Evolution and genome specialization of Brucella suis biovar 2 Iberian lineages

Seroprevalence study of brucellosis in wild boar hunted for private consumption in northeast Portugal

Brucellosis is an important infectious disease caused by bacteria of the genus Brucella. In the northeast region of Portugal, infection with Brucella melitensis is endemic in small ruminants, and there are also humans' cases. However, the epidemiological role of the wild boar in the dynamics of this disease in this region is unknown. In this study, a total of 332 blood samples were collected from wild boar hunted in thirty-six hunting areas during the 2022/2023 hunting season. All were taken by the hunters for private consumption, with no evisceration or examination in the field. Serum samples were tested by indirect ELISA (i-ELISA). It was observed that 88 wild boars were exposed to Brucella spp., pointing to a seroprevalence of 26.5% (95% CI: 21.8 - 31.3%). This high prevalence underlines the importance that wild boar may have in the dynamics of this disease in the region and its potential transmission to other animals, and to humans (for example, during the handling of carcasses). Increased awareness and knowledge of brucellosis in wild boar is essential for the implementation of effective practices and habits and, consequently, for the control and prevention of this important zoonosis.

Phylogeography of Brucella suis biovar 2 with focus on Slovenian wildlife

Brucella suis commonly infects swine but occasionally also other animal species and humans. Wild boars are the most important reservoir of B. suis biovar 2, continually infecting susceptible hosts through close contact. Nevertheless, the genetic diversity of B. suis in wildlife remains understudied. Here, we typed 17 Slovenian B. suis biovar 2 isolates obtained in 2017-2019 from wild boars (n = 16) and a hare (n = 1) using whole-genome sequencing (WGS). To assess the global phylogenetic diversity of B. suis, we compared them to 126 publicly available B. suis genomes. All Slovenian isolates fell within the biovar 2 lineage, confirming the previous multiplex PCR typing results. According to MLST-21, the wild boar isolates were of sequence types (STs) ST16 (n = 8) and ST153 (n = 8); the maximum genetic distance between isolates of the same ST was 28 wgMLST alleles. The ST153 isolates were restricted to the Slovenian-Croatian border and clustered together with the Croatian ST153 isolates from swine, indicating cross-border transmission of B. suis ST153 strain. The hare isolate was of ST40 and was genetically distant (≥ 489 alleles) from the wild boar isolates. The genome-wide phylogeny clearly separated different B. suis biovars. The present study is the first report on the population structure of B. suis in wildlife in Slovenia and shows that the Slovenian B. suis population is genetically heterogeneous. At the species level, B. suis biovars are clearly separated in the WGS-based phylogenetic tree and can therefore be reliably predicted using WGS.

The first study on seroprevalence and risk factors for zoonotic transmission of ovine and caprine brucellosis in the Province of Bam, Burkina Faso

Background and Aim:

Brucellosis is a bacterial disease notorious for its ability to infect a wide range of domestic and wildlife animals, as well as humans. This study aimed to determine the seroprevalence of ovine and caprine brucellosis and the associated risk factors in the Province of Bam in Burkina Faso.

Materials and Methods:

The individual serological status of 300 unvaccinated sheep and 300 unvaccinated goats was determined by Rose Bengal and indirect enzyme-linked immunosorbent assay (iELISA) serological tests used in parallel. The frequency of behaviors conferring risk of developing this zoonotic disease was determined through two epidemiological questionnaires, which identified known risk factors for the transmission of brucellosis between animals and humans.

Results:

Individual seroprevalence was estimated at 6.0% (18/300) in sheep and 4.3% (13/300) in goats. The “herd” prevalence of brucellosis was estimated at 60% in sheep while 40% in goats. Positivity in the iELISA serological test was significantly associated with age, sex, and husbandry system in sheep and goats.

Conclusion:

These results indicate that Brucella melitensis circulates in sheep and goat farms in the Province of Bam in Burkina Faso. As B. melitensis is highly pathogenic to humans, adequate measures must be taken to protect the population against this zoonotic disease.

Adhesive Functions or Pseudogenization of Type Va Autotransporters in Brucella Species

Adhesion to host cells is a key step for successful infection of many bacterial pathogens and may define tropism to different host tissues. To do so, bacteria display adhesins on their surfaces. Brucella is an intracellular pathogen capable of proliferating in a wide variety of cell types. It has been described that BmaC, a large protein that belongs to the classical (type Va) autotransporter family, is required for efficient adhesion of Brucella suis strain 1330 to epithelial cells and fibronectin. Here we show that B. suis 1330 harbors two other type Va autotransporters (BmaA and BmaB), which, although much smaller, share significant sequence similarities with BmaC and contain the essential domains to mediate proper protein translocation to the bacterial surface. Gain and loss of function studies indicated that BmaA, BmaB, and BmaC contribute, to a greater or lesser degree, to adhesion of B. suis 1330 to different cells such as synovial fibroblasts, osteoblasts, trophoblasts, and polarized epithelial cells as well as to extracellular matrix components. It was previously shown that BmaC localizes to a single bacterial pole. Interestingly, we observed here that, similar to BmaC, the BmaB adhesin is localized mostly at a single cell pole, reinforcing the hypothesis that Brucella displays an adhesive pole. Although Brucella species have strikingly similar genomes, they clearly differ in their host preferences. Mainly, the differences identified between species appear to be at loci encoding surface proteins. A careful in silico analysis of the putative type Va autotransporter orthologues from several Brucella strains showed that the bmaB locus from Brucella abortus and both, the bmaA and bmaC loci from Brucella melitensis are pseudogenes in all strains analyzed. Results reported here evidence that all three autotransporters play a role in the adhesion properties of B. suis 1330. However, Brucella spp. exhibit extensive variations in the repertoire of functional adhesins of the classical autotransporter family that can be displayed on the bacterial surface, making them an interesting target for future studies on host preference and tropism.

