By Advika Sadasivan, The Village School, Houston, Texas, United States
Abstract
As climate change causes higher average global temperatures, both permafrost and glaciers continue to melt at an unprecedented rate, causing the release of formerly-frozen pathogens such as Anthrax, a disease caused by infection of Bacillus anthracis, posing threats to public health. While there is an abundance of existing research surrounding the effects of permafrost melting on Anthrax incidence, there is less conversation surrounding the effects of glacier melt. This paper assesses existing glacial extent and Anthrax occurrence data to test for correlations. It concludes that Anthrax abundance is driven more by cattle populations than glacial extent, due to glaciers having less organic matter than permafrost, and bacteria transfer between hosts being more prevalent.
Introduction
Glaciers are a large accumulation of crystalline ice, snow, rock, sediment, and often liquid water that originates on land and moves down-slope under the influence of its own weight and gravity (USGS et al. 2023). Evidence has shown that temperatures worldwide have risen in the past two decades by about 0.3 degrees celsius over land ( NASA et al., 2020 ). This has led to numerous environmental and socio-economic impacts, including sea-level rise, water scarcity, and natural hazards such as flooding and landslides (Hughes et al., 2013), and rapid glacial melt (Batchelor et al., 2023). As climate change intensifies, it is essential we understand its various implications. Recent studies suggest a link between glacier melting and Anthrax abundance (Varghese et al., 2023; Yarzábal et al 2021).
Anthrax is a serious bacterial infection caused by Bacillus anthracis. In recent years, there has been a notable increase in cases of anthrax outbreaks in areas near melting glaciers. As the glaciers melt, the soil underneath becomes exposed, and previously frozen bacteria, such as B. anthracis, can become activated and infectious (Walsh et al., 2018). Anthrax is endemic to cattle and wild animals in many parts of the world, and can cause severe disease in humans who are exposed to infected animals or meat through inhalation of spores or cutaneous exposure. Anthrax is potentially fatal once exposed, and has a mortality rate of 20-80 % in unvaccinated humans, depending on route of exposure (Kamal et al., 2011; Biswas et al. 2011).
Existing literature explores the relationship between permafrost melting and Anthrax outbreaks (Stella et al., 2020), however, there is less conversation on the relationship between glacier melting and Anthrax. This research paper aims to explore the link between glacier melting and anthrax outbreaks worldwide.
Methods
We reviewed the existing literature on the topic and analyzed data on the prevalence of both glaciers and anthrax. We used anthrax occurrence data from the United Nations Food and Agriculture Organization Empres-i dataset (EMPRES-i, 2021), and glacial extent data from GLIMS (Global Land Ice Measurements from Space). We used data from Ritchie et al. (Meat and Dairy Production - Our World in Data) to assess the role of cattle population in driving anthrax cases.
We tested which is a more important driver of anthrax–cattle population, or glacier extent. Using the R software suite, we assessed the correlations between glacial extent and anthrax occurrence at a global scale, using regions as data-points. We assessed normality using a Shapiro-Wilk test, and assessed correlations using a Spearman’s rank-correlation test, or Pearson’s test, depending on distributions.
Results
Figure 1: Anthrax occurrences and glacier extent in sq. km (p = 0.17, Spearman-rank correlation test rho = 0.36).
Figure 2: Anthrax Occurrences correlated with cattle population in million ( p = 0.002, rho = 0.74).
As observed, anthrax cases were highest in the eastern Asia region (6919 cases), and lowest in Melanesia (2), in the period we looked at (2013-2023). Glacial extent was highest in North America with 200,325 km2 of glacial coverage, and lowest in Australia and New Zealand, with 5893 km2. The Caribbean, Central America, Eastern Africa, Melanesia, Middle Africa, Northern Africa, South America, Southern Africa, and Western Africa had 0 km2 glacier extent, and 0 glaciers. The number of individual glaciers was highest in Central Asia with 123,563 glaciers in the database, and lowest in Eastern Europe with 2964 glaciers.
In Figure 1 Glacial Extent is graphed against the log of anthrax occurrences. The log of anthrax occurrences is taken to account for outliers in the data and the gap between various data points. The p value is 0.1 and rho of 0.36 indicates that there is no correlation between glacial extent and anthrax occurrence.
Figure 2 depicts cattle population is graphed against anthrax occurrences. The p value is 0.002 and rho of 0.74 indicate a clear correlation between anthrax occurrences and cattle population.
Discussion
As observed, there is no distinct correlation between glacial extent and anthrax levels. This could be attributed to several different factors. First of all, microbial cell concentrations within glaciers tend to be 102 to 104 cells ml−1 in most glacier-ice samples which is considered to be significantly lower than other environments such as seawater or soils. (Zhong et al., 2021) Since permafrost is composed of organic matter, it is likely that there is a much higher presence of disease within it. Additionally, global warming, and the subsequent thawing of permafrost results in an increase in the depth of the active layer which supports a high population of soil bacteria such as Actinobacteria, Firmicutes, Cyanobacteria as well as Archaea (Tas et al. 2014). Recent studies conducted regarding thawing permafrost revealed numerous and diverse viruses. Notably, these viruses, otherwise known as DNA bacteriophages, only affect bacteria. As permafrost begins to thaw, these viruses display a shift in community structure, transitioning to aquatic assemblage like viruses. (Wu et al. 2022) In contrast, organic matter is present within glaciers, but to a less significant extent (Stubbins et al. 2011).
Additionally, glacial extent does not necessarily correlate perfectly with the rate of glacial melt (Barry, 2006), as some locations–such as Greenland (Rignot et al., 2010), Scandinavia, and Russia (Shugar et al., 2020)–are seeing glaciers melt at higher rates than others. This could be a contributing factor in the lack of relationship seen between anthrax cases and glacier extent.
Cattle populations are a more significant determinant of anthrax cases as observed by the data. In areas with significant cattle populations, bacteria is more susceptible to being transferred between hosts. Additionally, it can be difficult to provide adequate vaccination to cattle when populations are so high, making disease spread more likely (Alam et al. 2022).
Issues in reporting data within rural areas that are usually home to high cattle populations present a limitation to this study, warranting further research on this topic. To our knowledge, this paper is the first to address the connection between glacier melting and the abundance of Anthrax, building on significant research regarding permafrost melting and Anthrax incidence. As temperatures continue to warm, and public health threats due to emerging diseases become more imminent, it is imperative we understand the implications of climate change on public health.
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