Torah Insights Into Bacteria and Infectious Diseases


Rabbi Zamir Cohen

This applies regardless of whether the person is healthy or not, for a person may carry bacteria that do not harm him, but can be dangerous to others.”

The subject of medicine and the knowledge of healing were well known in ancient times. The Talmud mentions cures for a long list of maladies, including at least one cure that is more advanced than what medical technology offers today. It describes a type of surgery to remove a brain tumor, in which a drug was given to the patient to put him to sleep and a mixture of herbs was boiled, cooled, and poured on the patient’s head until his skull became soft, allowing it to be cut open and the growth removed. Two millennia before MRIs and CT scans, medical practitioners had a way to determine the exact location of a brain tumor and an incredibly detailed understanding of human anatomy.

Unfortunately, many, if not all, of those remedies were specific to that era, and with passage of time, directions for their use were forgotten, along with much of the medical wisdom alluded to in the Talmud.

In recent centuries, however, we have seen remarkable advances in the field of medicine. Before the microscope revealed to us the hidden world of bacteria, physicians never dreamt that creatures existed that were invisible to the naked eye.

The size of average bacteria is about two microns by half a micron (a micron being a millionth of a meter, or a millionth of 39.37 inches). This means that laid end to end, there are 500,000 bacteria in a meter (or in 39.37 inches), or 2,000,000 lying side by side.

The first step towards discovering the existence of bacteria was taken by the Dutch scientist Antony van Leeuwenhoek (1632-1723), using an early form of microscope which he helped develop. This was a simple brass plate fitted with a single polished lens capable of magnifying 200 times. Despite its relatively weak power, it allowed Leeuwenhoek to discern tiny creatures moving within materials taken from between people’s teeth.

But it was only in the second half of the 19th century that the existence of bacteria and their role as vectors of disease was finally verified. The famous French scientist Louis Pasteur (1822-1895) was the most important 19th century researcher of microorganisms and their relationship to various diseases. After discovering the existence of bacteria, Pasteur introduced disinfectant methods into hospitals and clinics to rid them of these invisible menaces. Prior to Pasteur’s work, a single dirty scalpel might have been used to perform multiple surgeries, unwittingly transferring bacteria from one patient to another, thus resulting in an extremely high death rate among surgery patients. No one had previously drawn a connection between the bacteria-laden instruments and patient deaths. After Pasteur introduced his disinfectant methods, patient death rates dropped sharply.

Continuing his research, Pasteur found that heat could destroy harmful bacterial present in cow’s milk. As a result of this discovery, millions of infants previously unable to breastfeed were saved from death. The process he developed was subsequently named after him – pasteurization.

It has been less than 160 years since scientists made the following important discoveries:

* The existence of bacteria.

* The fact that bacteria cause and transmit disease through the blood or other bodily secretions of an infected patient.

* The fact that bacteria can be destroyed by heat. (Another recent discovery has shown that high body temperature brought on by infections itself serves to destroy bacteria within the body.)

One of the more recent discoveries in the field of microbiology is the possibility of a person carrying a dangerous strain of bacteria without being sick, and transmitting the bacteria to others who then take ill.

Germs in the Talmud

Remarkable, long before COVID-19, the notion of invisible harmful bacteria is mentioned in ancient Jewish texts. The Shulhan Aruch (Orah Haim 170:16) rules:

“A man shall not drink from a cup then give it to another, because of life threatening dangers.”

This idea is explained in the teachings of the Tanna Rabbi Eliezer (cited by the commentary of the Taz to the Shulhan Aruch):

“For perhaps there is an illness in his body, which might go from his mouth into the cup, making his friend ill.”

Rabbi Eliezer, who lived some 2,000 years ago, already knew that:

* Illness can be attributed to invisible factors, which are present not only within the affected organ, but throughout the sick person’s body, including his bodily secretions.

* These invisible transmitters can pass from person to person indirectly, such as by their sharing the same cup, whereby the second person becomes infected.

* Most importantly, even a healthy person must not share his cup with others, lest “there is an illness in his body.” In other words, even an apparently healthy person may carry a strain of bacteria that is harmless to him, but might cause illness in another.

Further evidence that the sages knew of the existence of microbes and bacteria may be drawn from the following statement of the Talmud (Masechet Avodah Zarah 28a), written some 1,600 years ago:

“Shemuel said: An open wound caused by a piece of iron is to be regarded as life threatening, and one is allowed to violate Shabbat [in order to treat it].”

Shabbat desecration is permitted only for the purpose of treating life-threatening illnesses, and therefore treating a simple wound is generally forbidden on Shabbat if it entails a Shabbat violation. However, when a wound was caused by a piece of iron, it should be treated even with procedures that involve Shabbat desecration, because even a superficial wound of this type can be life-threatening.

Did medical experts of the time find this statement puzzling, seeing that it refers to a relatively minor wound? And why is such a wound considered life-threatening?

Today, we know that rusty iron contains bacteria that can cause a tetanus infection, also known as lockjaw, and that the entry of these bacteria into the body through even a superficial wound can ultimately be lethal. The Torah sages knew this before the advent of modern science. Scientific opinion at the time (and till centuries later) denied any connection between superficial wounds and life-threatening illness. Indeed, before the discovery of bacteria, there was no good reason to imagine that a small wound could cause death. Non-Jewish medical experts would have claimed that the patient died from some previous, internal disease. And undoubtedly, they would not have recommended that a Jew violate Shabbat to treat a patient under such circumstances. Yet, despite the sages’ efforts to preserve the sanctity of Shabbat, they were not ready to accept the current medical opinion in this case. Their knowledge had been passed on from generation to generation, and they knew that a wound caused by iron could be life-threatening. Appropriately, they gave practical instructions to treat such a wound, big or small, as it could cause a massive lethal infection. As we know today, scientists eventually reached the same conclusion through their research.

Medical Insights in the Talmud

We can now see that through their study of the Torah, the Sages knew the following:

  1. A. Tiny, invisible creatures exist in our natural world.
  2. B. These creatures, now called bacteria (from the Greek word for “small staff,” because the first observed bacteria were rod shaped), can cause the transmission of infectious diseases from one person to another.
  3. C. Bacteria are present throughout the sick person’s body and not only in the affected organ. This includes bodily secretions such as saliva.
  4. D. We should therefore be careful not to drink from someone else’s cup, in case he is sick and the bacteria in his saliva prove contagious.
  5. E. This applies regardless of whether the person is healthy or not, for a person may carry bacteria that do not harm him, but can be dangerous to others.
  6. F. Particularly dangerous bacteria can be found in rusty iron. Thus, we may violate the Shabbat prohibitions in order to treat even a superficial wound of this type. Obviously, such permission is granted only in the case of a wound through which tetanus bacteria can enter and cause infection, and not in the case of a light scrape or bruise.
  7. G. Boiling a liquid will help to destroy bacteria it may contain.
  8. H. To prevent bacterial infections during surgery, the maximum level of cleanliness should be maintained.


Rabbi Zamir Cohen is the founder of the Hidabroot organization and has written several books on the topics of Jewish thought and law.