Abstract
BackgroundReliable information on host use by arthropod vectors is required to study pathogen transmission ecology and to predict disease risk. Direct observation of host use is often difficult or impossible and indirect methods are therefore necessary. However, the reliability of currently available methods to identify the last host of blood-feeding arthropods has not been evaluated, and may be particularly problematic for ticks because host blood has been digested at capture. Biases in host detection may lead to erroneous conclusions on both vector ecology and pathogen circulation.MethodsHere, we experimentally tested for biases in host detection using the generalist three-host tick Ixodes ricinus as a model system. We fed ticks using an artificial feeding system and amplified blood meal traces post-moult (i.e., in the succeeding unfed life stage) via both a quantitative real-time polymerase chain reaction assay and a reverse line blotting method. We then experimentally tested for three types of biases in host detection: 1) time post-moult, 2) tick life stage and 3) host type (non-nucleated mammal blood versus nucleated avian blood), and compared these biases between the two molecular methods.ResultsOur results show that all three factors can influence host detection in ticks but not necessarily in the expected way. Although host detection rates decreased with time post-moult, mammal blood tended to be more readily detected than bird blood. Tick life stage was also an important factor; detection was higher in nymphs than in adults and, in some cases, remnants from both larval and nymphal blood meals could be detected in the adult stage. These biases were similar for the two detection techniques.ConclusionsWe show that different factors associated with questing ticks may influence our ability to correctly infer previous host use and that these factors may bias inferences from field-based studies. As these biases may be common to other vector-borne disease systems, their implications for our understanding of vector ecology and disease transmission require more explicit consideration.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1043-7) contains supplementary material, which is available to authorized users.
Highlights
Reliable information on host use by arthropod vectors is required to study pathogen transmission ecology and to predict disease risk
To understand vector ecology and pathogen circulation, and to reliably predict disease risk, the contribution of different host types to local vector-host-pathogen interaction networks needs to be established [1,2,3,4]. Molecular techniques, such as groupspecific polymerase chain reaction (PCR), restriction fragment length polymorphisms (RFLP), reverse lineblot hybridisation (RLBH) and DNA barcoding, are currently employed to identify host use in a wide range of blood-feeding arthropods without the need to directly collect the vector on the host [5, 6]
Data analysis We considered three variables associated with host detection: 1) the detection threshold obtained with the quantitative real-time polymerase chain reaction (qPCR) method, a continuous variable defined by the Ct cycle at which a positive amplification was found and which reflects the relative quantity of host DNA present; the lower the Ct, the higher the amount of DNA template, 2) the detection rate, that is, the proportion of positive samples found for each experimental group with both RLBH and qPCR techniques and 3) the tick size and how it varied according to host blood type
Summary
Reliable information on host use by arthropod vectors is required to study pathogen transmission ecology and to predict disease risk. To understand vector ecology and pathogen circulation, and to reliably predict disease risk, the contribution of different host types to local vector-host-pathogen interaction networks needs to be established [1,2,3,4]. Molecular techniques, such as groupspecific polymerase chain reaction (PCR), restriction fragment length polymorphisms (RFLP), reverse lineblot hybridisation (RLBH) and DNA barcoding, are currently employed to identify host use in a wide range of blood-feeding arthropods (e.g., mosquitoes, ticks, reduviid bugs, sandflies, fleas, tsetse flies, biting midges) without the need to directly collect the vector on the host [5, 6]. We conducted a controlled experiment to identify and quantify potential biases in host detection in ticks using the well-known generalist tick Ixodes ricinus (Acari, Ixodidae) as a model system
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