13. Future perspectives
The future is bright for disease diagnosis and pathogen detection. The molecular biology revolution of the past quarter century has matured through the experimental, labour driven phase to high volume automated systems delivering reliable, high quality information. The revolution is likely to continue, with new methods being developed annually, increasing the options available to the diagnostic virologist. In the 1960’s, 70’s and 80’s the development of semi-automated, sensitive serological assays precipitated a similar revolution in pathogen detection that made more insightful research into disease and epidemiology possible. The most pioneering honey bee virology revelations were made during this time, in particular the discovery and serological characterisation of most of the honey bee viruses that we know today. Several of these remain to be characterised at the nucleic acid level. The development of cheap, high throughput mass sequencing of genomes and transcriptomes has overtaken these efforts somewhat, leading to the identification of novel viral nucleic acid sequences in bee and mite samples that may very well represent the genomes of viruses that had already been discovered previously. Matching these historical virus discoveries and their serological data to these nucleic acid genomes is therefore an important and urgent task, to avoid confusion in bee virus classification and to make sure that the historical literature on these viruses remains relevant in the current molecular age.
The principal criteria for an ideal diagnostic system are sensitivity, accuracy, reliability, universality, simplicity, speed and cost. Most modern detection technologies are now sensitive enough to detect down to a single target molecule. This means that any future development will increasingly focus on quantitative detection (depending on the diagnostic requirements), with a concomitant change to a more integrated, quantitative disease management style. Accuracy of detection at the molecular level (and virus detection is largely molecular) depends essentially on the nature of the primary molecular recognition event, i.e. the interaction between target and probe. In this regard, nucleic acid-based detection has a considerable advantage over serological detection, since the kinetics of nucleic acid hybridisation is much more predictable and reliable than that of protein interactions. This also makes nucleic acid-based detection much more adaptable to changing requirements due to the discovery or emergence of new virus variants. The principal area of concern for molecular virus detection is reliability, i.e. avoiding misdiagnosis due to false-positive or false-negative results. The nucleic acid genomes of viruses are naturally highly variable and can evolve very quickly, while current molecular diagnostic methods are highly sensitive to minor variations in the nucleic acid target, making it prone to possible false-negative errors. This sensitivity is largely linked to the enzymes used for molecular detection and future developments in molecular virus diagnostics may therefore increasingly feature enzyme-free technologies (Liepold et al., 2005).
The variability of virus genomes is an important component of a virus’ adaptive response. It is in many ways a defining and unique characteristic for individual viruses. Other areas of virology now distinguish which viral forms offer increased pathogenicity, or which spread more easily. New methods that can directly describe and quantify this variability, such as HRMC, may become increasingly important in honey bee virology to clarify how the interactions between host factors, individual variants, combinations of variants or the variability as a whole, can induce a diseased state.
Disease is the result of a breakdown in a host’s normal physiological state due to the presence or proliferation of a pathogenic agent. The simpler component of this interaction is the pathogen, and its detection. Future developments however, will increasingly focus on the host component of disease and the interplay between pathogen and host. This means that future technological direction in disease diagnosis will emphasise multiplexing, miniaturisation (Fiorini and Chui, 2005) and automation (Service, 2006; Belák et al., 2009), to provide epigenetic data to better understand how the breakdown in the homeostasis between host and pathogen results in disease. Such information is important, since it can inform disease prevention, treatment and potential cures.
Finally, automation and increased demand for simpler, faster and cheaper technologies for routine diagnosis with wide applicability in low-tech settings (Higgins et al., 2003; Schaad et al., 2003) will ultimately drive the costs down to where disease surveillance and routine monitoring becomes cost-effective (Service, 2006), even in low priority areas like honey bee pathology.