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Showing posts with label genome. Show all posts
Showing posts with label genome. Show all posts

The impact of cell culture on virus as highlighted by deep sequencing..[UPDATED]

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Alignment of complete or near complete MERS-CoV
genomes made using Geneious v6.1.7.
The Neighbor-Joining tree was made using MEGA with
1000 bootstraps. Red stars indicate virus from same patient. 
Vertical bars to the right indicate Clade A (dark blue)
and B (pale blue). Sequences from the the 2013 Al-Ahsa
hospital outbreak are boxed in pink. GenBank
accession numbers are indicated at the end of
each sequence name which also includes region
of detection, host and date of sample collection.
Click on image to enlarge.
Just a quick post to note the difference that "passage" in cell culture (isolation of an infectious virus using lab cells inoculated with the original virus-positive patient material, some of which is taken off and added to a new flask of cells and this process repeated as needed)  can do to the virus as it changes to grow most effectively in the new environment...this is akin to the adaptive changes seen when a virus first jumps to a an entirely different species.

Apparently the 2 starred (red stars in the figure) virus genomes are from the same 60-year old male patient [1,2,3; ] but the original variant, EMC/2012, was sequenced from material after 6 rounds of cell culture [3] while the Bisha_1 variant was not [1]; it was subjected to deep sequencing directly after nucleic acid preparation using an original respiratory sample aliquot (nasopharyngeal swab)[1]. 

Given that cell culture passage seems to be related to the positioning of EMC/2012 in Clade A versus Bisha_1 in Clade B (indicated by a pale blue line), does this mean there is no Clade A (dark blue vertical bar) and that it's just an artefact??

Probably not. Why? Because the Jordan-N3/2012 virus that is also found in Clade A and it also originates from a human specimen collected in 2012. It is listed as having been sequenced from a bronchial sample. There is no mention of cell culture on its GenBank record - which does not mean there was no culture. But when that sample was passaged through culture and sequenced (N3/2012 MG167; sequence not shown in this tree) it remained 99.95% identical to the original sequence; just 2 nucleotide differences out of 30,028nt. 1 difference in the spike gene and 1 Open Reading Frame 1a). These are unlikely to be enough to switch its clade  but I'm realigning with this sequence included just to be sure about that!

I thought that was kinda interesting.

NB. There may be some concern over the specimen labelling used to identify samples for sequencing of EMC/2012 or Bisha_1. I'm attempting to sort our by following this up with the lead author.[1]

Reference...
  1. Transmission and evolution of the Middle East respiratory syndrome coronavirus in Saudi Arabia: a descriptive genomic study. Cotten et al. Lancet 2012;382:1993-2002
  2. 60-year old man from Bisha who died in a Jeddah hospital (EMC/2012 variant)
    Isolation of a Novel Coronavirus from a Man with Pneumonia in Saudi Arabia. Zaki et al. N Engl J Med 2012; 367:1814-1820
  3. Genomic workup on EMC/2012
    Genomic Characterization of a Newly Discovered Coronavirus Associated with Acute Respiratory Distress Syndrome in Humans. van Boheemen. mBio 2002; 3(6): e00473-12
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New MERS-CoV genome sequence on GenBank...

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I'm a little bogged down in my day-job for lots of posts just now (and too busy at nights hanging Christmas lights at home!) but just thought I'd post about the latest Middle East respiratory syndrome coronavirus complete genome sequence that's dropped onto GenBank.

It was submitted in October but came online 7-Dec.

I've added in the likely FluTracker's case number - this is the nearest match to the collection date but it may be from the index case (FT#31); both detected in France, the former form the United Arab Emirates.

Key features...
  • Name: Middle East respiratory syndrome coronavirus isolate FRA/UAE, complete genome 
  • Date of sample collection: 7-May-2013, France
  • Sequence length: 29,901nt
  • MERS-CoV case: FT#34; 
  • GenBank accession number: KF745068
  • Link: http://www.ncbi.nlm.nih.gov/nuccore/KF745068.1
  • Authors: Enouf,V., Briand,D. and van der Werf,S.
  • Virus sample source: Vero cell culture isolate
  • Sequencing type: Sanger
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Dutch researchers in collaboration with Qatar are at work sequencing MERS-CoV from camels...

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And from the WHO comes confirmation of some of my earlier bits and pieces about the MERS-CoV in camels story from earlier....


Further, some very interesting titbits from a Twitter exchange this evening.

Firstly Prof. Marion Koopmans, Head of Virology at the Laboratory for Infectious Diseases of the National Institute of Public Health in the Netherlands confirmed that this was the MERS-CoV and not something requiring lengthy sentences filled with "probable" and "MERS-CoV-like"...


..and that for the most useful conclusions to be drawn from any sequencing being undertaken..


..but that despite all sorts of great leaps in technology, not to mention in distance-spanning scientific collaborations, things don't just happen overnight. 

