Brucellosis

• Brucellosis is a bacterial zoonotic disease that is caused by various Brucella species, which mainly infect cattle, swine, goats, sheep and dogs, and primarily affects the reproductive system, causing abortion.
• The causative agent of Brucella spp is an aerobic gram-negative bacteria that is small (0.5 to 0.7 by 0.6 to 1.5 µm), nonencapsulated, nonmotile, and facultatively intracellular coccobacilli.
• Brucella species possess a unique ability to invade both phagocytic and nonphagocytic cells.
• Brucella species survive in the intracellular environment by finding ways to avoid the immune system.
• Brucella species are obligate parasites and each species has a preferred natural host which serves as a reservoir of infection.
• Common types of Brucella include Brucella abortus, which is found in cattle, water buffalo, and bison; Brucella melitensis, which is more common in goats and sheep and less common in cattle; Brucella suis, which is occasionally isolated in seropositive cows but does not cause clinical signs or transmission; and Brucella ovis, which is found only in sheep.
• Brucella infection is transmitted via the venereal transmission of infected bulls to susceptible cows, but may also occur via artificial insemination when semen is contaminated with Brucella and is deposited to the uterus, and not when the semen is deposited midcervix.
• Brucella may also enter via the mucous membrane, conjunctivae, wounds, or intact skin in humans and animals.
• Brucella may enter the body via ingestion of organisms which are largely present in aborted fetus, fetal membranes, uterine and amniotic fluids.
• Ingestion of infected feeds or water, licking of contaminated genitals, and other factors can lead to Brucella infection.
• Due to challenges in standardization, the CFT is gradually being substituted by ELISAs (Enzyme-Linked Immunosorbent Assays).
• Treatment for brucellosis in animals is often ineffective because of the bacteria's ability to reside and multiply within cells, making complete eradication difficult.
• Vaccinating calves or heifers is regarded as the most effective method for managing Brucella in regions where the disease is prevalent.
• During slaughter, confirming suspected acute or chronic brucellosis primarily involves examining tissues such as the genital and oropharyngeal lymph nodes, spleen, mammary gland, and associated lymph nodes.
• Disinfecting premises can contribute to prevention since commonly available disinfectants are effective against Brucella organisms.
• Though the test displays excellent specificity, some literature suggests it lacks high sensitivity.
• The process of continuously testing and eliminating any animals that test positive is necessary for eventual eradication.
• To enhance sensitivity in liquid samples such as milk or blood, the utilization of a biphasic medium like the Castaneda medium is employed.
• The Complement Fixation Test (CFT) is utilized to identify anti-Brucella antibodies capable of activating complement.
• Control programs should prioritize the detection of infected herds and prevent the transmission of infection to uninfected herds.
• Routinary brucellosis blood tests are eligible for cow and bulls over 24 months old.
• The Farrell medium is commonly utilized for isolating Brucella spp., as it contains antibiotics capable of inhibiting the growth of other bacteria present in clinical samples.
• Additional serologic assays include enzyme-linked immunoassay, Rivanol precipitation plate agglutination testing, and acidified antigen procedures.
• Brucellosis is a zoonotic disease which displays a strong tissue tropism and replicates within the vacuoles.
• Among cattle immunoglobulins (Ig), both IgG and IgM can trigger bovine complement.
• About 90% of the Brucella-containing vacuoles will be degraded due to the apoptosis by the lysosome, but the remaining 10% will survive as they fused instead.
• The lysosome breakdown worn out cell parts by helping the affected organelles induce apoptosis or programmed cell death.
• Brucella fuses with the lysosome in a controlled manner.
• Brucella attacks the ER thru autophagy as when they fused with the lysosome, the surviving bacteria was able to retain the lysosomal function.
• Brucella replicates in macrophages, dendritic cells, monocytes, trophoblasts, bone cells (osteoclasts, osteoblasts), granulocyte progenitors, adipocytes, and infects other cells such as neutrophils, lymphocytes, and erythrocytes.
• The surviving BCV will head to and reach the endoplasmic reticulum (ER) cellular niches.
• After ER replication, the Brucella traffic toward the autophagy-like vacuoles.
• Brucella first invades the host cells after transmission.
• The phagocyte has been modified by the bacteria into an idiosyncratic (individual) membrane-bound vacuole.
• Initial replication occurs in the regional lymph nodes.
• Most of the time, Brucella occurs in the Rough Endoplasmic Reticulum of chorioallantoic trophoblasts (Placental cells).
• Organs with high replication rates are called Gold Organs (placenta, epididymis, mammary glands, lymph nodes, spleen, liver, lungs, and bone marrow) correlate with clinical manifestations of the disease.
• Brucella-containing vacuoles (BCVs) occur when the bacteria become enclosed within a membrane-bound compartment.
• The membranes of the ER sequester parts of the cytoplasm.
• The incubation period of Brucella may last from 1-4 weeks or in some cases, several months.