Climate change affects the spread of typhoid pathogens

Abstract

Typhoid fever is caused by Salmonella enterica serotype Typhi (Salmonella Typhi). Syndromes in patients vary from asymptomatic carriers to severe or death outcomes, which are frequently reported in African and Southeast Asian countries. It is one of the most common waterborne transmission agents, whose transmission is likely impacted by climate change. Here, we claimed the evidence and consequences of climate‐related foodborne and waterborne diseases have increased and provided possible mitigations against Typhoidal Salmonella dissemination.

Given the increasing threats to public health, here we elaborate on the potential effects of climate change on the dissemination of Salmonella enterica serovar Typhi and highlight variable consequences. The future endeavors should be consistent with the guidelines set forth by the WHO.

Typhoid fever, estimated to cause over 100,000 deaths annually (Walker et al., 2023), is a bacterial infectious disease caused by the gram‐negative bacterium Salmonella enterica serovar Typhi (S. Typhi). As an ancient companion of humanity, S. Typhi was identified during the 19th century and disproportionately burdened low‐ and middle‐income countries, especially in Africa and Southeast Asia, where sanitation remains inadequate. Patients, particularly children, commonly exhibit symptoms such as nausea, pain, diarrhoea, vomiting or constipation following an asymptomatic period lasting 7–14 days (Hu et al., 2022). Similar to other waterborne pathogens, S. Typhi is primarily transmitted through contaminated food or water.

Multiple studies have substantiated that climate change accelerates the prevelance of typhoid fever (Dietrich et al., 2023; Feng et al., 2023; Liu et al., 2018). Specifically, ‘global warming’, ‘rising sea levels’ and ‘frequent weather disasters’ have been highlighted by the World Health Organization (WHO) and deemed as the ‘greatest global health threat of the twenty‐first century’ (Luo et al., 2023).

Rising typhoid fever infection rates are especially concerning, given that prevention and treatment are becoming more challenging. Although the existing typhoid vaccine offers a protection rate of more than 80% and remains effective for up to 7 years (Milligan et al., 2018), the challenge lies in timely vaccine distribution in regions experiencing severe weather conditions, which is predicted to become more common. At the same time, S. Typhi is increasingly resistant to three widely prescribed front‐line antimicrobials—chloramphenicol, co‐trimoxazole and amoxicillin (Birger et al., 2022; Jia et al., 2023). This issue has been attributed to the expansion of antimicrobial use in response to increasing typhoid fever infection rates.

Given the substantial risks to public health, here we elaborate on the potential effects of climate change on the dissemination of S. Typhi and highlight some appropriate interventions. These endeavours are consistent with the guidelines set forth by the WHO (2022).

GLOBAL WARMING

Typhoid outbreaks typically manifest during the summer months, with elevated temperatures as a contributing factor (European Food Safety Authority and European Centre for Disease Prevention and Control, 2021). This pattern has been observed across different regions globally. Generally, nations at higher latitudes exhibit lower typhoid incidences than those with warmer climates. Elevated temperatures can expedite the growth and reproduction rate of S. Typhi in the environment, facilitating its transmission to humans through heat‐affected and spoiled food (Figure 1).

FIGURE 1.

The impact of climate change on typhoid pathogens dissemination. Climate change could accelerate the rate of typhoid pathogens proliferation. (A) The rise in precipitation increases the probability of typhoid pathogens congregating in shallow waters. (B) The prevalence of perishable food has elevated the chances of typhoid pathogen infections.

The Sixth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) asserts that global temperatures are projected to rise (IPCC, 2022). Some studies have suggested that an increase of 1°C in the mean weekly minimum temperature can lead to a 5.8% rise in the weekly number of typhoid cases (Zhang et al., 2010). Especially consequential is bacterial proliferation in food during production, storage and distribution.

FLOODS

Floods create vulnerability to faecal‐oral transmission of typhoid and other pathogens due to obstructed urban drains and the release of untreated sewage or faecal matter. In situations where access to clean water is challenging, people are more inclined to consume water from surface sources, which are contaminated by floodwaters, potentially carrying Salmonella.

Floods have been recognized as the most frequent and devastating natural disaster worldwide and are projected to increase due to changing precipitation patterns and rising sea levels. Research shows that compared to no floods, the risk of typhoid fever infection is 1.76 times higher during floods (Liu et al., 2018). Although the mitigation of typhoid transmission may follow the dissipation of short‐term flood effects, a sustained increase in precipitation can establish a persistent risk of typhoid fever transmission (Thindwa et al., 2019).

EXTREME WEATHER

Weather extremes can enhance the transmission of S. Typhi. For example, across various intensity levels, tropical cyclones elevate the risk of infectious diarrhoea linked to typhoid (Kang et al., 2015). Additionally, insects may serve as transient vectors during hurricanes, broadening the range of transmission (Shi & Thakur, 2023). Extreme weather events, including tsunamis and hurricanes, wield substantial impacts on human production, livelihoods and ecosystems. Displacement of families from their homes due to extreme weather frequently results in overcrowded and unsanitary conditions, thereby amplifying the mortality rate associated with typhoid. Humanitarian crises caused by severe weather can endure for an extended duration, compounding the challenges already faced by vulnerable populations. The specific impacts vary depending on distinct events and are contingent upon various factors, including the nature of the disaster, its repercussions on sanitation systems, the congregation of displaced populations and the accessibility of healthcare services.

APPROPRIATE RESPONSES

Effective responses require increased technical and financial support to low‐ and middle‐income countries, given the disproportionate prevalence of typhoid fever. Ensuring access to clean water and enhancing environmental monitoring are critical in mitigating the incidence of typhoid fever. Furthermore, regions highly susceptible to typhoid outbreaks should have additional consideration to promote vaccines and more rational antibiotic use. A study conducted in China unveiled a gradual reduction in typhoid fever incidence from 1984 to 2007, credited to enhancements in water quality and heightened vaccination rates. These interventions have also exhibited effectiveness in diverse global regions, including sub‐Saharan Africa, South and Southeast Asia and Oceania (Li et al., 2022)

However, achieving enhanced S. Typhi monitoring remains challenging, primarily due to the abundance of bacterial species in the environment, including surface water, and the considerable number of carrier populations. Consequently, employing sensitive detection techniques, such as real‐time polymerase chain reaction or other in‐field diagnostic approaches, is a feasible alternative. Additionally, recognizing the robust correlation between typhoid fever and environmental factors, contemplating more general indicators, such as the total number of Escherichia coli as proxies for the risk of typhoid fever or other waterborne agents, warrants consideration.

Finally, more research is needed to better project the impact of climate change on S. Typhi occurrence and to assess the effectiveness of interventions. To safeguard future strategies, consistent with the COP28 UAE Declaration on Climate and Health, we also call for more research on the causal link between climate change and the mitigation of antimicrobial‐resistant S. Typhi (Zhou et al., 2023).

AUTHOR CONTRIBUTIONS

Chenghao Jia: Data curation (equal); investigation (equal); writing – original draft (equal). Qianzhe Cao: Investigation (equal); writing – original draft (equal). Zining Wang: Investigation (equal); methodology (equal). Annemieke van den Dool: Validation (equal); writing – review and editing (equal). Min Yue: Conceptualization (equal); supervision (equal); validation (equal); writing – review and editing (equal).

CONFLICT OF INTEREST STATEMENT

None.

Jia, C. , Cao, Q. , Wang, Z. , van den Dool, A. & Yue, M. (2024) Climate change affects the spread of typhoid pathogens. Microbial Biotechnology, 17, e14417. Available from: 10.1111/1751-7915.14417