Edward B. Breitschwerdt

Bartonella Infection in Animals: Carriership, Reservoir Potential, Pathogenicity, and Zoonotic Potential for Human Infection

Recent observations have begun to support a role for Bartonella spp. as animal as well as human pathogens. Bartonella spp. are vector-transmitted, blood-borne, intracellular, gram-negative bacteria that can induce prolonged infection in the host. Persistent infections in domestic and wild animals result in a substantial reservoir of Bartonella organisms in nature that can serve as a source for inadvertent human infection. The prevalence of bacteremia can range from 50 to 95% in selected rodent, cat, deer, and cattle populations. Dogs infected with Bartonella spp. can develop lameness, endocarditis, granulomatous lymphadenitis, and peliosis hepatis, lesions that have also been reported in association with human infection. Understanding the role of Bartonella spp. as pathogens in cats and other wild or domestic animals awaits the results of additional studies. Considering the extensive animal reservoirs and the large number of insects that have been implicated in the transmission of Bartonella spp., both animal and human exposure to these organisms may be more substantial than is currently believed.

Bartonella Spp. in Pets and Effect on Human Health

Pets represent a large reservoir for human infection.

Vector transmission of Bartonella species with emphasis on the potential for tick transmission

Abstract Bartonella species are gram‐negative bacteria that infect erythrocytes, endothelial cells and macrophages, often leading to persistent blood‐borne infections. Because of the ability of various Bartonella species to reside within erythrocytes of a diverse number of animal hosts, there is substantial opportunity for the potential uptake of these blood‐borne bacteria by a variety of arthropod vectors that feed on animals and people. Five Bartonella species are transmitted by lice, fleas or sandflies. However, Bartonella DNA has been detected or Bartonella spp. have been cultured from numerous other arthropods. This review discusses Bartonella transmission by sandflies, lice and fleas, the potential for transmission by other vectors, and data supporting transmission by ticks. Polymerase chain reaction (PCR) or culture methods have been used to detect Bartonella in ticks, either questing or host‐attached, throughout the world. Case studies and serological or molecular surveys involving humans, cats and canines provide indirect evidence supporting transmission of Bartonella species by ticks. Of potential clinical relevance, many studies have proposed co‐transmission of Bartonella with other known tick‐borne pathogens. Currently, critically important experimental transmission studies have not been performed for Bartonella transmission by many potential arthropod vectors, including ticks.

Bartonellosis: an emerging infectious disease of zoonotic importance to animals and human beings.

OBJECTIVE To provide a review of clinically relevant observations related to Bartonella species as emerging pathogens in veterinary and human medicine. DATA SOURCES Literature as cited in PubMed and as generated by each of the authors who have contributed to various aspects of the clinical understanding of bartonellosis. HUMAN DATA SYNTHESIS Important historical and recent publications illustrating the evolving role of animal reservoirs as a source of human infection. VETERINARY DATA SYNTHESIS Comprehensive review of the veterinary literature. CONCLUSIONS In addition to inducing life-threatening illnesses, such as endocarditis, myocarditis, and meningoencephalitis and contributing to chronic debilitating disease, such as arthritis, osteomyelitis, and granulomatous inflammation in cats, dogs, and potentially other animal species; pets and wildlife species can serve as persistently infected reservoir hosts for the transmission of Bartonella spp. infection to veterinary professionals and others with direct animal contact.

Managing canine vector-borne diseases of zoonotic concern: part two

Despite recent achievements in scientific knowledge related to canine vector-borne diseases (CVBDs) of zoonotic concern, their management is still impaired by several neglected issues related to accurate diagnosis and effective treatment of both single and co-infections. A better understanding of the pathogenesis and the progression of clinical, hematological and biochemical abnormalities of CVBDs will be important in choosing appropriate diagnostic tests and in establishing the best strategies for treatment and control. Nonetheless, the diagnosis and control of zoonotic infections in clinically healthy dogs remain challenging. This review discusses the crucial aspects involved in the diagnosis, treatment, prevention and control of CVBDs of zoonotic concern.

Tick-borne infectious diseases of dogs

Tick-transmitted infections are an emerging problem in dogs. In addition to causing serious disease in traditional tropical and semi-tropical regions, they are now increasingly recognized as a cause of disease in dogs in temperate climates and urban environments. Furthermore, subclinically infected companion animals could provide a reservoir for human tick-transmitted infectious agents, such as Ehrlichia chaffeensis, Ehrlichia ewingll, the Ehrlichia phagocytophila group and Rickettsia conorii. Here, we discuss the emergence of new canine tick-transmitted diseases, which results from several factors, including the expansion of the tick range into urban and semi-urban areas worldwide, the movement of infected dogs into previously non-endemic areas, and the advent of novel molecular techniques for diagnosis and pathogen identification.

