Browsing by Subject "SNP-Analyse"

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Untersuchung der spatio-temporalen Verbreitung von Brucellose-Ausbruchsstämmen in Ägypten mittels cgSNP-Analyse und Multi Lokus VNTR-Analyse
(2022) Holzer, Katharina; Beyer, Wolfgang
Brucellosis is a worldwide zoonosis caused by the genus Brucella, which includes 12 species, and it is of great importance for the public health sector. In animals, the disease can lead to abortions, which entails high economic losses. The disease can be transmitted from animals to humans directly by penetrating through mucous membranes and wounds in the skin, or indirectly by consuming unpasteurized milk, milk products made from it, or meat that has not been sufficiently heated. The bacteria can also be transmitted via aerosols, which among other things categorizes these pathogens in risk class three. Contact with infected animals, especially their reproductive organs, aborted fetuses and discharges therefore represent a risk factor. The disease in humans is serious, an antibiotic treatment lasting several weeks is necessary. Although many countries are considered brucellosis-free, African countries, for example, are still badly affected. This work focuses on Brucella from Egypt. Although brucellosis is endemic in Egypt, there is just one publication with very little data about outbreak analysis of the species Brucella (B.) melitensis and B. abortus based on whole genome sequencing. Some other earlier publications are based on the so-called Multiple Locus VNTR analysis (MLVA), which in this present work turned out to be unsuitable for epidemiological analysis or outbreak analysis. VNTR means variable number of sequence repetitions in the DNA. In order to make concrete statements on outbreak analysis, a so-called single nucleotide polymorphism analysis of the core genome (cgSNP analysis) was carried out based on whole genome sequencing. While the MLVA includes highly mutable DNA regions, in the cgSNP analysis they are excluded. Therefore, the cgSNP analysis enables a more precise classification of the genotypes and thus also the classification of the outbreak strains, while the MLVA can just be used for the differentiation of isolates due to the use of highly mutable sequence regions. This became clear through the direct comparison of both methods including the metadata, so that previously published data that described the outbreak analysis for Brucella using the MLVA cannot be used. Over and above that in contrast to an in silico MLVA based on genome sequencing, a laboratory-based MLVA is prone to errors. In a direct comparison, the in silico MLVA showed reliable results in 100% of the cases and should therefore replace the laboratory-based MLVA. For the cgSNP analysis a total of 185 isolates from animals and humans were available. Out of a total of 185 samples, 137 were classified as B. melitensis and 49 as B. abortus, suggesting that B. melitensis infections are more common than B. abortus infections in Egypt. Furthermore, conserved outbreak strains in Egypt, detected by the cgSNP analysis and genetically differing only minimally, have persisted for several years and have spread or are still spreading, as well as constantly newly introduced outbreak strains or infections. Among the B. abortus isolates, B. abortus RB51 vaccine strains from aborted animals could be detected, confirming that the RB51 vaccine strain also causes abortions. While most B. melitensis strains are assigned to West Mediterranean origin, one isolate each is assigned to American and East Mediterranean origin. Such a classification by a so-called canonical SNP assay (canSNP assay), as was carried out for the B. melitensis isolates, is not possible for B. abortus for methodological reasons. A further cgSNP analysis was used to check existing public database entries from other countries for possible sources of introduction of the detected Egyptian outbreak strains. Italian origin is likely for most B. melitensis isolates, while UK origin is likely for a certain group of B. abortus isolates. The remaining B. abortus isolates could not be assigned unequivocally, but would possibly be close to the isolates from the USA. In order to confirm or refute possible relatives, much more isolates from different regions are necessary for a comparison. Due to the large number of different outbreak strains in Egypt, the origin of these outbreak strains should be outside the country, so that importations can be assumed.