Let's assume there is a city heavily dependent on trade--either it sits at a nexus of trade routes or it possesses a large port, for example.
Next, let's assume a plague breaks out inside the city. How does the city respond? Does it try to isolate infected away from markets/ports? Does it still let ships come into harbor and trade caravans come through? Or does trade follow an alternate path for a time, in effect putting the city under quarantine?
Thanks in advance.
I will use Venice as my example city since I don't think anyone can really argue that it wasn't one of the biggest trade cities in the Mediterranean at the time of the Black Death.
Generally, after people realized that plague was a problem, any ships sailing into port had to go through a quarantine period to make sure no one aboard was carrying the disease. The quarantine period lasted from 30-40 days. People inside the city who had the plague were generally boarded up in their houses. Early on, priests would be the only ones to visit in order to give people last rites. but then those priests would then spread the disease around town.
Because of the poor hygiene and living conditions, the poor were the hardest hit in big cities.
It was believed that fire would stop the disease, so oftentimes there were small bonfires on street corners.
Many people turned to God. Unfortunately, this devolved into the persecution of the city's Jewish population. This is because some people believed that the plague was God's displeasure towards the Jews, as they are the ones who crucified Christ.
In general, most trade completely stopped once a city was infected. Both because people stopped going to that city to trade, and because the city itself would let few to no one inside.
Interestingly, Venice's sister city of Milan was quite effective at stopping the plague in its tracks. Milan officials quickly stopped everyone and everything from entering the city once they heard that plague was striking Italy. As a result, Milan was mostly spared.
In conclusion, most cities involved with trade tried to shut it down once plague became a problem. Unfortunately, most of the time these attempts at stopping the plague were too little too late. In the 1575-77 outbreak, around 50,000 Venetians died. To give some context, the total population of Venice before the 1575 outbreak was 170,000. The only times that the attempts to shut down trade worked were very rare, the biggest one being Milan, and it only worked in Milan because the officials shut down the city before the plague was in the region, not after.