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 Figure 2. Anaplasma phagocytophilum morulae (arrow) in the cytoplasm of a feline neutrophil noted after infestation of a cat with wild-caught Ixodes scapularis.
Some commercial laboratories offer serologic testing
or PCR assays to amplify A. phagocytophilum DNA
from blood. In experimental infections, DNA is amplified from blood prior to seroconversion for most cats.5 Approximately 30% of cats with proven clinical infections induced by A. phagocytophilum are seronegative when first assessed serologically, but most of the proven cases evaluated to date have ultimately seroconverted. Therefore, cats with suspected anaplasmosis may
need convalescent serum samples to prove infection. Alternatively, antibody testing could be combined with PCR testing of whole blood in acute cases. The SNAP 4DX Plus (IDEXX Laboratories) has been shown to
be accurate for the detection of A. phagocytophilum antibodies in cats but is not labeled for this purpose.5 In addition, another peptide (P44-4) than the one used on the commercial assays detected antibodies even sooner.5
Several antibiotics have been administered to naturally infected cats, but most cats treated in the field become clinically normal within 24 to 48 hours after initiation of tetracycline or doxycycline administration and recurrence has not been reported in any cat to my knowledge.7,11 While clinically normal, the organism DNA can still be amplified from the blood of some cats which suggests that treatment with tetracyclines for 21 to 30 days may be inadequate for eliminating the organism from the
An Urban Experience
body. In one of our recent studies, the fact that an owner paid for a tick control product was not associated with decreased risk of having A. phagocytophilum antibodies in serum.15 These results suggest lack of compliance
or lack of efficacy. As repeat new infections can occur, it is imperative to maintain tick control at all times, even in cats that have been previously infected.13
DNA homologous with A. platys has been amplified from the blood of cats in some countries with Rhipicephalus sanguineus.16,17 Further studies will be required to determine if disease associations exist with this agent in cats.
Feline Borreliosis
Borrelia burgdorferi is the cause of Lyme disease and is transmitted by Ixodes spp. Clinical illness in dogs and people is most common in the United States. While B. burgdorferi antibodies have been detected in the serum of cats for years, whether the agent induces illness in cats is still controversial.18-21
Recently, two groups have attempted to ascribe clinical illness to B. burgdorferi infection in cats.15,22 The
cats that were positive for B. burgdorferi antibodies in Belgium, Sweden, and Germany had weakness, ataxia, and lameness as the most common clinical signs and doxycycline was apparently effective for treatment.22 The biggest limitation in that study was the failure to report results of assays for other feline disease agents that may be responsive to doxycycline, in particular A. phagocytophilum. The cats in Maine with suspected borreliosis were seropositive to B. burgdorferi C6 peptide but negative for A. phagocytophilum antibodies; had fever, weakness, lameness, lethargy, and inappetence
as clinical signs; and had apparent responses to doxycycline.15 The biggest limitation in that study was the failure to perform A. phagocytophilum PCR or other diagnostic assays to evaluate for other feline disease agents that may be responsive to doxycycline. Recently, use of cefovecin was shown to be effective for the treatment of borreliosis in dogs.23 Whether this will prove to be true for cats remains to be determined. Currently there are no feline B. burgdorferi vaccines. In dogs, use of acaricides can block transmission of the agent and repeat infections can occur in cats.13,24 Thus, use of acaricides is imperative for the control of this agent.
Feline Cytauxzoonosis
Cats in the United States and Europe are infected by Cytauxzoon spp.4,25 Excellent review articles from European authors26 and American authors27 have recently been published. It is apparent that Cytauxzoon felis infections in the United States (transmitted by Amblyomma americanum) can be very pathogenic when compared with the Cytauxzoon spp infections occurring in cats in other countries. This may represent different species in different countries28; however, C.
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