Bluetongue virus changes the emission of volatile organic chemicals in the body odour of sheep and cattle during infection

Mammals, including humans, constantly emit hundreds of volatile organic chemicals (VOCs) as part of body odour and their individual composition alters in response to underlying biological and environmental influences. These chemicals will also change in response to diseases and infections. Innovative new technologies are being used to explore odour-based biomarkers in breath, skin emissions and excretions as diagnostics tools for the early detection of difficult-to-diagnose conditions like cancer and tuberculosis. The emission of VOCs is of particular importance for vector-borne pathogens such as the malaria parasite or arthropod-borne viruses (arboviruses) such as Zika virus, as insects who transmit these pathogens use specific chemicals in body odour (semiochemicals) as one way of finding their host. An emerging field of research is investigating how vector-borne pathogens modify the body odour of infected hosts to identify if infection-induced changes to body odour semiochemicals subsequently alter the attraction of insect vectors. Studies based on human: mosquito: malaria interactions are at the forefront of this research and recent high-profile outcomes have reported that mosquitoes are more attracted to infected individuals. Most intriguingly vector mosquitoes might be specifically attracted to those infection stages of the parasite that will enhance successful transmission.

Despite the overall importance surprising little is known in regards to the effect of arbovirus infections on body odour modification and subsequent insect vector attraction. Most arbovirus infections of humans and animals are acute and characterised by shorter periods of virus presence in the blood (viraemia), making the collection of body odour emissions during natural infections across rapidly changing stages of infection challenging. In contrast, while the development of mouse models of infection offers flexibility and a vast associated array of interrogative tools, they are limited in their relevance to natural infections.

Arboviruses cause highly important diseases also in livestock. Culicoides-borne viruses such as bluetongue virus (BTV) can cause devastating disease in some species of ruminants and are a current major threat to the UK agriculture sector due to ongoing outbreaks in continental Europe. Combining the unique expertise of all project partners we have created a novel and flexible infection system that remains relevant to the real world and translatable to field application. In a proof-of-concept study we will investigate the hypothesis that BTV infection changes VOC profiles in the body odour of the main natural hosts, cattle and sheep. Detected BTV-induced host odour changes can subsequently be assessed for their potential to modify the attraction of insect vectors as well as highlight opportunities for novel diagnostic tools. BTV causes more severe disease in sheep than in cattle despite an equally high level of virus in the blood. Therefore this study system will also determine if odour based diagnostic technology can be developed to detect viral infections even in the absence of clinical signs. The latter is of vital importance as odour-based detection of non-diseased but infected individuals could transform both pen-side diagnostic systems and control measures such as repellent and attractant chemicals available for insect vector control.

Study outcomes will immediately improve our understanding of BTV transmission and highlight opportunities for targeted control of Culicoides vectors. Importantly study results can in the future be transferred to other highly important viral pathogens of livestock and identify if different virus species induce specific odour changes. Demonstrating this will be of vital interest not only for other vector-borne viral diseases including those of humans, but also significantly advance the emerging field of odour-based detection of viral infections.

Infection with pathogens can change the emission of volatile organic chemicals (VOCs) in host body odours which is of specific relevance to arthropod-borne viruses (arboviruses), as arthropod vectors use VOCs to locate their host. Thus arbovirus-induced host odour changes could enhance insect vector attraction selectively to infected individuals. Culicoides-borne viruses such as bluetongue virus (BTV) are a significant economic and welfare concern to ruminant production in Europe. The BTV in-vivo study system that we have developed provides a unique opportunity to investigate the importance and diagnostic potential of viruses modifying host body odour with a high degree of experimental control. The aim of this proof-of-principle study is to demonstrate that infection with an arbovirus consistently modifies the emission of VOCs in the body odour of its hosts. Difference in clinical severity of BTV in sheep and cattle will further reveal if virus replication alone, even in the absence of overt disease, results in detectable odour changes.

We will collect VOC emissions of the whole animal body odour of cattle and sheep at multiple time points before and during BTV infection (initiation, peak viraemia, disease and convalescence) to identify infection/disease associated compounds of interest (COIs) using GC-MS. We will also collect VOC emissions specifically from the skin and breath for comparison and to identify future diagnostic targets. Longitudinal measurements of BTV infection and immune parameters in cattle and sheep will be carried out through quantification of BTV in blood (qPCR, titration), anti-BTV immunoglobulins and cytokines in serum (SNT, ELISA). Study results will create a unique research platform which can transform our understanding of insect vectors attraction to infected hosts in arbovirus transmission and create novel vector control opportunities as well as unlock enormous diagnostic potential of odour-based detection of viral infections.

The study will create a unique research platform which can in the short term transform our understanding of the transmission of BTV and other arboviruses by identifying the importance of virus induced host odour changes for the specific or general attraction of blood feeding insect vectors, later further translated into vector control measures. Project outcomes will also highlight opportunities for longer-term innovative and novel non-invasive diagnostic technologies based on odour detection of infected individuals transferable to other important viral pathogens of livestock. The project will therefore create multiscale benefit opportunities through evidence-based control policies, transferable diagnostic potential and product development and subsequent improvements to animal and human health.

Benefits to the industry sector through R&D opportunities
Semiochemical-based detection of disease is an emerging and vibrant R&D area and this project will provide a flexible system that can in the future be utilised for product development. Study results will determine if detectable levels of host odour modification are induced by viral replication alone, even in the absence of clinical signs. The ability to identify asymptomatic viral carriers would create enormous diagnostic potential, especially when combined with mobile collectors and point-of collection analysis. The study system can further be transferred to other high-impact viral diseases of ruminants to characterise if different viral species induce specific odour biomarkers. Volatile organic compounds that increase or decrease insect attraction can be synthetically commercialised as repellents or baits for insect traps (push-pull systems) and mitigate pathogen transmission through disruption of transmission cycles, critical to integrated arthropod vector control in the context of increasing insecticide resistance.

Benefits to policy makers, public health veterinarians and other agriculture stakeholders
The project will enhance disease control policies by improving the evidence base for intervention strategies. We foresee shorter-term benefits to both animal welfare and productivity by identifying key attraction stages of infected ruminants to Culicoides vectors leading to opportunities for targeted prevention of insect host seeking, thereby mitigating the spread of important Culicoides-borne viruses. In addition, the project will also lead to the development of control measures based on natural repellent chemistry and specific attractants for insects that can be used for both monitoring and control purposes. Long-term benefits can also be achieved across other livestock systems and the horticultural and crop production sectors through broader exchange of knowledge and sampling technologies. The potential to detect virus infected hosts rapidly and in the absence of clinical manifestation via non-invasive technology would have the ability to greatly reduce the risk associated with global livestock trade, through port-of-entry screening. All of these areas are likely to influence approaches to both risk assessment and outbreak response in the medium to long-term, ultimately leading to significant downstream economic savings.

Benefits to the wider public
The possibility of detecting chronic or infectious diseases early through chemical biomarkers in individual body odour has captivated the general public. Additionally Culicoides are notorious in the UK for their nuisance biting in Scotland and Northern England and high profile outbreaks of Culicoides transmitted viruses causing severe disease in cattle and sheep have further enhanced society interest. The wider public will therefore benefit immediately through increased engagement and knowledge addressing these high-topic research areas. Any long-term development of non-invasive odour biomarker detection of viral infections could be transferred to humans and thereby significantly enhance human health.