Babesiosis

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1) Epidemiology :

Babesia spp. = intraerythrocytic protozoan parasite. Categories :

large and small based on morphologic phenotype.

·

Dogs : worldwide importance (B. canis vogeli, B. canis canis, B. gibsoni, B. canis

rossi...).

·

Cats :

B. felis = small highly pathogenic strain (southern Africa & Sudan).

Image1

·

Transmission :

o ticks :

sporozoïtes released during feeding --> endocytosed by erythrocytes -->

sexual reproduction and merogony --> daughter cells infect new erythrocytes

--> infected erythrocytes are ingested by naïve ticks --> merozoïte

becomes gamete in the vertebrate host or tick --> gametes fuse to form

zygote in the tick midgut --> zygote invades epithelial cell of tick gut +

sporogony --> ookinetes leave epithelial cells and invade salivary glands or

ovary. image2

o directly

between vertebrate hosts : fighting contact (American pit bull terriers),

transplacental or blood transfusions.

·

Pathogenesis :

o Pathogenicity

determined by species and strain, age of host, immunologic response.

o Hemolysis : multiple

mechanisms.

o Thrombocytopenia (can be observed

alone) : rarely bleeding. Possible DIC in severe forms of B. canis rossi.

o Tissue hypoxia (due to anemia, shock,

vascular stasis,...) --> damage kidneys and lactic acid generation (leading

to metabolic acidosis).

o Atypical complications : multiple

organ dysfunction syndrome complications resulting from SIRS : AKI, hepatopathy,

immune-mediated hemolysis, pulmonary edema, rhabdomyolysis, and cerebral

dysfunction (B. canis canis and B. canis rossi).

2) Clinical findings

·

Hyperacute

symptoms : hypothermia,shock, DIC, coma, metabolic acidosis, death.

·

Acute

symptoms : hemolytic anemia, icterus, splenomegaly, lymphadenopathy, vomiting.

·

Chronic

Symptoms : intermittent pyrexia, partial anorexia,loss of body

condition.

·

Cats : less than 3 years, lethargy, anorexia, weakness, rough haircoat, diarrhea. Fever

and icterus less common. Mostly chronic disease.

·

« Severe »

babesiosis :

o AKI : !

disproportionate rise of serum urea can be related to catabolism of lysed RBC.

o Cerebral

babesiosis : vascular stasis from sludging of parasitized RBC and their stroma within

capillary beds.

o Coagulopathy (thrombocytopenia

and DIC), hepatopathy, IMHA, ARDS, hemoconcentration, hypotension, cardiac-related

alterations, acute pancreatitis, acide-base disturbances.

·

Low T3 syndrome : IL-6 concentration.

3) diagnostic investigations

·

Laboratory

findings :

o Regenerative

anemia, thrombocytopenia, leukocytosis, neutrophilia, neutropenia,

lymphocytosis, eosinophilia, or leukopenia.

o Positive

autoagglutination and direct Coombs’ test.

o Hemoglobinemia,

hyperglobulinemia, mildly increased liver enzyme activities,

hyperbilirubinemia, hyperkaliemia, hypokaliemia, hypoglycemia, azotemia and

metabolic acidosis.

o Bilirubinuria,

hemoglobinuria, proteinuria, granular casts.

o B. Felis : elevated AST/ALT and

bilirubin. polyclonal hyperglobulinemia can occur. Renal parameters unaffected.

·

Microscopic

identification : image3. Poor sensitivity. Erythrocytes adjacent to

buffy coat or peripheral blood smear.

o B. canis : large, pyriform-shaped

organisms, singly or in pairs.

o B. gibsoni : smaller single intracellular organisms.

·

Serologic

testing :

Indirect

fluorescent antibody test : titers B.

canis or B. gibsoni > or = to

64 --> supportive of exposure.

Cutoff titer of > or = to 320 = B. conradae

infection. Very young dogs or dogs tested

early in the disease : false negatives (also reported in adult dogs)!! No commercially available ELISA assay in USA. Cross reactivity between Babesia spp.

·

Molecular

genetic detection : Most sensitive and specific.

o Species

identification : DNA sequencing or specific PCR assays.

o Broad-range

Babesia PCR : detect multiple Babesia spp.

4) treatment/prevention

·

Imidocarb

dipropionate : eliminate B.

canis and ticks engorging on treated animals up to 4 weeks after treatment

+ prophylactic activity up to

6 weeks. Do not clear B. gibsoni infections but reduce mortality and morbidity.

Pretreatment with atropine can be used to reduce side effects.

·

Combination

atovaquone and azithromycin for B. gibsoni. If fails : metronidazole + docycycline +

clindamycin for 3 months. PCR 60 and 90

days after treatment for follow-up.

·

Cats :

Primaquine phosphate ! effective dose close to lethal dose !

·

Supportive treatment :

packed erythrocyte transfusion. Glucocorticoids controversial.

·

Prevention :

o Control

of vector tick (minimum 2-3 days of feeding for transmission).

o Premunition

in areas where virulent strains of Babesia

are endemic.

o Vaccine

(B. canis canis or bivalent B. canis canis and B. canis rossi) available in Europe (70 to 100% efficacy). No

cross-protection.

·

Public

health : risk to immunocompromised (chemotherapy, HIV or splenectomized) people unknown. People (B.

microti and B. divergens) = accidental host and domestic

animals = source of exposure to ticks.