Common Haemoprotozoa in Dogs

1. Babesia spp. - Canine Babesiosis

Large Babesia (paired piroplasms in RBCs)

• Babesia canis - worldwide distribution; three subspecies:
  • B. canis canis - transmitted by Dermacentor reticulatus (Europe)
  • B. canis rossi - transmitted by Haemaphysalis leachi (Africa); most virulent
  • B. canis vogeli - transmitted by Rhipicephalus sanguineus (worldwide); least pathogenic

Small Babesia (single piroplasm per RBC)

• Babesia gibsoni - common in Asia, USA, Europe; transmitted by Rhipicephalus sanguineus and also via dog bites/blood transfusion; notoriously difficult to cure
• Babesia conradae - found in California
• Unnamed "large Babesia" of USA - B. canis-like, transmitted by Dermacentor variabilis

Transmission

Pathogenesis & Clinical Signs

• Intraerythrocytic replication causes mechanical destruction and immune-mediated haemolysis
• Fever, haemolytic anaemia, haemoglobinuria ("red water"), jaundice, splenomegaly, thrombocytopenia
• Severe cases: shock, organ failure, death

Diagnosis

• Blood smear: paired (large Babesia) or single (small Babesia) piroplasms in RBCs
• PCR of whole blood (more sensitive)
• Serology (IFA, ELISA)

Treatment

• Large Babesia: imidocarb dipropionate (drug of choice)
• Small Babesia (B. gibsoni): atovaquone + azithromycin combination; carrier state common

2. Hepatozoon spp. - Canine Hepatozoonosis

Hepatozoon canis

• Worldwide distribution (Europe, Africa, Asia, Americas)
• Vector: Rhipicephalus sanguineus (brown dog tick)
• Transmission: Dogs are infected by ingesting the tick (not by tick bite) - ingestion of infected ticks
• Gametes infect neutrophils and monocytes (visible as gamonts in white blood cells on blood smear)
• Most infections are subclinical; severe disease in immunocompromised animals
• Signs: Fever, weight loss, anaemia, lethargy

Hepatozoon americanum

• USA only (Gulf Coast states, expanding range)
• Vector: Amblyomma maculatum (Gulf Coast tick)
• Transmission: Ingestion of infected tick OR paratenic vertebrate hosts
• Tissue meronts localize in skeletal muscle causing severe myositis
• Signs: Fever, severe muscle/bone pain, reluctance to move, "painful puppy syndrome," periosteal proliferation on radiographs
• Diagnosis: Muscle biopsy (meronts in skeletal muscle), PCR, blood smear (gamonts in WBCs)
• Treatment: Ponazuril or trimethoprim-sulfa + clindamycin + azithromycin, followed by long-term decoquinate; prognosis is guarded

3. Leishmania spp. - Canine Leishmaniosis

• Species: Primarily Leishmania infantum (syn. L. chagasi in Americas)
• Distribution: Mediterranean basin, Middle East, Latin America, parts of Asia; now emerging in North America
• Vector: Sandfly (Phlebotomus spp. in Old World; Lutzomyia spp. in New World)
• Zoonotic: Dogs are the main domestic reservoir for human visceral leishmaniasis
• The parasite resides as amastigotes within macrophages (not strictly intraerythrocytic, but classified as haemoprotozoa)
• Clinical signs: Skin lesions (exfoliative dermatitis, alopecia, ulcers), lymphadenopathy, epistaxis, ocular lesions, weight loss, renal failure, splenomegaly, hepatomegaly
• Diagnosis: Cytology/biopsy (amastigotes in macrophages), serology (IFA, ELISA), PCR
• Treatment: Meglumine antimoniate ± allopurinol; miltefosine; lifelong management often needed
• Zoonotic risk must be communicated to owners

4. Trypanosoma spp. - Canine Trypanosomiasis

Trypanosoma cruzi - Chagas Disease

• Distribution: Central and South America, southern USA
• Vector: Triatomine bugs ("kissing bugs," Triatoma spp.)
• Transmission: Contamination of skin/mucous membranes with infected triatomine feces; also by ingestion of triatomine bugs, blood transfusion, transplacental
• Pathology: Acute phase - trypomastigotes in blood; chronic phase - cardiac involvement (dilated cardiomyopathy, arrhythmias), which is the main cause of death
• Clinical signs: Acute: fever, lymphadenopathy, myocarditis. Chronic: cardiac arrhythmias, sudden death
• Diagnosis: Blood smear (acute), PCR, serology
• Zoonotic (important public health concern)

