Host Population Dynamics Research Articles

A novel Alteromonas phage with tail fiber containing six potential iron-binding domains.

Viruses play a vital role in regulating microbial communities, contributing to biogeochemical cycles of carbon, nitrogen, and essential metals. Alteromonas is widespread and plays an essential role in marine microbial ecology. However, there is limited knowledge about the interactions of Alteromonas and its viruses (alterophages). This study isolated a novel podovirus, vB_AmeP-R22Y (R22Y), which infects Alteromonas marina SW-47 (T). Phylogenetic analysis suggested that R22Y represented a novel viral genus within the Schitoviridae family. R22Y exhibited a broad host range and a relatively large burst size, exerting an important impact on the adaptability and dynamics of host populations. Two auxiliary metabolic genes, encoding Acyl carrier protein and AAA domain-containing protein, were predicted in R22Y, which may potentially assist in host fatty acid metabolism and VB12 biosynthesis, respectively. Remarkably, the prediction of the R22Y tail fiber structure revealed six conserved histidine residues (HxH motifs) that could potentially bind iron ions, suggesting that alterophages may function as organic iron-binding ligands in the marine environment. Our isolation and characterization of R22Y complements the Trojan Horse hypothesis, proposes the possible role of alterophages for marine iron biogeochemical cycling, and provides new insights into phage-host interactions in the iron-limited ocean.IMPORTANCEIron (Fe), as an essential micronutrient, is often a limiting factor for microbial growth in marine ecosystems. The Trojan Horse hypothesis suggests that iron in the phage tail fibers is recognized by the host's siderophore-bound iron receptor, enabling the phage to attach and initiate infection. The potential role of phages as iron-binding ligands has significant implications for oceanic trace metal biogeochemistry. In this study, we isolated a new phage R22Y with the potential to bind iron ions, using Alteromonas, a major siderophore producer, as the host. The tail fiber structure of R22Y exhibits six conserved HxH motifs, suggesting that each phage could potentially bind up to 36 iron ions. R22Y may contribute to colloidal organically complexed dissolved iron in the marine environment. This finding provides further insights into the Trojan Horse hypothesis, suggesting that alterophages may act as natural iron-binding ligands in the marine environment.

Ectoparasite infection levels differ between fish from upwelling-exposed and sheltered rocky reefs areas in Brazil

Ubiquitous and abundant within marine ecosystems, parasites play essential ecological roles such as shaping host population dynamics, altering competition between species, and influencing energy flows through communities. Their diversity and population dynamics are demonstrably shaped by both seasonal and geographic variations. These variations have been often explored at broad spatial scale. However, parasite communities can exhibit significant disparities even at small spatial scales, driven by factors such as wave exposure, temperature fluctuations, and benthic habitat composition. We investigated how crustacean parasites of fish – caligids and gnathiids - differed between two distinct habitats, which are separated solely by a few kilometres, at Arraial do Cabo, Brazil. These two habitats are characterised by a sheltered embayment (hereinafter referred to as “inside”) or an exposed upwelling habitat (hereinafter referred to as “outside”). Individual fish from four species were examined in both habitats. We found that the infestation rate of caligids varied among fish species and, gnathiids varied between the two sampling sites. Gnathiids were absent from fish outside, while they were present on fish inside the embayment. This disparity suggests a critical role of local environmental factors in shaping gnathiid distribution. Potential drivers include temperature fluctuations, substrate composition, and wave exposure, which differed markedly between the two sites. Conversely, caligid parasites infected fish in both locations. While environmental factors may also influence caligid abundance, they appear to exhibit greater tolerance compared to gnathiids. These findings emphasize the importance of incorporating fine-scale environmental heterogeneity when investigating parasite distribution patterns.

Estimating the impact of sarcoptic mange epidemic on the population size of wild raccoon dogs (Nyctereutes procyonoides) from wildlife rescue data

