disease 255
is why quarantine worked as a control method for plague in early modern Europe
(Cliff et al., 2009); it stopped human movement and human trade transporting
infected fleas around—there was no need to stop rats moving around. Other signifi-
cant parallels between plague and malaria that are worth noting here are that the
effects of temperature and humidity (the sort of climatic variables used to define the
Mediterranean environment here) on fleas and on mosquitoes are in fact quite similar
(Gill, 1928).
So far it has been shown that the Mediterranean pathogen community was created
and enlarged over a period of about 3000 years by steadily-increasing human interac-
tions between more and more distant regions, first within the Mediterranean itself
and neighboring areas and second with more distant parts of the world. This cata-
logue of biological invasions (Groves and di Castri, 1991 discussed the general theme
of biological invasions of Mediterranean-type ecosystems) raises the fundamental eco-
logical and ontological question of whether what was created was merely a random
collection of pathogens with no significant interactions between them or alternatively
a structured community of organisms which interacted with each other and displayed
emergent properties as an ecological community.
Mirko Grmek introduced the concept of pathocoenosis in 1966 to designate the
concept of a community of pathogens in a particular geographical area (Grmek, 1969;
Biraben, 1998; Gourevitch, 2005; Sallares, 2005). The term was inspired by the con-
cept of biocoenosis, which is widely employed in continental European ecological
literature to signify a community of living organisms. Grmek postulated that within a
pathocoenosis “the frequency and overall distribution of each disease depends on the
frequency and distribution of all the other diseases within a given population.” He
maintained that mathematical considerations suggest that “each pathocoenosis must
have a small number of common diseases and a great number of rare ones” and reck-
oned that “a pathocoenosis tends toward a state of equilibrium expressible in rela-
tively simple mathematical expressions; that state is especially perceptible under stable
ecological conditions.” This is perhaps the most controversial aspect of the concept of
pathocoenosis, since as has already been shown the Mediterranean pathogen com-
munity has been regularly disrupted by invasions of new pathogens throughout
recorded history. Grmek also made the fundamental observation that “two diseases
belonging to a single pathocoenosis can be in a state of symbiosis, antagonism, or
indifference to each other” (Grmek, 1989: 2–4). This question of disease interactions
is a very important topic for which there is unfortunately no space in this chapter
(Sallares, 2002: 123–140; Sallares, 2005). Suffice it to say here that co-infections with
two or more pathogens were very common in the past and many diseases do display
significant interactions with other diseases. The interaction between malaria and
tuberculosis was very important, both in ancient Egypt (Lalemruata et al., 2013) and
early modern Italy (Sallares, 2002: 138–139). The unfortunate aforementioned
Eleonora of Toledo was infected with tuberculosis as well as leishmaniasis and died at
the age of 40 from her problems in Florence in 1562 ce, as demonstrated by biomo-
lecular techniques (Bianucci et al., 2012).
It is reasonable to describe malaria as the dominant member of the Mediterranean
pathocoenosis for most of the last 2000 years because demographic analysis of mortal-
ity rates for historical European populations consistently shows that populations
which suffered from endemic malaria had much worse demographic profiles than