Serological survey of Toxoplasma gondii,feline immunodeficiency virus and feline leukaemia virus in urban stray cats in Belgium

Three hundred and forty-six serum samples taken between 1998 and 2000 from urban stray cats in the city of Ghent were tested for antibodies to Toxoplasma gondii and feline immunodeficiency virus (FIV), and antigens of feline leukemia virus (FeLV). Of these 346 samples, 243 (70.2 per cent) were seropositive for Tgondii. Thirty-nine cats (11.3 per cent) had antibodies against FIV and 13 (3.8 per cent) had circulating antigens of FeLV. Fewer of the female cats had FIV and heavier cats had a higher seroprevalence of FIV. Exact logistic regression showed that cats that were infected with FIV were more likely to be infected with T gondii (P = 0.04), and the cats with FIV had a higher titre of Tgondii antibodies than FIV-negative animals. However, FeLV was not associated with either T gondii or FIV.     

Immunization-induced decrease of the CD4+:CD8+ ratio in cats experimentally infected with feline immunodeficiency virus.

In a previous experiment a group of 15 specified pathogen free (SPF) cats were experimentally infected with a Swiss isolate of feline immunodeficiency virus (FIV). A group of 15 SPF cats served as FIV negative controls. Nine cats of each group were vaccinated with a recombinant feline leukemia virus (FeLV) vaccine, six cats in each group with a placebo vaccine. All vaccinated cats developed high antibody titers to FeLV and were protected against subsequent FeLV challenge infection. In both control groups five of six cats became persistently infected with FeLV. Unexpectedly, the primary immune response to the vaccine antigen was significantly higher in the FIV positive group than in the FIV negative. The secondary response was stronger in the FIV negative cats. The goal of the present investigation was to further study the immune response in these 30 cats. They were immunized twice with the synthetic peptide L-tyrosine-L-glutamic acid-poly(DL-alanine)-poly(L-lysine) (TGAL) 21 days apart. Blood samples were collected on four occasions during the immunization process. They were tested for antibodies to TGAL, complete blood cell counts and CD4+, CD8+ and pan-T-lymphocyte counts. The following observations were made: (1) in contrast to the FeLV vaccine experiment, the primary immune response to TGAL was not significantly stronger in the FIV positive cats when tested by enzyme-linked immunosorbent assay (2). The absolute size of the CD4+ lymphocyte population was distinctly smaller in the FIV positive than in the FIV negative cats. The lowest CD4+ values were found in the dually FIV/FeLV infected cats. (3) A population of CD8+ lymphocytes was identified that was characterized by a distinctly weaker fluorescence. The size of this population increased in FIV positive and decreased in FIV negative cats during the TGAL immunization experiment. (4) The CD4+:CD8+ ratio increased in FIV negative cats during TGAL immunization from 1.9 to 2.3. In contrast, in FIV positive animals the CD4+:CD8+ ratio decreased significantly from 1.9 to 1.3 during the same period. From these and earlier data it was concluded that in short-term FIV infection the immune response to T-cell dependent antigens may be increased over that of the controls. Immune suppression develops gradually with duration of the infection. The significant drop of the CD4+:CD8+ ratio over a 5 week immunization period suggests that antigenic stimulation may accelerate the development of immune suppression in FIV positive cats. If this is a general feature, FIV infection may provide a particularly interesting model for studying the pathogenesis of AIDS.     

Efficacy and safety field trials of a recombinant DNA vaccine against feline leukemia virus infection.

A new recombinant gp70 vaccine was found to be safe and effective for prevention of infection by FeLV. The vaccine incorporates a unique purified saponin adjuvant with the recombinant antigen. Serious systemic reactions were not observed during the efficacy trial. Local reactions were transient and mild. More than 2,000 doses were administered to a cross section of household cats in a field safety trial. Only 1 cat had hypersensitivity reaction, which resolved. Among veterinarians who used the vaccine and the cat owners, the vaccine was judged satisfactory and safe. After rigorous intraperitoneal challenge exposure without use of immunosuppressants, 100% of the controls in the efficacy trial became infected, 70% of which remained persistently infected with FeLV. Among vaccinates, 45% were never viremic and 40% cleared transient infection within 12 weeks after challenge exposure. Of the 20 vaccinated cats, 3 were persistently infected. Overall, 85% of cats vaccinated with this recombinant DNA FeLV vaccine resisted persistent FeLV infection after stringent challenge exposure, which translates to preventable fraction of 78.6%.     

