'Accidents waiting to happen'-Insights from a simple model on the emergence of infectious agents in new hosts

Parasitoid speciation and diversification

Parasitoid wasps may well be the most species-rich animal group on Earth, and host-parasitoid interactions may thereby be one of the most common types of species interactions. Understanding the major mechanisms underlying diversification in parasitoids should be a high priority, not the least in order to predict consequences from high extinction rates currently observed. The two major hypotheses explaining host-associated diversification are the escape-and-radiate hypothesis and the oscillation hypothesis, where the former assumes that key innovations are major drivers of radiation bursts, whereas the latter rather assumes that diversification depends on processes acting on the standing genetic variation that influences host use. This paper reviews the recent literature on parasitoid speciation in light of these major hypotheses to identify potential key innovations and host use variability underlying diversification. The paper also calls upon recent theoretical advances from a similar system, plant-butterfly interactions, to provide shortcuts in the development of theories explaining the high diversity of parasitoid wasps.

HOST TRAITS EXPLAIN MORE VARIATION IN OCCUPANCY OF GENERALISTS THAN SPECIALISTS DUE TO STRONG HOST PREFERENCES AMONG GENERALISTS

The range of hosts a parasite can successfully occupy is partially determined by the niche breadth, that is, the set of environmental conditions necessary to maintain a stable population. Niche breadth is often quantified using host specificity, which encompasses the number of host species a parasite can exploit and the parasite's distribution among its hosts. Parasites with a wider niche breadth can potentially occupy more host species and are often more evenly distributed among hosts than parasites with a narrower niche breadth. However, parasites interact with potential hosts within the context of a geographic locality and the set of environmental characteristics associated with it. The extent to which environmental filters associated with host individuals and the geographic context explain variation in occupancy of parasites, and the extent to which variation in occupancy is associated with host range and specificity, is poorly understood. Using data from small mammals and ectoparasites in Vermont, I used a multiscale, multispecies occupancy model (MSOM) to (1) estimate ectoparasite occupancy at 10 geographic sites and on individual hosts within each site, (2) quantify the variation in occupancy explained by the site and host levels of the model using Bayesian R2, and (3) evaluate associations between explained variation and host range of ectoparasites. For ectoparasites collected from at least 4 different host species, I calculated structural specificity to determine the distribution of these parasites across the hosts, and β-specificity to evaluate changes in host use across habitats. Host range was significantly associated with host-level Bayesian R2: generalist parasites had more variation in occupancy explained by host-level covariates than specialist parasites. This result may be explained by differences in structural specificity: many generalists disproportionally occurred on a single-host species, suggesting that host characteristics act as habitat filters for these parasites. There were no significant associations between site-level Bayesian R2 and host specificity. However, some generalists demonstrated high β-specificity, suggesting these parasites may "switch" hosts, depending on host availability. These results highlight that the terms specialist and generalist are context dependent and may not accurately describe the niche breadth of parasite taxa. Understanding variation in host specificity as it pertains to potential habitat filters may be important for predicting which parasites can bypass host filters and "jump" to a novel host, which has implications for the surveillance and management of vector-borne diseases.

Phylogenetic Triage and Risk Assessment: How to Predict Emerging Phytoplasma Diseases

Phytoplasma diseases pose a substantial threat to diverse crops of agricultural importance. Management measures are usually implemented only after the disease has already occurred. Early detection of such phytopathogens, prior to disease outbreak, has rarely been attempted, but would be highly beneficial for phytosanitary risk assessment, disease prevention and mitigation. In this study, we present the implementation of a recently proposed proactive disease management protocol (DAMA: Document, Assess, Monitor, Act) for a group of vector-borne phytopathogens. We used insect samples collected during a recent biomonitoring program in southern Germany to screen for the presence of phytoplasmas. Insects were collected with malaise traps in different agricultural settings. DNA was extracted from these mass trap samples and subjected to PCR-based phytoplasma detection and mitochondrial cytochrome c oxidase subunit I (COI) metabarcoding. Phytoplasma DNA was detected in two out of the 152 insect samples analyzed. Phytoplasma identification was performed using iPhyClassifier based on 16S rRNA gene sequence and the detected phytoplasmas were assigned to 'Candidatus Phytoplasma asteris'-related strains. Insect species in the sample were identified by DNA metabarcoding. By using established databases, checklists, and archives, we documented historical associations and records of phytoplasmas and its hosts in the study region. For the assessment in the DAMA protocol, phylogenetic triage was performed in order to determine the risk for tri-trophic interactions (plant-insect-phytoplasma) and associated disease outbreaks in the study region. A phylogenetic heat map constitutes the basis for risk assessment and was used here to identify a minimum number of seven leafhopper species suggested to be monitored by stakeholders in this region. A proactive stance in monitoring changing patterns of association between hosts and pathogens can be a cornerstone in capabilities to prevent future phytoplasma disease outbreaks. To the best of our knowledge, this is the first time that the DAMA protocol has been applied in the field of phytopathology and vector-borne plant diseases.

