Investigating the cause of a disease is like investigating the cause of a crime. Just as the detection of a suspect’s DNA at a crime scene doesn’t prove they committed the crime, so the detection of the DNA of a virus in a patient doesn’t prove it caused the disease.
Consider the case of Epstein-Barr Virus (EBV) for example. It can cause serious diseases like arthritis, multiple sclerosis and cancer. A Japanese study in 2003 found that 43% of patients suffering from Chronic Active Epstein-Barr Virus (CAEBV) died within 5 months to 12 years of infection.
Yet EBV is one of the most common viruses in humans and has been detected in 95% of the adult population. Most of those infected are either asymptomatic or show symptoms of glandular fever, which can have similar symptoms to ‘long Covid.’
If an advertising agency attempted to create demand for an EBV treatment with daily TV and radio ads representing positive EBV tests as ‘EBV Cases’ and deaths within 28 days as ‘EBV Deaths,’ they’d be prosecuted for fraud by false representation so quickly their feet wouldn’t touch the ground.
How Viruses Are Detected
Before the invention of PCR, the gold standard for detecting viruses was to grow them in a culture of living cells and count damaged cells using a microscope.
The disadvantage of cell cultures is they need highly skilled technicians and can take weeks to complete. The advantage is they only count living viruses that multiply and damage cells. Dead virus fragments that do neither are automatically discounted.
The invention of PCR in 1983 was a game changer. Instead of waiting for viruses to grow naturally, PCR rapidly multiplies tiny amounts of viral DNA exponentially in a series of heating and cooling cycles that can be automated and completed in less than an hour.
PCR revolutionised molecular biology but its most notable application was in genetic fingerprinting, where its ability to magnify even the smallest traces of DNA became a major weapon in the fight against crime.
But, like a powerful magnifying glass or zoom lens, if it’s powerful enough to find a needle in a haystack it’s powerful enough to make mountains out of molehills.
Even the inventor of PCR, Kary Mullis, who won the Nobel Prize in Chemistry in 1993, vehemently opposed using PCR to diagnose diseases: “PCR is a process that’s used to make a whole lot of something out of something. It allows you to take a very miniscule amount of anything and make it measurable and then talk about it like it’s important.“
PCR has certainly allowed public health authorities and the media around the world to talk about a new variant of Coronavirus like it’s important, but how important is it really?
The Dose Makes The Poison
Anything can be deadly in high enough doses, even oxygen and water. Since the time of Paracelsus in the 16th century, science has known there are no such things as poisons, only poisonous concentrations:
“All things are poison, and nothing is without poison; the dosage alone makes the poison.” (Paracelsus, dritte defensio, 1538.)
This basic principle is expressed in the adage “dosis sola facit venenum“ – the dose alone makes the poison – and is the basis for all Public Health Standards which specify Maximum Permissible Doses (MPDs) for all known health hazards, from chemicals and radiation to bacteria, viruses and even noise.
Public Health Standards, Science and Law
Toxicology and Law are both highly specialised subjects with their own highly specialised language. Depending on the jurisdiction, Maximum Permissible Doses (MPDs) are also known as Health Based Exposure Limits (HBELs), Maximum Exposure Levels (MELs) and Permissible Exposure Limits (PELs). But, no matter how complicated and confusing the language, the basic principles are simple.
If the dose alone makes the poison then it’s the dose that’s the biggest concern, not the poison. And if Public Health Standards in a liberal democracy are regulated by the rule of law then the law needs to be simple enough for a jury of reasonably intelligent lay people to understand.
Although the harm caused by any toxin increases with the dose, the level of harm depends not only on the toxin, but the susceptibility of the individual and the way the toxin is delivered. Maximum Permissible Doses have to strike a balance between the benefit of increasing safety and the cost of doing it. There are many Political, Economic and Social factors to consider besides the Technology (PEST).
Take the case of noise for example. The smallest whisper may be irritating and harmful to some people, while the loudest music may be nourishing and healthy for others. If the Maximum Permissible Dose was set at a level to protect the most sensitive from any risk of harm, life would be impossible for everyone else.
Maximum Permissible Doses have to balance the costs and benefits of restricting exposure to the level of No Observable Effect (NOEL) at one end of the scale, and the level that would kill 50% of the population at the other (LD50).
Bacteria and viruses are different from other toxins, but the principle is the same. Because they multiply and increase their dose with time, maximum permissible doses need to be based on the minimum dose likely to start an infection known as the Minimum Infective Dose (MID).
Take the case of listeria monocytogenes for example. It’s the bacteria that causes listeriosis, a serious disease that can result in meningitis, sepsis and encephalitis. The case fatality rate is around 20%, making it ten times more deadly than Covid-19.
Yet listeria is widespread in the environment and can be detected in raw meat and vegetables as well as many ready-to-eat foods, including cooked meat and seafood, dairy products, pre-prepared sandwiches and salads.
The minimum dose in food likely to cause an outbreak of listeriosis is around 1,000 live bacteria per gram. Allowing a suitable margin of safety, EU and US food standards set the maximum permissible dose of listeria in ready-to-eat products at 10% of the minimum infective dose , or 100 live bacteria per gram.
If Maximum Permissible Doses were based solely on the detection of a bacteria or virus rather than the dose, the food industry would cease to exist.
Protection of the Vulnerable
The general rule of thumb for setting maximum permissible doses used to be 10% of the MID for bacteria and viruses, and 10% of the LD50 for other toxins, but this has come under increasing criticism in recent years: first with radiation, then Environmental Tobacco Smoke (ETS), then smoke in general, then viruses.