Bartonella spp. infections in rodents of Cambodia, Lao PDR, and Thailand: identifying risky habitats

Bartonella Species in Cambodia, Ghana, Laos, and Peru: Results from Vector and Serosurveys

Background: Bartonella species are fastidious gram-negative vector-borne bacteria with a wide range of mammalian reservoirs. While it is understood that some species of Bartonella are human pathogens, the extent of human exposure to Bartonella species (both pathogenic and nonpathogenic) is yet to be fully understood. Materials and Methods: To this end, residual sera from participants enrolled in undifferentiated fever studies in Cambodia, Ghana, Laos, and Peru were screened for the presence of IgG antibodies against Bartonella quintana and Bartonella henselae, using the FOCUS diagnostics Dual Spot- Bartonella IgG Immunofluorescence assay. Forty-eight patients with suspected or confirmed Bartonella bacilliformis exposure or infection in Peru were screened to assess cross-reactivity of the FOCUS assay for IgG against other Bartonella species. Results: Ten of 13 patients with confirmed B. bacilliformis infection were Bartonella-specific IgG positive, and overall, 36/48 of the samples were positive. In addition, 79/206, 44/200, 101/180, and 57/100 of the samples from Peru, Laos, Cambodia, and Ghana, respectively, were Bartonella-specific IgG positive. Furthermore, ectoparasite pools from Cambodia, Laos, and Peru were tested using quantitative real-time PCR (qPCR) for the presence of Bartonella DNA. Of the sand fly pools collected in Peru, 0/196 were qPCR positive; 15/140 flea pools collected in Cambodia were qPCR positive; while 0/105 ticks, 0/22 fleas, and 0/3 louse pools collected in Laos tested positive for Bartonella DNA. Conclusion: Evidence of Bartonella in fleas from Cambodia supports the possibility that humans are exposed to Bartonella through this traditional vector. However, Bartonella species were not found in fleas, ticks, or lice from Laos, or sand flies from Peru. This could account for the lower positive serology among the population in Laos and the strictly localized nature of B. bacilliformis infections in Peru. Human exposure to the Bartonella species and Bartonella as a human pathogen warrants further investigation.

Phlebotomine sand flies (Diptera: Psychodidae) and sand fly-borne pathogens in the Greater Mekong Subregion: a systematic review

Phlebotomine sand flies are proven or suspected vectors of several pathogens of importance, including leishmaniasis, bartonellosis and sand fly fevers. Although sand flies have a worldwide distribution, there has been limited research published on sand flies and sand fly-borne pathogens throughout the Greater Mekong Sub-region (GMS). This review followed the PRISMA guidelines to determine the biodiversity and presence of phlebotomine sand flies and their associated pathogens in the GMS, specifically Cambodia, Thailand, the Lao People's Democratic Republic (Laos), Malaysia and Vietnam. A total of 1472 records were identified by searching electronic databases, scanning reference lists of articles and consulting experts in the field. After screening of title and abstracts, 178 records remained and were further screened for original data (n = 34), not having regional data (n = 14), duplication of data (n = 4), records not available (n = 4) and no language translation available (n = 2). A total of 120 studies were then included for full review, with 41 studies on sand fly-related disease in humans, 33 studies on sand fly-related disease in animals and 54 entomological studies focused on sand flies (5 papers contained data on > 1 category), with a majority of the overall data from Thailand. There were relatively few studies on each country, with the exception of Thailand, and the studies applied different methods to investigate sand flies and sand fly-borne diseases, impacting the ability to conduct meaningful meta-analysis. The findings suggest that leishmaniasis in humans and the presence of sand fly vectors have been reported across several GMS countries over the past 100 years, with local transmission in humans confirmed in Thailand and Vietnam. Additionally, local Mundinia species are likely transmitted by biting midges. Findings from this study provide a framework for future investigations to determine the geographic distribution and risk profiles of leishmaniasis and other associated sand fly-borne disease throughout the GMS. It is recommended that researchers expand surveillance efforts across the GMS, with an emphasis placed on entomological surveys, syndromic and asymptomatic monitoring in both humans and animals and molecular characterization of sand flies and sand fly-borne pathogens, particularly in the understudied countries of Cambodia, Vietnam and Laos.

