Clinical Manifestations and Pathogenesis of
Obligately Intracellular Bacterial Tick-borne
Diseases in the US
DAVID H. WALKER, M.D. The Carmage and Martha Walls Distinguished University Chair in
Tropical Diseases
Professor and Chairman, Department of Pathology
Executive Director,
Center for Biodefense and Emerging Infectious Diseases
University of Texas Medical Branch
Agents & Vectors of Tick-Borne Obligately
Intracellular Bacterial Diseases in the US Agents Ticks Diseases
Rickettsia rickettsii Dermacentor variabilis
D. andersoni
Rhipicephalus sanguineus
Rocky Mountain spotted fever
R. parkeri Amblyomma maculatum Maculatum spotted fever
R. prowazekii ? Amblyomma imitator Typhus
R. massiliae Rhipicephalus sanguineus unnamed
R. philippi 364D D. occidentalis unnamed
R. amblyommii A. americanum unnamed
Ehrlichia chaffeensis A. americanum Human monocytotropic ehrlichiosis
E. ewingii A. americanum Ewingii ehrlichiosis
E. muris-like agent Ixodes scapularis unnamed
Anaplasma phagocytophilum I. scapularis Human granulocytic anaplasmosis
Pathogenic Sequence of Events in
Rickettsial Infections
Spread in the Body
• From portal of entry most likely via
dermal lymphatic vessels to regional
lymph node (e.g., R. slovaca, R. africae,
R. sibirica strain mongolitimonae)
• Hematogenous spread to endothelium
throughout the body
• Cell-to-cell spread of SFG rickettsiae
• No extravascular spread other than
vascular smooth muscle (R. rickettsii)
and occasional perivascular
macrophage
Rickettsia rickettsii in
Human Vascular Endothelium
Pathophysiology of Rickettsial Diseases
Increased vascular permeability
Edema (life threatening in brain and lungs)
Low blood volume
Hypotension
Decreased perfusion of organs
Organ dysfunction
(e.g., acute renal failure: prerenal azotemia)
Increased Vascular Permeability in
R. conorii-infected Mouse Retina
RMSF: Early Rash
Petechial Rash
Ischemic Necrosis of
Distal Digits 2º Severe
Rickettsial Injury to
Microcirculation
Non-occlusive Hemostatic Plug
Rash in Rocky Mountain Spotted Fever
Involvement of palms and soles: 36-82%
Onset after day 5: 43%
Petechiae in center of
maculopapules: 41-59%
Appearance on or after day 6: 74%
Cutaneous necrosis or peripheral gangrene: 4%
%
Occurrence 89-91
Onset day 1 14
days 1-3 49
days 5-6 18-20
Rickettsia Infection of Microcirculation
RMSF: Non-cardiogenic Pulmonary Edema
Cerebral Perivascular Edema in
Rickettsial Encephalitis
%
Confusion 28
Stupor or delirium 21-26
Ataxia 5-18
Coma 9-10
in nonfatal cases 6
in fatal cases 86
Seizures 8
CSF pleocytosis 34-38
CSF protein concentration increased 30-35
Lumbar puncture performed 48-60
Neurological Manifestations of
Rocky Mountain Spotted Fever
Gastrointestinal Manifestations of Rocky Mountain Spotted Fever
Early course
nausea and/or vomiting 38-56%
abdominal pain 30-34%
diarrhea 9-20%
Abdominal tenderness 8-42%
Guaiac positive stools or vomitus 10%
Exploratory laparotomy for acute surgical
abdomen or massive g.i. hemorrhage: 14 patients
