Bartonella and Cat Scratch Disease

Joel (snowathlete) continues his series on zoonotic pathogens with an introduction to Bartonelliosis

Photo by girlstyle
Photo by girlstyle

Bartonella is a zoonotic that frequently infects humans causing diseases termed Bartonelliosis. Probably the most commonly known is cat scratch disease (CSD) which, you guessed it, you catch from cats (especially cute kittens). Cat scratch disease is caused by two species of Bartonella: B. henselae and B. clarridgeiae. But more than a dozen species of Bartonella can cause diseases in humans including B. bacilliformis which causes Carrion’s disease, and B. quintana which causes trench fever. It is not uncommon for people with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) to test positive for Bartonella.

Now I have to be honest, I find it hard to take the name ‘cat scratch disease’ seriously. Sure, trench fever sounds pretty rough going, and Carrion’s disease sounds even worse until you realize it was named after Mr Carrion, not decaying flesh, but ‘cat scratch disease’…Seriously?

I thought chronic fatigue syndrome (CFS) was bad. I mean, it sounds so mild, doesn’t it? And people get scratched by cats all the time and nothing bad befalls them…Well, often it seems that it is mild, but not always. In addition, there is some evidence that other forms of Bartonellosis are most severe.

Bartonella is an intracellular, rod-shaped bacterium and possesses whip-like flagella. They are Gram-negative, which means that they have a cell wall which is hard to penetrate (it doesn’t absorb the dye when a Gram staining protocol is performed) and this means they are more resilient to attack from the immune system or antibiotic treatments. B. henselae for instance, is resistant to penicillin and nafcillin.


Let’s start by looking at how you can get it. As I mentioned already, cats are one of the reservoirs of CSD and humans are often infected via a scratch or bite. Cat fleas are also thought to be a possible route of transmission [1, 2].

Rodents are also reservoirs for the pathogen and ticks have been shown to carry Bartonella as well [3]. Many people infected with other tick-borne infections such as Borrelia or Rickettsia also have Bartonella. Nonetheless, transmission from ticks has not been conclusively proven and some research argues against it [4].

Other species of Bartonella can be transmitted by vectors such as flies in the case of Carrion’s disease and body lice as in the case of trench fever. Transmission of some species of Bartonella from dogs to humans is also thought, by some, to be a possibility, but this is not widely accepted yet.


Infection usually occurs in childhood and is often mild and self-limiting. However, in some cases – especially in those with weakened immune systems – treatment may be required.

In a study in San Francisco, 41 percent of cats were found to be infected with B. henselae [5]. As this was a snap-shot of infection in these cats, and other species of Bartonella were not looked for, it seems reasonable to assume that over the life of a cat, the infection rate of Bartonella may be higher still.


There are many species of Bartonella. B. henselae is the most commonly known and studied, but other species are not well studied and most cannot be tested in mainstream labs. Many are better understood in reference to animals, not just cats but dogs too, and these species may be more damaging to humans than the species that cause CSD [6].


If you were infected via a cat or a cat flea, then it is not uncommon to be infected with toxoplama at the same time. If you got it from a tick then there are a multitude of other infections that you may have received in the deal, including Borrelia (you can read about that here), Babesia, Rickettsia or Ehrlichia. All of these co-infections complicate the picture, making it harder to diagnose and treat, and reducing your chance of recovery. There is evidence suggesting that a concurrent infection with both Bartonella and Borrelia may result in a disease complex which is able to infect and damage the nervous system [7].


Bartonella (Image by AJC1)
Bartonella (Image by AJC1)

In CSD the first signs of infection are papules or pastules at the site of injury, and later swelling of the lymph nodes sometimes occurs near the site of infection. Fever and fatigue, malaise, headache, chills, backache, insomnia, and less commonly weight loss, arthritis, rashes and sore throat may also occur. You may also get marks on the skin that look like – and are often misdiagnosed as – stretch marks.

In more extreme cases you may suffer from encephalopathy (brain dysfunction), neuroretinitis (eye infection) and impaired vision, osteomyelitis (bone infection) or Parinaud oculoglandular syndrome (a granulomatous conjunctivitis) and cardiomyopathy.

As it is thought that some people may be infected with other species of Bartonella that cause non-CSD Bartonellosis, it is possible that symptoms could be different in these cases, and it is also possible to carry the infection (perhaps with resulting immune suppression?) but be asymptomatic.

Can these symptoms be mistaken for ME/CFS? Maybe. It is not uncommon for people diagnosed with ME/CFS to test positive for Bartonella infection and because of the symptom overlap people often suffer with Bartonella for a long time before they are diagnosed with it and treated. It is most likely that it is an opportunistic infection, but there has not been sufficient research carried out to rule it out as a possible cause.