Evolutionary Challenges to Humanity Caused by Uncontrolled Carbon Emissions: The Stockholm Paradigm

This review paper discusses the Stockholm Paradigm (SP) as a theoretical framework and practical computational instrument for studying and assessing the risk of emerging infectious diseases (EIDs) as a result of climate change. The SP resolves the long-standing parasite paradox and explains how carbon emissions in the atmosphere increase parasites' generalization and intensify host switches from animals to humans. The SP argues that the growing rate of novel EID occurrence caused by mutated zoonotic pathogens is related to the following factors brought together as a unified issue of humanity: (a) carbon emissions and consequent climate change; (b) resettlement/migration of people with hyper-urbanization; (c) overpopulation; and (d) human-induced distortion of the biosphere. The SP demonstrates that, in an evolutionary way, humans now play a role migratory birds once played in spreading parasite pathogens between the three Earth megabiotopes (northern coniferous forest belt; tropical/equatorial rainforest areas; and hot/cold deserts), i.e., the role of "super-spreaders" of parasitic viruses, bacteria, fungi and protozoa. This makes humans extremely vulnerable to the EID threat. The SP sees the +1.0-+1.2 °C limit as the optimal target for the slow, yet feasible curbing of the EID hazard to public health (150-200 years). Reaching merely the +2.0 °C level will obviously be an EID catastrophe, as it may cause two or three pandemics each year. We think it useful and advisable to include the SP-based research in the scientific repository of the Intergovernmental Panel on Climate Change, since EID appearance and spread are indirect but extremely dangerous consequences of climate change.

Ecological super-spreaders drive host-range oscillations: Omicron and risk space for emerging infectious disease

The unusual genetic diversity of the Omicron strain has led to speculation about its origin. The mathematical modelling platform developed for the Stockholm Paradigm (SP) indicates strongly that it has retro-colonized humans from an unidentified nonhuman mammal, likely originally infected by humans. The relationship between Omicron and all other SARS-CoV-2 variants indicates oscillations among hosts, a core part of the SP. Such oscillations result from the emergence of novel variants following colonization of new hosts, replenishing and expanding the risk space for disease emergence. The SP predicts that pathogens colonize new hosts using pre-existing capacities. Those events are thus predictable to a certain extent. Novel variants emerge after a colonization and are not predictable. This makes it imperative to take proactive measures for anticipating emerging infectious diseases (EID) and mitigating their impact. The SP suggests a policy protocol, DAMA, to accomplish this goal. DAMA comprises: DOCUMENT to detect pathogens before they emerge in new places or colonize new hosts; ASSESS to determine risk; MONITOR to detect changes in pathogen populations that increase the risk of outbreaks and ACT to prevent outbreaks when possible and minimize their impact when they occur.

Food security and emerging infectious disease: risk assessment and risk management

Climate change, emerging infectious diseases (EIDs) and food security create a dangerous nexus. Habitat interfaces, assumed to be efficient buffers, are being disrupted by human activities which in turn accelerate the movement of pathogens. EIDs threaten directly and indirectly availability and access to nutritious food, affecting global security and human health. In the next 70 years, food-secure and food-insecure countries will face EIDs driving increasingly unsustainable costs of production, predicted to exceed national and global gross domestic products. Our modern challenge is to transform this business as usual and embrace an alternative vision of the biosphere formalized in the Stockholm paradigm (SP). First, a pathogen-centric focus shifts our vision of risk space, determining how pathogens circulate in realized and potential fitness space. Risk space and pathogen exchange are always heightened at habitat interfaces. Second, apply the document-assess-monitor-act (DAMA) protocol developing strategic data for EID risk, to be translated, synthesized and broadcast as actionable information. Risk management is realized through targeted interventions focused around information exchanged among a community of scientists, policy practitioners of food and public health security and local populations. Ultimately, SP and DAMA protect human rights, supporting food security, access to nutritious food, health interventions and environmental integrity.