Potentially lethal g.i. lesions:
ruptured appendix
gangrenous gallbladder
Jaundice 8-9%
Factors in Severity of
Rickettsial Illness
Older age
Male gender
Glucose-6-phosphate dehydrogenase deficiency (and possibly other causes of hemolysis)
Diabetes mellitus
Alcoholism
Sulfonamide treatment
Probably other co-morbid conditions (e.g., cardiovascular disease)
IFN-γ SNP genetic polymorphism
Clinical Features of Rickettsia parkeri Rickettsiosis
Clinical
Characteristic
R. parkeri
Rickettsiosis
(n = 16) %
Fever 100
Inoculation eschar(s)
Any 94
Multiple 17
Rash
Any type 88
Macules or papules 83
Petechiae 17
Vesicles or pustules 42
On palms or soles 45
Clinical
Characteristic
R. parkeri
Rickettsiosis
(n = 16) %
Headache 83
Lymphadenopathy 25
Nausea or vomiting 8
Diarrhea 0
Coma, delirium, or
seizure
0
Hospitalization 33
Death 0
Rocky Mountain Spotted Fever
United States, 1920 - 2008
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
Year
Nu
mb
er
of
Cases
0
10
20
30
40
50
60
70
80
90
100
Perc
en
t o
f C
ases t
hat
were
Co
nfi
rmed
Confirmed
Probable
Percent Confirmed
Confirmed vs. Probable RMSF Cases,
1992-2007 (NNDSS)
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
3.5%
4.0%
CFRConf CFRProb
Case Fatality Rate among Confirmed and Probable Cases
Perc
en
t D
ied
2000-2003
2004-2007
RMSF Case Fatality Rate by Confirmed vs.
Probable Case Status, 2000-2007 (CRFs)
High Level of Exposure to Lone Star Ticks is
Associated with a High Prevalence of Antibodies to
Spotted Fever Group Rickettsiae
Evidence for Human Infection
with Rickettsia amblyommii
• In a study of soldiers undergoing training in an
environment with heavy exposure to R. amblyommii -
infected lone star ticks, numerous seroconversions to
SFG rickettsiae occurred.
• 56% of seroconversions were asymptomatic.
• Significantly more seroconverters than
nonseroconverters reported fever, chills, headache,
myalgia, rash, arthralgia, dyspnea, and confusion (odds
ratio > 2).
Dengue Syndrome in Mexico
Among 394 suspected cases of dengue fever, 25.1% had
antibodies to typhus group rickettsiae
Rickettsia prowazekii Isolated from Ticks
in Mexico
Amblyomma imitator
female
Case Report of
Rickettsia prowazekii Infection
50 year old man from New Mexico
Vacationed at Padre Island in May- early June 1999
10 days later: fever, headache
June 20: admitted to hospital with fever, stiff neck,
photophobia, abdominal pain
CSF: 30 cells/μl (60% lymphocytes, 40% PMNs)
protein 58 mg/dl
Case Report of
Rickettsia prowazekii Infection
3 days later CSF: 46 cells/μl (73% PMNs),
protein 73 mg/dl
Typhus group Rickettsia IgG-IFA; 1:256 → 1:512
Doxycycline → defervesence
2 CSF samples 17kDa gene PCR:
Rickettsia prowazekii DNA
Massung et al, Clinical Infectious Diseases 32:979-82, 2001
Human Anaplasmataceae Infections
(human ehrlichioses)
Human monocytic ehrlichiosis (HME) -
Ehrlichia chaffeensis
Human granulocytic anaplasmosis (HGA) -
Anaplasma phagocytophilum
Ehrlichiosis “Ewingii” - caused by E.
