Malaria in the River Thames
Malaria was a common affliction in populations that lived beside the River Thames until the middle of the Victorian era, not only in its estuary, but even in central London. It was frequently lethal. Some cases continued to occur until early in the 20th century. Why malaria died out in England is rather unclear.
Thames marshes
Malaria was commonplace in the Thames marshes, including London, and was called "ague" or "marsh fever". While not all agues were caused by malaria, most scholars believe true malaria – the protozoan infection – was indeed present. Descriptions in early 19th century medical textbooks leave little doubt, since: It was mainly transmitted by the mosquito Anopheles atroparvus, and was frequently lethal, though this has been disputed. It was so bad that most clergymen refused to reside in their parishes, where these were near the marshes.Introduction of the disease to Britain
Possibly malaria was introduced by the Roman invaders; evidence from skeletons suggests the disease was present in Anglo-Saxon England.Endemicity
It was anyway rife by the 16th century, though the climate was colder than today. James I and Oliver Cromwell were thought to have died of it, and it was prevalent in London before and after the Great Fire. Shakespeare mentions ague in eight of his plays as if his London audiences would be familiar with aspects of the disease.Mary Dobson said that
Writing around 1800, Edward Hasted noted
The heavy use of opium and alcohol to fight the fever was commonplace. Later, the disease was combated with quinine; that this treatment was effective tends to confirm it was malaria, and not some unrelated malady.
London
At Guy's Hospital they frequently received ague cases from the Thames marshes, William Gull told the House of Commons in 1854. About a half came from Woolwich and Erith, but cases also came from Wapping and Shadwell, and along the river from Bermondsey and Lambeth and even Westminster.Decline and disappearance
Generally, deaths started to decline after 1800, although there was a fairly sharp peak around 1860. Some cases occurred in all parts of England, but by far the worst area was in the Thames.By the end of the Victorian era indigenous malaria had nearly disappeared from England, but a few cases survived into the 20th century enabling the disease to be positively identified by blood tests. It was probably caused by the protozoan parasite Plasmodium vivax.
While the draining of the Thames marshes did not, by itself, eradicate malaria – in places the mosquito still abounds – it may have been a contributory cause. Why it did disappear is complex and uncertain. The mosquito prefers to take blood from livestock, so increasing livestock densities may have diverted biting from humans to domestic animals. Other factors may have included better housing, health care, sanitation and hygiene, smaller rural populations as manual labour was replaced by machinery, and better insulation of houses in winter.