Nucleotide sequence of feline immunodeficiency virus: classification of Japanese isolates into two subtypes which are distinct from non-Japanese subtypes

Decreased Sensitivity of the Serological Detection of Feline Immunodeficiency Virus Infection Potentially Due to Imported Genetic Variants

Feline immunodeficiency virus (FIV) is a lentivirus of domestic cats worldwide. Diagnosis usually relies on antibody screening by point-of-care tests (POCT), e.g., by enzyme-linked immunosorbent assays (ELISA), and confirmation using Western blot (WB). We increasingly observed ELISA-negative, WB-positive samples and aimed to substantiate these observations using 1194 serum/plasma samples collected from 1998 to 2019 primarily from FIV-suspect cats. While 441 samples tested positive and 375 tested negative by ELISA and WB, 81 samples had discordant results: 70 were false ELISA-negative (WB-positive) and 11 were false ELISA-positive (WB-negative); 297 ambiguous results were not analyzed further. The diagnostic sensitivity and specificity of the ELISA (82% and 91%, respectively) were lower than those reported in 1995 (98% and 97%, respectively). The diagnostic efficiency was reduced from 97% to 86%. False ELISA-negative samples originated mainly (54%) from Switzerland (1995: 0%). Sixty-four false ELISA-negative samples were available for POCT (SNAP^TM/WITNESS^R): five were POCT-positive. FIV RT-PCR was positive for two of these samples and was weakly positive for two ELISA- and POCT-negative samples. Low viral loads prohibited sequencing. Our results suggest that FIV diagnosis has become more challenging, probably due to increasing travel by cats and the introduction of new FIV isolates not recognized by screening assays.

Feline immunodeficiency virus in Northern Ceará, Brazil

Objectives

The objectives of this study were to confirm the prevalence of feline immunodeficiency virus (FIV) infection in domestic cats in the region north of Ceará, Brazil, and to determine the factors associated with infection and the major circulating subtypes of the virus in this area.

Methods

Samples from 148 cats were collected and tested using anti-FIV antibody screening, with confirmation of positive results by PCR. Univariate analysis was performed considering the epidemiological characteristics and FIV status. Sequencing and phylogenetic analysis of the gag and pol genes were performed to confirm the FIV subtype.

Results

Nine cats (6.1%) tested positive for FIV – one female (0.7%) and eight males (5.4%). Male cats were significantly more likely to be infected (P <0.05). Phylogenetic analysis of gag and pol gene sequences indicated that the FIV isolates circulating in the study area belonged to subtype B.

Conclusions and relevance

In this study, we demonstrated a low prevalence for FIV in the northwest of Ceará, north-eastern Brazil. Male sex is a significant risk factor for FIV infection and the best predictive factor for FIV status. All isolates examined in this study clustered within subtype B, which is the predominant subtype in Brazil. This is the first report of genetic characterization of FIV in the state of Ceará, Brazil.

Prevalence of feline immunodeficiency virus and feline leukaemia virus in domestic cats in Hungary

OBJECTIVES

Feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) are retroviruses affecting cats worldwide. The objectives of the study were to estimate the prevalence of these retroviruses in domestic cats in Hungary and to characterise the phylogenetic relationships of FIV strains.

METHODS

A total of 335 anticoagulated whole-blood samples obtained from both a healthy and ill cat population were examined for the presence of FIV and FeLV with two methods: ELISA and PCR. Statistical analysis was carried out to analyse the data obtained. Sequencing and phylogenetic analysis of partial polymerase (pol) gene sequences was performed to describe circulating FIV subtypes.

RESULTS

Statistical analysis showed 11.8% and 9.9% true prevalence of FeLV and FIV, respectively, with ELISA. The apparent prevalence calculated from the PCR results were 17.3% for FeLV and 13.1% for FIV. Phylogenetic analysis of partial pol gene sequences obtained from 22 FIV strains showed that all observed Hungarian strains belonged to FIV subtype B. The strains were grouped into several monophyletic subgroups reflecting the geographic locations of the origin of the samples. The overall mean genetic similarity between the analysed strains was 98.2%.

CONCLUSIONS AND RELEVANCE

We report the first thorough overview of the prevalence of FeLV and FIV in Hungary, which is relatively high, and give insight into the genetic diversity of Hungarian strains of FIV.

Lessons Learned in Developing a Commercial FIV Vaccine: The Immunity Required for an Effective HIV-1 Vaccine

The feline immunodeficiency virus (FIV) vaccine called Fel-O-Vax^® FIV is the first commercial FIV vaccine released worldwide for the use in domestic cats against global FIV subtypes (A⁻E). This vaccine consists of inactivated dual-subtype (A plus D) FIV-infected cells, whereas its prototype vaccine consists of inactivated dual-subtype whole viruses. Both vaccines in experimental trials conferred moderate-to-substantial protection against heterologous strains from homologous and heterologous subtypes. Importantly, a recent case-control field study of Fel-O-Vax-vaccinated cats with outdoor access and ≥3 years of annual vaccine boost, resulted in a vaccine efficacy of 56% in Australia where subtype-A viruses prevail. Remarkably, this protection rate is far better than the protection rate of 31.2% observed in the best HIV-1 vaccine (RV144) trial. Current review describes the findings from the commercial and prototype vaccine trials and compares their immune correlates of protection. The studies described in this review demonstrate the overarching importance of ant-FIV T-cell immunity more than anti-FIV antibody immunity in affording protection. Thus, future efforts in developing the next generation FIV vaccine and the first effective HIV-1 vaccine should consider incorporating highly conserved protective T-cell epitopes together with the conserved protective B-cell epitopes, but without inducing adverse factors that eliminate efficacy.

