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Prakash A, Fenner F, Shit B, Salminen TS, Monteith KM, Khan I, Vale PF. IMD-mediated innate immune priming increases Drosophila survival and reduces pathogen transmission. PLoS Pathog 2024; 20:e1012308. [PMID: 38857285 PMCID: PMC11192365 DOI: 10.1371/journal.ppat.1012308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Revised: 06/21/2024] [Accepted: 05/31/2024] [Indexed: 06/12/2024] Open
Abstract
Invertebrates lack the immune machinery underlying vertebrate-like acquired immunity. However, in many insects past infection by the same pathogen can 'prime' the immune response, resulting in improved survival upon reinfection. Here, we investigated the mechanistic basis and epidemiological consequences of innate immune priming in the fruit fly Drosophila melanogaster when infected with the gram-negative bacterial pathogen Providencia rettgeri. We find that priming in response to P. rettgeri infection is a long-lasting and sexually dimorphic response. We further explore the epidemiological consequences of immune priming and find it has the potential to curtail pathogen transmission by reducing pathogen shedding and spread. The enhanced survival of individuals previously exposed to a non-lethal bacterial inoculum coincided with a transient decrease in bacterial loads, and we provide strong evidence that the effect of priming requires the IMD-responsive antimicrobial-peptide Diptericin-B in the fat body. Further, we show that while Diptericin B is the main effector of bacterial clearance, it is not sufficient for immune priming, which requires regulation of IMD by peptidoglycan recognition proteins. This work underscores the plasticity and complexity of invertebrate responses to infection, providing novel experimental evidence for the effects of innate immune priming on population-level epidemiological outcomes.
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Affiliation(s)
- Arun Prakash
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Florence Fenner
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | | | - Tiina S. Salminen
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Katy M. Monteith
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | | | - Pedro F. Vale
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
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2
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Rovenolt FH, Tate AT. The Impact of Coinfection Dynamics on Host Competition and Coexistence. Am Nat 2022; 199:91-107. [DOI: 10.1086/717180] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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3
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Host exposure history modulates the within-host advantage of virulence in a songbird-bacterium system. Sci Rep 2019; 9:20348. [PMID: 31889059 PMCID: PMC6937340 DOI: 10.1038/s41598-019-56540-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Accepted: 12/14/2019] [Indexed: 11/08/2022] Open
Abstract
The host immune response can exert strong selective pressure on pathogen virulence, particularly when host protection against reinfection is incomplete. Since emerging in house finch populations, the bacterial pathogen Mycoplasma gallisepticum (MG) has been increasing in virulence. Repeated exposure to low-doses of MG, a proxy for what birds likely experience while foraging, provides significant but incomplete protection against reinfection. Here we sought to determine if the within-host, pathogen load advantage of high virulence is mediated by the degree of prior pathogen exposure, and thus the extent of immune memory. We created variation in host immunity by experimentally inoculating wild-caught, MG-naïve house finches with varying doses and number of exposures of a single pathogen strain of intermediate virulence. Following recovery from priming exposures, individuals were challenged with one of three MG strains of distinct virulence. We found that the quantitative pathogen load advantage of high virulence was strongly mediated by the degree of prior exposure. The greatest within-host load advantage of virulence was seen in hosts given low-dose priming exposures, akin to what many house finches likely experience while foraging. Our results show that incomplete host immunity produced by low-level prior exposure can create a within-host environment that favors more virulent pathogens.
