1. Tick-borne infections that predominate in the U.S. include:
Lyme disease (Borrelia burgdorferi)
Human monocytic ehrlichiosis (Ehrlichia chaffeensis)
Human granulocytic anaplasmosis (Anaplasma phagocytophilum)
Rocky Mountain spotted fever (Rickettsia rickettsii)
Tularemia (Francisella tularensis)
Babesiosis (Babesia microti)
Relapsing Fever (Borrelia hermsii, B. parkeri, B. turicatae; louse borne relapsing fever due to B. recurrentis)
Colorado tick fever (Coltivirus)

2. Tick Vectors Hard Ticks Ixodes Amblyomma Dermacentor Rhipicephalus
Soft Ticks
Ornithodorus

3. Rocky Mountain Spotted Fever
Originally described in the 1800’s in Western U.S. but currently more prevalent in the South Atlantic region
Caused by Rickettsia rickettsii
The number of cases is increasing with the most cases ever reported in the U.S. occurring in 2004.
The ecology of rickettsial infection is also changing
R. rickettsii has been detected in species of ticks (R. sanguineous; GA and AZ) not previously considered vectors of the infection and in non-typical areas of the U.S. (Arizona)
R. parkeri recently implicated in case of human infection in U.S.

4. RMSF - Ecology D. variabilis D. andersoni Vector
D. variabilis (dog tick) in East
D. andersoni (Rocky Mtn. wood tick) in the West
Adult ticks responsible for transmission
Rhipicephalus sanguineus (common brown dog tick) = newly described vector (NEJM. 2005)
transovarial and transstadial transmission.
Small mammals = as a reservoir for infection of ticks
D. andersoni

5. Distribution and Number of Cases of RMSF 1514 reported cases in 2004
Distribution and Number of Cases of RMSF 1514 reported cases in NC accounted for 35% of cases
Incidence highest in male children (5-9 years)
Highest incidence in SE/South Central U.S
90% of cases in April through September

6. R. rickettsii Member of the spotted fever group (SFG)
SFG also includes the human pathogens: R. akari, R. parkeri, R. felis as well as 5 other species
Gram negative obligate intracellular coccobacillus (0.7 – 2.0 x 0.3 – 0.5 um)
Infects all organs of the tick (salivary glands – horizontal transmission, ovaries – transovarial transmission)
Transmitted to humans during feeding via saliva

7. Diagnosis – Direct Detection
Culture not routine
DFA staining of skin biopsy
provides earliest laboratory diagnosis. Positive before serologic tests but not everyone gets a rash.
70% sensitive, but lower if receiving antibiotic therapy (must perform within 48 hours of therapy).
Not routinely available.
PCR
Most sensitive method for early diagnosis. Performed on skin biopsy. Available at CDC
Immunoperoxidase stain

8. Diagnosis - Serology Antibody detectable 7 – 9 days after onset.
IFA = gold standard (94–100% sensitive, ~100% specific)
Diagnostic titer is >/= 1:64
Antibody persists for years therefore testing of acute and convalescent sera in parallel recommended
LA = rapid serologic test (71–94% sensitive and 96–99% specific)
Detects primarily IgM
Diagnostic titer is >/=1:128
Titers decline to non-detectable within a few months
Positive result suggests recent infection
Anti-human IgG-FITC
Patient IgG
R. rickettsii

9. Human Ehrlichioses Includes 3 recently described infections
Human Monocytic Ehrlichiosis (HME)
Human Granulocytic Anaplasmosis (HGA; formerly HE)
E. ewingii ehrlichiosis
Subclinical to fatal infection, typically - febrile syndrome with headache, myalgias and malaise
Transmitted by several species of hard tick

10. HME
Transmission
Vector = A. americanum (lone star tick) nymph and adult
Ticks may be co-infected with E. ewingii or B. lonestari
Incidence
Southcentral and southeastern states
482 cases reported between 1997 and 2001 (0.7/million)
More common in adults, median age 50 years
70–80% of patients recall tick bite
70% of cases occur in May - July

11. E. chaffeensis
Non-motile, gram negative, obligate intracellular bacteria
Replicate in cytoplasm of white blood cells - monocytes
Form intracytoplasmic morulae containing up to 50 organisms
Inhibit phagosome-lysosome fusion

12. HME-Diagnosis Direct Detection Serology Blood smear = insensitive
Culture not routine
PCR = 80 –87% sensitive during acute disease on whole blood samples. Amplification from other fluids is of unknown sensitivity.
Available via Referral testing at Mayo medical laboratories
Detects E. Chaffeensis, E. ewingii and A. phagocytophilum
Serology
IFA with E. chaffeensis antigen (94-100% sens with paired samples)
Confirmed case = seroconversion/4x change in IgG titer on acute and convalescent sera collected 2 to 3 week apart
IgM testing sensitivity not well defined.
Probable case = IgG >1:64 and compatible disease
Ab often not detectable during 1st 7 days of illness
Cross reactions with E. ewingii

