Sequential infection can decrease virulence in a fish–bacterium–fluke interaction: Implications for aquaculture disease management

Hosts are typically infected with multiple strains or genotypes of one or several parasite species. These infections can take place simultaneously, but also at different times, i.e. sequentially, when one of the parasites establishes first. Sequential parasite dynamics are common in nature, but also in intensive farming units such as aquaculture. However, knowledge of effects of previous exposures on virulence of current infections in intensive farming is very limited. This is critical as consecutive epidemics and infection history of a host could underlie failures in management practices and medical intervention of diseases. Here, we explored effects of timing of multiple infections on virulence in two common aquaculture parasites, the bacterium Flavobacterium columnare and the fluke Diplostomum pseudospathaceum. We exposed fish hosts first to flukes and then to bacteria in two separate experiments, altering timing between the infections from few hours to several weeks. We found that both short‐term and long‐term differences in timing of the two infections resulted in significant, genotype‐specific decrease in bacterial virulence. Second, we developed a mathematical model, parameterized from our experimental results, to predict the implications of sequential infections for epidemiological progression of the disease, and levels of fish population suppression, in an aquaculture setting. Predictions of the model showed that sequential exposure of hosts can decrease the population‐level impact of the bacterial epidemic, primarily through the increased recovery rate of sequentially infected hosts, thereby substantially protecting the population from the detrimental impact of infection. However, these effects depended on bacterial strain–fluke genotype combinations, suggesting the genetic composition of the parasite populations can greatly influence the degree of host suppression. Overall, these results suggest that host infection history can have significant consequences for the impact of infection at host population level, potentially shaping parasite epidemiology, disease dynamics and evolution of virulence in farming environments

Are Sick Individuals Weak Competitors? Competitive Ability of Snails Parasitized by a Gigantism-Inducing Trematode

Peer reviewe

Parasite avoidance behaviours in aquatic environments

Parasites, including macroparasites, protists, fungi, bacteria and viruses, can impose a heavy burden upon host animals. However, hosts are not without defences. One aspect of host defence, behavioural avoidance, has been studied in the terrestrial realm for over 50 years, but was first reported from the aquatic environment approximately 20 years ago. Evidence has mounted on the importance of parasite avoidance behaviours and it is increasingly apparent that there are core similarities in the function and benefit of this defence mechanism between terrestrial and aquatic systems. However, there are also stark differences driven by the unique biotic and abiotic characteristics of terrestrial and aquatic (marine and freshwater) environments. Here, we review avoidance behaviours in a comparative framework and highlight the characteristics of each environment that drive differences in the suite of mechanisms and cues that animals use to avoid parasites. We then explore trade-offs, potential negative effects of avoidance behaviour and the influence of human activities on avoidance behaviours. We conclude that avoidance behaviours are understudied in aquatic environments but can have significant implications for disease ecology and epidemiology, especially considering the accelerating emergence and re-emergence of parasites.peerReviewe

Establishment and interspecific associations in two species of Ichthyocotylurus (Trematoda) parasites in perch (Perca fluviatilis)

Background: Co-infections of multiple parasite species in hosts may lead to interspecific associations and subsequently shape the structure of a parasite community. However, few studies have focused on these associations in highly abundant parasite species or, in particular, investigated how the associations develop with time in hosts exposed to co-infecting parasite species for the first time. We investigated metacercarial establishment and interspecific associations in the trematodes Ichthyocotylurus variegatus and I. pileatus co-infecting three age cohorts of young perch (Perca fluviatilis). Results: We found that the timing of transmission of the two Ichthyocotylurus species was very similar, but they showed differences in metacercarial development essentially so that the metacercariae of I. pileatus became encapsulated faster. Correlations between the abundances of the species were significantly positive after the first summer of host life and also within the main site of infection, the swim bladder. High or low abundances of both parasite species were also more frequent in the same host individuals than expected by chance, independently of host age or size. However, the highest abundances of the species were nevertheless observed in different host individuals and this pattern was consistent in all age cohorts. Conclusions: The results suggest similar temporal patterns of transmission, non-random establishment, and facilitative rather than competitive associations between the parasite species independently of the age of the infracommunities. However, we suggest that spatial differences in exposure are most likely responsible for the segregation of the parasite species observed in the few most heavily infected hosts. Regardless of the underlying mechanism, the result suggests that between-species associations should be interpreted with caution along with detailed examination of the parasite distribution among host individuals.peerReviewe

Life-history genotype explains variation in migration activity in Atlantic salmon (Salmo salar)

