Parasitology and the Late Middle Ages
The Hanseatic League was a commercial organization
that grew to nation-like power across northwestern Europe.
It flourished from the late 1100s through the mid 1400s,
dominating trade through the Baltic Sea and across the
northern coast of continental Europe.
The field of molecular archaeoparasitology has identified
significant developments in its founding city of Lübeck.
Material from the city's latrines and cesspits show a significant
change in diet around 1300.
That's right, Lübeck's latrines reveal information
about economic and cultural changes.
First, the parasites, because they're been around since the origin of mankind.
There have always been enteric parasites,
creatures that live inside the human digestive tract.
Parasites have complex life cycles.
Most of the ones known as human parasites spend part of their life
in an entirely different form inside a different animal —
fish, snails, cows, pigs, birds.
There may even be more than one intermediate stage and host.
Diphyllobothrium, for example, has at least two intermediate hosts,
first a crustacean and then one or more freshwater fish.
Its definitive host, where it lives as an adult, is a mammal.
Worms — Round, Flat, and Tape
The nematodes or roundworms are a diverse
animal phylum found in nearly every ecosystem.
They've been found down to 3.6 kilometers into the lithosphere
in South African gold mines.
They make up 90% of the animals on the deep ocean floor,
and 80% of all individual animals on Earth.
So, simply saying "we found nematodes" doesn't mean much.
They're transmitted by the fecal-oral route, so human infections
are still common in areas with poor sanitation.
The nematode or roundworm Trichuris trichiura,
known as whipworm, a common human parasite.
The nematodes or roundworms fit the name "worms".
They're roughly cylindrical in shape
with a tubular digestive system open at both ends.
Nutrients enter at a mouth and waste exits at an anus.
The trematodes or flatworms generally look
like their name suggests — imagine a roundworm pressed flat.
They still have a tubular digestive system with openings at both ends,
so they eat and excrete in a reasonably animal-like way.
The cestodes or tapeworms
are where it gets weird.
They're flatter than flatworms, like a ribbon or strip of tape.
They have no digestive tract.
Instead of a head and mouth there's a scolex at one end.
Its hooks and suckers anchor that end to the interior of the
host's digestive system.
The long ribbon-like body floats downstream in the host's digestive flow,
absorbing nutrients and exchanging gases through its outer covering.
Tapeworm bodies are a long chain of similar units called
proglottids growing out of the head end.
These are packages of eggs which are regularly shed,
to be excreted with the feces and thereby infect other organisms.
Oh, and if that's not weird enough, the flatworms are all hermaphrodites.
A lonely tapeworm can crank out egg-filled proglottids on its own.
So, any adult tapeworm is a tapeworm-producing machine.
We Learn from the Worms
Nematodes usually infect humans through the fecal-oral route.
The organisms or their eggs in human feces contaminate food.
This could be through intentional human action,
like fertilizing crops with human waste.
Or, just waste getting onto hands used to prepare or consume food.
Distribution of nematodes or their eggs can tell you about patterns
of settlement and standards of sanitation.
Unless you can spot patterns of which strains of nematodes,
you can't get much more detailed than that.
The cestodes or tapeworms, however, have specific intermediate hosts.
Tapeworms infect humans when we eat uncooked or under-cooked food.
And, given how each species of tapeworm has its own specific intermediate
host, that tells us which under-cooked animal was the previous step.
Taenia saginata (synonym Taeniarhynchus saginatus),
commonly known as the beef tapeworm, is a zoonotic tapeworm belonging
to the order Cyclophyllidea and genus Taenia.
Taenia saginata is commonly known as the beef tapeworm,
because cattle are the intermediate hosts.
Taenia solium is the pork tapeworm.
The eggs enter the animal with food, and then hatch within the
digestive tract, penetrate the intestinal wall to enter the bloodstream,
and make their way to skeletal muscles or organs such as the liver or lungs.
Veterinarians would say that the livestock have
taeniasis if they're infected.
A larva then develops into a cyst, which becomes a fluid-filled
Once the cysticerci are in place, the veterinarians or food inspectors
would say that the livestock have cysticercosis.
