Bartonellosis: An emerging and potentially hidden epidemic?
Of all known organisms, 61% are zoonotic, and of the emerging pathogens, the vast majority are zoonotic organisms.
Veterinarians and physicians should talk to each other more frequently than we have in the past. Of all known organisms, 61% are zoonotic,1,2 and of the emerging pathogens, the vast majority are zoonotic organisms. My research at the Intracellular Pathogens Research Laboratory at the North Carolina State University College of Veterinary Medicine focuses on vector-transmitted organisms, of which 22% are zoonotic.1,3 In recent years, the genus Bartonella has been the major focus of our vector-borne research efforts.
BARTONELLA SPECIES COMPLEXITIES
The organism that causes cat scratch disease in people was identified as a Bartonella species in 1992. As researchers have continued to study these bacteria, we've learned that the intraerythrocytic component of the infection with a Bartonella species has been somewhat overemphasized. My research laboratory and others have demonstrated that Bartonella species are endotheliotropic bacteria that use a specialized invasion process to enter endothelial cells and can move about the body by infecting macrophages, with localization in a variety of tissues.3
Knowing more about Agrobacterium species and the pathogenic mechanisms it uses to induce tumors in plants will probably benefit physicians and veterinarians in better understanding what Bartonella species are doing to promote vasculoproliferative disorders in our patients.4
Researchers have learned that Bartonella species are the first bacteria identified to have an ability to invade CD34+ progenitor cells in bone marrow.5 This may be why we find Bartonella organisms in cats in only a low percentage (3%) of their erythrocytes.
The genus Bartonella is also unusual because it appears that no other infectious agent is transmitted by more vectors. We now know that sand flies, human body lice, cat fleas, rodent fleas, and probably many other flea species are capable of transmitting certain Bartonella species. And cattle, deer, elk, and sheep all have their own Bartonella species that appear to be transmitted by biting flies or keds (wingless flies).6
Our laboratory wondered whether ticks could transmit Bartonella species. Currently, the answers appear to be yes and maybe.7 Good case-based evidence exists in the human and veterinary medical literature that suggests ticks may transmit Bartonella species. And in many laboratories around the world, PCR testing reveals Bartonella species DNA in ticks, particularly in Ixodes species ticks. Researchers in France have nearly demonstrated Ixodes ricinus transmission of Bartonella henselae.8 Interestingly, Bartonella henselae is prevalent in I. ricinus ticks in southern Germany and in France.9 However, although tick transmission of Bartonella species is possible, it hasn't yet been definitively proven for ticks in North America.
IS A HIDDEN EPIDEMIC POSSIBLE?
In my opinion, a hidden epidemic is possible if several conditions are met.
- First, you start with an unknown bacterial genus, which was the situation for Bartonella in North America and much of the world until the human immunodeficiency virus (HIV) epidemic of the late 1980s and 1990s.
- Second, the organism must behave as a stealth pathogen that is capable of hiding in the host, as is true for Bartonella species.10
- Third, a large number of diverse animal reservoir hosts for the organism are maintained in nature—and that too is the case for the genus Bartonella. Several mammals—grey squirrels, flying squirrels, groundhogs—have their own genetically distinct Bartonella species that have coevolved in those animals and have a high prevalence in their respective hosts in nature.
- Finally, the organism creatively facilitates its transmission, not only through vectors, but by direct transmission through bites and scratches, which has been reasonably well-established for dogs and cats and for rabbits in Europe.11
AN UNDER-RECOGNIZED ZOONOSIS
In my opinion, physicians and veterinarians need to come together regarding bartonellosis, because it appears to be an important and under-recognized zoonosis. Depending on their immune competence, people with bartonellosis exhibit tremendous differences in disease expression. And with regard to immunocompetence, we have to consider not only people with severe immunosuppressive illnesses such as infection with HIV, but also pregnant women, children, geriatric people, transplant recipients, and patients treated with immunosuppressive drugs. Furthermore, diagnostic test sensitivity for documenting infection with this genus of bacteria is extremely poor, and based upon recent experience in our laboratory, patient response to treatment is frequently incomplete.
Endocarditis can be induced by a spectrum of Bartonella species in dogs and human patients and is the best example of documented disease causation for this genus. Historically, Bartonella species have been a cause of culture-negative endocarditis in people and dogs because the diagnostic methods that microbiology laboratories used were not adequate to isolate these bacteria. Now, by using specialized techniques, a spectrum of Bartonella species are being identified in research and diagnostic laboratories in different parts of the world—in heart valves or in blood cultures from people and dogs with endocarditis.12 And what's important for physicians and veterinarians to recognize is that some of these Bartonella species are found in cats, dogs, rats, ground squirrels, and rabbits. In 1992, two Bartonella species were known to exist, and in 2009, over 26 named or candidatus species exist.
