Rocky Mtn Spotted Fever

Question 1

Rickettsia rickettsia

Answer 1

Tick-transmitted rickettsial
Rod, coccoid, pleomorphic
Gram negative staining, cell walls, no flagella
Intracellular: multiples in reticuloendothelium, endothelial cells

Question 2

Distribution

Answer 2

Affects several vertebrates including man

Mainly atlantic coast and SE states

Question 3

Epizootiology

Answer 3

Distribution depends on vector etiology

• -Dermacentor andersoni = wood tick
• -Dermacentor variabilis = American dog tick

Question 4

Dermacentor andersoni

Answer 4

3 host tick - larval, nymph in rodents; adults in large mammals
Adults in spring, summer
Dogs exposed in canyons (west)
Transmit other dz 
--Tularemia

Question 5

Dermacentor variabilis

Answer 5

Main vector in eastern states
3H tick
–Larvae, nymphs feed on rodents
–Adults feed on large mammals
Most RMSF is reported in Eastern states as D variabilis has more affinity for dogs than D andersoni
Children more susceptible than adults
Other ticks incriminated in transmission of RMSF to man

Question 6

Dermacentor variabilis - how ticks infected

Answer 6

Ticks infected by:
–vertical transmission
–When feed on same animal as other infected ticks
Dogs of minor importance in the maintenance of RMSF in a tick population

Question 7

Dermacentor variabilis - additional facts

Answer 7

–Dogs are carriers of ticks that spread to man
–Ticks must ingest large number of organisms to be infected and for transovarial transmission to occur
Prevalence in ticks is low
Ticks can survive for years without a blood meal
–Ticks can loose infection after 8mo
Organisms need to become avirulent in ticks during the cold months
Need to attach for 5-20 hrs to transmit infection
–Only need to feed 1x btw molts

Question 8

Pathogenesis

Answer 8

Tick bite –> enters circulation –> infects, replicates in endothelial cells
Necrotizing vasculitis –> vascular necrosis to the point of blood extravasation from vessels
If extensive:
–edema
–organ failure
–Shock
Skin, brain, heart, kidneys often affected

Question 9

Clinical features (1)

Answer 9

Clinical/subclinical dz - immunity lasts 3yr
Purebred dogs (German Shepards) severely affected 
Clinical picture is quite variable 
Ticks rarely found on dogs when present with signs

Question 10

Clinical features (2)

Answer 10

Fever 
--within 2-3d of tick attachment
Cutaneous
--edema
--hyperemia of lips, scrotum 
--NO SCLERAL INJ

Question 11

Clinical Features (3)

Answer 11

Petechial hemorrhages 
--Ocular, oral, genital MM
WL
Epistaxis 
Lymphadenopathy 
Splenomegaly
Multisystemic

Question 12

Lab: CBC

Answer 12

Leukopenia then leukocytosis (left shift)
Longer the illness, higher the leukocytosis
THROMBOCYTOPENIA
Anemia (normocytic/normochromic)
Occassionally see DIC indicators
Often positive Coombs

Question 13

Lab: Chem Panel

Answer 13

Increased ALT, AST, AlkP
Increased cholesterol 
Decreased albumin 
Increased BUN, proteinuria --> terminally 
CSF usually normal - PMNs, mononuclear

Question 14

Dx

Answer 14

CS, hx, lab abN
Serology
Direct FA on skin biopsy - quick, definitive
–positive by day 4 PI

Question 15

Dx Serology

Answer 15

Micro - IF: most commonly used
Not always got titers when present with signs (IgG)
Therefore: document rising titers
–4 fold increase after 3 weeks
Titers: decrease 3-5mo PI, usually negative 10mo PI
Titers may rise after treatment (dogs)
Slight or no cross reactivity with Ehrilichia, Anaplasma
Latex agglutination: rapid and specific but false positive

Question 16

Response to therapy

Answer 16

Acute phase: rapid response (24-48hrs) –> fever goes
Tx = rickettsiostatic –> immune removal
Steroids do not affect outcome
Poor recovery DT CNS dz or organ failure
Relapses = uncommon
Supportive care treatment: shock, DIC, organ failure

Question 17

Prevention

Answer 17

Dogs show good immunity against re-infection
--Once recover, never reinfected 
No vax available 
Avoid ticks 
Rapidly remove ticks from dogs 
Tick control: collars, monthly
Screen blood donors

Question 18

Public Health Considerations

Answer 18

Serious zoonotic disease - 1000 cases/yr
Eastern states
Approx 10% human cases only exposed to dogs
Most cases from tick fluids, not dog fluids
Remove ticks with forceps/wear gloves
Wear appropriate clothing in tick areas

Question 19

Haemobartonellosis

Answer 19

Haemobartonella canis 
--epicellular parasite 
Tightly attached to RBC surface 
Usually rod
Forms chains on surface of RBC

Question 20

Haemobartonellosis: Epizootiology

Answer 20

World wide distribution
Vector: Rhicephalus sanguineus
Blood transmission important in transmission

Question 21

Haemobartonellosis Pathogenesis

Answer 21

Not pathogenic in healthy dogs

Dogs will develop dz if splenectomized, immunosuppresion or have other blood parasites

Question 22

Haemobartonellosis Clinical Features

Answer 22

Often difficult to separate from underlying disease
Anemia often associated with parasitemia
Parasitemia often cyclical
Severity of signs depends on the rate of development and degree of the anemia

Question 23

Haemobartonellosis Lab

Answer 23

CBC
--anemia --> regenerative 
Biochem
--bilirubinemia, hemoglobinemia/uria
--Coomb's positive, slide agglutination positive

Question 24

Haemobartonellosis Dx

Answer 24

Hx of splenectomy
Organisms in RBC
Serology NOT available