Cat Scratch Fever in Cats and Humans: Part 2 of 3


Now the hard part: Humans and cat scratch disease.

Cat Scratch Disease is no longer as simple a topic as when I first learned about it 30 years ago in veterinary college. Even worse, I’m surprised at how little medical science—in spite of the tons of research being done—can still tell us with absolute certainty about the problem. A bit of personal disclosure before I begin. Firstly, one of our many jobs as veterinarians is to be constantly on the look-out for zoonotic diseases. These are diseases that can affect both humans and animals.

As a matter of fact, this public health aspect of our business morally and ethically takes precedence over saving the lives of cats and dogs. Second, even though I can’t (or won’t) legally give human medical advice, my clients will still often seek my opinion anyway. And so I try to keep up on this stuff. Other than medical conferences, my main sources of information when wanting to further expand my knowledge of zoonotic diseases are the Centers for Disease Control (CDC) and the American Academy of Family Physicians (AFP) websites. For the bulk of this informational blog, I shamelessly rely upon—but try to simplify—their advice.

Bartonella Rash: Photo from http://www.Lyme

Cat Scratch Disease in Humans and Adults

In children and adults with healthy immune systems, the first and foremost thing to remember is that most cat scratches do not result in cat scratch disease. If this was indeed the case, caring and loving, health-conscious, mothers would long ago have eliminated the domestic cat from the planet! With the exception of one of the vet technicians who worked at the practice where I interned at, in the whole of my 25 years since I’ve hung up my shingle I’ve not heard of a single case of the disease. I have, however, suspected it a few times in cats.

Enlarged Lymph Node; Photo by CDC

That having been said, it is estimated that there are up to 24,000 cases a year in the U.S. that require some degree of hospitalization. Although anyone of any age can catch cat scratch fever, people less than 21 years old are the most likely to become infected. As a general rule, symptoms of the disease appear 3 – 14 days after a scratch, bite, or lick. And because they state the symptoms of cat scratch disease in humans so clearly, I’ll use the following quote from a CDC website:

“About three to 14 days after the skin is broken, a mild infection can occur at the site of the scratch or bite. The infected area may appear swollen and red with round, raised lesions and can have pus. The infection can feel warm or painful. A person with Cat Scratch disease may also have a fever, headache, poor appetite, and exhaustion. Later, the person’s lymph nodes closest to the original scratch or bite can become swollen, tender, or painful.”

Enlarged Lymph Node: Photo by CDC


My recent researches of the human medical literature suggest there is some controversy regarding treatment of cat scratch fever. I’ll again quote a CDC webpage: “The use of antibiotics to shorten the course of disease is debated. Most cases of cat scratch disease (CSD) resolve without treatment, although some patients may develop complications from disseminated disease [my emphasis]. The antibiotic azithromycin has been shown to decrease lymph node volume more rapidly compared to no treatment.”

A Defense of My Human Physician Colleagues

Even after 25 years of practicing veterinary medicine, every once I still get that mysterious sick dog or cat where I have to stand back, scratch my head, and ask myself, “what in the heck (not the exact word I use) is going on here. Before continuing on with my sharing of what I know about complicated cases of cat scratch fever in both healthy and immune compromised people, I need to make a bit of an editorial.

“Some patients may develop complications from disseminated disease.” This innocent-looking, little sentence fragment from the above mentioned Centers For Disease Control’s quote is what makes me thank our dear God daily that I decided to go into veterinary vs. human medicine.

After much very in-depth reading of the seemingly infinite and contradicting diagnoses possible as the result of an infection (or not) with Bartonella henselae, I don’t envy my physician counterparts one bit in their struggle to come to some sort of conclusion with regards to cat scratch fever and their affected patients. The absence of a consistently reliable test, the fact that there are so many other diseases that can mimic (look like) the disease, and the even the lack of agreement as to how the disease is spread or of how it should be treated—all of which has to be filtered through our present-day “managed healthcare” system—makes a doctor’s job, in my opinion, nearly impossible to accomplish.

Disseminated Disease In People With a Healthy Immune System

“Disseminated disease” (as stated by the Centers For Disease Control’s quote above) is a medical term referring to a disease that is spread throughout an organ or the body. In people with a healthy immune system, the American Academy of Family Physicians’ website mentions that the following are rare complications of cat scratch disease:
●encephalopathy, a broad term for any brain disease that alters the brain’s function, which in cat scratch fever can manifest itself as severe headache and acute confusion one to six weeks after the onset of the enlargement of a patient’s lymph nodes. Seizures may occur, and some patients may have focal neurological deficits (nerve disease that affects a specific location in the body such as a tongue, either arm, one side of a face, one eye, etc.) that are self-limiting, but can last up to one year.
●endocarditis, an infection of the inside of the heart, usually involving the heart valves.
●meningoencephalitis, an inflammation or infection of the brain and/or spinal cord.
●Parinaud oculoglandular syndrome (POS), a severe conjunctivitis “pink-eye” that involves the lymph nodes of the neck. [I’ve tried to make the description of this eye disease as easy to understand as possible. POS is a lot more complicated and has many more causes.]
●Neuroretinitis, is an inflammation of the nerves of the retina of the eye and the optic nerve, leading to partial loss of vision.
●And probably a lot more as-of-yet undiscovered disease connections.