We should all be mindful that there are many steps between taking a (hopefully adequate) sample(s) from a human or animal, and reaching any useful conclusion about how the molecularly characterized virus might have travelled (human to dromedary, vice versa or via some other vector or intermediate)...


As Prof Andrew Rambaut, Institute of Evolutionary Biology, University of Edinburgh, noted...


And on the subject of whether the new sequences will lead to an indication of which direction this particular cluster of infections is travelling i.e. from human-to-camel or camel-to-human, Prof. Rambaut had this thought on following the viral genome's sequence variations (polymorphisms)...


This is all really great to watch. A fast and fruitful collaboration between sample holders and laboratory researchers, expert in their fields.
Click on image to enlarge.
Those POS for a fragment of MERS-CoV or
MERS-CoV-like virus sequence are highlighted
in red. Whether there are other intermediates
remains to be confirmed.

At this point, I believe (and it is just a belief) that the camel is looking good for a source of MERS-CoV acquisition by humans. Is it an endemic camel virus? Well, we still have the knowledge that bats seem to harbour a lot of CoVs, and there is that pesky Taphozus perforatus sequence discovered from earlier in the year. It looked an awful lot like a fragment of the MERS-CoV genome. Baboons - I'm holding out for them to be the link between bats and camels...but that is a hope in the absence of any data whatsoever!

Today's confirmation of a cluster of 3 POS camels among 14 represents 21% of the animals POS in a single area. 

If we consider this to be human-to-camel transmission, then this would be a much steeper proportion of positives than we normally see when we look at studies of close contacts of human MERS cases. Camels must be very susceptible to MERS-CoV infection because human contact testing just does not show this level of onward transmission. More susceptible to humans? No, I think we're getting closer to confirming that it's a camel-to-human thing...but we are not there yet.

Work continues, but today was a significant day and one in which I give thanks for the ability of people from all over the world to work together towards common goals in preventing human disease. 
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Molecular epidemiology of Middle East respiratory syndrome coronavirus (MERS-CoV)

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And a newcomer to the MERS-CoV birthday celebrations! What great timing to have this released today.

The Lancet paper accompanying those recent partial and full genome sequences has been released form its cage. It's a collaborative effort by authors affiliated with the Global Centre for Mass Gatherings Medicine (Ministry of Health Saudi Arabia), Welcome Trust Sanger Institute (United Kingdom) and many other locations.

A few highlights of the largest MERS-CoV molecular epidemiology study to date, which includes some great transmission figures and trees (hat tip to the graphics people at Lancet):
  • Genetic diversity analyses 3 distinct genotypes were identified from human cases in Riyadh 
  • The Al-Ahsa hospital cluster may have had more than 1 viral introduction
  • Other clusters and standalnone cases can be representd as distinct genoytpes of MERS-CoV, posisbly indicating multiple different virus acquisitions from different sources
  • Predictive evolutionary analysis suggests an evolutionary rate of 6.3x10-4 substitutions per nucleotide site per year suggesting a time to the most recent common viral ancestor was July 2011 (ranging from July 2007- June 2012). So we can rule out my harebrained "What If.." MERS-CoV was an endemic virus that we had only just discovered
  • This evolutionary rate of change suggest more than 1 jump from animal to human was the cause of the outbreak. Unlikely to be just a single introduction followed by human-to-human transmission across Saudi Arabia and beyond. This also reduced any possible R0 value (the number of cases that 1 case generates, on average, over it's period of infectivity) since transmission events were not a continuous chain but likely to be multiple different spillovers
  • The rates also suggest it's been substantial period since these viruses shared a common ancestor - so an intermediate host is still a likely culprit for spillover into humans (ongoing studies are examining camels, bats, goats, sheep, dogs, cats, rodents and others - no baboons?)
  • Contact with goats and camels has been reported in some cases and we know that camels from Oman and Egypt have antibodies to a MERS-CoV-like virus
  • A particular change in the Spike protein that may impact on its role as a site for enzymatic cleavage (by endosomal furin or trypsin-like proteases) should be further examined (codon 1020; all recent MERS-CoV S protein differ here from the EMC/2012 strain of MERS-CoV exported to the Erasmus Medical Center researchers).
The authors conclude it is imperative that a better understanding of the exposures causing these spillover events be identified.


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17 new MERS-CoV sequences bind perfectly to frontline screening PCR assay for MERS...

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Click to enlarge. The primers/probe are depicted as grey boxes.
If mismatches existed they would show up as horizontal black
lines within the grey box. No mismatches are evident.
The GenBank accession numbers are
shown on the left of this alignment of 17 MERS-CoV
sequences.
Only 17 of the 45 sequences seem to include the region covered by the upE laboratory assay I just posted about in the WHO laboratory testing update but of those, the forward and reverse oligonucleotide primers and the probe all bind without any mismatch.

While that may sound like an obvious statement considering that these viruses were probably detected using that assay it isn't.