Ecological fitness and strategies of adaptation of Bartonella species to their hosts and vectors

Bartonella spp. are facultative intracellular bacteria that cause characteristic host-restricted hemotropic infections in mammals and are typically transmitted by blood-sucking arthropods. In the mammalian reservoir, these bacteria initially infect a yet unrecognized primary niche, which seeds organisms into the blood stream leading to the establishment of a long-lasting intra-erythrocytic bacteremia as the hall-mark of infection. Bacterial type IV secretion systems, which are supra-molecular transporters ancestrally related to bacterial conjugation systems, represent crucial pathogenicity factors that have contributed to a radial expansion of the Bartonella lineage in nature by facilitating adaptation to unique mammalian hosts. On the molecular level, the type IV secretion system VirB/VirD4 is known to translocate a cocktail of different effector proteins into host cells, which subvert multiple cellular functions to the benefit of the infecting pathogen. Furthermore, bacterial adhesins mediate a critical, early step in the pathogenesis of the bartonellae by binding to extracellular matrix components of host cells, which leads to firm bacterial adhesion to the cell surface as a prerequisite for the efficient translocation of type IV secretion effector proteins. The best-studied adhesins in bartonellae are the orthologous trimeric autotransporter adhesins, BadA in Bartonella henselae and the Vomp family in Bartonella quintana. Genetic diversity and strain variability also appear to enhance the ability of bartonellae to invade not only specific reservoir hosts, but also accidental hosts, as shown for B. henselae. Bartonellae have been identified in many different blood-sucking arthropods, in which they are typically found to cause extracellular infections of the mid-gut epithelium. Adaptation to specific vectors and reservoirs seems to be a common strategy of bartonellae for transmission and host diversity. However, knowledge regarding arthropod specificity/restriction, the mode of transmission, and the bacterial factors involved in arthropod infection and transmission is still limited.

Prevalence of infectious diseases in feral cats in Northern Florida.

Objectives of this study were to determine prevalence of infection in feral cats in Northern Florida with a select group of infectious organisms and to determine risk factors for infection. Blood samples or sera from 553 cats were tested with a panel of antibody, antigen or PCR assays. Male cats were at higher risk for FIV, Mycoplasma haemofelis, and M. haemominutum. Infection with either FeLV or FIV was associated with increased risk for coinfection with the other retrovirus, M. haemofelis, or M. haemominutum. Bartonella henselae had the highest prevalence and was the only organism that did not have any associated risk for coinfection with other organisms. Feral cats in this study had similar or lower prevalence rates of infections than those published for pet cats in the United States. Thus, feral cats assessed in this study appear to be of no greater risk to human beings or other cats than pet cats.

The increasing recognition of rickettsial pathogens in dogs and people

Dogs and people are exposed to and susceptible to infection by many of the same tick-borne bacterial pathogens in the order Rickettsiales, including Anaplasma phagocytophilum, Ehrlichia canis, E. chaffeensis, E. ewingii, Rickettsia rickettsii, R. conorii, and other spotted fever group rickettsiae. Recent findings include descriptions of novel Ehrlichia and Rickettsia species, recognition of the occurrence and clinical significance of co-infection, and increasing awareness of Rhipicephalus sanguineus-associated diseases. Newer molecular assays are available, although renewed efforts to encourage their use are needed. This review highlights the ecology and epidemiology of these diseases, and proposes avenues for future investigation.

Detection of medically important Ehrlichia by quantitative multicolor TaqMan real-time polymerase chain reaction of the dsb gene.

Ehrlichia species are the etiological agents of emerging and life-threatening tick-borne human zoonoses, in addition to causing serious and fatal infections in companion animals and livestock. We developed the first tricolor TaqMan real-time polymerase chain reaction assay capable of simultaneously detecting and discriminating medically important ehrlichiae in a single reaction. Analytical sensitivity of 50 copies per reaction was attained with templates from Ehrlichia chaffeensis, Ehrlichia ewingii, and Ehrlichia canis by amplifying the genus-specific disulfide bond formation protein gene (dsb). Ehrlichia genus-specific dsb primers amplified DNA from all known Ehrlichia species but not from other rickettsial organisms including Anaplasma platys, Anaplasma phagocytophilum, Rickettsia conorii, or Rickettsia typhi. High species specificity was attained as each species-specific TaqMan probe (E. chaffeensis, E. ewingii, and E. canis) identified homologous templates but did not cross-hybridize with heterologous Ehrlichia templates at concentrations as high as 10(8) copies. Identification of E. chaffeensis, E. ewingii, and E. canis from natural and experimental infections, previously confirmed by polymerase chain reaction and serological or microscopic evidence, demonstrated the comparable specificity and sensitivity of the dsb real-time assay. This assay provides a powerful tool for prospective medical diagnosis for human and canine ehrlichioses and for ecologic and epidemiological studies involving arthropod and mammalian hosts.