Opossums, Cats, Fleas, & Zoonotic Disease

A client presents a young adult, neutered male domestic shorthair cat for vaccinations, FELV/FIV testing, fecal flotation, deworming, and an overall health check.

History. The owner found the cat a few days previously in her suburban neighborhood in southern California. She saw the cat foraging for food in her garbage cans after opossums had knocked them over. The cat seemed friendly, so the owner elected to make him a pet; there are no other pets in the household. The cat has been eating well; the only problem the owner has noticed is the presence of fleas. She asks if she could “catch something” from the fleas.

Physical Examination. Findings were within normal limits except for “flea dirt” and several Ctenocephalides felis (cat flea) ectoparasites.

Laboratory Results. Complete blood count, serum biochemical profile, and urinalysis results were within normal limits. Findings from fecal flotation and FELV/FIV testing were negative.

ASK YOURSELF….Ctenocephalides felis is a vector for which of the following bacterial pathogens that infect humans?A. Rickettsia felisB. Rickettsia typhiC. Bartonella speciesD. All of the above

Correct Answer:D. All of the above

Ctenocephalides felis is a common ectoparasite that feeds on many mammals, including dogs, cats, opossums, and humans. Cat fleas are important vectors for murine typhus and bartonellosis in people.

Rickettsia typhi. Murine typhus is caused by Rickettsia typhi, a member of the typhus group Rickettsia. Fever, headache, rash, and arthralgia most commonly characterize the disease in humans.^1,2 A cycle involving opossums and cat fleas maintains the organism in suburban areas,^1,2 and disease risk is associated with proximity to seropositive opossums.³ Most cases of murine typhus in the continental United States are documented in California and Texas, where reporting is mandatory.

Rickettsia felis. Rickettsia felis is a recently discovered organism that shares some phenotypic characteristics with typhus group Rickettsia. However, genotypic studies show that it is more closely related to spotted-fever-group Rickettsia.^1,4 Clinical signs of infection in humans mimic those of murine typhus.

Of note, routine serologic tests do not distinguish between R felis and R typhi, and, in endemic areas, R felis infects cat fleas more commonly than R typhi.^1,5,6 Accordingly, some cases of murine typhus originally attributed to R typhi were actually caused by R felis.¹

Opossums in murine typhus–endemic areas are seropositive, and R felis has been detected in opossum tissues.⁶ Whether opossums are reservoirs for R felis is not yet known. Because R felis can be transstadially and transovarially transmitted in the cat flea, the organism may be maintained in nature without a mammalian reservoir.^1,5

Cats are seropositive for R typhi and R felis in many states, suggesting that exposure is common.^7,8 Furthermore, R felis DNA has been amplified from fleas collected from cats in several states, Canada, and other countries.^7,9,10

Experimental infection in cats with R felis and R typhi results in seroconversion but no clinical signs. R felis can be demonstrated in blood transiently after experimental infection.^2,11 Natural infection has not been verified despite efforts to amplify DNA from cats infested with infected fleas.⁷ This may occur due to low numbers of circulating organisms or because the rickettsiemia is transient or intermittent.⁷

Fever was not associated with natural exposure of cats to R felis in 1 study.¹² Another study suggested that lymphadenopathy and polycythemia may be associated with infection.⁸ Although the role of R typhi and R felis as disease-causing agents in cats is unclear, transfer of infected cat fleas from opossums to cats is thought to increase the risk for infection in humans.^1,5

Bartonella. The cat flea is also a vector for Bartonella henselae and is considered a likely vector for B koehlerae and B clarridgeiae.¹³ In contrast to R felis and R typhi, cats are well-established reservoir hosts for B henselae. The spectrum of disease associated with B henselae, B koehlarae, and B clarridgeiae in humans and cats has recently been reviewed.<sup13–15sup> The extent to which members of the genus Bartonella are pathogenic for cats remains unclear.

Other Organisms. Mycoplasma haemofelis, Candidatus M haemominutum, and Candidatus M turicensis also commonly infect cats.¹⁶ Cat fleas can be infected with Mycoplasma species, and they are thought to play a role as vectors.¹⁷ Disease caused by these organisms in cats has been reviewed.^16,18 Although M haemofelis is not usually considered a human pathogen, coinfection with B henselae and an M haemofelis–like agent was recently reported in an immunocompromised cat owner.¹⁹

Plan. Discuss the importance of instituting a flea control program and instruct the owner to tighten garbage can lids and clear brush to limit exposure to opossums.