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4
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Khan I, Prakash A, Agashe D. Pathogen susceptibility and fitness costs explain variation in immune priming across natural populations of flour beetles. J Anim Ecol 2019; 88:1332-1342. [DOI: 10.1111/1365-2656.13030] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 05/10/2019] [Indexed: 01/03/2023]
Affiliation(s)
- Imroze Khan
- National Centre for Biological Sciences, Tata Institute of Fundamental Research GKVK Bangalore India
- Ashoka University Sonepat Rai India
| | - Arun Prakash
- National Centre for Biological Sciences, Tata Institute of Fundamental Research GKVK Bangalore India
| | - Deepa Agashe
- National Centre for Biological Sciences, Tata Institute of Fundamental Research GKVK Bangalore India
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5
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Abstract
A central challenge in the fields of evolutionary immunology and disease ecology is to understand the causes and consequences of natural variation in host susceptibility to infectious diseases. As hosts progress from birth to death in the wild, they are exposed to a wide variety of microorganisms that influence their physical condition, immune system maturation, and susceptibility to concurrent and future infection. A central challenge in the fields of evolutionary immunology and disease ecology is to understand the causes and consequences of natural variation in host susceptibility to infectious diseases. As hosts progress from birth to death in the wild, they are exposed to a wide variety of microorganisms that influence their physical condition, immune system maturation, and susceptibility to concurrent and future infection. Thus, multiple exposures to the same or different microbes can be important environmental drivers of host immunological variation and immune priming. In this perspective, I discuss parasite infracommunity interactions and their imprint on host immunity in space and time. I further consider feedbacks from parasite community dynamics within individual hosts on the transmission of disease at higher levels of biological organization and highlight the promise of systems biology approaches, using flour beetles as an example, for studying the role of multiple infections on immunological variation in wild populations.
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6
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Vigneron A, Jehan C, Rigaud T, Moret Y. Immune Defenses of a Beneficial Pest: The Mealworm Beetle, Tenebrio molitor. Front Physiol 2019; 10:138. [PMID: 30914960 PMCID: PMC6422893 DOI: 10.3389/fphys.2019.00138] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Accepted: 02/07/2019] [Indexed: 12/04/2022] Open
Abstract
The mealworm beetle, Tenebrio molitor, is currently considered as a pest when infesting stored grains or grain products. However, mealworms are now being promoted as a beneficial insect because their high nutrient content makes them a viable food source and because they are capable of degrading polystyrene and plastic waste. These attributes make T. molitor attractive for mass rearing, which may promote disease transmission within the insect colonies. Disease resistance is of paramount importance for both the control and the culture of mealworms, and several biotic and abiotic environmental factors affect the success of their anti-parasitic defenses, both positively and negatively. After providing a detailed description of T. molitor's anti-parasitic defenses, we review the main biotic and abiotic environmental factors that alter their presentation, and we discuss their implications for the purpose of controlling the development and health of this insect.
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Affiliation(s)
- Aurélien Vigneron
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, United States
| | - Charly Jehan
- UMR CNRS 6282 BioGéoSciences, Équipe Écologie Évolutive, Université Bourgogne-Franche Comté, Dijon, France
| | - Thierry Rigaud
- UMR CNRS 6282 BioGéoSciences, Équipe Écologie Évolutive, Université Bourgogne-Franche Comté, Dijon, France
| | - Yannick Moret
- UMR CNRS 6282 BioGéoSciences, Équipe Écologie Évolutive, Université Bourgogne-Franche Comté, Dijon, France
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7
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Kutzer MAM, Kurtz J, Armitage SAO. A multi-faceted approach testing the effects of previous bacterial exposure on resistance and tolerance. J Anim Ecol 2019; 88:566-578. [PMID: 30697699 PMCID: PMC6487967 DOI: 10.1111/1365-2656.12953] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Accepted: 12/03/2018] [Indexed: 01/03/2023]
Abstract