ANIMAL RESERVOIR HOSTS
Bartonella species are present in a multitude of animal species. One of the most recently identified Bartonella species, Bartonella australis, was found in kangaroos.13 Unexpectedly, 82% of beef cattle in North Carolina have Bartonella bovis in their blood.14 My laboratory can isolate a Bartonella species from one or two out of three feral cats in North Carolina,15 and other laboratories around the world have documented similar levels of bacteremia in flea-infested cats.
Another important point for physicians and veterinarians to consider is that many of their patients and clients have pocket pets, some of which tend to scratch and bite. Unfortunately, numerous Bartonella species have been identified in the blood of various rodent species. For example, the overall prevalence was 26% in the population of wild and captive animals brought to Japan to be sold as pocket pets.16 The human medical literature in the United States reveals case reports of previously healthy people with no evidence of louse exposure and a history of cat exposure who presented to their physicians for evaluation of lymphadenopathy or seizures and were found to be infected with Bartonella quintana.17 More recently, our laboratory isolated B. quintana from cats and from a woman who was bitten by one of those cats.17
Another reason why I think the One Medicine initiative (veterinarians and physicians working together to fight disease) is important: In reviewing the human literature, as it relates to B. quintana, it told me, as a veterinary internist, what I should be looking for in my canine patients if I suspect that this organism is causing disease. And vice versa: I would suggest that physicians review data and observations that veterinarians are generating in regard to this genus of bacteria, because clearly some of us now are much more concerned about the genus Bartonella than anyone is at the National Institutues of Health (NIH) or Centers for Disease Control and Prevention (CDC).
SIMILARITIES OF DISEASE EXPRESSION IN PEOPLE AND ANIMALS
Bartonella species can induce a number of what I think are fairly well established pathologies in either dogs or people.18
The first dog we cultured Bartonella species from was a 3-year-old female Labrador retriever called Tumbleweed. Briefly, the dog had a history of a positive antinuclear antibody test result and had been receiving increasing doses of immunosuppressant drugs. Within a one-year time frame, Tumbleweed developed polyarthritis, seizures, vasculitis, epistaxis, and aortic and mitral valve endocarditis. We ultimately identified the first Bartonella species infection in a dog, and the novel organism was named Bartonella vinsonii subspecies berkhoffii.19
Cases similar to Tumbleweed's have occurred in people. For example, Duke University Medical Center and the Mayo Clinic have described patients who were treated with immunosuppressant drugs, based on finding antineutrophil cytoplasmic antibodies, and subsequently developed Bartonella species endocarditis.20,21
So we're seeing that what's occurring in people is also occurring in dogs—for example, about 80% of people and about 80% of dogs have endocarditis selectively involving the aortic valve. And based on the veterinary literature, physicians may want to put bartonellosis on their differential lists for children with unexplained epistaxis.19,22,23
BETTER DETECTION OF BARTONELLA SPECIES INFECTIONS
After the first isolation of B. vinsonii ssp. berkhoffii, we had difficulty isolating Bartonella species in other dogs by using culture or by detecting Bartonella DNA in patient samples by PCR testing, even though we could detect antibodies by using an immunofluorescent antibody assay. In our laboratory, we had discussed that these bacteria seem to be happier in insects than they do in dogs, so we decided to develop an optimized insect cell culture media to enhance the growth of Bartonella species.24,25 The insect cell culture media—Bartonella alpha Proteobacteria Growth Medium, or BAPGM (Galaxy Diagnostics, www.galaxydx.com)—combined with PCR testing now allows us to grow and detect these bacteria in animals and immunocompetent people better than any other diagnostic test currently available.26-28
My laboratory has found that 50% of dogs and people infected with B. henselae or B. vinsonii subsp. berkhoffii do not have detectable antibodies to any of the six different Bartonella species antigens used in our testing.18,26,27 So antibody testing for Bartonella species is proving to be very insensitive.
INITIAL BAPGM RESULTS AND POTENTIAL SEQUELAE OF BARTONELLA SPECIES INFECTION
Using BAPGM, our laboratory has recently started testing people in collaboration with physicians at Duke University Medical Center and elsewhere, as a component of an Institutional Review Board-approved research study. In the first subgroup, which was primarily composed of veterinarians, 14 of 42 people had positive Bartonella species cultures and several had Bartonella species coinfections.26 Using a survey instrument that we developed, this group of people with occupational animal contact and vector exposure described having headaches, insomnia, memory loss, muscle pain, and joint pain.26 Similar to our findings, physicians in Israel have generated a nice body of evidence regarding the long-term follow up of patients with cat scratch disease29-31 and have shown that a subset of those patients later develop chronic arthritis, chronic myalgia, and chronic musculoskeletal pain as components of their illness.
