disease 257
extremely high transmission rate for falciparum malaria in tropical Africa, with each
person receiving multiple infections from early childhood onwards. The result is that
malaria is essentially a disease of childhood in tropical Africa. There are very high
levels of infant mortality, but those who survive childhood have developed immunity.
Consequently the worst clinical syndromes, such as cerebral malaria, are generally not
observed among adults in parts of tropical Africa with holo-endemic malaria.
In contrast, in the Mediterranean world transmission was only possible in summer
and early autumn and the mosquitoes were less efficient vectors. Transmission rates
were lower. Moreover, in the Mediterranean malaria had a patchy distribution, which
was linked to the patchy distribution of wetlands that served as mosquito breeding
sites (Sergent and Sergent, 1928: 73–74). As a result people often grew up in locali-
ties where there was no malaria and then moved to other areas where malaria was
endemic seeking work as agricultural laborers and so encountered the disease for the
first time as adults, not in childhood. The outcome of all these factors is that falcipa-
rum malaria affected adults to a much greater extent in Mediterranean countries in
the past than it does in tropical Africa today. That is why there are so many references
in European historical sources to adults suffering from and dying from malaria, a pat-
tern not observed in tropical Africa today. The demographic consequences were that
in malaria hotspots in the Mediterranean, adult life expectancy (life expectancy at
age 20) was severely depressed by malaria, as shown for example by studies of the
demography of Grosseto in Tuscany in the nineteenth century ce (Sallares, 2002). In
contrast in tropical Africa it is principally life expectancy at birth that is reduced by
malaria. These effects of malaria were not purely a matter of biology and demography,
but were intimately connected to the nature of agricultural and social systems. For
example, in early modern Italy rice cultivation in the Po valley required a predomi-
nantly female labor force to plant rice seedlings in paddy fields, resulting in there
being more cases of malaria among women than men in northern Italy. However the
plough agriculture needed for wheat cultivation in central and southern Italy required
a male labor force. As a result there were many more cases of malaria in the Santo
Spirito hospital for men than in the San Giovanni hospital for women in Rome
(Snowden, 2003).
If we now turn to make comparisons with the medical situation in northern Europe,
clear contrasts again emerge. Malaria was certainly common in some parts of northern
France, Britain, Holland, Germany (Knottnerus, 2002) and even occurred in as cold
a country as Finland, where it had the character of an indoor disease (Huldén et al.,
2005). However Plasmodium falciparum could not survive north of the limits of the
Mediterranean climatic zone. In northern Europe, malaria was caused mainly by
another species, Plasmodium vivax, which has lower temperature requirements.
P. vivax certainly does sometimes cause severe clinical symptoms, as recent medical
research has increasingly emphasized, but it does not do so as frequently as P. falcipa-
rum. P. vivax tends to produce chronic ill-health, which can still have a major impact
on agricultural populations. It also formed part of the Mediterranean pathocoenosis
in the past, but tends to be overshadowed by P. falciparum where the two pathogens
coexist. Consequently malaria in the Mediterranean had a more severe character than
malaria in northern Europe in the past.
The heavier disease burden in the Mediterranean was certainly noticed by medieval
travelers from northern Europe who frequently fell victim to falciparum malaria.