Proviral organization and sequence analysis of feline immunodeficiency virus isolated from a Pallas' cat

Comprehensive Investigation on the Interplay between Feline APOBEC3Z3 Proteins and Feline Immunodeficiency Virus Vif Proteins

As the hosts of lentiviruses, almost 40 species of felids (family Felidae) are distributed around the world, and more than 20 feline species test positive for feline immunodeficiency virus (FIV), a lineage of lentiviruses. These observations suggest that FIVs globally infected a variety of feline species through multiple cross-species transmission events during a million-year history. Cellular restriction factors potentially inhibit lentiviral replication and limit cross-species lentiviral transmission, and cellular APOBEC3 deaminases are known as a potent restriction factor. In contrast, lentiviruses have evolutionary-acquired viral infectivity factor (Vif) to neutralize the APOBEC3-mediated antiviral effect. Because the APOBEC3-Vif interaction is strictly specific for viruses and their hosts, a comprehensive investigation focusing on Vif-APOBEC3 interplay can provide clues that will elucidate the roles of this virus-host interplay on cross-species transmission of lentiviruses. Here, we performed a comprehensive investigation with 144 patterns of a round robin test using 18 feline APOBEC3Z3 genes, an antiviral APOBEC3 gene in felid, and 8 FIV Vifs and derived a matrix showing the interplay between feline APOBEC3Z3 and FIV Vif. We particularly focused on the interplay between the APOBEC3Z3 of three felids (domestic cat, ocelot, and Asian golden cat) and an FIV Vif (strain Petaluma), and revealed that residues 65 and 66 of the APOBEC3Z3 protein of multiple felids are responsible for the counteraction triggered by FIV Petaluma Vif. Altogether, our findings can be a clue to elucidate not only the scenarios of the cross-species transmissions of FIVs in felids but also the evolutionary interaction between mammals and lentiviruses.

IMPORTANCE Most of the emergences of new virus infections originate from the cross-species transmission of viruses. The fact that some virus infections are strictly specific for the host species indicates that certain “species barriers” in the hosts restrict cross-species jump of viruses, while viruses have evolutionary acquired their own “arms” to overcome/antagonize/neutralize these hurdles. Therefore, understanding of the molecular mechanism leading to successful cross-species viral transmission is crucial for considering the menus of the emergence of novel pathogenic viruses. In the field of retrovirology, APOBEC3-Vif interaction is a well-studied example of the battles between hosts and viruses. Here, we determined the sequences of 11 novel feline APOBEC3Z3 genes and demonstrated that all 18 different feline APOBEC3Z3 proteins tested exhibit anti-feline immunodeficiency virus (FIV) activity. Our comprehensive investigation focusing on the interplay between feline APOBEC3 and FIV Vif can be a clue to elucidate the scenarios of the cross-species transmissions of FIVs in felids.

USE OF CLINDAMYCIN IN PALLAS' CATS [OTOCOLOBUS (FELIS) MANUL] TO REDUCE JUVENILE TOXOPLASMOSIS-ASSOCIATED MORTALITY RATES

Pallas' cat [Otocolobus (Felis) manul] experiences a high mortality rate from toxoplasmosis. During the period 2006-2016, the overall mortality rate for this species from all causes during the first year of life was 71.59% in European Association of Zoos and Aquaria institutions, with the most significant infectious cause from systemic toxoplasmosis (20.6%) as confirmed by postmortem examination and histopathology. Clindamycin was used starting in 2014 in two collections that had previously experienced 100% mortality rates by toxoplasmosis in kittens less than one year of age, covering key Toxoplasma gondii exposure periods for kittens (n = 17) as a prophylactic measure. This protocol resulted in a 67.03% (95% confidence interval 41.76-78.61%) reduction in the first year mortality rate over a two-year period to 5.88% in those animals treated.

