Protective effect of the Nramp1 BB genotype against Brucella abortus in the water buffalo (Bubalus bubalis)

Characterization of innate immune response to Brucella melitensis infection in goats with permissive or restrictive phenotype for Brucella intramacrophagic growth

Caprine brucellosis is a chronic, world-wide distributed disease which causes reproductive failure in goats and Brucella melitensis, its causative agent, bears a great zoonotic potential. There is evidence suggesting that some cattle and pigs have an innate ability to resist Brucella infection, but this has not yet been investigated in goats. In this study, we compared caprine macrophages that exhibit extreme restriction and permissiveness to B. melitensis' intracellular growth in vitro. Monocyte derived macrophages (MDMs) from 110 female goats were cultured and challenged in vitro with B. melitensis 16 M. After initial screening, 18 donor goats were selected based on their macrophages ability to restrict or allow bacterial intracellular growth and some elements of humoral and cellular immunity were studied in depth. MDMs that were able to restrict the pathogen's intracellular growth showed enhanced bacterial internalization, although there were no differences between groups in the production of reactive oxygen and nitrogen intermediates following 48 h treatment with heat-killed B. melitensis. Moreover, there were no differences between groups in the level of antibodies reacting with keyhole limpet hemocyanin (natural antibodies, NAbs) or with Brucella LPS antigens (cross-reacting antibodies, CrAbs), although a strong positive correlation between individual levels of IgM NAbs and IgM CrAbs was detected. Altogether, these results represent an initial step in understanding innate primary host response to B. melitensis, and deciphering which mechanisms may determine a successful outcome of the infection in goats.

Microsatellite markers reveal polymorphisms at the 3′ untranslated region of the SLC11A1 gene in Zhongdian Yellow cattle (Bos taurus)

Solute carrier family 11-member A1 (SLC11A1) gene encodes natural macrophage resistance-associated protein which regulates activity of macrophages against intracellular pathogens. The objective of this study was to study the polymorphism in the microsatellites present at 3′ untranslated region (UTR) of the SLC11A1 gene in 113 Zhongdian Yellow cattle (Bos taurus). Using DNA bi-directional sequencing, we detected seven alleles (GT10–16) for the first microsatellite (MS1), five alleles (GT12–16) for MS2, and four alleles (GT4–7) for MS3. MS3 is studied for the first time and revealed four novel variants (alleles GT4–7). Alleles GT12 (45.1%), GT13 (59.3%), and GT5 (85.4%) were the most frequent alleles at MS1, MS2, and MS3, respectively, Genotypes G12/12, G13/13, and G5/5 had the highest frequency 0.239, 0.540, and 0.743 at MS1, MS2, and MS3, respectively. Haplotypic data revealed that GT12/GT13 was the most frequent haplotype observed followed by GT12/14 haplotype. Three nucleotide variations were observed in MS1 and MS2. Comparative analysis of GT12/GT12 and GT13/GT13 genotype with other bovine genotypes showed significant difference (P > 0.05). Our results suggest that the homozygous genotypes GT12/GT12 and GT13/GT13 in Zhongdian Yellow cattle might be related to disease resistance. The findings reported in this study would be helpful in cattle breeding programs.

Poly I:C stimulation in-vitro as a marker for an antiviral response in different cell types generated from Buffalo (Bubalus bubalis)

The innate immune system is activated upon virus invasion of a host cell by recognizing viral component, such as dsRNA through specific receptors, resulting in the production of type- I IFNs, which confer an antiviral state within the invaded as well as surrounding cells. In the present study, fibroblast, monocyte and macrophage cells derived from water Buffalo (Bubalus bubalis) were exposed to a synthetic dsRNA analogue, poly I:C to mimic viral invasion in each cell type. Recognition of poly I:C through cytosolic helicase receptors RIG-I and MDA5 molecule lead to the activation of the RLR pathway, subsequently activating the MAVS-IRF3/7 cascade and the production of antiviral effector molecule like IFNβ and ISGs. Within the different cell types, we identified variability in RLR receptor and IFNβ expression after poly I:C administration. Fibroblasts responded quickly and strongly with IFNβ production, followed by macrophages and monocytes. Despite absolute expression variability among different cell types the expression trend of RLRs pathway genes were similar. Length of poly I:C molecule also influence IFNβ expression in response of RLR pathway. Short (LMW) poly I:C induce stronger IFN-β expression in myeloid (macrophage and monocyte) cells. In contrast long (HMW) poly I:C preferably elicit higher IFNβ expression in non-myeloid (fibroblast) cell. Therefore, MDA5 and RIG-1 plays an indispensable role in eliciting antiviral response in non- immune (fibroblast) host cell. Thus, stimulation of RLR pathway with suitable and potentially cell-type specific agonist molecules successfully elicit antiviral state in the host animal, with fibroblasts conferring a stronger antiviral state compared with the monocytes and macrophages.

