Zoonotic Bacterial Diseases

Question 1

Societal factors leading to emergence of zoonotic infections

Answer 1

• 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

Question 2

Major pathways of transmission of zoonotic infections

Answer 2

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

Question 3

Individuals at highest risk for zoonotic infections

Answer 3

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

Question 4

Plague: epidemiology

Answer 4

• 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)

Question 5

Types of plague

Answer 5

• Bubonic plague
• Septicemic plague
• Pneumonic plague

Question 6

Bubonic plague

Answer 6

• 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

Question 7

Septicemic plague

Answer 7

• 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

Question 8

Pneumonic plague

Answer 8

• 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

Question 9

Epidemiologic terms for plague

Answer 9

• 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)

Question 10

Plague: appearance and prevention

Answer 10

• 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

Question 11

Tularemia

Answer 11

• 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

Question 12

Brucellosis

Answer 12

• 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

Question 13

Lyme disease: cause and presentation

Answer 13

• 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

Question 14

Lyme disease: stages of infection

Answer 14

• 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

Question 15

Lyme disease: diagnosis and epidemiology

Answer 15

• 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

Question 16

Lyme disease: treatment and prevention

Answer 16

• 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