Epilogue• 285relations among the four players: microbe, flea, rodent, and human. It is im-
possible to sort out all the possible changes in this ménage à quatre,as Dr.
Henri Mollaret, emeritus expert on plague at the Pasteur Institute, has
noted. Nevertheless, several intriguing hypotheses merit consideration.^45
Improvements in sanitation, hygiene, and general living conditions have
sharply reduced the threat of infectious disease over the past three centuries.
Did they come early enough to help explain the disappearance of plague
from Britain after the Great Plague of 1665 and from the rest of Western Eu-
rope a few decades later? A popular myth holds that the Great Fire of 1666
started the downward cycle of plague by clearing out the rat-infested dwell-
ings of London. The myth dies hard: the fire actually took out the wealthy
core of the city, leaving most pestered buildings in poor suburban areas intact
as breeding grounds for black rats and their fleas. In the long run, such new
behaviors as frequent changes of clothing and bedding cut down on the
proximity of fleas to humans, and the elimination of thatched roofs and the
building of brick houses kept the rats at bay.
A further deterrent was the disappearance in the eighteenth century of the
urban-dwelling black rat. Its successor, the Norwegian brown rat, did not
live close to humans and could not swim, making it a less likely source of
plague transference to human communities.
Many historians of epidemics now favor the hypothesis that external quar-
antine sharply reduced the prospect of a plague outbreak in Europe during
the eighteenth and nineteenth centuries.^46 European officials, suspecting
that plague epidemics began with the importation of plague on people and
goods from the East, posted guards at the Turkish border and quarantined
ships at European ports. This may have placed a hold on suspected goods
and people, but it stretches credulity to believe that this cordon sanitairecould
have kept back all the infected rats and fleas. Some fleas on clothing and rats
in grain sacks would have passed through, bearing the microbial agent. The
infected fleas could have lived 230 to 396 days by varying modern calcula-
tions, long enough to take them across Europe.^47 At that point, environmen-
tal conditions favorable to wild rodents and fleas that remained in European
communities would probably have been tinder for a new pestilential confla-
gration.
The search for causes of plague’s disappearance and failure to return to
Europe therefore leads inevitably to Yersinia pestisitself. We can assume that,
if plague bacilli remained or were reimported, the wild rodent primary hosts
settled into a coexistence with their bacterial tormenter. This theory states
that the rats did not die, and the fleas had no need to leave this primary host