African swine fever is a highly contagious viral disease of mandatory declaration to the World Organization for Animal Health (OIE). The lack of available vaccines makes its control difficult; thus, African swine fever virus (ASFV) represents a major threat to the swine industry. Inactivated vaccines do not confer solid protection against ASFV. Conversely, live attenuated viruses (LAV), either naturally isolated or obtained by genetic manipulation, have demonstrated reliable protection against homologous ASFV strains, although little or no protection has been demonstrated against heterologous viruses. Safety concerns are a major issue for the use of ASFV attenuated vaccine candidates and have hampered their implementation in the field so far. While trying to develop safer and efficient ASFV vaccines, we found that the deletion of the viral CD2v (EP402R) gene highly attenuated the virulent BA71 strainin vivo. Inoculation of pigs with the deletion mutant virus BA71ΔCD2 conferred protection not only against lethal challenge with the parental BA71 but also against the heterologous E75 (both genotype I strains). The protection induced was dose dependent, and the cross-protection observedin vivocorrelated with the ability of BA71ΔCD2 to induce specific CD8⁺T cells capable of recognizing both BA71 and E75 virusesin vitro. Interestingly, 100% of the pigs immunized with BA71ΔCD2 also survived lethal challenge with Georgia 2007/1, the genotype II strain of ASFV currently circulating in continental Europe. These results open new avenues to design ASFV cross-protective vaccines, essential to fight ASFV in areas where the virus is endemic and where multiple viruses are circulating.IMPORTANCEAfrican swine fever virus (ASFV) remains enzootic in most countries of Sub-Saharan Africa, today representing a major threat for the development of their swine industry. The uncontrolled presence of ASFV has favored its periodic exportation to other countries, the last event being in Georgia in 2007. Since then, ASFV has spread toward neighboring countries, reaching the European Union's east border in 2014. The lack of available vaccines against ASFV makes its control difficult; so far, only live attenuated viruses have demonstrated solid protection against homologous experimental challenges, but they have failed at inducing solid cross-protective immunity against heterologous viruses. Here we describe a new LAV candidate with unique cross-protective abilities: BA71ΔCD2. Inoculation of BA71ΔCD2 protected pigs not only against experimental challenge with BA71, the virulent parental strain, but also against heterologous viruses, including Georgia 2007/1, the genotype II strain of ASFV currently circulating in Eastern Europe.

Significance: COVID-19 is the most devastating pandemic in recent history. As with many emerging infectious diseases, it is of zoonotic origin, meaning that animals played a major role in the initial transmission events. Despite SARS-CoV-2 being highly adapted to jump from human to human, several animal species are naturally susceptible to SARS-CoV-2, including pets such as cats. In the present report, a cat from a family with several relatives affected by COVID-19 developed severe respiratory clinical signs, leading to humanitarian euthanasia. Due to the suspicion of a potential COVID-19 infection in the cat, different antemortem and postmortem tests were assayed. The clinical condition was finally attributed to a feline hypertrophic cardiomyopathy, but the animal was also infected by SARS-CoV-2.

The structure of the infectious prion protein (PrP^Sc), which is responsible for Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy, has escaped all attempts at elucidation due to its insolubility and propensity to aggregate. PrP^Sc replicates by converting the non-infectious, cellular prion protein (PrP^C) into the misfolded, infectious conformer through an unknown mechanism. PrP^Sc and its N-terminally truncated variant, PrP 27–30, aggregate into amorphous aggregates, 2D crystals, and amyloid fibrils. The structure of these infectious conformers is essential to understanding prion replication and the development of structure-based therapeutic interventions. Here we used the repetitive organization inherent to GPI-anchorless PrP 27–30 amyloid fibrils to analyze their structure via electron cryomicroscopy. Fourier-transform analyses of averaged fibril segments indicate a repeating unit of 19.1 Å. 3D reconstructions of these fibrils revealed two distinct protofilaments, and, together with a molecular volume of 18,990 ų, predicted the height of each PrP 27–30 molecule as ~17.7 Å. Together, the data indicate a four-rung β-solenoid structure as a key feature for the architecture of infectious mammalian prions. Furthermore, they allow to formulate a molecular mechanism for the replication of prions. Knowledge of the prion structure will provide important insights into the self-propagation mechanisms of protein misfolding. The structure of the infectious prion (PrP^Sc), which is responsible for Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy, has escaped all attempts at elucidation due to its propensity to aggregate. Here, we use the repetitive organization inherent in amyloid fibrils to analyze the structure of GPI-anchorless PrP 27–30 via electron cryomicroscopy. Fourier-transform analysis of averaged fibril segments indicates a repeating unit of 19.1 Å. In agreement with this observation, 3D reconstructions reveal that each fibril contains two distinct protofilaments and that the height of each PrP 27–30 molecule in these fibrils is ~17.7 Å. Together the data indicate a four-rung β-solenoid structure as a key feature for the architecture of infectious mammalian prions. The data conflict with all previous models for the structure of PrP^Sc and allow the formulation of a molecular mechanism for the replication of prions.

The ability of prions to infect some species and not others is determined by the transmission barrier. This unexplained phenomenon has led to the belief that certain species were not susceptible to transmissible spongiform encephalopathies (TSEs) and therefore represented negligible risk to human health if consumed. Using the protein misfolding cyclic amplification (PMCA) technique, we were able to overcome the species barrier in rabbits, which have been classified as TSE resistant for four decades. Rabbit brain homogenate, either unseeded or seeded in vitro with disease-related prions obtained from different species, was subjected to serial rounds of PMCA. De novo rabbit prions produced in vitro from unseeded material were tested for infectivity in rabbits, with one of three intracerebrally challenged animals succumbing to disease at 766 d and displaying all of the characteristics of a TSE, thereby demonstrating that leporids are not resistant to prion infection. Material from the brain of the clinically affected rabbit containing abnormal prion protein resulted in a 100% attack rate after its inoculation in transgenic mice overexpressing rabbit PrP. Transmissibility to rabbits (>470 d) has been confirmed in 2 of 10 rabbits after intracerebral challenge. Despite rabbits no longer being able to be classified as resistant to TSEs, an outbreak of “mad rabbit disease” is unlikely.