Evaluation of efficacy and safety of an inactivated virus vaccine against feline leukemia virus infection.

An inactivated virus vaccine was developed for prevention of FeLV infection in domestic cats. When given in 2 doses, 3 weeks apart, to cats that were greater than or equal to 9 weeks old at the time of first vaccination, the vaccine prevented persistent viremia from developing in 132 of 144 (92%) vaccinates after oronasal challenge exposure with virulent FeLV. In contrast, persistent viremia developed after oronasal challenge exposure with FeLV in 39 of 45 (87%) age-matched nonvaccinated control cats. Transient viremia, indicated by early detection of p27 by ELISA in serum of cats protected from persistent viremia at 12 weeks after challenge exposure, was found in 10 of 132 (8%) vaccinates. Cats that were aviremic 12 to 16 weeks after challenge exposure were examined for reactivation of latent FeLV infection; 4 weekly doses of methylprednisolone were administered, followed by in vitro culture of bone marrow cells. Latent infection was readily reactivated in 6 of 8 (75%) nonvaccinated control cats that had been transiently viremic after challenge exposure. However, latent infection was reactivated in only 5 of 48 (10%) protected vaccinates, and in none of 38 vaccinates in which transient viremia had not been detected. In a safety field trial, only 34 mild reactions of short duration were observed after administration of 2,379 doses of vaccine to cats of various ages, breeds, and vaccination history, for a 1.43% reaction rate. Results indicate that the aforementioned inactivated virus vaccine is safe and efficacious for the prevention of infection with FeLV.     

Tumor necrosis factor alpha levels in cats experimentally infected with feline immunodeficiency virus: effects of immunization and feline leukemia virus infection.

Tumor necrosis factor alpha (TNF alpha) levels were determined by enzyme-linked immunosorbent assay (ELISA) and by cell culture bioassay in supernatants of lipopolysaccharide-stimulated feline monocyte cultures and in cat serum samples. There was a good correlation between the results obtained by the two methods. From the fact that TNF alpha was neutralized quantitatively by antibodies to human TNF alpha in feline monocyte supernatants and in feline sera, it was concluded that feline TNF alpha immunologically cross-reacts with human TNF alpha and that the human TNF alpha ELISA can be used to quantitate feline TNF alpha. During the first 6 months after experimental feline immunodeficiency virus (FIV) infection no differences in serum TNF alpha values were observed between infected and non-infected cats. TNF alpha levels increased significantly after primary vaccination with a feline leukemia virus (FeLV) vaccine in FIV infected cats over those in the non-infected controls. During secondary immune response TNF alpha levels rose transiently for a period of a few days in both the FIV positive and the FIV negative cats. After FeLV challenge, TNF alpha levels increased in all animals challenged with virulent FeLV for a period of 3 weeks. This period corresponded to the time necessary to develop persistent FeLV viremia in the control cats. It was concluded from these experiments that in the asymptomatic phase of FIV infection no increased levels of TNF alpha are present, similar to the situation in asymptomatic HIV infected humans. Activation of monocytes/macrophages in FIV infected cats by stimuli such as vaccination or FeLV challenge readily leads to increased levels of TNF alpha.     

Enhancement after feline immunodeficiency virus vaccination.

Cats were vaccinated with one of the three preparations: purified feline immunodeficiency virus (FIV) incorporated into immune stimulating complexes (ISCOMs), recombinant FIV p24 ISCOMs, or a fixed, inactivated cell vaccine in quil A. Cats inoculated with the FIV ISCOMs or the recombinant p24 ISCOMs developed high titres of antibodies against the core protein p24 but had no detectable antibodies against the env protein gp120 or virus neutralising antibodies. In contrast, all of the cats inoculated with the fixed, inactivated cell vaccine developed anti-env antibodies and four of five had detectable levels of neutralising antibody. However, none of the vaccinated cats were protected from infection after intraperitoneal challenge with 20 infectious units of FIV. Indeed there appeared to be enhancement of infection after vaccination as the vaccinated cats become viraemic sooner than the unvaccinated controls, and 100% of the vaccinated cats became viraemic compared with 78% of the controls. The mechanism responsible for this enhancement remains unknown.     

