Development rates of two Xenopsylla flea species in relation to air temperature and humidity

A One Health Perspective on the Resurgence of Flea-Borne Typhus in Texas in the 21st Century: Part 1: The Bacteria, the Cat Flea, Urbanization, and Climate Change

Flea-borne typhus (FBT), due to Rickettsia typhi and R. felis, is an infection typically causing fever, headache, rash, hepatitis, and thrombocytopenia. About one quarter of patients suffer pulmonary, neurologic, hematologic, renal, hepatic, cardiac, ocular or other complications. In the 21st century, the incidence of FBT has increased in both Texas and California compared to the 1990s. In this paper, county-level epidemiological data for the number of cases of FBT occurring in Texas for two decades, 1990-1999 and 2010-2019, were compared with respect to county of residence, urbanization, and climatic region. Human population growth in Texas has promoted FBT by increased urbanization and the abundance of pet dogs and cats, stray/feral dogs and cats, and opossums. Increasing temperatures in Texas in the new millennium have increased the flea-borne transmission of FBT by promoting host infestation and flea feeding and defecation, accelerating the flea life cycle, and increasing rickettsial replication within the flea. Increased numbers of opossums and stray cats and dogs in the urban/suburban landscape have increased the risk of flea transfer to humans and their pets.

Detection of Bartonella spp. in foxes' populations in Piedmont and Aosta Valley (NW Italy) coupling geospatially-based techniques

Bartonella is a genus of bacteria known to cause various rare but potentially dangerous diseases in humans and wildlife. The objective of this study was to investigate the presence of Bartonella spp. in red foxes (Vulpes vulpes) from Piedmont and Aosta Valley (NW Italy) and to explore the potential association between environmental humidity and Bartonella infection using remote sensing data. A total of 114 spleen samples were collected from hunted red foxes and screened for Bartonella spp. DNA using a qPCR assay targeting the ssrA locus. Samples that tested positive were further analyzed using end-point PCR to detect the ssrA, gltA, and rpoB loci. The overall prevalence of Bartonella spp. infection was found to be 7.9% (9/114), with a prevalence of 6.9% (7/101) in foxes from Piedmont and 15.4% (2/13) in foxes from Aosta Valley. Sequencing results identified Bartonella schoenbuchensis R1 as the most commonly isolated species (5/9, 62.5%), followed by Candidatus "Bartonella gerbillinarum" in two samples (2/9, 28.6%). To investigate the relationship between environmental factors and Bartonella infection, data from NASA USGS Landsat missions (TOA collection) from 2011 to 2022 were processed using Google Earth Engine. The Tasseled Cap Wetness Index (TCW), an indicator of landscape moisture, was calculated for each meteorological season. The study found that Bartonella spp. infections in foxes were positively associated with higher TCW values (>0.7). Canonical Correspondence Analysis further demonstrated a strong link between pathogen prevalence and municipal-level TCW, suggesting that TCW could be used as a parameter to facilitate disease management and control. This study provides a starting point for a more comprehensive epidemiological assessment of Bartonella spp. on a national scale and highlights the potential role of environmental humidity in influencing pathogen distribution.

On-host flea phenology and flea-borne pathogen surveillance among mammalian wildlife of the pineywoods of East Texas

Flea-borne diseases are endemic in Texas, U.S.A., with an increasing incidence of flea-borne typhus and cat scratch disease. Knowledge of flea natural history could provide information to protect public health, yet many knowledge gaps remain outside of plague-endemic regions. Our objective was to characterize seasonal activity patterns of fleas on common mammalian wildlife species and test fleas and wildlife for Rickettsia and Bartonella pathogens. We performed one year of monthly trapping for rodents and medium-sized mammals in a national forest with high recreational use and urban encroachment in East Texas. From 90 mammal captures representing seven species, 101 fleas were collected representing Polygenis spp., Ctenocephalides felis, and Orchopeas species. Virginia opossums (Didelphis virginianus) hosted 99% of the collected fleas (100 fleas) and a single flea was on an eastern woodrat (Neotoma floridana). Flea infestation prevalence of opossums was 79% (23/29). Mean flea abundance was 4.39 fleas, with intensity peaking in spring. One cat flea removed from an opossum was positive for Bartonella henselae. Furthermore, we identified tissue or blood of four raccoons (Procyon lotor) and one golden mouse (Ochrotomys nuttalli) positive for Rickettsia amblyommatis. These findings provide an ecological basis for the maintenance of vectors and pathogens from sylvatic settings.

Parasite traits, host traits, and environment as determinants of dark diversity affinity in flea and gamasid mite assemblages from the Palearctic

A species set in a site comprises species that are present (realized diversity) and species that could inhabit this site but are absent (dark diversity; DD). DD can be both species-driven (a species' traits preclude its presence, independently of site features) and site-driven (site features preclude the species' presence, independently of its traits). DD affinity (DDA) is a measure of species' tendencies to be absent from sites that they could inhabit or of sites' tendencies to lack species that could be present. Decomposition of DDA into DDA for species (ddasp) and for sites (ddasite) allows (a) disentangling these two mechanisms and (b) detecting species traits and site features contributing to their DDA. The species-site unified model is a Bayesian statistical model aimed at simultaneously estimating ddasp and ddasite. We applied it to flea and mite assemblages (a) within a host species across regions (component metacommunities; CtM; ddasite = ddaregion) and (b) within a region across host species (compound metacommunities; CdM, ddasite = ddahost). In CtMs, ddasp and ddaregion equally contributed to DD, whereas the relative contributions of ddasp and ddahost to DD in CdMs varied from the former being higher than the latter and vice versa. In CtM and CdM, ddasp increased in low-abundance ectoparasites exploiting a restricted number of hosts. In CtMs, ddaregion was associated with the regional environment, but we failed to find host traits affecting ddahost in CdMs. We conclude that ectoparasite species and either regions in CtMs or host species in CdMs independently contribute to DD.

Host and habitat shape ectoparasite diversity on Mastomys natalensis and Mastomys coucha (Muridae)

Mastomys natalensis and M. coucha are commensal rodent species endemic to Africa. A recent taxonomic revision within Mastomys leaves the parasite–host list of M. natalensis questionable and that of M. coucha incomplete. The current study aimed to develop a better understanding of the ectoparasite diversity associated with the 2 distinct but closely related rodent species and to explore the influence of host and habitat type on ectoparasite infestations. Between 2014 and 2020, 590 rodents were trapped in 3 habitat types (village, agriculture and natural) across a wildlife-human/domestic animal interface. In total 48 epifaunistic species (45 ectoparasitic and 3 predatory) represented by 29 genera from 4 taxonomic groups (fleas, lice, mites and ticks) were recorded. Only 50% of the epifauna were shared between the 2 rodent species, with mites the most speciose taxon in both host species. The abundance of epifaunistic individuals, and also those of mites and fleas, were significantly higher on male M. natalensis, while ticks were significantly higher on reproductively active M. natalensis. For both rodent species, infestations by most epifaunistic taxa (on M. natalensis) and some taxa (on M. coucha) were significantly lower in the village as opposed to the less disturbed agricultural and natural habitat types. The study highlights the importance of host life history, even in closely related rodent species, in shaping parasite profiles and a loss of parasite diversity in more extreme anthropogenic habitats.

