Francisellaceae

Question 1

F. tularensis

Answer 1

Pleomorphic, nonmotile, GN bipolar coccobacilli

• catalase negative
• strict aerobe!!

Question 2

What are the 2 causes of tularemia?

Answer 2

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

Question 3

Pathogenesis of F. tularensis

Answer 3

• 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

Question 4

Method of intracellular survival

Answer 4

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

Question 5

Prevention of phagosomal-lysosomal fusion

Answer 5

Genes located on chromosome = intracellular growth locus

• allow escape from the phagosome
• regulatory gene (mgIA) regulates Igl genes

Question 6

From the point of entry, F. tularensis spreads to _______

Answer 6

Lymph nodes

- bacteremia followed by focal, granulomatous lesions in lymph nodes and viscera = necrosis and suppuration

Question 7

Human infection is ______, ______, and _______

Answer 7

Acute, febrile, and granulomatous

Question 8

Ulceroglandular

Answer 8

75-85% of human cases

• transmitted via tick bite
• papule, ulcer, lymph node enlargement
• purulent exudate from lymph nodes

Question 9

Glandular form of disease

Answer 9

Lymphadenopathy without papule/ulceration

Question 10

Oropharyngeal form of disease

Answer 10

Ingestion of contaminated meat or water

• ulcerative = exudative stomatitis and pharyngitis with or without tonsilar involvement
• regional neck lymphadenitis

Question 11

What animal species is most commonly affected?

Answer 11

Sheep, followed by cats

• clinical infection reported in dogs, pigs, and horses
• cattle appear to be resistant
• incubation period: 1-10 days

Question 12

Localized

Answer 12

Papule, ulceration, lymphadenopathy

Question 13

Septic

Answer 13

High fever, lethargy, anorexia, abdominal pain, hepatomegaly, icterus, splenomegaly

Question 14

____ and _____ forms are also possible

Answer 14

Pneumonic and gastrointestinal

Question 15

Transmission

Answer 15

Contact with infected animals or discharges

Question 16

How are humans infected?

Answer 16

• direct contact with infected animals (ex: skinning rabbits)
• insect vectors
• ingestion of contaminated water/meat
• inhalation (ex: fecal droppings from ticks)

Question 17

What is the primary reservoir in the US?

Answer 17

Cottontail rabbit

Question 18

Diagnosis

Answer 18

Grows on cysteine-blood agar, causes greenish discoloration of media

• guinea pig inoculation –> antibody detection via agglutination or ELISA
• direct fluorescent antibodies (DFA)

Question 19

Treatment

Answer 19

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)

Question 20

Biowarfare potential

Answer 20

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