A conflict of interest: the evolutionary arms race between mammalian APOBEC3 and lentiviral Vif

Apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 3 (APOBEC3) proteins are mammalian-specific cellular deaminases and have a robust ability to restrain lentivirus replication. To antagonize APOBEC3-mediated antiviral action, lentiviruses have acquired viral infectivity factor (Vif) as an accessory gene. Mammalian APOBEC3 proteins inhibit lentiviral replication by enzymatically inserting G-to-A hypermutations in the viral genome, whereas lentiviral Vif proteins degrade host APOBEC3 via the ubiquitin/proteasome-dependent pathway. Recent investigations provide evidence that lentiviral vif genes evolved to combat mammalian APOBEC3 proteins. In corollary, mammalian APOBEC3 genes are under Darwinian selective pressure to escape from antagonism by Vif. Based on these observations, it is widely accepted that lentiviral Vif and mammalian APOBEC3 have co-evolved and this concept is called an "evolutionary arms race." This review provides a comprehensive summary of current knowledge with respect to the evolutionary dynamics occurring at this pivotal host-virus interface.

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.

Patterns of seroprevalence of feline viruses among domestic cats (Felis catus) and Pallas’ cats (Otocolobus manul) in Daursky Reserve, Russia

Few data are available on the prevalence of feline viruses in the wild and little is known about natural sources of infections. The aim of this study was to estimate patterns of seroprevalence to feline viruses (feline immunodeficiency virus (FIV), feline calicivirus (FCV), feline panleukopenia virus (FPV), feline herpesvirus (FHV), and feline leukemia virus (FeLV)) in two cat species, domestic cats (Felis catus L., 1758) (n = 61) and Pallas’ cats (Otocolobus manul (Pallas, 1776)) (n = 24), living in the same area, in Daursky Reserve, Russia. Our results indicate that four of five viruses are circulating in the study area, with the exception of FHV. The pattern of FCV and FPV prevalence differed from FIV and FeLV. FCV and FPV seroprevalence did not depend on the sex and predominated in the group of cats living in the village (76% and 55%, respectively). No Pallas’ cats were seropositive to these viruses. The prevalence of FIV and FeLV were similar in areas with different cat densities (at the stations (16% for both viruses) and in the village (16% for both viruses)). The patterns of seroprevalence between species testify to the low rate of interspecific contacts. In Pallas’ cats, we found the presence of antibodies to FIV to be 5% and antigens of FeLV to be 5%, pathogens for which transmission demand close direct contacts between animals (mainly aggressive and (or) sexual contact), which is typical in the breeding season. Arid climate may also reduce patterns of viral prevalence in the study area, decreasing the risk of infection for both cat species.

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.

Feline immunodeficiency virus (FIV) in wild Pallas' cats

Feline immunodeficiency virus (FIV), a feline lentivirus related to HIV, causes immune dysfunction in domestic and wild cats. The Pallas' cat is the only species from Asia known to harbor a species-specific strain of FIV designated FIV(Oma) in natural populations. Here, a 25% seroprevalence of FIV is reported from 28 wild Mongolian Pallas' cats sampled from 2000 to 2008. Phylogenetic analysis of proviral RT-Pol from eight FIV(Oma) isolates from Mongolia, Russia, China and Kazakhstan reveals a unique monophyletic lineage of the virus within the Pallas' cat population, most closely related to the African cheetah and leopard FIV strains. Histopathological examination of lymph node and spleen from infected and uninfected Pallas' cats suggests that FIV(Oma) causes immune depletion in its' native host.

