Sarah Brun Bar-Yaacov PhD Candidate, University of Liverpool
Orthohantaviruses are a group of segmented negative-sense RNA viruses maintained as asymptomatic infections in rodent, insectivore and bat populations (Vaheri, Strandin, et al. 2013). They are Bunyaviruses and to date 41 orthohantavirus species have been officially recognized (ICTV 2014). Among orthohantaviruses, the rodent-borne are the most studied, as these are the only ones associated with human disease.
Orthohantaviruses are found in endemic regions across the globe. Each viral species is closely associated with a specific carrier host and the presence of a specific virus in a geographic location is dependent on the presence of its carrier. Seoul orthohantavirus (SEOV) is carried by rats (rattus norvegicus) and consequently is the only orthohantavirus that is globally distributed (Jonsson et al. 2010; Vaheri, Henttonen, et al. 2013).
Orthohantavirus transmission to humans
The rodent hosts are persistently infected and they shed the virus in saliva, urine and feces. Transmission to humans is mainly the result of inhalation of aerosolized contaminated rodent excreta under circumstances in which humans come into direct contact with the animals or their dwelling, e.g. while cleaning out a cabin after winter (Vaheri, Strandin, et al. 2013).
Clinical manifestations of infection
Orthohantavirus infections are associated with two syndromes; hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HPS). The major difference between the two syndromes is the primary afflicted organ. In HFRS this is the kidneys, whereas in HPS the lungs are the main target (Krautkrämer et al. 2013). HPS is the disease caused by orthohantaviral strains found on the American continent. This is a rare, but very severe infection with high mortality rates (up to 60 % mortality has reported in certain outbreaks) (Jonsson et al. 2010). HFRS occurs in Europe and Asia and is a disease of highly variable severity. Depending on the infecting viral species, HFRS has mortality rates of < 1% – 15 % (Jonsson et al. 2010). Mostly the infection causes a self-limiting influenza-like illness. Both HPS and HFRS affects the blood vessels and alter the barrier functions of the vascular endothelium, causing systemic vascular leakage, i.e. hemorrhaging.
The Emergence of orthohantavirus in Britain
Orthohantaviruses have historically not been considered enzootic to the UK, but in the current decade three novel orthohantaviral species have been isolated from rodents in the country (Jameson, Logue, et al. 2013; Jameson, Taori, et al. 2013; Pounder et al. 2013). Two genetically distinct strains of SEOV have been identified, one in wild and one in pet rats. Both were identified as a result of investigations into the etiology of severe cases of acute kidney injury (AKI) (Jameson, Logue, et al. 2013; Jameson, Taori, et al. 2013). Subsequently, a further 8 cases with domestic origin have been confirmed in the UK. Most of them have been linked to transmission from pet rats. The 3rd viral species identified in the UK was isolated form a field vole (microtus agrestis) (Pounder et al. 2013). The pathogenic potential to humans of this particular virus remains unknown, as no cases of human disease have been associated with it.
Proteomics is the study of the proteins in a biological system, i.e. using analytical tools to identify and quantify proteins, determine their structure and function, or investigate protein interactions (Van Oudenhove & Devreese 2013). A proteome encompasses all expressed proteins, including post-translational modifications, produced by a cell or tissue. The proteome is a dynamic entity, and what is expressed varies depending on the specific condition the cell or tissue is experiencing at the time of investigation (Vizcaion 2015). The field of clinical proteomics aims to answer questions of clinical significance using proteomic methods. Knowledge of relative and absolute concentrations of plasma proteins can prove useful for monitoring and diagnosing disease, and an essential aspect of clinical proteomics is comparing the relative quantity of plasma proteins in healthy and diseased conditions (Nanjappa et al. 2014). Potential plasma and serum biomarkers for a range of pathologies, such as stroke, autoimmune disorders and infectious diseases, have been investigated (Zimmermann-Ivol et al. 2004; Bauer et al. 2006; Sawai et al. 2010; Kumar et al. 2012; Huang et al. 2014).
Looking for biomarkers of orthohantavirus infection
By analysing patient sera via mass spectrometry it is possible to determine changes in the proteome of orthohantavirus infected patients compared to healthy controls. Mass spectrometry is a high throughput method that allows for simultaneous quantification and identification of hundreds of proteins in a single experiment, without the need for a priori knowledge about specific proteins of interest (Nanjappa et al. 2014).
Mass spectrometers measure the molecular weight of a sample, or more specifically, the mass-to-charge (m/z) ratio of charged ions. The basic components of a mass spectrometer are; an ion source that ionizes sample molecules, an analyzer that uses electromagnetic fields to separates ions based on their mass, and a detector that records the presence of ions. The results are plotted as a mass spectrum with m/z on the x-axis and ion intensity on the y-axis, which, when searched against established databases predicts the identity of peptides and proteins in a sample (Parker CE et al. 2010).
This can potentially reveal diagnostic or prognostic biomarkers of acute infection and, on a mechanistic level, give insights into the biology driving the disease and host response. AKI is a hallmark of HFRS, and ideally, these biomarkers would be able to specifically point to orthohantavirus as the causative agent in these cases. AKI is, however, a common complication in hospital settings, brought about by a range of underlying pathologies, both infectious and non-infectious. Effective treatment is dependent on treatment of the underlying cause, so biomarkers that can aid in differentiating distinct causes of AKI would be very useful for prompt initiation of appropriate, possibly life-saving, treatments.