Vibrio cholerae is the causative agent of cholera and is linked with the aquatic environment. More than 200 serotypes of Vibrio cholerae have already been identified and several of them can cause different symptoms: from mild symptoms, not requiring medical attention (observed in 80% of patients), to serious gastroenteritis, causing profuse diarrhoea, leading to dehydration and, in the most severe cases – to death (observed in 20% cases) [44–45]. The toxigenic strains of Vibrio cholerae serogroups O1 and O139 have been identified in cholera epidemics and pandemics [45–46]. In the past two centuries, cholera emerged and spread from the Delta of Ganges six times causing six pandemics: 1817–1823, 1826–1838, 1846–1863, 1865–1875, 1883–1896, and 1899–1923 [47]. The classical biotype was the etiological factor responsible for them. The seventh pandemic, lasting in 1961–1975, spread from Indonesia and the etiological factor was the biotype El Tor [48–50]. In the contemporary world cholera still remains a major cause of morbidity and mortality, particularly in lower-income countries with poor sanitary infrastructure and low hygiene [51]. The WHO estimates that the officially reported cholera cases represent only 5–10% of the actual number occurring annually worldwide. Of the estimated 3 to 5 million cases that occur globally every year, about 100,000 to 120,000 end in death [52].
Our research indicates a higher risk of death from cholera among women than men. This is in line with observations coming from current cholera epidemics. The WHO report [53] points to traditional social roles as a factor responsible for the surplus of deceased women and girls over men and boys. The higher incidences of cholera among women result from their potentially frequent contact with contaminated water when preparing and cooking meals, feeding, caring for and washing children, and caring for sick family members. A link between the increased morbidity and deaths from cholera and traditional division of roles, assigning women to run the household and to care for the sick, are confirmed by studies of cholera epidemics in northern Jakarta [54] and in James Town, a community from the sub-Metropolitan area in Accra, Ghana [55]. A greater risk for symptomatic cholera in females than males was also confirmed by studies of cholera epidemics in Bangladesh [56], in nomadic pastoralist groups from the sub-Saharan parts of Uganda [57], and in Columbia [58]. Female cholera cases outnumbered male cases in Mpumalanga Province, South Africa [59], which also had their socio-cultural justification. Men migrated from the Province in search for work and education more often than women, hence women predominated the Province population [59]. The example of cholera epidemic in Sierra Leone in 2012 also attributes the high morbidity and mortality rates among women to their roles in traditional society, i.e. running of the household and the care for children and the sick. The prevalence of women as rural traders travelling to markets in commercial centres also increased their vulnerability to contracting and transmitting the disease [60]. Some gender differences were observed in eating practices: women in rural areas of Sierra Leone often practiced eating in groups, shared their food and ate with hands, while men used their own bowls and ate with spoons. Moreover, in the case of female traders, food was rather eaten raw than cooked [60]. In turn, the cases of cholera epidemics in the Democratic Republic of Congo and Zanzibar show that the disease affected everybody regardless of gender, age and class, while in western Kenya, women were much more vulnerable to cholera than men [61]. Some African studies confirmed cholera cases more likely in males than in females [62–63]. In fishing villages from Uganda men were at a higher risk of cholera due to frequent access to contaminated water than women [62]. This example reinforces the role of social factors responsible for the gender-specific cholera mortality.
Recently, attempts have been made to look for answers concerning sexual dimorphic differences in morbidity and mortality from cholera in biological reasons. Watanabe and a team [64] have reported that female mice are more sensitive to cholera toxin than male ones. According to the authors, the level of some proteins (ARH1 protein) may affect the gender specificity in the response to cholera toxins.
In our research the intensity of cholera epidemics, and hence the number of deaths, varied between urban and rural centres: cholera epidemics took the greatest toll in large cities, for example in the city of Poznań, while the smallest one in villages. The cholera epidemic in 1852 killed 1,724 people in Poznań, i.e. 3.9% of the city population, 97 Poznań inhabitants died due to cholera in 1855, and in 1866 the disease killed 2.4% of the city population [65]. There was also some variation in deaths numbers from cholera between Poznań districts. In a poor working-class district of Poznań, located on the right bank of the Warta River, deaths from cholera accounted for as many as 6% of all deaths [66], while deaths in the group of 2–14 years constituted of almost 9 % of all deaths in this age category [67]. In the wealthier city centre deaths due to cholera epidemics in the 1850s, 1866 and 1873 accounted for almost 5% of all deaths [66]. The outbreak of cholera epidemic in the wealthier Poznań city centre confirmed earlier assumptions that cholera had attacked only the poorest classes were wrong. In 1866 the epidemic was probably brought to Poznań in June to one of the taverns in the Old Market Square by raftsmen from Szczecin [68].
The 19th -century Poznań was an overcrowded city, especially the downtown was suffocating within the walls of the fortifications. The city suffered from deficient infrastructure. Until the mid-1860s Poznań had no modern water supply system and for many inhabitants, the Warta River flowing through the city, was the source of drinking water [69]. The lack of the municipal sewage system contributed to poor conditions in the city (it was built as late as the end of the 19th century) [66–69]. Thus, in small towns the cholera death rate was lower than in cities. For example, the town of Leszno owed the absence of epidemics of infectious diseases to its high sanitary and epidemiological conditions, exemplary for those times. Already in the mid-1840s Leszno citizens drew fresh water from dug or drilled wells nearby their homes. Additionally, a gravity-flow water-supply system operated in the town. The network of pipes distributing fresh water throughout the town was steadily expanded, along with the increase in the number of inhabitants [37, 41]. In Leszno deaths from cholera accounted for only 0.26% of all deaths [37]. In the light of statistics, the epidemic threat was the lowest in villages of the Poznań Province. This was due to the low population density, including no access to contaminated water. In the studied Jastrzębsko Stare Parish, for instance, deaths from cholera accounted for about 0.1% of all deaths recorded there [37].
Cholera epidemics in the Poznań Province in the second half of the 19th century killed more women than men. Our results have confirmed that deaths of girls (teenagers and young women) and adult women during cholera epidemics outnumbered deaths of males (teenagers, young men and adult men). In the same age categories of non-epidemic periods, it was male deaths which outnumbered female ones, and this was a typical mortality pattern [37]. The increase in female deaths in times of cholera epidemic may have resulted from different social roles between females and males, which has already been discussed earlier in this work. Differences in cholera death rates may have had their source in societal norms, in the light of which women cared for the sick in homes, hospitals and shelters. Women performed water-related household activities and could have potentially contacted contaminated water by cooking, food preparation, cleaning and washing, etc., much more frequently than men. In the city of Poznań women drew water from shallow wells, which were often polluted with harmful sewage discharged directly to the Cybina River, the Warta River and the moats. They used water from the rivers directly for cooking, cleaning and washing. The annual sanitary reports on water cleanliness indicated the contamination with nitric acid, chlorine, ammonia, and hydrogen sulphide. There were also primitive street gutters with ineffective drainage full of contaminated water during the summer heat periods, into which women poured sewage [69–71].