Prevalence and risk factor analysis for feline haemoplasmas in cats from Northern Serbia, with molecular subtyping of feline immunodeficiency virus

Objectives

The objectives of this study were to estimate the prevalence of feline haemoplasma infections in Northern Serbia, identify potential risk factors and perform molecular subtyping of feline immunodeficiency virus (FIV).

Methods

PCR analysis for feline haemoplasmas was performed on surplus EDTA blood samples from 373 cats from the Belgrade region, Serbia. An ELISA was used to determine the prevalence of feline leukaemia virus (FeLV) and FIV; PCR was performed on a subpopulation of these cats. FIV subtyping was performed using PCR.

Results

Within this population, 64/373 cats (17.2%) were infected with one or more haemoplasma species. Mycoplasma haemofelis was detected in 20/373 cats (5.4%), ‘Candidatus Mycoplasma haemominutum’ in 47/373 cats (12.6%) and ‘Candidatus Mycoplasma turicensis’ in 23/373 cats (6.2%). Coinfections were observed in 21/373 cats (5.6%). Based on ELISA serological retroviral testing, 4/310 cats (1.3%) were infected with FeLV, whereas 78/331 (23.6%) were infected with FIV. Multivariable analysis identified significant associations between haemoplasma infection and anaemia (anaemic/non-anaemic, odds ratio [OR] 2.7, 95% confidence interval [CI] 1.04–7.1; P = 0.041]), male gender (male/female, OR 4.5, 95% CI 2.22–9.03; P <0.0005), outdoor access (yes/no, OR 5.2, 95% CI 2.28–11.92; P <0.0005), non-pedigree breed (non-pedigree/pedigree, OR 5.5, 95% CI 1.24–24.84; P = 0.025) and FIV seropositive status (positive/negative, OR 2.4, 95% CI 1.21–4.83; P = 0.012). PCR analysis of the FIV ELISA-positive samples revealed clade D as being the most prevalent.

Conclusions and relevance

All three known species of feline haemoplasma were detected, confirming their presence in Serbia; ‘Candidatus Mycoplasma haemominutum’ was the most prevalent. We found a high prevalence of FIV-infected cats and FIV clade D was most prevalent.

Feline immudeficiency virus subtypes B and A in cats from São Luis, Maranhão, Brazil

Feline immunodeficiency virus (FIV) is a retrovirus of the genus Lentivirus that is distributed worldwide, with prevalence rates varying between 2.5% and 44%. FIV causes immunosuppression, with depletion of TCD4⁺ lymphocytes, with the majority of clinical signs caused by secondary and opportunistic infections. Blood samples were collected from nine domestic cats (Felis catus domesticus) from the city of São Luís, Maranhão State, Brazil. All samples were positive in a rapid immunochromatographic test (SNAP® Combo FeLV Ag/FIV Antibody Test) and in a polymerase chain reaction (PCR) assay. Phylogenetic analysis showed that six samples clustered within subtype B, one within subtype A, and two did not cluster with any known subtype. Five unique haplotypes (Hap-1, Hap-2, Hap-3, Hap-5 and Hap-6) and a shared haplotype (Hap-4) were found, this last one being the most frequent. This is the first report on the genetic diversity of FIV in the city of São Luís and the first report of subtype A in Brazil. New variations of the virus are also reported.

First Nearly Complete Genome Sequence of Feline immunodeficiency virus from Brazil

Feline immunodeficiency virus (FIV) has worldwide distribution; nevertheless, only a few FIV genomes from domestic cats are available. This is the first report of a nearly complete genome of FIV from a Brazilian cat (8,967 nucleotides [nt]), including the entire coding region and the 3′ untranslated region.

Phylodynamics of the Brazilian feline immunodeficiency virus

Feline immunodeficiency virus (FIV), like other retroviruses, displays large genomic divergence when different isolates are compared. In this study, 31 FIV positive samples of domestic cats from Porto Alegre, RS, Brazil were used aiming at a detailed genomic characterization and a better understanding of the molecular epidemiology of the virus in Brazil. The proviral env genes were partially amplified, sequenced and compared with another 237 sequences from different continents. We identified several Brazilian highly supported clades (A, B1, B2, C and D) that suggest independent events of introduction of FIV in Brazil. Forty six reference-sequences from the GenBank were used with our 31 sequences to infer the virus subtypes. Our sequences belong to the subtype B and three of them result from a recombination with the previously described subtype F. The other 28 Brazilian samples belonging to subtype B and another 46 Brazilian sequences from the GenBank were used to estimate the time to the most recent common ancestor of each Brazilian clade, using a Bayesian approach and a relaxed molecular clock model. The analyses of Brazilian sequences suggest several different entries of the virus in the Brazilian cat population between 1981 and 1991.

