Feline Tick Fever (Feline Tick-Borne Hemoparasitic Disease)

1. Cytauxzoonosis (Cytauxzoon felis)

• Reservoir host is the bobcat, which tolerates infection with mild or no illness. Domestic cats are incidental, often fatal, hosts.
• Transmitted by tick bite (as early as 36-48 hours after tick attachment).
• The parasite first infects mononuclear phagocytes, forming large schizont-laden macrophages that occlude small veins and capillaries throughout the body (lung, spleen, liver, lymph nodes) - this vascular obstruction, not just anemia, drives the severe/fatal disease. The organism then invades erythrocytes as piroplasms, visible on blood smear.

• High fever, up to 106°F (41°C), depression, anorexia, lethargy
• Icterus (jaundice), lymphadenopathy, hepatosplenomegaly
• Dyspnea/tachypnea, tachycardia, generalized pain, vocalization
• Pale mucous membranes and pigmenturia from hemolytic anemia
• Advanced/terminal stage: hypothermia, recumbency, seizures, ataxia, nystagmus (CNS ischemia), coma, death - often within 2-3 days of fever onset if untreated

• Blood smear: piroplasms (small round to oval, "signet ring"-shaped) inside red blood cells, and/or large schizont-filled macrophages on smears from lymph node, spleen, or bone marrow aspirates
• PCR is the most sensitive/specific confirmatory test
• CBC: pancytopenia is classic, but thrombocytopenia and leukopenia are the most consistent single findings; anemia may lag behind other signs early on

• Drug of choice: atovaquone (15 mg/kg PO q8h) + azithromycin (10 mg/kg PO q24h), combined with aggressive supportive care - IV fluids, blood transfusion, heparin (to counter DIC/microvascular obstruction), antipyretics, nutritional support, oxygen if dyspneic
• Historically considered almost universally fatal; with early recognition and this combination protocol, survival has improved to roughly 60%
• Cats that present with hypothermia or respiratory distress carry a very poor prognosis
• Survivors can become chronic subclinical carriers, maintaining low-level parasitemia

2. Feline Babesiosis (Babesia felis / B. leo)

• Seen mainly in South Africa (also reported in parts of Asia, e.g. India, Sri Lanka)
• Unlike the dog form, fever and icterus are uncommon in cats; presenting signs are usually nonspecific: anorexia, lethargy, weakness, rough hair coat
• Disease is driven by hemolytic anemia from erythrocyte parasitism; cats often compensate for anemia surprisingly well
• Diagnosis: blood smear (intraerythrocytic piroplasms) and PCR
• Treatment: antiprotozoal drugs plus supportive care (transfusion if severely anemic, fluids, nutritional support). Untreated infection is commonly fatal - in one series, all untreated cats died, while treated cats generally responded well, though relapse/chronic carriage can occur.
• Prevention relies on tick control - note cats cannot tolerate permethrin, so flumethrin or fipronil-based products are used instead.

3. Ehrlichiosis / Anaplasmosis in cats

• Generally milder than the above two; signs include fever, lethargy, anorexia, and sometimes lameness or lymphadenopathy
• Diagnosed via serology/PCR; treated with doxycycline
• Rarely as severe as cytauxzoonosis, and often resolves with treatment

General prevention (applies to all forms)

• Consistent use of feline-safe tick preventives (fipronil, flumethrin - never permethrin-only products)
• Keeping cats indoors, especially in endemic regions and tick season
• Prompt tick removal
• No vaccine is available for any of these feline tick-borne diseases

Recent evidence check