Climate Change and Human Health in Africa in Relation to Opportunities to Strengthen Mitigating Potential and Adaptive Capacity: Strategies to Inform an African "Brains Trust"

Background

Africa faces diverse and complex population/human health challenges due to climate change. Understanding the health impacts of climate change in Africa in all its complexity is essential for implementing effective strategies and policies to mitigate risks and protect vulnerable populations. This study aimed to outline the major climate change-related health impacts in Africa in the context of economic resilience and to seek solutions and provide strategies to prevent or reduce adverse effects of climate change on human health and well-being in Africa.

Methods

For this narrative review, a literature search was conducted in the Web of Science, Scopus, CAB Abstracts, MEDLINE and EMBASE electronic databases. We also searched the reference lists of retrieved articles for additional records as well as reports. We followed a conceptual framework to ensure all aspects of climate change and health impacts in Africa were identified.

Results

The average temperatures in all six eco-regions of Africa have risen since the early twentieth century, and heat exposure, extreme events, and sea level rise are projected to disproportionately affect Africa, resulting in a larger burden of health impacts than other continents. Given that climate change already poses substantial challenges to African health and well-being, this will necessitate significant effort, financial investment, and dedication to climate change mitigation and adaptation. This review offers African leaders and decision-makers data-driven and action-oriented strategies that will ensure a more resilient healthcare system and safe, healthy populations-in ways that contribute to economic resiliency.

Conclusions

The urgency of climate-health action integrated with sustainable development in Africa cannot be overstated, given the multiple economic gains from reducing current impacts and projected risks of climate change on the continent's population health and well-being. Climate action must be integrated into Africa's development plan to meet the Sustainable Development Goals, protect vulnerable populations from the detrimental effects of climate change, and promote economic development.

Interspecific differences in developmental mode determine early cognitive abilities in teleost fish

Most studies on developmental variation in cognition have suggested that individuals are born with reduced or absent cognitive abilities, and thereafter, cognitive performance increases with age during early development. However, these studies have been mainly performed in altricial species, such as humans, in which offspring are extremely immature at birth. In this work, we tested the hypothesis that species with other developmental modes might show different patterns of cognitive development. To this end, we analysed inhibitory control performance in two teleost species with different developmental modes, the zebrafish Danio rerio and the guppy Poecilia reticulata, exploiting a simple paradigm based on spontaneous behaviour and therefore applicable to subjects of different ages. Zebrafish hatch as larvae 3 days after fertilisation, and have an immature nervous system, a situation that mirrors extreme altriciality. We found that at the early stages of development, zebrafish displayed no evidence of inhibitory control, which only begun to emerge after one month of life. Conversely, guppies, which are born after approximately one month of gestation as fully developed and independent individuals, solved the inhibitory control task since their first days of life, although performance increased with sexual maturation. Our study suggests that the typical progression described during early ontogeny in humans and other species might not be the only developmental trend for animals' cognition and that a species' developmental mode might determine variation in cognition across subjects of different age.

Climate-driven marmot-plague dynamics in Mongolia and China

The incidence of plague has rebounded in the Americas, Asia, and Africa alongside rapid globalization and climate change. Previous studies have shown local climate to have significant nonlinear effects on plague dynamics among rodent communities. We analyzed an 18-year database of plague, spanning 1998 to 2015, in the foci of Mongolia and China to trace the associations between marmot plague and climate factors. Our results suggested a density-dependent effect of precipitation and a geographic location-dependent effect of temperature on marmot plague. That is, a significantly positive relationship was evident between risk of plague and precipitation only when the marmot density exceeded a certain threshold. The geographical heterogeneity of the temperature effect and the contrasting slopes of influence for the Qinghai-Tibet Plateau (QTP) and other regions in the study (nQTP) were primarily related to diversity of climate and landscape types.

Ecological interactions, local people awareness and practices on rodent-borne diseases in Africa: A review

Several anthropogenic activities exposure humans to the risk of rodent-borne diseases. These activities are but not limited to logging, clearing land for crop cultivation, and consuming rodents. Rodents are a highly diverse mammalian group and harbor many zoonotic diseases. This review focuses on dominant rodent-flea species, rodent-borne zoonotic diseases and awareness and management practices against rodent-borne diseases in Africa. Relevant academic literature spanning from 1974 to 2021 was analysed. Dominant rodent species reported in Africa included:- Mastomys natalensis and Rattus rattus, while dominant flea species included Xenopsylla brasiliensis and Xenopsylla cheopis. Rodents were reported as hosts to a wide range of parasites which can be passed to humans. Rodents were also reported as hosts to some protozoans, trematodes, cestodes, nematodes, bacteria and viruses which are transmissible to humans. Some studies conducted in West Africa revealed good knowledge and practices on plague and Lassa fever diseases among respondents, whereas other studies reported poor practices on Lassa fever management. In part of Southern Africa, some studies reported poor knowledge and practices on plague disease. Further research on rodent-borne disease awareness and management strategies in African countries is desirable.

Cost-Effective PCR-Based Identification of Tunga penetrans (Siphonaptera) Larvae Extracted from Soil Samples Containing PCR Inhibitor-Rich Material

Tungiasis is a neglected tropical disease caused by skin-penetrating female Tunga penetrans fleas. Although tungiasis causes severe health problems, its ecology is poorly understood and morphological descriptions of the larvae are unavailable. To identify T. penetrans immature stages and sites where they develop, diagnostic PCRs are required. However, flea larvae feed on soil organic matter rich in PCR inhibitors. Here, three DNA preparation methods, including a soil DNA kit that removes inhibitors, a simple ammonium acetate precipitation approach (AmAcet) and a crude lysate of larvae (CL), were combined with amplification by the highly processive FIREPol^® Taq or the inhibitor-resistant Phusion^® polymerase. Independent of the polymerase used, the frequency of successful amplification, C_q values and PCR efficacies for the low-cost CL and AmAcet methods were superior to the commercial kit for amplification of a 278 bp partial internal transcribed spacer-2 (ITS-2) and a 730 bp pan-Siphonaptera cytochrome oxidase II PCR. For the CL method combined with Phusion^® polymerase, the costs were approximately 20-fold lower than for the methods based on the soil DNA kit, which is a considerable advantage in resource-poor settings. The ITS-2 PCR did not amplify Ctenocephalides felis genomic or Tunga trimammilata ITS-2 plasmid DNA, meaning it can be used to specifically identify T. penetrans.

