Molecular detection, seasonality, epidemiology and effect of Brucella melitensis infection on the hematological profile of cattle breeds.

Brucellosis is a bacterial zoonosis caused by various Brucella species, affecting both animals and humans. The incidence is particularly high in tropical and subtropical regions that are known for higher tick density. Present study was designed to improve our knowledge regarding Brucella melitensis infection in Pakistani cattle. A total of 903 blood samples were collected. Three cattle breeds, Holstein Friesian (N = 298), Sahiwal (N = 299), and crossbred (N = 306), were enrolled along with epidemiological data during March 2022 till April 2023 from district Multan in Punjab province. A PCR-based approach targeting IS711 estimated an overall prevalence of 4% (39/903). Representative partial IS711 sequences of three Pakistani isolates revealed a single genotype that was similar to Brucella melitensis sequences reported from aborted fetus in China. All cattle breeds were equally susceptible to this infection. For Sahiwal breed, bacterial infection varied between sampling seasons. Epidemiological factor analysis revealed that farms where only cattle were reared and dogs at farm having tick load had higher Brucella melitensis infection rates. Red blood cells, lymphocyte (%), monocyte (%), mean cell volume, hematocrit, mean corpuscular hemoglobin concentration and platelet count were significantly disturbed in Brucella melitensis positive cattle of all three breeds. A longitudinal survey and phylogenetic positioning of Brucella melitensis is recommended for epidemiological correlation, diagnosis and treatment of brucellosis in Pakistan.