Molecular Epidemiology of <i>Brucella abortus</i> in Northern Ireland—1991 to 2012

<div><p>Background</p><p>Brucellosis is the most common bacterial zoonoses worldwide. Bovine brucellosis caused by <i>Brucella abortus</i> has far reaching animal health and economic impacts at both the local and national levels. Alongside traditional veterinary epidemiology, the use of molecular typing has recently been applied to inform on bacterial population structure and identify epidemiologically-linked cases of infection. Multi-locus variable number tandem repeat VNTR analysis (MLVA) was used to investigate the molecular epidemiology of a well-characterised <i>Brucella abortus</i> epidemic in Northern Ireland involving 387 herds between 1991 and 2012.</p><p>Results</p><p>MLVA identified 98 unique <i>B</i>. <i>abortus</i> genotypes from disclosing isolates in the 387 herds involved in the epidemic. Clustering algorithms revealed the relatedness of many of these genotypes. Combined with epidemiological information on chronology of infection and geographic location, these genotype data helped to identify 7 clonal complexes which underpinned the outbreak over the defined period. Hyper-variability of some VNTR loci both within herds and individual animals led to detection of multiple genotypes associated with single outbreaks. However with dense sampling, these genotypes could still be associated with specific clonal complexes thereby permitting inference of epidemiological links. MLVA- based epidemiological monitoring data were congruent with an independent classical veterinary epidemiology study carried out in the same territory.</p><p>Conclusions</p><p>MLVA is a useful tool in ongoing disease surveillance of <i>B</i>. <i>abortus</i> outbreaks, especially when combined with accurate epidemiological information on disease tracings, geographical clustering of cases and chronology of infection.</p></div

<i>Brucella abortus</i> confirmed herd incidence in Northern Ireland 1991–2012.

<p><a href="http://www.dardni.gov.uk/index/statistics/animal-disease-statistics/statistics-brucellosis.htm" target="_blank">http://www.dardni.gov.uk/index/statistics/animal-disease-statistics/statistics-brucellosis.htm</a></p

Individual and 11 VNTR combined loci discrimination indices (DI) 95% confidence intervals and number of loci observed in study meta population and sub-populations.

<p>* indicates a locus not included in the originally described VNTR21 scheme [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136721#pone.0136721.ref004" target="_blank">4</a>]but taken from the panel described by Le Fleche <i>et al</i> 2006 characterising 80 repetitive loci [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136721#pone.0136721.ref020" target="_blank">20</a>].</p><p>Individual and 11 VNTR combined loci discrimination indices (DI) 95% confidence intervals and number of loci observed in study meta population and sub-populations.</p

Dendrogram of 98 1^st isolate genotypes.

<p>Strain genotype and clonal complex assignation indicated.</p

Clonal complex disclosing isolate frequencies by year of outbreak and geographical location (DARD DVO).

<p>Percentage breakdown of each Clonal Complex by DVO also included.</p

eBurst Minimum Spanning Trees of 98 disclosing isolate MLVA11 genotypes.

<p>Clonal Complex designation based on genotype similarity and epidemiological information indicated. Blue nodes indicate putative founder genotypes for a complete cluster. Yellow nodes indicate putative founders of sub clusters within larger clusters. Node size is related to frequency of observance of a specific genotype. Lines connecting node pairs are indicative of single locus variation.</p

MLVA11 primer sequences.

<p>* indicates a locus not included in the originally described VNTR21 scheme [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136721#pone.0136721.ref004" target="_blank">4</a>]but taken from the panel described by Le Fleche <i>et al</i> 2006 characterising 80 repetitive loci [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136721#pone.0136721.ref020" target="_blank">20</a>].</p><p>MLVA11 primer sequences.</p

Frequencies of all disclosing isolates by assigned strain clonal complex and year of outbreak.

<p>Frequencies of all disclosing isolates by assigned strain clonal complex and year of outbreak.</p