13. Human Granulocytic Anaplasmosis
HGA first described in 1994 as a severe acute febrile illness in individuals from the upper midwest
Similar to HME clinically but organisms present in PMNs rather than monocytes
Caused by Anaplasma phagocytophilum
Infection is treatable with appropriate therapy however, delay in diagnosis and treatment may be associated with significant morbidity/mortality

14. HGA Vectors I. scapularis, I pacificus, I. spinipalpis and I. ricinus
Nymphal ticks most likely to bite humans (small size)
Coinfection with A. phagocytophilum and B. burgdorferi and/or Babesia microti is not uncommon
Epidemiology
Most cases of HGA reported in upper Midwest and Northeast
Peak in April through August - coincides with activity of nymphal Ixodes ticks
Disease primarily diagnosed in older individuals (median age = 51 years)

15. HGA - Diagnosis Direct Detection Wright or Giemsa stained blood smear
20 – 80% sensitive at presentation.
Usually, less than 0.1% of PMNs infected
Disappear from blood after 24 – 72 hours of treatment
PCR
Most sensitive method for acute infection – 60 to >90%
Available via referral testing at Mayo labs
Culture - not routinely available
Serology
Antibody detectable by 2 weeks of onset therefore not always useful for diagnosis of acute infection (30 – 60% sensitive, 70 – 95% during convalescence (1:64 cutoff). Most sensitive method after acute infection
Confirmed case = seroconversion/4x change in IgG titer on acute and convalescent sera collected 2 to 3 week apart
Probable = compatible illness with positive IgG on single sample

16. E. Ewingii Ehrlichiosis
E. ewingii = gram negative, intracellular bacterium found in neutrophils of dogs and infected humans
First reported in 1999
Transmitted by A. americanum in SE U.S.
Few cases identified, disease more likely in immunosuppressed hosts
Clinical manifestations similar to HME but usually milder
Molecular diagnosis typically used; serologic tests can not differentiate between E. ewingii and E. chaffeensis

17. Borrelia burgdorferi Fastidious, microaerophilic spirochete
0.2 x 30um, linear chromosome + 9 circular and 12 linear plasmids
Slow growing (12-24 hour doubling time), cultured in liquid medium
3 pathogenic species
B. burgdorferi– U.S.
B. afzelii – Europe and Asia
B. garinii – Europe and Asia

18. Lyme Disease - Ecology Vectors I. scapularis, I. pacificus, I. ricinus
Nymphal stage = predominant vector for human infection
Other species infected but not common human biters
Reservoirs
White-footed mouse important for infection of larvae (no transovarial transmission)
White tail deer important in the tick life cycle. Transstadial transmission occurs
Human disease corresponds to distribution of tick vector, except in the SE
www-bml.ucdavis.edu/.../Ixodespacificus.jpg

19. Lyme Disease Epidemiology
Most commonly reported arthropod-borne disease in North America and Europe
Most cases of in NE and upper midwest
Approximately 20,000 cases reported annually
Most infections occur in May – July
Most frequent in boys age 5-19 and persons >30 years old

20. Lyme Disease – Diagnosis Based clinical findings, exposure risk, laboratory studies
© DermAtlas;
©2008 UpToDate®

21. Lyme Disease - Diagnosis
Direct Detection
Culture not commonly used
PCR available - Most sensitive in leading edge of skin lesion, joint fluid, CSF
Serology
2 tiered algorithm
Screen with polyvalent ELISA.
C6 ELISA
Confirm positives/equivocals by Western Blot.
IgG and IgM blots available. Do not perform IgM blot after 4 weeks due to false positives.
IgM: 2 of p24, 39, 41
IgG: 5 of p18, 21, 28, 30, 39, 41, 45, 58, 66, 93
Most patients have strong Ab response after 1 month.
CSF may be positive in acute neuroborreliosis, less sensitive in chronic neuroborreliosis. Assess CSF/serum index

22. Issues with Lyme Serology
Standardization
False positives
Other borrelial infections and spirochetal diseases, viral illness, autoimmune disease, cross-reactions due to intestinal commensals and gram negative UTI pathogens
5% of normal population will test positive by ELISA
Low sensitivity in early disease
Up to 6 – 8 week seronegative window
Serology 20 –30% sensitive during EM, 70-80% on repeat
Co-infection with B. microti or A. phagocytophilum may occur
The vast majority of patients with early disseminated and late Lyme disease are seropositive
Late neurologic disease (peripheral neuropathy) not associated with CSF antibody
Test result for people without objective signs of lyme disease or a lack of exposure to endemic areas are of low predictive value.
Vaccine recipients may give positive ELISA and some reactivity on WB for several years

23. Southern Tick-Associated Rash Illness
EM-like rash associated with bite of A. americanum
B. lonestari found in 1 – 3% of ticks
SE and S central U.S.
Doesn’t appear to crossreact serologically with B. burgdorferi