The Impact of Human Activity on Cave Ecosystems - Mike Buchanan 2022

Opening Salvo

Carbonate cave systems and associated karst landscapes host complex, interdependent biological communities, microbes, fungi, protists, invertebrates and vertebrate-associated microbiomes. That have co‑evolved with the physical and chemical gradients of the subterranean environment; naturally occurring pathogens are therefore not anomalous intruders but intrinsic members of this biome, playing roles in nutrient cycling, population regulation and ecological resilience while reflecting the cave’s hydrology, substrate chemistry, and biological connectivity to surface ecosystems. Human activities, surface land use change, groundwater contamination, cave tourism, mining and introduction of non-native organisms, alter these delicately balanced conditions. Shifting microbial community composition and sometimes increasing the abundance or distribution of opportunistic or zoonotic agents, which raises occupational and public‑health considerations without transforming caves into static “hazmat” zones; instead, evidence supports a risk‑management approach grounded in monitoring, source‑control of contaminants, training and protective practices for cave users and conservation of karst catchments to preserve the ecological functions that both sustain endemic life and naturally regulate pathogen dynamics.

“In the hush beneath the earth, where stone remembers water's first journeys, life persists in quiet economies, unseen, interwoven and neither benign nor malevolent, but simply doing what living systems do: adapt, exchange and endure.”

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Abstract

Caves are unique ecosystems that host a diverse array of microorganisms and species, many of which are sensitive to environmental changes. This white paper discusses the risks associated with human activity in caves, particularly the transfer of pathogens, the introduction of non-native species, and the environmental impact of caving gear. It emphasizes the need for responsible caving practices to protect these fragile ecosystems.

Introduction

Caves serve as natural incubators, providing high humidity, constant temperatures, and elevated carbon dioxide levels that create ideal conditions for microbial growth. However, human visitation can introduce pathogens and disrupt the delicate balance of cave ecosystems. This paper explores the mechanisms of pathogen transfer, the implications of non-native species, and the environmental impact of caving gear.

Human Impact on Cave Ecosystems

Endemic Biological Communities

Humans carry their own unique microbial communities, which can alter cave ecosystems upon entry. The notion that humans become contaminants after their first visit underscores the need for stringent access protocols to protect cave environments.

Recommendations for Cavers

  1. Limit Visits: Reduce the frequency of trips to sensitive caves to allow ecosystems to recover.
  2. Use Minimal Gear: Consider using gear that minimizes the risk of contamination and microplastic shedding.
  3. Educate and Advocate: Promote awareness among cavers about the ecological impacts of their activities and the importance of protecting cave environments.

Pathogens and Transfer Mechanisms

Sporotrichosis and Wood Products

Sporothrix schenckii, the causative agent of sporotrichosis, can latch onto dry wood products, posing a risk when these materials are transported into caves. The introduction of non-native organisms can disrupt the delicate balance of cave ecosystems, potentially leading to the extinction of native biofilms and other microorganisms (Sigler and Kauffman, 2013).

Virus Pathogens

Haemorrhagic fever Viruses

Both Marburg and Ebola viruses have equatorial origins and are linked to caves due to their association with bat populations that serve as natural reservoirs. The Marburg virus was first identified in 1967, with significant occurrences in Kitum Cave in Kenya, where humans contracted the virus after contact with infected fruit bats. Similarly, the Ebola virus, first identified in 1976 near the Ebola River in the Democratic Republic of Congo, has been traced back to fruit bats, with outbreaks often occurring in regions near caves or forests where these bats roost. Both viruses highlight the importance of monitoring wildlife habitats in equatorial regions to prevent zoonotic spillover events that can lead to human outbreaks. While the association of Ebola and Marburg viruses with caves primarily stems from the presence of certain bat species, it is important to note that not all fruit bats roost in caves. The connection to caves is more pronounced for specific bat species that may inhabit these environments (WHO, 2020).

Coronaviruses

Coronaviruses, including SARS-CoV, MERS-CoV, and SARS-CoV-2, can have serious implications for both wildlife and human health. Many coronaviruses are found in bat populations, which often inhabit caves. When humans enter caves, they may come into contact with bat droppings or respiratory secretions, increasing the risk of zoonotic transmission. Caves can function as incubators for these pathogens, allowing them to thrive and proliferate (Wu et al., 2020).

Hantaviruses

Hantaviruses are a group of viruses carried by rodents, which cause both Haemorrhagic Fever with Renal Syndrome (HFRS) and Hantavirus Cardiopulmonary Syndrome (HCPS), are primarily carried by rodents, people become infected by inhaling the virus from rodent droppings, urine, or saliva. Therefore, these diseases can be found in environments where infected rodents live, including caves, though direct evidence of cave transmission is not explicitly highlighted, it is a potential site for exposure to rodent habitats. Cavers and researchers who enter caves with rodent populations are at risk of hantavirus exposure, which can lead to severe respiratory distress and fever (Hjelle and Glass, 2000).

Bacterial Pathogens

  • Brucella spp.: These bacteria can cause brucellosis, a zoonotic disease affecting various mammals, including humans. The introduction of Brucella into cave environments can disrupt local wildlife populations and potentially affect human health (Pappas et al., 2006).
  • Mycobacterium tuberculosis: This bacterium can survive in various environments, including caves, posing a risk to both cave-dwelling species and humans (World Health Organization, 2020).
  • Leptospira spp.: These bacteria cause leptospirosis, which can be transmitted through contaminated water or soil. Leptospira can thrive in moist cave environments, potentially affecting both wildlife and humans (Levett, 2001).

