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Bartonella in cats: healthy carriers, tests and cat scratch disease

Bartonella henselae is a blood bacterium carried by many cats, most often young cats with fleas. Nearly all of them look perfectly healthy. The same bacterium causes cat scratch disease in people, which is why owners ask about testing. Here is what the tests can and cannot tell you.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Cats are the main reservoir of Bartonella henselae, and most infected cats show no signs. Fleas spread it between cats; a scratch with flea dirt under the claws spreads it to people. A positive antibody test shows exposure, not current infection: fewer than half of antibody-positive cats have the bacterium in their blood. Culture and PCR find the bacterium itself. Testing healthy cats is mainly useful for blood donors and homes with an immunocompromised person. Year-round flea control is the key prevention.

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Most infected cats are healthy carriers

Cats are the main reservoir of Bartonella henselae; B. clarridgeiae is the other common species in cats [1, 3]. Infected cats usually show no clinical signs, and a link with illness has rarely been proven [1]. Cats can carry the bacterium in their blood for months and even years [2]. Long-lasting blood infection is mainly seen in cats under 2 years of age, and young cats infected in a study kept a relapsing bacteremia for up to 454 days [1].

Antibody rates in European cats range from 8% to 53% depending on the study [1].
StudyCatsBacterium in blood (culture)Antibodies
Paris area, France [4]436 pet cats16.5%41.1%
Strasbourg, France [11]94 stray cats53%–
Four US regions [5]271 pet cats, 3 months to 2 years24%51%
San Francisco shelter [7]193 kittens and 158 young adults25.9% of kittens, 41.1% of young adults10% of kittens, 46.2% of young adults

How cats get Bartonella

  • Fleas: the cat flea (Ctenocephalides felis) picks up the bacterium with blood, and it multiplies in the flea’s gut. Flea droppings on the skin end up under the claws when the cat scratches itself [1].
  • Proof from experiments: fleas taken from infected cats passed the infection to kittens, while kittens living with infected kittens without fleas stayed free of it [6].
  • Not by simple contact: in a flea-free home, it did not spread by bites, grooming, shared litter boxes or food bowls, mating, or from mother to kittens [1].
  • Blood transfusion can also transmit it [1].

Risk factors in surveys: young age, fleas, adoption from a shelter or as a stray, and living with other cats [3, 4, 5].

What the blood work shows

  • Usually nothing: the blood count, chemistry panel and urinalysis are frequently normal in infected cats [2]. See cat blood work explained.
  • In sick cats, reported changes include anemia, a high eosinophil count, high total protein and globulins, a low neutrophil count and low platelets [2]. See anemia in cats and eosinophils.
  • Globulins: antibody-positive cats were more likely to have high globulins, but antibody rates were no higher in anemic cats than in others [1].
  • Another blood bacterium spread among cats is covered in Mycoplasma haemofelis in cats.

How to read the antibody line

Here is an example line from a young cat tested before joining a blood donor program.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
Bart IFA Bartonella henselae antibodies (IFA)1:256titer< 1:64H
  1. Abbreviation Also written B. henselae IgG or Bartonella serology. Antibodies to B. henselae cross-react with B. clarridgeiae, so the test cannot name the species [3].
  2. Result 1:256 in this illustrative line: antibodies are still detected when the serum is diluted 256 times. High titers often go with a positive culture or PCR [2].
  3. Unit A titer is a dilution, so it has no unit. IFA means indirect immunofluorescence; ELISA is another method [1].
  4. Laboratory interval The positive cut-off is set by each laboratory: 1:64 was used in one Italian study [10]. Methods are not standardized between laboratories [3].
  5. Flag H: above the cut-off. It shows exposure, not current infection: fewer than half of antibody-positive cats are actively infected [3].

Antibody tests, culture and PCR

  • Antibody test (IFA or ELISA): better at ruling infection out than in. The positive predictive value is 32–46% and the negative predictive value 85–97% [3]. In a French study of 436 cats, no antibodies meant no bacteremia in 97.3% of cases [4].
  • A negative test in a kitten is less reassuring: in a shelter study, culture-positive kittens were 9.4 times more likely than young adults to have no antibodies [7].
  • Blood culture is the gold standard, but it needs a specialized laboratory and is slow. A positive culture proves infection, not that the bacterium causes the cat’s illness [1, 3].
  • PCR finds the bacterium’s DNA faster. Bacteremia can come and go, so repeated cultures or PCR on more than one sample reduce false negatives [1, 3].

Who should be tested? Guidelines recommend testing for blood donor cats, cats living with an immunocompromised person, and when a person in the home has a Bartonella-related disease [1, 2]. For blood donors, the minimum standard is a negative PCR; the optimal donor is also antibody-negative [8]. Testing healthy cats otherwise brings little benefit [1].

Because the cat is often healthy, a diagnosis of Bartonella disease (for example uveitis or heart valve infection, both rare) requires ruling out other causes [1]. Other infections to check in a cat: FeLV and FIV and toxoplasmosis.

