The Kenneth W. Smith Professor in Small Animal Clinical Veterinary Medicine, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
The primary objective of this session is to learn the clinical signs of vector-borne diseases in cats so that appropriate diagnostic tests, treatments, and preventions can be used.
Multiple vector-borne diseases can affect cats; those transmitted by ticks (multiple agents), fleas (multiple agents), mosquitoes (Dirofilaria immitis), and sandflies (Leishmania spp.) are among the most common. The Companion Animal Parasite Council (https://capcvet.org), European Scientific Counsel Companion Animal Parasites (www.esccap.org/guidelines), and Companion Vector-Borne Diseases (www.cvbd.com) are excellent sources of information about vector-borne diseases in cats.
As high as 80% of fleas collected from cats contain at least one organism that could induce illness in cats or people. Bartonella spp., the haemoplasmas, and Rickettsia felis are most common. Fever is one of the most common manifestations of both bartonellosis and haemoplasmosis in cats. Bartonella spp. and R. felis both can cause clinical diseases in people. Haemoplasmosis is one of the most common causes of hemolytic anemia in cats. Other notable flea-borne parasites in cats include Dipylidium caninum (the flea is ingested to induce infection) and Yersinia pestis (rodent fleas). Whether fleas are common vectors for Coxiella burnetii is currently unclear.
Most of the tickborne diseases diagnosed in dogs have now been identified in cats. Many of these tickborne agents have been grown or amplified from blood or have induced serum antibodies in the serum of normal cats or those with clinical signs such as fever. In some countries, however, thorough evaluation of cats for tickborne disease agents has not been completed. In those situations, dog results can be used as evidence for the presence of individual agents in the region that could potentially infect cats. Most cats exposed to these agents do not develop clinical illness. But when illness occurs, most of the clinical and laboratory findings of tickborne diseases in dogs have been identified in cats. Thus, if you have a suspected agent in dogs in your area, you should also consider it as a differential for cats with similar clinical findings. Results of studies from regional ticks can also be used as evidence for risk in cats.
The most common tickborne diseases in cats are Anaplasma phagocytophilum (Ixodes spp.), A. platys (Rhipicephalus sanguineus), Borrelia burgdorferi (Ixodes spp.), and Ehrlichia spp. (Rhipicephalus sanguineus). Some Cytauxzoon spp. are pathogenic—in particular, those in the United States. Hepatozoon spp. infections are fairly uncommon in cats, and it is unclear how often Francisella tularensis infections are transmitted to cats by ticks. It is also not clear what role the Spotted fever group rickettsioses play in cats, but fever is a likely clinical finding if fever exists. Rickettsia rickettsii would be the most common agent infecting cats in the United States. In Spain, R. conorii and R. massiliae antibodies were found in cat serum and DNA amplified from cat blood (Segura et al. 2014).
Antibodies can be detected against some of the agents using IFA or other serological tests (in particular, Anaplasma phagocytophilum, Bartonella spp., Borrelia burgdorferi, Ehrlichia canis, and Rickettsia spp.). However, serologic tests have not been optimized for use with cat sera for most of the agents, and serological test results can be falsely negative in the acute stages of illness. Thus, currently amplification of agent-specific DNA by PCR assay is the best way to prove infection. For the haemoplasmas, there is no currently available serological test and so cytology and PCR are the only way to prove infection.
When clinical disease associated with a flea or tickborne agent is suspected—particularly Anaplasma spp., Bartonella spp., B. burgdorferi, Ehrlichia spp., and Rickettsia spp.—administration of doxycycline at 5 mg/kg, PO, twice daily or 10 mg/kg, PO, once daily generally is effective. It is possible that minocycline will also prove to be effective for some agents. Care should be taken to avoid esophageal strictures depending on the tetracycline compound being used. Cytauxzoon felis is treated with the combination of atovaquone and azithromycin (Cohn et al. 2011). Optimal duration of therapy is unknown for most of the agents, but clinical signs of fever and cytopenias generally resolve quickly.
Other than the Spotted fever group agents, permanent immunity is not induced by flea or tickborne agents, so reinfection can occur. Thus, since vaccines are not currently available for any of the agents for cats, it is imperative that flea and tick control be maintained on all cats. There is no danger for direct zoonotic infection of owners, but infected fleas or ticks harbored by infected cats could be brought into the home.
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