Health and Disease
The missionary families came from England where mortality from disease was high, particularly among children. Infectious diseases and those arising from poor sanitation took their toll on both families. – two of nine siblings of Henry and William died young, but Marianne, on the other hand, lost seven of hers to childhood diseases. Henry and William’s father died of typhoid.
Epidemiologically New Zealand was virgin territory. Vectors of major tropical diseases were absent, and Māori were isolated from most communicable infections until Europeans arrived. Chronic diseases such as tuberculosis and venereal diseases were transmitted from the time of early European contact. Europeans and their ships were the primary means by which disease was transported. Once cross-Tasman and other commercial shipping became frequent, channels for regular disease transmission were well established. Whereas European adults who survived childhood diseases had developed immunity, most of the adult Māori population had never been exposed to infection, and were vulnerable.
The missionary community, Māori, and Europeans in general, were equally ignorant as to the causes of their illnesses, although Māori associated increasing prevalence and mortality with the presence of Europeans. The germ theory of disease, settled by Pasteur, did not emerge until later in the nineteenth century. In earlier times infections were thought to originate with one or more of evil spirits, vengeful gods, Satan, miasmas, putrefaction or foul air. Each culture had its own ideas. William Williams, though a trained surgeon, thought that the cause of sickness was sin, and the work of Satan, and prevention or cure lay in repentance and affirmation of belief. A priest at the bedside in those days was thought to be as beneficial as a doctor.
The journals and letters of the missionaries frequently report episodes of illness in their families –the gamut of childhood diseases; including whooping cough, measles, and scarlet fever, was a constant threat. Influenza was a frequent and worrying visitor repeatedly infecting people with different strains, without conferring immunity- much as it does today. Then there were numerous unexplained fevers, not able to be diagnosed.
They possessed a range of treatments some of which were taken into the field. More than 40 medicines, including salts of chemical compounds, herbal remedies, opiates, emetics, and laxatives, have been noted as being in the hands of missionaries.  William Williams carried a number of surgical instruments and records giving one of his children an opiate injection (probably morphine) for the relief of acute dysentery. Long standing practices such as cupping, bleeding and blistering were employed. Palliative care was the best weapon, and relatively few missionary families succumbed. As they moved about the country, the missionaries encountered pockets of disease among Māori, sometimes devastating, that they would treat as best they could.
Māori also treated disease or injury, using a small range of herbal remedies, while accepting a supernatural or spiritual dimension to illness and its treatment. Traditional practices, including those applied by the tohunga were no match for new diseases, leading those suffering to solicit missionary help.
Apart from a small pocket of infection among Northland Māori, smallpox did not establish in New Zealand, although it remained one of the most feared of diseases. Smallpox vaccination or inoculation was well known by the time the missionaries reached New Zealand. William Williams had sufficient material to vaccinate his children and later extended the practice to Māori he visited in the field.
The impact of disease on Māori was severe, and probably the major cause of population decline in the mid to late 19thcentury. Data collection and analysis was dependant on personal observation and anecdote, but even allowing for the wide variation in estimates, the trends were consistent and obvious. East Coast estimates suggest a population decline of more than 60%, which, even allowing for inaccuracies, is highly significant. 
Complications of childbirth were a leading cause of death in Britain, and the potential was a cause of concern here – Marianne herself had a narrow escape.  Although midwifery was not much regulated until the early 20th century, the Church for some time claimed connection and authority where midwives were concerned especially as the newly born were subject to baptisms and christening by ordained ministers. In England, in the early 19th century, midwifery was about to be brought under male authority, and male missionaries in New Zealand were known to attend childbirth. Nevertheless, missionary women were trained and experienced in this field and attended both Māori and Pakeha, notwithstanding that the former had long-standing birth rituals and practices.
A constant problem for the mission was the “shipping” which when it arrived at Kororāreka resulted in the girls in their charge being enticed away by male relatives, to trade their services for items offered by the sailors. They could spend up to three weeks on board, acquiring a variety of goods as well as venereal diseases, which became widespread and probably impacted Māori fertility.
 pp. 47, 48. Porter, F., (ed.), 1974. The Turanga Journals, 1840-1850. Price Milburn and Victoria University Press, 659pp. In spite of his belief as to fundamental causes, William Williams actively treated those who were sick, or who required surgery, and believed in the value of vaccination.
 p. 9, Owens, J M R, 1972. Missionary Medicine and Maori Health: The Record of the Wesleyan Mission to New Zealand
before 1840. The Journal of the Polynesian Society, 81(4): 418-436.
 p. 43, Porter, F. (ed), 1974, loc.cit. This would seem to be a remarkably early (1848) use of a hypodermic.
 p. 333, Porter, F. 1974. Loc cit.; Fitzgerald, C. 2004. Letters from the Bay of Islands, the story of Marianne Williams. Penguin, Auckland, p. 153.
 Pp. 50-51, Oliver, W H and Thomson, J M, 1971. Challenge and Response. The East Coast Development Research Association, Gisborne., 251 pp.
 p. 161, Fitzgerald, C., 2004, loc. cit.
 pp. 51, 52, Porter, F. 1974, loc. cit.
William Williams' medical chest. Private collection.