Limited sex differences in plastic responses suggest evolutionary conservatism of thermal reaction norms: A meta-analysis in insects

Temperature has a profound effect on the growth and development of ectothermic animals. However, the extent to which ecologically driven selection pressures can adjust thermal plastic responses in growth schedules is not well understood. Comparing temperature-induced plastic responses between sexes provides a promising but underexploited approach to evaluating the evolvability of thermal reaction norms: males and females share largely the same genes and immature environments but typically experience different ecological selection pressures. We proceed from the idea that substantial sex differences in plastic responses could be interpreted as resulting from sex-specific life-history optimization, whereas similarity among the sexes should rather be seen as evidence of an essential role of physiological constraints. In this study, we performed a meta-analysis of sex-specific thermal responses in insect development times, using data on 161 species with comprehensive phylogenetic and ecological coverage. As a reference for judging the magnitude of sex specificity in thermal plasticity, we compared the magnitude of sex differences in plastic responses to temperature with those in response to diet. We show that sex-specific responses of development times to temperature variation are broadly similar. We also found no strong evidence for sex specificity in thermal responses to depend on the magnitude or direction of sex differences in development time. Sex differences in temperature-induced plastic responses were systematically less pronounced than sex differences in responses induced by variations in larval diet. Our results point to the existence of substantial constraints on the evolvability of thermal reaction norms in insects as the most likely explanation. If confirmed, the low evolvability of thermal response is an essential aspect to consider in predicting evolutionary responses to climate warming.

Fitness consequences of host colonization in two generalist fleas: Context-dependency and the effect of spatial co-occurrence

We studied the fitness consequences of colonizing a novel host by experimental lines of fleas (Synosternus cleopatrae and Xenopsylla ramesis) maintained for 18-22 generations on the principal or novel (sympatric or allopatric) hosts via number, developmental success and size of the offspring of the fleas exploiting these hosts. We asked whether (a) fitness on non-principal hosts increases after prolonged maintenance; (b) the colonization success depends on the spatial co-occurrence of a flea and a host and (c) colonization of a novel host is accompanied by a decreased ability to exploit an original host. The ability of fleas to colonize novel hosts differed between species, with S. cleopatrae, but not X. ramesis, increasing its offspring production on novel hosts. Spatial co-occurrence did not affect colonization success. Maintenance on an alternative host was not accompanied by decreased adaptation to the original host. When fleas returned to the original host, their reproductive output was higher than that of their ancestors. We conclude that the success of colonizing a novel host is (a) context-dependent and varies between flea and host species and (b) not accompanied by the loss of ability to exploit an ancestral host but may lead to an increase in this ability.

Potential Effects of Environmental Conditions on Prairie Dog Flea Development and Implications for Sylvatic Plague Epizootics

Fleas are common ectoparasites of vertebrates worldwide and vectors of many pathogens causing disease, such as sylvatic plague in prairie dog colonies. Development of fleas is regulated by environmental conditions, especially temperature and relative humidity. Development rates are typically slower at low temperatures and faster at high temperatures, which are bounded by lower and upper thresholds where development is reduced. Prairie dogs and their associated fleas (mostly Oropsylla spp) live in burrows that moderate outside environmental conditions, remaining cooler in summer and warmer in winter. We found burrow microclimates were characterized by stable daily temperatures and high relative humidity, with temperatures increasing from spring through summer. We previously showed temperature increases corresponded with increasing off-host flea abundance. To evaluate how changes in temperature could affect future prairie dog flea development and abundance, we used development rates of O. montana (a species related to prairie dog fleas), determined how prairie dog burrow microclimates are affected by ambient weather, and combined these results to develop a predictive model. Our model predicts burrow temperatures and flea development rates will increase during the twenty-first century, potentially leading to higher flea abundance and an increased probability of plague epizootics if Y. pestis is present.

Drivers of the Ectoparasite Community and Co-Infection Patterns in Rural and Urban Burrowing Owls

Simple Summary

We analyzed the ectoparasite community of a monomorphic and non-social bird, the burrowing owl, Athene cunicularia, breeding in rural and urban habitats. Such community was composed by two lice, one mite and one flea species. Rural individuals had more fleas and less mites than urban ones. Adult birds harbored less ectoparasites than young ones and females harbored more lice than males. The presence of lice was positively related to the presence of fleas. On the contrary, the presence of mites was negatively related to the presence of fleas and lice. The study of parasite communities in urban and rural populations of the same species can shed light on how urban stressor factors impact the physiology of wildlife inhabiting cities and, therefore, the host-parasite relationships.

Abstract

Urbanization creates new ecological conditions that can affect biodiversity at all levels, including the diversity and prevalence of parasites of species that may occupy these environments. However, few studies have compared bird–ectoparasite interactions between urban and rural individuals. Here, we analyze the ectoparasite community and co-infection patterns of urban and rural burrowing owls, Athene cunicularia, to assess the influence of host traits (i.e., sex, age, and weight), and environmental factors (i.e., number of conspecifics per nest, habitat type and aridity) on its composition. Ectoparasites of burrowing owls included two lice, one flea, and one mite. The overall prevalence for mites, lice and fleas was 1.75%, 8.76% and 3.50%, respectively. A clear pattern of co-infection was detected between mites and fleas and, to less extent, between mites and lice. Adult owls harbored fewer ectoparasites than nestlings, and adult females harbored more lice than males. Our results also show that mite and flea numbers were higher when more conspecifics cohabited the same burrow, while lice showed the opposite pattern. Rural individuals showed higher flea parasitism and lower mite parasitism than urban birds. Moreover, mite numbers were negatively correlated with aridity and host weight. Although the ectoparasitic load of burrowing owls appears to be influenced by individual age, sex, number of conspecifics per nest, and habitat characteristics, the pattern of co-infection found among ectoparasites could also be mediated by unexplored factors such as host immune response, which deserves further research.

