A serosurvey of viral infections in lions (Panthera leo), from Queen Elizabeth National Park, Uganda

Serum samples from 14 lions (Panthera leo) from Queen Elizabeth National Park, Uganda, were collected during 1998 and 1999 to determine infectious disease exposure in this threatened population. Sera were analyzed for antibodies against feline immunodeficiency virus (FIV), feline calicivirus (FCV), feline herpesvirus 1 (feline rhinotracheitis: FHV1), feline/canine parvovirus (FPV/CPV), feline infectious peritonitis virus (feline coronavirus: FIPV), and canine distemper virus (CDV) or for the presence of feline leukemia virus (FeLV) antigens. Ten lions (71%) had antibodies against FIV, 11 (79%) had antibodies against CDV, 11 (79%) had antibodies against FCV, nine (64%) had antibodies against FHV1, and five (36%) had antibodies against FPV. Two of the 11 CDV-seropositive lions were subadults, indicating recent exposure of this population to CDV or a CDV-like virus. No lions had evidence of exposure to FeLV or FIPV. These results indicate that this endangered population has extensive exposure to common feline and canine viruses.     

Hypocomplementemia associated with naturally occurring lymphosarcoma in pet cats.

Eighty cats were classified by indirect immunofluorescence and histologic diagnosis into four categories: normal, feline leukemia virus (FeLV) infected; normal noninfected; lymphosarcoma-FeLV infected; lymphosarcoma, no FeLV present. All viremic cats with lymphosarcoma were found to be hypocomplementemic and activation of the complement system had occurred via the classical pathway. Sera of cats with lymphosarcoma in the absence of FeLV had varying levels of total hemolytic complement (TCH50) ranging from normal to hypocomplementemic. Approximately 50% of the cats that were viremic but histologically and clinically free of disease had TCH50 levels within normal range, and the remainder exhibited varying degrees of hypocomplementemia.     

Induction of protective immune response in cats by vaccination with feline leukemia virus iscom

An effective candidate subunit vaccine consisting of the gp 70/85 of feline leukemia virus (FeLV) was prepared by using the immunostimulating complex (iscom) method for the presentation of membrane proteins of enveloped viruses. Two 32-wk-old specific pathogen-free (SPF) cats were immunized with a FeLV iscom vaccine prepared from the supernatant fluid of the FL74 tumor cell line without adjuvant. Both cats developed FeLV serum antibodies, as measured in an enzyme-linked immunosorbent assay (ELISA) and in a virus neutralization test. A proportion of the antibodies were directed to an epitope located on gp70/85, which was shown in competition ELISA with a peroxidase-labeled virus-neutralizing monoclonal antibody to be shared by all three subtypes of FeLV. The protective effect of FeLV iscom was studied by vaccinating six 8-wk-old SPF cats with iscom prepared from cell culture supernatant of another tumor cell line F422, followed by oronasal challenge with 10(6) ffu FeLV-A (strain Glasgow-1). Six unvaccinated cats were also challenged with the same dose of FeLV. The vaccinated cats developed FeLV serum antibodies, some of which were directed to the shared epitope on gp70/85. At 10 wk after challenge, none was viremic, whereas three of the control cats had developed FeLV viremia. The potential of FeLV iscom as a vaccine against FeLV-associated disease in cats, and of iscom vaccines for protection against mammalian retrovirus infections, is discussed.     