Commercially Available Enzyme-Linked Immunosorbent Assay and Polymerase Chain Reaction Tests for Detection of Feline Immunodeficiency Virus Infection

BACKGROUND

Feline immunodeficiency virus (FIV) infection is an important cause of disease of cats worldwide. Initial screening is commonly performed by commercially available point-of-care (POC) ELISA tests. Confirmatory testing for positive POC test results is recommended. Polymerase chain reaction (PCR) tests for FIV are commonly used additional testing methods; however, reported measures of diagnostic accuracy vary widely between PCR tests, making interpretation of results difficult.

HYPOTHESIS/OBJECTIVE

There is very good agreement between results of a commercially available PCR test and a POC ELISA test for FIV for specimens collected from owned and shelter-housed cats.

ANIMALS

Blood samples from 168 cats from 2 adoption guarantee shelters, an FIV Sanctuary, and 64 private homes were used.

METHODS

This was a prospective study. Whole blood samples were collected in K₂ -EDTA, divided, and submitted for PCR and ELISA testing. Follow-up whole blood samples were collected in lithium heparin from cats with discordant results and submitted for virus isolation (VI).

RESULTS

There was very good agreement between ELISA and PCR (kappa 0.87; P < .001; 95% CI 0.79, 0.95). Of 168 cats, eleven had discordant ELISA/PCR results: 7 ELISA+/PCR- and 4 ELISA-/PCR+. Using VI as a reference standard, there were 4 false-positive PCR results, 5 false-positive ELISA results, and 1 false-negative PCR result (1 cat lost to follow-up).

CONCLUSIONS AND CLINICAL IMPORTANCE

While there was good agreement between the POC ELISA and PCR tests, the discordant results highlight the importance of cautious interpretation of test results and the necessity of confirmatory testing.

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.

Horses naturally infected with EIAV harbor 2 distinct SU populations but are monophyletic with respect to IN

Equine infectious anemia virus (EIAV) causes lifelong infections ranging from acutely fatal, to chronic, to asymptomatic. Within infected animals, EIAV is found as a quasispecies. Many experimental studies on EIAV, carried out in the U.S. over the past 70 years, have used either the highly virulent Wyoming (EIAVWYO) field strain or various derivatives of that strain. These infections have provided insights into the variety of genetic changes that accumulate in the env gene and LTR in experimentally infected horses. In the current study, we obtained EIAV sequences from blood samples collected from naturally infected Texas horses between 2000 and 2002. We found surface (SU) and long terminal repeat (LTR) sequences clearly related to EIAVWYO and its cell culture-adapted derivatives. Some blood samples yielded SU or LTR sequences belonging to 2 discrete clusters. In these cases, SU and LTR variation between animals was no greater than sequence variation within animals. In contrast, a portion of integrase (IN) was more homogeneous within animals than between animals. These results suggest that specific selective pressures are applied to SU and LTR sequences, potentially driving generation of two distinct sequence clusters within a horse. We speculate that viruses in one cluster may be more highly expressed and easily transmitted while those in the second cluster support long-term inapparent infection. The presence of homogeneous IN sequences within a horse supports the hypothesis that SU and LTR sequences diverged after the initial infection.

A Naturally Occurring Domestic Cat APOBEC3 Variant Confers Resistance to Feline Immunodeficiency Virus Infection

Apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3; A3) DNA cytosine deaminases can be incorporated into progeny virions and inhibit lentiviral replication. On the other hand, viral infectivity factor (Vif) of lentiviruses antagonizes A3-mediated antiviral activities by degrading A3 proteins. It is known that domestic cat (Felis catus) APOBEC3Z3 (A3Z3), the ortholog of human APOBEC3H, potently suppresses the infectivity of vif-defective feline immunodeficiency virus (FIV). Although a recent report has shown that domestic cat encodes 7 haplotypes (hap I to hap VII) of A3Z3, the relevance of A3Z3 polymorphism in domestic cats with FIV Vif has not yet been addressed. In this study, we demonstrated that these feline A3Z3 variants suppress vif-defective FIV infectivity. We also revealed that codon 65 of feline A3Z3 is a positively selected site and that A3Z3 hap V is subject to positive selection during evolution. It is particularly noteworthy that feline A3Z3 hap V is resistant to FIV Vif-mediated degradation and still inhibits vif-proficient viral infection. Moreover, the side chain size, but not the hydrophobicity, of the amino acid at position 65 determines the resistance to FIV Vif-mediated degradation. Furthermore, phylogenetic analyses have led to the inference that feline A3Z3 hap V emerged approximately 60,000 years ago. Taken together, these findings suggest that feline A3Z3 hap V may have been selected for escape from an ancestral FIV. This is the first evidence for an evolutionary “arms race” between the domestic cat and its cognate lentivirus.

IMPORTANCE Gene diversity and selective pressure are intriguing topics in the field of evolutionary biology. A direct interaction between a cellular protein and a viral protein can precipitate an evolutionary arms race between host and virus. One example is primate APOBEC3G, which potently restricts the replication of primate lentiviruses (e.g., human immunodeficiency virus type 1 [HIV-1] and simian immunodeficiency virus [SIV]) if its activity is not counteracted by the viral Vif protein. Here we investigate the ability of 7 naturally occurring variants of feline APOBEC3, APOBEC3Z3 (A3Z3), to inhibit FIV replication. Interestingly, one feline A3Z3 variant is dominant, restrictive, and naturally resistant to FIV Vif-mediated degradation. Phylogenetic analyses revealed that the ancestral change that generated this variant could have been caused by positive Darwinian selection, presumably due to an ancestral FIV infection. The experimental-phylogenetic investigation sheds light on the evolutionary history of the domestic cat, which was likely influenced by lentiviral infection.

