Conference 24 - 2014 Case: 02 20150506

Signalment:

7-year-old castrated male DLH cat, Felis catsThe cat was seen at the AUCVM Small Animal Teaching Hospital critical care service with a 1-2 day history of pancytopenia, dehydration, and dull mentation according to the referring veterinarian. The owners had not seen the cat drinking or using the litter box for the past few days. The cat was indoor-only, with no other feline or canine housemates. He did have access to a screened porch and was on Frontline but no heartworm preventative. Upon arrival at the AUCVM, the cat was quiet and dull with marked icterus of the sclera and oral mucous membranes. The animal's temperature was 105.2°, pulse rate 120 bpm, and respirations were 88 bpm. The mucous membranes were dry and had a capillary refill time of -3 seconds. Heart and lung sounds were normal.

Gross Description:

The cat was in good physical condition, but moderately overweight. All tissues were severely icteric. Multiple fleas were present. There was a significant amount of serosanguineous fluid in the trachea and large bronchi. The liver had a diffuse lobular pattern throughout the parenchyma. The edges of the liver lobes were rounded. There was a moderate amount of dark red to black fecal material in the large intestine. The spleen was markedly enlarged and bluish-black. The mesenteric lymph nodes were diffusely dark red.

Histopathologic Description:

Blood vessels throughout the lung, liver, pancreas, adrenal glands, kidneys, and gastrointestinal tract are partially to almost completely occluded by few to numerous macrophages containing protozoal schizonts consistent with Cytauxzoon felis. Similar organisms are within macrophages filling subcapsular, cortical, and medullary sinuses of lymph nodes as well as within the splenic red pulp.

Morphologic Diagnosis:

Parasitemia, diffuse, severe, whole body with intralesional schizonts containing protozoal organisms consistent with Cytauxzoon felis

Lab Results:

Diagnostic tests included CBC, chemistry panel, and thoracic and abdominal radiographs. Radiographic findings included a prominent interstitial lung pattern, Pertinent CBC and chemistry findings are given below.

Parameter
HCT(%)	20.6	30-45
MCV (fl)	45.2	39-55
MCHC (g/dL)	33.1	30-36
RDW	18.3	11-17
Platelets (/uL)	28,000	200,000-700,000
Reticulocyte Count (/uL)	3,000	15,000-81,000
WBC (/uL)	2,460	5,500-19,500
Neutrophils (/uL)	812	2,500-12,500
Bands (/uL)	1,255	0-300
Total Protein (g/dL)	4.73	6.2-7.7
Albumin (g/dL)	2.0	2.8-4.2
Globulin (g/dL)	2.7	2.4-4.4
Total Bilirubin (mg/dL)	9.78	0. 1-0.2
Blood Urea Nitrogen (mg/dL)	50.1	5-30

Treatment and case outcome: Intravenous crystalloid fluids and broad-spectrum antibiotics were initiated on the night of 6/14/08, along with one unit of packed red blood cells. The next morning the cat was still dull and dysphoric and soon developed cardiac and respiratory arrest. Resuscitation efforts were unsuccessful. A necropsy was performed.

Condition:

Cytauxzoon felis

Contributor Comment:

Cytauxzoon felis is a protozoal parasite that infects wild and domestic cats. It is transmitted by a tick vector (Dermocenter variabilis). Bobcats and possibly other wild felids are believed to serve as the reservoir host.(4) The organism exists in two tissue forms; a piroplasm erythrocyte stage and a schizont tissue phase found within macrophages primarily in the spleen, liver, and lung. Clinical findings include acute illness with fever, depression, anorexia, pallor, icterus, and usually death within a few days.(4) Some cats do survive natural infections.(2) Diagnostic findings often include pancytopenia with nonregenerative anemia. The urine in the early hemolytic phase is highly concentrated, acidic and contains large amounts of protein, bile and blood.(6)

Previously, antemortem diagnosis was made by identification of erythrocyte piroplasms, but PCR assays for this agent are now available. This more sensitive method of detection has lead to the identification of cats that either have subclinical infection or that have recovered from an infection and become chronic carriers.(2) Genetic variability of Cytauxzoon felis has been proposed as a possible explanation for why some animals recover from infection or fail to develop clinical signs.(1)

JPC Diagnosis:

1. Lymph node: Lymphadenitis, histiocytic, diffuse, mild, with lymphoid depletion, hemorrhage, thrombosis, and numerous intravascular intrahistiocytic schizonts.
2. Lung: Pneumonia, interstitial, histiocytic, diffuse, mild, with numerous intravascular intrahistiocytic schizonts.

Conference Comment:

Two different slides were distributed for this case, both exhibiting numerous intravascular apicomplexans typical of Cytauxzoon felis. C. felis spends its lifecycle in circulation following introduction through a tick vector. The schizonts within circulating macrophages demonstrated in this case are first cycle of schizogony, and in chronic disease, cytomeres are released and infect erythrocytes during the second cycle of schizogony to form the piroplasm ring (signet ring) often evident on cytology.(6)

The disease is uncommon, but often fatal in cats when it occurs.(4) The intrahistiocytic phase leads to systemic circulatory compromise due to partial or complete vascular obstruction.(4) The erythrocytic phase is characterized by persistent parasitemia with anemia which may exacerbate ischemic tissue damage. Ischemic damage can also cause cerebral necrosis, appearing similar in some respects to feline ischemic encephalopathy and thiamine deficiency.(3) Dyspnea is also common clinical finding of infected cats, and interstitial pneumonia seems to be a consistent finding and may be the largest contributor to respiratory difficulty, possibly leading to acute respiratory distress syndrome in some cases.(5)

References:

1. Brown HM, Berghaus RD, et al. Genetic variability of Cytauxzoon felis from 88 infected domestic cats in Arkansas and Georgia. J Vet Diagn Invest 21:59-63; 2009.

2. Brown HM, Latimer KS, et al. Detection of persistent Cytauxzoon felis infection by polymerase chain reaction in three asymptomatic domestic cats. J Vet Digan Invest 20:485-488; 2008.

3. Clarke LL, Rissi DR. Neuropathology of natural Cytauxzoon felis infection in domestic cats. Vet Pathol. 2015 Jan 8. pii: 0300985814564986. [Epub ahead of print]

4. Fry WM, McGavin MD: Bone Marrow Blood Cells and Lymphatic System In: Pathologic Basis of Veterinary Disease, eds. McGavin MD and Zachary JF, 4th ed., pp.783. Mosby, Inc., Philadelphia, 2007.

5. Snider TA, Confer AW, Payton ME. Pulmonary histopathology of Cytauxzoon felis infections in the cat. Vet Pathol. 2010;47(4): 698-702.

6. Valli VEO: Hematopoietic System In: Jubb, Kennedy, and Palmer's Pathology of Domestic Animals, Vol 3. ed. Maxie MG. 5th ed., pp 243. Saunders, Philadelphia,2007.