had counts of 31,952 oocysts per gram. Comparable figures for nematode faecal egg counts were 911 per gram in myxomatosis-infected animals and 427 per gram in uninfected animals. The elevated nematode faecal egg counts in rabbits with myxomatosis reflects increased worm burdens already reported, but the elevated counts of coccidial oocysts have not previously been reported. This would suggest that myxomatosis could compromise rabbit immunity to nematodes and coccidia.     

结核分枝杆菌与巨噬细胞相互作用的研究进展

结核分枝杆菌（Mycobacterium tuberculosis,MTB）是一种典型的胞内致病菌,巨噬细胞是MTB在体内的主要宿主细胞。巨噬细胞具有强大的吞噬功能,在机体固有免疫和适应性免疫中均发挥着重要作用,可有效保护宿主免受结核分枝杆菌的感染。MTB在与宿主巨噬细胞的长期相互作用过程中,逐渐形成多种逃避杀灭的有效策略,得以在宿主体内存活并增殖。该文从巨噬细胞抗MTB感染及MTB逃避巨噬细胞杀灭两个方面综述国内外的研究进展。     

Progression of pulmonary tuberculosis and efficiency of bacillus Calmette-Guérin vaccination are genetically controlled via a common sst1-mediated mechanism of innate immunity

Using a mouse model for genetic analysis of host resistance to virulent Mycobacterium tuberculosis, we have identified a genetic locus sst1 on mouse chromosome 1, which controls progression of pulmonary tuberculosis. In vitro, this locus had an effect on macrophage-mediated control of two intracellular bacterial pathogens, M. tuberculosis and Listeria monocytogenes. In this report, we investigated a specific function of the sst1 locus in antituberculosis immunity in vivo, especially its role in control of pulmonary tuberculosis. We found that the sst1 locus affected neither activation of Th1 cytokine-producing T lymphocytes, nor their migration to the lungs, but rather controlled an inducible NO synthase-independent mechanism of innate immunity. Although the sst1(S) macrophages responded to stimulation with IFN-gamma in vitro, their responsiveness to activation by T cells was impaired. Boosting T cell-mediated immunity by live attenuated vaccine Mycobacterium bovis bacillus Calmette-Guérin or the adoptive transfer of mycobacteria-activated CD4(+) T lymphocytes had positive systemic effect, but failed to improve control of tuberculosis infection specifically in the lungs of the sst1(S) animals. Thus, in the mouse model of tuberculosis, a common genetic mechanism of innate immunity mediated control of tuberculosis progression in the lungs and the efficiency of antituberculosis vaccine. Our data suggest that in immunocompetent humans the development of pulmonary tuberculosis and the failure of the existing vaccine to protect against it, in some cases, may be explained by a similar defect in a conserved inducible NO synthase-independent mechanism of innate immunity, either inherited or acquired.     

Diversity,Antimicrobial Action and Structure-Activity Relationship of Buffalo Cathelicidins

Cathelicidins are an ancient class of antimicrobial peptides (AMPs) with broad spectrum bactericidal activities. In this study, we investigated the diversity and biological activity of cathelicidins of buffalo, a species known for its disease resistance. A series of new homologs of cathelicidin4 (CATHL4), which were structurally diverse in their antimicrobial domain, was identified in buffalo. AMPs of newly identified buffalo CATHL4s (buCATHL4s) displayed potent antimicrobial activity against selected Gram positive (G+) and Gram negative (G-) bacteria. These peptides were prompt to disrupt the membrane integrity of bacteria and induced specific changes such as blebing, budding, and pore like structure formation on bacterial membrane. The peptides assumed different secondary structure conformations in aqueous and membrane-mimicking environments. Simulation studies suggested that the amphipathic design of buCATHL4 was crucial for water permeation following membrane disruption. A great diversity, broad-spectrum antimicrobial action, and ability to induce an inflammatory response indicated the pleiotropic role of cathelicidins in innate immunity of buffalo. This study suggests short buffalo cathelicidin peptides with potent bactericidal properties and low cytotoxicity have potential translational applications for the development of novel antibiotics and antimicrobial peptidomimetics.     

Innate and acquired resistance to African trypanosomiasis

The review discusses the current field status of human and bovine trypanosomiases, and focuses on the molecular basis of innate and acquired control of African trypanosomes in people, cattle, and Cape buffalo.     

Peptidoglycan recognition proteins: pleiotropic sensors and effectors of antimicrobial defences

Peptidoglycan recognition proteins (PGRPs) are innate immunity molecules that are present in most invertebrate and vertebrate animals. All PGRPs function in antimicrobial defence and are homologous to the prokaryotic peptidoglycan-lytic type 2 amidases. However, only some PGRPs have the catalytic activity that protects the host from excessive inflammation, and most PGRPs have diversified to carry out other host-defence functions. Insect and mammalian PGRPs defend host cells against infection through very different mechanisms. Insect PGRPs activate signal transduction pathways in host cells or trigger proteolytic cascades in the haemolymph, both of which generate antimicrobial effectors. By contrast, mammalian PGRPs are directly bactericidal. Here, we review these contrasting modes of action.     

