Human Babesiosis – An Update
Patricia J. Holman
Department of Veterinary Pathobiology
College of Veterinary Medicine and Biomedical Sciences
Texas A&M University
College Station, TX
Babesiosis
• Emerging tick-borne disease
• Zoonosis caused by intraerythrocytic
protozoan parasites
• Infections may range from
asymptomatic to severe, or even fatal
• Most cases occur in the U.S.;
worldwide where ticks occur
• Phylum – Apicomplexa
– Babesia, Plasmodium, Toxoplasma,
Cryptosporidium
– Unique organelles comprise apical complex
Electron micrograph
courtesy of
Dr. R.E. Droleskey
USDA
College Station, TX
Babesia - Two-host life cycle
Sexual reproduction in the vector tick
Asexual reproduction in
mammalian red blood cells
Vertebrate
Tick
Salivary
glands
Kinete
Ovaries,
Eggs
Gut
Zygote
Gamont
Babesia microti
Tick transstadial
transmission
2. Tick picks up
infection from
parasitemic host
3. Tick molts to
nymph - now
infective
1. Larval
ticks hatch
4. Tick feeds
on mice or
other hosts;
transmits
6. Adult tick
feeds on
host, then
females drop
to lay eggs
5. Tick loses ability to
transmit infection
during molt from
nymph to adult unless
it feeds on an infected
host as a nymph
Babesia divergens
Tick transovarial
transmission
1. Adult tick picks
up infection from
parasitemic host
2. Infected
larval ticks
hatch
3. Tick feeds
on cattle or
other hosts;
transmits
Babesia
Babesiosis
• Symptoms 1-6 wks after tick feeds
• Variable
– Asymptomatic infection
– Mild to moderate illness
– Severe disease – usually immunosuppressed
•
•
•
•
Medication
Splenectomy
HIV co-infection
Malignancy
Babesiosis
• Symptoms
– Fatigue
– Intermittent fever
• Chills, sweats, headache, arthralgia, anorexia, cough, nausea
Asymptomatic infection
• Clinical Presentation
– Fever, pallor
– Splenomegaly
– Hepatomegaly
• May last a week or months
• Prolonged recovery; persistent parasitemia
Babesiosis – Severe form
• Most common complications
– Respiratory failure
– Congestive heart failure
– DIC
– Liver and kidney failure
– Splenic rupture
– Immunocompromised – 21% mortality
Diagnosis
• CBC
– Hemolytic anemia with elevated reticulocytes
– Thrombocytopenia
– Normal to slightly decreased leukocyte count
• Blood chemistry
– Elevated serum liver enzymes (~ ½ of patients)
– Proteinuria, elevated blood urea nitrogen and
serum creatinine
Diagnosis
• Microscopic identification
– Giemsa stained thick or thin blood films
– Babesia ring forms can be mistaken for
malaria
• Serology - IFA
– B. microti
• B. duncani does not cross-react
– B. divergens
• Sera from B. divergens or B. ventorum patients
cross react
Diagnosis
• Polymerase chain reaction
– Highly sensitive and specific
– Useful for extremely low parasitemias
• Confirm infection
• Determine species
• FISH
– Detects Babesia DNA in patient blood film
– Specific probe binds to DNA
– Highly specific; not as sensitive as PCR
IGeneX
Diagnosis
• Subinoculation into laboratory animals
– 2-4 weeks for parasites to appear in
circulation
– Hamster – Babesia microti
– No known laboratory host for all of the
human Babesia spp.