Adaptation to a novel host and performance trade-off in host-generalist and host-specific insect ectoparasites

We investigated the performance trade-offs of fleas (Siphonaptera) while adapting to a novel host using two host generalists (Xenopsylla conformis and Xenopsylla ramesis) and one host specialist (Parapulex chephrenis) maintained on their principal hosts (Meriones crassus for Xenopsylla and Acomys cahirinus for P. chephrenis). We asked whether, over generations, (i) a host generalist may become a specialist by evolving the ability to exploit a novel host and losing the ability to exploit an original host and (ii) a host specialist can become a generalist by evolving the ability to exploit a novel host without losing the ability to exploit an original host. We established an experimental line of each species on a novel host (Acomys russatus for Xenopsylla and M. crassus for P. chephrenis) and maintained this line on this host during 23 generations. We compared reproductive performance of progenitors of each line and their descendants when they exploited either original or novel host in terms of egg number and size, hatching success, offspring production, and offspring size. We found changes in performance over generations in female offspring size only. Xenopsylla conformis demonstrated a tendency to become a host specialist (increased performance on the novel host with a concomitant decreased performance on the original host), whereas P. chephrenis demonstrated a tendency to become a host generalist (increased performance on the novel host without a concomitant decreased performance on the original host). We conclude that the probability of generalist to specialist transition, and vice versa, is context-dependent and varies between species.

Dark diversity of flea assemblages of small mammalian hosts: effects of environment, host traits and host phylogeny

An assemblage of species in a locality comprises two components, namely (i) species that are present (realised diversity) and (ii) species from the regional pool that may potentially inhabit this locality due to suitable ecological conditions, but that are absent (dark diversity). We investigated factors affecting the dark diversity of component communities of fleas parasitic on small mammals in the northern Palearctic at two scales. First, we considered the dark diversity of flea assemblages of the same host (for 13 host species) across regions and tested for the effects of environmental factors and the number of available host species on the dark diversity of within-region flea assemblages. Second, we considered the dark diversity of fleas across host species within a region (for 20 regions) and asked whether within-host dark diversity is associated with host phylogeny and/or traits. We found that the dark diversity of flea assemblages harboured by small mammals varied substantially (i) within the same host species across space (in 12 of 13 host species) and (ii) between host species within a region (in eight of 20 regions). The size of the dark diversity of flea assemblages of the same host across regions was generally affected by environmental factors (mainly by the amount of green vegetation), whereas the size of the dark diversity of flea assemblages of a host species within a region was affected by host traits (mainly by the degree of host sociality and the structure of its shelter and, to a lesser degree, by its geographic range size) but was not associated with host phylogenetic affinities. We conclude that application of the dark diversity concept to parasite communities across space or hosts allows a better understanding of the factors affecting the species richness and composition of these communities.

Colonization of a novel host by fleas: changes in egg production and egg size

We studied the success of fleas, Synosternus cleopatrae and Xenopsylla ramesis, in switching to a novel host by establishing experimental lines maintained on different hosts for 18 generations. Fleas fed on principal (P-line) or novel hosts, either sympatric with (S-line) or allopatric to (A-line) a flea and its principal host, then we assessed their reproductive performance via the number and size of eggs. We compared reproductive performance between hosts within a line and between lines within a host asking: (a) whether fleas adapt to a novel host species after multiple generations; (b) if yes, whether the pattern of adaptation differs between novel host species sympatric with or allopatric to a flea and its principal host; and (c) adaptation to a novel host is accompanied with a loss of success in exploitation of an original host. Fleas from the S- and A-lines increased their egg production on a novel host (except X. ramesis from the S-line). S. cleopatrae from the S-line but not the A-line increased egg size on a novel host, whereas X. ramesis from the A-line but not the S-line produced larger eggs from a novel host. We found no indication of a loss of reproductive performance on the original host while adapting to a novel host. We conclude that fleas are able to switch rapidly to a new host with the pattern of a switch to either sympatric or an allopatric host depending on the identities of both flea and host species.

Yersinia pestis: the Natural History of Plague

The Gram-negative bacterium Yersinia pestis is responsible for deadly plague, a zoonotic disease established in stable foci in the Americas, Africa, and Eurasia. Its persistence in the environment relies on the subtle balance between Y. pestis-contaminated soils, burrowing and nonburrowing mammals exhibiting variable degrees of plague susceptibility, and their associated fleas. Transmission from one host to another relies mainly on infected flea bites, inducing typical painful, enlarged lymph nodes referred to as buboes, followed by septicemic dissemination of the pathogen. In contrast, droplet inhalation after close contact with infected mammals induces primary pneumonic plague. Finally, the rarely reported consumption of contaminated raw meat causes pharyngeal and gastrointestinal plague. Point-of-care diagnosis, early antibiotic treatment, and confinement measures contribute to outbreak control despite residual mortality. Mandatory primary prevention relies on the active surveillance of established plague foci and ectoparasite control. Plague is acknowledged to have infected human populations for at least 5,000 years in Eurasia. Y. pestis genomes recovered from affected archaeological sites have suggested clonal evolution from a common ancestor shared with the closely related enteric pathogen Yersinia pseudotuberculosis and have indicated that ymt gene acquisition during the Bronze Age conferred Y. pestis with ectoparasite transmissibility while maintaining its enteric transmissibility. Three historic pandemics, starting in 541 AD and continuing until today, have been described. At present, the third pandemic has become largely quiescent, with hundreds of human cases being reported mainly in a few impoverished African countries, where zoonotic plague is mostly transmitted to people by rodent-associated flea bites.

Impacts of environmental conditions on fleas in black-tailed prairie dog burrows

Sylvatic plague, caused by the bacterium Yersinia pestis and transmitted by fleas, occurs in prairie dogs of the western United States. Outbreaks can devastate prairie dog communities, often causing nearly 100% mortality. Three competent flea vectors, prairie dog specialists Oropsylla hirsuta and O. tuberculata, and generalist Pulex simulans, are found on prairie dogs and in their burrows. Fleas are affected by climate, which varies across the range of black-tailed prairie dogs (Cynomys ludovicianus), but these effects may be ameliorated somewhat due to the burrowing habits of prairie dogs. Our goal was to assess how temperature and precipitation affect off-host flea abundance and whether relative flea abundance varied across the range of black-tailed prairie dogs. Flea abundance was measured by swabbing 300 prairie dog burrows at six widely distributed sites in early and late summer of 2016 and 2017. Relative abundance of flea species varied among sites and sampling sessions. Flea abundance and prevalence increased with monthly mean high temperature and declined with higher winter precipitation. Predicted climate change in North America will likely influence flea abundance and distribution, thereby impacting plague dynamics in prairie dog colonies.