Then, when humans eat the cysticerci-infected meat without adequately
cooking it, the larvae find themselves in their definitive hosts.
It's time to transition into their adult form and live in the human,
possibly for years.
The unending sequence of proglottids come out in the human feces,
contaminate livestock feed, and the cycle continues around.
Human infection rates in the U.S. are low,
but 25% of the cattle sold there are still infected.
Cook your beef.
Diphyllobothrium latum, commonly
known as the broad tapeworm or fish tapeworm,
is native to Scandinavia, western Russia, and the Baltics.
This makes it especially relevant to the history of the Hanseatic League.
Diphyllobothrium is a genus of tapeworms which can infect
humans, dogs, cat, bears, and other mammals as its definitive host.
The eggs in that host's feces enter a stream or body of water.
Freshwater crustaceans such as a copepod ingest the eggs,
and the eggs hatch into procercoid larvae.
That just means larvae infecting the first intermediate host.
Copepods are small, typically 1 to 2 millimeters in length.
They're numerous, with about 2,800 freshwater species.
And to keep it complex, about half of the 13,000 described species
of copepods are themselves parasitic.
That's right, a parasitic larva inside a parasitic copepod.
Copepods can appear in unfiltered municipal water supplies, like
that of New York City.
As copepods are tiny crustaceans, they aren't kosher.
That led to intense debate over the kosher status of the water.
In 2004 the NYC water was
judged to be kosher.
The infected small crustacean is then eaten by a second intermediate host,
such as a minnow or other small freshwater fish.
The procercoid larvae are released from the crustacean
and migrate into the fish's flesh.
There, they develop into plerocercoid larvae.
If you haven't guessed, that means larvae infecting the second and later
Those are infectious, but human's don't generally eat undercooked
minnows and similar small freshwater fish.
However, the minnows are eaten by larger predator fish,
such as trout, perch, walleye, and pike.
The procercoid larvae, or sparganum,
migrates to the muscle tissue of the predator fish.
Those fish are eaten by humans and other mammals.
Diphyllobothrium latum tapeworms can reach lengths of 10 meters
or more, meaning the full length of the human digestive tract.
A worm of that length might have more than 3,000 proglottids.
In humans, eggs typically begin to appear in the feces within four to six weeks
of eating the undercooked infected meat.
Up to a million eggs could be passed every day in the host's feces
for the life of the tapeworm, possibly up to 20 years.
Cook your freshwater fish, or freeze it at -10 °C
for 24 to 48 hours.
Either kills the encysted larvae.
The good news, at least for historical researchers,
is that the species of tapeworm tells you what the person was eating —
beef, pork, or freshwater fish.
The good news from a medical viewpoint is that there are effective
However, in the U.S., the effective drugs
cost about 1,000 times what they do in the developing world.
And now, back to history...
The Hanseatic League
The Hanseatic League was a multi-national commercial
organization formed in the mid to late 1100s.
It dominated trade through the Baltic Sea and across the northern coast
of continental Europe through the late 1400s.
It grew in power until it was almost a nation-state of its own.
Hanse, later spelled Hansa,
was the Old High German word for "convoy".
A group of merchants traveling between cities by either land or sea
was called a Hansa.
The powerful Henry the Lion, Duke of Saxony and Bavaria,
had captured an area in northern Germany from Adolf II,
the Count of Schauenburg and Holstein.
German and other states around 1512.
There wasn't a nation-state of Germany back then.
There were many small states, some of
which were German in culture and language.
Much of the area was under the control of the Holy Roman Empire which,
to quote the standard cliché, trite but true,
"was neither Holy, nor Roman, nor truly an Empire."
Adolf II rebuilt the town of Lübeck in 1159.
It was on the east coast of the base of the Danish peninsula,
connected to the Baltic sea and its market ports to the east.
There were trade routes, some upriver and inland as far as
Novgorod in Kievan Rus',
but many of the trips were trading adventures and explorations
rather than large scale organized commerce.
Merchants from Visby, a Swedish island in the Baltic,
established a trading post at Novgorod called Gutagard or Gotenhof in 1080.
