Parasite spread in experimental metapopulations: resistance, tolerance and host competence

Abstract West Nile virus (WNV) was first identified in North America almost 20 yr ago. In that time, WNV has crossed the continent and established enzootic transmission cycles, resulting in intermittent outbreaks of human disease that have largely been linked with climatic variables and waning avian seroprevalence. During the transcontinental dissemination of WNV, the original genotype has been displaced by two principal extant genotypes which contain an envelope mutation that has been associated with enhanced vector competence by Culex pipiens L. (Diptera: Culicidae) and Culex tarsalis Coquillett vectors. Analyses of retrospective avian host competence data generated using the founding NY99 genotype strain have demonstrated a steady reduction in viremias of house sparrows over time. Reciprocally, the current genotype strains WN02 and SW03 have demonstrated an inverse correlation between house sparrow viremia magnitude and the time since isolation. These data collectively indicate that WNV has evolved for increased avian viremia while house sparrows have evolved resistance to the virus such that the relative host competence has remained constant. Intrahost analyses of WNV evolution demonstrate that selection pressures are avian species-specific and purifying selection is greater in individual birds compared with individual mosquitoes, suggesting that the avian adaptive and/or innate immune response may impose a selection pressure on WNV. Phylogenomic, experimental evolutionary systems, and models that link viral evolution with climate, host, and vector competence studies will be needed to identify the relative effect of different selective and stochastic mechanisms on viral phenotypes and the capacity of newly evolved WNV genotypes for transmission in continuously changing landscapes.

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Viremia profiles and host competence index for West Nile virus (Flavivirus, Flaviviridae) in three autochthonous birds species from Argentina

Journal of Ornithology ◽

10.1007/s10336-010-0538-4 ◽

2010 ◽

Vol 152 (1) ◽

pp. 21-25 ◽

Cited By ~ 7

Author(s):

Luis Adrián Diaz ◽

Fernando Sebastián Flores ◽

Marta Silvia Contigiani

Keyword(s):

West Nile Virus ◽

West Nile ◽

Host Competence

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Assessment of data on vector and host competence for Japanese encephalitis virus: A systematic review of the literature

Preventive Veterinary Medicine ◽

10.1016/j.prevetmed.2018.03.018 ◽

2018 ◽

Vol 154 ◽

pp. 71-89 ◽

Cited By ~ 7

Author(s):

Ana R.S. Oliveira ◽

Erin Strathe ◽

Luciana Etcheverry ◽

Lee W. Cohnstaedt ◽

D. Scott McVey ◽

...

Keyword(s):

Systematic Review ◽

Japanese Encephalitis Virus ◽

Japanese Encephalitis ◽

Encephalitis Virus ◽

Review Of The Literature ◽

Host Competence

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Stress hormones predict a host superspreader phenotype in the West Nile virus system

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2017.1090 ◽

2017 ◽

Vol 284 (1859) ◽

pp. 20171090 ◽

Cited By ~ 21

Author(s):

Stephanie S. Gervasi ◽

Sarah C. Burgan ◽

Erik Hofmeister ◽

Thomas R. Unnasch ◽

Lynn B. Martin

Keyword(s):

West Nile Virus ◽

Stress Hormones ◽

Activity Levels ◽

West Nile ◽

Viral Loads ◽

Pathogen Dynamics ◽

Host Competence ◽

Host Mortality ◽

Host Metabolism ◽

Virus System

Glucocorticoid stress hormones, such as corticosterone (CORT), have profound effects on the behaviour and physiology of organisms, and thus have the potential to alter host competence and the contributions of individuals to population- and community-level pathogen dynamics. For example, CORT could alter the rate of contacts among hosts, pathogens and vectors through its widespread effects on host metabolism and activity levels. CORT could also affect the intensity and duration of pathogen shedding and risk of host mortality during infection. We experimentally manipulated songbird CORT, asking how CORT affected behavioural and physiological responses to a standardized West Nile virus (WNV) challenge. Although all birds became infected after exposure to the virus, only birds with elevated CORT had viral loads at or above the infectious threshold. Moreover, though the rate of mortality was faster in birds with elevated CORT compared with controls, most hosts with elevated CORT survived past the day of peak infectiousness. CORT concentrations just prior to inoculation with WNV and anti-inflammatory cytokine concentrations following viral exposure were predictive of individual duration of infectiousness and the ability to maintain physical performance during infection (i.e. tolerance), revealing putative biomarkers of competence. Collectively, our results suggest that glucocorticoid stress hormones could directly and indirectly mediate the spread of pathogens.

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General Microbiota of the Soft Tick Ornithodoros turicata Parasitizing the Bolson Tortoise (Gopherus flavomarginatus) in the Mapimi Biosphere Reserve, Mexico

Biology ◽

10.3390/biology9090275 ◽

2020 ◽

Vol 9 (9) ◽

pp. 275

Author(s):

Sergio I. Barraza-Guerrero ◽

César A. Meza-Herrera ◽

Cristina García-De la Peña ◽

Vicente H. González-Álvarez ◽

Felipe Vaca-Paniagua ◽

...

Keyword(s):

Defense Mechanisms ◽

Chihuahuan Desert ◽

Biosphere Reserve ◽

Abundant Species ◽

Soft Tick ◽

Operational Taxonomic Units ◽

Bacterial Microbiota ◽

Host Competence ◽

Mapimí Biosphere Reserve ◽

Zoonotic Bacteria

The general bacterial microbiota of the soft tick Ornithodoros turicata found on Bolson tortoises (Gopherus flavomarginatus) were analyzed using next generation sequencing. The main aims of the study were to establish the relative abundance of bacterial taxa in the tick, and to document the presence of potentially pathogenic species for this tortoise, other animals, and humans. The study was carried-out in the Mapimi Biosphere Reserve in the northern-arid part of Mexico. Bolson tortoises (n = 45) were inspected for the presence of soft ticks, from which 11 tortoises (24.4%) had ticks in low loads (1–3 ticks per individual). Tick pools (five adult ticks each) were analyzed through 16S rRNA V3–V4 region amplification in a MiSeq Illumina, using EzBioCloud as a taxonomical reference. The operational taxonomic units (OTUs) revealed 28 phyla, 84 classes, 165 orders, 342 families, 1013 genera, and 1326 species. The high number of taxa registered for O. turicata may be the result of the variety of hosts that this tick parasitizes as they live inside G. flavomarginatus burrows. While the most abundant phyla were Proteobacteria, Actinobacteria, and Firmicutes, the most abundant species were two endosymbionts of ticks (Midichloria-like and Coxiella-like). Two bacteria documented as pathogenic to Gopherus spp. were registered (Mycoplasma spp. and Pasteurella testudinis). The bovine and ovine tick-borne pathogens A. marginale and A. ovis, respectively, were recorded, as well as the zoonotic bacteria A. phagocytophilum,Coxiella burnetii, and Neoehrlichia sp. Tortoises parasitized with O. turicata did not show evident signs of disease, which could indicate a possible ecological role as a reservoir that has yet to be demonstrated. In fact, the defense mechanisms of this tortoise against the microorganisms transmitted by ticks during their feeding process are still unknown. Future studies on soft ticks should expand our knowledge about what components of the microbiota are notable across multiple host–microbe dynamics. Likewise, studies are required to better understand the host competence of this tortoise, considered the largest terrestrial reptile in North America distributed throughout the Chihuahuan Desert since the late Pleistocene.

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