Epidemiological characteristics and genetic diversity of Bartonella species in rodents from southeastern China

Rodents are the primary hosts of Bartonella species and carry more than 22 Bartonella species. However, the information on epidemiological characteristics and genetic diversity of Bartonella species in rodents in southeastern China is limited. From 2015 to 2020, 1,137 rodents were captured. Bartonella-positive DNA was detected in 14.9% (169/1,137) of rodents by PCR for both the ssrA and gltA genes. A highest Bartonella prevalence was detected in Apodemus agrarius (33.5%) and lowest in B. indica (1.8%). The probability of Bartonella infection in summer (20.1%) was higher than in spring (14.6%; p = .011, OR = 1.756). Sequencing and phylogenetic analysis revealed that nine known Bartonella species were identified in rodents, including B. tribocorum, B. grahamii, B. rattimassiliensis, B. queenslandensis, B. elizabethae, B. phoceensis, B. coopersplainsensis, B. japonica and B. rochalimae. In our study, Bartonella species exhibited a strong association with their hosts. Zoonotic B. tribocorum, B. grahamii, B. elizabethae and B. rochalimae were found in synanthropic rodent species in southeastern China, which pose a potential threat to the public health. To prevent the spread of zoonotic Bartonella species to humans, preventive and control measures should be implemented, and more research is needed to confirm the pathogen's association with human disease.

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.

Detection of zoonotic Bartonella species in ticks and fleas parasitizing free-ranging cats and dogs residing in temples of Bangkok, Thailand

Bartonellosis is a vector-borne disease caused by intraerythrocytic bacteria known as Bartonella spp. The potential vectors that transmit Bartonella spp. are fleas, ticks, sand flies, and lice. Several Bartonella spp. cause diseases in humans; however, there is few molecular evidence of Bartonella spp. in vectors in Thailand. The objectives of this study were to investigate Bartonella spp. and to evaluate the spatial distribution of Bartonella spp. prevalence in the ectoparasites parasitizing free-ranging cats and dogs in temple clusters of Bangkok, Thailand. In total, 343 ectoparasites were studied to extract their genomic DNA. Species of all specimens were identified using an identification key and conventional polymerase chain reaction (cPCR) was applied to confirm flea and tick species. Extracted DNA samples were processed using primers that targeted the gltA, rpoB, ftsZ, and ribC genes of Bartonella spp. Then, PCR-positive amplicons were sequenced and a phylogenetic tree was constructed. Recorded data were statistically analyzed using descriptive statistics, the chi-square test, Fisher's exact test, and the odds ratio. Area data were analyzed and a prevalence distribution map was plotted. The major parasitizing ticks and fleas in this study were Rhipicephalus sanguineus and Ctenocephalides felis, respectively. Overall, the prevalence of Bartonella spp. in ectoparasites was 7.00%. The gltA amplicons revealed the presence of B. henselae (4.78%) and B. clarridgeiae (4.78%) in C. felis, and B. koehlerae (1.25%) and B. phoceensis (1.25%) in R. sanguineus. Bartonella DNA was encountered in 16/39 (41.03%) districts and 28.57% of the temple clusters. Bang Khun Thian district had the highest positive proportion and Bang Bon district showed co-evidence of different Bartonella species. In addition, the intervening zones were a risk factor of Bartonella (p < 0.05), and the distribution map showed a scattered pattern of Bartonella-positive clusters. Finally, fleas showed to be important vector reservoirs for Bartonella spp., especially zoonotic species, however, experimental studies are needed to prove the Bartonella transmission in ticks.