Phylogenetic analysis of feline immunodeficiency virus strains from naturally infected cats in Belgium and The Netherlands

Feline immunodeficiency virus (FIV) is a major pathogen in feline populations worldwide, with seroprevalences up to 26%. Virus strains circulating in domestic cats are subdivided into different phylogenetic clades (A-E), based on the genetic diversity of the V3-V4 region of the env gene. In this report, a phylogenetic analysis of the V3-V4 env region, and a variable region in the gag gene was made for 36 FIV strains isolated in Belgium and The Netherlands. All newly generated gag sequences clustered together with previously known clade A FIV viruses, confirming the dominance of clade A viruses in Northern Europe. The same was true for the obtained env sequences, with only one sample of an unknown env subtype. Overall, the genetic diversity of FIV strains sequenced in this report was low. This indicates a relatively recent introduction of FIV in Belgium and The Netherlands. However, the sample with an unknown env subtype indicates that new introductions of FIV from unknown origin do occur and this will likely increase genetic variability in time.

Sequence variation of the feline immunodeficiency virus genome and its clinical relevance

The ongoing evolution of feline immunodeficiency virus (FIV) has resulted in the existence of a diverse continuum of viruses. FIV isolates differ with regards to their mutation and replication rates, plasma viral loads, cell tropism and the ability to induce apoptosis. Clinical disease in FIV-infected cats is also inconsistent. Genomic sequence variation of FIV is likely to be responsible for some of the variation in viral behaviour. The specific genetic sequences that influence these key viral properties remain to be determined. With knowledge of the specific key determinants of pathogenicity, there is the potential for veterinarians in the future to apply this information for prognostic purposes. Genomic sequence variation of FIV also presents an obstacle to effective vaccine development. Most challenge studies demonstrate acceptable efficacy of a dual-subtype FIV vaccine (Fel-O-Vax FIV) against FIV infection under experimental settings; however, vaccine efficacy in the field still remains to be proven. It is important that we discover the key determinants of immunity induced by this vaccine; such data would compliment vaccine field efficacy studies and provide the basis to make informed recommendations on its use.

Virus-host interaction in feline immunodeficiency virus (FIV) infection

Feline immunodeficiency virus (FIV) infection has been the focus of several studies because this virus exhibits genetic and pathogenic characteristics that are similar to those of the human immunodeficiency virus (HIV). FIV causes acquired immunodeficiency syndrome (AIDS) in cats, nevertheless, a large fraction of infected cats remain asymptomatic throughout life despite of persistent chronic infection. This slow disease progression may be due to the presence of factors that are involved in the natural resistance to infection and the immune response that is mounted by the animals, as well as due to the adaptation of the virus to the host. Therefore, the study of virus-host interaction is essential to the understanding of the different patterns of disease course and the virus persistence in the host, and to help with the development of effective vaccines and perhaps the cure of FIV and HIV infections.

Feline immunodeficiency virus in South America

The rapid emergence of AIDS in humans during the period between 1980 and 2000 has led to extensive efforts to understand more fully similar etiologic agents of chronic and progressive acquired immunodeficiency disease in several mammalian species. Lentiviruses that have gene sequence homology with human immunodeficiency virus (HIV) have been found in different species (including sheep, goats, horses, cattle, cats, and several Old World monkey species). Lentiviruses, comprising a genus of the Retroviridae family, cause persistent infection that can lead to varying degrees of morbidity and mortality depending on the virus and the host species involved. Feline immunodeficiency virus (FIV) causes an immune system disease in domestic cats (Felis catus) involving depletion of the CD4+ population of T lymphocytes, increased susceptibility to opportunistic infections, and sometimes death. Viruses related to domestic cat FIV occur also in a variety of nondomestic felids. This is a brief overview of the current state of knowledge of this large and ancient group of viruses (FIVs) in South America.

Emerging viruses in the Felidae: shifting paradigms

The domestic cat is afflicted with multiple viruses that serve as powerful models for human disease including cancers, SARS and HIV/AIDS. Cat viruses that cause these diseases have been studied for decades revealing detailed insight concerning transmission, virulence, origins and pathogenesis. Here we review recent genetic advances that have questioned traditional wisdom regarding the origins of virulent Feline infectious peritonitis (FIP) diseases, the pathogenic potential of Feline Immunodeficiency Virus (FIV) in wild non-domestic Felidae species, and the restriction of Feline Leukemia Virus (FeLV) mediated immune impairment to domestic cats rather than other Felidae species. The most recent interpretations indicate important new evolutionary conclusions implicating these deadly infectious agents in domestic and non-domestic felids.

