TOPIC 17: Typhus

Question 1

what causes typhus?

Answer 1

Caused by Rickettsia prowazekii
* Obligate intracellular organism
* Infects endothelial cells lining blood vessels (easy spread to blood!)

Question 2

what is the other name for typhus?

Answer 2

epidemic typhus

Question 3

how is typhus spread?

Answer 3

Spread to humans from body louseà Pediculus humanis
* Lice
* Not a reservoir because the louse is killed within 1 week of infection- a vector

Question 4

why are lice a vector, not resevoir for typhus?

Answer 4

because the bacterium kills the lice within one week of infection!! cannot persist as a resevoir

Question 5

Louse collects Rickettsia when taking a blood meal from a ______
* When the infected louse takes a blood meal from another human, fecal matter
is deposited on the skin
* Infected feces or crushed louse can be rubbed into bite wounds

Answer 5

human

Question 6

Common in crowded locations where louse can easily be spread from
person to person, like…?

Answer 6

prisons and refugee camps

Question 7

T/F: typhus is associated with poor hygiene

Answer 7

true!!

Question 8

______ prefers cooler temperatures- mountainous regions
* Found in the Himalayan area of Asia

Answer 8

typhus

Question 9

why is typhus Also associated with cooler months?

Answer 9

warmer clothes promote lice infestation
when hygiene/sanitation are poor

Question 10

T/F: Mortality rate of typhus when untreated can be as high as 60%
* Especially in the elderly and those who are not well nourished

Answer 10

true!!

Question 11

______ multiplies in the gut of the louse, lysing the vector
* Able to remain viable in dead louse vector for prolonged periods of time

Answer 11

Rickettsia

Question 12

In the human host it multiplies in the cytoplasm of the ______-prevents fusion of the phagosome and the lysosome

Answer 12

endothelial cell

Eventually the infected endothelial cell ruptures releasing Rickettsial cells to the
interstitial fluid (goes everywhere!!)

Question 13

Damage to the vasculature results from…?
* Blood loss, protein loss, shock and multiple organ failure

Answer 13

lysis of endothelial cells

Question 14

what is the incubation period of typhus?

Answer 14

Incubation period is ~12 days (range of 7-14 days)

Question 15

what are the sudden onset symptoms of typhus?

Answer 15

Sudden onset of high grade fever that can last for 2 weeks, chills,
severe headache, coughing, weakness, exhaustion, myalgia

Question 16

what happens after the sudden onset symptoms of typhus resolve?

Answer 16

~ 1 week after the initial onset of symptoms patients go on to develop
a dark colored macular rash
* Located on the upper trunk eventually spreading to the remainder of the body
* Does not occur on the face, palms of the hands or the soles of the feet

Question 17

Presentation of _____ can be misinterpreted as leptospirosis, typhoid fever,
other Rickettsia infection, dengue, malaria as well as others
* Thorough exam and history are needed to ensure proper diagnosis

Answer 17

typhus

Question 18

because Rickettsia goes into endothelial cells, what is important from the antibiotic we choose to treat with?

Answer 18

need great tissue penetration to get into host cells AND track down disseminated bacterium

Question 19

______ disease:
Occurs in typhus patients years after initial infection- recrudescence
* Never cleared in these individuals- becomes latent
* Does not involve louse
* Reactivation often associates with poor nutrition and underlying conditions

Answer 19

Brill-Zinsser Disease (reactivated Rickettsia)

Question 20

______:
Presents as a less severe form of typhus
* May or may not include a rash
* High grade fever and chills as well as cough
* Bacteremia occurs- Rickettsia can be picked up by louse- potential
cause of epidemic typhus

Answer 20

brill-zinsser disease

Question 21

how do we diagnose typhus infection?

Answer 21

Diagnosed with immunoglobulin assays
* Four fold increase in antibody titer between acute and convalescent phase

Question 22

Antibodies are detectable _____ after the onset of symptoms of typhus
* PCR is possible using blood sample prior to antibody detection

Answer 22

~10 days

Question 23

Previous antibody agglutination tests used antigen from Proteus
vulgaris- called the Weil-Felix test (had more cross-reactivity so was less accurate)
* Antigen from _____ is used today

Answer 23

Rickettsia

Question 24

how do we treat typhus?

Answer 24

Doxycycline is given orally for ~7-10 days
* Two times per day until fever is absent for 48 hours
* Helps to prevent severe infection but also decreases likelihood of an epidemic

Question 25

why can't we use doxycycline in children under 8?

Answer 25

Can’t be used in children under 8 * Changes coloring of the teeth

Question 26

Single dose therapy for typhus has also shown to be effective, where would this be optimal?

Answer 26

Good option in refugee camps and other locations with access to medical resources are limited * Can be given to all suspected cases during epidemics- empirical treatment- helps to control the epidemic

Question 27

what preventative measures can we take against typhus?

Answer 27

Regular changing of clothes and bedding Use of permethrin insecticide is also recommended * Dust clothing and bedding * Repetition every 6 weeks is needed when louse infestation