LECTURE 11 (Zoonotic infections) Flashcards
What are Zoonoses?
Infections in humans acquired by either direct or indirect contact with animals
PROPERTIES:
- there are bacterial, viral, fungal and parasitic zoonoses
- either acquired directly from animal reservoirs or indirectly transmitted by vectors (mosquitoes, fleas)
Describe Brucella
- Causes Brucellosis (Undulant fever)
- Small, cocobacillary, gram-negative rods
- Non-spore forming
- No capsule
- Growth is slow
[requires 2-3 days of aerobic incubation in enriched media] - Catalase +ve, Oxidase +ve and Urease +ve
- Does not ferment carbohydrates
What are the three major Brucella human pathogens and their animal reservoirs?
- Brucella melitensis = goats + sheep
- Brucella abortus = cattle
- Brucella suis = pigs
What is Brucellosis?
A chronic infection that persists for life in animals and is an important cause of abortion, sterility and decreased milk production in cattle, goats and hogs
What is Brucella?
Gram-negative, non-encapsulated, non-motile coccobacilli that cause brucellosis (undulant fever)
INCUBATION PERIOD:
7-21 days
EPIDEMIOLOGY:
- spread among animals by direct contact with infected tissues + ingestion of contaminated feed
- organisms enter the human body by ingestion of contaminated milk products/through skin by direct contact
- bacterial gain access through cuts in skin, contact with mucous membranes, inhalation/ingestion
- pasteurisation of milk kills the organism
PATHOGENESIS:
- evade immune system after penetrating skin + mucous membranes
- enter + multiply in macrophages in liver sinusoids, spleen, bone marrow + form granulomas (tiny cluster of WBC)
MANIFESTATIONS:
- fever
- chills
- fatigue
- malaise
- enlarged lymph nodes, liver and spleen
PROLONGED ILLNESS:
- periodic undulant fever continues for weeks, months , even 1-2 years
- patients become chronically ill (associated body aches, headache, anorexia)
- weight loss of up to 20kg
DIAGNOSIS:
- specimens from blood/biopsy of liver, bone marrow or lymph nodes
TREATMENT:
- PRIMARY TREATMENT: doxycycline with rifampin or gentamycin
- ciprofloxacin + trimethoprim-sulfamethoxazole
Describe Francisella
- Gram-negative coccobacilli
- Obligate aerobe that requires cysteine for growth
- Oxidase -ve, Catalase weak +ve, Urease -ve
- Smooth colonies
[Chocolate agar = grey-white, Cysteine heart agar = greenish-blue]
What is Francisella Tularensis?
An aerobic, gram-negative coccobacilli that is non-motile, non-sporing and causes Tularemia
INCUBATION PERIOD:
2-5 days
RESERVOIR:
- rabbits, squirrels and ticks
TRANSMISSION:
- bite of tick, deerfly or infected animals
- direct contact with infected animal tissue
- inhaled aerosolised organisms
- ingestion of contaminated meat or water
- easily transmitted to lab personnel
PATHOGENESIS:
- bacteria multiply within macrophages, hepatocytes kidney and alveolar epithelial cells -> organism then infects RETICULOENDOTHELIAL ORGANS forming granulomas
- caseation necrosis and abscesses can occur
- symptoms caused by endotoxin (NO EXOTOXIN!!!)
SYMPTOMS:
- inhalation of organism -> pneumonic tularaemia
- ingestion of large numbers -> typhoidal tularaemia -> abdominal manifestations + similar to typhoid fever
- ULCEROGLANDULAR FORM: local papule at inoculation site becomes necrotic and ulcerative + regional lymph nodes become swollen and painful
- OCULOGLANDULAR FORM: follows conjunctival inoculation + local lesion is a painful purulent conjunctivitis
COMPLICATIONS:
any form may progress to a systemic infection with lesions in multiple organs
PREVENTION:
- use of rubber gloves + eye protection
- prompt removal of ticks
DIAGNOSIS:
- culturing is rarely done (since high risk to lab workers by inhalation)
- agglutination test
- fluorescent-antibody staining of infected tissue
TREATMENT:
- gentamycin or streptomycin + doxycycline
Describe Yersinia Pestis
- Enterobacteriae
- Non-motile + non-spore forming
- Pleomorphic
- Freshly isolated organisms possess a capsule
- Loss of capsule -> loss of virulence
- One of the most virulent bacteria capable of causing disease
What are the virulence factors of Yersinia Pestis?
- Envelope capsular antigen (called F-1) which protects against phagocytosis
- Endotoxin + exotoxin
- V antigen and W antigen
[allow organism to survive + grow intracellularly]
Describe the protein envelope (F-1) in Yersinia Pestis
- Plasmid coded
- Present only in virulent strains
- Heat labile
- Best developed at 37 degrees Celsius
- Inhibits phagocytosis
- Antibody to antigen is protective in mice
Describe the V and W antigens in Yersinia Pestis
- Always produced together
- Plasmid mediated
- Inhibits phagocytosis + intracellular killing of bacilli
What is Yersinia Pestis?
A non-motile, non-spore forming, gram-negative bacillus with a tendency towards pleomorphism and bipolar staining that caused the “Black Death” (Bubonic plague)
RESERVOIR:
wild rodents [SYLVATIC], city rats [URBAN], squirrels
TRANSMISSION:
- flea bite
[humans enter the urban cycle from the flea bite + flea bite is the first event of the “bubonic plague” which is not contagious to other humans]
- contact with infected animal tissue
- inhaled aerosolised organisms (human to human transmission)
[secondary “pneumonic plague” develops by bacteraemic spread to the lungs which is highly contagious via respiratory droplet route]
PATHOGENESIS:
Grow in flea producing virulence factors unique to that environment -> bacteria enter human skin + subepithelial tissue via bite -> new warmer temp of body produces new set of virulence factors (e.g F1 protein capsule) -> Yersinia outer membrane proteins begin to be produced -> cell is destroyed + organisms evade phagocytosis
MANIFESTATIONS:
- Bubonic plague
- Pneumonic plague (5% of bubonic plague victims develop pneumonic plague)
DIAGNOSIS:
- Bubo aspirate, blood and sputum specimens [gram smears show bipolar-staining gram-negative bacilli]
- Immunofluorescence technique
- Catalase test = Catalase +ve
- Oxidase + urease test = Urease, indole + oxidase -ve
- Motility test = Non-motile between 35-37 degrees
PREVENTION:
- Rat control + use of insecticides
- Avoiding sick or dead rodents and rabbits
TREATMENT:
- Streptomycin/Gentamycin with or with our doxycycline
Describe Yersinia Pestis
- Facultative anaerobe
- Virulence factors are temperature sensitive (37 degrees Celsius - temp inside macrophages)
- Virulence is plasmid mediated
What is the Bubonic plague?
An infection of Y. pestis spread mostly to humans by infected fleas that travel to rodents
INCUBATION PERIOD:
2-7 days
SYMPTOMS:
- fever
- painful bubo (swollen lymph nodes) in the groin + axilla
COMPLICATIONS:
without treatment, 50-75% of patients progress to bactedemiia and die in Gram-negative septic shock within hours or days
What is Pneumonic plague?
A secondary infection when Y. Pestis infects the lungs
INCUBATION PERIOD:
2-3 days
SYMPTOMS:
- fever + malaise + tightness in the chest
- cough + production of sputum
- dyspnea (air hunger)
- terminal cyanosis
COMPLICATIONS:
death can occur on the 2nd-3rd day without antibiotic therapy
