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Cytauxzoonosis 235

Cytauxzoonosis Bonus Material
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mild or subclinical infection compared to the
BASIC INFORMATION
liver, and spleen are indicated to identify
rapidly progressive and usually fatal disease blood smear, tissue aspirates of lymph node,
Definition seen in domestic cats. infected macrophages. These cells range in
Cytauxzoon felis is a protozoal organism • The organism is transmitted by A. size from 15-250 microns in diameter, typi-
transmitted by ticks that causes potentially americanum (suspected predominant vector) cally have a large distinct nucleolus, and their
fatal illness in domestic cats. or Dermacentor variabilis ticks during cytoplasm is filled with numerous small (1-2
feeding. micron) basophilic particles (i.e., developing
Epidemiology • Sporozoites released from the tick salivary merozoites).
SPECIES, AGE, SEX glands infect macrophages. • CBC: pancytopenia (normocytic, normochro-
C. felis infects only domestic and wild cats, • Asexual reproduction occurs within the host mic, nonregenerative anemia, leukopenia,
with no age or sex predisposition. macrophage during the schizogenous phase, and thrombocytopenia) is the classic finding,
causing infected cells to grow to enormous but monocytopenias or bicytopenias may
RISK FACTORS size (≥250 microns in diameter). These occur.
Outdoor cats with tick exposure in endemic schizont-laden macrophages then occlude • Serum biochemistry profile: elevated liver
areas are at risk. Specific risk factors include arterioles, venules, and capillaries, causing enzymes (frequently lower than expected
urban-edge habitats and close proximity to organ failure and clinical illness. for the degree of hyperbilirubinemia),
wooded or unmanaged areas. It is common • When the schizonts rupture, merozoites are hyperbilirubinemia (mild to moderate),
for multiple cats from the same household or released to infect erythrocytes. Merozoites are and hyperglycemia are the most common
neighborhood to become infected. minimally pathogenic but may cause initial findings.
hemolysis. • Urinalysis reveals bilirubinuria.
CONTAGION AND ZOONOSIS • Healthy, recovered cats can harbor erythro- • Imaging studies do not contribute directly
Requires tick vector for transmission cyte piroplasms for years; they can transmit to the diagnosis.
the pathogen to ticks during feeding. ○ Abdominal imaging: splenomegaly and
GEOGRAPHY AND SEASONALITY hepatomegaly common
C. felis infection has been reported in the south DIAGNOSIS ○ Thoracic radiographs: ± pleural effusion,
central and southeastern United States, but its pulmonary infiltrates
range appears to be expanding north and east, Diagnostic Overview • Coagulation testing may be consistent with
corresponding to changes in distribution of Early diagnosis through blood smear exami- disseminated intravascular coagulation (DIC)
the tick Amblyomma americanum. Most cases nation or aspiration of lymph nodes, spleen, (p. 269).
occur between March and September, with a or bone marrow is indicated when a clinical
peak incidence between March and June and a suspicion exists. Although most often diagnosed Advanced or Confirmatory Testing
second wave of infections occurring in August by microscopic identification of piroplasms in • Polymerase chain reaction (PCR) testing
and September. red blood cells (RBCs), illness can occur before can confirm infection before appearance
appearance of piroplasms, and piroplasms may of schizonts or piroplasms but will also be
Clinical Presentation be seen in low number in chronic carriers. Iden- positive in chronic carriers.
DISEASE FORMS/SUBTYPES tification of schizont-laden macrophage on the • Necropsy with histopathology can confirm
• Acute cytauxzoonosis (classic severe illness) feathered edge of a blood smear or by cytology the diagnosis and is usually how cytauxzo-
• Chronic carrier state (cats recovered from of fine-needle aspirates is pathognomonic for onosis is first recognized in regions that were
illness or even discovered with incidental disease. previously considered nonendemic.
erythroparasitemia)
Differential Diagnosis TREATMENT
HISTORY, CHIEF COMPLAINT • Toxoplasmosis
Clinical signs are acute and nonspecific and • Cholangitis/cholangiohepatitis Treatment Overview
include acute onset of anorexia, lethargy, • Pancreatitis New treatments with antiprotozoal therapy
dyspnea, icterus, and pallor. Cats may be • Hemotropic Mycoplasma infection have proved effective along with supportive
reported to seem as if in pain. • Feline infectious peritonitis care in this disease, which was previously
• Immune-mediated hemolytic anemia considered universally fatal. Because the disease
PHYSICAL EXAM FINDINGS • Feline leukemia virus infection progression is very rapid, specific treatment
• Affected cats are usually febrile (103°F-107°F • Feline immunodeficiency virus should be instituted immediately in suspected
[39.4°C-41.7°C]), but hypothermia is seen • Tularemia cases.
in moribund cats. Icterus and/or pallor are • Virulent systemic calicivirus
common, as is elevation of the nictitans. • Feline panleukopenia virus Acute General Treatment
• Abdominal palpation reveals splenomegaly • Minimal stress and handling is recommended;
and hepatomegaly. Initial Database early placement of nasogastric tube (p. 1107)
• Tachypnea, tachycardia, altered mentation, Blood smear: pleomorphic (round, oval, ana- may facilitate administration of medication
vocalization, seizures, and coma can be seen plasmoid, bipolar [binucleated], or rod-shaped) and nutrition with less stress.
in the later stages of disease. organism; the round and oval piroplasm forms • Crystalloid fluids: to correct dehydration,
• Most cases exhibit a rapid course, with death are most common (0.8-2.2 microns in diameter; restore intravascular volume, and maintain
occurring within 1 week of onset of signs if typical erythrocyte diameter ≈8 microns). perfusion
left untreated. Infected macrophages may occasionally be seen • In anemic animals, oxygen delivery to tissues
on the feathered edge and may be mistaken for must be restored with a transfusion (p. 1169)
Etiology and Pathophysiology platelet clumps at low power. of whole blood (20 mL/kg IV administered
• The natural host is thought to be the eastern • If cytauxzoonosis is suspected but not over 4 hours) or packed RBCs (20 mL/kg
bobcat (Lynx rufus rufus), which develops a immediately detected by examination of a IV administered over 4 hours) (p. 1169).
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