Genetic epidemiology of the Alpine ibex reservoir of persistent and virulent brucellosis outbreak

While it is now broadly accepted that inter-individual variation in the outcomes of host-pathogen interactions is at least partially genetically controlled, host immunogenetic characteristics are rarely investigated in wildlife epidemiological studies. Furthermore, most immunogenetic studies in the wild focused solely on the major histocompatibility complex (MHC) diversity despite it accounts for only a fraction of the genetic variation in pathogen resistance. Here, we investigated immunogenetic diversity of the Alpine ibex (Capra ibex) population of the Bargy massif, reservoir of a virulent outbreak of brucellosis. We analysed the polymorphism and associations with disease resistance of the MHC Class II Drb gene and several non-MHC genes (Toll-like receptor genes, Slc11A1) involved in the innate immune response to Brucella in domestic ungulates. We found a very low neutral genetic diversity and a unique MHC Drb haplotype in this population founded few decades ago from a small number of individuals. By contrast, other immunity-related genes have maintained polymorphism and some showed significant associations with the brucellosis infection status hence suggesting a predominant role of pathogen-mediated selection in their recent evolutionary trajectory. Our results highlight the need to monitor immunogenetic variation in wildlife epidemiological studies and to look beyond the MHC.

Genetic characterization of ovine herpesvirus 2 strains involved in water buffaloes malignant catarrhal fever outbreaks in Southern Italy

Ovine herpesvirus 2 (OvHV-2) was responsible for two outbreaks of malignant catarrhal fever (MCF) on two water buffalo farms in Southern Italy. In this study, the presence of this virus in the nasal swabs from sick animals as well as in the organs of dead buffaloes was ascertained by a Real-time PCR assay. Positive samples also underwent a relative quantitative analysis of the viral DNA in them. All the dead animals had the highest relative viral quantities, while buffaloes recovering from the virus had intermediate quantities, and asymptomatic OvHV-2-positive sheep had the lowest relative quantities (as compared with the calibrator). The strains involved in the MCF outbreaks underwent genetic characterization by sequencing segments of their ORF50, ORF75 and Ov9.5 genes. The results showed that the outbreaks were caused by two specific genetic variants of OvHV-2, and that these variants exhibit nucleotide differences at the loci analysed. Sheep living in the surrounding farms, as well as sheep kept with buffaloes, were also investigated as possible transmitters of the virus. In this regard, local strategies for the control of MCF should consider separating reservoir species from susceptible animals.

Molecular comparison of Slc11a1 and Slc11a2 genes of swamp- and riverine-type water buffaloes

Solute-linked carrier 11a and 11a2 (Slc) have been associated with disease resistance and/or susceptibility across animal species. These genes have an important mechanism in the regulation against intracellular infection. This study analysed the genetic characteristic of Slc 11a and 11a2 in swamp-type and riverine-type water buffaloes to understand their immunological distinction. Characterization of Slc11a1 and Slc11a2 genes from swamp- and riverine-type water buffaloes was carried out by molecular cloning, sequencing and phylogenetic analysis. The cloned cDNA of Slc11a1 and Slc11a2 contained an open reading frame of 1647 and 1723 nucleotides, encoding 549 and 574 amino acids, respectively. Nucleotide sequence homology of both Slc11a1 and Slc11a2 had 99% in swamp and riverine type, which gives almost identical polypeptide. However, Slc11a1 and Slc11a2 have substitutions of 5 and 1 amino acid residues, correspondingly. These substitutions suggest as a potential gene markers for resistance and/or susceptibility to intracellular infection. Furthermore, phylogenetic analysis confirmed the degree of relationship between the bubaline species and justifies the distinctness of each breed by the bootstrap value generated.