Disseminated Disease in People Who Are Immunosuppressed

Besides any of the above ailments, Immunosuppressed people who are unfortunate enough become infected with Bartonella henselae and/or its “cousin” Bartonella quintana potentially can fare much worse. The two most frequently mentioned diseases are:
●Bacillary angiomatosis, a disease characterized by the formation of red, round, nodules in the skin cause by the uncontrolled growth of blood vessels. While this skin form is the most common, it can occur in other parts of the body as well including the respiratory and GI tract, the brain, bone marrow, lymph nodes, liver and spleen.
●Bacillary peliosis, a not-well-understood disease in which the liver and/or spleen become affected by cystic, blood-filled cavities.

Ticks: Photo from

Bartonella henselae and Ticks

This is one of two other considerations to keep in mind with regards to cat scratch fever: the first is the possibility of Bartonella henselae being spread by ticks, and the other is the concept of Bartonella henselae co-infection with Lyme disease. I’ll start off by saying that the evidence for cat scratch fever being spread by ticks is quite strong, but there is no objective scientific proof that transmission of the disease actually can happen. The greatest proof of this spread being a real possibility is that researchers in both the U.S. and Europe have found the organism in the Ixodes Scapularis tick (the species of “deer tick” responsible for Lyme disease.)

Bartonella and Other Co-infections

Finally, I would like to end this brief summary of cat scratch fever by calling attention to the concept of co-infections of Bartonella henselae (as well as other tick-borne diseases) and Lyme disease. (Co-infections means being infected with two or more diseases.) I must again make it clear, that as of this writing, medical science is still undecided as to whether Bartonella co-infections (as well as the other tick-transmitted organisms) can result in more serious illness.

In a 2013 survey of over 3000 critically affected Lyme disease patients sponsored by, tick-borne co-infections were confirmed by serological testing in over 53.3% of the individuals who responded! The rate of co-infection with a Bartonella species was 28.3%. As an aside, here was the co-infection breakdown for the other tick-borne diseases.
●Babesia, 28.3%
●Ehrlichia, 14.5%
●Anaplasma, 15.1%
●Mycoplasma, 5.1%
●Rocky Mountain Spotted Fever, 5.6%
●Tularemia, 0.8%

Author’s Cat Tuxie

My Humble Conclusions

In conclusion, I’d like to share my thoughts on these last two issues. Yes! it is frustrating how little medical science can give us with regards to a straight answer as to the concept of co-infections; even something as seemingly simple as to whether or not animals and humans can catch the disease from a tick bite! But this is because the problem is not simple! Ticks have been on this earth for over a hundred million years an they’ve learned to adapt to every situation the world has presented them with. Scientist have even found a Borrelia species (the bacteria that causes Lyme disease) in a 15 million year old tick that had been preserved in amber!

But with that having been said, in the course of my daily life as both a veterinarian and a living, attentive person, I see an awful lot of very sick people (and a few animals) who have been diagnosed—or not—with Lyme disease, whose doctors just can’t seem to help them any longer.

Therefore I close with what I believe is the most prudent advice I found as it pertains to cat scratch fever, ticks, and co-infection with Lyme disease. It is given on the Columbia University Medical Center-Lyme website and I quote it directly. It is presented, somewhat, in medical jargon, but the last sentence brings it all home:

[The bold emphasizes are my own.] “The clinical manifestations of tick-transmitted bartonellosis are essentially unknown. They may resemble cat scratch disease, take other clinical forms, or be benign. It is also unclear if Bartonella co-infection with other tick-transmitted organisms can result in more serious illness; some of the few reported cases of concurrent B. burgdorferi (the bacteria that causes Lyme disease) and B. henselae (once again, the bacteria that causes cat scratch fever) infection in the medical literature appear to suggest this could be the case. Thus, it may be prudent to consider the possibility of Bartonella co-infection in cases of poorly resolving or apparent relapsing Lyme disease.”

A few More Resources

Cat-Scratch Disease in Children

The Official Lyme Report

A Non-veterinarian Resource For Cat Owners


Dear Reader: Thank you. If you feel this article can help a friend who may be suffering from Lyme disease—any of the tick-borne diseases—please share.

One Comment on “Cat Scratch Fever in Cats and Humans: Part 2 of 3

  1. Pingback: Cat Scratch Fever in Cats and Humans: Part 1 – The Other Dr. Oz

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