The leader protein is necessary for the establishment of persistent infection by type O foot-and-mouth disease virus
Résumé
Background/Introduction
The consequence of persistence of FMD virus (FMDV) in ruminants after clinical recovery remains problematic, with underlying mechanisms that are still poorly understood. A prolonged infection may occur if a virus can counteract the host immune response. For FMDV, the major viral protein known to be involved in innate immune escape during acute infection is the leader protease (Lpro). It was previously shown that type A leaderless FMDV are highly attenuated in vivo. Both wild type and leaderless viruses may replicate in the nasopharynx, the primary site of infection, but leaderless viruses failed to cause viremia and generalized disease. It was however not explored if the leaderless FMDV could establish a persistent infection. In the framework of the ICRAD FMDV_PersIstOmics project, we have investigated if a recombinant leaderless FMDV O could persist in vitro in multilayer cells from bovine dorsal soft palate (DSP) grown at the air-liquid interface (ALI) and in vivo in cattle.
Material and methods
DSP-ALI cells were inoculated with either recombinant wildtype (wt) FMDV O/FRA/1/2001 and its leaderless derivative. The upper multilayer was washed 6, 12, 24 and 48h post-infection, then each two or three days until 35dpi. In a parallel in vivo study, two groups of eight cattle each were inoculated with either wt FMDV or its leaderless derivative by intranasopharyngeal deposition, then observed and sampled for 35 days. Two cattle from each group were euthanized 24 hpi and tissue samples were collected to evaluate early-stage virus distribution.
Results
In vitro, live wt virus was isolated from supernatants of 5 of 6 cultures, while no leaderless live virus was detected after 48h post-inoculation of DSP-ALI. Likewise, leaderless viral RNA decreased from 7dpi until 28dpi and was undetectable at 35dpi. In vivo, the remaining six cattle in the wt group developed pronounced generalized disease and shed large amounts of virus during the first 10 to 14 days of the experiment. In contrast, leaderless-FMDV-infected cattle did not show any clinical signs of FMD, nor was any virus detected in serum or secretions. Two of six animals in the wt group remained persistently infected until the end of the trial at 35dpi. There was no evidence of persistent infection in leaderless-FMDV-infected cattle.
Discussion and conclusions
Overall, our results show that leaderless FMDV O cannot establish a prolonged or persistent infection in DSP-ALI cells and is strongly attenuated in cattle and unable to persist (Litz et al, 2024).