Detection and Molecular Characterization of Brucella Spp. in Raw Milk and Serological Evidence of Human Exposure
Author(s):
Saif Mohammed Hamzah
Date: 08/10/2026
doi: https://doi.org/10.5281/zenodo.8425890
Abstract
Background: Brucellosis is a neglected zoonotic disease of major veterinary and public health concern
in Iraq. Consumption of raw milk and occupational exposure remain key transmission routes. This study
investigated the occurrence of Brucella spp. in raw milk from cattle, sheep, and goats, and evaluated
serological evidence of human exposure among high-risk individuals. Methods: In total, one hundred fifty
raw samples of milk from cattle, sheep and goats were all tested from both the farm and local markets.
Also, 100 serum samples of humans were tested with 70 from high risk exposed people and 30 from lower
risk control. Milk cultures were done on selective media Brucella agar containing antibiotics and incubated
under 5 to 10% CO2 to facilitate growth of brucella. Gram staining, biochemical testing and PCR
confirmed the presence of brucella by testing for bcsp31 and IS711. Expression levels of host immune
response genes (IFN-γ, TNF-α, IL-6, IL-10) were determined by using RT-qPCR from peripheral blood
leukocytes of ELISA positive and ELISA negative humans. IgG in milk (animals) and IgG in serum
(humans), was tested by indirect ELISA. ROC curves were created for assessing the accuracy of
diagnoses.. Results: Among the 150 analyzed milk samples, 12% (eighteen) tested positive for Brucella
spp. Cattle had a positive rate of 12%, sheep had 8%, while goats had the highest rate of 16%. Of the
eighteen isolates, the PCR results were 94.4% for bcsp31 and 88.9% for IS711. The percentage of high
risk humans who were positive by ELISA was 25.7% (eighteen out of seventy); while 3.3% one out of
thirty were positive among controls. ROC curve analysis demonstrated an excellent ELISA performance
for humans and a good performance for the milk ELISA. Additionally, gene expression analyses indicated
the presence of significantly higher quantities of cytokines (IFN-γ and TNF-α) in the seropositive
individuals' serum compared to seronegative individuals. IL-10 was also elevated, indicating a possible
mixed Th1 and anti-inflammatory regulatory profile due to positive serology.. Conclusion: This study
confirms the circulation of Brucella spp.
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