New world origins for haemoparasites infecting United Kingdom grey squirrels (Sciurus carolinensis), as revealed by phylogenetic analysis of bartonella infecting squirrel populations in England and the United States

Emerging rodent-associated Bartonella: a threat for human health?

Background

Species of the genus Bartonella are facultative intracellular alphaproteobacteria with zoonotic potential. Bartonella infections in humans range from mild with unspecific symptoms to life threatening, and can be transmitted via arthropod vectors or through direct contact with infected hosts, although the latter mode of transmission is rare. Among the small mammals that harbour Bartonella spp., rodents are the most speciose group and harbour the highest diversity of these parasites. Human–rodent interactions are not unlikely as many rodent species live in proximity to humans. However, a surprisingly low number of clinical cases of bartonellosis related to rodent-associated Bartonella spp. have thus far been recorded in humans.

Methods

The main purpose of this review is to determine explanatory factors for this unexpected finding, by taking a closer look at published clinical cases of bartonellosis connected with rodent-associated Bartonella species, some of which have been newly described in recent years. Thus, another focus of this review are these recently proposed species.

Conclusions

Worldwide, only 24 cases of bartonellosis caused by rodent-associated bartonellae have been reported in humans. Possible reasons for this low number of cases in comparison to the high prevalences of Bartonella in small mammal species are (i) a lack of awareness amongst physicians of Bartonella infections in humans in general, and especially those caused by rodent-associated bartonellae; and (ii) a frequent lack of the sophisticated equipment required for the confirmation of Bartonella infections in laboratories that undertake routine diagnostic testing. As regards recently described Bartonella spp., there are presently 14 rodent-associated Candidatus taxa. In contrast to species which have been taxonomically classified, there is no official process for the review of proposed Candidatus species and their names before they are published. This had led to the use of malformed names that are not based on the International Code of Nomenclature of Prokaryotes. Researchers are thus encouraged to propose Candidatus names to the International Committee on Systematics of Prokaryotes for approval before publishing them, and only to propose new species of Bartonella when the relevant datasets allow them to be clearly differentiated from known species and subspecies.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05162-5.

Hedgehogs and Squirrels as Hosts of Zoonotic Bartonella Species

Free-living animals frequently play a key role in the circulation of various zoonotic vector-borne pathogens. Bacteria of the genus Bartonella are transmitted by blood-feeding arthropods and infect a large range of mammals. Although only several species have been identified as causative agents of human disease, it has been proposed that any Bartonella species found in animals may be capable of infecting humans. Within a wide-ranging survey in various geographical regions of the Czech Republic, cadavers of accidentally killed synurbic mammalian species, namely Eurasian red squirrel (Sciurus vulgaris), European hedgehog (Erinaceus europaeus) and Northern white-breasted hedgehog (Erinaceus roumanicus), were sampled and tested for Bartonella presence using multiple PCR reaction approach targeting several DNA loci. We demonstrate that cadavers constitute an available and highly useful source of biological material for pathogen screening. High infection rates of Bartonella spp., ranging from 24% to 76%, were confirmed for all three tested mammalian species, and spleen, ear, lung and liver tissues were demonstrated as the most suitable for Bartonella DNA detection. The wide spectrum of Bartonella spp. that were identified includes three species with previously validated zoonotic potential, B. grahamii, B. melophagi and B. washoensis, accompanied by ‘Candidatus B. rudakovii’ and two putative novel species, Bartonella sp. ERIN and Bartonella sp. SCIER.

Prosthetic Valve Endocarditis with Bartonella washoensis in a Human European Patient and Its Detection in Red Squirrels (Sciurus vulgaris)

Members of the genus Bartonella are fastidious Gram-negative facultative intracellular bacteria that are typically transmitted by arthropod vectors. Several Bartonella spp. have been found to cause culture-negative endocarditis in humans. Here, we report the case of a 75-year-old German woman with prosthetic valve endocarditis due to Bartonella washoensis The infecting agent was characterized by sequencing of six housekeeping genes (16S rRNA, ftsZ, gltA, groEL, ribC, and rpoB), applying a multilocus sequence typing (MLST) approach. The 5,097 bp of the concatenated housekeeping gene sequence from the patient were 99.0% identical to a sequence from a B. washoensis strain isolated from a red squirrel (Sciurus vulgaris orientis) from China. A total of 39% (24/62) of red squirrel (S. vulgaris) samples from the Netherlands were positive for the B. washoensis gltA gene variant detected in the patient. This suggests that the red squirrel is the reservoir host for human infection in Europe.

Bartonella washoensis infection in red squirrels (Sciurus vulgaris) and their ectoparasites in Lithuania

This is the first study to investigate the presence of Bartonella infections in different internal organs of red squirrels and their ectoparasites in Lithuania. A total of 39 roadkill red squirrels were collected. Squirrels were infested with Ixodes ricinus ticks (191) and Ceratophyllus sciurorum fleas (36). The presence of Bartonella spp. was screened using 16 S-23 S rRNA internal transcribed spacer region and bacteria were detected in 38.5 % (15/39) samples of squirrels, 1.0 % (2/191) samples of ticks and 55.5 % (20/36) samples of fleas. The infection rate of different internal organs of squirrels varied from 11.1%-47.4%. The 16 S-23 S rRNA ITS region sequences showed that Bartonella washoensis were detected in squirrels and their ectoparasites. The results from this study support the hypothesis that S. vulgaris and their fleas, C.sciurorum, serve as a major reservoir and a vector, respectively, of zoonotic B. washoensis in Lithuania.

