Malaria and Rome: A History of Malaria in Ancient Italy Page 15
¹⁴¹ North (1896: 103–5); De Tournon (1831: i. 201–2); Baccelli (1881: 191–2). The advantages of tall buildings against ‘bad air’ might have been discussed in Rutilius’ book de modo aedificiorum (Suetonius, Augustus 89). However, it should be noted that contrary views were also expressed in antiquity. The medieval Arab writer Ibn Ridwan quoted Rufus of Ephesus as recommending flight from cities with tall buildings and narrow streets because they were unhealthy (Dols (1984: 105) ). Similar sentiments were expressed by Sabinus in the second century (Nutton (2000 b: 69–70)).
¹⁴² Knight (1805: 33).
¹⁴³ Gamage-Mendis et al. (1991). The study of Barber and Rice (1935) in Greece reached inconclusive results in relation to the question of malaria and housing.
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indicates that the necessary precautions had not previously been taken on Corcyra (modern Corfu):
Did not our Varro here, when the army and fleet were on Corcyra and all the houses were full of the sick and dead, make his comrades and servants healthy again by constructing new windows to let in the north wind and excluding the pestilential winds, by changing [the positions of ] doors, and by other measures of this kind?¹⁴⁴
Since it is quite common for blood feeds by female mosquitoes to be interrupted and then finished on another person, it is possible for one mosquito to infect several people in a single household.¹⁴⁵
Certain houses which are particularly badly exposed to mosquitoes may become foci of malarial infection within a community. Households with children are most likely to end up playing this role, since gametocytes (the blood stage of the parasite’s life cycle which can reinfect mosquitoes) are mainly found in children in areas where malaria is endemic. The acquired immunity of those adults who survive infection in childhood reduces gametocyte production to insignificant levels in such areas. The dangerous species of mosquito either show a definite preference for human blood (so A.
sacharovi), or at least are as willing to bite humans as they are to bite other animals (so A. labranchiae). These two species enter houses or other man-made structures without hesitation. In contrast, other species of Anopheles mosquito in Italy which are not significant vectors of malaria prefer to bite other animals, generally cattle, and show little interest in entering houses. Hackett and his co-workers demonstrated this in their comparison of Val di Chiana in Tuscany, an area of anophelism without malaria in the early twentieth century, with Fiumicino, which had some of the most intense malaria in the world.¹⁴⁶
It is very important to bear in mind the possibility that the geographical distribution of mosquito species may change over time, following local environmental change. This is doubtless what happened at Ravenna, for example. Consequently regions with anophelism without malaria within the last hundred years were not necessarily like that in earlier periods of history. The southern end ¹⁴⁴ Varro, RR 1.4.6: Non hic Varro noster, cum Corcyrae esset exercitus ac classis et omnes domus reple-tae essent aegrotis ac funeribus, immisso fenestris novis aquilone et obstructis pestilentibus ianuaque permuta-ta ceteraque eius generis diligentia suos comites ac familiam incolumes reduxit?
¹⁴⁵ Conway and McBride (1991).
¹⁴⁶ Missiroli et al. (1933); Hackett (1937: 38–41, 75–6, 209–12).
Ecology of malaria
16. The
southern end
of the Val di
Chiana and
Lago Trasimeno, viewed
from the
Fortezza
Medicea
above
Cortona.
