Brucella and Yersinia Overview

Overview of Brucella and Yersinia

• These are significant bacterial pathogens classified as zoonotic diseases
• Brucella causes brucellosis (undulant fever)
• Yersinia species cause plague and other serious conditions
• Knowledge of these pathogens is vital for medical professionals

General Features of Brucella

• Brucella is a facultative intracellular pathogen that can survive and reproduce inside host cells
• It is Gram-negative aerobic coccobacilli
• Brucella are non-motile, non-capsulated, and non-spore forming
• Brucellosis is also known as Malta fever, undulant fever, or Mediterranean fever
• Transmitted from animals to humans under normal conditions

Brucella Species

• B. melitensis primarily infects goats and sheep
• It is the most virulent species for humans resulting in severe brucellosis
• B. abortus mainly infects cattle causing abortion in infected animals
• It can be transmitted to humans via unpasteurized dairy products
• B. suis primarily infects pigs and can cause chronic infections with localized tissue damage in humans
• B. canis causes abortion in cattle and can infect dogs and less commonly infects humans

Brucella Pathogenesis in Animals

• Bacteremia occurs as organisms circulate in the blood
• Placental infection occurs with Brucella settling in the placenta, which contains erythritol, a growth factor
• Placentitis is an infection, causing inflammation of the placenta
• Can lead to abortion

Brucella in Humans vs. Animals

• In animals, brucella causes abortion
• This is due to erythritol in the animal placenta
• The organism settles in the mammary gland and is secreted in milk, creating a transmission route to humans and other animals
• Infected animals show signs of reproductive failure, decreased milk production, and weight loss
• Brucella does not cause abortion in humans because the human placenta does not contain erythritol
• Instead, human infection typically manifests as undulant fever with fluctuating temperature patterns, fatigue, headache, and joint pain
• Chronic infections can lead to complications affecting various organ systems

Brucella Transmission Modes

• Ingestion occurs due to the consumption of unpasteurized milk products like cheese, yogurt, and raw milk
• Inhalation occurs due to breathing in aerosolized particles containing Brucella
• Laboratory-acquired infection is a significant source of transmission
• Veterinarians and slaughterhouse workers are at high risk
• Mucous membranes can be infected by accidental inoculation via aerosolization: eye splashes, or mouth/nose exposure
• Direct contact occurs through contact with infected animals or their tissues: skin abrasions or during animal birthing

Brucella as a Bioterrorism Agent

• Brucella as a Category B select agent by the CDC due to its potential use in bioterrorism
• Microbiology labs must be notified when brucellosis is suspected
• Handling requires biosafety level 3 laboratory conditions to prevent laboratory-acquired infections

Brucellosis Lab Diagnosis: Acute Stage

• Identify the pattern of intermittent fever, which is characteristic of bacteremia
• Collect two bottles of blood culture from the patient during febrile episodes
• Incubate one bottle aerobically and the second in 5-10% CO2, especially for B. abortus
• Brucella may require up to 21 days to grow during prolonged incubation

Brucellosis Lab Diagnosis: Chronic Stage

• Diagnosis relies on serological methods to detect antibodies against Brucella
• Perform a standard Agglutination Test (SAT) that measures total antibody response
• ELISA, a more sensitive and specific test that can differentiate between IgG and IgM antibodies
• PCR, molecular techniques are used for direct detection of Brucella DNA in clinical samples

Biosafety Considerations for Brucella

• Culture requires a BSL-3 Laboratory
• Use specialized gear (PPE) to prevent exposure
• Rigorous safety procedures are required. This includes controlled air handling, negative pressure rooms, and specialized containment equipment
• Lab personnel must be properly trained and adhere to strict safety protocols when handling suspected Brucella samples.

Introduction to Yersinia

• Yersinia pestis is the causative agent of plague
• Alexandre Yersin discovered it during the Hong Kong plague epidemic of 1894
• Yersinia enterocolitica causes gastroenteritis with symptoms
• Diarrhea, fever, and abdominal pain
• Often transmitted through contaminated food or water
• Yersinia pseudotuberculosis causes mesenteric lymphadenitis that can mimic appendicitis
• Primarily a zoonotic infection transmitted from animals to humans

Yersinia pestis Characteristics

• Gram-negative bacilli with distinctive bipolar staining
• Described as having a "safety pin" appearance when stained with Giemsa or methylene blue
• Non-motile bacteria, unlike other Yersinia species, which are motile at lower temperatures
• Non-capsulated in its natural state, though it can produce an antiphagocytic capsule at 37°C in the host
• Classified as a Category A bioterrorism agent due to its high mortality rate and potential for person-to-person spread

