Yes, germs can cause disease

There are some today who not only downplay the impact of the SARS-Cov-2 virus that causes Covid-19, but deny its very existence.

Some pushing this argument are engaging in germ theory denial, rejecting the scientific consensus that germs – microorganisms that include bacteria, viruses, fungi and parasites – can cause diseases.

Germ theory denial has existed in obscure corners of alternative medicine for many years but has flourished during the Covid-19 pandemic. It can range from soft denial – a belief that germs don’t cause disease – to rejecting the existence of germs altogether. It has historically been associated with some chiropractors and naturopaths.

Several online forums are devoted to germ theory denial, including a Facebook community with 24,000 members, where members regularly discuss pseudoscientific methods to prevent disease, and to rid their bodies of ‘‘toxins’’.

Germ theory denial goes hand in hand with anti-vaccination views. Measures such as using vaccines, masks, and physical distancing are pointless if Covid19 isn’t caused by a virus.

Germ theory originated in the 16th century but was popularised through the work of Louis Pasteur in the 19th century. It replaced the more common miasma theory, which held that noxious fumes from rotting organic matter (such as dead bodies) caused disease.

Since then, the evidence for germ theory has grown. Vaccines targeting specific disease-causing microbes have eradicated smallpox, and severely limited the range of polio. Both smallpox and polio are infectious diseases caused by viruses. Vaccines mean oncecommon illnesses such as measles and whooping cough are now less common and rarer in the Western world. Modern techniques also allow for the full genome sequencing of viruses such as the SARS-Cov-2 virus, which was fully sequenced within weeks of its appearance.

Few doctors or scientists reject the theory, which has become a fundamental tenet of medicine. If germs did not cause disease, vaccines would not work, nor would antibiotics. Handwashing in hospitals would be unnecessary. There would be no need to cook chicken to prevent salmonella infection, and no reason to avoid drinking water polluted with animal faeces.

Some germ theory deniers instead believe in ‘‘terrain theory’’, which holds that the quality of the terrain – in this case, the human body – is more important in determining whether someone gets sick, rather than an external force.

Terrain theory believers will sometimes refer to the work of Antoine Be´champ, the rival of Pasteur who proposed a theory of disease similar to modern terrain theory. Some have claimed that Pasteur renounced germ theory on his deathbed, but there is no evidence this occurred.

Most doctors and scientists accept that health and lifestyle factors can indeed influence the course of a disease. People who are unhealthy or immunocompromised may struggle to mount an effective immune response if they become infected by a pathogen.

This does not mean such factors are solely responsible for all illnesses or negate the considerable body of evidence built over more than a century showing germs do exist, and can cause disease.

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This story was reviewed by The Whole Truth: Covid-19 Vaccination expert panel member Dr Dianne Sika-Paotonu, a senior lecturer in pathology and molecular medicine.