Single infection with Batrachochytrium dendrobatidis or Ranavirus does not increase probability of co-infection in a montane community of amphibians

Co-infection is linked to infection prevalence and intensity in oysters amidst high environmental and spatial variation

Co-infecting parasites modify infection outcomes in the wild. However, it is unclear how multiple environmental factors influence co-infection. The Chesapeake Bay metapopulation of the eastern oyster, Crassostrea virginica, provides an opportunity to test the importance of co-infection across heterogeneous environments because multiple parasites infect oysters across a broad salinity gradient. This study leverages Maryland and Virginia oyster monitoring for a large-scale survey of four co-infecting organisms, including two tissue parasites and two shell bio-eroding parasites. We diagnosed infection in 440 oysters across 16 paired harvested and unharvested reefs and tested the importance of co-infecting organisms for each parasite relative to environmental conditions, host traits, and marine spatial management. Microscopic visual methods were used to diagnose prevalence and intensity of tissue infections with Perkinsus marinus (the causative agent of dermo disease) and Haplosporidium nelsoni (the causative agent of MSX disease). Macroscopic visual methods were used to diagnose prevalence and intensity of shell infections with Cliona boring sponges and blister-inducing Polydora worms. For the three oyster parasites that were detected [H. nelsoni infections were absent in all oysters], salinity was the overall strongest predictor, corresponding to bay-wide patterns of parasite prevalence and/or intensity. Despite high environmental and spatial variation, co-infections corresponded to altered prevalence and/or intensity for all three oyster parasites. The correlational patterns suggest that P. marinus acts as a lynchpin in co-infection, as its intensity increased with Cliona sponge prevalence and P. marinus co-infection predicted higher Polydora blister intensity. Oyster shell height, reef habitat, and harvest status also predicted parasite prevalence and intensity, further reflecting the multivariate drivers of infections in this system. Unharvested reefs had greater vertical habitat structure and higher intensities of Cliona sponge infections, but no differences in the prevalence of any of the three parasites. Spatial patterns unexpectedly show that reef-level predictors of parasite patterns were more important than differences between tributaries. This correlational survey provides novel insights through the statistical relationships between the three oyster parasites, environmental conditions, host traits, and human resource management. New and more detailed scenarios are needed to expand disease ecological theory to encompass co-infection in anthropogenically impacted wildlife populations.

Relationship between two pathogens in an amphibian community that experienced mass mortalities

Because host species tend to harbor multiple parasitic species, coinfection in a host is common. The chytrid fungus Batrachochytrium dendrobatidis (Bd) and the viruses in the genus Ranavirus (Rv) are responsible for the decline of amphibians worldwide. Despite wide geographical co-occurrence and the serious conservation problem that coinfection with these pathogens could represent, little is known about their possible synergistic interactions and effects in a host community. We investigated the occurrence and associations between these two pathogens in an amphibian community after Rv-driven disease outbreaks were detected in four populations of the Iberian ribbed newt (Pleurodeles waltl) in northwestern Spain. We collected tissue samples from amphibians and fish and estimated Bd and Rv infection loads by qPCR. A few months after the most recent mass mortality event, Rv infection parameters at the affected sites decreased significantly or were lower than such registered at the sites where no outbreaks were recorded. Both pathogens were simultaneously present in almost all sites, but coinfection in a single host was rare. Our findings suggest that the co-occurrence of Bd and Rv does not predict adverse outcomes (e.g., enhanced susceptibility of hosts to one pathogen due to the presence or infection intensity of the other) following an outbreak. Other variables (such as species identity or site) were more important than infection with a pathogen in predicting the infection status and severity of infection with the other pathogen. Our results highlight the importance of host-specific and environmental characteristics in the dynamics of infections, coinfection patterns, and their impacts.

High-intensity acute exercise impacts motor learning in healthy older adults

Healthy aging is associated with changes in motor sequence learning, with some studies indicating decline in motor skill learning in older age. Acute cardiorespiratory exercise has emerged as a potential intervention to improve motor learning, however research in healthy older adults is limited. The current study investigated the impact of high-intensity interval exercise (HIIT) on a subsequent sequential motor learning task. Twenty-four older adults (aged 55-75 years) completed either 20-minutes of cycling, or an equivalent period of active rest before practicing a sequential force grip task. Skill learning was assessed during acquisition and at a 6-hour retention test. In contrast to expectation, exercise was associated with reduced accuracy during skill acquisition compared to rest, particularly for the oldest participants. However, improvements in motor skill were retained in the exercise condition, while a reduction in skill was observed following rest. Our findings indicate that high-intensity exercise conducted immediately prior to learning a novel motor skill may have a negative impact on motor performance during learning in older adults. We also demonstrated that exercise may facilitate early offline consolidation of a motor skill within this population, which has implications for motor rehabilitation.

