Cat Scratch Fever.
While it may be a catchy song title, the “real thing” is incredibly scary. Ted Nugent will want to stick to singing the song, and leave the disease alone.
Cat Scratch Fever is also known as Cat Scratch Disease (CSD) and Bartonellosis, after the genus of the causative organism, Bartonella. Most cases result from infection with Bartonella henselae, however, other species may also be involved in specific cases in a variety of species.
CSD was first described in 1950 by French researchers, Debre’, et al. However, they incorrectly identified the causality. Bartonella was discovered in later research.
Cats are known to be the main reservoir of this organism, and it is transmitted from one to another by the cat flea, Ctenocephalides felis.
Epidemiologists estimate there are in excess of 20,000 cases of CSD in humans in the United States each year, costing many millions of dollars to treat. Bartonella spp. are hemotropic (meaning they like to live in blood) and intraerythrocytic, meaning they like to live inside red blood cells (RBCs).
Most cases occur because of a scratch or bite from a cat, although transmission by an infected flea or tick is also known to occur. CSD also occurs in intravenous (IV) drug users.
Humans usually experience lymphadenopathy, a swelling of lymph nodes in the region draining the inoculation site (bite or scratch). That site will usually swell, then develop pus. Atypical manifestations may also include infection of the heart, central nervous system, liver, bone, joints and kidneys. Infection and resulting inflammation of the brain is the worst syndrome, but even that usually resolves in most patients within a year, with no ongoing problems.
Most cats test positive for the presence of, or previous exposure to, Bartonella spp. through a technique called serology. Serology, however, simply tells us that a certain organism has been in the body and the immune system has responded to it. Serology does not tell us whether the organism is currently causing illness. Therefore, researchers face a dilemma. What syndromes are actually being caused by CSD-associated organisms, and what syndromes have other causes in cats who just happen to also be infected by Bartonella spp? In other words, we clinicians find ourselves asking, “Is he sick from Bartonella, or does he tolerate the Bartonella bacteria which are always there, and his illness is something else?” It is often a riddle with no clear answer.
Researchers know that some Bartonella-infected cats do exhibit fever, lymphadenopathy, central nervous system (CNS) disorders, decreased appetite, lethargy and redness with swelling at the site of inoculation. Interference with breeding and pregnancy may also be observed in queens (intact female cats). Gingivitis (gum inflammation) and eye inflammation may also be present, along with endocarditis, an inflammation/infection of the interior lining of the heart.
In dogs, it is known that tick-related diseases, including Erlichiosis, Rocky Mountain Spotted Fever, Babesiosis, Lyme Disease, Tularemia and Anaplasmosis can adversely affect the immune system and cause illnesses that might not have debilitated a healthy dog.
Some species of Bartonella commonly cause endocarditis in dogs, and lesions inside the heart can be dramatic, even fatal. On the other hand, those same organisms are isolated from clinically healthy dogs, implying that some immune system suppression must be present in order to make certain dogs susceptible to both infection and illness.
If immunocompromised persons in a household are planning to add a cat of unknown background, Bartonella testing should be performed on that cat first. Failure to identify possible Bartonella infection could result in human illness and/or death from the individual’s inability to mount an immune system defensive response. Antibiotic treatment alone rarely, if ever, eliminates the organism from a cat’s body.
As of this writing, no cases of transmission of Bartonella from dogs to humans have been documented.
Treatment for humans includes a variety of options, according to the organ system(s) involved.
See you next week, Dr. Randolph.
Our thanks go to Dr. Bruno Chomel, et al, for their comprehensive article in The AVMA Journal entitled “Cat Scratch Disease and other zoonotic Bartonella infections.”