Merchants from northern Germany established their own trading post at
Novgorod in the 1220s.
Alexander Nevsky was Prince of Novgorod (1236–40 and 1240–56 and 1258-1259),
Grand Prince of Kiev (1236–52) and Grand Prince of Vladimir (1252–63).
In 1242 the Republic of Novgorod, led by Nevsky,
defeated the crusader army led by the Livonian branch of the Teutonic Knights.
That was the Battle on the Ice, as depicted in the
That was invasion in the name of proselytization.
The Russians were Christian, but they weren't the right sort of Christian
as the Teutonic Knights saw things.
However, business continued and was soon to flourish.
The infrequent "trading adventures" changed with the
establishment of the Hanseatic League,
based in Lübeck.
Sea and land trade routes in medieval northern Europe.
Lübeck quickly became a central node in the trading network
during the 13th century.
It became a base for merchants in Saxony and Westphalia who were
trading toward the east and north.
Lübeck formed an alliance with Hamburg in 1241.
This was a precursor to the League.
That gave those two cities control of most of the regional salt-fish trade.
Cologne joined them in the Diet of 1260.
In 1266, Henry III of England granted them a charter for operating
They soon established a Hanseatic colony in London.
Merchants in several other cities formed guilds, or Hansa.
Some of these cities were German, like Stettin and Danzig.
Other trade ports were organized and operated by German immigrants.
The Hanseatic League in 1400, full-sized map
The eastern Baltic was less developed economically,
but it was a source of timber, wax, resin, honey, amber, and furs.
Also, rye and wheat were brought downriver to Baltic ports.
Lübeck signed a treaty with the Visby Hansa, gaining access
to Novgorod and soon building their own trading post there.
Cloth and manufactured goods moved from Flanders and England to the east.
Copper ore, iron ore, and herring moved south from Sweden.
The network grew to 70 to 170 cities, depending on who was counting,
including Bruges in Flanders, and Bergen in Norway.
In the northeast, Reval (now Tallinn), Dorpat (now Tartu),
and Riga became members.
Many of these cities retain some features of their Hanseatic days.
Tallinn, Estonia, Reval during Hanseatic days,
with its port on the Gulf of Finland.
The main square of Tallinn.
The towns raised their own armies,
and the guilds were required to provide manpower as needed.
That developed to the point that the Hanseatic cities had their own
legal system, and their own armies for mutual protection.
Commercial ships often carried soldiers and their arms.
The city walls around the old center of Tallinn.
All the same, the Hanseatic League wasn't a state.
Neither was it a confederation of city-states.
Only a few of the member cities were as autonomous as a free imperial city,
meaning a self-ruling city within the Holy Roman Empire.
Assemblies of representatives of the Hanseatic towns met irregularly in
Lübeck starting in 1356.
However, many town chose not to send representatives, and decisions
of the assemblies weren't binding.
St Olav's Church in Tallinn, called Oleviste Kirik in Estonian.
This church is thought to have been originally built in the 1100s.
It was the center of the Scandinavian community in
Tallinn before Denmark conquered Estonia in 1219.
Around 1500, the building's spire reached a height of 159 meters.
One motivation was for it to serve as a maritime navigational aid.
Between 1549 and 1625, it was the tallest building in the world.
The spire burned down after being struck by lightning in 1625,
and after a number of reconstructions, it's now 123 meters tall.
Decline and End of the Hansa
By 1500 the growing Swedish Empire had taken control of much of the Baltic Sea,
and the Hanseatic League was weakening.
Individual cities were putting their own interests before those of the League.
The German princes controlling areas around some of the cities had begun
on limit the independence of the merchants and the nearly independent cities.
The League built the Adler von Lübeck, the largest ship in the world
at the time, for military use against Sweden during the Northern Seven
Years' War of 1563-1570.
However, it was never put to military use.
The League was collapsing, losing its power and no longer able to deal
with its own internal struggles.
The Protestant Reformation had accompanied social and political changes.
Dutch and English merchants had become much more powerful.
The Ottoman Empire was expanding into former territory and trade routes
of the Holy Roman Empire.