Harrison's rule scales up to entire parasite assemblages but is determined by environmental factors

Harrison's rule states that parasite body size and the body size of their hosts tend to be positively correlated. After it was proposed a century ago, a number of studies have investigated this trend, but the support level has varied greatly between parasite/host associations. Moreover, while the rule has been tested at the individual species level, we still lack knowledge on whether Harrison's rule holds at the scale of parasite and host communities. Here, we mapped flea (parasites) and rodent (hosts) body sizes across Mongolia and asked whether Harrison's rule holds for parasite/host assemblages (i.e. whether a parasite's average body size in a locality is positively correlated with its host's average body size). In addition, we attempted to disentangle complex relationships between flea size, host size and environmental factors by testing alternative hypotheses for the determinants of fleas' body size variation. We gathered occurrence data for fleas and rodents from 2,370 sites across Mongolia, constructed incidence matrices for both taxa and calculated the average body sizes of fleas and their hosts over half-degree cells. Then, we applied a path analysis, accounting for spatial autocorrelation, trying to disentangle the drivers of the correlation between parasite and host body sizes. We found a strong positive correlation between average flea and host size across assemblages. Surprisingly though, we found that environmental factors simultaneously affected the body sizes of both fleas and hosts in the same direction, leading to a most likely deceptive correlation between parasite and host size across assemblages. We suggest that environmental factors may, to a great extent, reflect the environmental conditions inside the hosts' burrows where fleas develop and attain their adult body size, thus influencing their larval growth. Similarly, rodent body size is strongly influenced by air temperature, in the direction predicted by Bergmann's rule. If our findings are valid in other host-parasite associations, this may explain the dissenting results of both support and lack thereof for Harrison's rule.

Climate drivers of plague epidemiology in British India, 1898-1949

Plague, caused by Yersinia pestis infection, continues to threaten low- and middle-income countries throughout the world. The complex interactions between rodents and fleas with their respective environments challenge our understanding of human plague epidemiology. Historical long-term datasets of reported plague cases offer a unique opportunity to elucidate the effects of climate on plague outbreaks in detail. Here, we analyse monthly plague deaths and climate data from 25 provinces in British India from 1898 to 1949 to generate insights into the influence of temperature, rainfall and humidity on the occurrence, severity and timing of plague outbreaks. We find that moderate relative humidity levels of between 60% and 80% were strongly associated with outbreaks. Using wavelet analysis, we determine that the nationwide spread of plague was driven by changes in humidity, where, on average, a one-month delay in the onset of rising humidity translated into a one-month delay in the timing of plague outbreaks. This work can inform modern spatio-temporal predictive models for the disease and aid in the development of early-warning strategies for the deployment of prophylactic treatments and other control measures.

Feeding performance on a novel host: no adaptation over generations and differential patterns in two flea species

To model the colonization of a novel host by fleas, Synosternus cleopatrae and Xenopsylla ramesis, we established experimental lines maintained for 15 generations on a principal or a novel host (either co-occurring with a flea or not). We compared the blood meal size and the energy expended for digestion by fleas from the 15th generation of each line on these hosts between hosts within a line and between lines within a host asking (a) whether fleas adapt to a novel host (increased blood consumption/decreased energy expended for digestion); (b) if yes, whether this adaptation leads to the loss of ability to exploit an original host, and (c) whether the success of adaptation to a novel host depends on its ecological co-occurrence with a flea. The blood consumption and digestion energetics of fleas fed on the principal host differed from those on other hosts. The effect of the principal host on feeding performance differed between fleas, with S. cleopatrae consuming less blood and expending more energy for digestion on the principal than on any other host, whereas the opposite was true for X. ramesis. No changes in feeding performance on a novel host over generations were found. We propose several explanations for the lack of adaptation to a novel host over time. We explain the poor performance of S. cleopatrae on its principal host via its immune response mounting pattern. We argue that the principal host of a parasite is not necessarily the host on which the parasite demonstrates the best performance.

Haemoplasmas in wild rodents: Routes of transmission and infection dynamics

The way that some parasites and pathogens persist in the hostile environment of their host for long periods remains to be resolved. Here, longitudinal field surveys were combined with laboratory experiments to investigate the routes of transmission and infection dynamics of such a pathogen-a wild rodent haemotropic bacterium, specifically a Mycoplasma haemomuris-like bacterium. Fleaborne transmission, direct rodent-to-rodent transmission and vertical transmission from fleas or rodents to their offspring were experimentally quantified, and indications were found that the main route of bacterial transmission is direct, although its rate of successful transmission is low (~20%). The bacterium's temporal dynamics was then compared in the field to that observed under a controlled infection experiment in field-infected and laboratory-infected rodents, and indications were found, under all conditions, that the bacterium reached its peak infection level after 25-45 days and then decreased to low bacterial loads, which persist for the rodent's lifetime. These findings suggest that the bacterium relies on persistency with low bacterial loads for long-term coexistence with its rodent host, having both conceptual and applied implications.

Drivers of flea (Siphonaptera) community structure in sympatric wild carnivores in northwestern Mexico

Host identity, habitat type, season, and interspecific interactions were investigated as determinants of the community structure of fleas on wild carnivores in northwestern Mexico. A total of 540 fleas belonging to seven species was collected from 64 wild carnivores belonging to eight species. We found that the abundances of some flea species are explained by season and host identity. Pulex irritans and Echidnophaga gallinacea abundances were significantly higher in spring than in fall season. Flea communities on carnivore hosts revealed three clusters with a high degree of similarity within each group that was explained by the flea dominance of E. gallinacea, P. simulans, and P. irritans across host identity. Flea abundances did not differ statistically among habitat types. Finally, we found a negative correlation between the abundances of three flea species within wild carnivore hosts. Individual hosts with high loads of P. simulans males usually had significantly lower loads of P. irritans males or tend to have lower loads of E. gallinacea fleas and vice-versa. Additionally, the logistic regression model showed that the presence of P. simulans males is more likely to occur in wild carnivore hosts in which P. irritans males are absent and vice-versa. These results suggest that there is an apparent competitive exclusion among fleas on wild carnivores. The study of flea community structure on wild carnivores is important to identify the potential flea vectors for infectious diseases and provide information needed to design programs for human health and wildlife conservation.

Can we predict the success of a parasite to colonise an invasive host?

To understand whether a parasite can exploit a novel invasive host species, we measured reproductive performance (number of eggs per female per day, egg size, development rate and size of new imagoes) of fleas from the Negev desert in Israel (two host generalists, Synosternus cleopatrae and Xenopsylla ramesis, and a host specialist, Parapulex chephrenis) when they exploited either a local murid host (Gerbillus andersoni, Meriones crassus and Acomys cahirinus) or two alien hosts (North American heteromyids, Chaetodipus penicillatus and Dipodomys merriami). We asked whether (1) reproductive performance of a flea differs between an alien and a characteristic hosts and (2) this difference is greater in a host specialist than in host generalists. The three fleas performed poorly on alien hosts as compared to local hosts, but the pattern of performance differed both among fleas and within fleas between alien hosts. The response to alien hosts did not depend on the degree of host specificity of a flea. We conclude that successful parasite colonisation of an invasive host is determined by some physiological, immunological and/or behavioural compatibility between a host and a parasite. This compatibility is unique for each host-parasite association, so that the success of a parasite to colonise an invasive host is unpredictable.