Feline immunodeficiency virus and puma lentivirus in Florida panthers (Puma concolor coryi): epidemiology and diagnostic issues

This study documents the seroprevalence of feline immunodeficiency virus (FIV) and puma lentivirus (PLV) in free-ranging and captive Florida panthers (Puma concolor coryi) (n = 51) and translocated Texas cougars (P. concolor stanleyana) (n = 10) from 1985 to 1998. The sera were tested for anti-FIV antibodies by enzyme-linked immunosorbent assay (ELISA) and Western blot tests. The ELISAs were read kinetically (KELA) and the sera were retrospectively examined by PLV peptide ELISA. Eleven panthers and one cougar were positive by KELA; 4 panthers and 4 cougars were equivocal; 35 panthers and 5 cougars were negative; and 1 panther had no data. Seven of the 11 KELA-positive panthers were also positive by Western blot tests and all but one were positive by PLV peptide ELISA. Ten KELA-negative and Western blot-negative cats, were positive by PLV peptide ELISA. KELA results varied within cats from one sample period to the next, but PLV peptide ELISA results were consistent. Territorial sympatry and mating behaviour, noted from radiotelemetry location data on the cats, may have contributed to viral transmission between seropositive animals. These findings suggest that Florida panthers and the introduced Texas cougars have been exposed to FIV and/or PLV.

Feline immunodeficiency. ABCD guidelines on prevention and management

Overview

Feline immunodeficiency virus (FIV) is a retrovirus closely related to human immunodeficiency virus. Most felids are susceptible to FIV, but humans are not. Feline immunodeficiency virus is endemic in domestic cat populations worldwide. The virus loses infectivity quickly outside the host and is susceptible to all disinfectants.

Infection

Feline immunodeficiency virus is transmitted via bites. The risk of transmission is low in households with socially well-adapted cats. Transmission from mother to kittens may occur, especially if the queen is undergoing an acute infection. Cats with FIV are persistently infected in spite of their ability to mount antibody and cell-mediated immune responses.

Disease signs

Infected cats generally remain free of clinical signs for several years, and some cats never develop disease, depending on the infecting isolate. Most clinical signs are the consequence of immunodeficiency and secondary infection. Typical manifestations are chronic gingivostomatitis, chronic rhinitis, lymphadenopathy, weight loss and immune-mediated glomerulonephritis.

Diagnosis

Positive in-practice ELISA results obtained in a low-prevalence or low-risk population should always be confirmed by a laboratory. Western blot is the ‘gold standard’ laboratory test for FIV serology. PCR-based assays vary in performance.

Disease management

Cats should never be euthanased solely on the basis of an FIV-positive test result. Cats infected with FIV may live as long as uninfected cats, with appropriate management. Asymptomatic FIV-infected cats should be neutered to avoid fighting and virus transmission. Infected cats should receive regular veterinary health checks. They can be housed in the same ward as other patients, but should be kept in individual cages.

Vaccination recommendations

At present, there is no FIV vaccine commercially available in Europe. Potential benefits and risks of vaccinating FIV-infected cats should be assessed on an individual cat basis. Needles and surgical instruments used on FIV-positive cats may transmit the virus to other cats, so strict hygiene is essential.

Genetically divergent strains of feline immunodeficiency virus from the domestic cat (Felis catus) and the African lion (Panthera leo) share usage of CD134 and CXCR4 as entry receptors

The env open reading frames of African lion (Panthera leo) lentivirus (feline immunodeficiency virus [FIV(Ple)]) subtypes B and E from geographically distinct regions of Africa suggest two distinct ancestries, with FIV(Ple)-E sharing a common ancestor with the domestic cat (Felis catus) lentivirus (FIV(Fca)). Here we demonstrate that FIV(Ple)-E and FIV(Fca) share the use of CD134 (OX40) and CXCR4 as a primary receptor and coreceptor, respectively, and that both lion CD134 and CXCR4 are functional receptors for FIV(Ple)-E. The shared usage of CD134 and CXCR4 by FIV(Fca) and FIV(Ple)-E may have implications for in vivo cell tropism and the pathogenicity of the E subtype among free-ranging lion populations.