The impact of infectious diseases on host populations is often not quantified because it is difficult to observe the host population and infectious disease dynamics. To address this problem, we developed a state-space model to simultaneously estimate host population and disease dynamics using wildlife rescue data. Using this model, we aimed to quantify the impact of sarcoptic mange on a Japanese raccoon dog population by estimating the change in their relative population size. We classified the status of rescued raccoon dogs into four categories: i) rescued due to infection with mange, ii) rescued due to traffic accidents without mange, iii) rescued due to traffic accidents with mange, and iv) rescued due to causes other than traffic accidents or mange. We modelled the observation process for each category and fitted the model to the reported number of raccoon dogs rescued between 1990 and 2010 at three wildlife rescue facilities in Kanagawa Prefecture, Japan. The mortality rate induced by mange was estimated to be 1.09 (95% credible interval (CI): 0.47–1.72) per year. The estimated prevalence of sarcoptic mange ranged between 4 and 80% in the study period. When a substantial prevalence of mange was observed (1995–2002), the host population size decreased by 91.2% (95% credible intervals: 86.3–94.7). We show that the impact of infectious disease outbreak on the wildlife population can be estimated from the time-series data of wildlife rescue events due to multiple causes. Our estimates suggest that sarcoptic mange triggered a substantial decrease in the Japanese wild raccoon dog populations.

Metacollinia emscheri n. sp., a novel sanguicolous apostome ciliate of freshwater amphipods (Gammarus spp.)

We describe a novel sanguicolous parasitic ciliate, Metacollinia emscheri n. sp., found in the freshwater amphipods Gammarus pulex and G. fossarum. This ciliate infected 8.05 % of the amphipods collected in a German stream catchment, the Boye, a tributary of the river Emscher. The ciliate showed morphological characteristics fitting the genus Metacollinia. Different life stages of variable size occurred simultaneously in the hemocoel throughout the hosts’ body. The tomont had 40–47 slightly spiraled kineties, a non-ciliated cortical band, a large macronucleus, and contractile vacuoles arranged in rows or scattered throughout the cytoplasm. The protomites/tomites with nine somatic kineties presented evidence of the buccal kineties x, y, and z reminiscent of those of the order Foettingeriida. Phylogenetic analyses of the 18S rRNA and COI regions confirm the ciliate placement in the Collinidae and a close relatedness to the type species of the genus Metacollinia, Metacollinia luciensis.We formally describe this new parasite as Metacollinia emscheri n. sp. using pathological, morphological, and nuclear/mitochondrial genetic data. The systemic infections observed in histological preparations and the pathogenicity of Metacollinia emscheri n. sp. suggest that this parasite might influence host population dynamics. Given the ecological importance of amphipods as keystone species in freshwater ecosystems, an outbreak of this parasite might indirectly impact ecosystem functioning.

Metagenomic time series reveals a Western English Channel viral community dominated by members with strong seasonal signals.

Marine viruses are key players of ocean biogeochemistry, profoundly influencing microbial community ecology and evolution. Despite their importance, few studies have explored continuous inter-seasonal viral metagenomic time series in marine environments. Viral dynamics are complex, influenced by multiple factors such as host population dynamics and environmental conditions. To disentangle the complexity of viral communities, we developed an unsupervised machine learning framework to classify viral contigs into "chronotypes" based on temporal abundance patterns. Analysing an inter-seasonal monthly time series of surface viral metagenomes from the Western English Channel, we identified chronotypes and compared their functional and evolutionary profiles. Results revealed a consistent annual cycle with steep compositional changes from winter to summer and steadier transitions from summer to winter. Seasonal chronotypes were enriched in potential auxiliary metabolic genes of the ferrochelatases and 2OG-Fe(II) oxygenase orthologous groups compared to non-seasonal types. Chronotypes clustered into four groups based on their correlation profiles with environmental parameters, primarily driven by temperature and nutrients. Viral contigs exhibited a rapid turnover of polymorphisms, akin to Red Queen dynamics. However, within seasonal chronotypes, some sequences exhibited annual polymorphism recurrence, suggesting that a fraction of the seasonal viral populations evolve more slowly. Classification into chronotypes revealed viral genomic signatures linked to temporal patterns, likely reflecting metabolic adaptations to environmental fluctuations and host dynamics. This novel framework enables the identification of long-term trends in viral composition, environmental influences on genomic structure, and potential viral interactions.