Examining the role of components of Slc11a1 (Nramp1) in the susceptibility of New Zealand sea lions (Phocarctos hookeri) to disease

The New Zealand sea lion (NZSL, Phocarctos hookeri) is a Threatened marine mammal with a restricted distribution and a small, declining, population size. The species is susceptible to bacterial pathogens, having suffered three mass mortality events since 1998. Understanding the genetic factors linked to this susceptibility is important in mitigating population decline. The gene solute carrier family 11 member a1 (Slc11a1) plays an important role in mammalian resistance or susceptibility to a wide range of bacterial pathogens. At present, Slc11a1 has not been characterised in many taxa, and despite its known roles in mediating the effects of infectious disease agents, has not been examined as a candidate gene in susceptibility or resistance in any wild population of conservation concern. Here we examine components of Slc11a1 in NZSLs and identify: i) a polymorphic nucleotide in the promoter region; ii) putative shared transcription factor binding motifs between canids and NZSLs; and iii) a conserved polymorphic microsatellite in the first intron of Slc11a1, which together suggest conservation of Slc11a1 gene structure in otariids. At the promoter polymorphism, we demonstrate a shift away from normal allele frequency distributions and an increased likelihood of death from infectious causes with one allelic variant. While this increased likelihood is not statistically significant, lack of significance is potentially due to the complexity of genetic susceptibility to disease in wild populations. Our preliminary data highlight the potential significance of this gene in disease resistance in wild populations; further exploration of Slc11a1 will aid the understanding of susceptibility to infection in mammalian species of conservation significance.

Identification of single nucleotide polymorphisms in Toll-like receptor candidate genes associated with tuberculosis infection in water buffalo (Bubalus bubalis)

Background

Toll-like receptors play a key role in innate immunity by recognizing pathogens and activating appropriate responses. Pathogens express several signal molecules (pathogen-associated molecular patterns, PAMPs) essential for survival and pathogenicity. Recognition of PAMPs triggers an array of anti-microbial immune responses through the induction of various inflammatory cytokines. The objective of this work was to perform a case-control study to characterize the distribution of polymorphisms in three candidate genes (toll-like receptor 2, toll-like receptor 4, toll-like receptor 9) and to test their role as potential risk factors for tuberculosis infection in water buffalo (Bubalus bubalis).

Results

The case-control study included 184 subjects, 59 of which resulted positive to both intradermal TB test and Mycobacterium bovis isolation (cases) and 125 resulted negative to at least three consecutive intradermal TB tests. The statistical analysis indicated that two polymorphisms exhibited significant differences in allelic frequencies between cases and controls. Indeed, the TT genotype at TLR9 2340 C > T locus resulted significantly associated with susceptibility to bovine tuberculosis (P = 0.030, OR = 3.31, 95% CI = 1.05-10.40). One polymorphism resulted significantly associated with resistance to the disease, and included the CC genotype, at the TLR4 672 A > C locus (P = 0.01, OR = 0.26, 95% CI = 0.08-0.80). Haplotype reconstruction of the TLR2 gene revealed one haplotype (CTTACCAGCGGCCAGTCCC) associated with disease resistance (P = 0.04, OR = 0.51, 95% CI = 0.27–0.96), including the allelic variant associated with disease resistance.

Conclusions

The work describes novel mutations in bubaline TLR2, TLR4 and TLR9 genes and presents their association with M. bovis infection. These results will enhance our ability to determine the risk of developing the disease by improving the knowledge of the immune mechanisms involved in host response to mycobacterial infection, and will allow the creation of multiple layers of disease resistance in herds by selective breeding.

In-vitro indicators of natural resistance and milk-producing ability in dairy buffaloes (Bubalus bubalis)

The aim of this study was to explore the possibility of detecting novel phenotypes of natural resistance at the molecular level through the in-vitro stimulation of monocyte-derived macrophages (MDMs). This study was conducted with 16 healthy buffaloes who were reared for milk production and for whom data on milk-producing ability were available for several lactations. MDMs from circulating monocytes were activated with interferon-gamma and lipopolysaccharide. The response was evaluated using Western blotting to detect the presence of 2 types of proteins separated by electrophoresis: tyrosine-phosphorylated proteins, which are indicators of the dynamic control of biochemical pathways, and IkB-alpha (Kappa light polipeptide gene enhancer in B-cells Inhibitor, alpha) protein, which controls the activity of nuclear factor kappa-light-chain-enhancer of activated B cells—a transcription factor that is responsible for the expression of proinflammatory cytokines. The results showed that the buffaloes who were positive for IkB-alpha proteins had a significantly higher milk-producing ability than the buffaloes who did not express IkB-alpha. On the contrary, no significant difference was detected between the high and low milk-producing buffaloes with regard to the presence of tyrosine-phosphorylated proteins. This preliminary study indicated that it may be possible to identify the more disease-resistant nonhuman animals on a molecular level. The results, therefore, indicate that an intense selection toward the increase of milk yield could impair natural disease resistance in future dairy buffalo generations.