Hosts can alter their strategy towards pathogens during their lifetime; that is, they can show phenotypic plasticity in immunity or life history. Immune priming is one such example, where a previous encounter with a pathogen confers enhanced protection upon secondary challenge, resulting in reduced pathogen load (i.e., resistance) and improved host survival. However, an initial encounter might also enhance tolerance, particularly to less virulent opportunistic pathogens that establish persistent infections. In this scenario, individuals are better able to reduce the negative fecundity consequences that result from a high pathogen burden. Finally, previous exposure may also lead to life‐history adjustments, such as terminal investment into reproduction. Using different Drosophila melanogaster host genotypes and two bacterial pathogens, Lactococcus lactis and Pseudomonas entomophila, we tested whether previous exposure results in resistance or tolerance and whether it modifies immune gene expression during an acute‐phase infection (one day post‐challenge). We then asked whether previous pathogen exposure affects chronic‐phase pathogen persistence and longer‐term survival (28 days post‐challenge). We predicted that previous exposure would increase host resistance to an early stage bacterial infection while it might come at a cost to host fecundity tolerance. We reasoned that resistance would be due in part to stronger immune gene expression after challenge. We expected that previous exposure would improve long‐term survival, that it would reduce infection persistence, and we expected to find genetic variation in these responses. We found that previous exposure to P. entomophila weakened host resistance to a second infection independent of genotype and had no effect on immune gene expression. Fecundity tolerance showed genotypic variation but was not influenced by previous exposure. However, L. lactis persisted as a chronic infection, whereas survivors cleared the more pathogenic P. entomophila infection. To our knowledge, this is the first study that addresses host tolerance to bacteria in relation to previous exposure, taking a multi‐faceted approach to address the topic. Our results suggest that previous exposure comes with transient costs to resistance during the early stage of infection in this host–pathogen system and that infection persistence may be bacterium‐specific.
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Affiliation(s)
- Megan A M Kutzer
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany.,IST Austria, Klosterneuburg, Austria
| | - Joachim Kurtz
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
| | - Sophie A O Armitage
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany.,Institute of Biology, Freie Universität Berlin, Berlin, Germany
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Schulz NKE, Sell MP, Ferro K, Kleinhölting N, Kurtz J. Transgenerational Developmental Effects of Immune Priming in the Red Flour Beetle Tribolium castaneum. Front Physiol 2019; 10:98. [PMID: 30837885 PMCID: PMC6389831 DOI: 10.3389/fphys.2019.00098] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Accepted: 01/28/2019] [Indexed: 11/13/2022] Open
Abstract
Immune priming, the increased chance to survive a secondary encounter with a pathogen, has been described for many invertebrate species, which lack the classical adaptive immune system of vertebrates. Priming can be specific even for closely related bacterial strains, last up to the entire lifespan of an individual, and in some species, it can also be transferred to the offspring and is then called transgenerational immune priming (TGIP). In the red flour beetle Tribolium castaneum, a pest of stored grains, TGIP has even been shown to be transferred paternally after injection of adult beetles with heat-killed Bacillus thuringiensis. Here we studied whether TGIP in T. castaneum is also transferred to the second filial generation, whether it can also occur after oral and injection priming of larvae and whether it has effects on offspring development. We found that paternal priming with B. thuringiensis does not only protect the first but also the second offspring generation. Also, fitness costs of the immune priming became apparent, when the first filial generation produced fewer offspring. Furthermore, we used two different routes of exposure to prime larvae, either by injecting them with heat-killed bacteria or orally feeding them B. thuringiensis spore culture supernatant. Neither of the parental larval priming methods led to any direct benefits regarding offspring resistance. However, the injections slowed down development of the injected individuals, while oral priming with both a pathogenic and a non-pathogenic strain of B. thuringiensis delayed offspring development. The long-lasting transgenerational nature of immune priming and its impact on offspring development indicate that potentially underlying epigenetic modifications might be stable over several generations. Therefore, this form of phenotypic plasticity might impact pest control and should be considered when using products of bacterial origin against insects.