Take-Home Messages

• Ctenocephalides felis (cat fleas) are vectors for the human pathogens Rickettsia felis, R typhi, and Bartonella species.• Conscientious flea control is recommended to help prevent infection with these and other agents in cats and their human companions.

For more information, read the following articles:

Flea Management: An Integrated ApproachFeline Bartonella PreventionGetting a Grip on Flea Control

OPOSSUMS, CATS, FLEAS, & ZOONOTIC DISEASE • Linda Kidd, Margaret Barr, & Edward B. Breitschwerdt

References1. Murine typhus: An unrecognized suburban vectorborne disease. Civen R, Ngo V. Clin Infect Dis 46:913-918, 2008.2. Flea-borne rickettsioses: Ecologic considerations. Azad A, Radulovic S. Emerg Infect Dis 3:319-327, 1997.3. Geographic association of Rickettsia felis-infected opossums with human murine typhus, Texas. Boostrom A, Beier M, Macaluso J, et al. Emerg Infect Dis 8:549-554, 2002.

1. Variations of plasmid content in Rickettsia felis. Fournier PE, Belghazi L, Robert C, et al. PLoS ONE 3:e2289, 2008.5. Rickettsia felis as emergent global threat for humans. Perez-Osorio CE, Zavala-Velazquez JE, Leon JJA, Zavala-Castro JE. Emerg Infect Dis 14:1019-1023, 2008.6. Detection of Rickettsia felis and Rickettsia typhi in an area of California endemic for murine typhus. Karpathy SE, Hayes EK, Williams AM, et al. Clin Microbiol Infect Dis Apr 3, 2009 [Epub].7. Prevalence of Rickettsia felis DNA in the blood of cats and their fleas in the United States. Hawley JR, Shaw SE, Lappin MR. J Feline Med Surg 9:258-262, 2007.

2. Bartonella henselae and Rickettsia seroreactivity in a sick cat population from North Carolina. Breitschwerdt EB, Levine JF, Radulovic S, et al. Intl J Appl Res Vet Med 3:287-302, 2005.

3. The prevalence of Bartonella, hemoplasma and Rickettsia felis infections in domestic cats and cat fleas in Ontario. Kamrani A, Parreira VR, Greenwood J, Prescott JF. Can J Vet Res 72:411-419, 2008.10. Evidence of Bartonella spp, Rickettsia spp and Anaplasma phagocytophilum in domestic, shelter and stray cat blood and fleas, Portugal. Alves AS, Milhano N, Santos-Silva M, et al. Clin Microbiol Infect Dis 2009 [Epub].

4. Infection and seroconversion of cats exposed to cat fleas (Ctenocephalides felis Bouche) infected with Rickettsia felis. Wedincamp J, Foil LD. J Vector Ecol 25:123-126, 2000.12. Prevalence of Rickettsia species antibodies and Rickettsia species DNA in the blood of cats with and without fever. Bayliss DB, Morris AK, Horta MC, et al. J Feline Med Surg 11:266-270, 2009.

5. Vector transmission of Bartonella species with emphasis on the potential for tick transmission. Billeter SA, Levy MG, Chomel BB, Breitschwerdt EB. Med Vet Entomol 22:1-15, 2008.14. Feline bartonellosis and cat scratch disease. Breitschwerdt EB. Vet Immunol Immunopathol 123:167-171, 2008.

6. Bartonella spp in pets and effect on human health. Chomel BB, Boulouis HJ, Maruyama S, Breitschwerdt EB. Emerg Infect Dis 12:389-394, 2006.

7. Prevalence of various hemoplasma species among cats in the United States with possible hemoplasmosis. Sykes JE, Terry JC, Lindsay LL, Owens SD. JAVMA 232:372-379, 2008.17. Prevalence of Bartonella species, haemoplasma species, Ehrlichia species, Anaplasma phagocytophilum, and Neorickettsia risticii DNA in the blood of cats and their fleas in the United States. Lappin MR, Griffen B, Brunt J, et al. J Feline Med Surg 8:85-90, 2006.18. New perspectives about hemotropic Mycoplasma (formerly, Haemobartonella and Eperythrozoon spp) infections in dogs and cats. Messick JB. Vet Clin North Am Small Anim Pract 33:1453-1465, 2003.19. Hemoplasma infection in HIV-positive patient, Brazil. Pires dos Santos AP, Pires dos Santos RP, Biondo AW, et al. Emerg Infect Dis 14:1922-1924, 2008.