Bartonella invade erythrocytes (red blood cells) and also inhabit the endothelium (the cells forming the interior layer of blood vessels).

There is some evidence that Bartonella hits the immune system, with one paper suggesting that a Bartonella species – B. bacilliformis – is immunosuppressive, and resembles AIDS [8].


It is often hard to diagnose, especially if you weren’t injured by a cat or your symptoms occurred sometime after such an event. Some experts believe it is routinely misdiagnosed as another illness. A PCR blood test for the two strains which cause CSD is widely available, but tests for other species are not easy to find. A lymph node biopsy may be performed if you have swollen lymph nodes and an enlarged spleen may be an aid to clinical diagnosis.


Often, Bartonella infection appears to be non-serious and will resolve without treatment, but in established cases where the immune system does not deal with the infection, antibiotics are prescribed and the antibiotic chosen depends on the strains found to cause the infection.

Doxycycline is often used for the species which cause CSD, as is Azithromycin (the treatment of choice in pregnant women), clarithromycin, rifampin, trimethoprim-sulfamethoxazole, or ciprofloxacin may also be given. And there are a multitude of others, depending on the strain and (just as important) who your doctor is.


As already pointed out, there is symptom overlap between the two diseases, some people diagnosed with ME/CFS subsequently test positive for Bartonella, and there are many strains that are not well-known. There is plenty of scope for Bartonella to be a factor in ME/CFS, most likely as a co-infection, but there is also some scope for it to be linked with the pathogenesis of the disease.

The surprising thing is that there has been little published research exploring possible links, which unfortunately means a lot of the evidence for a link is anecdotal. Not insignificant, just not necessarily reliable.

One piece of research shows that some people diagnosed with CFS were found to be positive for various species of Bartonella that they tested for [9] though the proportion of patients in the study with CFS was not large and some of the data in the study is not presented in a way that makes drawing conclusions straightforward.

The only published paper that I could find which looked specifically at ME/CFS and Bartonella was by Komaroff almost 20 years ago [10], which concluded that infection with the henselae strain of Bartonella was unlikely to be the cause of ME/CFS. Welcome, for sure, but hardly sufficient to rule out Bartonella altogether.

Some doctors do test for it, De Meirleir for one certainly tests for it. Others, such as Lerner, Montoya and Cheney, believe that heart problems are common in ME/CFS patients, which may suggest a link to Bartonella as some species are known to cause heart problems, particularly those species which infect dogs.

Are any of these doctors (or anyone else), looking closely at it?

Although there is only one published peer-reviewed paper on Bartonella in ME/CFS, that doesn’t mean that people haven’t looked. It just means that they didn’t find anything worth reporting. But with a lot still unknown about Bartonella species, it is by no means ruled out yet, so we shouldn’t be surprised if we hear more about it in the future. In the meantime, as with other zoonotic infections that may present with similar symptomology to ME/CFS (Borrelia, Staphylococcus, Giardia lamblia, etc.), it is well worth being tested for them if you haven’t been already, as ME/CFS is of course supposed to be a diagnosis of exclusion.

Joel was diagnosed with ME/CFS in 2009 but struggled with the illness for some time prior to this. He loves to write, and hopes to regain enough health to return to the career he loved and have his work published.



  1. Higgins JA, et al. 1996. Acquisition of the cat scratch disease agent Bartonella henselae by cat fleas (Siphonaptera:Pulicidae).
  2. Foil L, et al. 1998. Experimental infection of domestic cats with Bartonella henselae by inoculation of Ctenocephalides felis.
  3. Martin E Aldelson, et al. 2004. Prevalence of Borrelia burgdorferi, Bartonella spp., Babesia microti, and Anaplasma phagocytophila in Ixodes scapularis Ticks Collected in Northern New Jersey.
  4. Telford SR III, et al. 2010. Bartonella spp. transmission by ticks not established.
  5. Koehler JE, et al. 1994. Rochalimaea henselae infection. A new zoonosis with the domestic cat as reservoir.
  6. Edward B, et al. 2010. Bartonellosis: an emerging infectious disease of zoonotic importance to animals and human beings.
  7. Eskow E, et al. 2001. Concurrent infection of the central nervous system by Borrelia burgdorferi and Bartonella henselae: evidence for a novel tick-borne disease complex.
  8. Eduado Ticona, et al. 2009. The pathophysiology of the acute phase of human bartonellosis resembles AIDS.
  9. Maggie RG, et al. 2012. Bartonella spp. bacteremia and rheumatic symptoms in patients from Lyme disease-endemic region.
  10. Komaroff, et al. 1994. Persistent infection with Bartonella (Rochalimaea) henselae or Afipia felis is unlikely to be a cause of chronic fatigue syndrome.

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