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Affiliation(s)
- Nora K E Schulz
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
| | - Marie Pauline Sell
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
| | - Kevin Ferro
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
| | - Nico Kleinhölting
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
| | - Joachim Kurtz
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
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9
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Mondotte JA, Gausson V, Frangeul L, Blanc H, Lambrechts L, Saleh MC. Immune priming and clearance of orally acquired RNA viruses in Drosophila. Nat Microbiol 2018; 3:1394-1403. [PMID: 30374170 DOI: 10.1038/s41564-018-0265-9] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 09/06/2018] [Indexed: 12/17/2022]
Abstract
Immune responses in insects are differentially triggered depending on the infection route used by the pathogen. In most studies involving Drosophila melanogaster and viruses, infection is done by injection, while oral infection, which is probably the most common route of viral entry in nature, remains unexplored. Here, we orally infected adults and larvae from wild-type and RNA interference (RNAi) mutant flies with different RNA viruses. We found that, in contrast with what is observed following virus injection, oral infections initiated at larval or adult stages are cleared in adult flies. Virus elimination occurred despite a larger infectious dose than for injected flies and evidence of viral replication. RNAi mutant flies suffered greater mortality relative to wild-type flies following oral infection, but they also eliminated the virus, implying that RNAi is not essential for viral clearance and that other immune mechanisms act during oral infections. We further showed that information of infection by RNA viruses acquired orally leaves a trace under a DNA form, which confers protection against future reinfection by the same virus. Together, this work presents evidence of clearance and immune priming for RNA viruses in insects and challenges the current view of antiviral immunity in insects.
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Affiliation(s)
- Juan A Mondotte
- Institut Pasteur, Viruses and RNA Interference Unit, Department of Virology, CNRS Unité Mixte de Recherche 3569, Paris, France
| | - Valérie Gausson
- Institut Pasteur, Viruses and RNA Interference Unit, Department of Virology, CNRS Unité Mixte de Recherche 3569, Paris, France
| | - Lionel Frangeul
- Institut Pasteur, Viruses and RNA Interference Unit, Department of Virology, CNRS Unité Mixte de Recherche 3569, Paris, France
| | - Hervé Blanc
- Institut Pasteur, Viruses and RNA Interference Unit, Department of Virology, CNRS Unité Mixte de Recherche 3569, Paris, France
| | - Louis Lambrechts
- Institut Pasteur, Insect-Virus Interactions Group, Department of Genomes and Genetics, CNRS Unité Mixte de Recherche 2000, Paris, France
| | - Maria-Carla Saleh
- Institut Pasteur, Viruses and RNA Interference Unit, Department of Virology, CNRS Unité Mixte de Recherche 3569, Paris, France.
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10
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Khan I, Prakash A, Agashe D. Experimental evolution of insect immune memory versus pathogen resistance. Proc Biol Sci 2018; 284:rspb.2017.1583. [PMID: 29237849 DOI: 10.1098/rspb.2017.1583] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2017] [Accepted: 11/13/2017] [Indexed: 12/13/2022] Open
Abstract
Under strong pathogen pressure, insects often evolve resistance to infection. Many insects are also protected via immune memory (immune priming), whereby sublethal exposure to a pathogen enhances survival after secondary infection. Theory predicts that immune memory should evolve when the pathogen is highly virulent, or when pathogen exposure is relatively rare. However, there are no empirical tests of these hypotheses, and the adaptive benefits of immune memory relative to direct resistance against a pathogen are poorly understood. To determine the selective pressures and ecological conditions that shape immune evolution, we imposed strong pathogen selection on flour beetle (Tribolium castaneum) populations, infecting them with Bacillus thuringiensis (Bt) for 11 generations. Populations injected first with heat-killed and then live Bt evolved high basal resistance against multiple Bt strains. By contrast, populations injected only with a high dose of live Bt evolved a less effective but strain-specific priming response. Control populations injected with heat-killed Bt did not evolve priming; and in the ancestor, priming was effective only against a low Bt dose. Intriguingly, one replicate population first evolved priming and subsequently evolved basal resistance, suggesting the potential for dynamic evolution of different immune strategies. Our work is the first report showing that pathogens can select for rapid modulation of insect priming ability, allowing hosts to evolve divergent immune strategies (generalized resistance versus specific immune memory) with potentially distinct mechanisms.
