Today we are introducing you in brief to Tick-bourne encephalitis virus, another flavivirus spread by ticks!
Tick-bourne encephalitis virus (TBEV) is a positive sense single stranded RNA virus, belonging to the flavivirus family. See other flavivirus Dengue here.
The name self-explanatory, a virus which is carried by ticks and causes encephalitis! The first recorded case dates back to the 18th century Scandinavian church records (Lindquist & Vapalahti, 2008).
Ixodes spp. a species of tick, transmits the virus to humans, though the cycle includes birds and deer.
Nymphs have reduced host specificity – so are the most important for human transmission!
Dendritic cells found in the skin.
Neutrophils – a type of immune cell.
Ixodes spp. are responsible for transmission of TBEV to humans.
Habitats range from western Europe to the eastern coast of Japan (Lindquist & Vapalahti, 2008).
Did you know?
Recent studies indicate that the thread of TBEV in europe will escalate with climate change as climate change forces the viruses host northwards. (Nah et al, 2020).
Kuno G, Chang GJ, Tsuchiya KR, Karabatsos N, Cropp CB. Phylogeny of the genus Flavivirus. J Virol. 1998 Jan;72(1) 73-83. doi:10.1128/jvi.72.1.73-83.1998. PMID: 9420202; PMCID: PMC109351.
Labuda, M., Austyn, J. M., Zuffova, E., Kozuch, O., Fuchsberger, N., Lysy, J., & Nuttall, P. A. (1996). Importance of localized skin infection in tick-borne encephalitis virus transmission. Virology, 219(2), 357–366. https://doi.org/10.1006/viro.1996.0261
Nah, K., Bede-Fazekas, Á., Trájer, A.J. et al. The potential impact of climate change on the transmission risk of tick-borne encephalitis in Hungary. BMC Infect Dis 20, 34 (2020). https://doi.org/10.1186/s12879-019-4734-4
Did you know that there are over 1031 viruses on this earth…? That’s ten nonillion?!
This is Virus of the Week:
The Science Social has made it their mission to introduce a virus each week to help raise general understanding of virology. We don’t think we will get through all the viruses through this series, just a select few.
Here are some of the things that you will learn about each virus that we chose to present to you each week:
“Did you know…?”
And of course, a reference list from peer reviewed articles so you can be assured, we are not making it up!
But wait… I don’t know what any of that means…
Taxonomy is a tool used by scientists to classify all living things. Think of it as a bit like a really big, detailed family tree which shows you how closely related each living thing is. This was developed by a Swedish botanist named Carolus Linnaeus back in the 18th century. In short, all living things are grouped into 7 Kingdoms of life; e.g. Animalia, Plantae, Fungi, Chromista, Protozoa, Archaea and Bacteria. Each Kingdom of life are then split further into Phylum > Class > Phylum > Order > Family > Genus > Species.
The scientific classification of a human is:
Domain: Eukaryota Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Genus: Homo Species:sapiens
I’m sure you are all familiar with Homo sapiens, well this is how we, as humans, fit into the taxonomy hierarchy.
Live Science give a good overview of taxonomy here!
The Taxonomy of Viruses though?!
The International Committee on Taxonomy of Viruses (ICTV) are responsible for developing, refining and maintaining a universal virus taxonomy. You can find more out about them here.
This one literally means, where did the name come from.
We will be discussing what hosts the virus of the week can replicate in. We will be looking at viruses where the humans are the main host, but also others too.
This is a fancy scientific way of saying, which cells in the body (or organism) the virus is “attracted” too. For example, this virus infects mainly these cells.
How is the virus transmitted?! Through the air? A vector (for example a mosquito or a tick…?), contaminated food or water?
What does the infection of this particularly look like in the form of disease?
Did you know?:
We thought we would throw in a fun fact… just to attempt at making this interesting.
Remember we have a virology section on our blog which you can find here!
We hope you enjoy virus of the week – we are really excited to share this with you!
A second simultaneous Ebola outbreak has been confirmed in the Democratic Republic of Congo (DRC), (World Health Organization, 2020). This marks the 11th Ebola outbreak in central Africa which comes at a time when the continent also battles the COVID-19 pandemic.
First discovered in 1976, ebola viruses have since re-emerged across the African continent. The virus reached international attention during the longest and most extensive Ebola outbreak in West Africa between 2013 – 2015.