Prevalence of papular urticaria caused by flea bites and associated factors in children 1-6 years of age in Bogotá, D.C

Background

Papular urticaria is a chronic inflammatory disease caused by exposure to arthropod bites. The disease has been reported in children attending medical centers, but the causes as the risk factors associated with the disease have not been established. The objective of this study was to determine the prevalence of papular urticaria caused by flea bite and identify the risk factors in children between 1 to 6 years of age in Bogotá D.C, between March 2009 and June 2011.

Methods

A cross-sectional, two-stage, clustered study using random probability sampling and stratified with proportional allocation was carried out in children (1–6 years of age) in educational institutions in Bogotá D.C. to determine the prevalence of the disease. Children underwent a dermatological examination by general practitioners with a previous training. Furthermore, digital photographs of skin lesions were taken for further confirmation of the diagnosis by dermatologists. A structured survey was completed by the parents or caregivers, and it was evaluated using an unconditional logistic regression to identify factors associated with the disease.

Results

A total of 2437 children were included in the study. The prevalence of papular urticaria caused by flea bite in this population was 20.3% (CI 95%: 18.2 to 22.5%). The major risk factors associated with the disease were the presence of fleas in households (OR 1.74, CI 95%: 1.35 to 2.25), using mattresses without springs (OR 1.73, CI 95%: 1.20 to 2.50), the use of daily public transportation to carry the children to the educational institutions (OR 1.76, CI 95%: 1.07 to 2.89), having a soil/earth floor in the main bedroom (OR 6.81, CI 95%:1.16–39.96), and having siblings with a history of atopic dermatitis (OR 1.76 CI 95%: 1.07–2.89).

Conclusions

A high prevalence of papular urticaria caused by flea bite was found in Bogotá D.C. The main factors associated with the disease might be modified with the implementation of prevention, control strategies in housing, educational institutions, and public transportation.

Precipitation, Climate Change, and Parasitism of Prairie Dogs by Fleas that Transmit Plague

Fleas (Insecta: Siphonaptera) are hematophagous ectoparasites that can reduce the fitness of vertebrate hosts. Laboratory populations of fleas decline under dry conditions, implying that populations of fleas will also decline when precipitation is scarce under natural conditions. If precipitation and hence vegetative production are reduced, however, then herbivorous hosts might suffer declines in body condition and have weakened defenses against fleas, so that fleas will increase in abundance. We tested these competing hypotheses using information from 23 yr of research on 3 species of colonial prairie dogs in the western United States: Gunnison's prairie dog (Cynomys gunnisoni, 1989-1994), Utah prairie dog (Cynomys parvidens, 1996-2005), and white-tailed prairie dog (Cynomys leucurus, 2006-2012). For all 3 species, flea-counts per individual varied inversely with the number of days in the prior growing season with >10 mm of precipitation, an index of the number of precipitation events that might have caused a substantial, prolonged increase in soil moisture and vegetative production. Flea-counts per Utah prairie dog also varied inversely with cumulative precipitation of the prior growing season. Furthermore, flea-counts per Gunnison's and white-tailed prairie dog varied inversely with cumulative precipitation of the just-completed January and February. These results complement research on black-tailed prairie dog (Cynomys ludovicianus) and might have important ramifications for plague, a bacterial disease transmitted by fleas that devastates populations of prairie dogs. In particular, our results might help to explain why, at some colonies, epizootics of plague, which can kill >95% of prairie dogs, are more likely to occur during or shortly after periods of reduced precipitation. Climate change is projected to increase the frequency of droughts in the grasslands of western North America. If so, then climate change might affect the occurrence of plague epizootics among prairie dogs and other mammalian species that associate with them.

Parasite performance and host alternation: is there a negative effect in host-specific and host-opportunistic parasites?

Environmental fluctuations are expected to require special adaptations only if they are associated with a decrease in fitness. We compared reproductive performance between fleas fed on alternating (preferred and non-preferred) hosts and fleas fed solely on either a preferred or a non-preferred host to determine whether (1) host alternation incurs an immediate negative effect, and, if yes, then (2) whether this effect is greater in a host specialist (Parapulex chephrenis) than in host generalists (Xenopsylla conformis and Synosternus cleopatrae). We also compared flea performance under alternating host regimes with different host order (initial feeding on either a preferred or a non-preferred host). An immediate negative effect of alternating hosts on reproductive performance was found in P. chephrenis only. These fleas produced 44·3% less eggs that were 3·6% smaller when they fed on alternating hosts as compared with a preferred host. In contrast, X. conformis and S. cleopatrae appeared to be able to adapt their reproductive strategy to host alternation by producing higher quality offspring (on average, 3·1% faster development and 2·1% larger size) without compromising offspring number. However, the former produced eggs that were slightly, albeit significantly, smaller when it fed on alternating hosts as compared with a preferred host. Moreover, host order affected reproductive performance in host generalists (e.g. 2·8% larger eggs when the first feeding was performed on a non-preferred host), but not in a host specialist. We conclude that immediate effects of environmental fluctuation on parasite fitness depend on the degree of host specialization.

Effect of temperature and relative humidity on the development times and survival of Synopsyllus fonquerniei and Xenopsylla cheopis, the flea vectors of plague in Madagascar

Background

Plague, a zoonosis caused by Yersinia pestis, is found in Asia, the Americas but mainly in Africa, with the island of Madagascar reporting almost one third of human cases worldwide. In the highlands of Madagascar, plague is transmitted predominantly by two flea species which coexist on the island, but differ in their distribution. The endemic flea, Synopsyllus fonquerniei, dominates flea communities on rats caught outdoors, while the cosmopolitan flea, Xenopsylla cheopis, is found mostly on rats caught in houses. Additionally S. fonquerniei seems restricted to areas above 800 m. Climatic constraints on the development of the two main vectors of plague could explain the differences in their distribution and the seasonal changes in their abundance. Here we present the first study on effects of temperature and relative humidity on the immature stages of both vector species.

Methods

We examined the two species’ temperature and humidity requirements under experimental conditions at five different temperatures and two relative humidities. By employing multivariate and survival analysis we established the impact of temperature and relative humidity on development times and survival for both species. Using degree-day analysis we then predicted the average developmental threshold for larvae to reach pupation and for pupae to complete development under each treatment. This analysis was undertaken separately for the two relative humidities and for the two species.