Polymorphism of cytokine and innate immunity genes associated with bovine brucellosis in cattle

Genetic susceptibility to brucellosis is multifactorial, and it is known that impairment of the immune system could contribute to risk for getting brucellosis. The aim of the study was to find association of bovine brucellosis with 20 SNPs pertaining to bovine cytokine (IFNG, IFNGR1, IFNGR2, TNFA) and innate immunity (SLC11A1, TLR1, TLR4, and TLR9) genes using PCR-RFLP genotyping technique and it was observed that SLC11A1 (+1066 C/G), TLR1 (+1446 C/A), TLR1 (+1380 G/A), TLR4 (+10 C/T) and TLR4 (+399 C/T) loci were significantly (P≤0.05) associated with bovine brucellosis. The odds ratios (OR) of CG and CC genotypes versus GG genotype were 0.31 (0.12-0.82; 95% CI) and 0.18 (0.03-1.06; 95% CI) at SLC11A1 (+1066 C/G) locus in cases of brucellosis affected cattle. For TLR1 (+1380 G/A) locus, the OR for AG and AA genotypes versus GG genotypes were 0.15 (0.05-0.44; 95% CI) and 0.26 (0.04-1.47; 95% CI) which indicated that proportion of GG homozygote was significantly higher in brucellosis affected animals as compared to control. At TLR1 (+1446 C/A) locus the OR of AC genotype versus CC genotype was 0.24 (0.08-0.68; 95% CI) which revealed that relative proportion CC genotypes was significantly higher in case population. The TLR4 (+10 C/T) locus had three genotypes (TT, CT and CC) where OR of CT and CC genotypes versus TT genotype were near to zero. The OR of CT genotypes versus CC genotypes was 8.25 (0.94-71.92; 95% CI) at TLR4 (+399 C/T) locus and indicated that CT genotype had higher odds of bovine brucellosis than control animals.

In vitro expression of the SLC11A1 gene in goat monocyte-derived macrophages challenged with Mycobacterium avium subsp paratuberculosis

Johne's disease or paratuberculosis is a chronic, progressive intestinal disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). One of the genes that have been targeted with regard to resistance or sensitivity to paratuberculosis is the SLC11A1 (solute carrier family 11 member A1). Here we extend our previous work to the sequence and structure analysis of the caprine SLC11A1 gene and we assess the functional impact of the most frequent polymorphisms of the 3' UTR region of the SLC11A1 gene to its expression in goat macrophages exposed in vitro to MAP. The role of these polymorphisms in primary immune response is also investigated with connection to gene expression of two interleukins (IL), one of which pro (IL-1a), and the other anti-inflammatory (IL-10). In order to assess gene response, quantitative detection of the SLC11A1, IL-10 and IL1a mRNA was performed by real time PCR before, and at 1, 3 and 24h after exposure of primary cultures of peripheral blood monocyte-derived macrophages to MAP, collected from 54 goats of the Greek native goat breed. Sequence analysis of the 3' UTR end of the caprine SLC11A1 gene determined its full length to be 522 bases. Structure analysis confirmed the presence of two microsatellites consisted of a variable number of guanine-thymine repeats (regions A and B). The homozygous B7 genotype [B(GTn)7/7] was associated at a statistically significant level with increased expression of the SLC11A1 and IL-1α genes indicating increased in vitro responsiveness and therefore resistance of mononuclear derived macrophages to MAP infection.

