The evolution of transmission mode

Abstract

This article reviews research on the evolutionary mechanisms leading to different transmission modes. Such modes are often under genetic control of the host or the pathogen, and often in conflict with each other via trade-offs. Transmission modes may vary among pathogen strains and among host populations. Evolutionary changes in transmission mode have been inferred through experimental and phylogenetic studies, including changes in transmission associated with host shifts and with evolution of the unusually complex life cycles of many parasites. Understanding the forces that determine the evolution of particular transmission modes presents a fascinating medley of problems for which there is a lack of good data and often a lack of conceptual understanding or appropriate methodologies. Our best information comes from studies that have been focused on the vertical versus horizontal transmission dichotomy. With other kinds of transitions, theoretical approaches combining epidemiology and population genetics are providing guidelines for determining when and how rapidly new transmission modes may evolve, but these are still in need of empirical investigation and application to particular cases. Obtaining such knowledge is a matter of urgency in relation to extant disease threats.This article is part of the themed issue ‘Opening the black box: re-examining the ecology and evolution of parasite transmission’.

Evidence of potential vertical transmission of tilapia lake virus

“…Definite determination of vertical virus transmission from broodstock to progeny is challenging due to the complex interaction of pathogen and the host (Antonovics et al, and it was achieved for only several aquatic viruses. For example, the vertical infection route is important for the spread of infectious salmon anaemia virus (ISAV), infectious pancreatic necrosis virus (IPNV), viral haemorrhagic septicaemia virus (VHSV), lymphocystis disease virus (LCDV) and nervous necrosis virus (NNV) (Cano et al, ; Chaves‐Pozo et al, ; Kuo et al, ; Marshall et al, ; Smail & Munro, ).…”

Haemoplasmas in wild rodents: Routes of transmission and infection dynamics

“…Transmission is a fundamental process in disease ecology, determining the evolved virulence levels of the parasite/pathogen, the host response and host–parasite/pathogen dynamics (Antonovics et al., ; Ebert, ; Sorrell, White, Pedersen, Hails, & Boots, ). However, due to the challenges associated with sampling the mammalian hosts, the arthropod vectors and their parasites/pathogens in nature, for many parasites and pathogens, the exact routes of transmission are still unknown.…”

“…Transmission is a fundamental process in disease ecology, determining the evolved virulence levels of the parasite/pathogen, the host response and host-parasite/pathogen dynamics (Antonovics et al, 2017;Ebert, 2013;Sorrell, White, Pedersen, Hails, & Boots, 2009).…”

Lost in transmission…?

“…Finally, several articles raised current use (and misuse) of terminology as being a stumbling block to improved conceptual and practical understanding of transmission. Confusion exists regarding the definition of phrases like 'transmission mode', 'transmission route' and 'transmission pathway', which can only obscure attempts to define and understand the underlying transmission process [1,3]. This issue of consistent terminology is exemplified in the article by Wilson et al [15] which asks the question 'What is a vector?'.…”

“…The various participants then self-assembled into sub-groups to discuss these different aspects of transmission in full over the next 3 days. The articles in this issue [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] largely represent the outcome of this process, with a few solicited to expand on areas not wholly covered at the retreat. While the list of topics represented within this issue may not be a completely exhaustive list of key topics in transmission, we believe that the broad profile of attendees has ensured that we have captured the majority of key challenges facing researchers in this field.…”