There is convincing evidence that between the 16th and 19th centuries, individuals living in the coastal marshes of southern England were less healthy than those in inland areas. 1 Farr W Report on the mortality of cholera in England. W. Clownes, London1852 Google Scholar , 2 Dobson MJ Contours of death and disease in early modern England. Cambridge University Press, Cambridge1997 Crossref Google Scholar , 3 Dobson M “Marsh Fever”—the geography of malaria in England. J Histor Geog. 1980; 6: 357-389 Crossref PubMed Scopus (35) Google Scholar , 4 Dobson M Malaria in England: a geographical and historical perspective. Parassitologia. 1994; 36: 35-60 PubMed Google Scholar , 5 Dobson MJ History of malaria in England. J R Soc Med. 1989; 82: 3-7 PubMed Google Scholar This evidence comes from two main sources. Historical records such as diaries, surveys, and travellers' accounts, provide anecdotal information about conditions in the marshes, 6 Hasted E The history and topographical survey of the County of Kent. W. Bristow, Canterbury1797–1801 Google Scholar , 7 Defoe D. A tour through the whole island of Great Britain. London: Penguin Classics, 1742–46. Google Scholar and Anglican parish registers of burials and baptisms provide data from which demographic trends can be identified. 8 Wrigley E Schofield R The population history of England, 1541–1871: a reconstruction. Cambridge University Press, Cambridge1981 Google Scholar The insalubrious marshes were associated with a regularly occurring fever, known as ague, marsh fever, tertian fever, and intermittent fever. 9 Bruce-Chwatt LJ Ague as malaria, an essay on the history of two medical terms. J Trop Med Hyg. 1976; 79: 168-176 PubMed Google Scholar This ague is most likely to have been malaria because it was often characterised by typical symptoms of this infection, including splenomegaly and fevers every 48 h. 10 Boyd MF Malariology. A comprehensive survey of all aspects of this group of diseases from a global standpoint. Saunders WB, Philadelphia and London1949 Google Scholar , 11 Hunter M Gregory A An astrological diary of the seventeenth century. Samuel Jeake of Rye 1652–1699. Clarendon Press, Oxford1988 Google Scholar Most importantly, this fever of the marshes responded to treatment with quinine, 12 Sydenham T. The works of Thomas Sydenham. The Classics of Medicine Library: Adams Jr LB, 1848–50. Google Scholar , 13 Talbor R Pyretologia; a rational account of the cause and cure of agues, with a successful method for the cure of quartans. Robinson R, London1672 Google Scholar which is an effective antimalarial. The malaria parasite was probably Plasmodium vivax, rather than P falciparum, since vivax malaria always dominates in temperate climates 10 Boyd MF Malariology. A comprehensive survey of all aspects of this group of diseases from a global standpoint. Saunders WB, Philadelphia and London1949 Google Scholar and the UK climate is theoretically capable of supporting vivax transmission. 14 Lindsay SW Thomas CJ Global warming and risk of vivax malaria in Great Britain. Glob Change Hum Health. 2001; 2: 80-84 Crossref Google Scholar More compelling evidence comes from the identification of P vivax in bloodfilms obtained in 1917 from patients with the same symptoms as those described more than a century earlier. 15 James SP Malaria at home and abroad. Jonn Bale, Sons & Danielsson, London1920 Google Scholar We also know from feeding experiments with the mosquito Anopheles atroparvus—the only common vector species in the saltmarshes—that these mosquitoes could transmit vivax, but not falciparum malaria. 16 Ramsdale CD Coluzzi M Studies on the infectivity of tropical African strains of Plasmodium falciparum to some southern European vectors of malaria. Parassitologia. 1975; 17: 39-48 PubMed Google Scholar , 17 Shute PG Failure to infect English specimens of Anopheles maculipennis var. atroparvus with certain strains of Plasmodium falciparum of tropical origin. J Trop Med Hyg. 1940; 43: 175-178 Google Scholar