Microsatellite (GT)n polymorphism at 3'UTR of SLC11A1 influences the expression of brucella LPS induced MCP1 mRNA in buffalo peripheral blood mononuclear cells

A (GT)n microsatellite polymorphism at 3'UTR of SLC11A1(solute carrier family 11A1) is associated with the natural resistance to bovine brucellosis. A pleiotropic effect of SLC11A1 on other candidate genes influencing the host resistance including monocyte chemotactic/chemoattractant protein 1 (MCP1) is also hypothesized. In the present study, we report the cloning and characterization of the complete coding sequence of bubaline (bu) MCP1 and its tissue distribution at the transcript level. The buMCP1 exhibited as high as 99% and >80% of sequence identities with the bovine and other domestic animal species homologues. The buMCP1 mRNA was abundant across the different tissues: most abundant in liver and mammary gland, moderate in ovary, skeletal muscle and testis, and least in uterus. Further, quantitative real-time PCR (RTqPCR) analysis revealed that PBMCs carrying so called resistant GT13 allele produced more MCP1 mRNA endogenously as well as when induced with brucella LPS suggesting the pleiotropic roles of SLC11A1 in conferring resistance against the intracellular pathogens particularly against brucellosis. However, the underlying molecular mechanisms by which 3'UTR SLC11A1 concomitantly increases the production of chemokines like MCP1 are yet to be investigated.

Genetic analysis of the 3' untranslated region of the bovine SLC11A1 gene reveals novel polymorphisms

Polymorphisms in microsatellites at the 3' untranslated region (3'UTR) of the SLC11A1 (solute carrier family 11 member A1) gene have been associated with natural resistance to Brucella abortus and Mycobacterium bovis infection in livestock species. Here, we carried out an individual genetic analysis of the two microsatellites present at the 3'UTR SLC11A1 gene in 254 Bos taurus purebred, 125 B. indicus purebred and 54 B. taurus × B. indicus crossbred cattle. The genotyping by capillary electrophoresis showed the presence of four alleles (157, 159, 161 and 163) for the first microsatellite (MS1) and six alleles (175, 177, 179, 181, 183 and 185) for the second microsatellite (MS2). The alleles 159 and 175 were the most frequent in all breeds analyzed. B. taurus showed the most homogeneous haplotype and genotype for both microsatellites, whereas B. indicus showed the most heterogeneous haplotype and genotype. Two novel variants (alleles 161 and 163) within the MS1 are reported as well as novel variants in MS2 in Holstein breed. The knowledge of the polymorphisms distribution in both microsatellites at the 3'UTR of the SLC11A1 gene in cattle breeds is useful for future experimental design to evaluate the association between reported genotypes and natural resistance to pathogens infection.

Effect of polymorphisms in the Slc11a1 coding region on resistance to brucellosis by macrophages in vitro and after challenge in two Bos breeds (Blanco Orejinegro and Zebu)

The resistance/susceptibility of selected cattle breeds to brucellosis was evaluated in an F1 population generated by crossing animals classified as resistant (R) and susceptible (S) (R x R, R x S, S x R, S x S) based on challenges in vitro and in vivo. The association between single nucleotide polymorphisms identified in the coding region of the Slc11a1 gene and resistance/susceptibility was estimated. The trait resistance or susceptibility to brucellosis, evaluated by a challenge in vitro, showed a high heritable component in terms of additive genetic variance (h(2) = 0.54 ± 0.11). In addition, there was a significant association (p < 0.05) between the control of bacterial survival and two polymorphisms (a 3'UTR and SNP4 located in exon 10). The antibody response of animals classified as resistant to infection by Brucella abortus differed significantly (p < 0.05) from that of susceptible animals. However, there was no significant association between single nucleotide polymorphisms located in the Slc11a1 gene and the antibody response stimulated by a challenge in vivo.

Investigation of the association of the SLC11A1 gene with resistance/sensitivity of goats (Capra hircus) to paratuberculosis

SLC11A1 (solute carrier family 11 member A1) protein is located on the phagolysosome membrane of macrophages and participates in bacterial killing. Here we have extended our previous work on the investigation of the potential association of polymorphisms of the 3'untranslated region (UTR) of SLC11A1 gene with test-positivity of goats to Mycobacterium avium subsp. paratuberculosis (MAP). Blood, serum and faeces were collected from 223 adult goats, from nine goat farms from Greece with a long-term record of paratuberculosis but no vaccination or tuberculin testing. The samples were subjected to sequence and structure analysis of the SLC11A1 gene and were evaluated by ELISA, culture and real time polymerase chain reaction. The 3'UTR region of the targeted gene revealed 2 microsatellites consisting of a variable number of guanine-thymine repeats named regions A and B. Statistically significant association was recorded between genotypes of region B and ELISA results, whereas the presence of B(7) allele was found to contribute to ELISA negativity. The comparison of the SLC11A1 mRNA level pre- and post-exposure to MAP shows elevated gene expression especially at the 3-h time point, in all macrophages tested regardless of their genotype. Unfortunately the latter could not be linked at a statistically significant level with any of the targeted genetic polymorphisms separately. In conclusion it can be stated that the evidence reported here provide the first indications on the association of B genotypes of the SLC11A1 gene and the detection of MAP-specific antibody by ELISA in goats.