Pathogenicity and rapid growth kinetics of feline immunodeficiency virus are linked to 3' elements

Chimeric viruses constructed between a highly pathogenic Feline Immunodeficiency Virus isolate (FIV-C36) and a less pathogenic but neurotropic strain (FIV-PPR) have been used to map viral genetic determinants of in vivo pathogenicity. Chimeric virus FIV-PCenv, which contains FIV-C36 genome from the 3′ region of pol to upstream of the 3′LTR on an FIV-PPR backbone, was previously shown to be replication-competent in vivo, inducing altered CD4⁺ T-cell and neutrophil profiles intermediate between parental strains following a delay in viral replication during initial infection. Examination of FIV-PCenv proviral sequences recovered at week 11 post-infection revealed two changes compared to initial viral inoculum; the most significant being arginine to histidine in the integrase region of Pol at residue 813 (R813H). Pooled plasma from the initial in vivo study was used to inoculate a second cohort of cats to determine whether similar virulence and kinetics could be established following primary infection. Viral replication kinetics and immunocyte profiles were monitored in blood, bone marrow, and saliva over a one-year period. Passaged FIV-PCenv again displayed intermediate phenotype between parental strains, but unlike primary experiments, the onset of acute viremia was not delayed. CD4/8 alterations were noted in all groups of animals, though significant changes from controls were delayed in FIV-PPR infected animals compared to FIV-C36 and FIV-PCenv. In vivo passage of FIV-PCenv increased replication-competence relative to the initial molecularly-cloned chimera in association with one adaptive nucleotide change in the 5′ end of the genome relative to primary tissue culture inoculum, while mutations in the 3′ end of the genome were not detected. The results are consistent with the interpretation that 3′ elements contribute to heightened virulence of FIV-C36, and that integrase residue 813 plays an important role in facilitating successful in vivo replication.

Isolation and partial characterization of Brazilian samples of feline immunodeficiency virus

Feline immunodeficiency virus (FIV) causes a slow progressive degeneration of the immune system which eventually leads to a disease comparable to acquired immune deficiency syndrome (AIDS) in humans. FIV has extensive sequence variation, a typical feature of lentiviruses. Sequence analysis showed that diversity was not evenly distributed throughout the genome, but was greatest in the envelope gene, env. The virus enters host cells via a sequential interaction, initiated by the envelope glycoprotein (env) binding the primary receptor molecule CD134 and followed by a subsequent interaction with chemokine co-receptor CXCR4. The purpose of this study was to isolate and characterize isolates of FIV from an open shelter in São Paulo, Brazil. The separated PBMC from 11 positive cats were co-cultured with MYA-1 cells. Full-length viral env glycoprotein genes were amplified and determined. Chimeric feline × human CD134 receptors were used to investigate the receptor utilization of 17 clones from Brazilian isolates of FIV. Analyses of the sequence present of molecular clones showed that all clones grouped within subtype B. In contrast to the virulent primary isolate FIV-GL8, expression of the first cysteine-rich domain (CRD1) of feline CD134 in the context of human CD134 was sufficient for optimal receptor function for all Brazilian FIV isolates tested.

Phylogenetic characterisation of naturally occurring feline immunodeficiency virus in the United Kingdom

Feline immunodeficiency virus (FIV) is a significant pathogen of domestic and non-domestic felids worldwide. In domestic cats, FIV is classified into five distinct subtypes (A–E) with subtypes A and B distributed most widely. However, little is known about the degree of intrasubtype viral diversity and this may prove critical in determining whether monovalent vaccines are likely to protect against FIV strains within a single subtype. Here, we characterise novel env sequences from 47 FIV strains recovered from infected cats in the United Kingdom and its environs. Phylogenetic analyses revealed that all bar one sequence belonged to subtype A, the predominant subtype in Western Europe. A single sequence was identified as a likely subtype A/C recombinant, intriguing given that subtype C does not appear to exist in either the UK or North Western Europe and suggestive of a recombination event predating its introduction into the UK. Subtype A strains from the UK were not significantly differentiated from representative subtype A isolates found elsewhere suggesting multiple introductions of FIV into the country. Divergence among isolates was comparable to that observed for subtype A isolates worldwide, indicating that FIV in the UK covers the full spectrum of subtype A diversity seen globally. This study demonstrates that while subtype A is predominant in the UK, novel introductions may result in the emergence of novel subtypes or intersubtype recombinants, potentially circumventing vaccine strategies. However, the dominance of subtype A suggests that the development of a regional or subtype-specific protective vaccine for the UK could be achievable.

Adaptation of feline immunodeficiency virus subtype B strain TM2 to a feline astrocyte cell line (G355-5 cells)

Based on receptor usage during infection, feline immunodeficiency virus (FIV) isolates can be divided into two groups; those that require feline CD134 (fCD134) as a primary receptor in addition to CXCR4 to enter the cells, and those that require CXCR4 only. Most primary isolates, including strain TM2, belong to the former group and cannot infect a feline astrocyte cell line (G355-5 cells) due to a lack of fCD134 expression. In a previous study, we found that G355-5 cells transduced with fCD134 (termed G355-5/fOX40 cells) were susceptible to strain TM2 and the inoculated cells became persistently infected. In this study, we examined the phenotype of the virus prepared from the persistently infected cells (termed strain TM2PI). Intriguingly, strain TM2PI replicated well in naïve G355-5 cells and the inoculated G355-5 cells (termed G355-5/TM2PI cells) became persistently infected. The infection of TM2PI in G355-5 cells was inhibited by CXCR4 antagonist AMD3100 and TM2PI infected other fCD134-negative, CXCR4-positive cell lines, FeTJ and 3201 cells. Four amino acid substitutions were found in the Env protein of the strain TM2PI when compared with that of the parental strain TM2. Among the substitutions, the Env amino acid position at 407 of TM2PI was substituted to lysine which has been known to be responsible for the FIV tropism for Crandell feline kidney cells. The strain TM2PI will be useful for studying the receptor switching mechanism and FIV pathogenesis in cats.

