Effective Methods of Estimation of Pathogen Prevalence in Pooled Ticks

Abstract

Since tick-borne diseases (TBDs) incidence, both in human and animal populations, is increasing worldwide, there is the need to assess the presence, distribution and prevalence of tick-borne pathogens. Reliable estimates on tick-borne pathogens (TBPs) prevalence represent the public health foundation to create risk maps and take effective prevention and control actions against TBDs. Tick surveillance consists of collecting and testing (usually in pools) thousands of specimens. Construction and analysis of tick pools represent a challenge due to the complexity of tick-borne pathogens and tick-borne diseases ecology. The aim of this study is to provide a practical guideline on appropriate pooling strategies and statistical analysis of infection prevalence through: (i) reporting the different pooling strategies and statistical methodologies commonly used to calculate pathogen prevalence in tick populations and (ii) practical comparison between statistical methods utilising a real dataset of infection prevalence in ticks collected in Northern Italy. Reporting detailed information on tick pool composition and size is as important as the correct TBPs prevalence estimation. Among the prevalence indexes, we suggest using maximum-likelihood estimates of pooled prevalence instead of minimum infection rate or pool positivity rate given the merits of the method and availability of software.

Molecular prevalence of Bartonella spp. in bat flies in east coast Malaysia

“…The use of sample pooling methods in this study may also be a contributing factor to the higher Bartonella prevalence. For logistical and economic reasons, pool screening is a common method for analyzing arthropod vectors in veterinary and human medicine [ 57 ]. However, as the number of positive samples increases, there is a growing risk of misestimating the number of positive samples [ 58 ].…”

Biting Back: Advances in Fighting Ticks and Understanding Tick-Borne Pathogens

“…Fracasso et al [20] Ticks and TBP become more prevalent and spread in new areas of the world. As a result, the epidemiology of TBD grows more complex and becomes the centre of intensive research.…”

“…Therefore, it is pivotal to establish well-validated methods for monitoring and surveillance of TBP epidemiological trends. The article by Fracasso et al [20] provides insights on two important pillars of TBP epidemiological research: (a) the tick-pooling strategies applied before pathogen detection analyses, and (b) the statistical methodologies applied for the determination of pathogen prevalence in tick populations. Furthermore, to provide a practical comparison between the statistical methods discussed, the authors analyse data about infection prevalence collected in a previously published study on ticks from northeastern Italy [21].…”

“…Regarding the statistical analysis, three main methods were used in the retrieved papers: the pool positivity rate (PPR, the ratio of positive pools to the total number of pools tested), the minimum infection rate (MIR, the ratio of positive pool numbers to the total number of specimens tested), and the maximum-likelihood estimate of pooled prevalence (EPP, the infection rate most likely observed given the test results and an assumed probabilistic model). According to the estimations of the study [20], EPP should be preferred over the others, given its accuracy and flexibility in accounting for spatiotemporal confounding effects. Nevertheless, the authors suggest using, when possible, both the EPP and MIR methods so that comparison between studies is feasible, given that MIR is the most widely used method for analysis of results obtained from pooled samples [20].…”

“…According to the estimations of the study [20], EPP should be preferred over the others, given its accuracy and flexibility in accounting for spatiotemporal confounding effects. Nevertheless, the authors suggest using, when possible, both the EPP and MIR methods so that comparison between studies is feasible, given that MIR is the most widely used method for analysis of results obtained from pooled samples [20].…”