Serosurvey of viral infections in free-ranging Namibian cheetahs (Acinonyx jubatus)

Cheetahs (Acinonyx jubatus) in captivity have unusually high morbidity and mortality from infectious diseases, a trait that could be an outcome of population homogeneity or the immunomodulating effects of chronic stress. Free-ranging Namibian cheetahs share ancestry with captive cheetahs, but their susceptibility to infectious diseases has not been investigated. The largest remaining population of free-ranging cheetahs resides on Namibian farmlands, where they share habitat with domestic dogs and cats known to carry viruses that affect cheetah health. To assess the extent to which free-ranging cheetahs are exposed to feline and canine viruses, sera from 81 free-ranging cheetahs sampled between 1992 and 1998 were evaluated for antibodies against canine distemper virus (CDV), feline coronavirus (feline infectious peritonitis virus; FCoV/ FIPV), feline herpesvirus 1 (FHV1), feline panleukopenia virus (FPV), feline immunodeficiency virus (FIV), and feline calicivirus (FCV) and for feline leukemia virus (FeLV) antigens. Antibodies against CDV, FCoV/FIPV, FHV1, FPV, and FCV were detected in 24, 29, 12, 48, and 65% of the free-ranging population, respectively, although no evidence of viral disease was present in any animal at the time of sample collection. Neither FIV antibodies nor FeLV antigens were present in any free-ranging cheetah tested. Temporal variation in FCoV/FIPV seroprevalence during the study period suggested that this virus is not endemic in the free-ranging population. Antibodies against CDV were detected in cheetahs of all ages sampled between 1995 and 1998, suggesting the occurrence of an epidemic in Namibia during the time when CDV swept through other parts of sub-Saharan Africa. This evidence in free-ranging Namibian cheetahs of exposure to viruses that cause severe disease in captive cheetahs should direct future guidelines for translocations, including quarantine of seropositive cheetahs and preventing contact between cheetahs and domestic pets.     

A feline large granular lymphoma and its derived cell line

Summary A lymphoma cell line (MCC) was derived from an abdominal mass from a 13-yr-old castrated male cat. The cells resemble natural killer precursor cells, have membrane-bound granules, and are positive for chloroacetate esterase, α-naphthyl butyrate esterase, and tartrate-resistant acid phosphatase activities. The MCC cells are negative for rearranged feline T-cell receptor genes, negative for feline T-cytotoxic antigen, Ia, and surface μ, τ, and lambda chains and do not form E-rosettes. The MCC cell line is negative for the feline leukemia virus (FeLV); e.g., negative for exogenous FeLV (exU3) sequences, negative for cytoplasmic and surface FeLV major core protein of 27 000 daltons (p27) by indirect, immunofluorescence assay, negative for helper FeLV by clone 81 assay, and negative for release of soluble FeLV p27 by enzyme-linked immunosorbent assay. Electron microscopy reveals budding type C retrovirus particles and MCC cells react with anti-RD-114 (anti-endogenous feline retrovirus) reference serum. After in vitro infection, MCC replicate FeLV readily, but replication is noncytopathic. This project has been funded, at least in part, with funds from the U.S. Department of Health and Human services under grants AI 25722, DK41939, and CA 35742 and contract AI-62525.     

Evidence of feline immunodeficiency virus, feline leukemia virus, and Toxoplasma gondii in feral cats on Mauna Kea, Hawaii

We determined prevalence to feline immunodeficiency virus (FIV) antibodies, feline leukemia virus (FeLV) antigen, and Toxoplasma gondii antibodies in feral cats (Felis catus) on Mauna Kea Hawaii from April 2002 to May 2004. Six of 68 (8.8%) and 11 of 68 (16.2%) cats were antibody positive to FIV and antigen positive for FeLV, respectively; 25 of 67 (37.3%) cats were seropositive to T. gondii. Antibodies to FeLV and T. gondii occurred in all age and sex classes, but FIV occurred only in adult males. Evidence of current or previous infections with two of these infectious agents was detected in eight of 64 cats (12.5%). Despite exposure to these infectious agents, feral cats remain abundant throughout the Hawaiian Islands.     