Emerging diversity and ongoing expansion of the genus Brucella

Remarkable genetic diversity and breadth of host species has been uncovered in the Brucella genus over the past decade, fundamentally changing our concept of what it means to be a Brucella. From ocean fishes and marine mammals, to pond dwelling amphibians, forest foxes, desert rodents, and cave-dwelling bats, Brucella have revealed a variety of previously unknown niches. Classical microbiological techniques have been able to help us classify many of these new strains but at times have limited our ability to see the true relationships among or within species. The closest relatives of Brucella are soil bacteria and the adaptations of Brucella spp. to live intracellularly suggest that the genus has evolved to live in vertebrate hosts. Several recently discovered species appear to have phenotypes that are intermediate between soil bacteria and core Brucella, suggesting that they may represent ancestral traits that were subsequently lost in the traditional species. Remarkably, the broad relationships among Brucella species using a variety of sequence and fragment-based approaches have been upheld when using comparative genomics with whole genomes. Nonetheless, genomes are required for fine-scale resolution of many of the relationships and for understanding the evolutionary history of the genus. We expect that the coming decades will reveal many more hosts and previously unknown diversity in a wide range of environments.

Complete Genome Sequences of Four Brucella suis Strains Isolated from Swiss Wild Boars

We present the complete genomes of four Brucella suis biovar 2 isolates that were obtained from wild boars in Switzerland in 2008 and 2009. Genomes were sequenced with PacBio technology, contained two chromosomes each, had a genome size of 3.3 Mbp, and contained more than 3,225 genes per genome.

We present the complete genomes of four Brucella suis biovar 2 isolates that were obtained from wild boars in Switzerland in 2008 and 2009. Genomes were sequenced with PacBio technology, contained two chromosomes each, had a genome size of 3.3 Mbp, and contained more than 3,225 genes per genome.

Brucella Genomics: Macro and Micro Evolution

Brucella organisms are responsible for one of the most widespread bacterial zoonoses, named brucellosis. The disease affects several species of animals, including humans. One of the most intriguing aspects of the brucellae is that the various species show a ~97% similarity at the genome level. Still, the distinct Brucella species display different host preferences, zoonotic risk, and virulence. After 133 years of research, there are many aspects of the Brucella biology that remain poorly understood, such as host adaptation and virulence mechanisms. A strategy to understand these characteristics focuses on the relationship between the genomic diversity and host preference of the various Brucella species. Pseudogenization, genome reduction, single nucleotide polymorphism variation, number of tandem repeats, and mobile genetic elements are unveiled markers for host adaptation and virulence. Understanding the mechanisms of genome variability in the Brucella genus is relevant to comprehend the emergence of pathogens.

Phylogeography and epidemiology of Brucella suis biovar 2 in wildlife and domestic swine

Swine brucellosis due to Brucella suis biovar 2 (bv2) is enzootic in wild boar and hare in continental Europe and may cause major economic losses to the pig industry, mainly in free-ranged pig farms. The high nucleotide identity found among the B. suis biovar 2 isolates has long hindered the full understanding of the epidemiology and the phylogeography of the disease. Here, we used multilocus variable-number tandem-repeat (VNTR) analysis (MLVA) and whole-genome analysis to identify single-nucleotide polymorphisms (SNPs) in order to gain insights from the largest B. suis bv2 dataset analyzed so far composed of domestic pigs and wildlife isolates collected throughout Europe since the 1970s. We found four major clades with a specific phylogeographic pattern. The Iberian clade contains isolates exclusively from the Iberian Peninsula. The Central European clade includes most isolates from France, Northern Italy, Switzerland and an important proportion of those of Northern Spain. The Eastern European clade clustered isolates from Croatia and Hungary mainly but also from areas of France, Germany, Italy and Poland. Finally, a separated Sardinian clade grouped three isolates from this island. At fine scale, MLVA demonstrated an endemic status of the infection in Europe and it allowed tracking a large outbreak formed by different farms from Spain linked to the same infection source. The whole genome SNP analysis showed that the strains form genetically distinct clades, shared between wild boar and pigs, in agreement with the MLVA clades. Interestingly, all hare isolates clustered together within two groups composed exclusively of wildlife isolates. Our results support the hypothesis that maintenance and spread of B. suis bv2 in Europe is a dynamic process linked to the natural expansion of wild boar as the main wild reservoir of the infection, while spread over long distances is found largely dependent on anthropogenic activities.

Brucellosis: Evolution and expected comeback

Brucellosis is a serious infectious disease which causes great direct and indirect economic loses for animal holders worldwide such as the reduction of milk and meat production through abortions/culling of positive reactors, the expense of disease control/eradication and farmers compensation. Although the disease was eradicated from most of the industrial countries, it remains one of the most common zoonotic diseases in developing countries being responsible for more than 500,000 new cases yearly. Brucella is considered to be a bioterrorism organism due to its low infectious doses (10-100 bacteria), capability of persistence in the environment, rapid transmission via different routes including aerosols, and finally due to its difficult treatment by antibiotics.There are many reasons to believe that a new comeback of brucellosis may occur in near future. This expectation is supported by the recent discovery of new atypical Brucella species with new genetic properties and the recent reports of (man to man) disease transmission as will be discussed later. The development of new concepts and measurements for disease control is urgently required. In the present review, the evolution of Brucella and the different factors favoring its comeback are discussed.