Neglected vector-borne zoonoses in Europe: Into the wild

Wild vertebrates are involved in the transmission cycles of numerous pathogens. Additionally, they can affect the abundance of arthropod vectors. Urbanization, landscape and climate changes, and the adaptation of vectors and wildlife to human habitats represent complex and evolving scenarios, which affect the interface of vector, wildlife and human populations, frequently with a consequent increase in zoonotic risk. While considerable attention has focused on these interrelations with regard to certain major vector-borne pathogens such as Borrelia burgdorferi s.l. and tick-borne encephalitis virus, information regarding many other zoonotic pathogens is more dispersed. In this review, we discuss the possible role of wildlife in the maintenance and spread of some of these neglected zoonoses in Europe. We present case studies on the role of rodents in the cycles of Bartonella spp., of wild ungulates in the cycle of Babesia spp., and of various wildlife species in the life cycle of Leishmania infantum, Anaplasma phagocytophilum and Rickettsia spp. These examples highlight the usefulness of surveillance strategies focused on neglected zoonotic agents in wildlife as a source of valuable information for health professionals, nature managers and (local) decision-makers. These benefits could be further enhanced by increased collaboration between researchers and stakeholders across Europe and a more harmonised and coordinated approach for data collection.

Distribution and Diversity of Bartonella washoensis Strains in Ground Squirrels from California and Their Potential Link to Human Cases

We investigated the prevalence of Bartonella washoensis in California ground squirrels (Otospermophilus beecheyi) and their fleas from parks and campgrounds located in seven counties of California. Ninety-seven of 140 (69.3%) ground squirrels were culture positive and the infection prevalence by location ranged from 25% to 100%. In fleas, 60 of 194 (30.9%) Oropsylla montana were found to harbor Bartonella spp. when screened using citrate synthase (gltA) specific primers, whereas Bartonella DNA was not found in two other flea species, Hoplopsyllus anomalus (n = 86) and Echidnophaga gallinacea (n = 6). The prevalence of B. washoensis in O. montana by location ranged from 0% to 58.8%. A majority of the gltA sequences (92.0%) recovered from ground squirrels and fleas were closely related (similarity 99.4-100%) to one of two previously described strains isolated from human patients, B. washoensis NVH1 (myocarditis case in Nevada) and B. washoensis 08S-0475 (meningitis case in California). The results from this study support the supposition that O. beecheyi and the flea, O. montana, serve as a vertebrate reservoir and a vector, respectively, of zoonotic B. washoensis in California.

Bartonella infection in rodents and their flea ectoparasites: an overview

Epidemiological studies worldwide have reported a high prevalence and a great diversity of Bartonella species, both in rodents and their flea parasites. The interaction among Bartonella, wild rodents, and fleas reflects a high degree of adaptation among these organisms. Vertical and horizontal efficient Bartonella transmission pathways within flea communities and from fleas to rodents have been documented in competence studies, suggesting that fleas are key players in the transmission of Bartonella to rodents. Exploration of the ecological traits of rodents and their fleas may shed light on the mechanisms used by bartonellae to become established in these organisms. The present review explores the interrelations within the Bartonella-rodent-flea system. The role of the latter two components is emphasized.

Poxviruses and the passive quest for novel hosts

Poxviruses are famous, or infamous, as agents of disease introduced into novel host species and between populations of the same species. This discussion concerns selected examples of poxviruses associated with vertebrate infections, i.e., the Chordopoxvirus subfamily of the family Poxviridae. Brief note is made of examples of members of the genera Leporipoxvirus and Parapoxvirus-like agents that have been recognized to have significant trans-host species impact. The remaining bulk of the discussion involves examples of members of the genus Orthopoxvirus, which are known to be (have been) involved with human disease, and their zoonotic origins.

Diversity of bartonellae associated with small mammals inhabiting Free State province, South Africa

The prevalence and diversity of bartonellae infecting the blood of 10 small mammal species inhabiting nine Nature Reserves of the Free State province, South Africa, was assessed using phenotypic, genotypic and phylogenetic methods. Of 86 small mammals sampled, 38 animals belonging to five different species yielded putative bartonellae. Thirty-two isolates were confirmed as bartonellae and were characterized by comparison of partial citrate synthase gene (gltA) sequences. Phylogenetic reconstructions derived from alignment of these sequences with those available for other bartonellae indicated that the South African rodent-associated isolates formed two distinct clades within the radius of the genus Bartonella. One of these clades also included recognized Bartonella species associated with rodents native to Eurasia but not to the New World, whereas the second clade contained exclusively isolates associated with South African rodents. Comparison of gltA sequences delineated the isolates into a number of ecologically distinct populations and provided an indication that a combination of phylogenetics and the identification of sequence clusters in housekeeping protein-encoding genes could be developed as a key criterion in the classification of bartonellae. This study is the first to investigate wildlife-associated bartonellae in Africa, adding support to their ubiquity and broad diversity and to the paradigm that the phylogenetic positions of the Bartonella species encountered today have been influenced by the geographical distribution of their hosts.

