Role of Density and Habitat Structure on Eastern Newt Contact Rates and Pathogen Transmission
Malagon, D. A., E. D. Carter, L. A. Melara, O. F. Prosper, S. Lenhart, D. L. Miller, and M. J. Gray.  2019.  Zoological Society of London Symposium, London, England. April, 2019.

Batrachochytrium salamandrivorans (Bsal) is an invasive fungal pathogen emerging across Europe and appears to be highly pathogenic to many salamander species. The Eastern Newt (Notophthalmus viridescens) is a member of Salamandridae and known to be susceptible to Bsal. This species is one of the most widely distributed salamanders in North America. Given their widespread distribution and high abundance, this species has the potential to significantly influence Bsal epidemiology if the pathogen emerges in the USA. We designed two studies to estimate host contact rates given different host densities and habitat structure, and the probability of transmission from infected to susceptible individuals via direct contact. We found that Bsal transmission due to contact was very efficient between infected and susceptible newts even at early stages of infection when pathogen loads were low. We also found that contact rates were density dependent, and that adding habitat structure (i.e., plants) reduced contact at higher newt densities. Simulations from a system of ordinary differential equations show rapid transmission of Bsal among individuals, such that an entire population can become infected quickly under most scenarios. Disease-induced mortality of susceptible individuals following contact with an infected individual was relatively high (>75%) and fast (<30 days post-contact). These results demonstrate that Bsal can have severe population impacts on eastern newts. Moreover, this abundant amphibian species could play a major role in Bsal emergence if it is introduced in the USA. Reducing newt density or increasing habitat structure at Bsal positive sites might reduce transmission and outbreak size.