We now know that some people and some dogs can be coinfected with more than one Bartonella species, as is the case in cats that may be simultaneously infected with three hemotropic Mycoplasma species.32 It was the use of BAPGM that allowed us to culture B. quintana from a woman who had been bitten by a feral cat (although we had expected to culture B. henselae or Bartonella clarridgeiae instead). Months later, we used the BAPGM enrichment approach to culture B. quintana from the feral cat that had bitten her and another feral cat that lived on her property.17 We have also used the BAPGM platform to obtain the first DNA evidence of human infection with candidatus Bartonella melophagi,28 and CDC investigators used this approach to make the first isolates of Bartonella tamiae from febrile human patients.33
On a comparative medical basis, pericarditis can occur in people and dogs infected with Bartonella species.34-36 In severely immunocompromised people, it is well known that Bartonella causes bacillary angiomatosis and peliosis hepatis, as it does in dogs.37 For example, a dog with pancytopenia due to hypersplenism that had been immunosuppressed with prednisone and azathioprine developed cutaneous bacillary angiomatosis and B. vinsonii subsp. berkhoffii was identified.38 In collaboration with a physician at the University of Illinois College of Medicine in Chicago, we have also recently described infection with B. vinsonii ssp. berkhoffii in a boy with epithelioid hemangioendothelioma and in a dog with cutaneous hemangiopericytoma.39
MY FATHER'S ILLNESS AND BARTONELLA SPECIES
About two years ago, my 86-year-old father, who lived in a rural farm community and had developed gradual, progressive joint pain, was tested for Lyme disease, and the results were negative. He subsequently developed memory loss that was thought to be possible Alzheimer's disease. He then fell twice a few weeks apart, and a third time he fell, his hip fractured. He had many postoperative complications, and during his stay in a rehabilitation hospital he developed seizures.
At this point I became intimately involved in his medical evaluations, and because I direct the Intracellular Pathogens Research Laboratory at NCSU, I was given his aseptically obtained blood and CSF samples for testing. The results of PCR tests for Anaplasma, Ehrlichia, and Rickettsia species were negative. We ultimately identified what appears to be a new Bartonella species, most closely related to "Candidatus Bartonella volans," in his blood, as well as B. henselae and B. vinsonii ssp. berkhoffii.40
BARTONELLA SPECIES INFECTION AND ONE MEDICINE
There are several more examples in the literature that describe people with unexplained and chronic illnesses, who are identified as having positive Bartonella species test results. What I have described today doesn't prove causation of illness, but I think we have justification to worry about disease causation. Bartonella species infection is truly a problem in comparative medicine and a place where One Medicine applies. Veterinarians and physicians need to work closely to find solutions for the benefit of our respective patients. Although we still have much to learn about these bacteria, we now have a better way of detecting them in patient samples; therefore, we need to find out what they're doing in our patients and how often they're doing it.
Editor's note: In conjunction with Dr. Sushama Sontakke and North Carolina State University, Dr. Breitschwerdt holds U.S. Patent No. 7,115,385; Media and Methods for cultivation of microorganisms, which was issued October 3, 2006. He is the chief scientific officer for Galaxy Diagnostics, a newly formed company that provides diagnostic testing for the detection of Bartonella species infection in animals and in human patient samples.
Funding support for some of the research involving people at the NCSU Intracellular Pathogens Research Laboratory was provided by the ACVIM Foundation, the Kindy French Foundation, and Bayer Animal Health.
I would particularly like to acknowledge Drs. Ricardo Maggi, Silpak Biswas, Pedro Diniz, and Belen Cadenas for their molecular microbiological contributions to our research. I would also like to thank my graduate students and the staff of the Intracellular Pathogens Research Laboratory and the Vector Borne Diseases Diagnostic Laboratory at North Carolina State University.
Edward B. Breitschwerdt, DVM, DACVIM
Center for Comparative Medicine and Translational Research and the Department of Clinical Sciences
College of Veterinary Medicine
North Carolina State University
Raleigh, NC 27695
Presented at the physician/ veterinarian collaborative seminar "Pets, People, and Pathogens: Emerging Diseases" on November 18, 2009, in Providence, R.I. Coastal Medical (Providence, R.I.) and the Companion Animal Parasite Council jointly sponsored this seminar.
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