Erlichia Gatos

Vol. 22, No. 4 April 2000

CE

Refereed Peer Review

Feline Ehrlichiosis
FOCAL POINT #Feline ehrlichiosis is a differential
diagnosis for varied clinical syndromes and is being recognized with increased frequency worldwide. Colorado State University Protatek Reference Laboratory, Chandler, AZ

Cynthia J. Stubbs, DVM, MS
Colorado State University

Cynthia J. Holland, PhD
AnimalMedical Specialists, PC, Denver, CO

John S. Reif, MSc (Med), DVM, MS Steven Wheeler, DVM, MS Christa Bruns, MS
Colorado State University

KEY FACTS
I A granulocytic Ehrlichia species that infects cats and causes clinical disease has been isolated and characterized in Sweden. I Ehrlichia species infecting mononuclear cells of cats have been visualized cytologically in several countries. IDefinitive diagnosis of feline ehrlichiosis is made by demonstration of morulae in the cytoplasm of blood leukocytes or by detection through polymerase chain reaction. I Ehrlichiosis is a differential diagnosis for cats with fever, anemia, thrombocytopenia, hyperglobulinemia, lethargy, anorexia, weight loss, vomiting, polyarthritis, lameness, and ocular discharge.

Michael R. Lappin, DVM, PhDABSTRACT: The pathogenesis and route of transmission of Ehrlichia infection in cats are unknown. Clinical improvement occurs after administration of such antirickettsial drugs as tetracycline, doxycycline, chloramphenicol, and imidocarb dipropionate. Cats may be a reservoir for ehrlichial agents infecting other animals, including humans. Data from the literature and an 8-year serosurvey suggest thatehrlichiosis should be a diagnostic differential for varied clinical syndromes in cats.

M

embers of the family Rickettsiaceae, Ehrlichia species are pleomorphic, gram-negative, obligate intracellular microorganisms. Animals known to be naturally infected include dogs, horses, ruminants, mice, and humans.1 In 1986, the first naturally occurring case of feline ehrlichiosis was documented in Franceby Charpentier and Groulade.2 Morulae (i.e., intracytoplasmic inclusions formed by clusters of rickettsiae) can be found transiently in mononuclear cells, neutrophils, eosinophils, or platelets during acute illness (Figure 1). Ehrlichia morulae found in mononuclear cells include those from Ehrlichia canis, Ehrlichia chaffeensis, Ehrlichia sennetsu, Ehrlichia risticii, Ehrlichia bovis, andEhrlichia muris.1,3,4 Other species, such as Ehrlichia equi, Ehrlichia ewingii, and Ehrlichia phagocytophilia, as well as an unidentified agent that causes human granulocytic ehrlichiosis, have morulae in neutrophils and occasionally in eosinophils.1 Morulae in platelets are diagnostic for Ehrlichia platys infection.1,5 Ehrlichia morulae have been detected in feline neutrophils, eosinophils, andmononuclear cells.2,6–13 It is possible that more than one Ehrlichia species is involved in feline ehrlichiosis.

EXPERIMENTAL INFECTIONS Cats can be experimentally infected with E. risticii, the causative agent of Potomac horse fever.14 In one study,14 six specific pathogen–free cats were injected intravenously (IV) and two were injected subcutaneously with E. risticii–infected cell suspensions. Two ofthe six cats receiving IV injections seroconverted and developed fever and mild gastrointestinal signs, including anorexia and diarrhea. E. risticii was isolated by cell culture from the blood of these clinically ill cats

Small Animal/Exotics

Compendium April 2000

and used to infect a pony. Aling polymerase chain reaction though the other cats did not (PCR) positive for Ehrlichia becomeclinically ill, they did reacted with the Swedish seroconvert. In another study,15 granulocytic Ehrlichia species blood from five naturally exE. equi and E. phagocytophilposed, E. risticii–seropositive, ia,11 supporting the validity of IFA tests. clinically ill cats was inoculatIn general, minimal crossed into an E. risticii–seronegareactivity exists between antitive cat; neither clinical...