Prevalence of feline leukaemia virus and antibodies to feline immunodeficiency virus in cats in the United Kingdom

A representative sample of the pet cat population of the United Kingdom was surveyed. Blood samples from 1204 sick and 1007 healthy cats of known breed, age and sex were tested for antibodies to feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV). The prevalence of FIV was 19 per cent in sick cats and 6 per cent in healthy cats, and the prevalence of FeLV was 18 per cent in sick cats and 5 per cent in healthy cats; both infections were more common in domestic cats than in pedigree cats. Feline immunodeficiency virus was more prevalent in older cats but FeLV was more prevalent in younger cats. There was no difference between the prevalence of FeLV in male and female cats but male cats were more likely to be infected with FIV than female cats. No interaction was demonstrated between FIV and FeLV infections. Of the cats which were in contact with FIV in households with more than one cat, 21 per cent had seroconverted. The prevalence of FeLV viraemia in cats in contact with FeLV was 14 per cent. The clinical signs associated with FIV were pyrexia, gingivitis/stomatitis and respiratory signs, and with FeLV, pyrexia and anaemia. It was concluded that both viruses were significant causes of disease, and that the cats most likely to be infected with FIV were older, free-roaming male cats and for FeLV, younger, free-roaming cats.     

Therapeutic effects of recombinant feline interferon-omega on feline leukemia virus (FeLV)-infected and FeLV/feline immunodeficiency virus (FIV)-coinfected symptomatic cats

The clinical efficacy of a recombinant feline interferon, rFeIFN-omega, was evaluated for the treatment of cats presented with clinical signs associated with feline leukemia virus (FeLV) infection and FeLV/feline immunodeficiency virus (FIV) coinfection in the field. In this multicentric, double-blind, placebo-controlled trial, 81 cats meeting the inclusion criteria were randomly placed into 2 groups and treated subcutaneously with rFelFN-omega (1 million [M]U/kg per day) or placebo once daily for 5 consecutive days in 3 series (day 0, 14, 60). The cats were monitored for up to 1 year for clinical signs and mortality. During the initial 4-month period, interferon (IFN)-treated cats (n = 39) had significantly reduced clinical scores compared with placebo (n = 42), with all cats having received concomitant supportive therapies. Compared with the control, the IFN-treated group showed significantly lower rates of mortality: 39% versus 59% (1.7-fold higher risk of death for controls) at the 9-month time point and 47% versus 59% (1.4-fold higher risk of death for controls) at the 12-month time point. The IFN treatment was associated with minor but consistent improvement in abnormal hematologic parameters (red blood cell count, packed cell volume, and white blood cell count), apparently underlying the positive effects of IFN on clinical parameters. These data demonstrate that rFeIFN-omega initially has statistically significant therapeutic effects on clinical signs and later on survival of cats with clinical signs associated with FeLV infection and FeLV/FIV coinfection.     

No evidence of vertical transmission of naturally acquired feline immunodeficiency virus infection.

A naturally occurring feline immunodeficiency virus (FIV) infection in a closed breeding colony of cats, was studied for a period of 9 months. The colony consisted of 25 adult cats, of which six proved to be infected with FIV as judged by serological examination and virus isolation. In all, 48 kittens were monitored for levels of antibodies against FIV during their first 6 months of life. All the kittens (n = 30) born of FIV-infected queens showed maternal antibodies against FIV, although these declined to undetectable levels by the age of 5 months. Antibodies against FIV were not shown in any of 18 kittens born of FIV-negative queens. An attempt to isolate the virus from 12 kittens between 2 and 6 weeks of age did not succeed. None of the cats in the colony seroconverted during the observation period. In conclusion, neither vertical nor horizontal transmission of FIV infection were demonstrated in the colony during the 9-month investigation period.     

