Abstract
Brucellosis, caused by the bacteria of the genus Brucella, is one of the most neglected common zoonotic diseases globally with a public health significance and a high economic loss among the livestock industry worldwide. Since little is known about the distribution of B. abortus in Egypt, a total of 46 B. abortus isolates recovered between 2012–2020, plus one animal isolate from 2006, were analyzed by examining the whole core genome single nucleotide polymorphism (cgSNP) in comparison to the in silico multilocus variable number of tandem repeat analysis (MLVA). Both cgSNP analysis and MLVA revealed three clusters and one isolate only was distantly related to the others. One cluster identified a rather widely distributed outbreak strain which is repeatedly occurring for at least 16 years with marginal deviations in cgSNP analysis. The other cluster of isolates represents a rather newly introduced outbreak strain. A separate cluster comprised RB51 vaccine related strains, isolated from aborted material. The comparison with MLVA data sets from public databases reveals one near relative from Argentina to the oldest outbreak strain and a related strain from Spain to a newly introduced outbreak strain in Egypt. The distantly related isolate matches with a strain from Portugal in the MLVA profile. Based on cgSNP analysis the oldest outbreak strain clusters with strains from the UK. Compared to the in silico analysis of MLVA, cgSNP analysis using WGS data provides a much higher resolution of genotypes and, when correlated to the associated epidemiological metadata, cgSNP analysis allows the differentiation of outbreaks by defining different outbreak strains. In this respect, MLVA data are error-prone and can lead to incorrect interpretations of outbreak events.
Highlights
Brucellosis is a globally distributed zoonotic disease caused by bacteria of the genus Brucella, infecting mammals including humans [1]
Among these isolates from animals, ten isolates were directly recovered from milk, five from fetal abomasal contents, one from fetal liver, one from lung, three from lymph nodes, two from unspecified organs, one from the placenta, one from retropharyngeal lymph nodes, four from spleen, one from stomach contents, one from stomach contents of an aborted fetus, six from supramammary lymph nodes and nine from uterine discharge
Besides the vaccine batches 5842 and 5843 the following isolates were classified as RB51 related strains: 5261, 15646, HEA15, HEA16, HEA23, HEA30 and HEA45
Summary
Brucellosis is a globally distributed zoonotic disease caused by bacteria of the genus Brucella, infecting mammals including humans [1]. Out of 12 species, B. melitensis, B. abortus, and B. suis are considered to be the most important human pathogens with varying. B. melitensis and B. suis except biovar 2, are the most virulent species, whereas B. abortus provokes milder illness [4]. Small ruminants and bovines are the predominant hosts for B. melitensis and B. abortus respectively, while cross species transmission has been proven [5,6]. Humans acquire the disease through contact with infected animals and consumption of their products like unpasteurized milk being the most common source of infection in urban populations [10,11]. In Egypt, B. melitensis biovar 3 is responsible for most human and animal cases, followed by B. abortus biovar 1 [12,13]. The World Health Organization (WHO) and the World Organization for Animal Health (OIE) have recommended strategies and measures to control or even eradicate brucellosis, only several countries in Europe, Canada, Japan, Australia and New Zealand are believed to be free from brucellosis [14]
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