Abstract
BackgroundBrucellosis is the most common bacterial zoonoses worldwide. Bovine brucellosis caused by Brucella abortus 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 Brucella abortus epidemic in Northern Ireland involving 387 herds between 1991 and 2012.ResultsMLVA identified 98 unique B. abortus 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.ConclusionsMLVA is a useful tool in ongoing disease surveillance of B. abortus outbreaks, especially when combined with accurate epidemiological information on disease tracings, geographical clustering of cases and chronology of infection.
Highlights
Bovine brucellosis, the most common bacterial zoonoses worldwide [1,2], caused by the bacterium Brucella abortus, is a major public and animal health issue worldwide
Multi-locus variable number tandem repeat variable number of tandem repeat (VNTR) analysis (MLVA) identified 98 unique B. abortus genotypes from disclosing isolates in the 387 herds involved in the epidemic
Hyper-variability of some VNTR loci both within herds and individual animals led to detection of multiple genotypes associated with single outbreaks
Summary
The most common bacterial zoonoses worldwide [1,2], caused by the bacterium Brucella abortus, is a major public and animal health issue worldwide. Further elucidation of the epidemiology of the pathogen has been gained by use of data from the greater Yellowstone area of the western United States where both elk and bison are known wildlife reservoirs In this setting, animal density has been observed to play a crucial role in the likely outcome of a disease outbreak. Animal density has been observed to play a crucial role in the likely outcome of a disease outbreak Both elk and bison populations are at considerably greater risk of developing widespread infection if abortions occur during the winter period when grazing land is scarce leading to higher animal density [9]. Multi-locus variable number tandem repeat VNTR analysis (MLVA) was used to investigate the molecular epidemiology of a well-characterised Brucella abortus epidemic in Northern Ireland involving 387 herds between 1991 and 2012
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