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July 30, 2020 – For anyone who grew up in the 1970s, it’s hard not to think of Ted Nugent every time we hear about cat scratch disease/fever. All kidding aside, cat scratch disease can be a serious problem for both people and pets. But this disease is just one of many caused by Bartonella, a family of bacteria that is of growing importance in human and veterinary medicine.

Bartonella, an elusive family of bacteria

Although cat scratch disease was first described more than 100 years ago, pinning down the organism responsible bedeviled scientists for decades. It took a large-scale tragedy, the HIV/AIDS epidemic of the late 1970s and early 1980s, for scientists to finally identify the organism responsible for cat scratch disease.

Physicians treating late-stage AIDS patients noted that three rare diseases; bacillary angiomatosis, peliosis hepatis and peliosis splenitis, were much more common in these patients than expected. Closer examination of affected tissues revealed large numbers of bacteria, which in turn led to the isolation of the bacteria responsible.

Further studies showed that development of these unusual diseases was linked to cat exposure and physicians suspected that this organism might also be the elusive culprit behind cat scratch disease. The organism was identified as a member of the Bartonella family and was named Bartonella henselae.

Besides being associated with cat scratch disease, members of the Bartonella family also are responsible for trench fever, a scourge of World War I, and Carrion’s disease, a serious infectious disease found in South America.

There are now over 36 recognized species of Bartonella and the list of clinical signs and syndromes in people and animals continues to grow. Bartonella are found in all parts of the world, though there are some regional differences in disease prevalence.

Bartonella transmitted in many ways

Most members of the Bartonella family are transmitted by insects, including fleas, ticks, lice, bed bugs, biting flies, and even spiders. Insects transmit disease when they feed on an infected individual and then move on to bite another.

Although infected cats can transmit B. henselae via a bite or scratch, the disease can likely also be transmitted to people by infected cat fleas. Trench fever is transmitted by the human body louse and Carrion’s disease is transmitted by infected sand flies.

Cats are the primary reservoirs of Bartonella henselae

Many species of animals can be infected with Bartonella, including dogs, horses, cattle, rabbits, mice, bats and sheep. But cats remain the primary reservoir for B. henselae, the agent that causes cat scratch fever. There is evidence that other animal species can be incidental hosts for B. henselae, but transmission from animals other than cats to humans is still not clear.

Unlike healthy adult cats, younger cats and kittens infected with B. henselae tend to have higher levels of the bacteria in their bloodstream, even if they are not ill, making them more likely to transmit the disease.

In addition, kittens and young cats also are more likely to play and scratch their owners, increasing the risk of transmission. As cats age, they are better able to control or eliminate infections and are less likely to pass infections to people or other animals.

Clinical signs associated with Bartonella

The majority of cats (and even dogs) infected with any type of Bartonella show no signs of infection and, when they do, signs can take a variety of forms.

Some signs veterinarians (and human doctors) watch out for include:

  • Fever
  • Enlarged lymph nodes
  • Inflammation of the heart
  • Eye inflammation
  • Blood abnormalities

Other signs in cats:

  • Neurologic abnormalities
  • Urinary tract problems
  • Oral cavity inflammation
  • Sinus inflammation

Other signs in dogs:

  • Lameness
  • Neurologic abnormalities
  • Fluid effusions in body cavities

Unfortunately, signs of Bartonella overlap with many other diseases, and given that Bartonella often are found in healthy animals, it’s tough to know if Bartonella are responsible for illness in sick animals or if they’re an incidental finding. Complicating the picture is that animals (and people) can be infected with multiple strains of Bartonella at the same time.

A growing body of evidence suggests that Bartonella can trigger diseases as diverse as immune mediated hemolytic anemia and cancer in animals. This is an active area of research and if Bartonella are found to be involved in these diseases, they could provide a new target for treatment.

Detecting Bartonella remains a challenge

Technological improvements have helped scientists identify Bartonella and led to the discovery of many new Bartonella species.

However, it’s not easy to find the organism in animals that have clinical signs due to a suspected infection. Veterinarians are still trying to determine what a positive result actually means, and they use a combination of clinical signs coupled with test results to rule in or out a diagnosis of bartonellosis (the disease caused by Bartonella).

Several different diagnostic tests available to veterinarians and their patients include:

  • Culture of the organism from blood or tissue – this is very difficult because the bacteria are difficult to culture although techniques are improving.
  • Antibody tests – presence of antibodies suggests exposure at some point in time but they’re not specific for active disease and chronic illness occurs in the absence of a diagnostic antibody response in a subset of cats, dogs and humans.
  • PCR – A sensitive test for presence of bacteria and can confirm bartonellosis with compatible clinical signs but can also be positive in clinically normal animals.

Sometimes multiple tests are required to rule in or out Bartonella as contributing to signs of illness in a dog or cat.

Treatment and prevention

If Bartonella are suspected as causing clinical signs in a dog or cat, antibiotic therapy is recommended. Unfortunately, there is no single drug that appears superior to another, and there is controversy over duration of treatment.

In addition to antibiotics, other medications may be required to treat patients with Bartonella. These include heart medications in cases of heart infections, and supportive care in patients that aren’t eating or drinking.

Currently, no vaccines are available against Bartonella. The best way to prevent infection in dogs and cats is strict control of parasites such as fleas and ticks.

Bartonella is a public health concern

It’s important to remember that cat scratch disease is a zoonotic disease (transmitted from animals to people). Although most healthy people are capable of successfully fighting an infection, immunocompromised people can suffer from serious illnesses.

The Centers for Disease Control and Prevention recommend the following steps people can take to protect themselves from infection:

  • Avoid rough play with cats to prevent scratches
  • Wash hands after handling or playing with cats, especially if immunocompromised
  • Keep cats indoors if possible and avoid contact with stray cats
  • Control fleas and ticks on both dogs and cats
  • People who have weakened immune systems should avoid owning cats younger than one year old
Bartonella and One Health

One Health is a collaborative approach to understanding how animal, human and environmental health intersect with each other. Given Bartonella’s global distribution and the number of species that can be infected, Bartonella is becoming of interest as a One Health problem.

“I think Bartonella are the most important genus of bacteria causing disease worldwide that we didn’t know existed,” said Dr. Edward Breitschwerdt, professor of medicine and infectious diseases at North Carolina State University College of Veterinary Medicine and world recognized expert on Bartonella.

Both human and veterinary infectious disease experts are turning their attentions to this little-understood organism and feel that Bartonella could be playing a role in diseases as diverse as cat scratch disease, heart inflammation, immune mediated disease and even cancer.

Dr. Breitschwerdt has been studying the many members of the Bartonella family in animals for nearly three decades and says that he is amazed by what this family of bacteria can do.

“I believe that Bartonella will be the next medical paradigm changer because it is transmitted by more vectors than any other I’m aware of, many reservoirs, and medically it’s important because it can invade more types of cells than any other vector-borne bacterial infection. And we’re just learning what this bacteria can do once it invades.”