Typhus is a bacterial-borne disease which is transmitted by flea, tick, and mite bites. It can be fatal if untreated but, thankfully, in almost all cases antibiotics are effective. And by today’s standards, it’s rare; an understanding of the disease has led us to control pest populations better while emphasizing personal hygiene, limiting the ability for the bacteria to spread. But go back to World War II and that wasn’t the case. Typhus wasn’t as treatable and less sanitary conditions led to more epidemics. To keep the disease from spreading throughout military units, Nazi Germany policy required that soldiers avoid those afflicted.

And because of this, thousands of Jewish lives were able to be saved — with the help of a little medical misdirection.

The German typhus-prevention protocols were, as one would expect from such a regime, draconian when it came to Jews who had the disease —  Jewish patients were executed and their homes burned. But non-Jews were treated somewhat humanely — they were quarantined until such time that the disease passed. And when it came to typhus control, pragmatism triumphed. If an area had a large enough population of non-Jews with typhus, the Germans would quarantine the entire community, even if there was a significant Jewish population in the area.

It’s that latter fact that Eugene Lazowski, a Polish doctor (pictured above), exploited. The test for typhus was pretty simple. If the person had the disease, his or her blood would have antibodies that the immune system produced to fight off the infection, even though that battle was often a losing one. And as it turned out, those antibodies did not just react with the typhus-causing bacteria. They also reacted with a strain of the Proteus bacteria called OX-19, which can be rendered harmless to people. To test for typhus, a sample of a person’s blood was mixed with a strain of Proteus OX-19, according to Atlas Obscura. If the mixture became cloudy, the patient had typhus antibodies and, therefore, typhus.

That’s where Lazowski came in. Lazowski served in the resistance for much of World War II and provided medical services in his village, Rozwadów. He collected blood samples from people in the area — Jews and non-Jews, Poles and Germans — and sent them to the Germans for review. Lazowski realized that these blood samples could be used to protect thousands of Jews from concentration camps. If the Germans detected typhus among the non-Jews, Lazowski surmised, the Nazis would quarantine the area and, as a result, leave the Jews there alone. The only problem is: to do that, you actually had to spread typhus.

Until Lazowski found a workaround.

It turns out that by injecting people with the dead Proteus OX-19 bacteria strain, one could fool the test. The body would produce antibodies similar to the ones caused by a typhus infection and therefore result in a positive test when the person’s blood was tested — despite the fact that the person wasn’t ill. And injecting people with Proteus OX-19 was easier than one would think, at least for Lazowski. Because Lazowski was a doctor in the area, many laborers who passed through Rozwadów sought treatment from him. He injected them with the harmless Proteus strain and eventually, the Germans drew an inescapable conclusion: Rozwadów was a hotbed for typhus (even though it wasn’t). The area was off-limits for Nazi operatives, which meant that the Jews in the area were relatively safe.

Lazowski was able to “infect” enough people in and around a dozen different Jewish ghettos to save the lives of an estimated 8,000 people,  according to a publication by the American Medical Association. He may have been able to save more but the Germans ultimately grew wise to his scheme, and he had to flee Rozwadów. He made his way to Warsaw and then, after the war, moved to the United States. He passed away in 2006.