Proliferative kidney disease (PKD) is a disease affecting salmonid populations in European and North-American rivers. It is caused by the endoparasitic myxozoan Tetracapsuloides bryosalmonae, which exploits freshwater bryozoans (Fredericella sultana) as primary host. Clinical PKD is associated to a massive inflammatory response caused by the proliferation of parasite stages in the kidney and spleen of infected salmonid fish. Mortality can reach 90-100%. Moreover, it is known that the development and pathology of PKD are influenced by temperature. PKD has been present in brown trout population for a long time but has recently increased rapidly in incidence and severity; in addition, environmental changes are likely to cause PKD outbreaks in more northerly regions as warmer temperatures promote disease development.
Figure 1: A sketch of PKD complex transmission cycle.
Figure 2: Sac-like stages of T. bryosalmonae inside a bryozoan host (image by Sylvie Tops).
This project, involving many different partners, aims at understanding the influence of ecological, evolutionary and immunological processes in the epidemiology of aquatic pathogens, exploiting PKD as a “text-book” case due to the availability of long-term monitoring data for PKD prevalence in fish and the possibility to conduct laboratory experimentation across the full parasite life-cycle. The common work program is arranged in three broad themes: disease maintenance, disease spread and disease emergence.
The partners involved are:
– FIWI (Center for fish and wildlife health – University of Bern): development and transmission of PKD in natural brown trout;
– EAWAG (Swiss Federal Institute of Aquatic Science and Technology): local adaptation of T. bryosalmonae and its bryozoan host Fredericella sultana;
– Scottish Fish Immunology Research Centre – University of Aberdeen: Exploring molecular mechanisms underpinning bryozoan and parasite interactions;
– EPFL: spatially explicit epidemiological modelling of PKD in river networks.
In particular, our subproject develops a spatially explicit model of PKD epidemiology in riverine host metacommunity, contrasting and linking empirical and laboratory data on the modes of transmission of the disease and life-cycle of the parasite. This project will tackle following issues and key parameters of model development: (1) node characterization, each node will represent a significant water body or a river reach characterized by local disease dynamics; (2) short- and long-distance dispersal of parasite and hosts; (3) local disease dynamics, described by accounting for susceptible and infected bryozoans, susceptible and infected fish and T. bryosalmonae concentration in the water column; (4) age structure of the fish (juveniles and adults), susceptible and infected in each age class being tracked and assigned to different mortality, recovery and infection rates; (5) covert (non-transmissible) and overt (transmissible and castrating) stages of T. bryosalmonae in the bryozoan host; (6) epidemiological classes distinguishing between susceptible, resistant and infected bryozoans classifying them as infected with either overt or covert stages. Parameters characterizing the basemodel will be initially set according to the existing literature. Data collected in this project will then be used to calibrate the model, together with data on PKD prevalence from a major monitoring program (Fischnetz project). This research project is funded through a Sinergia grant from the SNSF.
- An epidemiological model for proliferative kidney disease in salmonid populations.
- Spread of proliferative kidney disease in fish along stream networks: A spatial metacommunity framework.