Evolution of feline immunodeficiency virus in Felidae: implications for human health and wildlife ecology

Genetic analyses of feline immunodeficiency viruses provide significant insights on the worldwide distribution and evolutionary history of this emerging pathogen. Large-scale screening of over 3000 samples from all species of Felidae indicates that at least some individuals from most species possess antibodies that cross react to FIV. Phylogenetic analyses of genetic variation in the pol-RT gene demonstrate that FIV lineages are species-specific and suggest that there has been a prolonged period of viral-host co-evolution. The clinical effects of FIV specific to species other than domestic cat are controversial. Comparative genomic analyses of all full-length FIV genomes confirmed that FIV is host specific. Recently sequenced lion subtype E is marginally more similar to Pallas cat FIV though env is more similar to that of domestic cat FIV, indicating a possible recombination between two divergent strains in the wild. Here we review global patterns of FIV seroprevalence and endemnicity, assess genetic differences within and between species-specific FIV strains, and interpret these with patterns of felid speciation to propose an ancestral origin of FIV in Africa followed by interspecies transmission and global dissemination to Eurasia and the Americas. Continued comparative genomic analyses of full-length FIV from all seropositive animals, along with whole genome sequence of host species, will greatly advance our understanding of the role of recombination, selection and adaptation in retroviral emergence.

Genomic organization, sequence divergence, and recombination of feline immunodeficiency virus from lions in the wild

BACKGROUND

Feline immunodeficiency virus (FIV) naturally infects multiple species of cat and is related to human immunodeficiency virus in humans. FIV infection causes AIDS-like disease and mortality in the domestic cat (Felis catus) and serves as a natural model for HIV infection in humans. In African lions (Panthera leo) and other exotic felid species, disease etiology introduced by FIV infection are less clear, but recent studies indicate that FIV causes moderate to severe CD4 depletion.

RESULTS

In this study, comparative genomic methods are used to evaluate the full proviral genome of two geographically distinct FIV subtypes isolated from free-ranging lions. Genome organization of FIVPle subtype B (9891 bp) from lions in the Serengeti National Park in Tanzania and FIVPle subtype E (9899 bp) isolated from lions in the Okavango Delta in Botswana, both resemble FIV genome sequence from puma, Pallas cat and domestic cat across 5' LTR, gag, pol, vif, orfA, env, rev and 3'LTR regions. Comparative analyses of available full-length FIV consisting of subtypes A, B and C from FIVFca, Pallas cat FIVOma and two puma FIVPco subtypes A and B recapitulate the species-specific monophyly of FIV marked by high levels of genetic diversity both within and between species. Across all FIVPle gene regions except env, lion subtypes B and E are monophyletic, and marginally more similar to Pallas cat FIVOma than to other FIV. Sequence analyses indicate the SU and TM regions of env vary substantially between subtypes, with FIVPle subtype E more related to domestic cat FIVFca than to FIVPle subtype B and FIVOma likely reflecting recombination between strains in the wild.

CONCLUSION

This study demonstrates the necessity of whole-genome analysis to complement population/gene-based studies, which are of limited utility in uncovering complex events such as recombination that may lead to functional differences in virulence and pathogenicity. These full-length lion lentiviruses are integral to the advancement of comparative genomics of human pathogens, as well as emerging disease in wild populations of endangered species.

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.

Expression of feline immunodeficiency virus Vif is associated with reduced viral mutation rates without restoration of replication of vif mutant viruses

The vif gene of lentiviruses has been demonstrated to be essential for efficient viral replication in many cell types. Although the Vif protein of feline immunodeficiency virus (FIV) displays limited homology to HIV-1 Vif, the role of vif in FIV replication is not known. We have examined the requirements of vif for replication of a FIV strain isolated from a non-domestic felid, Otocolobus manul (FIV-Oma). In agreement with others, we find that replication of FIV vif mutant molecular clones in CrFK cells is highly attenuated. Initial attempts to rescue vif mutant viruses in trans were limited by lack of detectable wild-type Vif expression from DNA constructs. We demonstrate that FIV-Oma Vif expression can be increased by re-synthesis of the gene to remove splice donor and acceptor sites as well as improving codon usage to a mammalian codon optimized model. Cellular localization of resynthesized Vif (Vif-RS) is cytoplasmic. Clonal stable transfectants expressing HA-tagged Vif-RS do not restore replication levels of vif mutant virus. However, in such cell lines, G-to-A mutation rates in replicating wild-type viruses are reduced.

