The experience with the in captive management of infected amphibians´ larvae has showed us that in certain circumstances some specimens can become non-infected with pathogenic fungus if they are simply kept isolated.
To understand why can this happen, we have to bear in mind how the chytrid fungus cycle develops on the skin of the amphibians. As each infected animal is a constant source of the pathogenic zoospores, being close to other infected animals makes it difficult for a specimen to overcome the infection. Thus, although the immune system of a specimen can erase the pathogen, it will become reinfected due to its proximity to other infected specimens.
For this reason, it is easier for a larva to become naturally non-infected if it is keep isolated, while others that are grouped do not get to be clean themselves. Furthermore, and although it is not easy at all, there can be more difficult procedures that allow the burden of the infection to “dissolve” above a certain level of hosts’ density.
To see the importance of these procedures, we have launched an experiment. We have used infected animals in the nature of the two most vulnerable species to the chytridiomycosis in the peninsula: the fire salamander and the common midwife toad. We place each larvae species in containers with the same volume of water, but with different density, so that in some of them there is only one specimen, in others 5 and in others 15. To study the trend of the burden of the fungus over the time, we take a sample of infection of the same specimen of each tray once a month. To identify every specimen, we watch the pattern of spots in the case of the salamanders, while the tadpoles of midwife toad are marked with an elastomer.
This easy experiment can help us to design strategies to mitigate the disease in the natural environment that, as you know, is the main goal of this project.