Isolation and evaluation of bacteriophage cocktail for the control of colistin-resistant Escherichia coli

The frequent emergence of colistin-resistant E. coli worldwide drives the exploration of alternative therapies, and bacteriophages (phages) have emerged as promising candidates to tackle this challenge. In this study, three E. coli phages were isolated, screened, and evaluated against 96 colistin-resistant strains obtained from diverse sources. The combined recognition rate for these strains was 43.6 %, while individually it ranged from 17.0 % to 24.5 %. Notably, among the tested phages (FJ3-79, SD1-92L, and FJ4-63), FJ4-63 demonstrated exceptional characteristics in regulating host population dynamics upon infection by exhibiting a shorter latent period (20 min) and a larger burst size (95.99 ± 3.61 PFU/cell). Furthermore, it exhibited relative stability at pH 3–11 and below 60 °C. Transmission electron microscopy and genomic analysis classified phage FJ4-63 belongs to the Dhakavirus genus within the Straboviridae family. Its genome comprised a linear double-stranded DNA measuring 169,669 bp (containing 272 coding sequences) with a GC content of 39.76 %, of which 93 (34.2 %) had known functions, and the remaining 177 were annotated as hypothetical proteins. Additionally, two tRNAs were recognized, possess the “holin-endolysin” lytic system, and no resistance or virulence genes were detected. The phylogenetic tree and average nucleotide identity (ANI) analysis revealed that phage FJ4-63 exhibited the highest similarity to Escherichia phage C6 (679410.1), indicating a consistent close relationship within the same branch. The cocktail comprising three phages exhibits enhanced in vitro bactericidal efficacy compared to a single phage. At high doses with MOI = 100, it rapidly and completely eradicates bacteria within 1 h while significantly reducing bacterial biofilms. All this evidence suggests that lytic phages offer an effective solution for clinical treatment, with a phage cocktail demonstrating greater potential in the alternative management of colistin-resistant E. coli infections.

Universal versus taxon-specific drivers of helminth prevalence and intensity of infection.

Two key epidemiological parameters, prevalence and mean intensity of infection, together capture the abundance of macroparasite populations, the strength of density-dependent effects they experience, their potential impact on host population dynamics and the selective pressures they exert on their hosts. Yet, the drivers of the extensive variation observed in prevalence and mean intensity of infection, even among related parasite taxa infecting related hosts, remain mostly unknown. We performed phylogenetically grounded Bayesian modelling across hundreds of amphibian populations to test the effects of various predictors of prevalence and intensity of infection by six families of helminth parasites. We focused on the potential effects of key host traits and environmental factors pertinent to focal host populations, i.e. the local diversity of the amphibian community and local climatic variables. Our analyses revealed several important determinants of prevalence or intensity of infection in various parasite families, but none applying to all families. Our study uncovered no universal driver of parasite infection levels, even among parasite taxa from the same phylum, or with similar life cycles and transmission modes. Although local variables not considered here may have effects extending across taxa, our findings suggest the need for a taxon-specific approach in any attempt to predict disease dynamics and impacts in the face of environmental and climatic changes.

Influence of weather variables on the host range and population dynamics of guava spiralling whitefly (Aleurodicus dispersus Russell) in Tiruchirappalli district of Tamil Nadu, India

Influence of weather variables on the host range and population dynamics of guava spiralling whitefly (Aleurodicus dispersus Russell) in Tiruchirappalli district of Tamil Nadu, India

Infection thresholds for two interacting pathogens in a wild animal population

We present a model for the dynamics of two interacting pathogen variants in a wild animal host population. Using the next-generation matrix approach we define the invasion threshold for one pathogen variant when the other is already established and at steady state. We then provide explicit criteria for the special cases where: i) the two pathogen variants exclude each other; ii) one variant excludes the other; iii) the population dynamics of hosts infected with both variants are independent of the order of infection; iv) there is no interaction between the variants; and v) one variant enhances transmission of the other.

Acclimation to warmer temperatures can protect host populations from both further heat stress and the potential invasion of pathogens.

Thermal acclimation can provide an essential buffer against heat stress for host populations, while acting simultaneously on various life-history traits that determine population growth. In turn, the ability of a pathogen to invade a host population is intimately linked to these changes via the supply of new susceptible hosts, as well as the impact of warming on its immediate infection dynamics. Acclimation therefore has consequences for hosts and pathogens that extend beyond simply coping with heat stress-governing both population growth trajectories and, as a result, an inherent propensity for a disease outbreak to occur. The impact of thermal acclimation on heat tolerances, however, is rarely considered simultaneously with metrics of both host and pathogen population growth, and ultimately fitness. Using the host Daphnia magna and its bacterial pathogen, we investigated how thermal acclimation impacts host and pathogen performance at both the individual and population scales. We first tested the effect of maternal and direct thermal acclimation on the life-history traits of infected and uninfected individuals, such as heat tolerance, fecundity, and lifespan, as well as pathogen infection success and spore production. We then predicted the effects of each acclimation treatment on rates of host and pathogen population increase by deriving a host's intrinsic growth rate (rm) and a pathogen's basic reproductive number (R0). We found that direct acclimation to warming enhanced a host's heat tolerance and rate of population growth, despite a decline in life-history traits such as lifetime fecundity and lifespan. In contrast, pathogen performance was consistently worse under warming, with within-host pathogen success, and ultimately the potential for disease spread, severely hampered at higher temperatures. Our results suggest that hosts could benefit more from warming than their pathogens, but only by linking multiple individual traits to population processes can the full impact of higher temperatures on host and pathogen population dynamics be realised.