A replication-competent feline leukemia virus, subgroup A (FeLV-A), tagged with green fluorescent protein reporter exhibits in vitro biological properties similar to those of the parental FeLV-A

We previously established that lymphoid tumors could be induced in cats by intradermal injection of ecotropic feline leukemia virus (FeLV), subgroup A, plasmid DNA. In preparation for in vivo experiments to study the cell-to-cell pathway for the spread of the virus from the site of inoculation, the green fluorescent protein (GFP) transgene fused to an internal ribosome entry site (IRES) was inserted after the last nucleotide of the env gene in the ecotropic FeLV-A Rickard (FRA) provirus. The engineered plasmid was transfected into feline fibroblast cells for production of viruses and determination of GFP expression. The virions produced were highly infectious, and the infected cells could continue to mediate strong expression of GFP after long-term propagation in culture. Similar to parental virus, the transgene-containing ecotropic virus demonstrated recombinogenic activity with endogenous FeLV sequences in feline cells to produce polytropic recombinant FeLV subgroup B-like viruses which also contained the IRES-GFP transgene in the majority of recombinants. To date, the engineered virus has been propagated in cell culture for up to 8 months without diminished GFP expression. This is the first report of a replication-competent FeLV vector with high-level and stable expression of a transgene.     

A serological survey of common feline pathogens in free-living European wildcats (<Emphasis Type="Italic">Felis silvestris</Emphasis>) in central Spain

Twenty-five serum samples of 22 free-living European wildcats (Felis silvestris) captured from 1991 to 1993 in central Spain were tested for evidence of exposure to seven feline pathogens. All the wildcats but one (95.4%) presented evidence of contact with at least one of the agents (mean = 2.2). Contact with feline leukemia virus (FeLV) was detected in 81% of the wildcats (antibodies, 77%; antigen p27, 15%). Antibodies to feline calicivirus (FCV, 80%), feline herpesvirus (FHV, 20%), feline parvovirus (FPV, 18%), and Chlamydophila sp. (27%) were also detected. Analyses were negative for feline immunodeficiency virus and feline coronavirus. The probability of having antibodies to FPV was inversely related with the concentration of serum cholesterol and with a morphometric index of body condition. Similarity in the composition of antibodies against disease agents (number and identity of detected and undetected antibodies) was significantly higher in pairs of female wildcats than in pairs of males or heterosexual pairs, suggesting that females had a more homogeneous exposure to pathogens. Seroprevalence for FHV was higher in males than in females. Antibodies to FHV and Chlamydophila sp. were more frequent in winter than in other seasons. In addition, the mean similarity of the pathogen community between pairs of serum samples was higher if both wildcats were caught during the same season than if they were not. Mean similarity was lowest when serum samples obtained in winter were compared with those from spring or summer. The results suggest that some agents probably had a reservoir in domestic cats and may cause some undetected morbidity/mortality in the studied wildcat population, whereas others, such as FeLV and FCV, may be enzootic.     

Feline viruses in wildcats from Scotland

Few data are available on the prevalence of feline viruses in European wildcats (Felis silvestris). Previous surveys have indicated that wildcats may be infected with the common viruses of domestic cats, apart from feline immunodeficiency virus (FIV). In the present study, 50 wildcats trapped throughout Scotland (UK) between August 1992 and January 1997 were tested for evidence of viral infection. All were negative for FIV by several serological or virological methods. By contrast, 10% of the cats were positive for feline leukemia virus (FeLV) antigen and infectious virus was isolated from 13% of a smaller subset. Of the wildcats tested for respiratory viruses, 25% yielded feline calicivirus (FCV) and although no feline herpesvirus was isolated, 16% of the samples had neutralizing antibodies to this virus. Antibodies to feline coronavirus (FCoV) were found in 6% of samples. Feline foamy virus (FFV) was an incidental finding in 33% of samples tested. This study confirms that wildcats in Scotland are commonly infected with the major viruses of the domestic cat, except for FIV.     

