A single polymerase (L) mutation in avian metapneumovirus increased virulence and partially maintained virus viability at an elevated temperature.
Previously, a virulent avian metapneumovirus, farm isolate Italy 309/04, was shown to have been derived from a live vaccine. Virulence due to the five nucleotide mutations associated with the reversion to virulence was investigated by their addition to the genome of the vaccine strain using reverse genetics. Virulence of these recombinant viruses was determined by infection of 1-day-old turkeys. Disease levels resulting from the combined two matrix mutations was indistinguishable from that produced by the recombinant vaccine, whereas the combined three L gene mutations increased disease to a level (P<0.0001) that was indistinguishable from that caused by the revertant Italy 309/04 virus. Testing of the L mutations individually showed that two mutations did not increase virulence, while the third mutation, corresponding to an asparagine to aspartic acid substitution, produced virulence indistinguishable from that caused by Italy 309/04. In contrast to the vaccine, the virulent mutant also showed increased viability at temperatures typical of turkey core tissues. The notion that increased viral virulence resulted from enhanced ability to replicate in tissues away from the cool respiratory tract, cannot be discounted.
Department of Infection Biology, University of Liverpool, Leahurst Campus, Neston, Cheshire CH64 7TE, UK.
Paul A
PA
Brown
Caterina
C
Lupini
Elena
E
Catelli
Jayne
J
Clubbe
Enrico
E
Ricchizzi
Clive J
CJ
Naylor
D000818:Animals; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D012321:DNA-Directed RNA Polymerases / Q000235:genetics* / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D006358:Hot Temperature; D029121:Metapneumovirus / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D050296:Microbial Viability; D009154:Mutation; D018184:Paramyxoviridae Infections / Q000662:veterinary* / Q000821:virology; D010957:Plasmids; D011201:Poultry Diseases / Q000821:virology*; D013997:Time Factors; D014422:Turkeys; D014709:Vero Cells; D014774:Virulence; D014779:Virus Replication
D012321:DNA-Directed RNA Polymerases