The new MERS-CoV sequences were determined using using unbiased 2nd generation high-throughput sequencing technologies that did not rely on these primers to generate them. So we are now able to check and see if there are any nucleotide changes at the target sites for the primers and probe, that would reduce the efficiency the assay.

There are no such oligonucleotide mismatches between primer and viral genes among those 17 sequences, which is good news for that assay's continued usefulness.

Built to last eh?
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New coronavirus genomes....not MERS yet

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Unfortunately they aren't MERS-CoV genomes.

Nonetheless, a whole lot of new feline, porcine, murine, SARS, 229E and HKU1, genomes have been directly released from the J. Craig Venter Institute.

These now appear on GenBank with non-sequential accession numbers around the KF272920-KF530271. The sequences were produced using next generation sequencing technology.

Looks like the virome is in the sights of the big data guys.
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Tracking MERS-CoV through time: a spikey problem

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This morning on Twitter, Helen Branswell (@HelenBranswell) asked this question, with a comment...

So I thought a little perspective might be nice. 

The SARS epidemic had its origins around Nov 16th 2002, although the major activity started in Feb of 2003. 
  • 64 human SARS-CoV genomes had been produced by September 2003 ([UPDATED:] see Science paper). That is by 317-days later, or 10-months, 13-days (perhaps less given that the genome sequences were possibly sequenced well before the paper was submitted e.g. late phase genome s seem to have been submitted to GenBank by July 2003). 
  • For MERS-CoV we currently have 9 genomes at 505-days (give or take), or 1-year, 4-months.
Not that anyone needs to be reminded, but 80% of MERS-CoV cases come from the Kingdom of Saudi Arabia. The world is relying on them, or their collaborators, to turn the nucleic acid extracts used to define these cases (PCR-POSs hopefully kept in a -80'C freezer), into templates for gene or genome sequencing.

I personally don't believe we need to have complete genomes right now in order to fulfil the fairly urgent public health need to monitor the virus and notice if it changes, or is changing, or is not changing. These changes tell us whether the virus is still adapting or has settled in - perhaps having done so prior to this outbreak's indicator, severe disease. 

What else to use to track adaptation?

Perhaps the 4,000nt Spike (S) gene, or some smaller but suitably variable portion of it, could be a target for sequencing? 

Zhang and colleagues have data showing it could be used to track an animal coronavirus's adaptation to humans, through its 3 pandemic phases. This was done using phylogeny (a way to show how one sequence relates to another through time and space) of nucleic acid sequences and alignments of the translated version of these sequences. All we need is primer sequences that could be used to reliably amplify the S gene of the MERS-CoV. If anyone has those already perhaps they could publish them...if they haven't already. A very brief look at the 9 MERS-CoV genomes already shows some variety. Perhaps unsurprisingly, there is very little change among the 4 Al-Ahsa genomes; their collection dates are separated in time by 17-days.

This shows a schematic of the aligned Spike genes. The black lines within the grey boxes represent nucleotides that differ from the consensus. More differences are obvious in the earlier sequences. The oldest MERS-CoV isolate is at the bottom, the most recent, at the top (detailed below). See the full version here at VDU.
Interestingly, the phylogeny of the complete Spike genes looks  similar to that of the complete MERS-CoV genomes. However  its doe snot place the isolates in order of increasing time to the extent that the full genomes do. I also looked at a 900bp fragment of the 3' of the Spike gene - easier to amplify but a very similar tree to that of the complete Spike.


All 9 complete MERS-CoV spike protein genes (nt). Alignment in Geneious Pro, tree in MEGA 5.10.
Full version will be here at VDU.

All 9 complete MERS-CoV genomes (nt). The arrow indicates moving forward in time; the oldest MERS-CoV isolates at the bottom, the most recent at the top. Alignment in Geneious Pro, tree in MEGA 5.10.
Full version will be here at VDU.

So where does that leave us?

Adaptive pressures on the SARS-CoV drove its genome towards settling down in the late stage of the 3-phase outbreak (defined by the Chinese SARS Molecular Epidemiology Consortium), with changes in the Spike gene occurring before that. Complete genomes are clearly the gold standard - so I dial down that personal belief from earlier.

The Spike gene still seems a useful target for MERS-CoV too, although not as accurate at plotting the time of virus isolation as complete MERS-CoV genomes were in my example above. Still, it, or some part of it, is still of use as an early-warning system to alert us to viral change and it will prove easier to amplify by smaller or less genomics-focussed laboratories. Something we need to consider in order to get some information, which is far better than none.

While we've seen predictive modelling for the age of MERS-CoV, we don't actually know when the virus came to be or when it started spilling over to humans. More full genome sequences would certainly help address that question. And finding its origin.

However, perhaps we should make the trade off and use the 3' end of the Spike gene now, in an effort to keep some sort of eye on how the MERS-CoV is travelling? Anyone else have a good region that fits the bill?
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