Bovine tuberculosis: the genetic basis of host susceptibility

The prevalence of bovine tuberculosis (BTB) in the UK remains a significant economic burden and problem for the agri-food industry. Much effort has been directed towards improving diagnostics, finding vaccine candidates and assessing the usefulness of badger culling. The contribution that host genotype makes to disease outcome has, until recently, been overlooked; yet, it is biologically untenable that genetic variation does not play a role. In this review, we highlight the evidence, past and present, for a role of host genetics in determining susceptibility to BTB in livestock. We then address some of the major issues surrounding the design of future studies tasked with finding the exact causative genetic variation underpinning the TB susceptibility phenotype. Finally, we discuss some of the potential future benefits, and problems, that a knowledge of the genetic component to BTB resistance/susceptibility may bring to the agricultural industries and the wider scientific community.     

Acid-base status and blood gas arterial values in free-ranging sika deer hinds immobilized with medetomidine and ketamine

Ten free-ranging female sika deer (Cervus nippon) were captured to obtain the reference values for acid-base status and blood gas when immobilized with the combination of medetomidine and ketamine. The mean +/- SE of PaCO2, PaO2, and HCO3- were 58.1 +/- 6.1 mmHg, 58.8 +/- 6.4 mmHg, and 36.0 +/- 4.4 mmol/l, respectively. Although acidosis and alkalosis occurred in three and two animals, respectively, no serious conditions were observed. The blood values, however, suggest that some degree of hypoxemia and respiratory acidosis with metabolic alkalosis are developed. The trapped deer showed a significantly higher than normal rectal temperature reflective of exertion.     

Hematologic effects of cytauxzoonosis in Florida panthers and Texas cougars in Florida.

Cytauxzoon felis is a long-recognized hemoparasite of free-ranging Florida panthers (Puma concolor coryi), but its prevalence and effect on the population has not been assessed. Red blood cell indices and white blood cell counts were compared between infected and noninfected Florida panthers and Texas cougars (Puma concolor stanleyana) from 1983-1997 in Florida (USA). The prevalence of cytauxzoonosis for both populations was 39% (11/28) for Texas cougars, 35% for Florida panthers (22/63) and 36% overall. Thirteen hematologic parameters were compared between C. felis positive and negative panthers and cougars. Florida panthers had significantly lower mean cell hemoglobin count (MCHC) and higher white blood cell (WBC), neutrophil, monocyte and eosinophil counts (P < or = 0.05) than Texas cougars. Infected Florida panthers had significantly lower mean cell hemoglobin (MCH) and monocyte counts and higher neutrophil and eosinophil counts than infected Texas cougars. Although statistically significant differences were measured for hematologic parameters in C. felis positive panthers and cougars, biologically significant differences were not likely because values were generally within expected reference ranges for healthy animals. Cytauxzoonosis does not appear to have a negative effect on the hematologic parameters of chronically infected panthers and cougars. Potential transient changes during initial infection were not evaluated.     

The host resistance locus sst1 controls innate immunity to Listeria monocytogenes infection in immunodeficient mice

Epidemiological, clinical, and experimental approaches have convincingly demonstrated that host resistance to infection with intracellular pathogens is significantly influenced by genetic polymorphisms. Using a mouse model of infection with virulent Mycobacterium tuberculosis (MTB), we have previously identified the sst1 locus as a genetic determinant of host resistance to tuberculosis. In this study we demonstrate that susceptibility to another intracellular pathogen, Listeria monocytogenes, is also influenced by the sst1 locus. The contribution of sst1 to anti-listerial immunity is much greater in immunodeficient scid mice, indicating that this locus controls innate immunity and becomes particularly important when adaptive immunity is significantly depressed. Similar to our previous observations using infection with MTB, the resistant allele of sst1 prevents formation of necrotic infectious lesions in vivo. We have shown that macrophages obtained from sst1-resistant congenic mice possess superior ability to kill L. monocytogenes in vitro. The bactericidal effect of sst1 is dependent on IFN-gamma activation and reactive oxygen radical production by activated macrophages after infection, but is independent of NO production. It is possible that there is a single gene that controls common IFN-dependent macrophage function, which is important in the pathogenesis of infections caused by both MTB and L. monocytogenes. However, host resistance to the two pathogens may be controlled by two different polymorphic genes encoded within the sst1 locus. The polymorphic gene(s) encoded within the sst1 locus that controls macrophage interactions with the two intracellular pathogens remains to be elucidated.