Human Babesiosis – An Update

Patricia J. Holman

Department of Veterinary PathobiologyCollege of Veterinary Medicine and Biomedical

SciencesTexas A&M UniversityCollege 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 micrographcourtesy of Dr. R.E. DroleskeyUSDACollege Station, TX

Babesia - Two-host life cycle

Tick Vertebrate

Salivary glands

Gut

Ovaries,Eggs

Gamont

Kinete

Zygote

Sexual reproduction in the vector tick Asexual reproduction in

mammalian red blood cells

1. Larvalticks hatch

3. Tick molts tonymph - now

infective

4. Tick feedson mice or

other hosts;transmits

2. Tick picks upinfection from

parasitemic host

5. Tick loses ability totransmit infectionduring molt from

nymph to adult unlessit feeds on an infected

host as a nymph

Babesia microtiTick transstadial

transmission

6. Adult tickfeeds on

host, thenfemales dropto lay eggs

Babesia divergens

Tick transovarial transmission

1. Adult tick picksup infection fromparasitemic host

2. Infectedlarval ticks

hatch 3. Tick feedson cattle orother hosts;

transmitsBabesia

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 PCRIGeneX

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

• 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 MO-1

• 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% +

B. divergens-like NR

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

rRNA ITS1 & ITS2 Percent Identities

KY NR Bdiv

KY 100 100 94

NR 100 100 94

Bdiv 90 90 100

SSUrRNA ITS1

5.8S ITS2 LSUrRNA

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

Nantucket Rabbit (NR774)

B. divergens

HumanBovine

Cottontail rabbit

HumanBovine

Cottontail rabbit

Human Bovine Human

HumanBovineHuman

Growth

YesNoYes

YesYesNo

Results - Morphometric

Parasite

Host RBC Size Stddev

NR HumanCottontail rabbitBovine

4.3 µm ± 0.48

4.2 µm ± 0.56N/A

Bdiv HumanBovineCottontail rabbit

3.1 µm* ± 0.53

2.2 µm ± 0.36N/A

KY Human (blood) 4.1 µm ± 0.58

PCR Culture Day Controls Principals Controls Principals Aspl Spleen Aspl Spleen Aspl Spleen Aspl Spleen

-17 - - - - - - - - - - - - 4 + + - - - - + (4) - - - - - 5 - + - - - - + (2) + (4) - - - - 6 + + - - - - + (2) + (2) - - - - 7 + + - - - - + (1) + (2) - - - - 9 + + - - - - ND ND - - - -

10 + + - - - - ND ND - - - - 11 + + - - - - ND ND - - - -

PCR Culture Day Controls Principals Controls Principals Aspl Spleen Aspl Spleen Aspl Spleen Aspl Spleen

-17 - - - - - - - - - - - - 4 + + - - - - + (4) - - - - - 5 - + - - - - + (2) + (4) - - - - 6 + + - - - - + (2) + (2) - - - - 7 + + - - - - + (1) + (2) - - - - 9 + + - - - - ND ND - - - -

10 + + - - - - ND ND - - - - 11 + + - - - - ND ND - - - -

Cattle Infection Study

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, TXDr. Heidi Goethert, Tufts University, MADr. Sam Telford, Tufts University, MADr. Will Goff, USDA, Pullman, WADr. Don Knowles, USDA, Pullman, WAAngela Spencer & Lorien Schoelkopf

Funding: NIH RO3, USDA/ARS, Texas Agricultural Experiment Station