ewingii, genetically like E. chaffeensis,
phenotypically like human anaplasmosis
Infection with E. muris-like agent in upper
midwest US and Russia
Median Percentages of Monocytotropic Ehrlichiosis Patients
with Specific Symptoms or Signs at Any Time
during the Course of Illness
Symptom or Sign (n = 234-422)
%
Fever 96
Myalgia 68
Headache 72
Malaise 77
Nausea 57
Vomiting 47
Diarrhea 25
Cough 28
Arthralgias 41
Rash 26
Stiff Neck 21
Confusion 20
Median Percentages of Monocytotropic Ehrlichiosis
Patients with Specific Abnormal Laboratory Findings
at any Time during the Course of Illness Laboratory Abnormality
(n = 250-308)
%
Leukopenia 60
Thrombocytopenia 79
Anemia 50
Elevated serum aspartate
transaminase
88
Elevated serum creatinine 24
Fishbein DB, Dawson JE, Robinson LE Human ehrlichiosis in the United States, 1985 to 1990 Ann Intern Med 120:736-43
Hematologic and Hepatic Enzyme Changes in HME
Established Clinical Forms of
Human Monocytic Ehrlichiosis
• Rocky Mountain spotted fever or toxic shock
syndrome-like multisystem disease
• Aseptic meningitis with multisystem disease
• ARDS with multisystem disease
• Overwhelming ehrlichial infection of severely
immunocompromised patients
• Asymptomatic presence of antibodies reactive
with E. chaffeensis ( ? stimulated by a less
pathogenic agent, such as E. ewingii)
Compensatory Hemopoietic Hyperplasia
Hemophagocytosis
Granulomas: A Host Defense
Hepatic Cell Death
Diffuse Alveolar Damage
Meningoencephalitis
Overwhelming Ehrlichia chaffeensis
in AIDS Patients
Fatal Toxic Shock-like Ehrlichiosis
Severe hepatic apoptosis and necrosis
mediated by CD8 T lymphocytes
Loss of antigen-specific IFN-γ producing
CD4+ lymphocytes associated with apoptosis
Overproduction of TNF-α by CD8 T cells and
IL-10 by nonadherent spleen cells
A weak Th1 response (low IL-12)
Ehrlichia chaffeensis Seroprevalence Among Children in the
Southeast and South-Central Regions of the United States
(Arch Pediatr Adolesc Med. 2002;156:166-170)
Epidemiology and Ecology
HGA – Anaplasma phagocytophilum
─ risk for disease increased with age, male gender
─ Incidence: Connecticut - 51 cases per 100,000 pop.
Northwestern Wisconsin - 58 cases per 100,000 pop.
─ Seroprevalence: Northwestern Wisconsin, up to
15% of tick- exposed Sweden, 15-20%
─ upper Midwest and northeast US, northern
California, Europe
─ transmitted by Ixodes spp. nymphs and adults
─ reservoir white-footed mice
(Peromyscus leucopus), deer
Median Percentages of Anaplasmosis Patients with Specific
Symptoms or Signs at Any Time during the Course of Illness
Symptom or Sign Granulocytotropic Anaplasmosis (n= 24-531)
Fever 100%
Myalgia 78% Headache 89% Malaise 97% Nausea 44% Vomiting 20% Diarrhea 17% Cough 20% Arthralgias 56% Rash 3% Stiff neck 22% Confusion 17%
Median Percentages of Anaplasmosis Patients with
Specific Abnormal Laboratory Findings at any Time
during the Course of Illness
Laboratory Abnormality Granulocytotropic
Anaplasmosis
(n= 59-344)
Leukopenia 55%
Thrombocytopenia 75%
Anemia 28%
Elevated serum aspartate 83%
transaminase
Elevated serum creatinine 15%
Kinetics of leukocyte and platelet counts
and hemoglobin concentrations in HGA
HGA Complications
• Septic or toxic shock-like syndrome
• Coagulopathy
• Atypical pneumonitis/Acute respiratory distress syndrome (ARDS)
• Acute abdominal syndrome
• Rhabdomyolysis
• Myocarditis
• Acute renal failure
• Hemorrhage
• Brachial plexopathy
• Demyelinating polyneuropathy
• Cranial nerve palsies
• Opportunistic infections
• Death ─ 0.5% case fatality rate
A. phagocytophilum-Induced
Neutrophil Functional Alterations
ACTIVATION
• Degranulation
• Inflammation
• Mobility
• Production of
– Proteases
– Chemokines
– Chemotactic factors
DEACTIVATION
• Respiratory burst
• Apoptosis
• Endothelial cell adhesion
• Transmigration
• Phagocytosis
• Microbial killing
Acknowledgements to Colleagues
Who Have Shared Slides Used in
This Presentation
J. Stephen Dumler
Jennifer McQuiston
Aaron Sanchez
Sherif Zaki