Pathology of the disease
There are four significant types of Brucella species that cause infection. The bacteria type that contains the highest pathogenicity is called Brucella melitensis. It is mostly found in sheep. The second one is called Brucella suis that occurs in pigs. Finally, Brucella abortus and Brucella canis are found in cattle and dogs, respectively. All these species cause either mild or moderate infection, but some cases exaggerate severe infections.
Microbiologically, the organism is a gram-positive coccobacilli that has a unique way of entering both into the phagocytic and nonphagocytic cells of the host organism, meanwhile avoiding any attack from the immune system. Because of the Brucella’s highly invasive nature, the bacteria have the ability to reach the deepest organs in the body and damage them.
Once the bacteria gain entry into the bloodstream, it quickly intrudes the cellular structures. It forms polymorphonuclear cells (PMNs) and macrophages which ultimately suppress the bactericidal actions through the host’s immune system. We know that the immune system has a vigorous action on any foreign particulate entry. It is important to note that the bacteria certainly changes the host organism to avoid the attack from the immune cells. Research conducted within animals shows that lipopolysaccharide coats around the bacteria helps them survive. Also, adenine and guanine monophosphate release prevents oxidative bursting activities within the host body, inhibiting phagocytic activity.
Additionally, the virulence and toxicity of the Brucella species are very low. This generates very low signals for chemotaxis. The inflammatory cells and the cytokines cannot track the bacterial entities, making almost 15%-30% of the total bacteria survive in the body. The remaining bacteria that travel to the lymphatic system start dividing there. The bacteria then also travel towards the kidneys, lungs, spleen, breast tissue, and other organs for further replication.
