Molecular characterization of feline immunodeficiency virus genome obtained directly from organs of a naturally infected cat with marked neurological symptoms and encephalitis

Lack of protection against feline immunodeficiency virus infection among domestic cats in New Zealand vaccinated with the Fel-O-Vax® FIV vaccine

Infections with feline immunodeficiency virus (FIV) are common in New Zealand, although the impact of those infections on the health status of the cats remains unclear. Although many cats are vaccinated yearly with a commercial FIV vaccine containing FIV subtypes A and D, the effectiveness of this vaccine in protection against infection with field FIVs is unclear, as a high proportion of New Zealand viruses belong to subtype C. The objective of the study was to compare the frequency of FIV infection among adult FIV-vaccinated and FIV-unvaccinated domestic cats with access to outdoors. Buccal swabs were collected by the participating veterinarians and tested for the presence of FIV provirus by quantitative PCR. Overall, 26/185 (14.0 %) samples were positive for FIV, including 7/82 (8.5 %) samples from FIV-unvaccinated and 19/103 (18.4 %) from FIV-vaccinated cats. There was no protective effect of vaccination on FIV infection among sampled cats (p = 0.05). Partial sequences of the FIV envelope gene from five New Zealand viruses were analysed by the maximum likelihood method. All clustered with other New Zealand FIV sequences from subtypes A (n = 2), C (n = 2) or putative recombinant viruses (n = 1). While the FIV vaccination did not prevent FIV infection among sampled cats, it may have had an impact on transmissibility of the virus or on disease progression. As neither was addressed in the current study, further research is needed to fully assess the potential benefits of FIV vaccination. Considering the frequency of FIV infection in FIV-vaccinated cats, FIV infection status should be monitored not only before the first vaccination, but before each yearly booster.

Phylogenetic characterisation of feline immunodeficiency virus in naturally infected cats in Croatia indicates additional heterogeneity of subtype B in Europe

This study was performed on 29 domestic cats with a variety of clinical signs, possibly related to FIV infection. Blood samples were tested by a rapid immunochromatographic (ICA) procedure for detection of FIV antibodies. Subsequently, polymerase chain reaction (PCR) was performed to amplify a portion of the proviral gag gene. All 11 positive PCR products were sequenced and compared with previously reported FIV sequences. Croatian proviral isolates that could be amplified were clustered within subtype B, and additional heterogeneity was confirmed by the formation of three separate clusters. Phylogenetic analysis of circulating strains in Croatia and in southeast Europe is necessary to improve diagnostic methods and selection of the appropriate vaccinal strains.

Molecular epidemiology of feline immunodeficiency virus in the domestic cat (Felis catus)

Studying the evolutionary mechanisms of feline immunodeficiency virus in the domestic cat (Felis catus), FIV(Fca), provides a good comparison to other lentiviruses, such as HIV and FIV(Pco) in the cougar (Puma concolor). We review the current epidemiological and evolutionary findings of FIV(Fca). In addition to the five accepted FIV(Fca), subtypes, several recent phylogenetic studies have found strains that form separate clades, indicative of novel subtypes. In New Zealand cats, these strains of unknown subtype have been found to be involved in complex patterns of intergenic recombination, and whole genome sequences are required to resolve these. Evidence of recombination events has been documented with the highest levels in the env gene, the region involved in host cell receptor recognition. Several cases of FIV(Fca) multiple infections, both inter- and intra-subtype, have been reported. The findings of both unknown subtypes and relatively high levels of recombination suggest the need for further testing of the current vaccine. Limited studies on the evolutionary rate of FIV(Fca) document a value twice to three times that of FIV in the cougar, a result suggesting the different levels of co-adaptation between the viruses and their respective hosts. We studied the tissue distribution of FIV(Fca) in feral domestic cats, finding the first case of FIV compartmentalisation, a phenomenon well documented in HIV-1 patients.

Recombination in feline immunodeficiency virus from feral and companion domestic cats

Background

Recombination is a relatively common phenomenon in retroviruses. We investigated recombination in Feline Immunodeficiency Virus from naturally-infected New Zealand domestic cats (Felis catus) by sequencing regions of the gag, pol and env genes.

Results

The occurrence of intragenic recombination was highest in env, with evidence of recombination in 6.4% (n = 156) of all cats. A further recombinant was identified in each of the gag (n = 48) and pol (n = 91) genes. Comparisons of phylogenetic trees across genes identified cases of incongruence, indicating intergenic recombination. Three (7.7%, n = 39) of these incongruencies were found to be significantly different using the Shimodaira-Hasegawa test.

Surprisingly, our phylogenies from the gag and pol genes showed that no New Zealand sequences group with reference subtype C sequences within intrasubtype pairwise distances. Indeed, we find one and two distinct unknown subtype groups in gag and pol, respectively. These observations cause us to speculate that these New Zealand FIV strains have undergone several recombination events between subtype A parent strains and undefined unknown subtype strains, similar to the evolutionary history hypothesised for HIV-1 "subtype E".

