Detection and genetic characterization of diverse Bartonella genotypes in the small mammals of Singapore

Molecular Detection of Bartonella Species in Rodents Residing in Urban and Suburban Areas of Central Thailand

Bartonella spp. are Gram-negative zoonotic bacteria transmitted to humans via various blood-sucking arthropods. Rodents have been identified as reservoir hosts of several zoonotic pathogens, including Bartonella spp. In Thailand, studies of Bartonella spp. in rodents from urban areas are limited; thus, a study in this area is necessary. The objectives of this study were to detect Bartonella spp. in rodents in Thailand and to compare the species’ distribution across different areas. In total, 70 blood samples from rodents in urban and suburban areas were tested for Bartonella spp. using a conventional polymerase chain reaction that targeted the citrate synthase (gltA) gene. All Bartonella-positive sequences were analyzed using polymorphism in order to build a phylogenetic tree. Approximately 38% of the rodents studied contained Bartonella DNA. Both Rattus exulans (Pacific rat) and R. tanezumi (Asian house rat) contained Bartonella spp. Four species of Bartonella were detected in blood samples: B. tribocorum, B. phoceensis, B. grahamii, and B. rattimassiliensis. In addition, eight Pacific rats contained the B. kosoyi–B. tribocorum complex. Bartonella phoceensis and B. tribocorum–B. kosoyi complexes were found in a specific habitat (p < 0.05). Interestingly, only seven haplotypes were identified in the sequences analyzed, and only haplotype A was found in both rodent species. Finally, a monitoring program for zoonotic Bartonella infection, especially the B. kosoyi–B. tribocorum complex, B. phoceensis, B. grahamii, and B. rattimassiliensis should be established, especially in high-risk areas.

High prevalence and diversity of Bartonella in small mammals from the biodiverse Western Ghats

Bartonella species are recognized globally as emerging zoonotic pathogens. Small mammals such as rodents and shrews are implicated as major natural reservoirs for these microbial agents. Nevertheless, in several tropical countries, like India, the diversity of Bartonella in small mammals remain unexplored and limited information exists on the natural transmission cycles (reservoirs and vectors) of these bacteria. Using a multi-locus sequencing approach, we investigated the prevalence, haplotype diversity, and phylogenetic affinities of Bartonella in small mammals and their associated mites in a mixed-use landscape in the biodiverse Western Ghats in southern India. We sampled 141 individual small mammals belonging to eight species. Bartonella was detected in five of the eight species, including three previously unknown hosts. We observed high interspecies variability of Bartonella prevalence in the host community. However, the overall prevalence (52.5%) and haplotype diversity (0.9) was high for the individuals tested. Of the seven lineages of Bartonella identified in our samples, five lineages were phylogenetically related to putative zoonotic species–B. tribocorum, B. queenslandensis, and B. elizabethae. Haplotypes identified from mites were identical to those identified from their host species. This indicates that these Bartonella species may be zoonotic, but further work is necessary to confirm whether these are pathogenic and pose a threat to humans. Taken together, these results emphasize the presence of hitherto unexplored diversity of Bartonella in wild and synanthropic small mammals in mixed-use landscapes. The study also highlights the necessity to assess the risk of spillover to humans and other incidental hosts.

Zoonotic bacterial infections cause both economic and health burdens to humans, especially in developing countries. Bartonella is a diverse group with several species that are infectious to humans. There is limited knowledge of Bartonella diversity and subsequent risk for spillover in several tropical countries, including India. This study, set in a biodiversity hotspot with high human density, reveals a high prevalence and diversity of Bartonella in the most common, and synanthropic small mammals. Several lineages identified are phylogenetically related to zoonotic species known to cause infections in humans. We suggest that there is unexplored diversity of Bartonella in small mammals that reside in human-modified landscapes in India, demonstrating an urgent need for further investigation. By identifying the natural reservoirs of pathogens, their ecology, and their relationship and proximity to humans, we will be able to proactively survey for these under-detected bacterial infections and minimize the burden.

Genetic diversity and expanded host range of astroviruses detected in small mammals in Singapore

Astroviruses are a genetically diverse group of viruses that infect a wide range of hosts, including small mammals. Small mammals were trapped at 19 sites across Singapore from November 2011 to May 2014. Pooled oropharyngeal and rectal swabs (n = 518) and large intestine tissue (n = 107) were screened using a PCR to detect the presence of Astrovirus RNA-dependent RNA polymerase (RdRp) gene. Astroviruses were detected in 93 of 625 (14.9%) of samples tested, with eight of 11 species of rats, shrews, and squirrels testing positive. This is the first detection of astroviruses in seven species (Callosciurus notatus, Mus castaneus, Rattus tanezumi, Rattus tiomanicus, Sundamys annandalei, Suncus murinus and Tupaia glis). Phylogenetic analysis of 10 RdRp gene sequences revealed that astroviruses from Singapore small mammals fall in three distinct clades, one that is specific to the common treeshrew (Tupaia glis), and two comprised of multiple species. One of these includes viruses from the cave nectar bat (Eonycteris spelaea), two rodent species, and a squirrel, suggesting that virus spillover from bats to small mammals may have occurred. Our results show an increased host range for astroviruses and highlight their potential for intra- and inter-species transmission.

