What causes autoimmune conditions such as systemic lupus is a question on every patient’s lips. Yet, a 2022 study published in Nature shows that autoimmune disorders like rheumatoid arthritis and systemic lupus may be the aftermath of the Black Death. This disease occurred long ago and inflicted sickness and death on many people.
Black Death Devastation
The Black Death, which began in 1347, spread seriously across Europe, Asia, and parts of the Middle East and North Africa. 
Some regions lost up to half of their population in just 4 years.
The Yersinia pestis bacteria, carried by fleas living on black rats, caused this Medieval Tsunami. When rat populations decreased, fleas shifted to feeding on humans.
The disease recurred over centuries. This includes a devastating outbreak in 1665 in the village of Eyam, Derbyshire, resulting in a 47% fatality rate within 14 months. 
A group of scientists from different countries like Canada, Denmark, France, the UK, and the US wanted to know why some people survived the sickness and if it had to do with a change in their genes.
To explore this, they needed DNA samples from people who lived before, during, and after the sickness. They were able to get samples from people who died during the sickness because scientists had already found a cemetery in London with bodies buried during that time.  They were hoping that these samples would give them more information, especially if a quick change in their genes helped protect them from the sickness.
The research team found three cemeteries in London and five in Denmark to collect DNA samples from. They separated the samples into three groups: before the Black Death, during the Black Death, and after the Black Death. 
The first group was of people who lived before the Black Death and were buried between 1000-1250 in London and 850-1350 in Denmark. The second group was of people who died during the Black Death and were buried in London’s East Smithfield cemetery between 1348-1349. The third group was from people buried after the Black Death ended, with burials in London dating to the 1530s and in Denmark dating to 1800.
In total, the team collected 516 DNA samples, with 318 from London and 198 from Denmark. The DNA was not in good condition because the remains were from almost a thousand years ago, but the team was able to sequence hundreds of immune-related genes using hybridization capture.
Their findings indicated that survivors of the Black Death possessed four distinctive genes. These genes caused a rapid mutation that produced proteins to defend the body and clear out infections but also caused harmful immune disorders.
The study found that four changes in genes helped people survive the plague. One of these genes, called ERAP2, made someone 40% more likely to live through the disease. This gene helped the body fight harmful bacteria. People who survived the plague passed down these changed genes to their children. Over time, as the plague became less prevalent, these genes that once preserved lives became linked to health issues.
ERAP2 is now a known cause of Crohn’s disease, a problem with the digestive system. Another gene, called RS11571319, is related to diseases like rheumatoid arthritis and systemic lupus erythematosus. Lupus used to be a deadly disease, but in the past 50 years, medicine has improved, and people can live with it for a long time. 
This study showed that changes in genes can happen quickly, but it also shows that the change can have both good and bad effects. Despite its occurrence long ago, the Black Death’s impact continues to affect people today. Potentially predisposing people to conditions such as, rheumatoid arthritis and systemic lupus erythematosus.