Coronavirus

1. A live, attenuated coronavirus comprising a variant replicase gene encoding polyproteins comprising a mutation in one or both of non-structural protein(s) nsp-10 and nsp-14, wherein the variant replicase gene encodes a protein comprising an amino acid mutation of Pro to Leu at the position corresponding to position 85 of SEQ ID NO: 6, and/or wherein the variant replicase gene encodes a protein comprising an amino acid mutation of Val to Leu at the position corresponding to position 393 of SEQ ID NO: 7.

2. The coronavirus according to claim 1 wherein the variant replicase gene encodes a protein comprising one or more amino acid mutations selected from:

an amino acid mutation of Leu to Ile at the position corresponding to position 183 of SEQ ID NO: 8; and

an amino acid mutation of Val to Ile at the position corresponding to position 209 of SEQ ID NO: 9.

3. The coronavirus according to claim 1 wherein the replicase gene encodes a protein comprising the amino acid mutations Val to Leu at the position corresponding to position 393 of SEQ ID NO: 7; Leu to Ile at the position corresponding to position 183 of SEQ ID NO: 8; and Val to Ile at the position corresponding to position 209 of SEQ ID NO: 9.

4. The coronavirus according to claim 1 wherein the replicase gene encodes a protein comprising the amino acid mutations Pro to Leu at the position corresponding to position 85 of SEQ ID NO: 6; Val to Leu at the position corresponding to position 393 of SEQ ID NO: 7; Leu to Ile at the position corresponding to position 183 of SEQ ID NO: 8; and Val to Ile at the position corresponding to position 209 of SEQ ID NO: 9.

5. The coronavirus according to claim 1 wherein the replicase gene comprises at least one nucleotide substitutions selected from:

C to Tat nucleotide position 12137; and

G to C at nucleotide position 18114;

compared to the sequence shown as SEQ ID NO: 1;

and optionally, comprises one or more nucleotide substitutions selected from T to A at nucleotide position 19047; and

G to A at nucleotide position 20139;

compared to the sequence shown as SEQ ID NO: 1.

6. The coronavirus according to claim 1 which is an infectious bronchitis virus (IBV).

7. The coronavirus according to claim 1 which is IBV M41.

8. The coronavirus according to claim 7 , which comprises an S protein at least, part of which is from an IBV serotype other than M41.

9. The coronavirus according to claim 8 , wherein the S1 subunit is from an IBV serotype other than M41.

10. The coronavirus according to claim 8 , wherein the S protein is from an IBV serotype other than M41.

11. The coronavirus according to claim 1 which has reduced pathogenicity compared to a coronavirus expressing a corresponding wild-type replicase, wherein the virus is capable of replicating without being pathogenic to the embryo when administered to an embryonated egg.

12. A variant replicase gene as defined in claim 1 .

13. A protein encoded by a variant coronavirus replicase gene according to claim 12 .

14. A plasmid comprising a replicase gene according to claim 12 .

15. A method for making the coronavirus according to claim 1 which comprises the following steps:

(i) transfecting a plasmid according to claim 14 into a host cell;

(ii) infecting the host cell with a recombining virus comprising the genome of a coronavirus strain with a replicase gene;

(iii) allowing homologous recombination to occur between the replicase gene sequences in the plasmid and the corresponding sequences in the recombining virus genome to produce a modified replicase gene; and

(iv) selecting for recombining virus comprising the modified replicase gene.

16. The method according to claim 15 , wherein the recombining virus is a vaccinia virus.

17. The method according to claim 15 which also includes the step:

(v) recovering recombinant coronavirus comprising the modified replicase gene from the DNA from the recombining virus from step (iv).

18. A cell capable of producing a coronavirus according to claim 1 .

19. A vaccine comprising a coronavirus according to claim 1 and a pharmaceutically acceptable carrier.

20. A method for treating and/or preventing a disease in a subject which comprises the step of administering a vaccine according to claim 19 to the subject.

21. The method of claim 20 , wherein the disease is infectious bronchitis (IB).

22. The method according to claim 20 wherein the method of administration is selected from the group consisting of; eye drop administration, intranasal administration, drinking water administration, post-hatch injection and in ovo injection.

23. The method according to claim 21 wherein the administration is in ovo vaccination.

24. A method for producing a vaccine according to claim 19 , which comprises the step of infecting a cell according to claim 18 with a coronavirus according to claim 1 .

25. The coronavirus according to claim 1 , further comprising a mutation in one or both of nsp-15 and nsp-16.