There can be few people who like having a swab pushed up their nose to get a test for the Covid-19 infection, SARS-CoV-2. Wouldn’t it be easier if we could have our saliva tested for the infection instead?
Several tasks in Ireland are looking at utilizing saliva for screening (to recognize individuals who may require a more conclusive diagnostic test) but the “untidy” nature of saliva implies it’s not constantly as easy as it sounds.
Untidy specimens
” We do not consistently utilize saliva to evaluate for breathing infections,” states medical virologist Dr Cillian de Gascun, who directs the National Virus Recommendation Lab at University College Dublin
” That’s partially because saliva can be an unpleasant sample to deal with. It consists of enzymes that can effect on PCR– the method that magnifies genetic product from the infection in a sample, so it can be more easily determined– and saliva can be rather thick and gloopy, so it is tough for some of the automated liquid-handling devices in the lab to deal with.”
There’s another issue too, according to de Gascun. “At the minute our company believe that saliva screening would be less sensitive than the current swabs we are taking [to test for the Covid-19 virus],” he states.
” So I don’t imagine saliva replacing swab samples, however saliva testing might be helpful for particular circumstances, such as testing kids, individuals in retirement home or where a person needs to take serial tests. If saliva has an acceptable sensitivity, it may be an extra specimen type to consider, considered that it would be much better than no sample at all.”
Saliva screens
Prof Cliona O’Farrelly sees worth in saliva screening, with the emphasis on screening. “We need to evaluate great deals of people, great deals of the time, many, many times,” says O’Farrelly, teacher of relative immunology at Trinity College Dublin “So we need something much quicker, simpler and less expensive than swabs and PCR. This is where saliva can come in. We will need to diagnose a small proportion of all the individuals we screen, as many [people] will likely be negative. This is when swabs and PCR can be found in helpful for diagnosis.”
In spite of its limitations, Prof Kingston Mills at Trinity College Dublin thinks saliva could be used to screen and possibly even diagnose great deals of individuals. “The big advantage of saliva would be that it prevents the requirement for screening centres, because an individual could drool into a tube and send out that off for analysis,” he says.
Mills leads the Trinity Covid-19 Immunology Task, where Prof Orla Sheils is screening saliva samples from trainees by utilizing loop-mediated isothermal amplification (LAMP) rather than PCR.
” The LIGHT assay is quick, it takes 30 minutes, it doesn’t require advanced devices and if there is infection present it appears as a colour modification,” says Mills. “The test we are performing is not a diagnostic test, however I think the LIGHT assay could be a video game changer, specifically utilizing saliva, to detect in addition to screen.”
Detergent to protect
One method to maintain a saliva sample is to store and transfer it in a detergent that inactivates the virus but protects the genetic material. Dr John Mac Sharry from APC Microbiome Ireland and associates were recently awarded Science Foundation Ireland financing to check out the impact of cleaning agent on SARS-CoV-2 in saliva samples.
” My location of research study is lung microbiology, and before Covid-19 we had actually been taking a look at levels of germs and fungis in the saliva of clients with asthma,” explains Mac Sharry, a lecturer in medical microbiology at University College Cork
” Then, when the pandemic begun, we decided to look for infections in saliva. We are including detergent to the saliva when it is gathered, to see what happens to the virus.
The project will also compare saliva samples and swabs from the same clients to see how the saliva test protocol compares, though he admits the saliva specimens have their limitations.
” No test is best,” he states. “And it is essential that individuals do not consume or drink anything or smoke for a period before the test is taken, as this can introduce more irregularity into the sample.”
On-the-spot colour modification
Dr Niamh Gilmartin, a biochemistry lecturer at TU Dublin, echoes the requirement for saliva to be as “clean” as possible when offering a sample. “Food particles in saliva are a big issue,” she says. “And there is probably more sample preparation needed compared to, say, blood or urine, which are easier samples to manage from a lab viewpoint.”
Gilmartin, Dr Steve Meaney and colleagues are developing a colour-based package to immediately evaluate for the virus in saliva. AptaGold utilizes aptamers– short pieces of DNA– that have been created to bind to a protein on the surface of SARS-CoV-2. The aptamers are covered onto nanoparticles of gold, then if they bind to the infection in a sample, the particles clump and alter the colour of the liquid from blue to red.
The innovation searches for a protein on the infection, instead of for genetic material that can be magnified by PCR. However Gilmartin anticipates the sensitivity level of the AptaGold assay will be fit for purpose. “The idea is to make Covid-19 screening accessible beyond a laboratory,” she discusses. “However the focus is on screening, this would not be a diagnostic test.”
Not the optimum for diagnosis
While the Covid-19 pandemic is altering how we do numerous things, de Gascun does not think it will press saliva testing beyond the realm of screening and into regular diagnostics. “It is not like individuals have not considered this prior to, and there are logisitic and sensitivity reasons that saliva is not the optimum specimen for definitive medical diagnosis,” he says.
“[Saliva] might have a function to play in particular scenarios, however I don’t see it altering the way we do diagnostics for respiratory infections, and in 12 months’ time, next winter season, I would be shocked if we are utilizing saliva as the preferred specimen type for regular diagnostic screening.”
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