Serological survey of feline leukemia virus infection and the outcome of antibody-positive cats

A serological survey was carried out to examine the presence of antibodies against feline leukemia virus (FeLV) and feline oncornavirus-associated cell membrane antigen (FOCMA) in 208 cat sera collected at Teikyo University School of Medicine. Seven cats (3.4%) were positive for FeLV antibodies by enzyme-linked immunosorbent assay whereas no cat was positive for FOCMA antibody by indirect membrane immunofluorescent test. Anemia, leukemia and/or lymphoma formation were not observed in these FeLV antibody-positive cats. But among these seven cats, three were positive for toxoplasma antibodies. One of them was also positive for Chlamydia psittaci antibody and it died in pneumonia. Among the four toxoplasma antibody negative cats, one was died in eosinophilic granuloma. Furthermore, two of three cats, which were used for experiments, had cold and took therapy.     

Molecular cloning and characterization of endogenous feline leukemia virus sequences from a cat genomic library.

Recombinant bacteriophage lambda clones from a cat genomic library derived from placental DNA of a specific pathogen-free cat were screened to identify endogenous feline leukemia virus (FeLV) sequences. Restriction endonuclease mapping of four different clones indicates that there are a number of similarities among them, notably the presence of a 6.0- to 6.4-kilobase pair (kbp) EcoRI hybridizing fragment containing portions of sequences homologous to the gag, pol, env, and long terminal repeat-like elements of the infectious FeLV. The endogenous FeLV sequences isolated are approximately 4 kbp in length and are significantly shorter than the cloned infectious FeLV isolates, which are 8.5 to 8.7 kbp in length. The endogenous elements have 3.3- to 3.6-kbp deletions in the gag-pol region and approximately 0.7- to 1.0-kbp deletions in the env region. These deletions would render them incapable of encoding an infectious virus and may therefore be related to the non-inducibility of FeLV from uninfected cat cells and the subgenomic expression of these endogenous sequences in placental tissue. It appears that there is conservation in the ordering of restriction sites previously reported in the proviruses of the infectious FeLVs in sequences corresponding to the pol and env boundary as well as the region spanning the env gene of the endogenous clones, whereas a greater divergence occurs among restriction sites mapped to the gag and part of the pol regions of the infectious FeLV. Such deleted, FeLV-related subsets of DNA sequences could have originated either by germ-line integration of a complete ecotropic virus followed by deletion, or by integration of a preexisting, defective, deleted variant of the infectious virus.     

Feline leukemia virus infection as a potentiating cofactor for the primary and secondary stages of experimentally induced feline immunodeficiency virus infection.

Preexistent feline leukemia virus (FeLV) infection greatly potentiated the severity of the transient primary and chronic secondary stages of feline immunodeficiency virus (FIV) infection. Of 10 FeLV-FIV carrier cats, 5 died of experimentally induced FIV infection, compared with 2 deaths in 10 cats infected only with FeLV and 1 death in 7 cats infected only with FIV. FIV-infected cats with preexistent FeLV infections developed severe depression, anorexia, fever, diarrhea, dehydration, weight loss, and leukopenia 4 to 6 weeks after infection and were moribund within 2 weeks of the onset of signs, whereas cats infected only with FIV developed much milder self-limiting gross and hematologic abnormalities. Pathologic findings in dually infected cats that died were similar to those observed previously in cats dying from uncomplicated primary FIV infection but were much more widespread and severe. Coinfection of asymptomatic FeLV carrier cats with FIV did not increase the levels of FeLV p27 antigen present in their blood over that seen in cats infected with FeLV alone. The amount of proviral FIV DNA was much higher, however, in dually infected cats than in cats infected only with FIV; there was a greater expression of FIV DNA in lymphoid tissues, where the genome was normally detected, and in nonlymphoid tissues, where FIV DNA was not usually found. Dually infedted cats that recovered from the primary stage of FIV infection remained more leukopenic than cats infected with FIV or FeLV alone, and their CD4+/CD8+ T-lymphocyte ratios were inverted. One of these cats developed what was considered to be an opportunistic infection. It was concluded, therefore, that a preexistent FeLV infection in some way enhanced the expression and spread of FIV in the body and increased the severity of both the resulting transient primary and chronic secondary stages of FIV infection. This study also demonstrated the usefulness of the FIV model in studying the role of incidental infectious diseases as cofactors for immunodeficiency-causing lentiviruses.     