How do host population dynamics impact Lyme disease risk dynamics in theoretical models?

Lyme disease is the most common wildlife-to-human transmitted disease reported in North America. The study of this disease requires an understanding of the ecology of the complex communities of ticks and host species involved in harboring and transmitting this disease. Much of the ecology of this system is well understood, such as the life cycle of ticks, and how hosts are able to support tick populations and serve as disease reservoirs, but there is much to be explored about how the population dynamics of different host species and communities impact disease risk to humans. In this study, we construct a stage-structured, empirically-informed model with host dynamics to investigate how host population dynamics can affect disease risk to humans. The model describes a tick population and a simplified community of three host species, where primary nymph host populations are made to fluctuate on an annual basis, as commonly observed in host populations. We tested the model under different environmental conditions to examine the effect of environment on the interactions of host dynamics and disease risk. Results show that allowing for host dynamics in the model reduces mean nymphal infection prevalence and increases the maximum annual prevalence of nymphal infection and the density of infected nymphs. Effects of host dynamics on disease measures of nymphal infection prevalence were nonlinear and patterns in the effect of dynamics on amplitude in nymphal infection prevalence varied across environmental conditions. These results highlight the importance of further study of the effect of community dynamics on disease risk. This will involve the construction of further theoretical models and collection of robust field data to inform these models. With a more complete understanding of disease dynamics we can begin to better determine how to predict and manage disease risk using these models.

CAN INFECTIOUS DISEASES THAT DO NOT CONFER IMMUNITY ERADICATE HOST SPECIES?

In SIS epidemic models with host population dynamics, two classes of incidence functions are identified for their potential to be linked to host extinction. Mildly upper density-dependent incidences are never linked to host extinction. Incidences that are positively homogeneous of degree one are linked to host extinction for certain parameter constellations and to mere host decline for others; a threshold parameter is identified that separates host decline from host extinction.

Insect population dynamics under Wolbachia-induced cytoplasmic incompatibility: Puzzle more than buzz in Drosophila suzukii.

In theory, the introduction of individuals infected with an incompatible strain of Wolbachia pipientis into a recipient host population should result in the symbiont invasion and reproductive failures caused by cytoplasmic incompatibility (CI). Modelling studies combining Wolbachia invasion and host population dynamics show that these two processes could interact to cause a transient population decline and, in some conditions, extinction. However, these effects could be sensitive to density dependence, with the Allee effect increasing the probability of extinction, and competition reducing the demographic impact of CI. We tested these predictions with laboratory experiments in the fruit fly Drosophila suzukii and the transinfected Wolbachia strain wTei. Surprisingly, the introduction of wTei into D. suzukii populations at carrying capacity did not result in the expected wTei invasion and transient population decline. In parallel, we found no Allee effect but strong negative density dependence. From these results, we propose that competition interacts in an antagonistic way with Wolbachia-induced cytoplasmic incompatibility on insect population dynamics. If future models and data support this hypothesis, pest management strategies using Wolbachia-induced CI should target populations with negligible competition but a potential Allee effect, for instance at the beginning of the reproductive season.

