What are the clinical features and treatment options for small form babesiosis in dogs?

Clinical Features and Treatment of Small Form Babesiosis in Dogs

Small form babesiosis in dogs presents with hemolytic anemia, thrombocytopenia, and lethargy, and is best treated with atovaquone plus azithromycin rather than imidocarb dipropionate alone, which may not eliminate the parasite completely. 1

Clinical Features

Small form babesiosis in dogs is caused by several species including Babesia gibsoni, Babesia conradae, Babesia microti-like piroplasms, and recently identified species such as Babesia negevi 2. The clinical presentation includes:

• Common clinical signs:

  • Extreme lethargy and weakness
  • Pale mucous membranes
  • Fever
  • Icterus (jaundice)
  • Anorexia
  • Hemoglobinuria 1, 3

• Laboratory findings:

  • Hemolytic anemia (hallmark finding)
  • Severe thrombocytopenia
  • Elevated liver enzymes (AST, ALT)
  • Increased total bilirubin
  • Elevated urea and creatinine levels
  • Proteinuria 3, 4

Small form babesiosis tends to be more resistant to treatment compared to large form babesiosis and often results in more persistent infections 2.

Diagnosis

Diagnosis of small form babesiosis requires:

1. Microscopic examination: Giemsa-stained thin blood smears to identify small intraerythrocytic parasites 5

   • Small Babesia species appear as simple chromatin dots that might be mistaken for stain precipitate

2. Molecular testing: PCR targeting the 18S rRNA and cox1 genes is essential for confirming the specific Babesia species, especially when organisms are not evident on blood smears 4, 6

3. Serological testing: May detect cross-reactive antibodies but is not always reliable for small Babesia species 6

Treatment Options

First-line Treatment

• Atovaquone (13.5 mg/kg PO q8h) plus azithromycin (10 mg/kg PO q24h) for 10 days 1
  • This combination has been shown to effectively eliminate small Babesia species in dogs
  • Recent evidence shows this combination successfully eliminated B. negevi infection after imidocarb dipropionate treatment failed 1

Alternative Treatment

• Imidocarb dipropionate (5-6.6 mg/kg IM, repeated in 14 days) 7, 2
  • FDA-indicated for dogs with clinical signs of babesiosis
  • While effective for large Babesia species, it often fails to completely eliminate small Babesia species
  • May help resolve clinical signs but parasites can persist, leading to carrier status 1, 2

Special Considerations

• Immunocompromised dogs: Particularly vulnerable to severe disease and persistent infection

  • Dogs that have undergone splenectomy or are receiving chemotherapy are at higher risk 6
  • These patients may require more aggressive treatment and monitoring

• Monitoring treatment response:

  • Clinical improvement should occur within 48-72 hours of initiating therapy
  • Monitor hematocrit and parasitemia levels until clearance
  • PCR testing 2-4 weeks after treatment completion to confirm parasite elimination 1

• Potential complications:

  • Persistent thrombocytopenia even after treatment
  • Development of carrier status
  • Relapse of clinical disease 4

Treatment Challenges

Small form babesiosis is notoriously difficult to completely eliminate. In a recent study, dogs treated with imidocarb dipropionate showed clinical improvement but still had detectable Babesia negevi DNA in blood samples up to seven months post-treatment. Only after treatment with atovaquone and azithromycin was the parasite completely eliminated 1.

The persistence of small Babesia species despite treatment highlights the importance of follow-up PCR testing to confirm parasite clearance and the potential need for combination therapy or alternative treatment protocols in cases that don't respond to standard therapy.