A Sneaky Peak at Models... Studying HABs and Pathogens.

Gaining an understanding in the biological and chemical interactions which control growth, toxicity, sources and means of transportation of pathogens and harmful algal blooms (HABs) is of importance to many water-related areas worldwide. This will lead to the development of predicting their presence and the risk to humans which use the water that these are present in, whether this is recreational bathing, drinking water or water where organisms are removed from for consumption. Attempts to recreate circumstances to accurately reflect these factors are achieved using coupled physical-biological models which aim to show population dynamics and hydrodynamic transport amongst other processes.

Infectious pathogens in the marine, and other aquatic environments can be from many human or animal sources, and show great diversity. The concentrations and toxicity of these pathogens can vary depending on several factors such as distance from source, dilution, predation, and mortality from temperature, pH, UV exposure and salinity amongst others. Pathogens tent to be approximated using fecal indicator bacteria (FIB) such as Enterococci and E. coli (see my last blog post). Toxic HAB species tend to be indigenous to aquatic systems, however they are able to become transported further than their natural capabilities allow by means of ballast water transfer and animals. When at bloom concentrations, they can infect by direct consumption when present in sea food, aerosol inhalation, direct contact by recreational water use, or by water consumption. Factors which affect the concentration and toxicity of HABs include nutrient concentrations, light, strain composition, life cycle transitions and the presence of grazers and competitors. In order to attempt to predict the outcomes of toxic HAB and pathogen outbreaks, models are required, but first these require an understanding of the forces acting upon the concentrations and toxicity at different scales (from cell diameter to mesoscale physical processes). Models tend to require significant amounts of information in order to give an accurate predictive output, however our knowledge of these environments, and all that affect them will always remain incompete, therefore restricting the potential for our models to reach accurate predictions.

The addition of field and lab observations and experiments combined with models will greatly strengthen the ways by which we can connect the effects of HABs and pathogens to human health impacts, as shown in the diagram to the left, which was taken from the paper. Combining all three methods has already proven successful in many experiments, including the observations and analyses of sediment and water samples at beaches to determine whether they are safe to remain open, or if they are to be temporarily closed to recreational activities due to the type and numbers of microbes present there.

Modelling systems can be of great assistance to meeting the challenges associated with the effects of toxic HABs and pathogens on human health. Predicting concentrations and toxicity of HABs and pathogens requires the identification of appropriate spatial and time scales to measure and model on, and to integrate the model predictions with assessments of risk to human health and mitigation strategies. By sharing resources and using laboratory, field and modelling all greatly increase the chances of understanding these processes, therefore improving our predictive capabilities, as well as collaborations between varying scientists who specialize in different fields which may all contribute to the system.

I initially enjoyed reading this review, however when it came to writing about it I found it difficult to try to condense the information into a few paragraphs. I ended out having to cut a lot out which is a shame. It is a good read, so if you want more information on identifying the space and time scales that HABs and pathogens interact with their environment, and integrating this with human health/risk management using model systems, I would suggest reading the full paper.


Dyble, J., Bienfang, P., Dusek, E., Hitchcock, G., Holland, F., Laws, E., Lerczak, J., McGillicudy Jr, D. J., Minnett, P., Moore, S. K., O'Kelly, C., Solo-Gabriele, H. & Wang, J. D. (2008). Environmental Controls, Oceanography, and Population Dynamics of Pathogens and Harmful Algal Blooms: Connecting Sources to Human Exposure. Environmental Health. 7 (Suppl 2): S5.

also available here: http://www.biomedcentral.com/content/pdf/1476-069X-7-S2-S5.pdf

Recently this article was in the news, it hasn't got much scientific information, but I enjoyed the read: http://www.bbc.co.uk/news/uk-21947492