eeb 255 3/12/2025

Emerging Infectious Diseases

• Emerging infectious diseases are those that have undergone one or more significant changes:

  • Geographic range expansion.

  • Host species transfer.

  • Increased severity or impact.

  • Changes in pathogenesis (the mechanisms of infection).

  • Caused by newly evolved pathogens.

• Example: COVID-19 and other zoonotic diseases (transmitted from animals to humans).

  • Zoonotic diseases impact wildlife populations and could increase disease spread.

  • 75% of emerging infectious diseases in humans are transmitted from animals.

    • Examples include COVID-19, bubonic plague, HIV, influenza, SARS, Ebola, rabies, Lyme disease, West Nile virus.

Role of Wildlife and Zoonoses

• Diseases such as COVID-19 are caused by pathogens that jump from animals to humans.

• Critique of bats as 'villains' in the spread of zoonotic diseases, especially during the COVID-19 pandemic.

• Research focused on whether animals like bats are more likely to spread disease due to their diversity:

  • Bats account for about 20% of mammal species with over 1,400 species.

  • They are closely followed by rodents in diversity.

• Study findings:

  • Rodents, bats, and primates contain the highest number of zoonotic diseases recorded.

  • Adjusting for species diversity shows a more even contribution of diseases across animal groups, including songbirds.

Chytridiomycosis: A Case Study

Overview

• Chytridiomycosis: a fungal disease affecting amphibians (frogs, toads, salamanders, caecilians).

Amphibian Characteristics

• Oldest tetrapods, with a long history dating back over 350 million years.

• Notable for permeable skin which facilitates breathing and absorption, yet increases susceptibility to diseases.

• Approximately 6,600 amphibian species globally; about 30% are threatened, higher than most vertebrate groups.

Impact of Chytridiomycosis

• Approximately 700 species of amphibians are infected, causing population declines in 200 species, extinction in at least three species:

  • Panamanian golden frog: Extinct in the wild, but held in captivity.

  • Sharp snouted frog: Last seen in 1997 and may be extinct.

  • Australian gastric brooding frog: Famous for its unique reproductive method; extinct in the wild.

Pathology of Chytridiomycosis

• Caused by a pathogenic chytrid fungus (BD fungus), it infects the skin, disrupting electrolyte balance and leading to cardiac arrest.

• Its motile larvae can swim and easily infect other amphibians.

Causes and Spread of Chytridiomycosis

• Likely spread related to the global amphibian trade and pet ownership, with historical evidence dating back to 1938.

• Factors contributing to spread:

  • High-density breeding in pools.

  • Metamorphosis period leads to immune suppression.

Treatment and Prevention

• Laboratory cures exist, but effective environmental treatments are lacking.

• Probiotic treatments show promise for individual-based cures.

  • Genetic diversity among amphibians may provide resistance.

White Nose Syndrome: Another Case Study

Overview

• White nose syndrome (WNS) affects bats and has led to the death of over 6 million bats in North America.

• Fungus (Pseudogymnoascus destructans) thrives in cold hibernacula, causing excessive waking and energy depletion in bats during hibernation.

Impact and Ecology

• Species affected demonstrates significant population declines (e.g., little brown bat, Myotis lucifugus).

• The fungus is host generalist and can survive without a host. It is not harmful to European bats, indicating specifics of American bat populations and ecology are at play.

Treatment and Management

• Prevention strategies must focus on controlling human movement between caves and educating the public on the disease’s impact.

• Techniques under investigation include:

  • Temperature regulation of caves to affect fungal growth.

  • Biological control using antifungal bacteria.

  • Efforts to genetically rescue bat populations for disease resistance.

Conclusion

• Understanding and combating emerging infectious diseases, such as chytridiomycosis and white nose syndrome, requires interdisciplinary approaches, including wildlife conservation, virology, and ecology.