Historical Ebola outbreaks have fatality rates as high as 88%, almost 9 out of 10 people would die as a result of infection. The West Africa outbreak, however, saw a drastic reduction in fatality rate, to around 40%. The reduction in fatality rate was likely a result of the increased basic support, advanced and more appropriate care for those infected and earlier case detection, allowing for better management of both patients and outbreak spread (Baseler et al., 2017).
The most recent outbreak is in Mbandaka in the Équateur region, 600 miles from the ongoing Kivu Ebola epidemic in the North Kivu and Ituri provinces. The cases in Mbandaka are thought to be separate from the Kivu Ebola epidemic and instead the result of a new ‘spillover’ event from an animal reservoir to humans.
As of the 10th of June, a total of 12 cases have been reported; 9 confirmed cases, 3 suspected cases and 6 deaths, (Bujakera, Holland and Heavens, 2020)*. Positive samples were confirmed via testing at the Institut National de Recherche Biomédicale (INRB) – the countries national medical research organisation.
Although case number is relatively small at present, this is likely to rise as contacts are traced and the incubation period of 2-21 days elapses. Whilst the outbreak has presented at an already challenging time, scientists and doctors are on the ground with capacity to trace and diagnose. This service was expanded and refined in 2018 in response to previous outbreaks (World Health Organization, 2020).
The Kivu Ebola epidemic began in August 2018, over 3,400 people have been infected and sadly 2,200 lives lost despite the implementation of aggressive control measures. A number of factors have hindered this operation including; stigmatization, civil unrest and logistical issues.
Community level prevention and outbreak measures are dependent on the public trusting local authorities, however 31.9% of 961 individuals surveyed in North Kivu trusted that local authorities were acting in their best interests. The same survey reported 25.5 % of those surveyed believed the outbreak was a hoax, (Vinck et al., 2019). Complicating this were populist politicians publishing their own doubts on the outbreak validity to gain support in the 2018 elections. The country had not yet had a peaceful transition of power since decolonialisation in 1960, (Moran, 2018).
However, deployment of an experimental vaccine, coupled with rapid diagnostics helped to halt the outbreak. Following emergency use in 2016, the Ervebo vaccine was finally approved for use in 2019, after clinical trial demonstrated safety and efficacy; 97.5% efficacy in preventing Ebola infection compared to no vaccination, (Regules et al., 2015; World Health Organization, 2019).
Although an effective vaccination is now available, this is by no means the end of the problem. Availability, difficulties in contact tracing and public perception are all challenges that must be addressed to manage the outbreak during an already arduous time.
It is hoped that authorities and individuals alike can action their learnings from previous outbreaks, to bring this new outbreak to a swift end.
The DRC is currently contending with outbreaks of cholera, SARS-CoV-2, measles and two separate Ebola clusters. This serves as a stark reminder that whilst the world fights against the SARS-CoV-2 pandemic, Ebola outbreaks will stop for no country and no person.
Viruses emerge, or spillover often in nature, ebola virus is an example of this. Check out our blog on viral emergence here, or our post about bats and viruses.
*Please note that this article is not by a scientific body and reports figures from a WHO press conference which could not be confirmed on WHO.int.
Written by Charlotte Rigby
Baseler, L. et al. (2017) ‘The Pathogenesis of Ebola Virus Disease’, Annual Review of Pathology: Mechanisms of Disease, 12(1), pp. 387–418. doi: 10.1146/annurev-pathol-052016-100506.
Bujakera, S., Holland, H. H. and Heavens, A. (2020) Up to 12 infected in Congo’s new Ebola outbreak: WHO, Reuters.
Moran, B. (2018) ‘Fighting Ebola in conflict in the DR Congo’, The Lancet. Elsevier, 392(10155), pp. 1295–1296. doi: 10.1016/S0140-6736(18)32512-1.
Regules, J. A. et al. (2015) ‘A Recombinant Vesicular Stomatitis Virus Ebola Vaccine’, New England Journal of Medicine. Massachusetts Medical Society, 376(4), pp. 330–341. doi: 10.1056/NEJMoa1414216.
Vinck, P. et al. (2019) ‘Institutional trust and misinformation in the response to the 2018–19 Ebola outbreak in North Kivu, DR Congo: a population-based survey’, The Lancet Infectious Diseases, 19(5), pp. 529–536. doi: https://doi.org/10.1016/S1473-3099(19)30063-5.
World Health Organization (2019) Preliminary results on the efficacy of rVSV-ZEBOV-GP Ebola vaccine using the ring vaccination strategy in the control of an Ebola outbreak in the Democratic Republic of the Congo: an example of integration of research into epidemic response. doi: 10.1016/j.surfcoat.2019.125084.
