SEASONALITY AND THE PERSISTENCE AND INVASION OF MEASLES

Sunday, 27th of January 2013

[source]Proceedings of the Royal Society of Biological Sciences[|source]

In this piece from the Proceedings of the Royal Society for Biological sciences, Conlan and Grenfell reviewed the factors likely to influence the critical community size for perpetuation of measles virus, ie, the threshold below which measles virus is not easily perpetuated. One interesting finding is that declines in the birth rate tend to raise the critical community size. However, seasonality of incidence affects the CCS, even under conditions of declining birth rates. To what extent do measles campaign planners take these factors into account when planning the timing of their campaigns?

So how do these factors affect efforts to stop measles transmission? With rapid urbanization of populations, resulting in more than half the world’s people now living in towns and cities, the epidemiology of measles will definitely change. Special attention has to be put to highly urbanizing countries with low birth rates. Since
viral seeding from town to country affects rural transmission, the dynamics
of urban transmission are also of interest to countries with large rural
populations.

Hope this read will add to the body of evidence to facilitate decision making in the timing of follow up campaigns, that remains one of the challenges to measles control/elimination

Good reading

 

Full text, with tables and figures, is at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1914306/pdf/rspb20060030.pdf

The critical community size (CCS) for measles, which separates persistent from extinction-prone populations, is arguably the best understood stochastic threshold in ecology. Using simple models, we explore a relatively neglected relationship of how the CCS scales with birth rate. A predominantly positive relationship of persistence with birth rate is complicated by the accompanying dynamical transitions of the underlying deterministic process. We show that these transitions imply a lower CCS for high birth rate less developed countries and contrary to the experience in lower birth rate, industrial countries, the CCS may increase after vaccination.We also consider the evolutionary implications of the CCS for the origin of measles; this analysis explores how the deterministic and stochastic thresholds for invasion and persistence set limits on the mechanism by which this highly infectious pathogen could have successfully colonized its human host.