The manganese transporter MntH is a critical virulence determinant for Brucella abortus 2308 in experimentally infected mice

The gene designated BAB1_1460 in the Brucella abortus 2308 genome sequence is predicted to encode the manganese transporter MntH. Phenotypic analysis of an isogenic mntH mutant indicates that MntH is the sole high-affinity manganese transporter in this bacterium but that MntH does not play a detectable role in the transport of Fe(2+), Zn(2+), Co(2+), or Ni(2+). Consistent with the apparent selectivity of the corresponding gene product, the expression of the mntH gene in B. abortus 2308 is repressed by Mn(2+), but not Fe(2+), and this Mn-responsive expression is mediated by a Mur-like repressor. The B. abortus mntH mutant MWV15 exhibits increased susceptibility to oxidative killing in vitro compared to strain 2308, and a comparative analysis of the superoxide dismutase activities present in these two strains indicates that the parental strain requires MntH in order to make wild-type levels of its manganese superoxide dismutase SodA. The B. abortus mntH mutant also exhibits extreme attenuation in both cultured murine macrophages and experimentally infected C57BL/6 mice. These experimental findings indicate that Mn(2+) transport mediated by MntH plays an important role in the physiology of B. abortus 2308, particularly during its intracellular survival and replication in the host.

Genomic expression profiling of peripheral blood leukocytes of pigs infected with highly virulent classical swine fever virus strain Shimen

Classical swine fever (CSF), caused by a virus of the same name (CSFV), is a highly contagious swine pyrexic disease featuring extensive haemorrhagic lesions and leukopenia, but little is known about the molecular mechanisms of its pathogenesis. To gain insight into the interaction between the virus and host cells, microarray analyses were performed to detect alterations in genomic expression of pig peripheral blood leukocytes (PBLs) following CSFV infection. Three healthy pigs were inoculated with a lethal dose of highly virulent CSFV strain Shimen. PBLs were isolated at the onset of typical clinical signs and total RNA was subjected to microarray analyses with Affymetrix Porcine Genome Array GeneChips. Of all 20 201 pig genes arrayed in the chip, 1745 showed altered expression (up- or downregulation) after infection. These were classified into eight functional groups, relating to cell proliferation (3.6 %), immune response (2.1 %), apoptosis (1.4 %), kinase activity (1.4 %), signal transduction (1.4 %), transcription (0.7 %), receptor activity (0.7 %) and cytokines/chemokines (0.4 %). The remaining 88.3 % of genes had unknown functions. Alterations in genomic expression were confirmed by real-time RT-PCR of selected cellular genes and Western blotting of annexin 2, a cellular protein relating to virus infection. The observed expression changes of numerous genes involved in immune and inflammatory responses and in the apoptosis process indicate that CSFV has developed sophisticated mechanisms to cause leukopenia in infected pigs. These data provide a basis for exploring the molecular pathogenesis of CSFV infection through an understanding of the interaction between viral and cellular components.

Heterogeneous shedding of Brucella abortus in milk and its effect on the control of animal brucellosis

AIMS

To ascertain whether in Brucella abortus-infected water buffalo herds, the number of newly infected animals could be reduced by culling superspreaders (the animals secreting > or =10(4) CFU per ml of milk).

METHODS AND RESULTS

The number of B. abortus present in the milk (CFU per ml) from 500 water buffaloes was measured by the culture. Each animal was tested three times, at one month intervals. The presence or the absence of B. abortus in each milk sample was confirmed by PCR. A majority of infected animals shed the pathogen at a low level (< or =10(3) CFU ml(-1)). However, a few infected individuals (superspreaders) shed large numbers of B. abortus (> or =10(4) CFU ml(-1)). Quantitative PCR of B. abortus positive milk samples gave comparable results to culture. Culling of the superspreaders was sufficient to arrest the spread of infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

The approach described here can reduce significantly the cost of controlling brucellosis. Culture and quantitative PCR tests identify superspreaders and, compared with the serological tests in use to detect brucellosis, provide also a more accurate estimate of the disease incidence.