Only nine members attended the last formal meeting of the Hanseatic League
in 1669, and only three of those — Lübeck, and Bremen, at or
near the League's core — remained as members until it was finally
disbanded in 1862, when Kaiser Wilhelm I created the German Empire.
All the same, some signs remain.
The most obvious is the German state airline Lufthansa, meaning "Air Hansa".
Some cities in Germany and the Netherlands refer to themselves as Hanse
cities, with car license plates prefixed H as in
"HL" for "Hansestadt Lübeck" or
"HB" for "Hansestadt Bremen".
Well, that's the history as far as we knew it.
Now we have learned more from the latrines, cesspits, and worms.
Molecular Archaeoparasitology and Lübeck's Latrines
The 2018 paper
archaeoparasitology identifies cultural changes in the
Medieval Hanseatic trading centre of Lübeck"
was written by an international team and published in
Proceedings B of the Royal Society.
They have observed that over 95% of pre-1700 latrine samples contain
helminth eggs (helminths being the general category including
nematodes, trematodes, and cestodes, or roundworms, flatworms,
The sturdy egg capsules, meant to protect the eggs in their passage through
a mammal's digestive system, contain useful ancient DNA.
They collected samples at a recent UNESCO excavation in the
Gründungsviertel (or founding quarter), 31 stratigraphed
latrine samples from eight houses dating between the twelfth and
seventeenth centuries CE.
The compared these to samples from sites in the UK, Germany, Czech Republic,
and Switzerland dating between Neolithic and Post Medieval periods.
They examined the latrine samples for worms and worm eggs,
and analyzed the nuclear and mitochondrial DNA of what they found.
The Lübeck Latrine Samples
All 31 latrine samples contained Trichuris and/or Ascaris
Those are nematodes, so that is no surprise.
They also found eggs from Diphyllobothrium latum or fish tapeworms,
Taenia saginata or beef tapeworms,
and Taenia solium or pork tapeworms.
14 of the 31 samples contained fish tapeworms,
19 of the 31 contained beef or pork tapeworms.
DNA analysis showed humans plus a number of potential food species including
cattle, pigs, sheep, goats, fowl, and several freshwater and marine fish
Cod and herring were the most common fish, unsurprising because in
both air-dried and salted forms they were major trading goods
of the Hanseatic League.
They also found freshwater fish DNA including perch, pike, eel, and others.
The Lübeck diet changed abruptly around 1300.
People stopped eating fish and started eating beef and pork.
We know this because of which eggs appeared in which stratigraphic
layers of latrine samples.
Diphyllobothrium latum or fish tapeworm eggs were found in most
pre-1300 latrine samples, but only two post-1300.
These came from were freshwater fish, based on mitochondrial sequences.
That makes sense, given the importance of freshwater fishing to Lübeck.
Imperial charters in 1188 and 1226 awarded the city formal control
of fishing rights in the local rivers and lakes.
In contrast, eggs of Taenia or beef and pork tapeworms
became more and more common in later samples.
The DNA sequences matched the beef tapeworm D. saginata
rather than the pork tapeworm T. solium.
The overall numbers of eggs were much larger than reported in any other
latrine archaeology studies, indicating that
the people of Lübeck consumed more uncooked or undercooked
red meat and fish than other people.
The city expanded around 1300, and the Wakenitz river to its west became
increasingly polluted with waste from increased meat and leather production.
That could have made fish less available or desirable.
Medieval French monastic toilets
Medieval Scottish monastic toilets
Medieval English monastic toilets
Also, the benedictine monastery was converted to a Cistercian nunnery.
The monastery had riverine fishing rights and owned stock ponds.
So, this change could have interrupted the availability of fish
which was contaminated by human waste from the monastery.
Additionally, the Black Death killed an enormous number of Europeans
during 1346-1350, after the best estimate of the dietary shift but
within bounds of best-fit errors on the trends.
Perhaps a shortage of fishermen led to a shortage of fish.
Another theory is that Lübeck's citizens were
rapidly becoming wealthier,
and that led to their consuming more beef.
Without, however, adequately cooking it.