LECTURE 11 (Zoonotic infections) Flashcards

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1
Q

What are Zoonoses?

A

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)

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2
Q

Describe Brucella

A
  • 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
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3
Q

What are the three major Brucella human pathogens and their animal reservoirs?

A
  • Brucella melitensis = goats + sheep
  • Brucella abortus = cattle
  • Brucella suis = pigs
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4
Q

What is Brucellosis?

A

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

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5
Q

What is Brucella?

A

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

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6
Q

Describe Francisella

A
  • 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]
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7
Q

What is Francisella Tularensis?

A

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

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8
Q

Describe Yersinia Pestis

A
  • 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
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9
Q

What are the virulence factors of Yersinia Pestis?

A
  • Envelope capsular antigen (called F-1) which protects against phagocytosis
  • Endotoxin + exotoxin
  • V antigen and W antigen
    [allow organism to survive + grow intracellularly]
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10
Q

Describe the protein envelope (F-1) in Yersinia Pestis

A
  • Plasmid coded
  • Present only in virulent strains
  • Heat labile
  • Best developed at 37 degrees Celsius
  • Inhibits phagocytosis
  • Antibody to antigen is protective in mice
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11
Q

Describe the V and W antigens in Yersinia Pestis

A
  • Always produced together
  • Plasmid mediated
  • Inhibits phagocytosis + intracellular killing of bacilli
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12
Q

What is Yersinia Pestis?

A

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

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13
Q

Describe Yersinia Pestis

A
  • Facultative anaerobe
  • Virulence factors are temperature sensitive (37 degrees Celsius - temp inside macrophages)
  • Virulence is plasmid mediated
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14
Q

What is the Bubonic plague?

A

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

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15
Q

What is Pneumonic plague?

A

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

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16
Q

What is Pasterurella Multocida?

A

A short, encapsulated gram-negative rod that exhibits bipolar staining and causes wound infections associated with cat and dog bites

EPIDEMIOLOGY:
- part of the normal flora in the mouths of animals (particularly cats and dogs)
- transmitted by biting

MANIFESTATIONS:
- diffuse cellulitis with a well-defined erythematous border (infection develops within 24 hrs)

LAB DIAGNOSIS:
- finding organism in a culture of a sample from the wound site

TREATMENT:
- Penicillin G

PREVENTION:
- people bitten by a cat should be given ampicillin

17
Q

What is Bartonella Henselae?

A

A small, pleomorphic gram-negative rod that is the cause of cat-scratch disease and bacillary angiomatosis

EPIDEMIOLOGY:
- cat scratches/bites (main mode of transmission to humans)
- organism is a member of oral flora of many cats
- low virulence -> affects immunocompromised individuals

MANIFESTATIONS:
- Cat-scratch disease (fever and tender, enlarged lymph nodes)
- Bacillary angiomatosis (raised, cherry-red vascular lesions in the skin + visceral organs)

LAB DIAGNOSIS:
- diagnosis made serogically

TREATMENT:
- NO ANTIBIOTIC THERAPY for CSD
- Doxycycline or erythromycin for BA