The phoretic mite (Arachnida: Acari) assemblage of the Douglas-fir beetle (Coleoptera: Curculionidae) in central British Columbia, Canada

Abstract The phoretic mite assemblage of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (Coleoptera: Curculionidae), has not been thoroughly documented. Phoretic mites can impact fitness and population dynamics of hosts; documenting a mite assemblage may provide information on their ecological roles. We caught Douglas-fir beetles in central British Columbia, Canada, and sorted associated mites into morphospecies. Representatives of the morphospecies were DNA barcoded (CO1 barcode region), indicating at least nine operational taxonomic units (OTUs). Representatives of all OTUs were slide-mounted and morphologically identified. There was a mean of 50.5 ± 4.7 mites per beetle, with both females and males carrying similar numbers of most mite species, except for OTU B1, which was found in higher numbers on females. OTU B1, Parawinterschmidtia furnissi (Woodring) (Astigmata: Winterschmidtiidae), was found in substantially higher numbers than all other OTUs and was always clustered in large aggregations in an anterior pocket on the beetles’ subelytral surface. When this OTU was removed from the calculation, the mean number dropped to 1.3 ± 0.2 mites per beetle. The consistent high numbers of OTU B1 in conjunction with its consistent anatomical aggregation suggests an important interaction between this particular mite species and the Douglas-fir beetle.

A computational framework for resolving the microbiome diversity conundrum

Recent empirical studies offer conflicting findings regarding the relation between host fitness and the composition of its microbiome, a conflict which we term ‘the microbial β- diversity conundrum’. The microbiome is crucial for host wellbeing and survival. Surprisingly, different healthy individuals’ microbiome compositions, even in the same population, often differ dramatically, contrary to the notion that a vital trait should be highly conserved. Moreover, gnotobiotic individuals exhibit highly deleterious phenotypes, supporting the view that the microbiome is paramount to host fitness. However, the introduction of almost arbitrarily selected microbiota into the system often achieves a significant rescue effect of the deleterious phenotypes. This is true even for microbiota from soil or phylogenetically distant host species, highlighting an apparent paradox. We suggest several solutions to the paradox using a computational framework, simulating the population dynamics of hosts and their microbiomes over multiple generations. The answers invoke factors such as host population size, the specific mode of microbial contribution to host fitness, and typical microbiome richness, offering solutions to the conundrum by highlighting scenarios where even when a host’s fitness is determined in full by its microbiome composition, this composition has little effect on the natural selection dynamics of the population.

Tick infestation in spur-thighed tortoise population: a pilot study for unraveling epidemiological patterns and demographic consequences

Ectoparasites, such as ticks, modulate host population dynamics by impacting demographic traits. They transmit infectious agents among their hosts, posing a critical threat to animal and public health. This study aimed to characterize and analyze the Hyalomma aegyptium infestation on one of its main hosts, the spur-thighed tortoise, its effects on demographic traits, and to determine the diversity of infectious agents present in both ticks and tortoises in the Maamora forest (northwestern Morocco). Our results show that 100% of the tortoises were parasitized by adult ticks in spring, an infestation intensity of 4 ticks/tortoise (5.1 and 3.6 ticks/tortoise in males and females, respectively; 4.2 and 3.3 ticks/tortoise in gravid and non-gravid females, respectively) and an abundance ranging from 1 to 12. Although without significant differences, male tortoises had higher tick abundances than females. The interaction of tortoise sex and body condition was significantly related to tick abundance, male body condition decreased with higher tick abundance in contrast to females. Nevertheless, the interaction of body condition and reproductive stage of females was not significantly related to tick abundance. Gravid females were significantly associated with tick abundance, showing a slightly higher infestation than non-gravid females. Molecular analysis of pooled tick samples revealed the presence of Ehrlichia ewingii, Candidatus Midichloria mitochondrii, and Rickettsia africae, with a minimum infection rate of 0.61 to 1.84%. However, blood sample analysis of the tortoises was infectious agent-free, pinpointing a lack of significant health problems. Given the possible effect on the transmission of zoonotic diseases by spur-thighed tortoises associated with their frequent collection as pets, it should be surveyed to control possible human health problems. In conservation terms, as a long-lived species, the role of tick infestation in demographic traits might be included in the management and conservation programs of spur-thighed tortoises.