First Detection of Bartonella spp. in Small Mammals from Rice Storage and Processing Facilities in Myanmar and Sri Lanka

(1) Background: Bartonella spp. are zoonotic bacteria with small mammals as main reservoirs. Bartonella spp. prevalence in small mammals from Myanmar and Sri Lanka are yet unknown. (2) Methods: Small mammals were snap trapped in Sri Lanka and Myanmar in urban surroundings. Spleens-derived DNA was screened for Bartonella spp. using conventional PCR based on three target genes. Positive samples were sequenced. (3) Results: 994 small mammals were collected comprising 6 species: Bandicota bengalensis, Bandicota indica, Rattus exulans, Rattus rattus, Mus booduga, and Suncus murinus. In Myanmar, the Bartonella prevalence in Bandicoot rats (68.47%) was higher than in Rattus rattus (41.67%), Rattus exulans (21.33%), and Suncus murinus (3.64%). Furthermore the prevalence in Myanmar (34%, n = 495) was twice as high as in Sri Lanka (16%, n = 499). In Sri Lanka, Bartonella spp. occurred almost exclusively in R. rattus. In Myanmar, Bartonella kosoyi was mainly detected (56%), followed by Bartonella sp. KM2529 (15%), Bartonella sp. SE-Bart D (12%) and Bartonella henselae (1%). In Sri Lanka, B. phoceensis (60%) and Bartonella sp. KM2581 (33%) were predominant. (4) Conclusions: Bartonella spp. were detected in all investigated small mammal species from Myanmar and Sri Lanka for the first time. Bartonella kosoyi and B. henselae are zoonotic. As these small mammals originated from urban settlements, human bartonellosis seems likely to occur.

High Prevalence of Rodent-Borne Bartonella spp. in Urbanizing Environments in Sarawak, Malaysian Borneo

Rodents are the most prominent animal host of Bartonella spp., which are associated with an increasing number of human diseases worldwide. Many rodent species thrive in urban environments and live in close contact with people, which can lead to an increased human risk of infection from rodent-borne pathogens. In this study, we explored the prevalence and distribution of Bartonella spp. in rodents in urban, developing, and rural environments surrounding a growing city in Sarawak, Malaysian Borneo. We found that although Bartonella spp. infection was pervasive in most rodent species sampled, prevalence was highest in urban areas and infection was most commonly detected in the predominant indigenous rodent species sampled (Sundamys muelleri). Within the urban environment, parks and remnant green patches were significantly associated with the presence of both S. muelleri and Bartonella spp., indicating higher localized risk of infection for people using these environments for farming, foraging, or recreation.

Changing landscapes of Southeast Asia and rodent-borne diseases: decreased diversity but increased transmission risks

The reduction in biodiversity from land use change due to urbanization and agricultural intensification appears to be linked to major epidemiological changes in many human diseases. Increasing disease risks and the emergence of novel pathogens result from increased contact among wildlife, domesticated animals, and humans. We investigated the relationship between human alteration of the environment and the occurrence of generalist and synanthropic rodent species in relation to the diversity and prevalence of rodent-borne pathogens in Southeast Asia, a hotspot of threatened and endangered species, and a foci of emerging infectious diseases. We used data from an extensive pathogen survey of rodents from seven sites in mainland Southeast Asia in conjunction with past and present land cover analyses. At low spatial resolutions, we found that rodent-borne pathogen richness is negatively associated with increasing urbanization, characterized by increased habitat fragmentation, agriculture cover and deforestation. However, at a finer spatial resolution, we found that some major pathogens are favored by environmental characteristics associated with human alteration including irrigation, habitat fragmentation, and increased agricultural land cover. In addition, synanthropic rodents, many of which are important pathogen reservoirs, were associated with fragmented and human-dominated landscapes, which may ultimately enhance the opportunities for zoonotic transmission and human infection by some pathogens.

Beyond abundance: How microenvironmental features and weather influence Bartonella tribocorum infection in wild Norway rats (Rattus norvegicus)