Treatment
• Atovoquone/azithromycin 7-10 days
– B. microti infections
– 15% adverse reactions
– Diarrhea and rash
• Clindamycin/quinine 7-10 days
– Recommended for severe babesiosis
– 72% adverse reactions
– Diarrhea; tinnitus and hearing loss
• Exchange transfusion - severe illness
Prevention
• Avoid areas with ticks, mice and deer
– Especially May-October
– Especially immune compromised people
• Anti-tick strategies
–
–
–
–
Long sleeves, long pants tuck cuffs into socks
Pyrethrins on clothing
DEET on exposed skin
Check for and remove ticks promptly after possible
exposure
Prevention II
• Property
– Keep grass short
– Remove leaf litter
– Discourage mice
• Seal potential den holes
• Pyrethrin treated cotton
– Discourage deer
• “Deer proof” plants
• Fencing
Prevention III
• Transfusion risk
– No FDA approved test for donated blood
– Agencies prohibit donations by people
who live in or visit endemic areas
– Research ongoing for ways to inactivate
organisms in blood
Zoonotic Babesia spp.
• Europe
– Babesia divergens - France, Ireland, Great Britain
(cattle production)
– Babesia venatorum – Austria, Italy, Germany
– Babesia microti
• Asia, Africa, and South America
– Babesia microti-like
– B. divergens-like
– Ovine Babesia-like
Babesia divergens
• Most cases occur in France & British Isles
–
–
–
–
30 reported human cases
Associated with cattle
84% asplenic patients; 42% fatality rate
Infection is considered a medical emergency
• Hosts
– Cattle, small mammals
– Ixodes ricinus
Babesia venatorum
• Three documented cases
– All asplenic and > 50 years
– Mild to severe, but not fatal
• Parasites – typical paired pyriform
• Hosts
– Roe deer
– Ixodes ricinus
Zoonotic Babesia spp.
• United States
– Babesia microti - Northeast
and upper midwest
– Babesia duncani – Washington state (WA1-3)
– California CA1-6 (similar to B. duncani ?)
– Babesia divergens-like – MO-1 and KY
(Nantucket Island)
– Babesia divergens-like –
Washington state
Babesia microti
• Most cases occur in the U.S.
– > 300 known cases – not a reportable disease
– Variable severity of disease
• Most symptomatic cases mild and self-limiting
• Immune suppressed or >50 yrs at higher risk of
severe disease
• 5% mortality rate
– Tick transmission May-October
– Transfusion or blood product associated cases
– Neonatal cases
Babesia microti
• U.S. endemic regions
–
–
–
–
Ixodes scapularis
White footed mouse
White-tailed deer maintain the vector tick
B. microti cannot infect deer
• Parasites in tetrads in “paired” form
Babesia microti
• Not considered a major human pathogen
in Europe
– High prevalence in rodents
– Ixodes trianguliceps vector tick – nest dwelling
– Ixodes ricinus
Babesia duncani
• Washington and California
• Five cases
– Spleen intact individuals
– Subclinical to severe illness
– 2 were acquired via transfusion
• Seroprevalence 4 to 17%
• Tick vector and reservoir host
unknown
• Parasites in tetrads in “paired” form
Babesia divergens-like
• One case in Washington state
– Asplenic, > 50 years
– Similar molecularly to Babesia divergens
– Tick and reservoir host not known
Babesia divergens-like
• Two cases - MO-1 and KY
– Both asplenic, > 50 years
– Both severe disease, 1 death
– Parasite endemic on Nantucket Island
• Eastern cottontail rabbits
• Ixodes dentatus
• Not infective to cattle
• No human cases on Nantucket Island
Babesia divergens-like cases of
Human Babesiosis
• KY isolate
– Critically ill man admitted to
emergency room in Kentucky
• Fever
• Chills
• Bloody urine
• Immediately started on doxycycline –
Ehrlichiosis?
Babesia divergens-like KY
• Blood smear - Numerous babesia organisms
• History
– Splenectomy 9 years previously
– Tick exposure
• Recreational hunter
• WTD and cottontail rabbits
Diagnosis and Treatment
• Negative for Ehrlichia and Babesia microti
• *** Babesia divergens *** (Beattie et al. 2002)
• Pathology - Asplenic
• Morphology
• 18S rRNA gene sequence
• Hospitalized for 12 days
• TX: Clindamycin, quinine, and doxycycline
B. divergens-like MO-1
• MO-1
–
–
–
–
Fever, chills, headache, sore throat, and joint pain
No improvement with erythromycin
Fatal infection (Herwaldt et al, 1996)
MO-1 18S rRNA gene identical to KY
B. divergens-like NR
• Nantucket (rabbit isolate)
– KY/MO-1 18S rRNA gene identical to NR
(Goethert & Telford 2003)
– 16% of rabbits positive by PCR
– Ixodes dentatus ticks, larval to nymphal stage 4% +
Babesia divergens Discrepancies
• Tick vector ?
