Zoonotic Diseases Lecture Notes PDF

Zoonotic diseases Department of Medical Microbiology & Immunology Faculty of Medicine-Menoufia University  ILOs Recognize the microbiological features and culture characteristics of Y. Pestis. Describe the pathogenesis and clinical infections caused by Y. Pestis...

Zoonotic diseases Department of Medical Microbiology & Immunology Faculty of Medicine-Menoufia University  ILOs Recognize the microbiological features and culture characteristics of Y. Pestis. Describe the pathogenesis and clinical infections caused by Y. Pestis. Recognize the microbiological features and culture characteristics of Brucella species. Formulate a systematic approach for laboratory diagnosis of infections caused by Brucella species.  Yersinia (Y. pestis) Morphology: They are Gram-negative short ovoid (coccobacilli), non-motile bacilli. In tissues, it forms a capsule-like outer envelope. When stained by methylene blue, Leishman, Geimsa or Wayson’s stains, it shows marked bipolar staining "safety pin appearance".  Cultural characters: » O2 requirement: They are facultative anaerobes. » Temperature: Optimum temperature 27-30°C. » Media: Grow on blood agar → not haemolytic colonies MacConkey's agar → non-lactose fermenting colonies. Disease caused by Yersinia pestis: Y. pestis is a highly virulent pathogen causes Plague= (black death)  Virulence factors Facultative intracellular organism live in monocyte and resist phagocytosis 1. Envelope F1 antigen → antiphagocytic 2. V-W antigen → rapid replication of bacteria 3. YOPS (Yersinia outer membrane protein) → inhibit host defenses as phagocytosis and cytokine release 4. Enzymes; coagulase and fibrinolysin produced at 28°C  Mode of transmission: Plague is an infection of wild rodents transmitted from one rodent to another and occasionally from rodents to humans by the bites of rate fleas. Bubonic plague. Septicaemic plague (black death). Pneumonic plague. Plague meningitis. The organism may be used in bioterrorism and is delivered by; aerosol to cause pneumonic plague, or using infected fleas to cause bubonic plague.  Brucella species There are four species with human diseases: Br. melitensis using infection in goats and sheep. Br. abortus causing abortion of cows. Br. suis causing infection in pigs. Br. canis causes infection in dogs.  Morphology: Gram-negative coccobacilli, non-motile, non-capsulated and non- spore forming. Culture characters: Aerobes. Incubation is done at 37°C (for 48 hours – 5 days). Br. abortus requires 10% CO2. Enriched media: Brucella agar. Brain-heart infusion broth  Pathogenesis: Virulence: Brucella can survive and multiply intracellularly when engulfed by phagocytes. They inhibit intracellular killing Endotoxin (lipopolysaccharide). Mode of transmission through: Abraded skin: contact with infected tissues or discharges. Mucous membranes: inhalation or through conjunctiva. Ingestion of: Infected milk. Cheese made from unpasteurized infected milk. Clinically: Chronic disease (for years) The disease is characterized by an acute bacteraemic stage (weakness, fatigue and fever) → the organism live in lymph node, liver, spleen, bone marrow and can persist in phagocyte for years lead to chronicity and granuloma formation (symptoms subside) → bouts of intermittent fever: febrile for 3-4 weeks, alternating with 3-4 weeks of a febrile period. Laboratory diagnosis: Specimens: Blood, bone marrow, biopsy material (lymph nodes or bone) and serum. Identification: Blood culture: (Blood is obtained during the febrile stage). Inoculation of → trypticase soy broth, brain-heart infusion broth incubation in CO2 and without CO2 at 37oC. Subculture (every few days) on Brucella agar or serum dextrose agar. Colonies are