Long-term survey discloses a shift in the dynamics pattern of an emerging disease of cockles Cerastoderma edule, marteiliosis, and raises hypothesis to explain it

Drivers of marine disease outbreaks are poorly understood in spite of their growing impact. We present here results from a unique case study examining how cockles Cerastoderma edule have responded to the introduction of the novel protistan Marteilia cochillia, which led in 2012 to cockle fishery collapse in Galician rias. Based on intensive survey for eight years (2011-2019) of two affected shellfish beds, inner and outer in the Ría de Arousa, involving monthly evaluation of cockle health status and estimation of mortality, detailed information is provided of the declining impact of marteiliosis over a wild cockle population with evidence suggesting its increasing resistance. Disease dynamics involved an annual “breaking wave” of prevalence and subsequent cockle mass mortality, causing the nearly extinction of every recruited cohort. A shift in this pattern, from a severe epidemic towards an endemic profile was observed in the inner shellfish bed since the cohort recruited in 2016, suggesting the hypothesis of increasing marteiliosis resistance through natural selection. Risk factors that may contribute to trigger marteiliosis outbreaks were analysed. Host age and sex did not influence susceptibility to marteiliosis. No clear relationships between environmental conditions (temperature, salinity and upwelling index) or cockle density and disease dynamics were found. Spatial differences in disease dynamics could be due to differences in the abundance of infective stages hypothetically linked to spatial differences in the population dynamics of a putative planktonic intermediate host. All these findings have potential implications for the management of diseased populations.

Pollinator attraction in the Ficus deltoidea complex: Varietal specificity in a fig wasp that likes to stay close to home

Species boundaries are maintained by limitations on gene flow between taxa. In flowering plants pollinator specificity can strongly influence gene flow patterns and facilitate speciation. Fig trees are species rich and ecologically significant plants. It was once believed that each species had its own unique pollinator fig wasp, but numerous exceptions are now known. The dioecious Ficus deltoidea complex is distributed across southern South-East Asia with 13 recognised varieties of uncertain status, seven of which are found in Peninsular Malaysia. We investigated the host preferences of one of their Blastophaga pollinators, reared from the epiphytic F. deltoidea var. angustifolia. Our series of experimental manipulations using free-flying fig wasps and figs on host trees showed that male figs were preferred, that only their natal variety was attractive and that pollinators only dispersed from their natal trees if no suitable figs were present there. Fig wasps can only reproduce in male hosts, so preferred entry to male figs has clear advantages for them, as does their reluctance to disperse from natal trees. This behaviour is likely to reduce seed set on female plants, with potential consequences for host population dynamics. The extreme specificity of the Blastophaga sp. suggests gene flow between varieties of F. deltoidea is low or absent and that different varieties may be different biological species.

Hantavirus in Panama: Twenty Years of Epidemiological Surveillance Experience.

Twenty years have passed since the emergence of hantavirus zoonosis in Panama at the beginning of this millennium. We provide an overview of epidemiological surveillance of hantavirus disease (hantavirus pulmonary syndrome and hantavirus fever) during the period 1999-2019 by including all reported and confirmed cases according to the case definition established by the health authority. Our findings reveal that hantavirus disease is a low-frequency disease, affecting primarily young people, with a relatively low case-fatality rate compared to other hantaviruses in the Americas (e.g., ANDV and SNV). It presents an annual variation with peaks every 4-5 years and an interannual variation influenced by agricultural activities. Hantavirus disease is endemic in about 27% of Panama, which corresponds to agroecological conditions that favor the population dynamics of the rodent host, Oligoryzomys costaricensis and the virus (Choclo orthohantavirus) responsible for hantavirus disease. However, this does not rule out the existence of other endemic areas to be characterized. Undoubtedly, decentralization of the laboratory test and dissemination of evidence-based surveillance guidelines and regulations have standardized and improved diagnosis, notification at the level of the primary care system, and management in intensive care units nationwide.

Contact-number-driven virus evolution: A multi-level modeling framework for the evolution of acute or persistent RNA virus infection.

Viruses evolve in infected host populations, and host population dynamics affect viral evolution. RNA viruses with a short duration of infection and a high peak viral load, such as SARS-CoV-2, are maintained in human populations. By contrast, RNA viruses characterized by a long infection duration and a low peak viral load (e.g., borna disease virus) can be maintained in nonhuman populations, and the process of the evolution of persistent viruses has rarely been explored. Here, using a multi-level modeling approach including both individual-level virus infection dynamics and population-scale transmission, we consider virus evolution based on the host environment, specifically, the effect of the contact history of infected hosts. We found that, with a highly dense contact history, viruses with a high virus production rate but low accuracy are likely to be optimal, resulting in a short infectious period with a high peak viral load. In contrast, with a low-density contact history, viral evolution is toward low virus production but high accuracy, resulting in long infection durations with low peak viral load. Our study sheds light on the origin of persistent viruses and why acute viral infections but not persistent virus infection tends to prevail in human society.