• Neither patient had traveled outside of
the US
• No known infection in U.S. cattle
despite high cattle population in
Kentucky and dairies on Nantucket
Island
SSUrRNA
ITS1
5.8S
ITS2
LSUrRNA
rRNA ITS1 & ITS2 Percent Identities
KY
NR
Bdiv
KY
100
100
94
NR
100
100
94
Bdiv
90
90
100
Infection Studies
• Source of parasites needed
– No blood from the case
• Rabbits
– Limited by extremely low circulating
parasitemias
• In vitro culture
– Produce quantities for additional
characterization
– Collaboration with Goethert and Telford, Tufts
University
Host erythrocyte specificity in vitro
Parasite
Host RBC
Serum
supplement
Growth
Nantucket
Rabbit
(NR774)
Human
Bovine
Cottontail
rabbit
Human
Bovine
Human
Yes
No
Yes
Human
Bovine
Cottontail
rabbit
Human
Bovine
Human
Yes
Yes
No
B. divergens
Results - Morphometric
Parasite
NR
Bdiv
KY
Host RBC
Size
Human
Cottontail rabbit
Bovine
4.3 µm
Human
Bovine
Cottontail rabbit
3.1 µm*
Human (blood)
4.1 µm
4.2 µm
N/A
2.2 µm
N/A
Stddev
± 0.48
± 0.56
± 0.53
± 0.36
± 0.58
Cattle Infection Study
PCR
Day
-17
4
5
6
7
9
10
11
Controls
Principals
Aspl Spleen Aspl Spleen
+ Day
- -17
4
+ 5
6
+ 7
+ 109
+ 11
+
Culture
Controls
Principals
Aspl Spleen Aspl
Spleen
- - - - PCR
Culture
Controls - Principals
Controls
Principals +
+
(4)
Aspl Spleen Aspl Spleen Aspl Spleen Aspl
Spleen
+- - - - -- -- - - -+ (2)- + -(4)- - - +
+
- - - - + (4)
- - +- + - - -- -- - - + (2)
+ (2)
+ (4) + -(2)- - - +
+
- - - - + (2) + (2)
- - ++ + - - -- -- - - + (1)
+ (1)
+ (2) + -(2)- - - ND
- - +++ ++ - -- --- --- -- - ND
ND
ND
ND
ND
- - - - -++ + - - -- -- - - NDNDND ND
+
- - - - ND ND
-
-
-
-
Conclusions
• KY and NR are conspecific
–
–
–
–
Identical 18S rRNA gene sequence
Identical ITS1 / ITS2 sequences
Size - large babesia
Morphology
• B. divergens distinct
–
–
–
–
–
ITS1 and ITS2 sequences vary from KY/NR
Size - small babesia in natural host
Morphology
Infective for cattle
Culture – Bovine RBC, not cottontail rabbit
Babesia divergens is not endemic in the U.S.
Acknowledgements
Dr. Andy Allen, Washington State University,
Pullman, WA
Dr. Jim Beattie, Bowling Green Associated
Pathologists, KY
Dr. Bob Droleskey, USDA, College Station, TX
Dr. Heidi Goethert, Tufts University, MA
Dr. Sam Telford, Tufts University, MA
Dr. Will Goff, USDA, Pullman, WA
Dr. Don Knowles, USDA, Pullman, WA
Angela Spencer & Lorien Schoelkopf
Funding: NIH RO3, USDA/ARS, Texas Agricultural
Experiment Station