Evolution of feline immunodeficiency virus Gag proteins

We evaluated the predicted biochemical properties of Gag proteins from a diverse group of feline immunodeficiency viruses (FIV) to determine how different evolutionary histories of virus and host have changed or constrained these important structural proteins. Our data are based on FIV sequences derived from domestic cat (FIVfca), cougar (FIVpco), and lions (FIVple). Analyses consisted of determining the selective forces acting at each position in the protein and the comparing predictions for secondary structure, charge, hydrophobicity and flexibility for matrix, capsid and nucleocapsid, and the C-terminal peptide, which comprise the Gag proteins. We demonstrate that differences among the FIV Gag proteins have largely arisen by neutral evolution, although many neutrally evolving regions have maintained biochemical features. Regions with predicted differences in biochemical features appear to involve intramolecular interactions and structural elements that undergo conformational changes during particle maturation. In contrast, the majority of sites involved in intermolecular contacts on the protein surface are constrained by purifying selection. There is also conservation of sites that interact with host proteins associated with cellular trafficking and particle budding. NC is the only protein with evidence of positive selection, two of which occur in the N-terminal region responsible for RNA binding and interaction with host proteins.

Going wild: lessons from naturally occurring T-lymphotropic lentiviruses

Over 40 nonhuman primate (NHP) species harbor species-specific simian immunodeficiency viruses (SIVs). Similarly, more than 20 species of nondomestic felids and African hyenids demonstrate seroreactivity against feline immunodeficiency virus (FIV) antigens. While it has been challenging to study the biological implications of nonfatal infections in natural populations, epidemiologic and clinical studies performed thus far have only rarely detected increased morbidity or impaired fecundity/survival of naturally infected SIV- or FIV-seropositive versus -seronegative animals. Cross-species transmissions of these agents are rare in nature but have been used to develop experimental systems to evaluate mechanisms of pathogenicity and to develop animal models of HIV/AIDS. Given that felids and primates are substantially evolutionarily removed yet demonstrate the same pattern of apparently nonpathogenic lentiviral infections, comparison of the biological behaviors of these viruses can yield important implications for host-lentiviral adaptation which are relevant to human HIV/AIDS infection. This review therefore evaluates similarities in epidemiology, lentiviral genotyping, pathogenicity, host immune responses, and cross-species transmission of FIVs and factors associated with the establishment of lentiviral infections in new species. This comparison of consistent patterns in lentivirus biology will expose new directions for scientific inquiry for understanding the basis for virulence versus avirulence.

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.

Seroprevalence and genomic divergence of circulating strains of feline immunodeficiency virus among Felidae and Hyaenidae species

Feline immunodeficiency virus (FIV) infects numerous wild and domestic feline species and is closely related to human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). Species-specific strains of FIV have been described for domestic cat (Felis catus), puma (Puma concolor), lion (Panthera leo), leopard (Panthera pardus), and Pallas' cat (Otocolobus manul). Here, we employ a three-antigen Western blot screening (domestic cat, puma, and lion FIV antigens) and PCR analysis to survey worldwide prevalence, distribution, and genomic differentiation of FIV based on 3,055 specimens from 35 Felidae and 3 Hyaenidae species. Although FIV infects a wide variety of host species, it is confirmed to be endemic in free-ranging populations of nine Felidae and one Hyaenidae species. These include the large African carnivores (lion, leopard, cheetah, and spotted hyena), where FIV is widely distributed in multiple populations; most of the South American felids (puma, jaguar, ocelot, margay, Geoffroy's cat, and tigrina), which maintain a lower FIV-positive level throughout their range; and two Asian species, the Pallas' cat, which has a species-specific strain of FIV, and the leopard cat, which has a domestic cat FIV strain in one population. Phylogenetic analysis of FIV proviral sequence demonstrates that most species for which FIV is endemic harbor monophyletic, genetically distinct species-specific FIV strains, suggesting that FIV transfer between cat species has occurred in the past but is quite infrequent today.