Bipolar Staining of Yersinia pestis

• Giemsa staining highlights the characteristic bipolar appearance of Yersinia pestis
• It shows intensely stained poles and a lighter center, resembling a safety pin
• Methylene blue also demonstrates the distinctive bipolar staining pattern
• Serves as an important preliminary identification method in the lab diagnosis of suspected plague cases

Plague Transmission

• Wild rodents serve as the natural reservoir for Yersinia pestis
• Fleas become infected by feeding on infected rodents
• Bacteria multiply at the site of the bite and spread through the lymphatic system
• Infected Fleas bite humans, transmitting the bacteria
• Transmitted from one rodent to another and from rodents to humans through bites of infected fleas
• Responsible for devastating plague outbreaks throughout human history, including the Black Death that killed millions in medieval Europe

Clinical Forms of Plague

• Bubonic Plague: Characterized by enlarged and painful lymph nodes (buboes)
• Pneumonic Plague: Affects the lungs and is highly contagious
• Septicemic Plague: Infection of the bloodstream that can occur primarily or secondary to bubonic plague
• Bubonic plague is characterized by enlarged, red, painful lymph nodes (buboes) near the site of the flea bite.
• Pneumonic plague affects the lungs and can spread from person to person through respiratory droplets, making it highly contagious and dangerous.
• Septicemic plague occurs when bacteria multiply in the bloodstream, causing septic shock, multiple organ failure, and death if not treated promptly.

Bubonic Plague Details

• Characterized by the sudden onset of fever, chills, weakness, and the development of extremely painful, swollen lymph nodes: buboes
• Can spread to the bloodstream or lungs without treatment
• Transmitted to humans by the bite of infected rat fleas (Xenopsylla cheopis)
• Controlling rodent populations and preventing flea bites are key prevention strategies
• Not directly transmitted person to person

Pneumonic Plague Details

• Develops from inhalation of infectious respiratory droplets from a person or animal with pneumonic plague
• Can occur as a complication of untreated bubonic or septicemic plague when bacteria spread to the lungs
• Highly contagious through respiratory droplets, making it the only form of plague that can spread directly between humans
• Nearly 100% fatal if not treated within 24 hours of symptom onset

Septicemic Plague Details

• Multiplication of Yersinia pestis in the bloodstream
• Develops from direct introduction of bacteria into the bloodstream or as a complication of untreated bubonic plague
• Symptoms include fever, extreme weakness, abdominal pain, and shock
• Acral gangrene (blackening of extremities) is a hallmark sign
• The condition is almost always fatal without prompt antibiotic treatment

Yersinia pestis as a Biological Weapon

• Untreated pneumonic plague leads to nearly 100% fatality rate
• The incubation period has a short time from exposure to severe symptoms (24-36h)
• Time to death has rapid progression without treatment (1-3 days)
• Classified as a Category A bioterrorism agent by the CDC

Lab Diagnosis of Plague

• Specimen Collection: Aspirate from enlarged lymph nodes, sputum, or blood depending on the form of plague
• Microscopic Examination: Gram stain and specialized stains to identify characteristic bipolar "safety pin" appearance
• Culture: Growth on appropriate media with biochemical testing for confirmation
• Molecular Testing: PCR for rapid identification of Yersinia pestis DNA

Specimen Collection for Plague Diagnosis

• Bubonic: Collect lymph node aspirate via needle aspiration of bubo into a sterile container, 4°C
• Pneumonic: Collect sputum via deep cough specimen into a sterile container at 4°C
• Septicemic: Collect blood via blood culture bottles at room temperature
• All forms: Collect serum via venipuncture into a serum separator tube, 4°C

Biosafety precautions for plague diagnosis

• Requires a BSL-3 Laboratory: Required for suspected plague samples
• Personal protective equipment is required with full protection for lab personnel
• Advance Notification: Alert lab before sending samples
• All specimens suspected of containing Yersinia pestis must be handled with extreme caution
• Laboratories must be notified in advance when plague is suspected
• Yersinia pestis cultures require biosafety level 3 facilities with negative pressure rooms, specialized containment equipment, and properly trained personnel that use appropriate personal protective equipment

Prevention for Brucellosis and Plague

• Brucellosis: Pasteurization of milk and dairy products, Vaccination of livestock, Testing and culling of infected animals
• Plague: Rodent control programs, Flea control measures, Avoidance of sick or dead animals, personal protective equipment for occupational exposure, laboratory biosafety practices
• Plague: Prophylactic antibiotics for exposed individuals, Isolation of pneumonic plague patients, Strict lab biosafety protocols