Endpoint dilution sequencing was used to confirm the consensus sequences of the putative recombinants and unknown subtype groups, providing evidence for the authenticity of these sequences. Endpoint dilution sequencing also resulted in the identification of a dual infection event in the env gene. In addition, an intrahost recombination event between variants of the same subtype in the pol gene was established. This is the first known example of naturally-occurring recombination in a cat with infection of the parent strains.

Conclusion

Evidence of intragenic recombination in the gag, pol and env regions, and complex intergenic recombination, of FIV from naturally-infected domestic cats in New Zealand was found. Strains of unknown subtype were identified in all three gene regions. These results have implications for the use of the current FIV vaccine in New Zealand.

Phylogenetic analysis of feline immunodeficiency virus in feral and companion domestic cats of New Zealand

Nested PCR was used to amplify envelope V3-V6 gene fragments of feline immunodeficiency virus (FIV) from New Zealand cats. Phylogenetic analyses established that subtypes A and C predominate among New Zealand cats, with clear evidence of intersubtype recombination. In addition, 17 sequences were identified that were distinct from all known FIV clades, and we tentatively suggest these belong to a novel subtype.

Feline lentiviruses demonstrate differences in receptor repertoire and envelope structural elements

Feline immunodeficiency virus (FIV) causes fatal disease in domestic cats via T cell depletion-mediated immunodeficiency. Pumas and lions are hosts for apparently apathogenic lentiviruses (PLV, LLV) distinct from FIV. We compared receptor use among these viruses by: (1) evaluating target cell susceptibility; (2) measuring viral replication following exposure to specific and non-specific receptor antagonists; and (3) comparing Env sequence and structural motifs. Most isolates of LLV and PLV productively infected domestic feline T cells, but differed from domestic cat FIV by infecting cells independent of CXCR4, demonstrating equivalent or enhanced replication following heparin exposure, and demonstrating substantial divergence in amino acid sequence and secondary structure in Env receptor binding domains. PLV infection was, however, inhibited by CD134/OX40 antibody. Thus, although PLV and LLV infection interfere with FIV superinfection, we conclude that LLV and PLV utilize novel, more promiscuous mechanisms for cell entry than FIV, underlying divergent tropism and biological properties of these viruses.

Prevalence of canine distemper virus, feline immunodeficiency virus and feline leukemia virus in captive African lions (Panthera leo) in Japan

Sero-prevalences of canine distemper virus (CDV), feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) were evaluated in 20 captive lions in two Japanese zoos. Anti-CDV antibody was detected in 13 of 20 lions. We could pursue antibody responses against CDV in three lions back to 1996. Sera collected in 1996 were negative for anti-CDV antibody, therefore, all of them showed sero-conversion in 2000. This result suggested that the epidemic of CDV infection in this zoo might have happened between 1996 and 2000. The lions were also examined for FIV and FeLV infections. We had no evidence for FeLV infection but eight lions were sero-positive for anti-FIV antibody.

Quantification of viral ribonucleic acid in plasma of cats naturally infected with feline immunodeficiency virus

OBJECTIVE

To assess plasma viral RNA concentration in cats naturally infected with feline immunodeficiency virus (FIV).

ANIMALS

28 FIV-infected cats.

PROCEDURE

Cats were categorized into 1 of the 3 following stages on the basis of clinical signs: asymptomatic (nonclinical) carrier (AC; n = 11), acquired immunodeficiency syndrome-related complex (ARC; 9), or acquired immunodeficiency syndrome (AIDS; 8). Concentration of viral RNA in plasma (copies per ml) was determined by use of a quantitative competitive polymerase chain reaction (QC-PCR) assay. Total lymphocyte count, CD4+ cell and CD8+ cell counts, and the CD4+ cell count-to-CD8+ cell count ratio were determined by use of flow cytometry.

RESULTS

Plasma viral RNA concentration was significantly higher in cats in the AIDS stage, compared with cats in AC and ARC stages. Most (5/7) cats in the AIDS stage had low total lymphocyte, CD4+ cell, and CD8+ cell counts.

CONCLUSIONS AND CLINICAL RELEVANCE

Concentration of plasma viral RNA is a good indicator of disease progression in FIV-infected cats, particularly as cats progress from the ARC to the AIDS stage. Determination of CD4+ and CD8+ cell counts can be used as supportive indicators of disease progression.

Inhibitory effect of stromal cell derived factor-1 on the replication of divergent strains of feline immunodeficiency virus in a feline T-lymphoid cell line

The effect of a CXC-chemokine, stromal cell derived factor-1 (SDF-1), on the replication of divergent strains of feline immunodeficiency virus (FIV) was examined in order to identify the mechanism of cell entry of FIV. A chemotaxis assay, using a modified Boyden chamber method, confirmed the biological activity of recombinant human (rh) SDF-1 for a feline T-lymphoid cell line (Kumi-1). The viral replication of FIV, as measured by the reverse transcriptase (RT) activity in the culture supernatant, was significantly suppressed by addition of rhSDF-1 in a dose-dependent manner in Kumi-1 cells. Furthermore, PCR analysis of the FIV proviral genome indicated that the inhibitory effect of rhSDF-1 on the replication of FIV in Kumi-1 cells was due to the inhibitory effect in the early event of replication. The inhibitory effect on viral replication by exogenous rhSDF-1 was shown for four divergent FIV isolates of subtypes A, B, and D in Kumi-1 cells.

