Description
Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) are fungi that cause chytrid disease, also called chytridiomycosis, in amphibians. They belong to a family of fungi that grow in the ground or parasitize plants and insects. The Batrachochytrium genus is the only known genus in the family to infect vertebrates. This fungus tends to thrive in cool, moist habitats. In the past, chytrid was likely either a regional disease that spread through increased human intercontinental travel or a previously widespread fungus that, due to recent worldwide environmental changes (i.e., pollution), has changed in its mechanisms of infection. How the fungus kills amphibians is still unknown, but it most likely disrupts skin function, such as gas exchange or movement of fluids, in and out of the amphibian’s body.
Transmission
Bd and Bsal spread through flagellated zoospores that “swim” through water to infect new hosts. These pathogens can also spread through direct contact with infected amphibians. The rates of infection vary between different species and life stages of amphibians. The fungus infects keratinized skin, which is found on adults and the mouthparts of tadpoles.
Clinical Signs
The skin of animals infected with Bd can appear reddish in color, especially on the abdomen and legs, and it may slough off. Infected animals will also lose weight and act very lethargic.
Bsal can cause ulcerations on some salamanders that sometimes appear as black spots. Infection of Bsal can also cause strange behavior and body posture in salamanders directly preceding death.
Wildlife Management Implications
Chytrid has been one of the most destructive wildlife diseases in terms of extinction numbers. Chytrid has caused mortalities for amphibians in Australia, New Zealand, the United States, Mexico, South America, and Southeastern Asia. To prevent the spread of chytrid, one should purchase amphibians from only a licensed, chytrid-free supplier. Do not transport amphibians from one body of water or area to another. Do not release any relocated amphibians into the wild.
Human Health Significance
Chytrid is not considered a health risk to humans.
References
- “Chytridiomycosis.” Environment.gov.au, Australian Department of Sustainability, Environment, Water, Population and Communities, www.environment.gov.au/system/files/resources/279bf387-09e0-433f-8973-3e18158febb6/files/c-disease_1.pdf.
- “Disease: Chytrid.” Froglife, www.froglife.org/what-we-do/disease-chytrid/#:~:text=Chytridiomycosis%20is%20an%20infectious%20disease,and%20extinction%2C%20of%20tropical%20species.
- Batrachochytrium Salamandrivorans (Bsal),
www.usgs.gov/centers/nwhc/science/batrachochytrium-salamandrivorans-bsal?qt-science_center_objects=0#qt-science_center_objects. - Malagon, Daniel A., et al. “Host Density and Habitat Structure Influence Host Contact Rates and Batrachochytrium Salamandrivorans Transmission.” Scientific Reports, vol. 10, no. 1, 2020, doi:10.1038/s41598-020-62351-x.