SLC11A1 gene polymorphisms are not associated to somatic cell score and milk yield in Chinese Holstein

It has been well established that mutations of the solute carrier family 11 A1 (SLC11A1) gene are responsible for susceptibility to a number of intracellular pathogens. Mastitis is the most common and most costly disease of dairy cattle, commonly caused by bacteria. As SLC11A1 protein is involved in bacterial killing, we assumed SLC11A1 gene as a candidate gene for bovine mastitis resistance. In this study, polymorphisms in the SLC11A1 gene were identified in the Chinese Holstein population. Genotypes were constructed, and their associations with somatic cell score and milk yield were determined. Single-strand conformation polymorphisms and DNA sequencing were used to reveal polymorphisms in SLC11A1 gene. A SNP in coding region and a variation of GT repeats in 3'-untranslated region were detected. The SNP resulted in an amino acid variation of p.P356A in transmembrane 8 of SLC11A1 peptide, which is the most conserved consecutive region. However, no associations were observed between the detected polymorphisms and somatic cell scores and milk yield in the Chinese Holstein population.

Mannose-binding lectin haplotypes influence Brucella abortus infection in the water buffalo (Bubalus bubalis)

A case-control study established that the haplotype pair HYA/HYA at the MBL (mannose binding lectin) locus of water buffalo is associated with resistance to Brucella abortus infection (P < 10(-7)) and the haplotype pairs LYD/LYD with susceptibility to the same pathogen (P < 10(-7)). The subjects included in the present study were tested twice-at a 1-month interval-for the presence of anti-B. abortus antibodies in the serum by agglutination, complement fixation and flow cytometry. Cases (335 subjects) included animals consistently positive to all these tests; controls (335 subjects) comprised animals exposed yet negative by the same tests. The serum from genetically resistant subjects displayed in vitro significantly higher antibacterial activity compared to the serum from genetically susceptible subjects, lending biological significance to the results from the association study. Inhibition of the antibacterial activity following heat treatment of the serum, addition of specific MBL inhibitors (EDTA, mannose, N-acetyl-D: -glucosamine) or anti-human MBL antiserum provide convincing evidence that the antibacterial activity present in the serum results from the interaction between MBL and B. abortus. A replication study (comprising 100 cases and 100 controls) confirmed the results from the original study.

NRAMP1 3' untranslated region polymorphisms are not associated with natural resistance to Brucella abortus in cattle

The NRAMP1 gene encodes a divalent cation transporter, located in the phagolysosomal membrane of macrophages, that has been associated with resistance to intracellular pathogens. In cattle, natural resistance against brucellosis has been associated with polymorphisms at the 3' untranslated region (3'UTR) of the NRAMP1 gene, which are detectable by single-strand conformational analysis (SSCA). This study aimed to evaluate the association between NRAMP1 3'UTR polymorphisms and resistance against bovine brucellosis in experimental and natural infections. In experimentally infected pregnant cows, abortion occurred in 42.1% of cows with a resistant genotype (SSCA(r); n = 19) and in 43.1% of those with a susceptible genotype (SSCA(s); n = 23). Furthermore, no association between intensity of pathological changes and genotype was detected. In a farm with a very high prevalence of bovine brucellosis, the percentages of strains of the SSCA(r) genotype were 86 and 84% in serologically positive (n = 64) and negative (n = 36) cows, respectively. Therefore, no association was found between the NRAMP1-resistant allele and the resistant phenotype in either experimental or naturally occurring brucellosis. To further support these results, bacterial intracellular survival was assessed in bovine monocyte-derived macrophages from cattle with either the resistant or susceptible genotype. In agreement with our previous results, no difference was observed in the rates of intracellular survival of B. abortus within macrophages from cattle with susceptible or resistant genotypes. Taken together, these results indicate that these polymorphisms at the NRAMP1 3'UTR do not affect resistance against B. abortus in cattle and that they are therefore not suitable markers of natural resistance against bovine brucellosis.