Chytrid fungus (Bd) in amphibians
Chytridiomycosis or chytrid fungus is an emerging infectious disease of amphibians (both frogs and salamanders) and has been noted as the most devastating infectious wildlife disease recorded and a global threat to amphibian populations. Chytrid is an infectious disease caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd). The disease has been documented in amphibians from Wisconsin and the Midwest, but to date, large mortality events have yet to be noted in this region. Population declines, extirpations and extinctions have been found in other regions of North and South America. Bd is closely related to salamander chytrid disease (Bsal) which primarily impacts salamanders.
The history of Bd in the United States is not well understood, but the lineage may date back as far as 1000 years. The oldest verified record of chytrid fungus in North America is from California in 1928. Studies have shown the highest infection rates in amphibians are observed during spring, largely in colder, wetter months with post-metamorphic frogs being most susceptible. It appears some amphibians may be more resistant to Bd than other species.
TRANSMISSION
The fungi spread via zoospores, which can be transmitted through infected soil or water and possibly via direct contact between amphibians. Amphibians that spend higher amounts of time in terrestrial habitats may be more prone to infection. Bd affects the epidermal layer (skin) and can inhibit the ability of infected amphibians to effectively thermoregulate, perform oxygen exchange through the skin and hydrate themselves which can result in mortality. Models predict chytrid may move northward with greater prevalence and intensity due to climate change.
CLINICAL SIGNS
Signs of the disease may vary by species, but common signs of infection are lethargy and loss of body weight, along with excessive shedding of skin or red skin, convulsions, inability to right themselves and abnormal feeding behavior.
DISEASE MANAGEMENT
Currently little is known about the transmission of this fungus. The zoospores can be transported by people via clothes, boots or equipment. When sick or dead amphibians (tadpoles, salamanders, frogs) are observed, care should be taken to prevent potentially moving any infectious diseases to another location. At a minimum, rinse off footwear and either air dry in the sun for a few days, disinfect with a 10% bleach solution or wipe off with 70% alcohol wipes before wearing to another water area.
PUBLIC HEALTH
There is no known risk to people or pets.