The risk of incomplete personal protection coverage in vector-borne disease

Abstract

Personal protection (PP) techniques, such as insecticide-treated nets, repellents and medications, include some of the most important and commonest ways used today to protect individuals from vector-borne infectious diseases. In this study, we explore the possibility that a PP intervention with partial coverage may have the counterintuitive effect of increasing disease burden at the population level, by increasing the biting intensity on the unprotected portion of the population. To this end, we have developed a dynamic model which incorporates parameters that describe the potential effects of PP on vector searching and biting behaviour and calculated its basic reproductive rate, R 0 . R 0 is a well-established threshold of disease risk; the higher R 0 is above unity, the stronger the disease onset intensity. When R 0 is below unity, the disease is typically unable to persist. The model analysis revealed that partial coverage with popular PP techniques can realistically lead to a substantial increase in the reproductive number. An increase in R 0 implies an increase in disease burden and difficulties in eradication efforts within certain parameter regimes. Our findings therefore stress the importance of studying vector behavioural patterns in response to PP interventions for future mitigation of vector-borne diseases.

Dynamic modelling of personal protection control strategies for vector-borne disease limits the role of diversity amplification

“…Ignoring personal protection for a moment, consider a population of humans of density N h homogeneously distributed throughout a unit area, V. We denote by f the average rate at which the human population is bitten by a single mosquito, also located within V. Following Miller et al [16], Yakob [41] and Antonovics et al [42], we assume a Holling type-II functional response [43 -45] for f:…”

“…The first considers separate protected and unprotected classes (e.g. [16,26,28,46]). We will refer to these types of model as 'static two-class models'.…”

“…Amplification is a potential risk whenever vectors preferentially concentrate attacks on sub-populations with high infection susceptibilities [26]. This occurs, for example, when partial personal protection coverage causes mosquitoes to divert from protected individuals and focus bites on unprotected individuals [16,27,28]. Diversion can lead to rapid disease spread within the unprotected sub-population and, consequently, personal protection models which incorporate vector diversion have the potential to display counterintuitive increases in disease severity [16,26,28,29].…”

“…Many vector-borne disease models which use multiple host classes and, by extension, potentially exhibit protectioninduced diversity amplification (e.g. [16,26,28,29]) suffer from a common shortcoming-assignment of individuals to protected and unprotected classes is assumed static. Some models do allow for hosts who only intermittently apply personal protection (such as hosts who sleep under bed nets only at night), but even in these cases, assignments to sporadically protected and completely unprotected classes typically remain fixed [28,29].…”

Displacement of sexual partnerships in trials of sexual behavior interventions: A model-based assessment of consequences

“…With some exceptions (Killeen et al, 2007; Knox, 1985; Kunkel et al, 2015; Lipsitch and Samore, 2002; Miller et al, 2016; Panagiotopoulos et al, 1999), the population-level benefit of interventions specifically designed to control the spread of infectious disease exceeds the sum of individual-level benefits; the paradigm examples are herd immunity from vaccine against communicable diseases (Fine, 1993) and contagion-reducing effects of treatment for infections like tuberculosis, HIV and other sexually transmitted infections, and malaria (Boily et al, 2012; Greenwood, 2010). However, the population-level benefit of interventions that utilize behavioral changes to control for sexually transmitted diseases, can be more complex (Kremer and Morcom, 1998).…”