Control of feline immunodeficiency virus infection - resubmission

Feline immunodeficiency virus (FIV) infects approximately 500 thousand domestic cats in the UK. Infected cats may develop numerous infections, tumours and display neurological signs. In our survey to find out what happened to infected cats, 53% died or were euthanased, 25% suffered recurrent episodes of illness and 22% remained healthy. To control FIV infection requires a safe, effective vaccine. However there are many obstacles to developing a vaccine, particularly because the virus continually changes its outer shell and thus hides from the immune system. Moreover, infected cats do not recover from infection; whereas influenza virus triggers an immune response that clears virus from the body, FIV infection persists. We aim to devise laboratory techniques that can determine whether an infected cat is likely to remain well for some years or whether it is more likely to become terminally ill and require euthanasia. This information will assist veterinarians and owners to manage each infected cat and will assist in the re-homing of infected animals. Our second aim is to determine why some virus isolates cause more serious disease than others. If we can identify the main characteristics of a strain of virus that are associated with disease in infected cats, we will be able to structure therapy and management more appropriately.

Feline immunodeficiency virus (FIV) infects approximately 0.5 million domestic cats in the UK. Infected cats may develop numerous infections, including gingivitis/stomatitis, anorexia and wasting, neurological signs and malignancies. In a recent survey to determine the prognosis for FIV-infected cats, 53% of infections proved fatal died or resulted in euthanasia, 25% suffered recurrent episodes of illness and 22% remained healthy. To control FIV infection requires a safe and effective vaccine. However there are many obstacles to developing such a vaccine, particularly because the virus is able to mutate rapidly and thus evade both the humoral and cellular arms of the immune system. Moreover, infected animals do not recover from infection; whereas influenza virus triggers an immune response that clears virus from the body, FIV infection persists in the face of a potent immune response. The first aim of this project is to devise laboratory techniques that will enable us to determine whether an infected cat is likely to remain well for some years or whether it is more likely to become terminally ill and require euthanasia. These studies are based on our recent findings that viruses isolated during the early and late phases of infection have distinct biological phenotypes in vitro and pathogenicities in vivo. Accordingly, if we can ascertain the biological phenotype of a virus reliably, we will be able to stage more accurately the infection and design appropriate therapeutic interventions and management strategies for veterinarians and owners. Env genes will be cloned from primary isolates of virus and their biological properties assessed in vitro by generating chimaeric molecular clones; the production of HIV (FIV) viral pseudotypes to assess the receptor usage and cell tropism, and comparing the in vitro growth of chimaeric viruses with the parent strains in a panel of feline cell lines and primary cells. In the second aim, we will ask whether quasispecies diversity is linked to pathogenicity. It is thought that a heterogeneous viral population may be more difficult for the host immune response to control and may also achieve higher viral loads and wider dissemination within the host. We have examined the diversity of a single highly pathogenic strain of FIV and have found it to contain a range of viable viral variants. We will investigate the diversity of env genes isolated from isolates of low and high virulence by direct amplification using PCR. We will compare the in vivo properties of viruses with a heterogeneous population of env genes with that of a single env species. If we can identify the main characteristics of a strain of virus that are associated with disease in infected cats, we will be able to structure therapy and management more appropriately. We will monitor infection to assess whether a single viral genotype dominates with time post-infection using high-throughput capillary sequencing and heteroduplex tracking assay (HTA).