Protection against feline leukemia virus challenge for at least 2 years after vaccination with an inactivated feline leukemia virus vaccine

Twelve cats were vaccinated at 8 and 11 weeks of age with a commercially available inactivated FeLV vaccine (Nobivac FeLV, Intervet/Schering-Plough Animal Health). Eleven cats served as age-matched, placebo-vaccinated controls. All cats were kept in isolation for 2 years after vaccination and were then challenged with virulent FeLV to evaluate vaccine efficacy and duration of immunity. Cats were monitored for 12 weeks after challenge for development of persistent viremia using a commercial FeLV p27 ELISA. Persistent viremia developed in all 11 (100%) of the control cats, whereas 10 of 12 (83%) vaccinated cats were fully protected from persistent viremia following challenge. The results demonstrate that the vaccine used in this study protects cats from persistent FeLV viremia for at least 2 years after vaccination.     

Plasma electrophoretogram in feline immunodeficiency virus (FIV) and/or feline leukaemia virus (FeLV) infections

The electrophoretogram of 89 cats, including those infected by feline immunodeficiency virus (FIV+), feline leukaemia virus (FeLV+) and non-infected, showed statistically significant differences in several of the fractions. FIV+ cats had very high protein values (mean, 8.10 g/dl), mostly because of hypergammaglobulinemia (mean, 2.81 g/dl) as compared with non-infected animals and FeLV+. In addition, in these FIV+ animals, the albumin/globulins ratio (A/G) was very low (mean, 0.72). Statistically significant differences in A/G and alpha2-globulin fraction were observed in FeLV+ group (A/G mean, 0.88 +/- 0.08; alpha2-globulin, mean, 0.84 +/- 0.07 g/dl) when compared with non-infected group (A/G mean, 1.06 +/- 0.08; alpha2-globulin mean, 0.68 +/- 0.04 g/dl). The alpha1-globulin fraction was higher in double infected animals (FIV and FeLV positive, F-F) (3.55 g/dl), than in FeLV+ or FIV+ cats (3.10 and 3.07 g/dl respectively), but no statistical conclusions may be drawn from this fact because of the low number of F-F animals. This technique may help to assess the initial clinical status of retrovirus-infected cats, and the clinical course of these chronic diseases, specifically during and after suitable therapy.     

Altered plasma concentrations of sex hormones in cats infected by feline immunodeficiency virus or feline leukemia virus

Gender differences may affect human immunodeficiency virus (HIV) infection in humans and may be related to fluctuations in sex hormone concentration. The different percentage of male and female cats observed to be infected by feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) has been traditionally explained through the transmission mechanisms of both viruses. However, sexual hormones may also play a role in this different distribution. To study this possibility, 17β-estradiol, progesterone, testosterone, and dehydroepiandrosterone (DHEA) concentrations were analyzed using a competitive enzyme immunoassay in the plasma of 258 cats naturally infected by FIV (FIV(+)), FeLV (FeLV(+)), or FeLV and FIV (F(-)F(+)) or negative for both viruses, including both sick and clinically healthy animals. Results indicated that the concentrations of 17β-estradiol and testosterone were significantly higher in animals infected with FIV or FeLV (P < 0.05) than in negative cats. Plasma concentrations of DHEA in cats infected by either retrovirus were lower than in negative animals (P < 0.05), and F(-)F(+) cats had significantly lower plasma values than monoinfected cats (P < 0.05). No significant differences were detected in the plasma concentration of progesterone of the four groups. No relevant differences were detected in the hormone concentrations between animal genders, except that FIV(+) females had higher DHEA concentrations than the corresponding males (P < 0.05). In addition, no differences were observed in the hormone concentrations between retrovirus-infected and noninfected animals with and without clinical signs. These results suggest that FIV and FeLV infections are associated with an important deregulation of steroids, possibly from early in the infection process, which might have decisive consequences for disease progression.     

