English abstract
Background: Given the zoonotic nature of brucellosis, identification of sources of the infection
and tracking of transmission paths are crucial for epidemiologic surveillance. The aim of this study
was to determine the genetic diversity of Brucella species circulating in livestock in Oman and
their geographical relatedness. This study also determined the prevalence of Brucella infection in
Al Dakhiliyah Governorate following an outbreak in both livestock and human.
Results: For genotyping study, nine Brucella melitensis strains were subjected to Multi Locus
Variable Number Tandem Repeat Analysis (MLVA-9). Clustering analysis indicated the presence
of nine different genotypes, thus showing the high genetic diversity of Brucella strains circulating
in Oman. Clustering analysis using UPGMA grouped two Brucella isolates into a clade with 90%
similarity specifically samples 2 and 5D from sheep and goat, respectively, were grouped into this
clade. The phylogeographic patterns of nine Brucella isolates were compared to 1,616 MLVA
profiles from the international database. Minimum spanning tree (MST) showed that five isolates
(samples 18, 5, 5D, 2, 3) are related to a big cluster including isolates from Germany, Greece, Iraq,
Syria, Spain, Turkey, France, China and Kazakhstan. Within this cluster, sample 18 shares
complete MLVA profile identity with these foreign isolates while the other samples differ in one
or two markers. The remaining isolates are spread across phylogenetic relationship with isolates
from Turkey, United Arab Emirates, China, France, Kazakhstan, Spain (sample POS); Greece,
Lebanon, Saudi Arabia, Spain, Kazakhstan, China (Sample 57); Greece, Israel, Portugal, Turkey,
China (sample 1); Portugal, Spain, Turkey (sample 4). For the prevalence study, 148 samples from
sheep and goats were subjected to three different diagnostic tests, namely Rose Bengal test (RBT),
Indirect-Enzyme-linked immunosorbent assay (I-ELISA), and polymerase-chain reaction (PCR).
PCR detected 64.2% (95/148) samples, followed by I-ELISA 7.4%, and RBT 0.7%.Statistical
analysis was used to determine risk factors (such as species, sex, age, and geographical location)
to Brucella infection. Goats were 87.8% (130/148) positive compared to only 12.2% in sheep
(18/148). Between sexes, females were 85.8% (127/148) positive versus 14.2% (21/148) for males.
As for age, animals over two years were 76% (51.4/148) positive compared to 48.6% (72/148) for
those under 2 years. Latitude was incorporated into this test as an external factor where animals
V
located in the highland areas were 64.2% (95/148) positive while those located in the lowland
areas were not as high, being just 35.8% (53/148).
Conclusion: The present study is the first to establish and relate Brucella strains in Oman to those
from the international database. Similar genetic profile of Brucella melitenesis were found in
animals from different species, farms and regions. Comparison between the performance of RBT
and I-ELISA tests revealed that both must be used for accurate results regarding Brucellosis
prevalence, whereas PCR proved to be the best detection method used in the study because its
more specific in detecting Brucella DNA.