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of the Val di Chiana (243–60 metres above sea level), particularly in the vicinity of Chiusi, was certainly unhealthy in the medieval and Renaissance periods, as Dante, Boccaccio, and other writers observed. Unfortunately there is no explicit evidence available for the health status of the area in antiquity. Dante bracketed the Val di Chiana with the Maremma and Sardinia as notoriously unhealthy regions: As the pain would be, if the diseases of the hospitals of the Val di Chiana, between July and September, and of the Maremma and Sardinia were all together in one ditch.¹⁴⁷
From the sixteenth century onwards repeated efforts were made to drain the flooded valley, especially by constructing a large canal, the Canal Maestro, to remove water to the Arno river. Leonardo da Vinci was the most famous of the numerous engineers who took an interest in the region’s problems. However, these efforts were vitiated for a long time by political rivalry between Rome and Florence as well as by the low gradient of the plain (the same problem as in the Pontine Marshes). Alexander’s detailed study of the Val di Chiana reached the conclusion that piecemeal drainage works were doomed to failure; only a grand plan dealing with the entire territory simultaneously would work, and this was not finally achieved until the late eighteenth and early nineteenth centuries by Vittorio Fossombroni. The drainage of the Val di Chiana did not eliminate Anopheles mosquitoes, but in some way facilitated a change in the balance between different species so that zoophilic species became prevalent. Similarly Pisa, whose territory suffered from intense malaria during the Renaissance period, had become an area of anophelism without malaria by the end of the nineteenth century, while the coastal region north of Pisa around Viareggio, which eventually became another area of anophelism without malaria, had been described as ‘marshy and pestilential’ ( paludosa e pestifera) in the seventeenth century.¹⁴⁸
¹⁴⁷ Dante Alighieri, La Commedìa. Inferno. Canto .46–9, ed. Lanza (1996): Qual dolor fora, se delli spedali | di Valdichiana tra ‘l luglio e ‘l settembre | e di Maremma e di Sardinia i mali | fossero in una fossa tutta insembre.
¹⁴⁸ Alexander (1984); Luchi (1981: 417–20), on the archaeology of the Val di Chiana in the territory of Chiusi, noted that Livy 5.36.3 indicates that at least part of it was exploited extensively instead of intensively ( latius possideant quam colant); Dennis (1878: 294); Pinto (1982: 10, 17–18, 30).
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4. 5 C
Roads and housing are good examples of factors which were very important at the local level. However, not all factors were so localized in their effects, above all climatic change. Huntington suggested in 1910 that the introduction of malaria to Italy occurred in the late third century as a result of increasing aridity (and hence, drier summers) which created more favourable environmental conditions for Anopheles mosquitoes. Although that idea was interesting in principle, far less was known in 1910 about climatic change in the past and its causes and consequences than is known today. The question requires a fresh examination. It has already been noted that the earth’s average temperature is now approaching levels that were last attained in the Neolithic period, before 3000 , probably as a result of anthropogenic global warming in the last few years. In between, the climate was generally cool-er, but there were still periodic fluctuations of temperature within these lower levels. The effects of these temperature fluctuations can be analysed by studying periodic advances and retreats of the glaciers in the Alps, which have occurred throughout the Holocene. The time of the Roman Empire was mostly a warm period, relative to the periods immediately before and immediately afterwards. The results from the glaciers can be corroborated by various types of proxy data, for example the spread of viticulture into Roman Britain as demonstrated by the recent archaeological finds at Wollaston in the Nene Valley in Northamptonshire. The time of the Roman Empire was warmer than the period of the ‘Little Ice Age’, c. 1500–1800, which encompasses much of the data that are available for studying the distribution of malaria in Italy in the early modern period. Consequently the climate was more favourable for the spread of malaria in Italy during the Roman Empire than it was, say, in 1782, when malaria occurred all over Lazio, except at high altitudes, as shown by Bonelli’s map.¹⁴⁹
Climatic ch
ange, then, is a very important factor that creates the expectation of a wider distribution of malaria in Italy during the Roman Empire than during the early modern period. It is not surprising, as has already been noted (see Ch. 4. 2 above), that ¹⁴⁹ Huntington (1910: 672–5); Fraccaro (1919: 66–70); Röthlisberger (1986: 60–1, 70–4); Bianchi and McCave (1999); Brown and Meadows (2000).
