Recent advances in the ecological framework of host-parasite interactions reveal the importance of community structure in disease emergence with processes such as the dilution effect (e.g. case of Lyme disease in North America). A particular case is the decoy effect where the presence of lowly competent hosts can reduce the transmission of infectious diseases in the community. Because parasites (especially free-living stages) can encounter several potential hosts before encountering (if they do) the target host, we can say that the different host species present in a community that might encounter the parasites could be perceived as different genotypes of a same host population by the parasite. Some hosts are competent, some are not, defining a gradient of competence from 0 to 100% and, therefore, when hosts a not competent, they are not compatible with the considered parasite. So here are my questions:
1) Am I understanding this correctly?
2) Is it correct to call a competent host a compatible host for the parasite and a non-competent host an incompatible host for the parasite?
Hi there,
have you seen those two papers:
1) Diversity, decoys and the dilution effect: how ecological communities affect
disease risk
2) Parasite diversity and coinfection determine pathogen infection success and host fitness
Hope that helps.
Hi Maciej,
Thanks for your comment. Yes, I read these papers a while ago. But there is no clear statements about the consequences of decoy hosts on the evolution of virulence if I remember correctly. Sorry for my unclear statements. Here I extend to the community level the point of view of classic epidemiological models where the population of hosts is made of 2 genotypes: one resistant and one susceptible. Did I miss something in the articles?
My answer is actually in Johnson group's "All hosts are not equal: explaining differential patterns of malformations in an amphibian community". Although there is no clear statement, they highly suggest it: competence is similar to compatibility.
Thanks!
I just wonder what would Robert Poulin say about this problem :) Please remember that 2 great parasitologists live in your country - Prof Heikki Henttonen and Dr Voitto Haukisalmi. you can always contact them for some comments on the topic.
Personally I think that the dilution effect is still a hypothesis and it is hard to apply this phenomenon into all parasitological interactions. But truly "All hosts are not equal" :)
Hi again,
Thanks for the names - i have never heard about these people. When I think about great parasitologists in Finland, I rather think about Tellervo Valtonen (who worked with Poulin and Marcogliese among others), probably because she has been working on fish parasites, my research system. But you are right and I actually asked Tellervo about parasite identification a while ago.
Concerning the dilution effect, I also think it is not really clear and I would rather say that increasing community can sometimes lead to a dilution of infection risk. However this is problematic for many reasons, the main one being that different processes act altogether to generate these patterns (e.g. predation, decoy hosts). Here I was only talking about dilution by the presence of decoy hosts. Moreover, the statement of dilution also sounds a bit paradoxical as community here refers to all the species present in the ecosystem but most studies do not take in account parasites as part of this biodiversity. Interactions between parasites (for instance co-infecting parasites) can change the outcome of a host-parasite interactions and I think that ignoring this can lead to wrong statements or result interpretation of monitoring data. May I ask your opinion about this and about the dilution effect in general as well? It would be nice hearing from other people about this topic too. Thanks in advance.
A little evolutionary background to help you potentially frame some research on the decoy and dilution effects. - dan
hi see this link
https://en.wikipedia.org/wiki/Ecological_competence
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