C. Lupini

Field avian metapneumovirus evolution avoiding vaccine induced immunity.

Live avian metapneumovirus (AMPV) vaccines have largely brought turkey rhinotracheitis (TRT) under control in Europe but unexplained outbreaks still occur. Italian AMPV longitudinal farm studies showed that subtype B AMPVs were frequently detected in turkeys some considerable period after subtype B vaccination. Sequencing showed these to be unrelated to the previously applied vaccine. Sequencing of the entire genome of a typical later isolate showed numerous SH and G protein gene differences when compared to both a 1987 Italian field isolate and the vaccine in common use. Experimental challenge of vaccinated birds with recent virus showed that protection was inferior to that seen after challenge with the earlier 1987 isolate. Field virus had changed in key antigenic regions allowing replication and leading to disease in well vaccinated birds.

In vitro antiviral activity of chestnut and quebracho woods extracts against avian reovirus and metapneumovirus.

Field evidences have suggested that a natural extract, containing tannins, could be effective against poultry enteric viral infections. Moreover previous studies have shown that vegetable tannins can have antiviral activity against human viruses. Based on this knowledge three different Chestnut (Castanea spp.) wood extracts and one Quebracho (Schinopsis spp.) wood extract, all containing tannins and currently used in the animal feed industry, were tested for in vitro antiviral activity against avian reovirus (ARV) and avian metapneumovirus (AMPV). The MTT assay was used to evaluate the 50% cytotoxic compounds concentration (CC(50)) on Vero cells. The antiviral properties were tested before and after the adsorption of the viruses to Vero cells. Antiviral activities were expressed as IC(50) (concentration required to inhibit 50% of viral cytopathic effect). CC(50)s of tested compounds were > 200 microg/ml. All compounds had an extracellular antiviral effect against both ARV and AMPV with IC(50) values ranging from 25 to 66 microg/ml. Quebracho extract had also evident intracellular anti-ARV activity (IC(50) 24 microg/ml). These preliminary results suggest that the examined vegetable extracts might be good candidates in the control of some avian virus infections. Nevertheless further in vivo experiments are required to confirm these findings.

Charged amino acids in the AMPV fusion protein have more influence on induced protection than deletion of the SH or G genes

Modifications to F, G and SH genes of an avian metapneumovirus (AMPV) field isolate were made by reverse genetics and their virulence and protective capacity were tested in young turkeys. Infection of one-day-old turkeys with a subtype A AMPV neither caused disease nor stimulated detectable protection against subsequent virulent challenge. While serial passage of this virus in tracheal tissue increased virulence, protection stimulated remained moderate. Substitution of the fusion protein from a protective AMPV very minimally increasing virulence but dramatically increased induced protection; and this was associated with five amino acid substitutions all involving charged amino acids which computational analysis predicted to affect protein surface properties but not immunodominant helper T-lymphocyte antigenic sites. When SH or G genes were deleted, viruses caused no disease but still conferred full protection to the majority of turkeys. In the case of the SH deletion, shed virus post-inoculation was undetectable. Partial SH deletions were found to confer protection related to the length of SH open reading frame remaining. Removal of both SH and G genes together produced a virus conferring negligible protection. We conclude that the characteristics of the AMPV fusion protein are important in inducing protection while the SH and G genes under investigation played a lesser role.