Treatment of Canine Babesiosis

Chapter 268


Treatment of Canine Babesiosis



Babesiosis typically is characterized by thrombocytopenia, hemolytic anemia, and splenomegaly. Canine babesiosis is an important disease worldwide and can be caused by many different species of Babesia (Table 268-1). Molecular characterization of the parasite is critical for selecting the treatment with the best efficacy and lowest cost. Serologic testing for antibodies against Babesia spp. can be useful in cases in which parasitemia is below the limit of detection for molecular assays but because of cross-reactivity cannot always be used to predict accurately which species are causing infection. Serologic studies and polymerase chain reaction (PCR) testing should be considered complementary assays and should be used together to maximize the chances of making a definitive or presumptive diagnosis of babesiosis. Empirical therapy should be started immediately in critical cases in which there is a high index of suspicion of babesiosis while results of molecular diagnostic tests are pending. The following responses to frequently asked questions regarding the treatment of babesiosis are based on the literature and the author’s experience.



TABLE 268-1


Recommended Treatment Options for Canine Babesiosis Based on Infecting Species



































Babesia Species Treatment of Choice Notes
Babesia gibsoni Atovaquone (13.3 mg/kg q8h PO) and azithromycin (10 mg/kg q24h PO) given simultaneously for 10 days Atovaquone should be given with a fatty meal to maximize absorption. The author’s preference is Mepron over Malarone because of anecdotal experience of Malarone’s causing severe adverse effects (vomiting). This dose and frequency are likely to eradicate or reduce parasitemia below detection limit of polymerase chain reaction testing in some dogs.
Babesia (canis) vogeli Imidocarb dipropionate (6.6 mg/kg IM or SC, repeat in 14 days) This dose and frequency are likely to eradicate parasites. Pretreatment with atropine or glycopyrrolate minimizes cholinergic adverse effects.
Babesia (canis) canis Imidocarb dipropionate (2 mg/kg IM or SC once for premunition; 6.6 mg/kg IM or SC, repeat in 14 days, for sterilization) This dose and frequency are likely to induce premunition but not eradicate the parasites. Pretreatment with atropine or glycopyrrolate minimizes cholinergic adverse effects.
Babesia (canis) rossi Diminazene aceturate (3.5 mg/kg IM once; or imidocarb dipropionate 6.6 mg/kg IM or SC, repeat in 14 days) This dose and frequency are likely to eradicate parasites. Pretreatment with atropine or glycopyrrolate minimizes cholinergic adverse effects.
Babesia sp. (Coco) Imidocarb dipropionate (6.6 mg/kg IM or SC, repeat in 14 days) There are not enough data to determine whether or not parasitemia is cleared consistently. Pretreatment with atropine or glycopyrrolate minimizes cholinergic adverse effects. Atovaquone and azithromycin should be considered if treatment fails to clear infection.
Babesia conradae Atovaquone (13.3 mg/kg q8h PO) and azithromycin (10 mg/kg q24h PO) given simultaneously for 10 days This dose and frequency are likely to eradicate or reduce parasitemia below the limit of detection in some dogs.
Babesia microti–like sp. Optimal treatment unknown  

IM, Intramuscularly; PO, orally; SC, subcutaneously.



Frequently Asked Questions



What Should I Expect When Treating Babesia gibsoni Infections?


After the discovery of Babesia gibsoni about a century ago every treatment that was used against it failed to clear infection. Then in 2004 the use of atovaquone and azithromycin was first described (Birkenheuer et al, 2004). Atovaquone and azithromycin combination therapy is the treatment of choice for B. gibsoni infection in dogs in North America in the author’s opinion. Despite this improvement in treatment, this combination therapy seems to be “Babesia-static,” not “Babesia-cidal,” and requires that the dog have an intact functional immune system for maximum efficacy. It is typical for clinical signs and hematologic abnormalities to begin improving within 1 week of starting treatment. In the United States where reinfection via tick vectors is unlikely, this treatment is associated with parasite clearance or reduction of parasite burden below the limit of detection in 80% to 85% of cases. This treatment appears to be very safe, and no adverse effects have been reported in dogs. Unfortunately, it can be expensive, with a single 750-ml bottle of atovaquone costing $700 to $1200 at the time this chapter was published. Although this bottle contains enough drug to treat three 20-kg dogs, many pharmacies require purchase of the entire bottle. Several compounding pharmacies will sell it by the dose.




Do I Have to Use Atovaquone and Azithromycin Together for Treatment of Babesia gibsoni?


Atovaquone and azithromycin must be used in combination. Each drug alone has some antiprotozoal activity, but together they have been shown to work synergistically in vivo and can clear Babesia infections. Since resistance can be selected for or develop quickly it is recommended that these drugs be administered only in combination. The author is concerned about selection of resistant parasites and usually does not administer azithromycin while waiting for the atovaquone to arrive. Instead, other treatments such as administration of imidocarb dipropionate and supportive care are used to assist in stabilizing the patient’s condition. Atovaquone is a hydroxynaphthoquinone that acts as a ubiquinone (coenzyme Q10) analog. By binding to cytochrome b, atovaquone blocks the action of ubiquinone, and the mitochondrial electron transport chain is disrupted. Once the electron transport chain is disrupted, the mitochondrial membrane potential is collapsed, which inhibits most mitochondrial functions such as pyrimidine biosynthesis. Because of differences in the structure of cytochrome b, atovaquone does not affect mammalian mitochondrial functions. The exact mechanism of action of azithromycin against protozoa is not known but is speculated to involve inhibition of mitochondrial 70S–like ribosomal function.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Treatment of Canine Babesiosis
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