Comparative study of the plasma globulin level, CD21(-) B-cell counts and FOXP3 mRNA expression level in CD4(+) T-cells for different clinical stages of feline immunodeficiency virus infected cats

Feline immunodeficiency virus (FIV) infection leads to hypergammaglobulinemia through mechanisms that remain poorly understood. We investigated changes in plasma globulin level, B cells, and T cells with progression of the clinical stage of FIV-infected cats. We classified FIV-infected cats into the stage of Asymptomatic carrier (AC) and AIDS-related complex (ARC) based on the clinical symptoms, and measured the plasma globulin level, the CD4(+) T-cell counts, and analyzed surface markers of B cells. We investigated the relationship between the plasma globulin level and regulatory T cells (Tregs) using the Forkhead box P3 (FOXP3) mRNA expression level. In FIV-infected cats, the plasma globulin level and the surface immunoglobulin (sIg)(+) CD21(-) B-cell counts were increased, whereas the CD4(+) T-cell counts were decreased compared with specific-pathogen free (SPF) cats. The mRNA expression of Blimp-1 (master gene of plasma cells) was increased in peripheral blood, and the FOXP3 mRNA expression level was decreased in CD4(+) T-cells. These immunological changes were marked in the ARC stage. These data indicate that the decrease of Tregs and the increase of plasma cells lead to hypergammaglobulinemia.

First molecular characterization of feline immunodeficiency virus in Turkey

In this study, strains of feline immunodeficiency virus (FIV), designated TR-D, TR-Mo and TR-Mi, isolated from three cats in Turkey, were characterized. PCR products (859 bp) from the envelope (env) gene region were amplified and sequenced, and possible geographical differences in the env gene region of Turkish FIV strains are discussed. Phylogenetic analysis of two strains showed that FIV subtype B was present in Turkey. Phylogenetic analysis showed that one new Turkish FIV strain occupies a separate branch from known clusters (subtypes A to E) from the USA, Canada, Europe and Japan.

A detailed phylogenetic analysis of FIV in the United States

Background

Feline immunodeficiency virus (FIV) is a lentivirus associated with AIDS-like illnesses in cats and has been used as a model for the study of human immunodeficiency virus (HIV). A feature of HIV and FIV infection is the continually increasing divergence among viral isolates between different individuals, as well as within the same individuals.

Methodology/Principal Findings

The goal of this study was to determine the phylogenetic patterns of viral isolates obtained within the United States (U.S.) by focusing on the variable, V3-V4, region of the FIV envelope gene.

Conclusions/Significance

Data indicate that FIV, from within the U.S., localize to four viral clades, A, B, C, and F. Also shown is the geographic isolation of strains where clade A and clade B are found predominately on the west coast; however, clade B is also found throughout the U.S. and represents the predominant clade. This study presents a complete and conclusive analysis of FIV isolates from within the U.S. and may be used as the essential basis for the development of an effective multi-clade vaccine.

An updated nation-wide epidemiological survey of feline immunodeficiency virus (FIV) infection in Japan

An updated nation-wide epidemiological survey of feline immunodeficiency virus (FIV) infection was conducted in Japan. Blood samples were collected from 1,770 outdoor accessing cats from March to October 2008. Serologically, 410 cats (23.2%) were positive for anti-FIV antibody. Proviral DNA of the FIV env V3-V5 region isolated from 348 cases could be phylogenetically analyzed. The present study disclosed a geographic distribution of four subtypes (A, B, C and D) of FIV in Japan. Even though an FIV vaccine was introduced in Japan, we do not currently know whether this vaccine is effective against all strains of FIV in Japan or not. Therefore, close attention still has to be paid to epidemic and genotypic trends of FIV.

Naturally acquired feline immunodeficiency virus (FIV) infection in cats from western Canada: Prevalence, disease associations, and survival analysis

This retrospective study evaluated epidemiologic features and disease associations of feline immunodeficiency virus (FIV) infection in client owned cats from western Canada. Among 1205 cats that were tested 66 (5.5%) were positive for FIV antibody (FIV(+)) with a higher prevalence in males than females. FIV(+) cats were older than the overall population. Epidemiologic features and disease associations were compared between 58 FIV(+), but feline leukemia virus negative (FeLV(-)) cats and 58 age and sex matched FIV-negative (FIV(-)), FeLV(-) cats. FIV positivity was associated with a history of bite wounds, increasing age, and male gender. Lethargy and oral diseases were significantly associated with FIV positivity. Although several FIV(+) cats were euthanized, the survival time of FIV(+) cats after diagnosis was not significantly different from that of FIV(-) cats. In summary, FIV prevalence was low in cats from western Canada, clinical signs/diseases were mild, and lifespan was not different in FIV(+) cats.

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.

Molecular subtyping of feline immunodeficiency virus from cats in Melbourne

OBJECTIVE

To determine the subtypes of feline immunodeficiency virus (FIV) present in the domestic cat population in Melbourne.

METHODS

Blood samples were collected from 42 cats that had serum antibodies against FIV. DNA was extracted and subjected to polymerase chain reaction (PCR) to amplify variable regions of the envelope (env) and group specific antigen (gag) genes of FIV. PCR products were directly sequenced or sequenced after cloning when direct sequencing yielded ambiguous results. Phylogenetic analysis was performed and comparisons made with representative sequences of different subtypes.