Protection from challenge following administration of a canarypox virus-vectored recombinant feline leukemia virus vaccine in cats previously vaccinated with a killed virus vaccine

OBJECTIVE: To compare protection against FeLV challenge obtained following administration of 2 doses of an adjuvanted, chemically inactivated, whole FeLV (FeLV-k) vaccine with protection obtained following administration of 1 dose of an FeLV-k vaccine followed by 1 dose of a canarypox virus-vectored recombinant FeLV (rCP-FeLV) vaccine. DESIGN: Prospective study. ANIMALS: Thirty-two 9-week-old domestic shorthair cats. PROCEDURE: Cats received 2 doses of the FeLV-k vaccine SC, 21 days apart (n = 11); 1 dose of the FeLV-k vaccine SC and, 21 days later, 1 dose of the rCP-FeLV vaccine transdermally (11); or 2 doses of physiologic saline (0.9% NaCl) solution (control; 10). Four weeks after the second vaccine dose, all cats were challenged with FeLV by means of oronasal administration. Blood samples were collected at weekly intervals beginning 21 days after challenge, and serum was tested for FeLV antigen. RESULTS: All 10 control cats became persistently infected (ie, FeLV antigen detected in > or = 3 consecutive serum samples) following FeLV challenge, whereas only 1 of 11 cats that received 2 doses of the FeLV-k vaccine and none of the 11 cats that received 1 dose of the FeLV-k vaccine and 1 dose of the rCP-FeLV vaccine did. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that protection against FeLV challenge obtained following SC administration of a single dose of an FeLV-k vaccine followed, 21 days later, by transdermal administration of a single dose of an rCP-FeLV vaccine was similar to that obtained following SC administration of 2 doses of the FeLV-k vaccine 21 days apart.     

Protection against feline leukemia virus infection by use of an inactivated virus vaccine.

The protective immunity induced by 3 experimental FeLV vaccines were evaluated: Prototype inactivated FeLV vaccine developed from a molecularly cloned FeLV isolate (FeLV-FAIDS-61E-A); a mixture of immunodominant synthetic peptides corresponding to regions of the FeLV-Gardner-Arnstein-B (FeLV-GA-B) envelope proteins; and an adjuvant-disrupted but non-activated virus prepared from a non-cloned FeLV field isolate comprised of subgroup A and B viruses (FeLV-05821-AB). Included as controls were parallel groups of cats inoculated with adjuvants alone or with an established commercial FeLV vaccine. After each inoculation and after virulent virus challenge exposure, sera from all cats were assayed for ELISA-reactive antibody against purified FeLV, FeLV neutralizing (VN) antibody, and FeLV antigenemia/viremia--viral p27 antigen in serum and within circulating leukocytes. Immunity was challenged by oral/nasal exposure of vaccinated and control cats with FeLV-FAIDS-61E-A or FeLV-05821-AB, an infective, noncloned, tissue-origin, FeLV field isolate containing subgroup-A and -B viruses. Vaccine-induced immunity was assessed by comparing the postchallenge-exposure incidence of persistent viremia and the pre- and postchallenge exposure titers of VN and ELISA antibody in cats of the control and vaccine groups. The percentage of cats, that resisted development of persistent viremia after FeLV challenge exposure and the preventable fraction (PF) for the vaccine groups (which adjusts for the severity of the challenge and the degree of innate resistance in the controls) were as follows: adjuvant controls, 26%; FeLV-FAIDS-61E-A inactivated virus vaccine, 95% (PF = 93.2%); FeLV-GA-B peptide vaccine, 5% (-28.4%); FeLV-05821-AB noninactivated vaccine, 67% (55.4%); and commercial FeLV vaccine, 35% (12.2%). The prechallenge exposure mean VN antibody titer for each group was: less than 1:8 in the adjuvant controls; 1:43 in the FeLV-FAIDS-61E-A-vaccinated cats; less than 1:8 in the peptide-vaccinated cats; 1:38 in the noninactivated virus-vaccinated cats group; and 1:12 in the cats vaccinated with the commercial vaccine. Thus, induction of VN antibody in the vaccinated cats, although modest, appeared to be correlated with induction of protective immunity as defined by resistance to FeLV challenge exposure. Results of these studies indicate that inoculation of cats with an experimental inactivated virus vaccine prepared from a molecularly cloned FeLV isolate was most effective in stimulating protective immunity against heterologous and homologous FeLV challenge exposure.     

Detection of feline immunodeficiency virus infection in bone marrow of cats.

