Impact of Hygiene, Famine and Environment on Transmission and Spread of Cholera

Abstract

Cholera is a bacterial disease caused by the bacterium Vibrio cholerae that requires optimal temperature and environmental conditions to survive. It is well known that climate change, influence of ecology, flood and droughts can affect the concentration of the bacterium in the environment. The goal of this article is to establish the effects of hygiene, famine, climate and environment on the transmission and spread of cholera. The transmission dynamics of the disease are modeled with a non-autonomous system of ordinary differential equations that is coupled to a model of intra-annual variation of Vibrio cholerae in the environment. When the intra-annual variation of Vibrio cholerae is not incorporated into the model, this latter becomes autonomous and we then give an explicit formulation of the basic reproductive number. In the non-autonomous case, we make analytically explicit two thresholds that allow to exhibit cases where disease extinction otherwise disease uniform persistence may occur. Finally, some numerical simulations allow to study the evolution of the cholera spread according the different environmental factors.The principal factors of outbreaks and spread of cholera are favorable in Africa. Severe outbreaks of cholera have been directly associated with flood and war [18,39]. The famine caused by war is also a parameter in Africa, because gastric acid failure is favorable to the spread of Vibrio cholerae [4,14,18,39].Many studies have focused on the association between weather factors and occurence of V. cholerae. Particulary, the relationship between the occurence of V. cholerae, temperature and salinity (measure of parts salt per thousand parts seawater(ppt)) were investigated. [7,8,15,18]. The most favorable salinity for V. cholerae is between 2 and 14 ppt, and the optimal salinity appeared to be between 2 and 8 ppt. The most favorable temperature is between 10 • C and 43 • C, the optimal temperature appeared at 37 • C [7, 8].However, there are studies that have investigated the relationship between the occurence of V. cholerae, river levels and vegetables. The pH of specific vegetables and water is an important factor that influences contamination by V. cholerae. The most favorable pH is between 5 and 10 with the optimal pH of contamination at 8 [4,18,22].The spread of disease is then influenced by the environment, weather factors and socioeconomic status. Thus, to study the dynamics of the transmission, it is important to take into account the following factors: climate (temperature and rainfall), environment (pollution, vegetation and proximity of lakes or rivers) and education of the population [18,22,26,39,41].Several kinds of mathematical models have been proposed to understand the dynamics of transmission of cholera, mainly described by SIR models, where are incorporated the effect of temporary immunity and a distinction between asymptomatic infected and symptomatic infected [9,11,42]. The direct and indirect transmission both have been considered in the previous models. The hyperinfectivity...

Epidemiology and Ecoepidemiology: Introduction to the Special Issue

“…In their study, E. Dangbé, D. Békollé, Damakoa Irépran and A. Perasso [5] have considered cholera studying the impact of hygiene, famine and environmental conditions on this disease spread. The optimal temperature and environmental condition are found to be the most important factors for the Vibrio cholerae bacteria survival.…”