Malaria and Rome: A History of Malaria in Ancient Italy, Robert Sallares [reading a book TXT] 📗

some further analysis. Table 5

shows that age-specific mortality was higher than predicted in Grosseto from age 5 to 9 and from 20 to 50. These characteristics of age-specific mortality emerge not only from the comparison with the communities of Stia and Pratovecchio in the Casentino given by del Panta, but also from the comparison with model life-tables.¹³⁹

Table 5. Number of deaths per person-years lived between age x and x+n (m(x) ) Age-group

Grosseto

South 2

Grosseto

South 2

(Males)

(Males)

(Females)

(Females)

0–4

16.5

18.0

17.7

17.3

5–9

2.3

1.5

3.0

1.7

10–19

1.2

0.9

1.0

1.1

20–9

1.8

1.6

1.5

1.6

30–9

3.0

1.7

2.2

0.9

40–9

3.5

2.3

2.8

1.9

50–9

5.9

3.6

6.8

3.0

Note: Bold type indicates items which deviate significantly from the values predicted by the model life-tables.

Del Panta was undoubtedly right to explain the excess age-specific mortality in the 5–9 age group in Grosseto as a direct consequence of P. falciparum malaria, as in tropical African countries today. Since direct mortality among adults from malaria was low in Grosseto, del Panta explained the excess adult mortality in terms of synergistic interactions with respiratory and gastro-intestinal diseases. Very high mortality rates required very high fertility rates if the population was to have a chance of reproducing itself. Consequently populations badly affected by malaria, such as Grosseto and the Sardinian populations mentioned earlier, had both higher mortality and higher fertility levels than other populations. Del Panta showed that the marriage patterns of Grosseto favoured very ¹³⁹ Del Panta (1989: 21); del Panta (1997) on infant mortality.

Demography of malaria

163

high fertility levels. Elsewhere he has described the coastal regions of central and southern Italy with intense malaria as characterized by neolocal marriage, with simple nuclear families and a predominance of agricultural wage labour.¹⁴⁰ Gregorovius made the following observation in Latium:

They marry very early in these parts—a young fellow of twenty one chooses frequently a girl who has only numbered fifteen summers.¹⁴¹

Table 6 demonstrates that an age-specific mortality pattern with some similarities to the data from Grosseto can be identified in the malarial parishes in the marshlands of south-east England.¹⁴²

Table 6. Number of deaths per person-years (m(x) ) for various age-groups Age-group

Marsh parishes

Model West 6

(Females)

0–4

9.5

10.0

5–9

0.9

0.9

10–14

1.1

0.7

15–19

1.3

1.0

20–9

2.0

1.3

30–9

2.7

1.6

40–9

4.2

1.9

50–9

4.7

2.9

60–9

5.9

5.7

Note: Bold type indicates items which deviate significantly from the values predicted by the model life-tables.

The demographic pattern found by Dobson in the English

marsh parishes is not dissimilar to the pattern of Grosseto, but with differences in detail; this is not surprising taking account of the fact that P. falciparum malaria was absent from England, not to mention numerous other environmental differences between England and Italy. In the English marsh parishes there was no deviation of the mortality level from the model’s expectations in the 5–9 age group.

This is comprehensible, since no significant degree of mortality produced directly by P. vivax in this age-group is to be expected.

P. vivax does not produce death directly itself in the same way that ¹⁴⁰ Del Panta et al. (1996: 162–4); Livi-Bacci (2000: 98–9, 145–6).

¹⁴¹ Gregorovius (1902: 90).

¹⁴² Data for the parishes of Canewdon, South Benfleet, Burnham and Tollesbury, which Dobson (1997: 169) compared to Coale and Demeny Model West Level 6.

164

Demography of malaria

P. falciparum does among children in tropical Africa today. The deviation in the English marsh parishes from the model pattern started at age 10, not 20, as in Grosseto, and steadily increased from the age of 30 onwards. Coale and Demeny Model West Level 6

gives a very good fit to English data up to the age of 20. However, Table 7 shows that this comparison is unsatisfactory from age 20

onwards.

Table 7. Number of people aged 20+ who die between ages x and y Interval

Marsh

West 6

West 2

West 1

parishes

20–9

18.3

14.1

19.1

20.7

20–39

36.8

28.8

37.7

40.4

20–49

58.6

44.1

53.5

56.7

20–59

75.9

61.2

69.9

73.0

20–69

87.4

80.3

87.0

89.1

Table 7 shows that from age 20 onwards the mortality rates predicted by Model West Level 6 are far too low. The attested rates of attrition are roughly consistent with Levels 1 and 2, with a life expectancy at birth of between 20 and 22.5, rather than 32.5 as in Level 6. In so far as the Coale–Demeny models are of any relevance at all, the English data indicate a drop from Level 6 mortality in the first ten years of life to a lower level from ages 10 to 20, followed by a sharp drop down to Level 1 or 2 from age 20 onwards.

Consequently life expectancy at birth in the English marsh parishes was probably rather lower than 33, the figure suggested by Level 6.

This would not be surprising in view of the exceedingly high crude death rates for the marsh parishes, up to 80 per 1,000. Nevertheless a more important conclusion, for the purposes of this chapter, is that when all the obvious environmental differences between the English marshlands and western central Italy are considered, the mortality patterns produced by P. vivax in England and the combination of P. falciparum and P. vivax in western central Italy were remarkably similar. Both were characterized by very excessive age-specific adult mortality relative to the prevailing levels of infant mortality.

Similarly Tognotti described deviations in the age-structure of mortality on Sardinia, which had some of the most intense malaria in the western Mediterranean. In Sardinia infant mortality in the Demography of malaria

165

first year of life was actually below the average of all the various regions of Italy (including regions where malaria did not occur at all).¹⁴³ In fact, infants in the first few months of life seem to be less severely affected by malaria than older infants. A variety of possible explanations have been offered for this phenomenon.¹⁴⁴ One possibility is that infants sleeping alongside their mothers have a much smaller surface area than their mothers, and move around more even when asleep, and so are less likely to attract mosquito bites.

Infants may also be carrying antimalarial antibodies derived from their mothers in the first few weeks after birth, although this may simply indicate a high transmission rate of malaria and have little effect on infections. Malarial parasites grow much more slowly in erythrocytes with foetal haemoglobin than in cells with the adult form of haemoglobin. Another possible explanation, noted in Chapter 5. 3 above, is that human breast milk contains an extremely low concentration of para-aminobenzoic acid, a chemical