Coinfection with chytrid genotypes drives divergent infection dynamics reflecting regional distribution patterns

By altering the abundance, diversity, and distribution of species-and their pathogens-globalization may inadvertently select for more virulent pathogens. In Brazil's Atlantic Forest, a hotspot of amphibian biodiversity, the global amphibian trade has facilitated the co-occurrence of previously isolated enzootic and panzootic lineages of the pathogenic amphibian-chytrid (Batrachochytrium dendrobatidis, 'Bd') and generated new virulent recombinant genotypes ('hybrids'). Epidemiological data indicate that amphibian declines are most severe in hybrid zones, suggesting that coinfections are causing more severe infections or selecting for higher virulence. We investigated how coinfections involving these genotypes shapes virulence and transmission. Overall, coinfection favored the more virulent and competitively superior panzootic genotype, despite dampening its transmission potential and overall virulence. However, for the least virulent and least competitive genotype, coinfection increased both overall virulence and transmission. Thus, by integrating experimental and epidemiological data, our results provide mechanistic insight into how globalization can select for, and propel, the emergence of introduced hypervirulent lineages, such as the globally distributed panzootic lineage of Bd.

Widespread amphibian Perkinsea infections associated with Ranidae hosts, cooler months and Ranavirus co-infection

Amphibians suffer from large-scale population declines globally, and emerging infectious diseases contribute heavily to these declines. Amphibian Perkinsea (Pr) is a worldwide anuran pathogen associated with mass mortality events, yet little is known about its epidemiological patterns, especially in comparison to the body of literature on amphibian chytridiomycosis and ranavirosis. Here, we establish Pr infection patterns in natural anuran populations and identify important covariates including climate, host attributes and co-infection with Ranavirus (Rv). We used quantitative (q)PCR to determine the presence and intensity of Pr and Rv across 1234 individuals sampled throughout central Florida in 2017-2019. We then implemented random forest ensemble learning models to predict infection with both pathogens based on physiological and environmental characteristics. Perkinsea infected 32% of all sampled anurans, and Pr prevalence was significantly elevated in Ranidae frogs, cooler months, metamorphosed individuals and frogs co-infected with Rv, while Pr intensity was significantly higher in ranid frogs and individuals collected dead. Ranavirus prevalence was 17% overall and was significantly higher in Ranidae frogs, metamorphosed individuals, locations with higher average temperatures, and individuals co-infected with Pr. Perkinsea prevalence was significantly higher than Rv prevalence across months, regions, life stages and species. Among locations, Pr prevalence was negatively associated with crayfish prevalence and positively associated with relative abundance of microhylids, but Rv prevalence did not associate with any tested co-variates. Co-infections were significantly more common than single infections for both pathogens, and we propose that Pr infections may propel Rv infections because seasonal Rv infection peaks followed Pr infection peaks and random forest models found Pr intensity was a leading factor explaining Rv infections. Our study elucidates epidemiological patterns of Pr in Florida and suggests that Pr may be under-recognized as a cause of anuran declines, especially in the context of pathogen co-infection.

Transcriptome mining extends the host range of the Flaviviridae to non-bilaterians

The flavivirids (family Flaviviridae) are a group of positive-sense RNA viruses that include well-documented agents of human disease. Despite their importance and ubiquity, the timescale of flavivirid evolution is uncertain. An ancient origin, spanning millions of years, is supported by their presence in both vertebrates and invertebrates and by the identification of a flavivirus-derived endogenous viral element in the peach blossom jellyfish genome (Craspedacusta sowerbii, phylum Cnidaria), implying that the flaviviruses arose early in the evolution of the Metazoa. To date, however, no exogenous flavivirid sequences have been identified in these hosts. To help resolve the antiquity of the Flaviviridae, we mined publicly available transcriptome data across the Metazoa. From this, we expanded the diversity within the family through the identification of 32 novel viral sequences and extended the host range of the pestiviruses to include amphibians, reptiles, and ray-finned fish. Through co-phylogenetic analysis we found cross-species transmission to be the predominate macroevolutionary event across the non-vectored flavivirid genera (median, 68 per cent), including a cross-species transmission event between bats and rodents, although long-term virus-host co-divergence was still a regular occurrence (median, 23 per cent). Notably, we discovered flavivirus-like sequences in basal metazoan species, including the first associated with Cnidaria. This sequence formed a basal lineage to the genus Flavivirus and was closer to arthropod and crustacean flaviviruses than those in the tamanavirus group, which includes a variety of invertebrate and vertebrate viruses. Combined, these data attest to an ancient origin of the flaviviruses, likely close to the emergence of the metazoans 750-800 million years ago.