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Affiliation(s)
- Imroze Khan
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bellary Road, Bangalore 560065, India .,Ashoka University, Plot No. 2, Rajiv Gandhi Education City, National Capital Region, P.O. Rai, Sonepat, Haryana 131029, India
| | - Arun Prakash
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bellary Road, Bangalore 560065, India
| | - Deepa Agashe
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bellary Road, Bangalore 560065, India
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11
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Fleming-Davies AE, Williams PD, Dhondt AA, Dobson AP, Hochachka WM, Leon AE, Ley DH, Osnas EE, Hawley DM. Incomplete host immunity favors the evolution of virulence in an emergent pathogen. Science 2018; 359:1030-1033. [PMID: 29496878 PMCID: PMC6317705 DOI: 10.1126/science.aao2140] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Accepted: 01/12/2018] [Indexed: 12/21/2022]
Abstract
Immune memory evolved to protect hosts from reinfection, but incomplete responses that allow future reinfection may inadvertently select for more-harmful pathogens. We present empirical and modeling evidence that incomplete immunity promotes the evolution of higher virulence in a natural host-pathogen system. We performed sequential infections of house finches with Mycoplasma gallisepticum strains of various levels of virulence. Virulent bacterial strains generated stronger host protection against reinfection than less virulent strains and thus excluded less virulent strains from infecting previously exposed hosts. In a two-strain model, the resulting fitness advantage selected for an almost twofold increase in pathogen virulence. Thus, the same immune systems that protect hosts from infection can concomitantly drive the evolution of more-harmful pathogens in nature.
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Affiliation(s)
- Arietta E Fleming-Davies
- Department of Biology, University of San Diego, San Diego, CA 92110, USA.
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA
- Department of Biology, Radford University, Radford, VA 24141, USA
| | - Paul D Williams
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
| | - André A Dhondt
- Lab of Ornithology, Cornell University, Ithaca, NY 14850, USA
| | - Andrew P Dobson
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
- Santa Fe Institute, Santa Fe, NM 87501, USA
| | | | - Ariel E Leon
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA
| | - David H Ley
- Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - Erik E Osnas
- U.S. Fish and Wildlife Service, Anchorage, AK 99503, USA
| | - Dana M Hawley
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA.
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12
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Leon AE, Hawley DM. Host Responses to Pathogen Priming in a Natural Songbird Host. ECOHEALTH 2017; 14:793-804. [PMID: 28766063 PMCID: PMC5726927 DOI: 10.1007/s10393-017-1261-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 06/14/2017] [Accepted: 06/14/2017] [Indexed: 06/07/2023]
Abstract
Hosts in free-living populations can experience substantial variation in the frequency and dose of pathogen exposure, which can alter disease progression and protection from future exposures. In the house finch-Mycoplasma gallisepticum (MG) system, the pathogen is primarily transmitted via bird feeders, and some birds may be exposed to frequent low doses of MG while foraging. Here we experimentally determined how low dose, repeated exposures of house finches to MG influence host responses and protection from secondary high-dose challenge. MG-naive house finches were given priming exposures that varied in dose and total number. After quantifying host responses to priming exposures, all birds were given a secondary high-dose challenge to assess immunological protection. Dose, but not the number of exposures, significantly predicted both infection and disease severity following priming exposure. Furthermore, individuals given higher priming doses showed stronger protection upon secondary, high-dose challenge. However, even single low-dose exposures to MG, a proxy for what some birds likely experience in the wild while feeding, provided significant protection against a high-dose challenge. Our results suggest that bird feeders, which serve as sources of infection in the wild, may in some cases act as "immunizers," with important consequences for disease dynamics.
