You have most probably seen them if you have already browsed through the death registries - tens of deaths in really short time, even in small parishes where are few deaths per year. Epidemies decimated our ancestors from time to time and here is overview of illnesses which caused epidemies in the past.
Plague, pestilence or the black death
The black death (mor in Czech, Pestilenz, Seuche in German) how this disease was called was European nightmare since the middle ages. This disease was caused by a bacteria Yersinia pestis (therefor pestilence) which was originally spreaded by rats. There were several forms of plague - bubonic (in lymph nodes), septicemic in blood vessels, pneumonic in lungs and so on.
It was called black death because of the skin color - it got dark red or black from the bleeding into the skin. The disease disappeared from Europe after improvement of living (and hygienic) conditions during the first half of 18th century.
There were two large epidemies which are trackable in Czech registries. First one took place in years 1680 to 1681, second one between 1711 and 1715. These epidemies killed huge number of people all around Europe and Czech Kingdom was also heavily struck. 80 percent of infected people died just a couple of days after the occurence of disease - and almost anyone who got in contact with this illness was infected.
Doctor in the anti-plague suit.
Typhus and typhoid fever
The plague disappeared in the first half of 18th century but new threat was coming - typhus (tyfus in Czech, Typhus in German). It was already known in Europe because there was large epidemy of this disease in 16th century, but plague was greater threat then so typhus got less attention.
There are two main types of this disease - typhus, caused by Rickettsia bacteria and spread by louses, dog-fleas and blood of the infected person, and typhoid fever, caused by Salmonella typhi bacteria and spread by contaminated food and water. Typhus was more common in 16th and 17th century, typhoid fever in following centuries. Death rate was around 60 percent when the illness was not cured.
Both diseased were often spread by soldiers moving aroung Europe - there was huge epidemy of typhoid fever in 1758 when Prussian armies invaded Moravia. We can record typhoid fever outbreaks quite regularly.
First epidemy of cholera (cholera both in Czech and German) in Europe took place in 1816 when it spreaded to Russia from India. Two largest epidemies in Czech lands took place in 1831-1832 and in 1866 (this epidemy was connected to the invasion of Prussian armies). There was another smaller epidemy in 1855 and outbreaks of this disease took place in smaller measures from time to time.
Cholera is an infection caused by Vibrio cholerae bacteria. Infection was followed by diarrhea and vomiting which often caused dehydration and death. Cure was easy - enough of clean water and minerals. But this cure was almost impossible in the environment where our ancestors lived. Death rate was around 50 percent.
Pox or variolla
Another disease which was highly fatal was variolla (pox, red plague, neštovice in Czechm Blattern in German). It was one of the main causes of death in 18th century as there was no cure for this disease. It is caused by Variola virus and this disease was endemic (present in the population without external inputs). About 10 percent of children died of this disease every year and it was also highly fatal for adults.