RESULTS

The variable region of the env gene was successfully amplified by PCR from 41 of the 42 cats. All 41 were found to cluster with subtype A env sequences. The variable region of the gag gene was successfully amplified by PCR from all 42 cats. Forty-one were found to cluster with subtype A gag genes and one was found to cluster with subtype B sequences, suggesting that it may be derived from a recombinant env A/gag B virus.

CONCLUSIONS

Subtype A is the predominant FIV type in Melbourne, although a subtype A/B recombinant was identified in the population of FIV positive cats. These results of env gene analysis were similar to those in a previous Australian study, suggesting that subtype A predominates in Australia. The results of the gag gene analysis show the importance of analysing multiple areas of the FIV genome when assigning FIV subtypes. Comparison with other major urban centres may provide useful information about the phylogenic diversity of FIV in Australia.

Antiviral activity of membrane fusion inhibitors that target gp40 of the feline immunodeficiency virus envelope protein

For the entry of lentivirus into target cells, fusion between its viral membrane and cellular membrane is essential. The present study was conducted to examine the inhibitory effect of modified peptides corresponding to heptad repeats (HR) 1 and 2 of feline immunodeficiency virus (FIV) envelope gp40 on the fusion between the viral and cellular membranes. FIV-N36 and FIV-C35 were synthesized as authentic peptides of the N-terminal HR1 domain and C-terminal HR2 domain of FIV gp40, respectively. FIV-C35EK1, FIV-C35EK2, and FIV-C35EK3 were peptides synthesized by modifying FIV-C35 as the X-EE-XX-KK concept to increase their solubility in water and the stability of their alpha-helicity. FIV-C35 and FIV-C35EK1 inhibited the cell membrane fusion mediated by FIV-infected cells and the replication of FIV. FIV-N36, FIV-C35EK2, and FIV-C35EK3 did not show any apparent inhibitory effect. These results indicated that the newly developed membrane fusion inhibitors could facilitate the development of novel anti-lentiviral chemotherapies.

A single site for N-linked glycosylation in the envelope glycoprotein of feline immunodeficiency virus modulates the virus-receptor interaction

Feline immunodeficiency virus (FIV) targets helper T cells by attachment of the envelope glycoprotein (Env) to CD134, a subsequent interaction with CXCR4 then facilitating the process of viral entry. As the CXCR4 binding site is not exposed until CD134-binding has occurred then the virus is protected from neutralising antibodies targeting the CXCR4-binding site on Env. Prototypic FIV vaccines based on the FL4 strain of FIV contain a cell culture-adapted strain of FIV Petaluma, a CD134-independent strain of FIV that interacts directly with CXCR4. In addition to a characteristic increase in charge in the V3 loop homologue of FIV_FL4, we identified two mutations in potential sites for N-linked glycosylation in the region of FIV Env analogous to the V1–V2 region of HIV and SIV Env, T271I and N342Y. When these mutations were introduced into the primary GL8 and CPG41 strains of FIV, the T271I mutation was found to alter the nature of the virus-CD134 interaction; primary viruses carrying the T271I mutation no longer required determinants in cysteine-rich domain (CRD) 2 of CD134 for viral entry. The T271I mutation did not confer CD134-independent infection upon GL8 or CPG41, nor did it increase the affinity of the CXCR4 interaction, suggesting that the principal effect was targeted at reducing the complexity of the Env-CD134 interaction.

Establishment of a feline astrocyte-derived cell line (G355-5 cells) expressing feline CD134 and a rapid quantitative assay for T-lymphotropic feline immunodeficiency viruses

Few laboratory strains of feline immunodeficiency virus (FIV) can infect Crandell feline kidney cells (an epithelial-type of cells), however, most primary isolates are T-lymphotropic. T-lymphotropic FIV requires both feline CD134 (an activation marker of helper T-lymphocytes) and CXCR4 (a chemokine receptor) in infection as primary and secondary receptors, respectively. Using feline T-lymphoblastoid cell lines, titration of primary FIV isolates was carried out, however the titration assay was laborious and time-consuming. In this study, using G355-5 cells (a feline astrocyte-derived cell line) transduced with a cDNA of feline CD134 as target cells, an assay system was developed to quantitate primary FIV isolates. With a previous method using a feline T-lymphoblastoid cell line (MYA-1 cells) highly sensitive to FIV, it took 12 days to complete the assay, however, it took only 2 days with the new method. The FIV-infected cells became in a state of persistent infection, producing a large amount of FIV, indicating that the cells will be useful for propagation of T-lymphotropic FIV strains.