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Affiliation(s)
- Ariel E Leon
- Department of Biological Sciences, Virginia Tech, 2119 Derring Hall (0406), Blacksburg, VA, 24061, USA.
| | - Dana M Hawley
- Department of Biological Sciences, Virginia Tech, 2119 Derring Hall (0406), Blacksburg, VA, 24061, USA
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13
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Kamiya T, Greischar MA, Mideo N. Epidemiological consequences of immune sensitisation by pre-exposure to vector saliva. PLoS Negl Trop Dis 2017; 11:e0005956. [PMID: 28991904 PMCID: PMC5648264 DOI: 10.1371/journal.pntd.0005956] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 10/19/2017] [Accepted: 09/12/2017] [Indexed: 11/25/2022] Open
Abstract
Blood-feeding arthropods—like mosquitoes, sand flies, and ticks—transmit many diseases that impose serious public health and economic burdens. When a blood-feeding arthropod bites a mammal, it injects saliva containing immunogenic compounds that facilitate feeding. Evidence from Leishmania, Plasmodium and arboviral infections suggests that the immune responses elicited by pre-exposure to arthropod saliva can alter disease progression if the host later becomes infected. Such pre-sensitisation of host immunity has been reported to both exacerbate and limit infection symptoms, depending on the system in question, with potential implications for recovery. To explore if and how immune pre-sensitisation alters the effects of vector control, we develop a general model of vector-borne disease. We show that the abundance of pre-sensitised infected hosts should increase when control efforts moderately increase vector mortality rates. If immune pre-sensitisation leads to more rapid clearance of infection, increasing vector mortality rates may achieve greater than expected disease control. However, when immune pre-sensitisation prolongs the duration of infection, e.g., through mildly symptomatic cases for which treatment is unlikely to be sought, vector control can actually increase the total number of infected hosts. The rising infections may go unnoticed unless active surveillance methods are used to detect such sub-clinical individuals, who could provide long-lasting reservoirs for transmission and suffer long-term health consequences of those sub-clinical infections. Sensitivity analysis suggests that these negative consequences could be mitigated through integrated vector management. While the effect of saliva pre-exposure on acute symptoms is well-studied for leishmaniasis, the immunological and clinical consequences are largely uncharted for other vector-parasite-host combinations. We find a large range of plausible epidemiological outcomes, positive and negative for public health, underscoring the need to quantify how immune pre-sensitisation modulates recovery and transmission rates in vector-borne diseases. Many diseases of health and economic importance are transmitted by arthropod vectors, like mosquitoes, sand flies, and ticks. When a blood-feeding arthropod bites a mammal, it injects saliva containing compounds that facilitate feeding. The immune responses elicited by previous exposure to vector saliva can alter disease severity if the host later becomes infected. Such pre-sensitisation of host immunity has been linked to either exacerbation or mitigation of symptoms in a number of disease systems. We develop a general model of vector-borne disease to examine how vector control efforts alter the frequency of immune pre-sensitisation and thus change the epidemiological impact of control. We show that the abundance of pre-sensitised infected hosts should increase when control efforts moderately increase vector mortality rates. When immune pre-sensitisation leads to longer infections—by generating sub-clinical cases for which treatment is not rapidly sought—killing vectors can lead to unexpected increases in the number of infected hosts. The rising case burden may go unnoticed unless sub-clinical individuals are tested for infection. Conversely, if immune pre-sensitisation leads to more rapid clearance of infection, increasing vector mortality rates may achieve greater than expected disease control. Our findings highlight the need to quantify how immune pre-sensitisation modulates clinical outcomes and parasite transmission in humans.
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Affiliation(s)
- Tsukushi Kamiya
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Megan A Greischar
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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14
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Tate AT. The Interaction of Immune Priming with Different Modes of Disease Transmission. Front Microbiol 2016; 7:1102. [PMID: 27468283 PMCID: PMC4942476 DOI: 10.3389/fmicb.2016.01102] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Accepted: 07/01/2016] [Indexed: 12/25/2022] Open
Affiliation(s)
- Ann T Tate
- Department of Biology and Biochemistry, University of Houston Houston, TX, USA
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