Transmissible spongiform encephalopathies (TSEs), also known as prion diseases, are lethal and infectious neurodegenerative diseases of humans and animals. The misfolding of the normal, or cellular isoform of the prion protein (PrPC) into the abnormal disease-associated isoform of PrP (PrPSc) could change the properties of PrP, consequently, PrPSc has lethal infectivity to transmit diseases. The proteinaceous infectious particle consisting mainly of PrPSc is called prion. Transmissibility of prions is strongly influenced by multiple factors including PrP polymorphisms, species barriers (PrP sequence specificity) and prion strains (conformational specificity) by unknown mechanisms. Even though the ability of prions to cross a species barrier has been recognized, the precise mechanisms of interspecies prion transmission remain unclear. This dissertation research was conducted in order to learn more about the molecular mechanisms of conversion, propagation and transmission of PrPSc; about determinants of genetic susceptibility to infection in prion diseases; and about understanding those mechanisms, which might govern the zoonotic potential of prion diseases. First, we investigated the transmissibility risk of multiple strains of Chronic Wasting Disease, which is a cervid TSE, with humanized transgenic mice and showed that the transmission barriers between cervid and the humanized mice are high. Next, the structural factors underlying the species barrier of prion diseases were studied using cell culture systems by systematically introducing amino acid substitutions in the regions of PrP, where the most divergences of different PrP species are recognized. Thirdly, we investigated the effects of the genetic susceptibility to prions as well as conversion kinetics and properties of PrPSc using Tg mice expressing ovine PrP polymorphism (OvPrP) at codon 136 either alanine (A) or valine (V). The templating characteristics of OvPrPSc-V136 were dominant over OvPrPSc-A136 under co-expressions of OvPrPC-A136 and OvPrPC-V136. Finally, the function of PrP was studied in relation to the pathogenesis of Alzheimer’s disease. These studies demonstrated that the conformational compatibility between PrPC and PrPSc contributed to the conversion kinetics and species barrier. We concluded that the conformational compatibility of PrPC to PrPSc is controlled not only by the PrP sequence specificity but also by the tertiary structure of PrPC.

Rodents have been reported to play a significant role as reservoirs of over 22 rodent-associated Bartonella species. In this study, we contrast prevalence and diversity of Bartonella infections in 377 small mammals, representative of three terrestrial rodent genera, namely Aethomys, Gerbilliscus and Rhabdomys and one subterranean mole-rat species (Bathyergus suillus). The latter was sampled in close proximity to an informal human settlement, whereas the afore-mentioned murid rodent genera were sampled across a range of landscapes inclusive of natural, agricultural, urban, peri-urban and rural settings, from three provinces (Free State, Gauteng and Western Cape) in South Africa. Molecular estimates of Bartonella infection rates were determined through multi-gene screening of DNA extracted from clinical samples, primarily heart and spleen. PCR assays targeting the citrate synthase (gltA) and NADH dehydrogenase gamma subunit (nuoG) and/or beta subunit of bacterial RNA polymerase (rpoB) genes were used to ensure enhanced molecular estimates of Bartonella prevalence. Aethomys had the highest infection rate (86.7%), whereas Rhabdomys had the lowest (15%). Nucleotide sequencing and phylogenetic analyses revealed that the different primers sets used for Bartonella screening have different affinities to the different strains present in rodents from South Africa. Furthermore, the presence of Bartonella co-infections, confirmed through the presence of multiple peaks at 15% of the nucleotide sequences sites, ranged from 33.8% (in Aethomys) to 42.9% (in Gerbilliscus species) for the gltA gene region. For Aethomys ineptus, of the discrete Bartonella lineages recovered, one was closely related to zoonotic B. elizabethae. The latter species, which is associated with Rattus hosts worldwide and has been linked to cases of human endocarditis, suggests spillover from invasive to indigenous rodents. This is supported by previous studies indicating that indigenous Micaelamys namaquensis, a highly adaptable species, which like Aethomys is capable of utilizing natural and modified landscapes also hosts B. elizabethae-related lineages. Of potential public health importance, Bathyergus suillus were shown to be infected with a zoonotic Bartonella species, B. rochalimae. Our results further indicate that the level of anthropogenic transformation is significantly correlated with Bartonella prevalence, with Rhabdomys sampled from rural settings in the Western Cape Province having infection rates of 36% versus 0% in a nearby urban setting. This study also uncovered high levels of strain diversity in members of the Gerbilliscus cryptic species complex, sampled from an agricultural setting. The overall Bartonella PCR-positivity rate was 67.5 % and the gltA gene phylogeny confirmed the presence of six discrete Bartonella gerbil-specific lineages (I-VI). Lineages I and II clustered with Bartonella strains identified previously in G. leucogaster sampled from Sandveld nature reserves in the Free State Province South Africa, whereas lineages III-VI comprised of lineages that were restricted to either G. leucogaster or to G. brantsii, indicative of host-specificity. From the findings of this study, it is clear that the public health importance of the Bartonella species present in indigenous rodents warrants further investigation as at least two species, with known zoonotic potential (B. elizabethae and B. rochalimae) were shown to be present in rodents sampled in close proximity to human settlements. / Thesis (PhD (Zoology))--University of Pretoria, 2019. / This research was made possible through the financial support from the (AZD-IRT), CDC Co-Ag 5 NU2GGH001874-02-00 and through the NRF incentive and SARChI PI funding awarded to ADSB. / Zoology and Entomology / PhD (Zoology) / Unrestricted

Giardia intestinalis is a single-celled intestinal parasite infecting humans and animals. The species is divided into eight genetic groups, assemblages, with different host specificity. Stool samples from 99 dogs, 61 cats and 22 chinchillas were examined for the presence of Giardia using microscopy and PCR diagnostics. The found populations were assigned to assemblages using a multi-locus genotyping scheme, with the goal of mapping the occurrence of zoonotic assemblages A and B and evaluating the risk of transmission of Giardia from pets to humans. The Giardia prevalence in examined dogs was 36,4%. The majority of dog infections was caused by dog-specific assemblages D and C. Individual cases of infection with assemblage F, or a mix of assemblages A+D, A+F, B+D, C+D and D+F were also detected. The prevalence in cats was 14.8%, and the dog assemblages C and D prevailed as well. In individual cases, cats were infected with assemblages A or F, which is specific for cats. The highest prevalence, 85.7%, was detected in chinchillas. The majority of chinchilla infections was caused by the zoonotic assemblage B (88.9%). The found sequences were compared to those obtained from animals with clinical giardiasis, but no identical matches were found between these two pools. The nature of mixed infections was studied by...