ECTOPARASITES OF GRAY SQUIRRELS IN TWO DIFFERENT HABITATS AND SCREENING OF SELECTED ECTOPARASITES FOR BARTONELLAE

Gray squirrels, Sciurus carolinensis, were livetrapped in 2 different habitat types, woodland (67 squirrels) and parkland (53 squirrels), in southeastern Georgia. Ectoparasites were recovered from anesthetized squirrels and compared between hosts from the 2 habitats. Because of the absence of low vegetation in parkland habitats, it was hypothesized that the ectoparasite fauna, especially ticks and chiggers, would be more diverse on woodland squirrels. The results were generally in agreement with this hypothesis. Seventeen species of ectoparasites were recovered from woodland squirrels, compared with 6 species from parkland squirrels. Five species of ticks and 3 species of chiggers parasitized the woodland squirrels compared with no ticks or chiggers on the parkland squirrels. Significantly higher infestation prevalences were recorded on woodland compared with parkland squirrels for the flea Orchopeas howardi, the tick Amblyomma americanum, and the mesostigmatid mite Androlaelaps fahrenholzi. The mean intensity for O. howardi also was significantly higher on woodland than on parkland squirrels. Because a new strain of Bartonella sp. was isolated recently from S. carolinensis in Georgia, selected ectoparasites from this study were screened for bartonellae by polymerase chain reaction (PCR). Some of the fleas and lice, but none of the mites tested, were PCR positive, suggesting that fleas, or lice, or both, might be vectors of bartonellae between squirrels. Six distinct strains of Bartonella sp. were detected, 2 in fleas and 4 in lice.

Isolation of Bartonella washoensis from a dog with mitral valve endocarditis

We report the first documented case of Bartonella washoensis bacteremia in a dog with mitral valve endocarditis. B. washoensis was isolated in 1995 from a human patient with cardiac disease. The main reservoir species appears to be ground squirrels (Spermophilus beecheyi) in the western United States. Based on echocardiographic findings, a diagnosis of infective vegetative valvular mitral endocarditis was made in a spayed 12-year-old female Doberman pinscher. A year prior to presentation, the referring veterinarian had detected a heart murmur, which led to progressive dyspnea and a diagnosis of congestive heart failure the week before examination. One month after initial presentation, symptoms worsened. An emergency therapy for congestive heart failure was unsuccessfully implemented, and necropsy evaluation of the dog was not permitted. Indirect immunofluorescence tests showed that the dog was strongly seropositive (titer of 1:4,096) for several Bartonella antigens (B. vinsonii subsp. berkhoffii, B. clarridgeiae, and B. henselae), highly suggestive of Bartonella endocarditis. Standard aerobic and aerobic-anaerobic cultures were negative. However, a specific blood culture for Bartonella isolation grew a fastidious, gram-negative organism 7 days after being plated. Phenotypic and genotypic characterizations of the isolate, including partial sequencing of the citrate synthase (gltA), groEL, and 16S rRNA genes, indicated that this organism was identical to B. washoensis. The dog was seronegative for all tick-borne pathogens tested (Anaplasma phagocytophilum, Ehrlichia canis, and Rickettsia rickettsii), but the sample was highly positive for B. washoensis (titer of 1:8,192) and, according to indirect immunofluorescent-antibody assay, weakly positive for phase II Coxiella burnetii infection.

Identification of Bartonella strains isolated from wild and domestic ruminants by a single-step PCR analysis of the 16S–23S intergenic spacer region

Of the 20 species or subspecies of Bartonella currently known, 7 cause various diseases in humans with many being zoonotic. However, some Bartonella species appear only to cause asymptomatic bacteraemia in their hosts. In ruminants, three Bartonella species (B. bovis, B. capreoli and B. schoenbuchensis) have recently been described. However, limited or no information has yet been published concerning their mode of transmission and their possible pathogenicity for domestic cattle. The phylogenetic relationship of these species with other bacteria of the Bartonella genus has only been recently investigated. It is therefore necessary to develop appropriate tools that will easily allow identification of these ruminant strains for epidemiological and clinical studies. A single-step PCR assay, based on the amplification of a fragment of the 16S-23S rRNA intergenic spacer (ITS), was evaluated for identification of Bartonella isolated from domestic cattle and from free-ranging or captive cervids. For each Bartonella species tested, the PCR assay led to a product that was unique either for its length or its sequence. All ruminant isolates tested could be easily differentiated among themselves and from the other Bartonella species. Furthermore, sequence analysis of the PCR products revealed a close relationship between all ruminant Bartonella strains. Therefore, ITS PCR testing appears to be a convenient tool for a quick diagnosis of ruminant Bartonella species.