A comparative assessment of track plates to quantify fine scale variations in the relative abundance of Norway rats in urban slums

Abstract

Norway rats (Rattus norvegicus) living in urban environments are a critical public health and economic problem, particularly in urban slums where residents are at a higher risk for rat borne diseases, yet convenient methods to quantitatively assess population sizes are lacking. We evaluated track plates as a method to determine rat distribution and relative abundance in a complex urban slum environment by correlating the presence and intensity of rat-specific marks on track plates with findings from rat infestation surveys and trapping of rats to population exhaustion. To integrate the zero-inflated track plate data we developed a two-component mixture model with one binary and one censored continuous component. Track plate mark-intensity was highly correlated with signs of rodent infestation (all coefficients between 0.61 and 0.79 and all p-values < 0.05). Moreover, the mean level of pre-trapping rat-mark intensity on plates was significantly associated with the number of rats captured subsequently (Odds ratio1.38; 95% CI 1.19-1.61) and declined significantly following trapping (Odds ratio 0.86; 95% CI 0.78-0.95). Track plates provided robust proxy measurements of rat abundance and distribution and detected rat presence even when populations appeared ‘trapped out’. Tracking plates are relatively easy and inexpensive methods that can be used to intensively sample settings such as urban slums, where traditional trapping or mark-recapture studies are impossible to implement, and therefore the results can inform and assess the impact of targeted urban rodent control campaigns.

Biocontrol of rats in an urban environment in Southeast Asia using Sarcocystis singaporensis

“…We regard the outcome of the biological rodent control campaign in Luang Prabang a success. Given that especially tracking plates/patches provide robust proxy measurements of rat abundance and distribution (our measurements in this and the previous study in Luang Prabang; see also) and detect the presence of rats even when populations appear to be at very low levels, we interpret the overall results to indicate a successful reduction of the rat population in the town. All abundance indicators directly (rodent activity, sightings by residents) or indirectly (trapping results, refer below) support this interpretation.…”

Rats About Town: A Systematic Review of Rat Movement in Urban Ecosystems

“…Visibly observing the tracks made by rats (e.g., in snow) allows for estimates of space use (Davis et al, 1948), but is naturally limited by the availability of snow. When the environment is not suitable for observing tracks, researchers can deploy track plates which become marked with characteristic "rat signs" when rats travel across them (Hacker et al, 2016). Rat movement may also be determined through bait consumption.…”

Using fine‐scale spatial genetics of Norway rats to improve control efforts and reduce leptospirosis risk in urban slum environments

“…Rattus norvegicus is the primary host reservoir, and control campaigns are conducted regularly to target rats for removal. However, rat populations rebound in size within 6–12 months, as indicated by surveys of rat activity and abundance (Hacker et al., ). Therefore, identifying the contributions of remnant eradication survivors vs. immigrant re‐colonizers to this rapid recovery is a central goal in the public health strategies designed to reduce leptospirosis in urban centers.…”

“…Defining eradication units also makes evaluating the effectiveness of an intervention campaign possible in a tractable way (Robertson & Gemmell, 2004). For example, rigorous estimates of rat population sizes, densities, and removal rates can be estimated for each of the defined units to monitor the efficacy of control campaigns (Hacker et al, 2016). Genetic data can provide another important facet of eradication success when samples can be compared before and after intervention campaigns to evaluate the degree of genetic variation that is lost or reduced via postintervention genetic bottlenecks (Abdelkrim, Pascal, Calmet, & Samadi, 2005;Russell et al, 2010;Veale et al, 2013).…”