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An Urban Experience
felis strain variations also play a role in whether clinical disease occurs within countries as well. For example, while fatal C. felis infections are common in some regions in the United States, cats that survive or have subclinical infections are also common.29,30 A recent study showed that C. felis could be transmitted between 36 and 48 hours of tick attachment and ingestion of A. americanum did not induce infections.31
In the United States, clinical infections are recognized most commonly in the spring, summer, and fall. Nonspecific complaints of lethargy and anorexia are reported frequently by owners. The infected cats have fever or hypothermia if presented in the final shock phase. Common physical examination findings that might lead to consideration of this agent as a differential diagnosis include pale mucous membranes, icterus, splenomegaly, and hepatomegaly. Discomfort and clinical evidence of central nervous system disease including seizures, tachypnea with or without respiratory distress, and sudden death on manipulation occur in some cats.
Piroplasms frequently can be seen on the erythrocytes but can be falsely negative in the acute stages of illness. The serious clinical signs of disease relate to the development of the schizonts in tissues. The syndrome can be diagnosed by cytologic demonstration of the piroplasms on erythrocytes; cytologic demonstration
of schizonts in spleen, liver, or bone marrow samples; or by PCR of Cytauxzoon spp DNA in blood or tissue aspirates.27
To date, clinically affected cats have the best response to the combination of azithromycin at 10 mg/kg, orally (PO), every 24 hours and atovaquone at 15 mg/kg, PO, every
8 hours32,33 with approximately 60% of treated cats responding. This combination is superior to diminazene
or imidocarb protocols.32,34 Minimal restraint techniques should be used during administration of supportive care to lessen the likelihood of sudden death.
The poor overall treatment responses in clinical cytauxzoonosis cases is a perfect example of why tick control can be so important. It is always better to prevent a vector-borne disease rather than attempt to treat it after illness has begun. Appropriate use of acaricides should lessen the risk of transmission of this agent.35
Feline Monocytotropic Ehrlichiosis
While canine ehrlichiosis is well characterized, less is known about the agents associated with disease in cats. It is likely that any country that has E. canis infections in dogs has E. canis infections in cats. Naturally exposed cats have been shown to have Ehrlichia like bodies or morulae in peripheral lymphocytes or monocytes, have had DNA consistent with E. canis amplified from the blood or tissues, and have had antibodies that react to E. canis morulae or peptides in many countries.36-45
In two separate experimental studies, however, we
have failed to amplify monocytotropic Ehrlichia spp
from blood or detect seroconversion in cats inoculated subcutaneously (SC) with different strains of cultured
E. canis (Lappin and Breitschwerdt, unpublished observations, 2007; Lappin and Little, unpublished observations, 2010). These results indicate the E. canis- like DNA amplified from naturally infected cats may be from a different Ehrlichia spp more infective to cats,
not all E. canis stains will infect cats, not all cats are susceptible to infection by E. canis, or SC inoculation is not an effective method for infecting cats with E. canis. In addition, we have had field cases that have been positive for DNA identical to E. canis at two genes that never seroconverted.36 It is likely that cats at greater risk for Rhipicephalus sanguineous infestation are more likely to have higher prevalence rates for E. canis in countries like in Brazil, where 9.4% of cats were PCR positive in one study.41 In Sicily, E. canis DNA was amplified from ticks collected from some cats.3
Fever, lethargy, and inappetence are commonly reported clinical abnormalities detected in cats with suspected ehrlichiosis and so testing may be indicated in these cats. Thrombocytopenia, anemia, and monocytosis appear
to be the most common clinical laboratory findings in naturally infected cats. Almost every abnormality noted in dogs with clinical ehrlichiosis has been detected in cats, including monoclonal gammopathy.42-46
A validated serologic assay is not currently available
and some cats with E. canis-like DNA in blood were seronegative.36 Positive serologic test results occur in both healthy and clinically ill cats, and so a diagnosis of clinical ehrlichiosis should not be based on serologic test results alone. Ehrlichia spp PCR and gene sequencing can be used to confirm infection and should be considered the tests of choice at this time.
Clinical improvement after therapy with tetracycline, doxycycline, or imidocarb dipropionate was reported for most cats with suspected monocytotropic ehrlichiosis. For some cats, however, a positive response to therapy was a criterion for the diagnosis of ehrlichiosis. The current recommendation of the ACVIM Infectious Disease Study Group ( is to administer doxycycline (10 mg/kg PO q24h or 5 mg/kg PO q12h for 28 days). For cats with treatment failure or those intolerant of doxycycline, imidocarb dipropionate can be administered [5 mg/kg intramuscularly (IM) or SQ twice, 14 days apart]. Salivation and pain at the injection site are the common adverse effects and imidocarb efficacy is in question for the treatment of canine monocytotropic ehrlichiosis. Pancytopenia occurs in cats with ehrlichiosis and when it occurs in dogs, it may not respond to treatment36; this is another example of why acaricides should be used to attempt to avoid infection with vector- borne disease agents.

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