Molecular analysis and pathogenesis of the feline aplastic anemia retrovirus, feline leukemia virus C-Sarma.

We describe the molecular cloning of an anemogenic feline leukemia virus (FeLV), FeLV-C-Sarma, from the productively infected human rhabdomyosarcoma cell line RD(FeLV-C-S). Molecularly cloned FeLV-C-S proviral DNA yielded infectious virus (mcFeLV-C-S) after transfection of mammalian cells, and virus interference studies using transfection-derived virus demonstrated that our clone encodes FeLV belonging to the C subgroup. mcFeLV-C-S did not induce viremia in eight 8-week-old outbred specific-pathogen-free (SPF) cats. It did, however, induce viremia and a rapid, fatal aplastic anemia due to profound suppression of erythroid stem cell growth in 9 of 10 inoculated newborn, SPF cats within 3 to 8 weeks (21 to 58 days) postinoculation. Thus, the genome of mcFeLV-C-S encodes the determinants responsible for the genetically dominant induction of irreversible erythroid aplasia in outbred cats. A potential clue to the pathogenic determinants of this virus comes from previous work indicating that all FeLV isolates belonging to the C subgroup, an envelop-gene-determined property, and only those belonging to the C subgroup, are potent, consistent inducers of aplastic anemia in cats. To approach the molecular mechanism underlying the induction of this disease, we first determined the nucleotide sequence of the envelope genes and 3' long terminal repeat of FeLV-C-S and compared it with that of FeLV-B-Gardner-Arnstein (mcFeLV-B-GA), a subgroup-B feline leukemia virus that consistently induces a different disease, myelodysplastic anemia, in neonatal SPF cats. Our analysis revealed that the p15E genes and long terminal repeats of the two FeLV strains are highly homologous, whereas there are major differences in the gp70 proteins, including five regions of significant amino acid differences and apparent sequence substitution. Some of these changes are also reflected in predicted glycosylation sites; the gp70 protein of FeLV-B-GA has 11 potential glycosylation sites, only 8 of which are present in FeLV-C-S.     

A putative thiamine transport protein is a receptor for feline leukemia virus subgroup A

Feline leukemia virus (FeLV) is a horizontally transmitted virus that causes a variety of proliferative and immunosuppressive diseases in cats. There are four subgroups of FeLV, A, B, C, and T, each of which has a distinct receptor requirement. The receptors for all but the FeLV-A subgroup have been defined previously. Here, we report the identification of the cellular receptor for FeLV-A, which is the most transmissible form of FeLV. The receptor cDNA was isolated using a gene transfer approach, which involved introducing sequences from a feline cell line permissive to FeLV-A into a murine cell line that was not permissive. The feline cDNA identified by this method was approximately 3.5 kb, and included an open reading frame predicted to encode a protein of 490 amino acids. This feline cDNA conferred susceptibility to FeLV-A when reintroduced into nonpermissive cells, but it did not render these cells permissive to any other FeLV subgroup. Moreover, these cells specifically bound FeLV-A-pseudotyped virus particles, indicating that the cDNA encodes a binding receptor for FeLV-A. The feline cDNA shares approximately 93% amino acid sequence identity with the human thiamine transport protein 1 (THTR1). The human THTR1 receptor was also functional as a receptor for FeLV-A, albeit with reduced efficiency compared to the feline orthologue. On the basis of these data, which strongly suggest the feline protein is the orthologue of human THTR1, we have named the feline receptor feTHTR1. Identification of this receptor will allow more detailed studies of the early events in FeLV transmission and may provide insights into FeLV pathogenesis.     