Fungal Pathogens

Histoplasma capsulatum

  • Histoplasma capsulatum is a dimorphic pathogenic fungus that transforms into yeast after crossing the alveolar membrane in humans and can adhere to caving gear and human skin due to its sticky outer casing. This characteristic makes it particularly challenging to eliminate, leading to concerns about cross-contamination when gear is transferred between caves. The persistence of this pathogen on surfaces necessitates strict protocols to avoid introducing it into new environments (Kauffman, 2007).
  • Batrachochytrium dendrobatidis (Bd): This chytrid fungus is responsible for chytridiomycosis, a disease that has devastated amphibian populations worldwide. If introduced into caves, Bd can spread to amphibians that inhabit these environments, leading to population declines (Berger, Speare and Daszak, 1998).
  • Aspergillus spp.: Some species of Aspergillus can produce mycotoxins and cause respiratory issues in humans and animals. The introduction of these fungi can affect both cave-dwelling species and cavers, particularly those with compromised immune systems (Culver and Pipan, 2009).
  • White-Nose Syndrome (WNS) (Frick, Pollock and Hicks, 2010).

WNS is caused by the fungus Pseudogymnoascus destructans, which infects hibernating bats, leading to significant mortality rates. Infected bats exhibit abnormal behaviours, such as waking frequently during hibernation, which depletes their fat reserves and ultimately leads to starvation. WNS has led to dramatic declines in bat populations across North America, disrupting the ecological balance, as bats play crucial roles in insect control and pollination. While WNS primarily affects bats, humans can inadvertently spread the fungus through contaminated gear and clothing (Lorch et al., 2013; Johnson et al., 2014).

Protozoan Pathogens

  • Giardia lamblia: This protozoan parasite causes giardiasis, a gastrointestinal illness. If introduced into cave water sources, Giardia can affect both wildlife and humans who come into contact with contaminated water (Culver and Pipan, 2009).
  • Cryptosporidium spp.: Similar to Giardia, Cryptosporidium can cause gastrointestinal illness, posing health risks to both animals and humans (Culver and Pipan, 2009).

Cleaning Limitations

Despite advances in decontamination, cleaning cave equipment is constrained by both material durability and pathogen resilience. Some fungi, such as Pseudogymnoascus destructans (the causative agent of White-Nose Syndrome), can persist on porous fabrics even after multiple washes (Lorch et al., 2013). Additionally, chemical disinfectants may degrade ropes and harnesses, limiting their long-term effectiveness (Johnson et al., 2014). Complete sterilisation is rarely feasible in field conditions, leaving a residual risk of cross-contamination between cave sites (Frick, Pollock and Hicks, 2010) (Lorch et al., 2013; Johnson et al., 2014) (US Fish and Wildlife Service, 2016).

Routine washing of caving attire and equipment.

Routine cleaning protocols are essential to minimise pathogen transfer between caves. The U.S. Fish and Wildlife Service recommends soaking gear in 10% bleach or commercial disinfectants (USFWS, 2016). For non-immersible gear, UV light treatment has been shown to reduce fungal viability (Palmer et al., 2018). Importantly, consistent decontamination after every cave visit should become standard practice, supported by caving organisations through training and awareness campaigns (Culver and Pipan, 2009). Integrating routine washing into caving culture not only protects wildlife but also reduces zoonotic risks to humans.

References

·         Kauffman, C. A. (2007). Histoplasmosis: A Review for Clinicians. The American Journal of Medicine, 120(4), 301-307. Link

·         Sigler, L., & Kauffman, C. A. (2013). Sporotrichosis: A Review. Clinical Microbiology Reviews, 26(2), 217-227. Link

·         Wu, F., Zhao, S., Yu, B., et al. (2020). A new coronavirus associated with human respiratory disease in China. Nature, 579(7798), 265-269. Link

·         Pappas, G., Papadimitriou, P., Akritidis, N., et al. (2006). The role of animal husbandry in the epidemiology of brucellosis. Clinical Microbiology Reviews, 19(3), 328-356. Link

·         World Health Organization. (2020). Global Tuberculosis Report 2020. Link

·         Levett, P. N. (2001). Leptospirosis. Clinical Microbiology Reviews, 14(2), 296-326. Link

·         Berger, L., Speare, R., & Daszak, P. (1998). Chytridiomycosis causes amphibian mortality associated with population declines in the rainforests of Australia and Central America. Proceedings of the National Academy of Sciences, 95(15), 9031-9036. Link

·         Hjelle, B., & Glass, G. E. (2000). Hantavirus in the Americas and its emergence as a zoonotic pathogen. Clinical Microbiology Reviews, 13(3), 440-453. Link

·         Frick, W. F., Pollock, J. F., & Hicks, A. C. (2010). An emerging disease causes regional population collapse of a common North American bat species. Science, 329(5992), 679-682. Link

·         Culver, D. C., & Pipan, T. (2009). The Biology of Caves and Other Subterranean Habitats. Oxford University Press. Link

 

 

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