A biological model of scabies infection dynamics and treatment explains why mass drug administration does not lead to elimination

TL;DR

This paper presents a compartmental model of scabies infection dynamics that explains why mass drug administration often fails to eliminate the disease, highlighting the challenges posed by non-ovicidal treatments and multiple treatment rounds.

Contribution

It introduces a novel mathematical model incorporating ovicidal and non-ovicidal treatments to analyze the limitations of mass drug administration in eradicating scabies.

Findings

Eradication is nearly impossible under non-ovicidal treatment schemes.

Multiple treatment rounds significantly reduce prevalence but do not guarantee elimination.

Even with many rounds, elimination remains highly challenging.

Abstract

Despite a low global prevalence, infections with Sarcoptes scabiei, or scabies, are still common in remote communities such as in northern Australia and the Solomon Islands. Mass drug administration (MDA) has been utilised in these communities, and although prevalence drops substantially initially, these reductions have not been sustained. We develop a compartmental model of scabies infection dynamics and incorporate both ovicidal and non-ovicidal treatment regimes. By including the dynamics of mass drug administration, we are able to reproduce the phenomena of an initial reduction in prevalence, followed by the recrudescence of infection levels in the population. We show that even under a `perfect' two-round MDA, eradication of scabies under a non-ovicidal treatment scheme is almost impossible. We then go on to consider how the probability of elimination varies with the number of treatment rounds delivered in an MDA. We find that even with infeasibly large numbers of treatment rounds, elimination remains challenging.