World Health Organization (2020) New Ebola outbreak detected in northwest Democratic Republic of the Congo; WHO surge team supporting the response. Available at: https://www.who.int/news-room/detail/01-06-2020-new-ebola-outbreak-detected-in-northwest-democratic-republic-of-the-congo-who-surge-team-supporting-the-response (Accessed: 2 June 2020).
Viral diseases have shaped human history. A sudden emergence has the power to cause huge social changes, like ones we’re currently experiencing. But how do they do this? What causes a virus to jump, or ‘spill over’ into a new species?
What is an emerging virus and how do they emerge?
An emerging virus is a virus which has entered a new population where it previously didn’t exist or is expanding its geographical range. Global disease emergence is increasing for many reasons and we’ll discuss why this is occurring and why most emerging viruses that normally infect animals are now infecting humans.
What’s important to remember is there are no singular reasons for viral disease emergence, and we might never know what occurred to cause a disease to break into new populations. But there’s many ways this can happen, ranging from the virus’s genetics all the way through to human-environment interactions. Here we’re going to focus on RNA viruses as these are the viruses which most commonly cross species barriers1. Let’s start with the genetics first.
RNA viruses contain an enzyme called RdRp. This enzyme replicates RNA. RNA is a form of genetic code like DNA, so it encodes genes. However, RdRp is prone to making mistakes, it might miss a base, it might use the wrong one and its common for this to happen. This means a virus can be produced with different properties, this can range from being able to target a new cell type to replicating faster. One case where this occurred was during the 1918 Spanish Flu, where a mutation allowed the virus to replicate in tissues outside the respiratory tract2.
Reassortment of segmented genomes
Reassortment is the process where genetic material might get ‘mixed up’. When a cell is infected with two different but closely related viruses there’s a chance this might occur. Think of it like mixing your favourite drinks. It could work, and you might have a new flavour, or it might not! It’s easier for segmented genomes, so the genetic code is in multiple segments and is common in viruses like influenza. H1N1 is an influenza virus which is made up of bird, pig and human influenza strains3.
Recombination of RNA genomes
Recombination is a random event which occurs when RdRp, the enzyme which makes new RNA, falls off the genome its copying onto a different one. It ultimately will produce an RNA genome which is a combination of two different viruses. This is another common event and many virus families have evidence of this occurring, including Herpesviruses, HIV and even Coronaviruses4,5.
Changes in weather
Climate change isn’t only impacting our weather, it’s also changing disease distributions through temperature but also causing changes in host territory. Ultimately this changes how we interact with hosts of viruses as well as their biology. For example, Japanese Encephalitis Virus (JEV). This virus is carried by mosquitoes, so a higher temperature alters host territory as well as allowing for mosquito development to occur where it didn’t previously. This is because mosquitos have a minimum temperature where development will occur, and for the mosquito which carries JEV its 22-23 °C. However, viral diseases can have a minimum transmission temperature, and JEV has one of 25-26 °C. If more countries have temperatures above this range, then the virus can be transmitted in new populations. What this all means is as global temperatures rise it’s very likely countries will experience diseases they haven’t previously6.
Bush meat and live animal markets
Consumption of bush meat and live animal markets remove natural barriers in place, meaning that close contact between animals and humans now occurs. Outbreaks may occur due to consumption of an animal which died of a disease, and not of more natural causes. This is how Ebola outbreaks have started before. However, it is important to consider the socio-economic conditions found within regions where consumption of bush meat occurs. Protein sources in these regions can be expensive and the local population may not have the choices we do7. Reducing disease emergence from live animal markets can be done safely by reducing inter-species interactions, essentially handling the animals less and making the markets less crowded. However, it could also be done through limiting the days of operation8.
Changing land use and farming practices
Deforestation of land for farming and urban development is forcing disease hosts to come into closer contact with humans, one example where this is occurring is Australia. Here, horse farms are traditionally where fruit bats reside however urbanisation has resulted in loss of the natural habitat, forcing greater interactions with the human population9.
So, there we have it. Several mechanisms on how viruses can emerge into human populations. But what about SARS-CoV-2? Well, the jury’s still out. Though early cases were linked to a seafood market many weren’t, indicating the source of the virus likely wasn’t here. In the meantime, scientists will be hard at work hoping to solve many puzzles, including this! If you have any questions about what was discussed drop us a message below or on Facebook, Twitter or Instagram and we’ll get back to you.