Results

Development times and time to death differed significantly, with the endemic S. fonquerniei taking on average 1.79 times longer to complete development and having a shorter time to death than X. cheopis under adverse conditions with high temperature and low humidity. Temperature had a significant effect on the development times of flea larvae and pupae. While humidity did not affect the development times of either species, it did influence the time of death of S. fonquerniei. Using degree-day analysis we estimated an average developmental threshold of 9 °C for S. fonquerniei, and 12.5 °C for X. cheopis.

Conclusions

While many vector-borne diseases are limited to warm, low-lying regions, plague in Madagascar is unusual in being most prevalent in the cool, highland regions of the country. Our results point towards the possibility that this is because the endemic flea vector, S. fonquerniei, is better adapted to cool temperatures than the exotic flea vector, X. cheopis. Future warming caused by climate change might reduce the area suitable for S. fonquerniei and may thus reduce the incidence of plague in Madagascar.

Flea fitness is reduced by high fractional concentrations of CO₂ that simulate levels found in their hosts' burrows

Nidicolous ectoparasites such as fleas and gamasid mites that feed on small and medium-sized mammals spend much of their time in their hosts' burrows, which provide an environment for living, and often feeding, to their pre-imaginal and/or adult stages. Thus, these ectoparasites should be adapted to environmental conditions in burrows, including high fractional concentrations of CO2 (F(CO2)). We examined how a high F(CO2) (0.04) affected survival and reproductive success of a hematophagous ectoparasite of burrowing rodents using fleas Xenopsylla ramesis and Sundevall's jirds Meriones crassus. In the first experiment, fleas fed on hosts housed in high-CO2 (F(CO2) =0.04) or atmospheric-CO2 (F(CO2) ≈0.0004) air, and were allowed to breed. In a second experiment, fleas were maintained in high CO2 or CO2-free air with no hosts to determine how CO2 levels affect survival and activity levels. We found that at high F(CO2) fleas laid fewer eggs, reducing reproductive success. In addition, at high F(CO2), activity levels and survival of fleas were reduced. Our results indicate that fleas do not perform well in the F(CO2) used in this experiment. Previous research indicated that the type and intensity of the effects of CO2 concentration on the fitness of an insect depend on the F(CO2) used, so we advise caution when generalizing inferences drawn to insects exposed to other F(CO2). If, however, F(CO2) found in natural mammal burrows brings about reduced fitness in fleas in general, then burrowing hosts may benefit from reduced parasite infestation if burrow air F(CO2) is high.

The Perfect Burrow, but for What? Identifying Local Habitat Conditions Promoting the Presence of the Host and Vector Species in the Kazakh Plague System

INTRODUCTION

The wildlife plague system in the Pre-Balkhash desert of Kazakhstan has been a subject of study for many years. Much progress has been made in generating a method of predicting outbreaks of the disease (infection by the gram negative bacterium Yersinia pestis) but existing methods are not yet accurate enough to inform public health planning. The present study aimed to identify characteristics of individual mammalian host (Rhombomys opimus) burrows related to and potentially predictive of the presence of R.opimus and the dominant flea vectors (Xenopsylla spp.).

METHODS

Over four seasons, burrow characteristics, their current occupancy status, and flea and tick burden of the occupants were recorded in the field. A second data set was generated of long term occupancy trends by recording the occupancy status of specific burrows over multiple occasions. Generalised linear mixed models were constructed to identify potential burrow properties predictive of either occupancy or flea burden.

RESULTS

At the burrow level, it was identified that a burrow being occupied by Rhombomys, and remaining occupied, were both related to the characteristics of the sediment in which the burrow was constructed. The flea burden of Rhombomys in a burrow was found to be related to the tick burden. Further larger scale properties were also identified as being related to both Rhombomys and flea presence, including latitudinal position and the season.

CONCLUSIONS

Therefore, in advancing our current predictions of plague in Kazakhstan, we must consider the landscape at this local level to increase our accuracy in predicting the dynamics of gerbil and flea populations. Furthermore this demonstrates that in other zoonotic systems, it may be useful to consider the distribution and location of suitable habitat for both host and vector species at this fine scale to accurately predict future epizootics.

Drivers of Intensity and Prevalence of Flea Parasitism on Small Mammals in East African Savanna Ecosystems

The relative importance of environmental factors and host factors in explaining variation in prevalence and intensity of flea parasitism in small mammal communities is poorly established. We examined these relationships in an East African savanna landscape, considering multiple host levels: across individuals within a local population, across populations within species, and across species within a landscape. We sampled fleas from 2,672 small mammals of 27 species. This included a total of 8,283 fleas, with 5 genera and 12 species identified. Across individual hosts within a site, both rodent body mass and season affected total intensity of flea infestation, although the explanatory power of these factors was generally modest (<10%). Across host populations in the landscape, we found consistently positive effects of host density and negative effects of vegetation cover on the intensity of flea infestation. Other factors explored (host diversity, annual rainfall, anthropogenic disturbance, and soil properties) tended to have lower and less consistent explanatory power. Across host species in the landscape, we found that host body mass was strongly positively correlated with both prevalence and intensity of flea parasitism, while average robustness of a host species to disturbance was not correlated with flea parasitism. Cumulatively, these results provide insight into the intricate roles of both host and environmental factors in explaining complex patterns of flea parasitism across landscape mosaics.

A non-stationary relationship between global climate phenomena and human plague incidence in Madagascar

BACKGROUND

Plague, a zoonosis caused by Yersinia pestis, is found in Asia and the Americas, but predominantly in Africa, with the island of Madagascar reporting almost one third of human cases worldwide. Plague's occurrence is affected by local climate factors which in turn are influenced by large-scale climate phenomena such as the El Niño Southern Oscillation (ENSO). The effects of ENSO on regional climate are often enhanced or reduced by a second large-scale climate phenomenon, the Indian Ocean Dipole (IOD). It is known that ENSO and the IOD interact as drivers of disease. Yet the impacts of these phenomena in driving plague dynamics via their effect on regional climate, and specifically contributing to the foci of transmission on Madagascar, are unknown. Here we present the first analysis of the effects of ENSO and IOD on plague in Madagascar.

METHODOLOGY/PRINCIPAL FINDINGS

We use a forty-eight year monthly time-series of reported human plague cases from 1960 to 2008. Using wavelet analysis, we show that over the last fifty years there have been complex non-stationary associations between ENSO/IOD and the dynamics of plague in Madagascar. We demonstrate that ENSO and IOD influence temperature in Madagascar and that temperature and plague cycles are associated. The effects on plague appear to be mediated more by temperature, but precipitation also undoubtedly influences plague in Madagascar. Our results confirm a relationship between plague anomalies and an increase in the intensity of ENSO events and precipitation.

