RESUMEN
The absence of urban yellow fever epidemics in East Africa remains a mystery amidst the proliferation of Aedes aegypti in this region. To understand the transmission dynamics of the disease, we tested urban (Mombasa, Kisumu, and Nairobi) Aedes mosquito populations in Kenya for their susceptibility to an East African yellow fever virus (YFV) genotype. Overall, 22% (n = 805) of the Ae. aegypti that were orally challenged with an infectious dose of YFV had a midgut infection, with comparable rates for Mombasa and Kisumu (χ2 = 0.35, df = 1, P = 0.55), but significantly lower rates for Nairobi (χ2 ≥ 11.08, df = 1, P ≤ 0.0009). Variations in YFV susceptibility (midgut infection) among Ae. aegypti subspecies were not associated with discernable cytochrome c oxidase subunit 1 gene haplotypes. Remarkably, no YFV dissemination or transmission was observed among the orally challenged Ae. aegypti populations. Moreover, Ae. aegypti mosquitoes that were intrathoracically inoculated with YFV failed to transmit the virus via capillary feeding. In contrast, dissemination (oral exposure) and transmission (intrathoracic inoculation) of YFV was observed among a few peri-domestic Ae. bromeliae mosquitoes (n = 129) that were assessed from these urban areas. Our study highlights an inefficient urban Ae. aegypti population, and the potential for Ae. bromeliae in sustaining an urban YFV transmission in Kenya. An assessment of urban Ae. aegypti susceptibility to other YFV genotypes, and vector potential of urban Ae. bromeliae populations in Kenya is recommended to guide cost-effective vaccination.
Asunto(s)
Aedes , Virus no Clasificados , Fiebre Amarilla , Animales , Virus ADN , Kenia/epidemiología , Mosquitos Vectores , Medición de Riesgo , Fiebre Amarilla/epidemiología , Virus de la Fiebre Amarilla/genéticaRESUMEN
Prions are unique agents that challenge the molecular biology dogma by transmitting information on the protein level. They cause neurodegenerative diseases that lack of any cure or treatment called transmissible spongiform encephalopathies. The function of the normal form of the prion protein, the exact mechanism of prion propagation between species as well as at the cellular level and neuron degeneration remains elusive. However, great amount of information known for all these aspects has been achieved thanks to the use of animal models and more precisely to transgenic mouse models. In this chapter, the main contributions of these powerful research tools in the prion field are revised.
Asunto(s)
Enfermedades por Prión/patología , Animales , Modelos Animales de Enfermedad , Humanos , Ratones Transgénicos , Enfermedades por Prión/genética , Priones/metabolismoRESUMEN
Classical bovine spongiform encephalopathy (BSE) is the only zoonotic prion disease described to date. Although the zoonotic potential of atypical BSE prions have been partially studied, an extensive analysis is still needed. We conducted a systematic study by inoculating atypical BSE isolates from different countries in Europe into transgenic mice overexpressing human prion protein (PrP): TgMet129, TgMet/Val129, and TgVal129. L-type BSE showed a higher zoonotic potential in TgMet129 mice than classical BSE, whereas Val129-PrP variant was a strong molecular protector against L-type BSE prions, even in heterozygosis. H-type BSE could not be transmitted to any of the mice. We also adapted 1 H- and 1 L-type BSE isolate to sheep-PrP transgenic mice and inoculated them into human-PrP transgenic mice. Atypical BSE prions showed a modification in their zoonotic ability after adaptation to sheep-PrP producing agents able to infect TgMet129 and TgVal129, bearing features that make them indistinguishable of sporadic Creutzfeldt-Jakob disease prions.
Asunto(s)
Encefalopatía Espongiforme Bovina , Enfermedades por Prión , Priones , Animales , Encéfalo/metabolismo , Bovinos , Europa (Continente) , Ratones , Ratones Transgénicos , Priones/genética , Priones/metabolismo , OvinosRESUMEN
Unlike other species, prion disease has never been described in dogs even though they were similarly exposed to the bovine spongiform encephalopathy (BSE) agent. This resistance prompted a thorough analysis of the canine PRNP gene and the presence of a negatively charged amino acid residue in position 163 was readily identified as potentially fundamental as it differed from all known susceptible species. In the present study, the first transgenic mouse model expressing dog prion protein (PrP) was generated and challenged intracerebrally with a panel of prion isolates, none of which could infect them. The brains of these mice were subjected to in vitro prion amplification and failed to find even minimal amounts of misfolded prions providing definitive experimental evidence that dogs are resistant to prion disease. Subsequently, a second transgenic model was generated in which aspartic acid in position 163 was substituted for asparagine (the most common in prion susceptible species) resulting in susceptibility to BSE-derived isolates. These findings strongly support the hypothesis that the amino acid residue at position 163 of canine cellular prion protein (PrPC ) is a major determinant of the exceptional resistance of the canidae family to prion infection and establish this as a promising therapeutic target for prion diseases.
