abstract: Epidemiological theory normally does not predict host extinction from infectious disease because of a host density threshold below which pathogens cannot persist. However, host extinction can occur when a biotic or abiotic pathogen reservoir allows for density-independent transmission. Amphibians are facing global population decline and extinction from the emerging infectious disease chytridiomycosis, caused by the fungus Batrachochytrium dentrobatidis (Bd). I use the model species Eleutherodactylus coqui to assess the impact of Bd on terrestrial direct-developing frog species, a common life history in the tropics. I tested the importance of two key factors that might influence this impact and then used laboratory experiments and published field data to model population-level impacts of Bd on E. coqui. First, I assessed the ontogenetic susceptibility of E. coqui by exposing juvenile and adult frogs to the same pathogen strain and dose. Juveniles exposed to Bd had significantly lower survival rates compared with control juveniles, while adult frogs often cleared infection. Second, I conducted experiments to determine whether E. coqui can become infected with Bd indirectly from contact with zoospores shed onto vegetation by an infected frog and from direct exposure to an infected frog. Both types of transmission were observed, making this the first demonstration that amphibians can become infected indirectly in non-aquatic habitats. Third, I tested the hypothesis that artificially-maintained cultures of Bd attenuate in pathogenicity, an effect known for other fungal pathogens. Comparing two cultures of the same Bd strain with different passage histories revealed reduced zoospore production and disease-induced mortality rates for a susceptible frog species (Atelopus zeteki) but not for the less-susceptible E. coqui. Finally, I used a mathematical model to project the population-level impacts of chytridiomycosis on E. coqui. Model analysis showed that indirect transmission, combined with either a high rate of zoospore production or low rate of zoospore mortality, is required for Bd to drive E. coqui populations below an extinction threshold. High rates of transmission plus frequent re-infection could lead to poor recruitment of infected juveniles and population decline. My research adds further insight into how emerging infectious disease is contributing to the loss of amphibian biodiversity. / Dissertation/Thesis / Ph.D. Biology 2013

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The present investigation was made in the Laboratories of microbiology of the Ability of Cattle Sciences of the Polytechnic Superior School of Chimborazo, with samples obtained in the Municipal Camal Riobamba and the Community of Tunshi San Nicolás. The incidence of Brucellosis was analyzed in six more important cattle areas of the county using the antigens Brucella abortus and Rosa of Flare. The experimental units were obtained under a systematic sampling. The experiment had a duration of 4 months. The experimental results underwent the following analyses: variance, percentages, stockings, standard deviation, limit for the estimate error. According to carried out analysis of the obtained results, you determines that the analysis technique by means of antigen Brucella abortus, detected more cases of brucellosis (16.59% ± 4.61%) regarding the technique with Rosa of Flare (9.98% ± 3.59%). The biggest percentage of suspicious cases met with the technical Rosa of Flare (9.57% ± 3.35%) regarding the technique of antigen Brucella abortus (5% ±2.5%). According to the sex we have that in more quantity they presented the females with 9.16% in relation to the males with 7.1%, this with the antigen Brucella abortus. With Rosa of Flare we have for the females 5.42% and the males 4.42%. We carry out a study of 17 animals of the Community of Tunshi San Nicolás, we find completely free of this bacterial infection, with the two studied methods.

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