Abstract:
In the field of mathematical biology, researchers are beginning to witness an overwhelming appreciation
of multiscale modelling as an essential and suitable technique as opposed to a traditional
single-scale modelling approach in predicting the dynamics of infectious disease systems.
Yet, there is still a lack of evidence that generally indicates which among the different categories
of multiscale models of infectious disease systems is more appropriate to use in multiscale modelling
of infectious disease systems at different levels of their organization. This research study
is the first of its kind to compare the suitability of the two fundamental categories of multiscale
models of infectious disease systems which are nested multiscale models and embedded
multiscale models in predicting disease dynamics with specific reference to environmentallytransmitted
diseases. Two environmentally transmitted diseases are used as case studies, namely
ruminant paratuberculosis and human ascariasis, to compare the two fundamental categories of
multiscale models in predicting disease dynamics. The two environmentally-transmitted diseases
considered in this study represent infectious disease systems with replication-cycle at microscale
(i.e. ruminant paratuberculosis) and infectious disease systems without replication cycle
at the microscale (i.e. human ascariasis). Firstly, the author develop a single-scale model at the
host-level that we progressively extend to different categories of multiscale models that we later
compare. The findings of this study (through both mathematical and numerical analysis of the
multiscale models) are that for ruminant paratuberculosis which has a pathogen replication-cycle
at the within-host scale both nested and embedded multiscale models can be used because both
the models provide the same prediction of disease dynamics. However, for human ascariasis the
findings are such that nested multiscale model is not appropriate in characterizing the disease
dynamics, only the embedded is appropriate. Although the comparison of different categories of
multiscale models in disease prediction carried out in this study are specific to paratuberculosis
in ruminants and human ascariasis, the results obtained in this study are robust enough to be applicable
to other infectious disease systems. Our results can be generalized to imply that for any
level of organization of an infectious disease systems, if the disease has a replication cycle at the
microscale, the nested multiscale and the embedded multiscle model provide the same accuracy
in predicting disease dynamics. However, when the disease has no replication cycle at the microscale,
only the embedded multiscle model is appropriate for predicting disease dynamics. In
such a case, a nested multiscale model is inappropriate. We anticipate that this study will enable
modelers to choose appropriate multiscale model category in the study of infectious diseases.