Asunto(s)
Ácido Aspártico/química , Ácido Glutámico/química , Priones/química , Priones/patogenicidad , Animales , Bioensayo , Encéfalo/patología , Perros , Ratones , ATPasas Transportadoras de Calcio de la Membrana Plasmática/metabolismoRESUMEN
The large chronic wasting disease (CWD)-affected cervid population in the USA and Canada, and the risk of the disease being transmitted to humans through intermediate species, is a highly worrying issue that is still poorly understood. In this case, recombinant protein misfolding cyclic amplification was used to determine, in vitro, the relevance of each individual amino acid on cross-species prion transmission. Others and we have found that the ß2-α2 loop is a key modulator of transmission barriers between species and markedly influences infection by sheep scrapie, bovine spongiform encephalopathy (BSE), or elk CWD. Amino acids that differentiate ovine and deer normal host prion protein (PrPC) and associated with structural rigidity of the loop ß2-α2 (S173N, N177T) appear to confer resistance to some prion diseases. However, addition of methionine at codon 208 together with the previously described rigid loop substitutions seems to hide a key in this species barrier, as it makes sheep recombinant prion protein highly susceptible to CWD-induced misfolding. These studies indicate that interspecies prion transmission is not only governed just by the ß2-α2 loop amino acid sequence but also by its interactions with the α3-helix as shown by substitution I208M. Transmissible spongiform encephalopathies, characterized by long incubation periods and spongiform changes associated with neuronal loss in the brain, have been described in several mammalian species appearing either naturally (scrapie in sheep and goats, bovine spongiform encephalopathy in cattle, chronic wasting disease in cervids, Creutzfeldt-Jakob disease in humans) or by experimental transmission studies (scrapie in mice and hamsters). Much of the pathogenesis of the prion diseases has been determined in the last 40 years, such as the etiological agent or the fact that prions occur as different strains that show distinct biological and physicochemical properties. However, there are many unanswered questions regarding the strain phenomenon and interspecies transmissibility. To assess the risk of interspecies transmission between scrapie and chronic wasting disease, an in vitro prion propagation method has been used. This technique allows to predict the amino acids preventing the transmission between sheep and deer prion diseases.
Asunto(s)
Ciervos/metabolismo , Proteínas Priónicas/metabolismo , Ovinos/metabolismo , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Animales , Pollos , Ratones Noqueados , Proteínas Priónicas/química , Dominios Proteicos , Pliegue de Proteína , Estructura Secundaria de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Especificidad de la EspecieRESUMEN
Bovine spongiform encephalopathy (BSE) is the only known zoonotic prion that causes variant Creutzfeldt-Jakob disease (vCJD) in humans. The major risk determinant for this disease is the polymorphic codon 129 of the human prion protein (Hu-PrP), where either methionine (Met129) or valine (Val129) can be encoded. To date, all clinical and neuropathologically confirmed vCJD cases have been Met129 homozygous, with the exception of 1 recently reported Met/Val heterozygous case. Here, we found that transgenic mice homozygous for Val129 Hu-PrP show severely restricted propagation of the BSE prion strain, but this constraint can be partially overcome by adaptation of the BSE agent to the Met129 Hu-PrP. In addition, the transmission of vCJD to transgenic mice homozygous for Val129 Hu-PrP resulted in a prion with distinct strain features. These observations may indicate increased risk for vCJD secondary transmission in Val129 Hu-PrP-positive humans with the emergence of new strain features.
Asunto(s)
Síndrome de Creutzfeldt-Jakob/patología , Resistencia a la Enfermedad/genética , Encefalopatía Espongiforme Bovina/inmunología , Proteínas Priónicas/inmunología , Valina/inmunología , Sustitución de Aminoácidos , Animales , Encéfalo/patología , Bovinos , Codón , Síndrome de Creutzfeldt-Jakob/transmisión , Encefalopatía Espongiforme Bovina/patología , Encefalopatía Espongiforme Bovina/transmisión , Expresión Génica , Humanos , Inyecciones Intraventriculares , Metionina/genética , Metionina/inmunología , Ratones , Ratones Transgénicos , Péptido Hidrolasas/química , Proteínas Priónicas/química , Proteínas Priónicas/genética , Valina/genéticaRESUMEN
The prion responsible for the Bovine Spongiform Encephalopathy (BSE) shows unique features when compared with other prions. One of these features is its ability to infect almost all experimentally tested animal models. In the paper published in The Journal of Neuroscience (1) we describe a series of experiments directed toward elucidating which would be the in vivo behavior of BSE if it would infect dogs and rabbits, two alleged prion resistant species. Protein misfolding cyclic amplification (PMCA) was used to generate canidae and leporidae in vitro adapted BSE prions. A characterization of their in vivo pathobiological properties showed that BSE prions were capable not only of adapting to new species but they maintained, in the case of rabbits, their ability to infect transgenic mice expressing human PrP. The remarkable adaptation ability of certain prions implies that any new host species could lead to the emergence of new infectious agents with unpredictable transmission potential. Our results suggest that caution must be taken when considering the use of any mammal derived protein in feedstuffs.