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P. falciparum malaria occurred in Umbria, far inland, by the fifth century . Temperature is very important in relation to malaria because of the requirements of the parasites for sporogony inside the mosquito. This developmental process, which is essential before the mosquito can infect anyone, takes only about 9 days at a mean temperature of 30°C, 10 days at 25°C, but up to 23 days at 20°C, in the case of P. falciparum. The time scale in the case of P. malariae is even longer, about 20 days at 25°C, and 4–5 weeks at 20°C. Even though on the surface such temperature levels are not maintained for long periods in Europe (taking account of the drop in temperature that occurs every night), nevertheless the longevity of P. malariae infections in humans assured its survival until the next favourable transmission period came along, and there are many references to quartan fever in historical sources from Europe. In the case of P. vivax the process takes only 9 days at 25°C, but 30 days at 16°C. The slowing down of sporogony caused by low temperatures impedes the transmission of malaria because few adult mosquitoes actually live as long as 3 or 4 weeks. Hackett noted that over 50% of mosquitoes are dead after a week in Italy during the summer.¹⁵⁰
The scale of the temperature changes in the Roman period can be roughly estimated. One recent study suggested that the mean July temperature in the Arctic about 411 ± 70 years (by C14
dating), at the peak of the Little Ice Age, was about 0.7°C lower than today. Wider studies have estimated a cooling of about 0.4–0.6°C during the Little Ice Age, explained by periodic variations in annual-mean radiation from the sun.¹⁵¹ Consequently it is likely that mean summer temperatures in Italy during the Roman Empire were a minimum of about 0.5°C higher (and quite possibly more) than the temperatures of the early modern period, which were already sufficient for P. falciparum malaria to be widely distributed in central and southern Italy. A temperature change of this magnitude may appear to be quite modest, but it is well known in ecology that small changes of this kind can have considerable effects on the distributions of living organisms. Moreover the effects of even small temperature changes would be most significant in geographical areas on the periphery of the distribution of P. falciparum, such as southern Europe, rather than in the tropics. Modern ¹⁵⁰ Hackett (1937: 67–9); Gilles and Warrell (1993: 111, 126–31).
¹⁵¹ Havström et al. (1995); Wigley and Kelly (1990).
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global warming is already creating more favourable conditions for the mosquito vectors of malaria and other diseases in many parts of the world.¹⁵² Some studies have argued that parts of the Roman period were even hotter, up to about 2°C warmer than the temperatures of the Little Ice Age in the early modern period, as well as being wetter than today. If so, the prospects for malaria during the time of the Roman Empire were that much better.¹⁵³
4. 6 A
Increasing temperature favoured the spread of both P. falciparum malaria itself and its vector mosquitoes in Italy during the time of the Roman Empire. There were other factors which were also of fundamental significance. Heat is good for malaria, but the mosquitoes still need to find suitable habitats for breeding sites. Human activity in the first millennium unwittingly made a crucial contribution to the spread of malaria by altering the hydrology, geomorphology, and vegetation cover of lowland areas on a scale which transcended anything achieved in earlier periods. In Etruria the combination of the different types of evidence yielded by archaeological field surveys (e.g. the Tuscania and Veii surveys), palaeobotany, and palynology indicates that very substantial population growth occurred during the development of the Etruscan cities. This human population growth was supported by Mediterranean polyculture (the triad of cereals, olives, and vines), a new agricultural system which developed in central Italy for the first time in the Early Iron Age. The same sort of intensification of land use occurred in Latium as well.¹⁵⁴ Deforestation of hills and mountain slopes caused increased run-off of rainwater. This raised the water table and increased the chances of flooding in the lowlands and eroded soil to be redeposited as alluvial deposits in the lowlands. These areas of alluvial deposition were very likely to become marshy. This process happened all over Italy. The Greek colony of Metapontum in southern Italy is a well-studied example.
Archaeological investigations have shown that the water table rose ¹⁵² Epstein (2000); Patz and Reisen (2001). The alternative view advocated by Rogers and Randolph (2000) seems to totally ignore all the evidence for the existence of P. falciparum malaria in the past in southern Europe, for example.
¹⁵³ Martinez-Cortizas et al. (1999); Reale and Dirmeyer (2000).
¹⁵⁴ Potter (1979: 74) summarized the explosion in site numbers in south-eastern Etruria; Barker (1988); Sallares (1991: 29–34) on the spread of new crops.