For more information on the origins of SARS-CoV-2 read our blogpost breaking down a Nature paper by Dr Jordan Clark here.
For more information on viral disease emergence check out ‘Spillover’ by David Quammen.
1.J Woolhouse, M. E., Adair, K. & Brierley, L. RNA Viruses: A Case Study of the Biology of Emerging Infectious Diseases. Microbiol. Spectr.1, 10.1128/microbiolspec.OH-0001–2012 (2013).
2.Taubenberger, J. K. The origin and virulence of the 1918 ‘Spanish’ influenza virus. Proc. Am. Philos. Soc.150, 86–112 (2006).
3.Vijaykrishna, D. et al. Reassortment of pandemic H1N1/2009 influenza A virus in swine. Science328, 1529 (2010).
4.Fleischmann, W. J. Medical Microbiology. (University of Texas Medical Branch, 1996).
5.Su, S. et al. Epidemiology , Genetic Recombination , and Pathogenesis of Coronaviruses. Trends Microbiol.24, 490–502 (2016).
6.Wu, X., Lu, Y., Zhou, S., Chen, L. & Xu, B. Impact of climate change on human infectious diseases : Empirical evidence and human adaptation. Environ. Int.86, 14–23 (2016).
7.Kurpiers, L. A., Schulte-Herbrüggen, B., Ejotre, I. & Reeder, D. M. Bushmeat and Emerging Infectious Diseases: Lessons from Africa BT – Problematic Wildlife: A Cross-Disciplinary Approach. in (ed. Angelici, F. M.) 507–551 (Springer International Publishing, 2016). doi:10.1007/978-3-319-22246-2_24
8.Karesh, W. B., Cook, R. A., Bennett, E. L. & Newcomb, J. Wildlife trade and global disease emergence. Emerg. Infect. Dis.11, 1000–1002 (2005).
9.Plowright, R. K. et al. Urban habituation, ecological connectivity and epidemic dampening: the emergence of Hendra virus from flying foxes (Pteropus spp.). Proceedings. Biol. Sci.278, 3703–3712 (2011).
The 17th of April marks International Bat Appreciation Day. This is because bats begin to emerge from hibernation at this time of year. Despite all the bad press bats get, especially in light of the coronavirus outbreak, they actually play an important roll in nature.
Bats are insectivorous creatures, and reduce the number of many annoying insects. Did you know a bat can eat up to 1000 mosquitoes in an hour?!
Bats are fascinating mammals. Unique in several ways, including their ability to fly, they also have a harmonious relationship with many viruses that can be devastating to humans.
Viruses such as Ebola virus, Coronaviruses (e.g. SARS), and Hendra virus are examples of Zoonotic viruses that are found in bats. Zoonotic is the term for viruses that jump species barriers or “spill over”, i.e. from bats to humans. These viruses often cause no physical symptoms in bats, and due to their lifestyle of roosting in large colonies, can spread easily through large populations.
Wynee and Wang (2013) from CSIRO Australian Animal Health Laboratory, Geelong, Australia, released an open-access article in PNAS asking whether bats are friends or foe. They remind us that bats are just as diverse as the viruses that infect them. The picture below, also found in their article shows different species of bats, and electron microscope images of the viruses that can infect them (1).
The reasons for why bats can tolerate these viruses are not fully understood, but there are some characterised differences in their immune system response that are thought to account for this (2).
One relatively well supported hypothesis for the underlying reason is due to their flight, which puts a large amount of stress on the body. Evidence suggests that they have managed to deal with this stress by the evolution of an altered immune response, which then allows the bats to control viral replication whilst minimising any counter-productive over response (3).
All of this is great for bats, but becomes a problem for us when these viruses jump into the human population. Our immune systems respond differently to bats, and this results in the diseases we see. So, what can we do?
To some, the obvious response may be to exterminate wild bat populations. Even without considering the obvious moral objections to this, it would also be counter-productive for many reasons. Bats are incredibly important to ecosystems, playing crucial roles in pollination, insect control, and seed dispersal (4).
In order to reduce the chances of spill over events, it is important to look at the ways that human activity brings us into more frequent contact with bats, such as deforestation and the possibility of bats passing diseases to us via animals in our food supply chains. We can then find ways to minimise these.
In the meantime, researchers can learn a lot from the differences between the immune system response of humans and bats, in order to identify ways in which ours is not effective in tackling viruses. (2).
We should appreciate these wonderful mammals, understand the ways they can be dangerous, and learn to live alongside them whilst minimising contact. It will suit both us and them!