Exposure to disease agents in the endangered Iberian lynx (Lynx pardinus)

The Iberian lynx (Lynx pardinus) is the most endangered felid species in the world. Lynx populations have decreased dramatically in size and distribution in the last four decades, thus becoming increasingly vulnerable to catastrophic events such as epizooties. From 1989 to 2000, serum samples were obtained from 48 free-ranging lynx captured in the Doñana National Park (DNP, n?=?31) and mountains of Sierra Morena (SM, n?=?17) in southern Spain. Samples were tested for antibodies against Toxoplasma gondii, feline herpesvirus 1 (FHV-1), feline calicivirus (FCV), feline/canine parvovirus (FPV/CPV), feline coronavirus, feline immunodeficiency virus (FIV), feline leukaemia virus and canine distemper virus (CDV) and for FeLV p27 antigen, to document baseline exposure levels. Antibodies against T. gondii were detected in 44% of lynx, with a significantly greater prevalence in DNP (61%) than in SM (12%). In DNP, prevalence was significantly higher in adult (81%) than in juvenile and sub-adult (41%) lynx, but no such difference was observed in SM. Low prevalences (≤11%) of minimally positive titres were found for FHV-1, FCV and FPV/CPV. This, combined with the lack of evidence for exposure to CDV, FIV and FeLV, suggests that these lynx populations are naïve and might be vulnerable to a disease outbreak in the future. Because of the reduced size of lynx populations, the documented low level of genetic variation (particularly in the DNP population) coupled with the recently documented state of immune depletion in a majority of necropsied lynx, it is important to better understand the threat and potential impact that disease agents might pose for the conservation of this endangered species. Future surveillance programs must include possible disease reservoir hosts such as domestic cats and dogs and other wild carnivores.     

Feline Leukemia Virus-B Envelope Together With its GlycoGag and Human Immunodeficiency Virus-1 Nef Mediate Resistance to Feline SERINC5

Human SERINC5 (SER5) protein is a recently described restriction factor against human immunodeficiency virus-1 (HIV-1), which is antagonized by HIV-1 Nef protein. Other retroviral accessory proteins such as the glycosylated Gag (glycoGag) from the murine leukemia virus (MLV) can also antagonize SER5. In addition, some viruses escape SER5 restriction by expressing a SER5-insensitive envelope (Env) glycoprotein. Here, we studied the activity of human and feline SER5 on HIV-1 and on the two pathogenic retroviruses in cats, feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV). HIV-1 in absence of Nef is restricted by SER5 from domestic cats and protected by its Nef protein. The sensitivity of feline retroviruses FIV and FeLV to human and feline SER5 is considerably different: FIV is sensitive to feline and human SER5 and lacks an obvious mechanism to counteract SER5 activity, while FeLV is relatively resistant to SER5 inhibition. We speculated that similar to MLV, FeLV-A or FeLV-B express glycoGag proteins and investigated their function against human and feline SER5 in wild type and envelope deficient virus variants. We found that the endogenous FeLV recombinant virus, FeLV-B but not wild type exogenous FeLV-A envelope mediates a strong resistance against human and feline SER5. GlycoGag has an additional but moderate role to enhance viral infectivity in the presence of SER5 that seems to be dependent on the FeLV envelope. These findings may explain, why in vivo FeLV-B has a selective advantage and causes higher FeLV levels in infected cats compared to infections of FeLV-A only.     

Recombination between feline leukemia virus subgroup B or C and endogenous env elements alters the in vitro biological activities of the viruses.

