Zoonotic Disease Flashcards
Zoonotic disease definition
infections that are transmitted between humans and other animals
Factors influencing zoonotic infections
- Transition from hunter-gatherer societies to agrarian societies
- Domestication of animals
- Increased population density
- Modification of the environment
- Emergence of immunosuppressed populations
- Many of these organisms can and have been used as bioterrorist weapons (e.g. Y. pestis, B. anthracis).
Causative organisms in the plague
Yersinia pestis
“Black Death” refers to purpura.
Hallmark of plague: is DIC with cutaneous petechiae, purpura and ecchymosis.
Yersinia pestis features
- introduced in US by rats on ships arriving in SF from China
- facultative bipolar-staining Gram-negative bacillus belonging to the Enterobacteriaceae
- has plasmids containing virulence factors (w/ complement resistance determinants and secreted proteins called “YOPS”–a tyrosine phosphatase that subverts normal activation mechanisms of phagocytic cells)
- antiphagocytic capsule
- iron/hemin uptake systems
- coagulase fibrinolysin that facilitates transmission from fleas
Y. enterocolitica/Y. pseudotuberculosis cause…
(less virulent relatives of Y. pestis) enterocolitis arthritis septicemia mesenteric adenitis
animal reservoirs of Y. pestis
- urban and forest rodents
- fleas usually transmit disease to humans
- domestic cats can provide connection b/t sylvatic (forest) foci and human populations.
Enzootic foci
-stable rodent-flea reservoirs of infection
epizootic plague
results from introduction into a new susceptible mammal population
zootic plague
transmission from animal host to humans
Location of plague cases in US and world
Southwestern US and Colorado from May-October
Currently prevalent in Africa, South America, SE Asia, India
Clinical features of bubonic plague
fever, painful lymphadenophathy (bubo, most commonly of groin, axilla, or neck).
Results from the bite of a flea on the arm or leg.
Clinical features of septicemic plague
fever, hypotension
rapidly fatal, frequently results from the ingestion of large numbers of organisms
Clinical features of pneumonic plague
can be primary or secondary to hematogenous spread, rapidly fatal.
***transmitted human to human
Diagnosis of plague
Wayson/Giemsa/Gram strains of a bubo aspirate; bubo/blood/sputum culture with confirmation by fluorescent antibody; serology
Tx of plague
streptomycin; supportive care
alternative: tetracycline, chloramphenicol and fluoroquinolones
* Need to be effective against intracellular pathogens
Prevention of plague
rodent and vector control
-killed vaccine gives short term protection to high risk indiv
Tularemia: associated animal; how infectious is it?
- rabbit associated illness
- one of most infectious bacterial organisms known (Infectious dose less than 50 organisms applied to unbroken skin; 5-10 organisms by respiratory route)
- less severe disease than Y. pestis
Features of Francisella Tularensis
small, aerobic, pleomorphic Gram-negative coccobacillus
virulent strains require cysteine for growth;
3 biotypes
The ability to survive intracellularly, aided by bacterial phase-variation, is believed to be important in pathogenesis.
cellular immunity is required for recovery.
Transmission: arthropid vectors or infected rabbits
Groups commonly infected with F. tularensis?
hunters/trappers, meat handlers, veterinarians, farmers, lab workers; peak incidence in summer (ticks) and December (hunting)
Does F. tularensis spread person-to-person?
NO!
Y. pestis can: pneumonic plague
Clinical features of F. tularensis
flu-like symptoms, persistent remitting constitutional symptoms lasting weeks.
GLANDULAR – lymph node only ULCEROGLANDULAR – necrotic ulcer with tender regional lymph node
OCULOGLANDULAR – from direct inoculation of eye
PHARYNGEAL – can be mistaken for streptococcal/EBV infection
TYPHOIDAL – systemic disease without localizing findings, requires a high dose from ingestion to cause disease.
PULMONARY – can result from inhalation or from hematogenous spread of another kind of infection.
Diagnosis of F. tularensis
- cultures need special media
- serologies positive in most pts by 1-2 weeks
Tx for F. tularensis
streptomycin or gentamicin;
alternatives: tetracycline, chloramphenicol and fluoroquinolones
Prevention: avoid exposure (don’t eat infected rabbits)
Causative organism in Lyme disease?
Borrelia burgdorferi
Features of Borrelia burgdorferi
- loosely coiled spriochete
- difficult to culture
- evades immune effector cells and crosses intracellular junctions
Reservoirs of Borrelia burgdorferi and location
white-footed mice and deer Ixodes tick (2 year life cycles-- humans are infected by bites from ticks in the nymph stage)
- Northeast
- Upper Midwest
- Far West
Also: Europe, Scandinavia, Russia, China, Japan, Australia
lyme disease: cutaneous features
spreading erythema with pale center at the site of a tickbite is called “erythema chronicum migrans” (“bulls eye rash”)
lyme disease: MSK sx
joint symptoms may be present early, but frank large joint arthritis (esp. knee) usually occurs months after exposure
lyme disease: neurologic features
manifestations of aseptic meningitis, encephalitis, cranial or other radiculoneuritis, or myelitis may be seen weeks to months or even years after the onset of infection.
lyme disease: cardiac sx
conduction block
Diagnosis of Lyme disease
- clinical features
- serology in later disease (but can’t distinguish between previous and active disease)
- ELISA w/ confirmation by Western blot
Rule out infection with: Babesia, Ehrlichia or tick-borne encephalitis
Tx of Lyme disease
doxycycline is effective in early disease, and also treats possible co-infection with Ehrlichia
alternatives: amoxicillin, cefuroxime, azithromycin
parenteral ceftriaxone x2-4 weeks used in neurologic infection
Prevention: insect repellant and check for ticks
Lyme Vaccine
No longer available. Why?
- costly
- effectiveness less than 80%
- 1,000 adverse event reports filed against it (arthritis-like side effects among other complaints)
- caused 4 deaths
Correcting card
Correcting card