Habitat impacts the abundance and network structure within tick (Acari: Ixodidae) communities on tropical small mammals

Ticks of small mammals pose a significant risk to public health but these hazards are poorly understood in the tropics due to the paucity of information on the disease ecology of ticks in these regions. Mapping and quantifying the diversity of small mammal/tick networks and the effects of habitat on these medically important systems is key to disease prevention. Singapore represents a microcosm of much of tropical Asia as it has a diverse, though poorly studied, community of ticks and small mammals. Singapore also has a range of terrestrial habitats exhibiting a gradient of degradation. Small mammals and their ticks were sampled across the island in four main habitat types (old secondary forest, young secondary forest, scrubland, urban) across 4.5 years. Four tick species were collected (Amblyomma helvolum, Dermacentor auratus, Haemaphysalis semermis, Ixodes granulatus) from 10 small mammal species. Habitat was found to have a significant effect on both the abundance and structure of tick communities on small mammals. Old secondary forest communities had the highest tick abundance, comparatively high connectance, niche overlap (among ticks), linkage density, and were the preferred habitat of the zoonotic tick I. granulatus. Therefore, future disease spillover is likely to emerge from small mammal-tick communities in old secondary forests.

Characterization of Bartonella taylorii Strains in Small Mammals of the Turkish Thrace

Rodents play role as a reservoir for some Bartonella species which cause different clinical manifestations in humans. Bartonella spp. existence in rodents of Turkish Thrace has been detected for the first time, and the risky habitat types were evaluated for the infection. Ninety individuals belonging to three small rodent species were screened by PCR, and the overall prevalence of Bartonella infection was 22.2%. The strains were characterized molecularly based on the phylogenetic analyses of two housekeeping genes, rpoB and gltA. They clustered with B. taylorii. The significant effects of habitat types and rodent species on Bartonella infections were observed. It was detected that B. taylorii prevalence was the highest in the swamp forest habitat and A. flavicollis species. The present study demonstrates that A. flavicollis is the reservoir of B. taylorii in the European part of Turkey.

When the Sum of the Parts Tells You More Than the Whole: The Advantage of Using Metagenomics to Characterize Bartonella spp. Infections in Norway Rats (Rattus norvegicus) and Their Fleas

Urban Norway rats (Rattus norvegicus) are a reservoir for Bartonella spp. - a genus of zoonotic bacteria transmitted by hematophagous vectors, particularly fleas. Rats and fleas may be infected with more than one Bartonella species; however, mixed infections may be difficult to detect using culture and/or mono-locus PCR. We set out to characterize Bartonella spp. using gltA PCR and Sanger sequencing on blood (n = 480) and Nosopsyllus fasciatus flea pools (n = 200) obtained from a population of urban Norways rats from Vancouver, Canada. However, when contamination of a subset of flea pools necessitated the use of a second target (ssrA) and the results of gltA and ssrA were discordant, a metagenomic approach was used to better characterize the Bartonella spp. present in these samples and our objective transitioned to comparing data obtained via metagenomics to those from PCR/sequencing. Among the Bartonella spp.-positive rats (n = 95), 52 (55.3%), and 41 (43.6%) had Sanger sequences consistent with Bartonella tribocorum and Bartonella vinsonii, respectively. One rat had a mixed infection. All sequences from Bartonella spp.-positive flea pools (n = 85), were consistent with B. tribocorum, and re-analysis of 34 bloods of varying Bartonella spp. infection status (based gltA PCR and sequencing) using ssrA PCR showed that the assay was capable of identifying B. tribocorum but not B. vinsonii. Metagenomics analysis of a subset of PCR-positive blood samples (n = 70) and flea pools (n = 24) revealed that both B. tribocorum and B. vinsonii were circulating widely in the study population with 31/70 (44.3%) rats and 5/24 (2.1%) flea pools infected with both species. B. vinsonii, however, made up a smaller relative proportion of the reads for samples with mixed infections, which may be why it was generally not detected by genus-specific PCR and Sanger sequencing. Further analysis of 16S−23S ITS sequences amplified from a subset of samples identified the B. vinsonii strain as B. vinsonii subsp. berkhoffii type II. This demonstrates the value of a metagenomic approach for better characterizing the ecology and health risks associated with this bacterium, particularly given that the less dominant species, B. vinsonii is associated with greater pathogenicity in people.

Emergence of the zoonotic tick Dermacentor (Indocentor) auratus Supino, 1897 (Acari: Ixodidae) in Singapore

Though ticks pose a significant public health risk, until recently, little research had focused on the diversity of ticks and tick-borne diseases in Singapore. To date, only fourteen tick species in five genera have been recorded there. For the first time, Dermacentor auratus is recorded from Singapore from a range of hosts, including humans. DNA sequences are provided at 2 loci, for D. auratus, the cytochrome c oxidase I (COI) for DNA barcoding and the 16S large subunit ribosomal RNA (16S lsu rRNA). The health risk posed by D. auratus in Singapore is discussed.