An important question in feline leukemia virus (FeLV) pathogenesis is whether, as in murine leukemia virus infection, homologous recombination between the infecting FeLV and the noninfectious endogenous FeLV-like proviruses serves as a significant base for the generation of proximal pathogens. To begin an analysis of this issue, several recombinant FeLVs were produced by using two different approaches: (i) the regions of the viral envelope (env) gene of a cloned FeLV (subgroup B virus [FeLV-B], Gardner-Arnstein strain) and those of two different endogenous proviral loci were exchanged to create specific FeLV chimeras, and (ii) vectors containing endogenous env and molecularly cloned infectious FeLV-C (Sarma strain) DNA sequences were coexpressed by transfection in nonfeline cells to facilitate recombination. The results of these combined approaches showed that up to three-fourths of the envelope glycoprotein (gp70), beginning from the N-terminal end, could be replaced by endogenous FeLV sequences to produce biologically active chimeric FeLVs. The in vitro replication efficiency or cell tropism of the recombinants appeared to be influenced by the amount of gp70 sequences replaced by the endogenous partner as well as by the locus of origin of the endogenous sequences. Additionally, a characteristic biological effect, aggregation of feline T-lymphoma cells (3201B cell line), was found to be specifically induced by replicating FeLV-C or FeLV-C-based recombinants. Multiple crossover sites in the gp70 protein selected under the conditions used for coexpression were identified. The results of induced coexpression were also supported by rapid generation of FeLV recombinants when FeLV-C was used to infect the feline 3201B cell line that constitutively expresses high levels of endogenous FeLV-specific mRNAs. Furthermore, a large, highly conserved open reading frame in the pol gene of an endogenous FeLV provirus was identified. This observation, particularly in reference to our earlier finding of extensive mutations in the gag gene, reveals a target area for potentially productive homologous recombination upstream of the functional endogenous env gene.     

In Vivo Evolution of a Novel, Syncytium-Inducing and Cytopathic Feline Leukemia Virus Variant

Studies of feline leukemia virus (FeLV) have illustrated the importance of the genotype of the infecting virus in determining disease outcome. In FeLV infections, as in other retroviral infections, it is less clear how virus variants that evolve from the transmitted virus affect pathogenesis. We previously reported an analysis of the genotypic changes that occur in the viral envelope gene (env) in cats infected with a prototype transmissible FeLV clone, 61E (J. Rohn, M. Linenberger, E. Hoover, and J. Overbaugh, J. Virol. 68:2458–2467, 1994). In one cat, each variant (81T) had evolved, in addition to scattered amino acid changes, a four-amino-acid insertion with respect to 61E. This insertion was located at the same site in the extracellular envelope glycoprotein where the immunodeficiency-inducing molecular clone 61C possesses a six-amino-acid insertion critical for its pathogenic phenotype, although the sequences of the insertions were distinct. To determine whether acquisition of the four-amino-acid insertion was associated with a change in the replication or cytopathic properties of the virus, we constructed chimeras encoding 81T env genes in a 61E background. One representative chimeric virus, EET(TE)-109, was highly cytopathic despite the fact that it replicated with delayed kinetics in the feline T-cell line 3201 compared to the parental 61E virus. The phenotype of this virus was also novel compared to other FeLVs, including both the parental virus 61E and the immunodeficiency-inducing variant 61C, because infection of T cells was associated with syncytium formation. Moreover, in single-cycle infection assays, the 81T-109 envelope demonstrated receptor usage properties distinct from those of both 61E and 61C envelope. Thus, these studies demonstrate the evolution of a novel T-cell cytopathic and syncytium-inducing FeLV in the host. The 81T virus will be valuable for dissecting the mechanism of T-cell killing by cytopathic variants in the FeLV model.     

Viral infections in wild-living European wildcats in Slovenia

Prevalence of feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) was investigated in wild-living European wildcats (Felis silvestris) in Slovenia. Seventeen blood samples of 15 wildcats (13 males and two females, two recaptures—1 and 1.5 years after capture) were collected between August 1999 and April 2006. Wildcats were anesthetized using ketamine and medetomidine. Specific antibodies against FIV and FeLV antigens were detected using commercial virus antibody test kits or commercial antigen detection kits, respectively. All investigated sera were negative for presence of specific antibodies against FIV and all investigated animals were negative for presence of FeLV, showing that the highest expected prevalence of the diseases in the population is low. This contrasts with the data from the domestic cats, suggesting a low level of contact between both populations. Apart from addressing the obvious concerns about the impact of infectious diseases on a wild population, epidemiology can be a useful tool for detection of the level of contact in cases when introgression of genes of a common or domestic subspecies/variety might pose a problem for conservation of a threatened species/population.