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Infectious Disease: Unit 2 > Zoonotic Bacterial Diseases > Flashcards

Flashcards in Zoonotic Bacterial Diseases Deck (16):

Societal factors leading to emergence of zoonotic infections

  • Agricultural and pastoral
  • Migration to city - have largely become occupational (farmers, vets, slaughterhouse workers, lab workers, etc.) and avocational (pet owners, hikers/hunters/trappers/fishermen)
  • Destruction of animals habitats --> animals come into city


Major pathways of transmission of zoonotic infections

  • Cutaneous transmission, including bites
  • Arthropod vector
  • Inhalation
  • Ingestion


Individuals at highest risk for zoonotic infections

  • People with occupational or avocational exposure to animals
  • Occupational:
    • Farmers
    • Vets
    • Slaughterhouse workers
    • Lab workers
  • Avocational:
    • Pet owners
    • Hikers
    • Hunters/trappers/fishermen


Plague: epidemiology

  • Caused by Yersinia pestis (facultatively intracellular Gram-negative rod)
  • Generally accepted as etiological agent for Black Death in Europe
  • Small pandemics up until about 1920, when rats on ships were "outlawed"
  • Spread by fleas (in CO, watch out for dead prairie dogs)
  • Discovered by a guy named Yersin (--> Yersinia)


Types of plague

  • Bubonic plague
  • Septicemic plague
  • Pneumonic plague 


Bubonic plague 

  • Most common form of plague in US
  • Lymph gland swelling resulting from flea bite 2-5 days earlier
  • 60-90% mortality if untreated
  • Lymph nodes extremely painful and swollen (buboes)
    • Usually inguinal or axillary


Septicemic plague

  • Invasion of almost all organs
  • No evidence of prior disease
    • Seems to come after direct bloodstream inoculation or consumption of plague-stricken animal
  • Death occurs in 12-24 hours
  • Presents with ecchymoses, petechiae, and DIC



Pneumonic plague

  • Less common but nasty
  • Transmitted human to human through aerosolized droplets
  • Primary or secondary lung infection
  • Highly infectious and 100% fatal if untreated
  • Untreated bubonic plague can get into lungs --> pneumonic plague 


Epidemiologic terms for plague

  • Enzootic plague
    • Stable rodent-flea infection
    • Not too much rodent mortality
    • Long-term reservoir
  • Epizootic plague
    • Occurs when plague bacilli introduced into rodent/small mammal populations that are more susceptible
  • Zootic plague
    • Transmission from animals to human
  • Demic plague
    • Transmission from human to human (pneumonic plague only)


Plague: appearance and prevention

  • Microscopically:
    • Bipolar, safety-pin type staining of Gram-negative rods (ends stain more than middle)
  • Animal reservoirs:
    • Cats, rabbits, camels
  • Virulence:
    • Has to do with how well Yersinia gets into non-endocytosing cells
    • Can kill or shut down macrophages
    • VW and F1 surface antigens cause extra virulence (encoded by plasmids)
  • Starves flea to make it keep biting people, then causes flea to regurgitate Yersinia-containing blood back into host
  • Can be weaponized (pneumonic form most lethal)
  • Prevention: avoidance



  • Caused by Francisella tularemia (Gram-negative coccobacillus)
  • Carried by rabbits
  • Generally found in and around AR and MO 
  • Requires cysteine for growth
  • Most cases are ulceroglandular
    • Direct contact with infected animals --> skin ulcers
    • Ulcers: black and well-demarcated + local swollen lymphadenopathy
  • Some are pulmonic
    • Inhalation of aerosolized rabbit - for real
  • Can also get it from tick bites or ingestion of contaminated material
  • Extremely virulent (10 organisms cause disease)
  • Unlike plague, cannot be spread person-to-person
  • Can be weaponized (pulmonary form most lethal)
  • Prevention: avoidance



  • Mostly acquired in US from consumption of unpasteurized goat cheese from Mexico
  • Doesn't cause primary skin ulcers or buboes
  • Presents with systemic relapsing-remitting flu-like symptoms (undulant fever
  • Rarely fatal


Lyme disease: cause and presentation

  • Caused by Borrelia burgdorferi, a spirochete
    • Very hard to culture
  • Spread through Ixodes tick bites
  • Causes arthritis (knee), fever, and skin rash (erythema migrans - spreading erythema with a pattern of central clearing)
    • Skin rash is pathognomonic
  • Symptoms caused by immune response (very high levels of IL-1)
  • Can present a lot of different ways, but most common:
    • Erythema migrans
    • Heart palpitations
    • Arthritis


Lyme disease: stages of infection

  • Stage I
    • Localized infection
    • Erythema migrans
  • Stage II
    • Disseminated infection
    • Meningitis
    • Carditis
    • Myositis
  • Stage III
    • Latent infection
    • Chronic arthritis
    • Neuropathy
    • Can go on for decades if untreated


Lyme disease: diagnosis and epidemiology

  • Very difficult to diagnose
    • Nymph stage of tick most frequently causes disease - bug is about the size of a letter on a penny
  • Once bug has fed on you for awhile, they're no longer necessary to cause disease (not a toxin)
  • Probability of getting Lyme disease increases dramatically with length of tick's feeding (72+ hours)
  • Geographically, cases clustered in:
    • Northeast
    • Around Minnesota (site of other hosts, white-footed mice and deer)
    • Climate change --> growth of geographic range
  • Cases most common in children and middle-aged


Lyme disease: treatment and prevention

  • Can't treat chronic infection with long-term abx
    • Postinfectious symptoms (e.g. arthritis) seem to be autoimmune
  • Acute Lyme disease:
    • Doxycycline
  • No vaccine on market
  • Prevention: tick repellant, prompt removal
  • PCR unhelpful for diagnosis