Francisella, Pasteurella, Bartonella (Ch4)

Question 1

What are the species and subspecies of Francisella?

Answer 1

• Francisella tularensis
- Subsepecies tularensis (A)
- Subspecies holartica (B)

• Francisella philomiragia

Question 2

What are the characteristics of Francisella tularensis

Answer 2

• Gram negative coccobacillus
• Non motile
• Displays bipolar staining with Giemsa stain
• Obligate aerobe
• weakly catalase positive
• Has thick capsule whose loss is accompanied by loss of
  virulence

Question 3

What are the reservoirs of Francisella?

Answer 3

• Rabbits, Rats, Squirrels, Mice
• Aquatic Rodents (Beavers, Muskrats)
• Blood sucking arthropods:
> Ticks
> Mosquitoes
> Biting Flies
• Dust/aerosols
• Contaminated water
(Francisella philomiragia)

Question 4

What are the routes of transmission?

Answer 4

– Tick and deer fly bites —> skin infection
– Skin contact with infected animals (dogs, cats, rabbits, rodents) —> skin or conjunctiva
– Ingestion of contaminated water—> GI tract infection
– Laboratory exposure
– Inhalation of contaminated dusts or aerosols —> respiratory tract infection

Question 5

What is worrying about Francisella tularensis?

Answer 5

The bacterium that causes tularemia is highly infectious and can enter the human body through the skin, eyes, mouth, throat, or lungs

Question 6

What symptoms result from the following routes of infection of Tularensis: Aerosol, Ingestion, Localized

Answer 6

• Aerosol or Ingestion
– Systemic infections, no localized ulcers or lymph gland swelling
• Aerosol
– Pneumonia
• Ingestion
– Gastrointestinal irritation
• Localized
– Enlargement of local lymph glands, ulcer at infection site

Question 7

Is tularemia contagious?

Answer 7

No

Question 8

What is the infectious dose for Tularemia?

Answer 8

• Infective dose
> 10 to 50 organisms when injected intradermally or when inhaled
> 10^8 organisms when ingested.

Question 9

What is the incubation period of Tularemia?

Answer 9

1-21 days (average=3-5 days)

Question 10

Mortality rate of tularemia?

Answer 10

Mortality — treated: low
untreated: moderate

Question 11

Compare Type A and Type B Francisella

Answer 11

Type A –tularensis
• Most common strain isolated in North America
• May be highly virulent in humans and animals
• Infectious dose of <10 CFU
• Mortality of 5-6% in untreated cutaneous disease

Type B—palaeartica (holartica)
• Thought to cause all of human tularemia in Europe and Asia
• Relatively avirulent
• Mortality of < 5% in untreated cutaneous disease

Question 12

What is the pathogenesis of Francisella tularensis?

Answer 12

1. During the first 3 to 5 days after cutaneous inoculation, F. tularensis multiplies locally and produces a papule; ulceration occurs 2 to 4 days after.
2. Organisms spread from the site of entry to regional lymph nodes and may disseminate via a lymphohematogenous route to involve multiple organs.
3. Bacteremia is probably common in this early phase,although it is only occasionally detected

Question 13

Virulence factor of Francisella?

Answer 13

1.Intracellular
2.Capsule
3.LPS

Question 14

What are the immediate symptoms and subsequent symptoms of Tularemia?

Answer 14

• Immediate Symptoms:
– Fever, headache, chills, rigors, sore throat
• Subsequent Symptoms:
– Loss of energy, appetite, and weight loss

Question 15

What are the forms of Tularemia?

Answer 15

 Ulceroglandular: cutaneous ulcer and swollen lymph node
 Glandular: primarily swollen lymph nodes without an evident cutaneous lesion
Ulceroglandular and glandular tularemia are rarely fatal
(mortality rate < 3%)
 Oculoglandular: eye involvement and swollen lymph nodes (either from contaminated fingers or from contaminated splashes and aerosols)
 Oropharyngeal (throat) : is the result of primary invasion through the oropharynx. The source may be contaminated foods or water or contaminated droplets.

 Typhoidal: systemic signs of sepsis
 Typhoidal tularemia is more acute form of disease (mortality rate 30-60 %)
 Typhoid like symptoms.
 Diarrhea, a major manifestation only in typhoidal tularemia, is loose and watery but only rarely bloody

 Pneumonic: pulmonary symptom.
 This is found in up to 20% of all tularemia cases and may occur at any age.
 It may result from direct inhalation of the organism or from secondary hematogenous spread to the lung.

Question 16

What is a major manifestation only in typhoidal tularemia?

Answer 16

Diarrhea

Question 17

What are the culture characteristics of Francisella tularensis?

Answer 17

• The organism is rarely seen on Gram-stained smears or in tissue biopsies and does not grow in routinely plated cultures

• F. tularensis may be recovered from blood, pleural fluid, lymph nodes, wounds, sputum, and gastric aspirates when processed on supportive media

• Optimal growth at 370 C, growth range 240 to 390 C. Survival rate is best at lower temperatures.

• Slow growing with a requirement for **iron and cysteine or cystine.+*

• No growth on routine culture media but small colony growth after 2 - 4 days on *+glucose-cysteine-blood agar or peptone-cysteine agar or BCYE agar**

• It may be recovered from thioglycolate broth, chocolate agar , modified Thayer-Martin medium, buffered charcoal-yeast agar, or cysteine heart agar with 9% chocolatized sheep blood

Question 18

What is the diagnosis of Francisella tularensis confirmed by?

Answer 18

• Confirmed by:
– Successful culture of bacteria
– Significant rise in specific antibodies

Question 19

What are the problems with the diagnostic used for Francisella?

Answer 19

– Culture is difficult and dangerous
– Response from antibody does not occur until several days after onset of disease. Definitive serologic diagnosis requires a fourfold or greater rise in titer between acute and convalescent specimens; serologies may need to be
repeated at 7- to 10-day intervals before a rise is demonstrated

Question 20

Prevention techniques for Francisella?

Answer 20

• Best Immunity (Permanent)
– Previous infection with a
virulent strain
• Vaccine
– Best prophylactic ? FDA?
– Use insect repellants