Differential growth and transmission in cats of feline leukaemia viruses of subgroups A and B

The outcome of infecting cats with FeLV of sub-groups A (FeLV-A) or B (FeLV-B) was different. After FeLV-A infection, virus was quickly recovered from the blood and oropharynx of most animals. Following infection with FeLV-B, only a small proportion of cats developed a viraemia, and this after a long interval. There was no evidence that FeLV-B was transmitted by contact. The result of infecting cats with mixtures of FeLV-A and B (FeLV-AB) was that to a large extent each virus operated independently. FeLV-A was recovered from the plasma first, in a high proportion of the cats, and FeLV-B appeared later but not in all cats. There was evidence of interaction, however, in that the proportion of cats which were viraemic with FeLV-B was greater following FeLV-AB infection than after infection with FeLV-B alone; also FeLV-B was transmitted by contact from cats excreting FeLV-AB. These results help to explain the apparent dependence of FeLV-B on FeLV-A under natural conditions and the frequency of occurrence of sugroups A and B in FeLV isolates.