Two Mutations Caused Black Death

The Black Plague of the Middle Ages happened by accident. It was enabled by two mutations to a bacterium, scientists claim.

The germ that caused the “Black Death” is only a young bug, “evolutionarily speaking,” say scientists at Northwestern. Although it had the ability to cause a severe respiratory illness early on, two mutations occurred that gave it the ability to spread rapidly through the air, leading to the pandemics that killed millions in Europe. A press release from Northwestern University says,

While studying Yersinia pestis, the bacteria responsible for epidemics of plague such as the Black Death, Wyndham Lathem, Ph.D., assistant professor in microbiology-immunology at Northwestern University Feinberg School of Medicine, found a single small genetic change that fundamentally influenced the evolution of the deadly pathogen, and thus the course of human history.

In a paper published in Nature Communications, Lathem and first author Daniel Zimbler, Ph.D., a Feinberg post-doctoral fellow, demonstrated how the acquisition of a single gene caused the shift of Y. pestis from causing a primarily gastrointestinal infection to a more serious and often fatal respiratory disease. They further showed how later modifications of this gene enhanced infections associated with the bubonic plague.

According to the researchers. Y. pestis evolved from a similar bacterium, Y. pseudotuberculosis, that is still around today and causes mild gut infections (Live Science). The first mutation from the oldest-known ancestral strain gave it the ability to infect the lungs and cause pneumonic plague, a disease spread by rodents carrying fleas.

A second mutation—a single amino acid change—gave Y. pestis 100 times the ability to affect deep tissues and lymph nodes. This is the fast-killing strain that caused bubonic plague. Since the first known pandemic was in the time of Justinian (6th century), the deadly combo must have occurred around that time. In all, the changes to Y. pestis from its ancestral form must have occurred within the last 10,000 years—making it extremely young, considering that bacteria are among the earliest life forms in the evolutionary timeline.

Comparing the earliest known strain of Y. pestis to the pneumonic plague version, “The ancestral strains lacked the gene for a certain protein, called PLA protease.” (*) Adding that one gene can turn the harmless strain into a strain that causes pneumonic plague. Other genetic differences between the two strains appear irrelevant to disease potential. The articles do not say if the germ acquired the gene through horizontal gene transfer, but a 2007 paper posted by PubMed suggests that it was; the authors of the new paper say that the method of acquisition is unknown.

One further mutation changed a single amino acid. That was sufficient to cause bubonic plague, they say. “Before the amino acid mutation, the bacteria would have had a much more difficult time moving into a person’s bloodstream and causing a body-wide infection, the researchers said.”

The Black Death of the 14th century was undoubtedly exacerbated by ignorance of the agent and poor sanitary practices. Bacteria were only detected in the 17th century by Leeuwenhoek. Even so, cleanliness, careful observation and clear thinking might have limited the spread of the disease. Medieval towns were filthy places, overrun by rats that carried the fleas carrying the germ. Y. pestis is still endemic in the United States, the researchers note, but there are only about 7 cases a year, primarily in the southwestern US.

It appears that the deadly pathogen emerged by mistake. “The emergence of new pathogenic clones has been directly linked with both the gain and loss of genetic elements by bacteria that were previously thought to be non-virulent,” the authors say in Nature Communications.  If the PLA protease gene was acquired by horizontal gene transfer, no new genetic information was involved. The mutations, moreover, occurred in historic times.

_{*A protease is an enzyme that acts on a protein; in this case, it lyses (disrupts) plasminogen activator (PLA). Hundreds of proteases are known. They operate in every kind of life. Some human proteases are involved in digestion. Other enzymes, protease inhibitors, regulate their action.}

This information can shed light on the Curse pronounced by God the Creator in Genesis 3 after Adam and Eve sinned. It was not necessary for God to create terrible agents of death from nothing, like new disease-causing bacteria, and turn them loose on the world. In some cases, all He needed to do was take His protective hands off the well-designed machinery of life and let accidents happen. A frequent sci-fi movie theme is to illustrate what can happen when well-designed robots, intended for good, run amok (e.g., Westworld). Another possibility is that Satan, the “god of this world” (who hates God’s works and loves death), was given temporary limited autonomy to use nature for harm (cf. the Book of Job).

These are mysteries only hinted at in Scripture. What’s interesting to note here is (1) how recently these changes occurred, and (2) how simple mistakes in well-oiled machinery can have catastrophic results. These bacteria did not “evolve into” something more advanced. There was no progress; there were mistakes. They turned harmless or symbiotic organisms into destroyers.

Looking at the foolish practices of some in the days of the Black Death, one can only wonder how much less severe the pandemic might have been if people had taken God’s rules on cleanliness seriously: not touching the dead, avoiding unclean animals, staying apart when contaminated, and washing before coming back into the community. He told the Israelites that if they would follow His laws, He would permit none of the diseases of Egypt to harm them, “for I am the Lord, your healer” (Exodus 15:26).

Since the first human pair had rejected their one and only Sovereign, the Creator, He let them suffer the consequences of the loss of His beneficence. But through it all, He did not leave himself without witness (Acts 14:15-17). He continued to do good to the rebels, and worked through history (His story) on a plan (Genesis 3:15) to bring redemption to those who would repent and trust Him. The plan was accomplished at the cross of Jesus (Galatians 4:4-5); it will end with the removal of the curse (Romans 8:18-25) and the re-creation of a new heavens and earth, with no more disease, suffering, or death (Revelation 21-22).

For now, we live in a world still afflicted with sin and disease. Medical science can help with some diseases, but it cannot prevent death. Even those who escaped the bubonic plague in the Middle Ages all died. It’s not a matter of if, but when. Eternal life was God’s original design for you. You can join the Creator’s plan by turning from your sin and trusting Him (Romans 10:8-13). To guide your thinking on this most important choice in life, here’s a map.