L95 Rickets

Question 1

Rickettsia Host

Answer 1

• Blood-feeding arthropods may serve as both hosts and vectors
• Humans are typically accidental hosts

Question 2

Two families in Rickettsiaceae Order?

Answer 2

1. Rickettsiacceae

2. Anaplamataceae

Question 3

Properties of the Rickettsiaceae

morphology etc

Answer 3

-Gram-negative, pleomorphic coccobacilli
• Glycocalyx is a slime layer

-Induce phagocytosis to enter host cells
• Escape phagosome
• Grow in cytoplasm and/or nucleus

-Can only be grown in cell culture

-Most survive only for short times outside of vector or mammalian host
• Quickly destroyed by heat, drying & bactericidal compounds

Question 4

4 Rickettsial species with specific arthropod or insect hosts

Answer 4

• American dog tick (don’t need to know the microbe)
• House mouse mite
• Human body louse
• Cat flea

Question 5

Rickettsial pathogenesis

Answer 5

• Rickettsiae multiply in endothelial cells of small blood vessels of the skin
and other organs
• Resulting damage leads to necrotizing vasculitis
• Major pathophysiologic effect: increased microvascular permeability
• Consequences: edema, hypovolemia, hypoalbuminemia, thrombo-
cytopenia, hypotension, reduced perfusion, multi-organ dysfunction

Question 6

4 Rickettsia we need to know

Answer 6

R. rickettsii (RMSF) 
-Rocky Mountain spotted fever 
-Western Hemisphere
R. akari
-Rickettsialpox
-Worldwide
R. prowazekii 
-Epidemic typhus
-Worldwide
R. typhi
-Murine (endemic) typhus
-Western Hemisphere Worldwide

Question 7

R. rickettsii

Answer 7

RMSF
Mammalian reservoirs: Rodents, rabbits, (dogs?)
Arthropod vectors (in USA):
--American dog tick
--Rocky Mtn. wood tick
--Brown dog tick (Important in AZ!)

Question 8

RMSF Hosts

Answer 8

Wild Rodents

Question 9

R. rickettsii and RMSF: Disease

Answer 9

Incubation period: 2 – 14 d

Signs/Symptoms:
Fever & severe headache (often w/ sudden onset); other non-specific signs/symptoms: myalgia, nausea, vomiting, etc. (see notes)

Rash (2 – 5 d after onset of fever; absent in ~10% cases) - often begins on wrists, forearms & ankles
- spreads to trunk (centripetal spread)

Question 10

What type of rash is a bad sign with RMSF?

Answer 10

if the macular rash becomes petechial

Question 11

R. rickettsii and RMSF: Disease
Complications:
Mortality rate:

Answer 11

Complications: Myocarditis, CNS dysfunction, renal failure, gangrene, pneumonia, and others (see notes)

Mortality rate: 20 – 40% without treatment 2 – 5% with treatment

Early treatment decreases severity of disease & risk of death!

Question 12

R. akari

Answer 12

-rickettsialpox
-cities, mice
Arthropod vector: House mouse mite
• Transovarial transmission occurs in the mite

Question 13

rickettsialpox: phases

Answer 13

1st phase: red papule at bite site which becomes vesicular & then forms an eschar

2nd phase: 3 – 7 d after skin lesion appears, abrupt onset of fever and severe headache; other signs/symptoms may occur, e.g., chills, rigors & profuse sweating, myalgia

Rash: 2 – 3 d after onset of fever; generalized pox-like rash that can include palms & soles

Self-limited within 2 – 3 wk, even without treatment; no mortality

Question 14

R. prowazekii

Answer 14

(louse-borne) typhus

Question 15

Is the feeding or defecating what causes disease?

Answer 15

Most common mode of transmission: infectious louse feces are scratched into a louse bite wound

Question 16

R. prowazekii and epidemic typhus: Epidemiology

Answer 16

Mammalian reservoir: Humans
Arthropod vector: Human body louse

NO transovarial transmission in lice!

