Abstract
This issue of JFMS features a detailed, timely and comprehensive review of the current knowledge related to Bartonella species infection in cats, on which the authors, Dr Bianca Stützer and Professor Katrin Hartmann, are to be congratulated. 1 When a bacterium is discovered, or, as in the case of Bartonella, rediscovered, numerous clinical, microbiological and pathological concepts related to disease causation and microbial pathogenesis are sequentially redefined. Subsequently, the medical relevance of the genus undergoes continued maturation, as knowledge of the organism, the host immune response, diagnostic test sensitivity and specificity, treatment efficacy and epidemiology expands. Since the rediscovery of this genus in the early 1990s, a paradigm of ongoing biological and medical redefinition of Bartonella species as important animal and zoonotic human pathogens has evolved.
The importance of fleas as vectors of serious and potentially life-threatening disease in cats and their human counterparts is rapidly coming to light. Courtesy of HESKA Corporation
For nearly two decades the extent to which Bartonella henselae causes illnesses such as fever, gingivitis, stomatitis, myocarditis neurological abnormalities and uveitis in cats has been studied, and the pathogenicity of this bacterium has been debated. In his homage to Lucretius, Vergil is credited with stating: ‘Happy is he who knows the causes of things.’ Based on ongoing discussions, it is obvious that clinicians, microbiologists and biomedical research scientists continue to struggle with ‘disease causation’, particularly in the assessment of the pathogenic role of microorganisms that produce persistent intravascular infections lasting months to years in a mammalian host, as occurs with Bartonella species infections in cats and other animals including man. Thus, comprehensive, sequential, long term studies will be necessary to establish whether cats pay a ‘biological price’ when chronically bacteremic with a Bartonella species.
As described in this current review, we now know that domestic and wild cats are natural reservoir hosts for several Bartonella species and that fleas are of substantial importance in the transmission of several of these species among cat populations. In addition to the expanding number of documented reservoir hosts, an increasing number of arthropod vectors, including biting flies, keds, lice, sandflies and ticks, as well as fleas, have been confirmed or suspected to be associated with the transmission of Bartonella species among animal populations. 2 Given the diversity of Bartonella species and subspecies, the large number of reservoir hosts and the spectrum of arthropod vectors, the clinical and diagnostic challenges posed by Bartonella transmission in nature appear to be much more complex than is currently appreciated in either human or veterinary medicine. 3 It has also become obvious that numerous other animals, including cows, dogs, dolphins, feral swine, horses, human beings, sea turtles and whales can become infected with B henselae, the most common Bartonella species infecting cats around the world; however, routes of B henselae transmission to these animals and to people remain unclear.
Because B henselae has been readily isolated by blood culture from healthy or sick cats, most seroepidemiological studies and most isolation studies have focused on this particular Bartonella species. Thus, the medical importance of other Bartonella species for feline health remains poorly understood. For example, B koehlerae is much more prevalent in fleas from the Middle East as compared with the United States (MRL, unpublished data). Yet, persistent human infection with B koehlerae has been reported from the US,4,5 and we have isolated this species from the blood of cats with seizures in Florida (EBB, unpublished data). As expressed by the authors of the current review, the role of B koehlerae as a feline pathogen is yet to be determined.
Furthermore, several research groups have generated data supporting variation in pathogenicity among B henselae strains. Increased strain virulence has recently been documented in experimental and naturally infected cats that developed B henselae myocarditis after exposure to fleas.6,7 Thus, although cats are often well-adapted reservoirs, virulent strains of B henselae can induce acute, fatal myocardial disease, as well as fatal or antibiotic-responsive endocarditis.6–8
In addition, infection with a ‘non-reservoir adapted’ Bartonella species, Bartonella vinsonii subspecies berkhoffii, which appears to have co-evolved with domestic and wild canids, induced persistent bacteremia in a cat spanning an 18-month time frame, in conjunction with hyperglobulinemia, plasmacytosis and recurrent osteomyelitis. 9 Thus, non-reservoir-adapted Bartonella species may also induce serious pathology in cats.
Importantly, future epidemiological studies and diagnostic efforts directed at feline patients should incorporate serological testing with an expanded panel of Bartonella species antigens so as to determine prior exposure, whereas enrichment blood culture prior to PCR testing, which has increased the sensitivity of Bartonella species detection in dogs10,11 and people,12,13 should be used to determine if a cat is actively infected. As an example, Sykes and colleagues recently reported that bacteremia, in contrast to seroreactivity, was associated with the presence of gingivitis/stomatitis in a group of cats. 14
Due to extensive contact with arthropod vectors and a spectrum of animal species, veterinary professionals appear to have an occupational risk of infection due to frequent exposure to Bartonella species.4,5,13,15,16 Therefore, these individuals should exercise increased precautions to avoid arthropod bites (ie, fleas and lice), arthropod feces, animal bites or scratches and direct contact with bodily fluids from sick animals. Physicians and veterinarians should be educated as to the large number of Bartonella species in nature, the extensive spectrum of animal reservoir hosts, and the diversity of confirmed and potential arthropod vectors, current limitations associated with diagnosis and treatment efficacy, and the ecological and unfolding medical complexity of these highly evolved intravascular, endotheliotropic bacteria.2,3,17 Veterinarians, in turn, should educate clients as to the rapidly evolving importance of fleas as vectors that cause serious and potentially life-threatening disease in cats and their human counterparts.
We’ve a way to go in our understanding of bartonellosis, but it’s clearly a disease that deserves One Health consideration.