Norway rats (Rattus norvegicus) inhabit cities worldwide and carry a number of zoonotic pathogens. Although many studies have investigated rat-level risk factors, there is limited research on the effects of weather and environment on zoonotic pathogen transmission ecology in rats. The objective of this study was to use a disease ecology approach to understand how abiotic (weather and urban microenvironmental features) and biotic (relative rat population abundance) factors affect Bartonella tribocorum prevalence in urban Norway rats from Vancouver, British Columbia, Canada. This potentially zoonotic pathogen is primarily transmitted by fleas and is common among rodents, including rats, around the world. During a systematic rat trap and removal study, city blocks were evaluated for 48 environmental variables related to waste, land/alley use and property condition, and rat abundance. We constructed 32 weather (temperature and precipitation) variables with time lags prior to the date we captured each rat. We fitted multivariable logistic regression models with rat pathogen status as the outcome. The odds of a rat testing positive for B. tribocorum were significantly lower for rats in city blocks with one or more low-rise apartment buildings compared to blocks with none (OR = 0.20; 95% CI: 0.04-0.80; p = .02). The reason for this association may be related to unmeasured factors that influence pathogen transmission and maintenance, as well as flea vector survival. Bartonella tribocorum infection in rats was positively associated with high minimum temperatures for several time periods prior to rat capture. This finding suggests that a baseline minimum temperature may be necessary for flea vector survival and B. tribocorum transmission among rats. There was no significant association with rat abundance, suggesting a lack of density-dependent pathogen transmission. This study is an important first step to understanding how environment and weather impacts rat infections including zoonotic pathogen ecology in urban ecosystems.

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

Bartonella species are arthropod-borne bacterial pathogens that infect numerous mammalian species. Small mammals play an important role as natural reservoirs of many Bartonella species, maintaining the greatest diversity of Bartonella described to date. Although Bartonella research has been conducted in Southeast Asia, no studies have been undertaken on small mammals in Singapore. Here, we report the detection and description of Bartonella in small mammals in Singapore during the period of November 2011 to May 2014. BartonellaDNA was detected in 20.8% (22/106) of small mammal spleens with a PCR amplifying the beta subunit of bacterial RNA polymerase (rpoB) gene. Commensal species Rattus norvegicus and Rattus tanezumi had the highest prevalence, 75% (3/4) and 34,5% (10/29), followed by Suncus murinus 30% (6/20), Tupaia glis 16,7% (1/6) and Mus castaneus 13.3% (2/15). Phylogenetic analysis of 18 rpoB gene sequences revealed five Bartonella genotypes circulating in the small mammals of Singapore. Bayesian tip-significance testing demonstrated strong structuring in the geographical signal, indicating that distribution of Bartonella species is correlated to the distribution of their hosts. Major deforestation and fragmentation in Singapore favour synanthropic species that traverse habitats and increase the possibility of spillover to incidental hosts.

Inferring the Ecological Niche of Toxoplasma gondii and Bartonella spp. in Wild Felids

Traditional epidemiological studies of disease in animal populations often focus on directly transmitted pathogens. One reason pathogens with complex lifecycles are understudied could be due to challenges associated with detection in vectors and the environment. Ecological niche modeling (ENM) is a methodological approach that overcomes some of the detection challenges often seen with vector or environmentally dependent pathogens. We test this approach using a unique dataset of two pathogens in wild felids across North America: Toxoplasma gondii and Bartonella spp. in bobcats (Lynx rufus) and puma (Puma concolor). We found three main patterns. First, T. gondii showed a broader use of environmental conditions than did Bartonella spp. Also, ecological niche models, and Normalized Difference Vegetation Index satellite imagery, were useful even when applied to wide-ranging hosts. Finally, ENM results from one region could be applied to other regions, thus transferring information across different landscapes. With this research, we detail the uncertainty of epidemiological risk models across novel environments, thereby advancing tools available for epidemiological decision-making. We propose that ENM could be a valuable tool for enabling understanding of transmission risk, contributing to more focused prevention and control options for infectious diseases.

Progress on research on rodents and rodent-borne zoonoses in South-east Asia

This review aims to synthesise knowledge regarding the taxonomy of South-east Asian murine rodents and the challenges associated with the identification of habitat preferences and associated rodent-borne diseases. Recent studies concerning the Rattini tribe have identified unclear species boundaries that would benefit from further investigation. The development of barcoding may allow more accurate identification of rodents, specifically for complex species. However, knowledge on the distribution and habitat specialisations of many common murine rodents is still scarce, particularly regarding the specific habitat preferences of most synanthropic rodent species (Rattus tanezumi or Rattus exulans). Several studies have analysed the prevalence of major rodent-borne diseases in South-east Asia and it appears that the greatest risk of rodent zoonoses are in the lowland rain-fed and irrigated landscapes, generally in and around rice fields.