Cat scratch disease in people

B. henselae causes cat scratch disease, a self-limiting swelling of the lymph nodes near the scratch; in immunocompromised people it can cause much more serious illness [1]. A small bump, then a pustule, appears at the scratch within 14 days, and lymph nodes swell within weeks; uncomplicated cases may take several months to resolve [3]. In the United States, about 12,000 outpatients and 500 hospitalized patients are diagnosed each year, with the highest rate in children aged 5 to 9 [9].

Many patients had close contact with kittens [3]. Wash a cat scratch or bite promptly with soap and water and ask your doctor for advice; avoid rough play, and do not let cats lick open wounds [3]. Treating a healthy carrier cat with antibiotics does not reliably remove the risk [1]. Strict flea control is the only proven prevention, and there is no vaccine [1].

Related articles

Mycoplasma haemofelis in cats

Feline infectious anemia: the blood smear and PCR.

Read the article

Toxoplasmosis in cats

Another cat infection people ask about, with its own antibody tests.

Read the article

FeLV and FIV in cats

The viral tests often run in the same young cats.

Read the article

En français : bartonellose du chat.

Questions to ask your veterinarian

  1. Does my cat need a Bartonella test, given who lives at home?
  2. Was it an antibody test, a culture or a PCR?
  3. If the antibodies are positive, does that mean my cat is infected now?
  4. Could my cat’s signs have another cause that should be ruled out first?
  5. Which flea control should all the pets in the house receive, all year?
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Frequently asked questions

Can cats recover from Bartonella?

Often, yes. Without treatment, bacteremia has lasted from weeks to months [3], lasting longest in young cats [1]. Many seropositive cats limit the bacteremia over time [8]. Antibodies do not protect, so a cat can be reinfected [1].

How did my cat get Bartonella?

Almost always through fleas or flea droppings. In a flea-free home it did not spread through bites, grooming or a shared litter box [1].

Can an indoor cat carry Bartonella?

Yes. In 271 young US pet cats, indoor-only status was not significantly linked to a lower rate of infection [5]. Fleas and a shelter or stray origin were risk factors [4, 5].

Can you get rid of Bartonella in a cat?

Not reliably. Antibiotics have cleared the bacteremia in some cats but not others, and treating healthy carriers is not recommended because of the risk of resistance [1, 3]. Flea control is the priority [1].

Is cat scratch fever the same as Bartonella?

Cat scratch fever (cat scratch disease) is the human illness caused by B. henselae, passed on mainly by a scratch [1]. If a scratch is followed by swollen lymph nodes or fever, see your doctor [3].

Sources

  1. Pennisi MG et al. Bartonella species infection in cats: ABCD guidelines on prevention and management. J Feline Med Surg. 2013;15(7):563-569. doi.org/10.1177/1098612X13489214
  2. Álvarez-Fernández A, Breitschwerdt EB, Solano-Gallego L. Bartonella infections in cats and dogs including zoonotic aspects. Parasit Vectors. 2018;11:624. doi.org/10.1186/s13071-018-3152-6
  3. Brunt J et al. American Association of Feline Practitioners 2006 Panel report on diagnosis, treatment, and prevention of Bartonella spp. infections. J Feline Med Surg. 2006;8(4):213-226. doi.org/10.1016/j.jfms.2006.05.006
  4. Gurfield AN et al. Epidemiology of Bartonella infection in domestic cats in France. Vet Microbiol. 2001;80(2):185-198. doi.org/10.1016/s0378-1135(01)00304-2
  5. Guptill L et al. Prevalence, risk factors, and genetic diversity of Bartonella henselae infections in pet cats in four regions of the United States. J Clin Microbiol. 2004;42(2):652-659. doi.org/10.1128/JCM.42.2.652-659.2004
  6. Chomel BB et al. Experimental transmission of Bartonella henselae by the cat flea. J Clin Microbiol. 1996;34(8):1952-1956. doi.org/10.1128/jcm.34.8.1952-1956.1996
  7. Fleischman DA et al. Bartonella infection among cats adopted from a San Francisco shelter, revisited. Appl Environ Microbiol. 2015;81(18):6446-6450. doi.org/10.1128/AEM.01864-15
  8. Wardrop KJ et al. Update on canine and feline blood donor screening for blood-borne pathogens. J Vet Intern Med. 2016;30(1):15-35. doi.org/10.1111/jvim.13823
  9. Nelson CA, Saha S, Mead PS. Cat-scratch disease in the United States, 2005-2013. Emerg Infect Dis. 2016;22(10):1741-1746. doi.org/10.3201/eid2210.160115
  10. Fabbi M et al. Prevalence of Bartonella henselae in stray and domestic cats in different Italian areas: evaluation of the potential risk of transmission of Bartonella to humans. Parassitologia. 2004;46(1-2):127-129 (in Italian). pubmed.ncbi.nlm.nih.gov/15305701
  11. Heller R et al. Prevalence of Bartonella henselae and Bartonella clarridgeiae in stray cats. J Clin Microbiol. 1997;35(6):1327-1331. doi.org/10.1128/jcm.35.6.1327-1331.1997

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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