Peer reviewe

Sopimuspalomiehen loukkaantuminen rakennuspalossa Kerimäellä 1.5.2021 : Tutkintalautakunnan raportti

Sisäministeriö päätti asettaa pelastuslain (379/2011) 107 § nojalla tutkintalautakunnan tutkimaan 1.5.2021 Kerimäellä tapahtunutta rakennuspaloa, jossa loukkaantui vakavasti paloa sammuttamassa ollut Etelä-Savon pelastuslaitoksen sopimuspalomies. Tutkinta asetettiin palon selvittämiseksi sekä pelastustoiminnan toimintamenetelmien arvioimiseksi ja kehittämiseksi. Tutkintaraportin tarkoituksena on turvallisuuden parantaminen sekä pelastustoimen kehittäminen. Tulipalo syttyi kesäasunnon pihapiirissä sijainneessa erillisessä saunarakennuksessa. Palo levisi koko saunarakennukseen ja siitä maaston kautta edelleen grillikatokseen ja kohti päärakennusta. Sammutustöiden alkuvaiheessa ensimmäisen pelastusryhmän sopimuspalomies jäi sortuneen grillikatoksen rakenteiden alle ja loukkaantui. Tutkintalautakunta selvitti tapahtumien kulun sekä siihen liittyvät tekijät ja teki tapahtuneeseen liittyen havaintoja ja selvityksiä. Tutkinnassa päädyttiin kuuteen suositukseen. Suositukset liittyvät pelastustoiminnan johtovastuun siirtämiseen pelastustoiminnan johtamisessa, sortumisvaaran huomioimiseen pelastustoimen koulutuksessa, viranomaisten yhteiseen toimintamalliin tilanteen muuttuessa äkillisesti, pelastustoimen henkilöstön ensihoito-osaamisen hyödyntämiseen, pelastustoimen oman henkilöstön pelastamisen harjoitteluun sekä pelastuslaitosten yhteiseen työturvallisuuden raportointijärjestelmään

Divergent Macroparasite Infections in Parapatric Swiss Lake-Stream Pairs of Threespine Stickleback (Gasterosteus aculeatus).

Spatial heterogeneity in diversity and intensity of parasitism is a typical feature of most host-parasite interactions, but understanding of the evolutionary implications of such variation is limited. One possible outcome of infection heterogeneities is parasite-mediated divergent selection between host populations, ecotypes or species which may facilitate the process of ecological speciation. However, very few studies have described infections in population-pairs along the speciation continuum from low to moderate or high degree of genetic differentiation that would address the possibility of parasite-mediated divergent selection in the early stages of the speciation process. Here we provide an example of divergent parasitism in freshwater fish ecotypes by examining macroparasite infections in threespine stickleback (Gasterosteus aculeatus) of four Swiss lake systems each harbouring parapatric lake-stream ecotype pairs. We demonstrate significant differences in infections within and between the pairs that are driven particularly by the parasite taxa transmitted to fish from benthic invertebrates. The magnitude of the differences tended to correlate positively with the extent of neutral genetic differentiation between the parapatric lake and stream populations of stickleback, whereas no such correlation was found among allopatric populations from similar or contrasting habitats. This suggests that genetic differentiation is unrelated to the magnitude of parasite infection contrasts when gene flow is constrained by geographical barriers while in the absence of physical barriers, genetic differentiation and the magnitude of differences in infections tend to be positively correlated

The Role of Parasitism in Adaptive Radiations - When Might Parasites Promote and When Might They Constrain Ecological Speciation?

Research on speciation and adaptive radiation has flourished during the past decades, yet factors underlying initiation of reproductive isolation often remain unknown. Parasites represent important selective agents and have received renewed attention in speciation research. We review the literature on parasite-mediated divergent selection in context of ecological speciation and present empirical evidence for three nonexclusive mechanisms by which parasites might facilitate speciation: reduced viability or fecundity of immigrants and hybrids, assortative mating as a pleiotropic by-product of host adaptation, and ecologically-based sexual selection. We emphasise the lack of research on speciation continuums, which is why no study has yet made a convincing case for parasite driven divergent evolution to initiate the emergence of reproductive isolation. We also point interest towards selection imposed by single vs. multiple parasite species, conceptually linking this to strength and multifariousness of selection. Moreover, we discuss how parasites, by manipulating behaviour or impairing sensory abilities of hosts, may change the form of selection that underlies speciation. We conclude that future studies should consider host populations at variable stages of the speciation process, and explore recurrent patterns of parasitism and resistance that could pinpoint the role of parasites in imposing the divergent selection that initiates ecological speciation