Trypanosoma brucei

• Distribution: Sub-Saharan Africa
• Vector: Tsetse fly (Glossina spp.)
• Causes nagana in dogs; trypomastigotes in blood
• Signs: Wasting, anaemia, CNS signs

5. Theileria spp.

• Theileria annae (now reclassified by some as Babesia microti-like) - reported in dogs, particularly in northwestern Spain
• Theileria equi has occasionally been reported in dogs (incidental)
• Less commonly documented in dogs compared to cattle

Summary Table

Clinical Tip

Reading CBC Clues for Haemoprotozoa in Dogs

The Core Rule

1. Babesia spp.

2. Hepatozoon canis

3. Ehrlichia canis (not a protozoan but commonly co-infects; worth knowing for comparison)

4. Leishmania infantum

5. Trypanosoma cruzi

Quick Diagnostic Algorithm from CBC

Anaemia + Thrombocytopenia in a ticked dog?
        |
        +---> Regenerative (high MCV, reticulocytes)?
        |           |
        |           +---> Leukopenia/lymphopenia → BABESIA (large)
        |           +---> Leukocytosis/neutrophilia → HEPATOZOON
        |
        +---> Non-regenerative (normal MCV)?
                    |
                    +---> Check chemistry for hyperglobulinaemia → LEISHMANIA
                    +---> Check for platelet count <50,000 → EHRLICHIA

What You Can See Directly on a CBC Blood Smear

Bottom Line

CBC Interpretation - 50-Day-Old Puppy

Extracted Values at a Glance

Key Abnormalities

1. Normocytic Normochromic Anaemia

• HCT 26.5%, HGB 9.2 g/dL, RBC 4.21 - all low
• MCV (62.9), MCH (21.9), MCHC (34.7) - all normal
• RDW normal (13.6%) - no significant anisocytosis
• This is normocytic, normochromic anaemia - the RBCs are normal in size and colour, but there are fewer of them

2. Thrombocytopenia

• PLT = 91 × 10³/µL - significantly reduced (normal >200)
• PCT (plateletcrit) = 0.07% - reduced
• MPV and PDW are normal - so existing platelets are of normal size and uniform distribution, suggesting this is a consumption or production issue, not a compensatory response

3. Neutrophilia (relative)

• GR = 10.0 × 10³/µL = 82.4% - flagged high
• Absolute granulocyte count is elevated proportionally
• Lymphocytes are relatively low at 12.6%

What Can We Suspect?

Age Context First - Very Important

• Physiologically lower HCT than adults (neonatal/juvenile anaemia is normal down to ~22-27%)
• This puppy's HCT of 26.5% is at the lower borderline of acceptable for this age - it is not purely physiological

Top Differentials

• Ancylostoma caninum (hookworm) is the #1 suspect in a 50-day-old puppy
• Hookworms cause blood-sucking anaemia + protein loss
• At this age, worm burden can be very heavy from transmammary transmission
• The normocytic normochromic pattern fits a chronic/early blood loss picture (iron stores not yet depleted)
• Thrombocytopenia can be seen with heavy worm loads

• CPV-2 causes anaemia + thrombocytopenia + neutropenia in most cases
• However, here WBC and neutrophils are high, not low - argues against classic parvo
• Early or recovering parvo could still be possible

• Anaemia + thrombocytopenia is the classic pattern for Babesia
• However: MCV is normal (not macrocytic/regenerative as expected in Babesia)
• MCHC is normal - no haemolytic picture
• 50 days is young for tick-borne disease, but not impossible if ticks were on the mother/pup
• Less likely as the primary cause here, but cannot be excluded

• The switch from fetal to adult Hb, plus rapid growth, causes a nadir in HCT around 3-6 weeks of age
• At 50 days, this should be recovering
• Normal MCV, normal RDW support this component contributing

• In early iron deficiency, RBCs can still appear normocytic before becoming microcytic
• At 50 days, dietary inadequacy is possible, especially in large litters

What the CBC Does NOT Show Here

• No regenerative response (reticulocytes not reported) - important to check manually
• No direct parasites visible on machine - need a blood smear to look for piroplasms in RBCs or gamonts in WBCs
• The machine flagged RBC (AT) on the histogram display - this "AT" flag can indicate atypical/abnormal RBC distribution, worth investigating on smear

Recommended Next Steps

Bottom Line