Envelope gene sequences encoding variable regions 3 and 4 are involved in macrophage tropism of feline immunodeficiency virus

The envelope is of cardinal importance for the entry of feline immunodeficiency virus (FIV) into its host cells, which consist of cells of the immune system including macrophages. To characterize the envelope glycoprotein determinants involved in macrophage tropism, chimeric infectious molecular clones were constructed containing envelope gene sequences from isolates that had been propagated in peripheral blood mononuclear cells (PBMC). The progeny virus was examined for growth in PBMC and bone marrow-derived macrophages and viruses with different replication kinetics in macrophages were selected. Envelope-chimeric viruses revealed that nucleotide sequences encoding variable regions 3 and 4 of the surface glycoprotein, SU, are involved in macrophage tropism of FIV. To assess the biological importance of this finding, the phenotypes of envelope proteins of viruses derived from bone marrow, brain, lymph node and PBMC of an experimentally FIV-infected, healthy cat were examined. Since selection during propagation had to be avoided, provirus envelope gene sequences were amplified directly and cloned into an infectious molecular clone of FIV strain Petaluma. The viruses obtained were examined for their replication properties. Of 15 clones tested, 13 clones replicated both in PBMC and macrophages, two (brain-derived clones) replicated in PBMC only and none replicated in Crandell feline kidney cells or astrocytes. These results indicate that dual tropism for PBMC and macrophages is a common feature of FIV variants present in vivo.

Interspecies transmission of feline immunodeficiency virus from the domestic cat to the Tsushima cat (Felis bengalensis euptilura) in the wild

Feline immunodeficiency virus (FIV) was isolated from a wild-caught Tsushima cat (Felis bengalensis euptilura), an endangered Japanese nondomestic subspecies of leopard cat (F. bengalensis). Phylogenetic analysis of the env gene sequences indicated that the FIV from the Tsushima cat belonged to a cluster of subtype D FIVs from domestic cats. FIVs from both the Tsushima cat and the domestic cat showed similar levels of replication and cytopathicity in lymphoid cell lines derived from these two species. The results indicated the occurrence of interspecies transmission of FIV from the domestic cat to the Tsushima cat in the wild.

Genetic heterogeneity of env gene of feline immunodeficiency virus obtained from multiple districts in Japan

Feline immunodeficiency virus (FIV) infection is widespread in many countries. FIV isolates have been classified into five distinct subtypes, A, B, C, D and E based on their env gene sequences. Several reports indicate that most of the FIVs isolated in Japan belong to subtype B which includes the first Japanese isolate, TM2 strain. To examine the distribution of FIV subtypes in Japan, proviral DNA sequences of the env gene were directly amplified by nested PCR from FIV-infected cats that had been kept in multiple districts throughout Japan. Phylogenetic analysis of the 11 strains showed that four FIV subtypes, A, B, C and D, were present in Japan. Among these subtypes, subtypes B and D were the two most common subtypes in Japan, and they were mainly distributed in the eastern and western parts of Japan, respectively. The present study provides information that is fundamental for development of a vaccine to protect against FIV infection in cats.

Molecular characteristics of malignant lymphomas in cats naturally infected with feline immunodeficiency virus

Neoplastic disease, especially malignant lymphomas, are often observed in cats infected with feline immunodeficiency virus (FIV). In order to clarify the characteristics of lymphoma cells and to investigate the pathogenesis in FIV-infected cats, we examined the lymphoma tissues developed in five cats naturally infected with FIV by Southern blot analyses using feline immunoglobulin (Ig), T-cell receptors (TCR) and FIV probes. All of the five cases were serologically positive for anti-FIV antibody and negative for feline leukemia virus antigen. Of these five lymphoma samples, two displayed rearrangement of the Ig heavy chain gene and deletion of the Ig light (kappa) chain gene, indicating that the tumor cells were committed to B-cell development. One tumor sample was identified as a T-cell lymphoma because of the presence of a rearranged TCR beta-chain gene. The other two cases were considered to be non-T non-B cell lymphoma because they did not show any rearrangement of the Ig and TCR genes. Therefore, no consistent tumor type was found in lymphoma cases infected with FIV. Clonal integration of FIV provirus was not detected in any of the five lymphoma samples obtained from FIV-infected cats using Southern blot analysis, although FIV proviral genome was detected in the genomic DNA of all the lymphoma samples by using a polymerase chain reaction (PCR). These results indicated that FIV might not play a direct role in tumorigenesis of lymphoma in cats.