Effects of parasites coinfection with other pathogens on animal host: A literature review

A parasite-host relationship is complicated and largely remained poorly understood, especially when mixed infections involving pathogenic bacteria and viruses are present in the same host. It has been found that most parasites are able to manipulate the host's immune responses to evade or overcome its defense systems. Several mechanisms have been postulated that may explain this phenomenon in different animal species. Recent evidence suggests that coinfections involving many parasitic species alter the host's vulnerability to other microorganisms, hinder diagnostic accuracy, and may negatively impact vaccination by altering the host's immune responsiveness. The objective of this review was to provide a comprehensive summary of the current understanding of how parasites interact with other pathogens in different animal species. A better understanding of this complex relationship will aid in the improvement efforts of disease diagnosis, treatment, and control measures such as novel and effective vaccines and therapeutics for infectious diseases.

Three Pathogens Impact Terrestrial Frogs from a High-Elevation Tropical Hotspot

Three infectious pathogens Batrachochytrium dendrobatidis (Bd), Ranavirus (Rv) and Perkinsea (Pr) are associated with widespread and ongoing amphibian population declines. Although their geographic and host ranges vary widely, recent studies have suggested that the occurrence of these pathogens could be more common than previously thought, even in direct-developing terrestrial species traditionally considered less likely to harbor these largely aquatic pathogens. Here, we characterize Bd, Rv, and Pr infections in direct-developing terrestrial amphibians of the Pristimantis genus from the highland Ecuadorean Andes. We confirm the first detection of Pr in terrestrial-breeding amphibians and in the Andean region, present the first report of Rv in Ecuador, and we add to the handful of studies finding Bd infecting Pristimantis. Infection prevalence did not differ significantly among pathogens, but infection intensity was significantly higher for Bd compared to Pr. Neither prevalence nor intensity differed significantly across locality and elevation for Bd and Rv, although low prevalence in our dataset and lack of seasonal sampling could have prevented important epidemiological patterns from emerging. Our study highlights the importance of incorporating pathogen surveillance in biodiversity monitoring in the Andean region and serves as starting point to understand pathogen dynamics, transmission, and impacts in terrestrial-breeding frogs.

Host-multiparasite interactions in amphibians: a review

Parasites, including viruses, bacteria, fungi, protists, helminths, and arthropods, are ubiquitous in the animal kingdom. Consequently, hosts are frequently infected with more than one parasite species simultaneously. The assessment of such co-infections is of fundamental importance for disease ecology, but relevant studies involving non-domesticated animals have remained scarce. Many amphibians are in decline, and they generally have a highly diverse parasitic fauna. Here we review the literature reporting on field surveys, veterinary case studies, and laboratory experiments on co-infections in amphibians, and we summarize what is known about within-host interactions among parasites, which environmental and intrinsic factors influence the outcomes of these interactions, and what effects co-infections have on hosts. The available literature is piecemeal, and patterns are highly diverse, so that identifying general trends that would fit most host–multiparasite systems in amphibians is difficult. Several examples of additive, antagonistic, neutral, and synergistic effects among different parasites are known, but whether members of some higher taxa usually outcompete and override the effects of others remains unclear. The arrival order of different parasites and the time lag between exposures appear in many cases to fundamentally shape competition and disease progression. The first parasite to arrive can gain a marked reproductive advantage or induce cross-reaction immunity, but by disrupting the skin and associated defences (i.e., skin secretions, skin microbiome) and by immunosuppression, it can also pave the way for subsequent infections. Although there are exceptions, detrimental effects to the host are generally aggravated with increasing numbers of co-infecting parasite species. Finally, because amphibians are ectothermic animals, temperature appears to be the most critical environmental factor that affects co-infections, partly via its influence on amphibian immune function, partly due to its direct effect on the survival and growth of parasites. Besides their importance for our understanding of ecological patterns and processes, detailed knowledge about co-infections is also crucial for the design and implementation of effective wildlife disease management, so that studies concentrating on the identified gaps in our understanding represent rewarding research avenues.