Friday, 17 July 2015

Haemorrhagic fever viruses...

A viral haemorrhagic fever (VHF) is an umbrella description for severe illnesses, usually discussed in relation to human and non-human primates, which can be associated with bleeding - although not always or even most of the time. VHF diseases often have fever and can affect multiple organs and systems within the body.

Outbreaks of VHFs are zoonotic (infection of humans after contact with an infected animal) and often irregular, reflecting sporadic transmission from an infected animal or insect host, spread between humans, or from an animal reservoir to other animal hosts.

As we learn more, it seems that the majority (?all) of viral infections result in outcomes that exist in a spectrum from severe to moderate to mild and even at times and perhaps controversially, asymptomatic infections (depending on what and how you measure and whether you look deeply enough and for long enough). Yet even though overt bleeding might not be obvious, there are frequently laboratory indications of clotting abnormalities in the blood of infected people-so the naming is still functional.[4] Bear in mind however, that "VHF" may not always be used to describe severe disease, but it will always be a term that pervades the historical literature.

VHF disease results mostly from infection by a number of viruses which have RNA genomes surrounded by a lipid envelope and which belong to a wide range of distinct viral families. Below I've listed some of these family names in italics (immediately adjacent to the filled bullet point) and under each family are some specific examples of viral species, also in italics (open bullet point):[3]
  • Arenaviridae including: 
    • Lassa mammarenavirus (disease: Lassa fever) 
    • Junín mammarenavirus (disease: Argentine haemorrhagic fever)
    • Machupo mammarenavirus (disease: Bolivian haemorrhagic fever)
  • Bunyaviridae including:
    • Crimean-Congo haemorrhagic fever virus 
    • Rift Valley fever virus (disease: Rift Valley fever)
    • Hantaan virus (diseases: hantavirus pulmonary syndrome [HPS], hantavirus haemorrhagic fever with renal syndrome [HFRS])
  • Filoviridae including: 
    • Zaire Ebolavirus (Ebola virus disease [EVD]) 
    • Marburg marburgvirus (Marburg virus disease)
  • Flaviviridae including: 
    • Yellow fever virus 
    • Dengue virus
    • Omsk hemorrhagic fever virus 
    • Kyasanur Forest disease virus
This blog has recently acquired quite a bit of knowledge about one of these VHF viruses - a variant of Zaire ebolavirus called Makona.You may have heard about what a single "sporadic" transmission is capable of in the right setting and circumstances.

Just like those all over the world who got caught out in different ways by the scale and ferocity of the EVD epidemic in West Africa last year and early this year, VDU knew little about the virus or the disease before March 2014. It took a lot of reading to get blog posts together in the early days and weeks. Over time VDU aims to learn more about the other viruses listed above so it can more effectively communicate about them...should the need arise; and that list is not exhaustive. As VDU learns, it will share that knowledge here. VDU isn't a textbook of course or is it a peer-reviewed source - its what's may be called community grey literature,[5,6] and there already many excellent resources for this knowledge. But as ever, I do this because it teaches me some new things as well as one or two of you - that makes it well worth my spare time and basically for purely selfish reasons! 

If you simply can't wait for more detail, you're now armed with a few go forth and learn more!