Francisellaceae Flashcards
(20 cards)
F. tularensis
Pleomorphic, nonmotile, GN bipolar coccobacilli
- catalase negative
- strict aerobe!!
What are the 2 causes of tularemia?
F. tularensis tularensis and F. tularensis holartica
- subspecies tularensis is more virulent –> predominant in North America –> reservoir is lagomorphs
- subspecies holartica is predominant in Europe and Asia –> carried by rodents
Pathogenesis of F. tularensis
- C3 is deposited on F. tularensis cell surface
- virulent strains –> C3b is inactivated to C3bi = prevention of complement mediated lysis
- O polysaccharide is necessary for serum resistance
Method of intracellular survival
After phagocytosis, the phagosome becomes tight fitting –> Francisella containing phagosome is arrested for 2-4 hrs does not fuse with lysosome
- Francisella gradually escapes to the cytosol and proliferates
Prevention of phagosomal-lysosomal fusion
Genes located on chromosome = intracellular growth locus
- allow escape from the phagosome
- regulatory gene (mgIA) regulates Igl genes
From the point of entry, F. tularensis spreads to _______
Lymph nodes
- bacteremia followed by focal, granulomatous lesions in lymph nodes and viscera = necrosis and suppuration
Human infection is ______, ______, and _______
Acute, febrile, and granulomatous
Ulceroglandular
75-85% of human cases
- transmitted via tick bite
- papule, ulcer, lymph node enlargement
- purulent exudate from lymph nodes
Glandular form of disease
Lymphadenopathy without papule/ulceration
Oropharyngeal form of disease
Ingestion of contaminated meat or water
- ulcerative = exudative stomatitis and pharyngitis with or without tonsilar involvement
- regional neck lymphadenitis
What animal species is most commonly affected?
Sheep, followed by cats
- clinical infection reported in dogs, pigs, and horses
- cattle appear to be resistant
- incubation period: 1-10 days
Localized
Papule, ulceration, lymphadenopathy
Septic
High fever, lethargy, anorexia, abdominal pain, hepatomegaly, icterus, splenomegaly
____ and _____ forms are also possible
Pneumonic and gastrointestinal
Transmission
Contact with infected animals or discharges
How are humans infected?
- direct contact with infected animals (ex: skinning rabbits)
- insect vectors
- ingestion of contaminated water/meat
- inhalation (ex: fecal droppings from ticks)
What is the primary reservoir in the US?
Cottontail rabbit
Diagnosis
Grows on cysteine-blood agar, causes greenish discoloration of media
- guinea pig inoculation –> antibody detection via agglutination or ELISA
- direct fluorescent antibodies (DFA)
Treatment
Streptomycin is first drug of choice, followed by gentamicin
- fluroquinolones and doxycyclines are recommended for post-exposure prophylaxis
- live attenuated vaccine is available for people at high risk (CMI)
Biowarfare potential
High virulence of the pathogen in humans, low infectious dose, ease of dissemination by aerosal have led to concerns of F. tularensis for utilization as a bioweapon