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17. The Monti
Cimini, viewed from
the site of the Roman
villa at Lugnano in
Teverina. Most of
the redoubtable
ancient forest has
now disappeared.
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105
by more than a metre over the whole territory of Metapontum from the sixth to the fourth centuries . This was accompanied by extensive alluviation, which created marshy conditions suitable for Anopheles mosquitoes. The necropolis at Pantanello, whose very name indicates marshy conditions, outside Metapontum has yielded several skeletons which show signs of thalassaemia, an inherited genetic condition which confers a degree of resistance to P. falciparum malaria. This constitutes indirect evidence for the likely existence and activity of P. falciparum in southern Italy as well as Sicily during the classical Greek period.¹⁵⁵
This is not the place for an extensive discussion of deforestation in Italy in antiquity. Suffice it to say that there were massive forests in Italy, which grew during the mid-Holocene climatic optimum, following the end of the last Ice Age. Delano Smith has suggested that even the Tavoliere in Apulia, a semi-arid region today, might have been substantially covered by forest in the early Neolithic period.¹⁵⁶ In western central Italy, which is much better watered than the Tavoliere, the climax vegetation in the absence of human interference undoubtedly would be large forests in many areas.
Many of these forests were broken up during the first millennium by the demands of an increasing human population for open land for agriculture and by the ever-increasing demand of the Romans for timber. For example, Livy describes the Ciminian Forest. It was said to be so dense and forbidding c.310 that people were afraid even to approach it. Hardly anything is left of it today.¹⁵⁷ Pliny the Younger described the ancient woods of very tall trees on the Appennine mountains, above his estate at Tifernum in Umbria.¹⁵⁸ Theophrastus described very large forests in Latium at the end of the fourth century .¹⁵⁹ These forests were well watered ¹⁵⁵ Henneberg et al. (1992: 455) on thalassaemia. Their claim to have also found evidence for treponemal diseases such as syphilis in the skeletal remains from Metapontum remains controversial. Nevertheless malaria probably played a major role in the depopulation of the territory of Metapontum in the third century described by Carter (1990).
¹⁵⁶ Delano Smith (1978: 53), cf. Caldara and Pennetta (1996).
¹⁵⁷ Livy 9.36.1–8, discussed by Meiggs (1982: 246) and Cornell (1995: 355–6); Pratesi and Tassi (1977: 49) described the remnants of the Ciminian Fores
t.
¹⁵⁸ Pliny, Ep. 5.6.7: montes summa sui parte procera nemora et antiqua habent.
¹⁵⁹ Theophrastus, HP 5.8.3 and 2, ed. Amigues (1993): Ó d† t0n Lat≤nwn πfudroß p$sa: ka≥ Ó m†n pedein¶ d3fnhn πcei ka≥ murr≤nouß ka≥ øxu¶n qaumast&n: thlikaıta g¤r t¤ m&kh tvmnousin ¿ste e”nai dianek0ß t0n Turrhn≤dwn ËpÏ t¶n trÎpin: Ó d† ørein¶ pe»khn ka≥
ƒl3thn. tÏ d† Kirka∏on kalo»menon e”nai m†n £kran Ëyhl¶n, dase∏an d† sfÎdra ka≥ πcein drın ka≥ d3fnhn poll¶n ka≥ murr≤nouß . . . tÏn d† tÎpon e”nai ka≥ toıton nvan prÎsqesin ka≥
prÎteron m†n oˆn n[son e”nai tÏ Kirka∏on, nın d† ËpÏ potam0n tinwn proskec0sqai ka≥
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Ecology of malaria
and had taller trees than the forests of southern Italy (although not as tall as those of Corsica). The lowland forests of bay, myrtle, and beech contained old trees tall enough to span the length of the keel of an Etruscan ship, while there were upland forests of fir and silver fir. The extant text seems confused, since beech ( Fagus silvatica, øx»h), which dominated the summits of the mountains of Lazio in the early modern period, belongs in the upland forests. If there were any beech forests in the lowlands of Latium c.300 , they were relics of previous colder periods, which were doomed to extinction during the warmer climate of the Roman Empire.¹⁶⁰