CONCLUSIONS/SIGNIFICANCE

This work widens the understanding of how climate factors acting over different temporal scales can combine to drive local disease dynamics. Given the association of increasing ENSO strength and plague anomalies in Madagascar it may in future be possible to forecast plague outbreaks in Madagascar. The study gives insight into the complex and changing relationship between climate factors and plague in Madagascar.

Differentiation of flea communities infesting small mammals across selected habitats of the Baltic coast, central lowlands, and southern mountains of Poland

Only a few studies comparing flea composition on the coast and in the mountains have been conducted. We investigated differences in flea communities infesting small mammals in selected habitats in northern, central, and southern Poland. We predicted (1) a greater number of flea species in the southeastern Poland and a lower number in the north, (2) a greater number of flea species in fertile and wet habitats than in poor and arid habitats, and (3) a low similarity of flea species between flea communities in western and eastern Poland. We found a negative effect of increasing latitude on flea species richness. We suppose that the mountains providing a variety of environments and the limits of the geographic ranges of several flea subspecies in southeastern Poland result in a higher number of flea species. There was a positive effect of increasing wetness of habitat on flea species richness. We found a high diversity in flea species composition between western and eastern Poland (beta diversity = 11) and between central and eastern Poland (beta diversity = 12). Re-colonization of Poland by small mammals and their ectoparasites from different (western and eastern) refugees can affect on this high diversity of flea species.

Host reproductive status and reproductive performance of a parasite: offspring quality and trade-offs in a flea parasitic on a rodent

We investigated offspring quality in fleas (Xenopsylla ramesis) feeding on non-reproducing, pregnant or lactating rodents (Meriones crassus) and asked whether (a) quality of flea offspring differs dependent on host reproductive status; (b) fleas trade off offspring quantity for quality; and (c) quality variables are inter-correlated. Emergence success was highest when parents exploited pregnant hosts, while development time was longest when parents exploited lactating hosts. Male offspring from fleas fed on non-reproductive and pregnant hosts were larger than those from lactating hosts whereas female offspring from fleas fed on pregnant hosts were larger than those from both lactating and non-reproductive hosts. Male offspring survived under starvation the longest when their parents exploited lactating hosts and the shortest when their parents exploited pregnant hosts. Female offspring of parents that exploited lactating hosts survived under starvation longer than those that exploited non-reproductive and pregnant hosts. Emergence success and development time decreased as mean number of eggs laid by mothers increased. Fleas that were larger and took longer to develop lived significantly longer under starvation. These results indicate the presence of a trade-off between offspring quantity and quality in fleas exploiting female Sundevall's jird in varying reproductive condition but this trade-off depended on the quality trait considered.

Age at weaning, immunocompetence and ectoparasite performance in a precocial desert rodent

We studied the effects of early weaning on immunocompetence and parasite resistance in a precocial rodent Acomys cahirinus. We hypothesized that if parasite resistance is energetically expensive and nutritional and immunological support from mothers are necessary for the long-term health of offspring, then early weaned animals would be immunologically weaker and less able to defend themselves against parasites than later weaned animals. We weaned pups at 14, 21, or 28 d after birth and assessed their immunocompetence and resistance against fleas Parapulex chephrenis when they attained adulthood. Immunocompetence was assessed using leukocyte concentrations (LC) and a phytohaemagglutinin injection assay (PHA test). To estimate resistance against fleas, we measured performance of fleas via the number of produced eggs and duration of development and resistance to starvation of the flea offspring. We found a significant positive effect of weaning age on the PHA response but not on LC. The effect of age at weaning on flea egg production was manifested in male but not female hosts, with egg production being higher if a host was weaned at 14 than at 28 d. Weaning age of the host did not affect either duration of development or resistance to starvation of fleas produced by mothers fed on these hosts. We concluded that even in relatively precocial mammals, weaning age is an important indicator of future immunological responses and the ability of an animal to resist parasite infestations. Hosts weaned at an earlier age make easier, less-resistant targets for parasite infestations than hosts weaned later in life.

Vertical nontransovarial transmission of Bartonella in fleas

Pathogens use diverse pathways to infect host populations by vertical and/or horizontal routes. Horizontal transmission of bacteria belonging to the Bartonella genus via haematophagous vectors is well known. Vertical transmission of Bartonella species was also suggested to occur but its routes remain to be unveiled. In a previous study, we showed the absence of transovarial transmission of Bartonella species OE 1-1 in Xenopsylla ramesis fleas, and that fleas feeding on Bartonella-positive jirds produced Bartonella-positive gut voids. This current study aimed to investigate whether vertical nontransovarial transmission of Bartonella occurs in fleas. For this aim, the X. ramesis-Bartonella sp. OE 1-1 model was used. Four groups of fleas including Bartonella-positive and Bartonella-negative female fleas and larval offspring had access to either Bartonella-negative or Bartonella-positive gut voids and faeces. Sixteen per cent of flea offspring that had access to Bartonella-positive faeces and gut voids became Bartonella positive. Our findings demonstrate that Bartonella-positive flea faeces and gut voids are proper infection sources for flea larvae and indicate that vertical nontransovarial transmission of bartonellae occurs in fleas. This information broadens our understanding of Bartonella transmission routes in flea vectors and enlightens pathways of bartonellae transmission and maintenance in flea populations in nature.

Effects of Bartonella spp. on flea feeding and reproductive performance

Numerous pathogens are transmitted from one host to another by hematophagous insect vectors. The interactions between a vector-borne organism and its vector vary in many ways, most of which are yet to be explored and identified. These interactions may play a role in the dynamics of the infection cycle. One way to evaluate these interactions is by studying the effects of the tested organism on the vector. In this study, we tested the effects of infection with Bartonella species on fitness-related variables of fleas by using Bartonella sp. strain OE 1-1, Xenopsylla ramesis fleas, and Meriones crassus jirds as a model system. Feeding parameters, including blood meal size and metabolic rate during digestion, as well as reproductive parameters, including fecundity, fertility, and life span, were compared between fleas experimentally infected with Bartonella and uninfected fleas. In addition, the developmental time, sex ratio, and body size of F1 offspring fleas were compared between the two groups. Most tested parameters did not differ between infected and uninfected fleas. However, F1 males produced by Bartonella-positive females were significantly smaller than F1 males produced by Bartonella-negative female fleas. The findings in this study suggest that bartonellae are well adapted to their flea vectors, and by minimally affecting their fitness they have evolved to better spread themselves in the natural environment.