Question 17

R. prowazekii and epidemic typhus: Disease

Answer 17

Incubation period: 7 – 14 d
Signs/Symptoms: Sudden onset of fever & severe headache;
tachypnea, myalgia, & other signs/symptoms may occur

Rash: 4 – 7 d after onset of fever (absent in ~20% of cases) - often begins on trunk
- spreads to extremities (centrifugal spread)

Bad if it becomes petechial

Question 18

R. prowazekii and epidemic typhus: Disease

Complications:

Mortality rate:

Answer 18

Complications: CNS dysfunction, myocarditis, pneumonia, renal failure, gangrene, multi-organ system failure

Mortality rate: 20 – 60% without treatment 3 – 4% with treatment

Early treatment decreases severity of disease & risk of death!

Question 19

R. prowazekii: Brill-Zinnser disease and sylvatic typhus

Answer 19

Brill-Zinnser disease (recrudescent typhus)

• recurrent form, can develop decades after initial infection
• symptoms less severe; rarely fatal

Sylvatic epidemic typhus (aka sylvatic typhus)

• small number of cases, primarily in eastern USA
• symptoms less severe; no reported fatalities
• reservoir: southern flying squirrel
• likely vector: squirrel flea

Question 20

R. typhi and murine (endemic) typhus: Epidemiology

Answer 20

Worldwide distribution, especially in urban & coastal port regions
• USA: 50 – 100 cases/yr, primarily in southern TX and southern CA

Mammalian reservoirs: Rats, mice, cats, opossums

Arthropod vectors: Fleas
• Transmission: Infectious flea feces inoculated into flea bite • Transovarial transmission occurs in fleas
Cat flea

Question 21

R. typhi and murine (endemic) typhus: Disease

Answer 21

Incubation period: 7 – 14 d

Signs/symptoms similar to those of epidemic typhus, but typically less severe and of shorter duration
• Rash occurs in ~50% of cases
• Respiratory involvement occurs in ~30% patients
• Low mortality (4% without treatment; <1% with treatment)

Maculopapular rash

Question 22

Diagnosis of rickettsioses

Answer 22

Presumptive diagnosis based on clinical presentation and patient history

Confirmatory diagnosis
• Serology (detectable titers after 1st week of infection) • Indirect immunofluorescent antibody (IFA) test
• Rash biopsy – PCR; immunohistochemical (IHC) stain

Question 23

Treatment & prevention of rickettsioses

Answer 23

Treatment
• DOC: Doxycycline
• Chloramphenicol if doxycycline is contraindicated

Treatment should not be delayed – do not wait for lab results or if initial results (e.g., PCR) are negative!

Prevention
• Avoidance of arthropod vectors
• Prompt removal of attached arthropods
• Control of reservoirs/vectors
• Rodent control
• Tick and flea control
• Mass delousing w/ insecticide to control epidemic typhus
• Vaccine for epidemic typhus no longer produced/available in USA

Question 24

Properties of the Anaplasmataceae

Answer 24

Gram-negative, pleomorphic coccobacilli
• Peptidoglycan reduced/absent
• Slime layer glycocalyx
Infect bone marrow-derived cells
• Primarily target circulating
leukocytes
• Multiply w/in membrane-bound
compartments, forming structures called morulae

Question 25

How do you distinguish between rickettsia and anaplasmosis with a stain?

Answer 25

Anaplasma stay in leukocytes and stain as “morulae”

Question 26

Vectors of the Anaplasmataceae

Answer 26

Lone star tick
Blacklegged tick

NO transovarial transmission in ticks

Question 27

Which anaplasmatoacceae will we study?

Answer 27

We will consider…
• Ehrlichia chaffeensis, which infects monocytes/macrophages and causes
human monocytic ehrlichiosis (HME)
• Anaplasma phagocytophilum, which infects neutrophils and causes human
granulocytic anaplasmosis (HGA)

Question 28

Ehrlichia chaffeensis and human monocytic ehrlichiosis (HME): Epidemiology

Answer 28

Worldwide distribution
• USA: ~500 - 1000 cases/yr within the last decade, primarily from southeastern & south-central US
• True incidence likely higher; estimated that appx. two-thirds of infections are asymptomatic (seroprevalence survey)

Question 29

E. chaffeensis and HME: Epidemiology

Mammalian reservoirs:

Tick vectors (in USA) :

Answer 29

Mammalian reservoirs: White-tailed deer, dogs, coyotes, other mammals

Tick vectors (in USA) : Lone star tick, other tick species