Development and validation of puma (Felis concolor) cytokine and lentivirus real-time PCR detection systems

Studies of immune correlates of disease outcome associate humoral immune response mediated by T-helper 2 cytokines (IL-4, IL-10) with more virulent disease relative to a cell-mediated response driven by T-helper 1 cytokines (IL-2, IFN-gamma), particularly in viral and other intra-cellular infections. Specifically, the kinetics of both human immunodeficiency virus (HIV) and feline immunodeficiency virus (FIV) infection are closely associated with Type 1 versus Type 2 cytokine profiles. Puma (Felis concolor) lentivirus (PLV) is closely related to FIV, but based on phylogenetic and clinical studies, is more ancient and less pathogenic. The aims of this study were to validate feline real-time PCR primer/probe systems for puma cytokines and PLV as sensitive, quantitative assays for use in investigations of PLV pathogenicity. We demonstrate that primer/probe systems for IL-4, IL-10, IFN-gamma, TNF-alpha, GAPDH, and the pol region of PLV-1695 amplify puma cytokines and PLV-1695 with high amplification efficiency and sensitivity. Detection of PLV-1695 provirus in experimentally inoculated domestic cats proved to be of equivalent sensitivity, specificity, and positive and negative predictive value to co-culture of one million peripheral blood mononuclear cells (PBMC). Evaluation of cytokine induction during naturally occurring PLV infection will allow insight into mechanisms of host control associated with apathogenic infection. In addition, determination of viral loads during different stages of PLV infection or in different tissues from domestic cats or pumas will further elucidate capacity of these viruses to replicate and establish infection.

Comparative replication kinetics of two cytopathic feline lentiviruses ex vivo

Feline immunodeficiency virus infection of cats provides a model to elucidate mechanisms of lentiviral pathogenesis. We isolated a non-domestic FIV from a Pallas' cat, FIV-Oma, which replicates in feline PBMCs and CRFK cells. To gain insights into FIV pathogenesis, we compared rates of viral replication and apoptosis of FIV-Oma with FIV-PPR in the MYA-1 T-cell line. To minimize heterogeneity of virus, infections were initiated with virus derived from molecular clones. Viral DNA and RNA levels, assessed by qPCR and qRT-PCR, apoptosis, and supernatant reverse transcriptase were slower in FIV-Oma infections. Immunostaining for cellular Gag showed that few cells were productively infected. The majority of cells infected with either virus instead became apoptotic. Apoptosis was detectable within 6 h PI, suggesting activation of a signaling pathway. We propose that apoptosis is due to interaction of virus with cells, and is the usual outcome of infection by cytopathic FIVs in these cells.

Patterns of feline immunodeficiency virus multiple infection and genome divergence in a free-ranging population of African lions

Feline immunodeficiency virus (FIV) is a lentivirus that causes AIDS-like immunodeficiency disease in domestic cats. Free-ranging lions, Panthera leo, carry a chronic species-specific strain of FIV, FIV-Ple, which so far has not been convincingly connected with immune pathology or mortality. FIV-Ple, harboring the three distinct strains A, B, and C defined by pol gene sequence divergences, is endemic in the large outbred population of lions in the Serengeti ecosystem in Tanzania. Here we describe the pattern of variation in the three FIV genes gag, pol-RT, and pol-RNase among lions within 13 prides to assess the occurrence of FIV infection and coinfection. Genome diversity within and among FIV-Ple strains is shown to be large, with strain divergence for each gene approaching genetic distances observed for FIV between different species of cats. Multiple in fections with two or three strains were found in 43% of the FIV-positive individuals based on pol-RT sequence analysis, which may suggest that antiviral immunity or interference evoked by one strain is not consistently protective against infection by a second. This comprehensive study of FIV-Ple in a free-ranging population of lions reveals a dynamic transmission of virus in a social species that has historically adapted to render the virus benign.

