L 78 Relapsing Fever & Leptospirosis

Question 1

What are the causative agents of relapsing fever?

Answer 1

Borrelia recurrentis and hermsii

Hermsii predominates, but up to 8 other species also possible

Question 2

Characteristics of Borrelia

Answer 2

Gram (-) spirochetes
Visualized in gram or Wright-Giemsa stained blood smears
Cultured on BSK medium (critical component is N-acetylglucosamine)

Question 3

Epidemic vs Endemic relapsing fever in terms of geography, cycle, hosts, vectors

Answer 3

Epidemic: Borrelia recurrentis, Louse vector Pediculus humanus (LBRF), makes louse and humans the hosts, europe, asia, africa

Endemic: Borrelia spp., Tick vector (TBRF), includes rodents in cycle of hosts, every continent except Australia, Antarctica and SW Pacific

Question 4

Explain the mechanism for the recurrence of symptoms in relapsing fever

Answer 4

Antigenic variation or switching occurs where a cassette mechanism allows the bacteria to switch out VMP’s (variable membrane proteins) in order to avoid detection and destruction by the immune system
There appears to be a signal to switch once the colony of cells reaches a certain threshold. However, the switch is then random in terms of the new gene that is expressed, so each cell has the potential to express a new and different surface protein.

Question 5

What kind of tick is the vector for relapsing fever?

Answer 5

Soft bodied tick called Ornithodoros hermsii
They can live 15-20 years and last 3 years without a blood feeding
These ticks feed rapidly and repeatedly as opposed to the hard ticks that feed once per stage and feed slow

Question 6

What are the animal hosts for Borrelia?

Answer 6

Rodents: rats, chipmunks, squirrels

Remember that blood and tissues from these host animals is infectious

Question 7

Where is relapsing fever found in the US?

Answer 7

Far west from washington down to texas

The ticks like log cabins, caves, and under buildings. They tend to not be out in the grass and vegetation.

Question 8

How is epidemic relapsing fever spread between louse and human?

Answer 8

Louse is initially infected by biting the already infected human. In order for human to get infected, must smash the louse. Being bitten actually does not transfer Borrelia to the human.

Question 9

Clinical Manifestations of relapsing fever

Answer 9

3 Stages:
1) Primary Spirochetemia: acute onset of high fever, chills, headache, tachycardia, arthralgia, myalgia, LBRF–unremitting for 3-6 days, TBRF–Sx occur in 1-3 day periods
Crisis after first fever episode: rigors, increased temp and pulse for 15-30 min then diaphoresis and falling temp and BP for several hours, can cause death

2) Latent phase where bac replicate and change antigens, bac can’t be isolated from blood

3) Secondary spirochetemia (relapse) TBRF 3-10 times, LBRF 1-2 times
Decrease duration and severity with each relapse

Question 10

Relapsing fever diagnosis

Answer 10

Hx of exposure to vectors or travel to areas
Visualize Borrelia in blood
Meningitis/encephalitis: consider spinal tap
Culture

Question 11

Relapsing fever treatment

Answer 11

Doxycycline/tetracycline
Tick: 7-14 days
Louse: single dose

Question 12

What are the potential consequences of treating relapsing fever?

Answer 12

Jarisch-Herxheimer response in 30=90% of patients

Question 13

Where does Leptospira interrogans come from?

Answer 13

It is the most common zoonosis in the world (though rare in the US)
Has no vector
Found in the renal tubes of many mammals => urinary shedding
Dogs, cats, livestock, rodents

Question 14

How is Leptospria interrogans transmitted?

Answer 14

Epidemic: seasonal rains or flooding
Endemic: tropical environment, rodent infestation
Sporadic: human contact with contaminated environment

Question 15

Characteristics of Leptospira interrogans

Answer 15

Spirochete, thin and tightly coiled
Both ends bent like a hook or questions mark
Highly motile, aerobic
Facultative intracellular
Difficult to see on microscope and can’t be used for diagnosis
Difficult to grow
Survive well in freshwater, soils, vegetation and mud

Question 16

Describe infection pathogenesis of Leptospira interrogans

Answer 16

Crosses mucous membranes
Enters bloodstream and tissue
OMP: mediates adhesion and factor H binding
Targets kidneys, liver, heart causing damage

Question 17

Clinical manifestations of Leptospira interrogans

Answer 17

Most are subclinical and self-limited
Septicemic anicteric: 4-7 days, abrupt onset, flu-like, spirochete in blood
After 1 week fever subsides and microbes disappear from blood, then fever recurs =>
Immune stage: result of immune response to microbe lasting 0-30 days, antibodies isolated form blood, microbe isolated from urine and may or may not be in blood/CSF, Aseptic meningitis, conjunctival suffusion, renal symptoms

Icteric stage: (Weil’s Disease) profound jaundice, most severe form of leptospirosis, renal, hepatic, pulmonary dysfunctions, also hemorrhagic diathesis

Question 18

When to consider leptospirosis as the diagnosis

Answer 18

Flu-like symptoms with:
Aseptic meningitis or
Disproportionately severe myalgia or
Conjunctival suffusion

Question 19

What is conjunctival suffusion?

Answer 19

Looks like normal conjunctivitis with redness of the eyes but without inflammatory exudates, swelling of the corners of the eyes also seen

This is unique to Weil’s disease, though it may also occur with hantavirus infection

Question 20

Diagnosis of Leptospira interrogans

Answer 20

Clinical findings consistent
Hx of rat contact or contaminated water by animal urine
Culture from blood/csf during septicemic stage
Culture from urine during immune stage
PCR
Serology detects antibodies Leptocheck
Microagglutination Test

Question 21

Treatment for Leptospira interrogans

Answer 21

Hydration

Antibiotics: doxycycline unless

Question 22

Leptospira interrogans Prevention

Answer 22

Avoid animal runoff water and stagnant water
Rodent control
Prophylaxis for at-risk people
Vaccinate animals