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 and genetic analysis of feline immunodeficiency virus gag, pol, and env genes from domestic cats undergoing nucleoside reverse transcriptase inhibitor treatment or treatment-naïve cats in Rio de Janeiro, Brazil

Feline immunodeficiency virus (FIV) is the Lentivirus responsible for an immunodeficiency-like disease in domestic cats (Felis catus). FIV is divided into five phylogenetic subtypes (A, B, C, D, and E), based on genetic diversity. Knowledge of the geographical distribution of subtypes is relevant for understanding different disease progressions and for vaccine development. In this study, viral sequences of 26 infected cats from Rio de Janeiro, 8 undergoing treatment with zidovudine (AZT) for at least 5 years, were successfully amplified from blood specimens. gag capsid (CA), pol reverse transcriptase (RT), and env gp120 (V3-V4) regions were analyzed to determine subtypes and to evaluate potential mutations related to antiretroviral drug resistance among treated cats. Subtyping based on phylogenetic analysis was performed by the neighbor-joining and maximum likelihood methods. All of the sequences clustered with subtype B in the three regions, exhibiting low genetic variability. Additionally, we found evidence that the same virus is circulating in animals in close contact. The analysis of FIV RT sequences identified two new putative mutations related to drug resistance located in the RT "finger" domain, which has 60% identity to human immunodeficiency virus (HIV) sequence. Amino acid change K-->R at codons 64 and 69 was found in 25% and 37.5% of the treated animals, respectively. These signatures were comparable to K65R and K70R thymidine-associated mutations found in the HIV-1 HXB2 counterpart. This finding strongly suggests a position correlation between the mutations found in FIV and the K65R and K70R substitutions from drug-resistant HIV-1 strains.

Intrahost evolution of envelope glycoprotein and OrfA sequences after experimental infection of cats with a molecular clone and a biological isolate of feline immunodeficiency virus

Feline immunodeficiency virus (FIV) is a member of the genus Lentivirus and causes AIDS-like disease in its natural host, the cat. Like other lentiviruses, FIV displays a high degree of nucleotide sequence variability that is reflected in both the geographic distribution of the viruses and the different cat species that are infected. Although a lot of data on sequence variation at the population level is available, relatively little is known about the intrahost variation of FIV sequences. In the present study, cats were infected with either a biological isolate of FIV or a molecular clone that was derived from the same isolate, AM19. After infection, the cats were monitored for up to 3 years and at various time points sequences were obtained of virus circulating in the plasma. Regions of the env gene and the orfA gene were amplified, cloned and their nucleotide sequence analyzed. Furthermore, the extent of sequence variation in the original inocula was also determined. It was found that FIV is displaying relative little sequence variation during infection of its host, both in the env and the orfA gene, especially after infection with molecular clone 19k1. Although the extent of variation was higher after infection with biological isolate AM19, a large portion of these variant sequences was already present in the inoculum.

Ocorrência do vírus da imunodeficiência felina e do vírus da leucemia felina em gatos domésticos mantidos em abrigos no município de Belo Horizonte

Investigou-se a ocorrência da infecção pelo vírus da imunodeficiência felina (FIV) e pelo vírus da leucemia felina (FeLV) em gatos domésticos, provenientes de dois abrigos, no município de Belo Horizonte. Amostras de sangue de 145 animais foram coletadas e testadas para detecção do FIV pela reação em cadeia da polimerase (PCR). Destas amostras, 40 foram testadas para o antígeno p26 de FeLV por meio de ELISA. Observaram-se duas fêmeas (1,4%) e quatro machos (2,8%) positivos para FIV e nove fêmeas (22,5%) e quatro machos (10,0%) positivos para FeLV.

New challenges for the diagnosis of feline immunodeficiency virus infection

Vaccination of cats against feline immunodeficiency virus (FIV) with a whole-virus vaccine results in rapid and persistent production of antibodies that are indistinguishable from those used for diagnosis of FIV infection. There are no diagnostic tests available for veterinary practitioners at the present time to resolve the diagnostic dilemma posed by use of whole-virus vaccines for protection of cats against FIV. There is a great need for development of commercially available rapid diagnostic tests that conform to differentiation of infected from vaccinated animals standards.

Vaccine protection against feline immunodeficiency virus: setting the challenge

Since feline immunodeficiency virus (FIV) was first isolated, international research efforts have been directed towards developing a protective vaccine, not least because it may provide a model for a candidate human immunodeficiency virus (HIV) vaccine. This article reviews the challenges facing vaccine development, the current state of knowledge and future prospects for FIV vaccination.

FIV as a Model for HIV: An Overview

Animal models for human immunodeficiency virus (HIV) infection play a key role in understanding the pathogenesis of AIDS and the development of therapeutic agents and vaccines. As the only lentivirus that causes an immunodeficiency resembling that of HIV infection, in its natural host, feline immunodeficiency virus (FIV) has been a unique and powerful model for AIDS research. FIV was first described in 1987 by Niels Pedersen and co-workers as the causative agent for a fatal immunodeficiency syndrome observed in cats housed in a cattery in Petaluma, California. Since this landmark observation, multiple studies have shown that natural and experimental infection of cats with biological isolates of FIV produces an AIDS syndrome very similar in pathogenesis to that observed for human AIDS. FIV infection induces an acute viremia associated with Tcell alterations including depressed CD4 :CD8 T-cell ratios and CD4 T-cell depletion, peripheral lymphadenopathy, and neutropenia. In later stages of FIV infection, the host suffers from chronic persistent infections that are typically self-limiting in an immunocompetent host, as well as opportunistic infections, chronic diarrhea and wasting, blood dyscracias, significant CD4 T-cell depletion, neurologic disorders, and B-cell lymphomas. Importantly, chronic FIV infection induces a progressive lymphoid and CD4 T-cell depletion in the infected cat. The primary mode of natural FIV transmission appears to be blood-borne facilitated by fighting and biting. However, experimental infection through transmucosal routes (rectal and vaginal mucosa and perinatal) have been well documented for specific FIV isolates. Accordingly, FIV disease pathogenesis exhibits striking similarities to that described for HIV-1 infection.