Ticks and tick-borne pathogens in animals and humans in the island nations of Southeast Asia: A review

Ticks are blood-feeding ectoparasites and major vectors of pathogens that cause infectious diseases in humans and animals worldwide including mammals, birds and reptiles. Despite the growing scientific effort in the 20th century, there is still limited information on ticks and tick-borne pathogens in Southeast Asia, especially concerning medical, veterinary, socioeconomic and agricultural aspects in the island nations. This review provides an overview of the current state of knowledge of ticks and their pathogens in the island nations of Southeast Asia and peninsular Malaysia. We aim to stimulate further research studies on ticks and tick-borne pathogens of human and veterinary importance in this geographical region.

Emerging zoonotic diseases originating in mammals: a systematic review of effects of anthropogenic land-use change

Zoonotic pathogens and parasites that are transmitted from vertebrates to humans are a major public health risk with high associated global economic costs. The spread of these pathogens and risk of transmission accelerate with recent anthropogenic land-use changes (LUC) such as deforestation, urbanisation, and agricultural intensification, factors that are expected to increase in the future due to human population expansion and increasing demand for resources.We systematically review the literature on anthropogenic LUC and zoonotic diseases, highlighting the most prominent mammalian reservoirs and pathogens, and identifying avenues for future research.The majority of studies were global reviews that did not focus on specific taxa. South America and Asia were the most-studied regions, while the most-studied LUC was urbanisation. Livestock were studied more within the context of agricultural intensification, carnivores with urbanisation and helminths, bats with deforestation and viruses, and primates with habitat fragmentation and protozoa.Research into specific animal reservoirs has improved our understanding of how the spread of zoonotic diseases is affected by LUC. The behaviour of hosts can be altered when their habitats are changed, impacting the pathogens they carry and the probability of disease spreading to humans. Understanding this has enabled the identification of factors that alter the risk of emergence (such as virulence, pathogen diversity, and ease of transmission). Yet, many pathogens and impacts of LUC other than urbanisation have been understudied.Predicting how zoonotic diseases emerge and spread in response to anthropogenic LUC requires more empirical and data synthesis studies that link host ecology and responses with pathogen ecology and disease spread. The link between anthropogenic impacts on the natural environment and the recent COVID-19 pandemic highlights the urgent need to understand how anthropogenic LUC affects the risk of spillover to humans and spread of zoonotic diseases originating in mammals.

Bartonella diversity and zoonotic potential in indigenous Tete Veld rats (Aethomys ineptus) from South Africa

Bartonellosis is a vector-borne disease that is often misdiagnosed due to a broad range of clinical symptoms, compounded by a lack of awareness regarding the prevalence, diversity and public health impacts of regional strains. Despite recent PCR-based confirmation of Bartonella in 9.7% of non-malarial, acute febrile patients in South Africa, data regarding reservoirs of infection are limited. As the majority of Bartonella species described to date are associated with rodent species globally, including zoonotic species such as B. elizabethae, and as rodent biodiversity is high in southern Africa, we evaluated Bartonella in the Tete Veld rat (Aethomys ineptus), a highly adaptable murid rodent that thrives in both natural and commensal settings. These rodents are infested with a broad range of ectoparasite species, and often occur in sympatry with Micaelamys namaquensis, an indigenous rodent previously shown to host B. elizabethae. DNA extracts from heart samples of 75 A. ineptus trapped over an eight-month period, from the Roodeplaat Nature Reserve (RNR), were evaluated using a multi-locus sequence analysis (MLSA) approach. Nucleotide sequencing and phylogenetic analyses of individual (gltA, ribC, rpoB and nuoG) and concatenated gene datasets confirmed the presence of three discrete Bartonella lineages (I-III). Lineages I and II, are genetically distinct from all currently recognised Bartonella species but cluster with strains present in other indigenous rodents from South and East Africa, whereas lineage III contained B. elizabethae, a zoonotic species associated with Rattus species globally. Records confirming R. tanezumi presence in this nature reserve, which is situated in close proximity to Pretoria, the administrative capital of South Africa, suggests the likelihood of spill-over from invasive to indigenous species. These results together with the high levels of infection (86.7%) and co-infection (33.8%), indicate that A. ineptus is a natural reservoir for multiple Bartonella species in South Africa, including one with zoonotic potential.

Ticks in the Lion City: a preliminary review of the tick fauna of Singapore

To this day, the tick fauna of Singapore remains poorly known. Although several studies of select species have been undertaken within Singapore, much of the information regarding Singaporean ticks is fragmentary. To facilitate future study of this group, the scattered information on Singaporean ticks is synthesised in the present work and includes a preliminary checklist of species reported to occur in Singapore, which comprised 14 species in 5 genera, with confirmed records of Argas pusillus, Amblyomma nitidum, Amblyomma varanense, Haemaphysalis doenitzi, Haemaphysalis nadchatrami, Haemaphysalis semermis, Ixodes granulatus, Rhipicephalus microplus, and Rhipicephalus sanguineus, and unconfirmed reports of Amblyomma cordiferum, Amblyomma geoemydae, Amblyomma helvolum, Amblyomma javanense and Amblyomma testudinarium.