The role of polymerase chain reaction and its newer developments in feline medicine

We give a brief overview on the principles of the polymerase chain reaction (PCR), reverse transcriptase PCR (RT-PCR), quantitative competitive PCR and real-time PCR (TaqMan technology). The literature dealing with PCR and its role in the diagnosis, pathogenesis and research of infectious diseases of the domestic cat is reviewed. Cross-contaminations which occasionally occur during handling of amplified DNA may be an important problem in the PCR laboratory. In many infectious diseases, PCR results are difficult to interpret as their predictive positive and negative values are not always known. Newer assays, such as TaqMan procedures, are becoming increasingly reliable and cost-effective. It can be expected that additional knowledge on how to interpret PCR results will soon be available.

The role of the chemokine receptor CXCR4 in infection with feline immunodeficiency virus

Infection with feline immunodeficiency virus (FIV) leads to the development of a disease state similar to AIDS in man. Recent studies have identified the chemokine receptor CXCR4 as the major receptor for cell culture-adapted strains of FIV, suggesting that FIV and human immunodeficiency virus (HIV) share a common mechanism of infection involving an interaction between the virus and a member of the seven transmembrane domain superfamily of molecules. This article reviews the evidence for the involvement of chemokine receptors in FIV infection and contrasts these findings with similar studies on the primate lentiviruses HIV and SIV (simian immunodeficiency virus).

CXCR4 is required by a nonprimate lentivirus: heterologous expression of feline immunodeficiency virus in human, rodent, and feline cells

A heterologous feline immunodeficiency virus (FIV) expression system permitted high-level expression of FIV proteins and efficient production of infectious FIV in human cells. These results identify the FIV U3 element as the sole restriction to the productive phase of replication in nonfeline cells. Heterologous FIV expression in a variety of human cell lines resulted in profuse syncytial lysis that was FIV env specific, CD4 independent, and restricted to cells that express CXCR4, the coreceptor for T-cell-line-adapted strains of human immunodeficiency virus. Stable expression of human CXCR4 in CXCR4-negative human and rodent cell lines resulted in extensive FIV Env-mediated, CXCR4-dependent cell fusion and infection. In feline cells, stable overexpression of human CXCR4 resulted in increased FIV infectivity and marked syncytium formation during FIV replication or after infection with FIV Env-expressing vectors. The use of CXCR4 is a fundamental feature of lentivirus biology independent of CD4 and a shared cellular link to infection and cytopathicity for distantly related lentiviruses that cause AIDS. Their conserved use implicates chemokine receptors as primordial lentivirus receptors.

Characterization of the transcription map and Rev activity of a highly cytopathic feline immunodeficiency virus

A highly cytopathic feline immunodeficiency virus, FIV-Oma, was previously isolated from a nondomestic cat. In this report, we describe experiments to characterize its transcription map and examine its Rev activity. The temporal progression of viral gene expression is similar to that of HIV-1. The splicing pattern of viral transcripts was determined by sequence analysis of RT-PCR-amplified viral cDNAs. In vitro transcription and translation of two putative rev cDNAs revealed that they encode at least one 22-kDa protein. The Rev-responsive element (RRE) of FIV-Oma, identified by computer-assisted RNA secondary structure analysis, was inserted into the intron of an HIV-1-derived reporter plasmid and used in a transient transfection assay for Rev activity. Cotransfection of the RRE construct with the two rev cDNA clones significantly increased the expression of the reporter gene linked to the RRE, indicating that both transcripts encode an active Rev protein. The Rev activity of FIV-Oma is 5 to 8 times higher than that of a domestic cat FIV isolate, FIV-PPR. Our experiments also demonstrate the heterologous interaction of FIV-PPR Rev with the FIV-Oma RRE, even though the RREs of the two viruses have very little nucleotide sequence identity.