Natural or experimental feline immunodeficiency virus (FIV) infection in cats is often associated with hematologic abnormalities which are similar to those observed in human immunodeficiency virus (HIV) infected patients. To determine if cells in bone marrow are infected with FIV and whether severity of hematopoietic disorder is correlated with the level of viral infection, bone marrow tissues from ten experimentally and two naturally FIV infected cats were examined by in situ hybridization for presence of FIV RNA. Seven of the 12 FIV infected cats were also naturally or experimentally coinfected with feline leukemia virus (FeLV). FIV RNA was detected mainly in megakaryocytes and unidentified mononuclear cells in the bone marrow of cats that were sick and had marrow hypercellularity and immaturity. These included all cats in the acute phase of FIV infection and two of seven long term FIV infected cats. One long term FIV infected cat with lymphosarcoma was also positive for FIV RNA in bone marrow cells. The other four long term FIV infected cats were relatively healthy, with normal bone marrow morphology, and were negative for FIV infected cells. Bone marrow from three non-infected and two cats infected with FeLV alone were also negative for FIV RNA by in situ hybridization. We concluded that megakaryocytes and mononuclear cells were targets of the viral infection and that the presence of FIV RNA in cells of the bone marrow correlated with marrow hypercellularity and immaturity, and severity of illness.     

Efficacy and safety of a feline immunodeficiency virus vaccine

Fel-O-Vax FIV is an inactivated virus vaccine designed as an aid in the prevention of infection of cats, 8 weeks or older, by feline immunodeficiency virus (FIV). It contains two genetically distinct FIV strains. The efficacy of this vaccine was demonstrated in a vaccination-challenge study designed to meet various regulatory requirements for registering the vaccine. Eight-week-old kittens were vaccinated with an immunogenicity vaccine which contained minimal release levels of FIV antigens formulated with a proprietary adjuvant system. Twelve months later, all vaccinates and controls were challenged with a heterologous FIV strain. Following the vigorous challenge exposure, cats were monitored for FIV viremia. It was found that 16% of the vaccinated cats developed viremia while 90% of the controls became persistently infected with FIV, which demonstrated that the vaccine was efficacious and the protective immunity lasted for at least 12 months. The safety of the vaccine was demonstrated by a field safety trial in which only 22 mild reactions of short duration were observed following administering 2051 doses of two pre-licensing serials of Fel-O-Vax FIV to cats of various breeds, ages and vaccination histories. Thus, Fel-O-Vax FIV is safe and efficacious for the prevention of FIV infection in cats.     

Feline leukaemia virus (FeLV) and feline immunodeficiency virus infections in cats in the Pisa district of Tuscany, and attempts to control FeLV infection in a colony of domestic cats by vaccination

The seroprevalence of feline immunodeficiency virus (FIV) in 203 apparently healthy domestic cats living in the district of Pisa, central Italy, was 11.3 per cent, and the prevalence of feline leukaemia virus (FeLV) was 8.4 per cent. The prevalence of FIV depended significantly on the lifestyle and age of the cats; cats living outdoors were more likely to be FIV-positive than cats living indoors, and the proportion of FIV-positive cats increased with age. In contrast, there was no significant relationship between these variables and the prevalence of FeLV. There was no significant relationship between the cats' seropositivity for FIV and FeLV. The results of a five-year field study to control FeLV infection by vaccination in a colony of 30 domestic adult cats naturally exposed to the infection suggest that the vaccination was effective in FIV-negative cats, but failed to protect FIV-positive cats against FeLV.     

Comparison of T-cell subpopulations in cats naturally infected with feline leukaemia virus or feline immunodeficiency virus

T-cell subsets were studied by flow cytometry in 58 feline leukaemia virus (FeLV)-positive cats with naturally acquired FeLV infection to determine whether the changes in CD4⁺ or CD8⁺ T cell populations differed from those observed in 55 feline immunodeficiency virus (FIV)-positive cats with naturally acquired FIV infection. The sole criterion for inclusion into the study was seropositivity. Mean (SD) CD4⁺ T cell values of FeLV positive cats were decreased to 31·1 (8·0) per cent and their CD8⁺ T cell values were increased to 22·8 (6·3) per cent in comparison with uninfected control cats (37·9 [9·5] per cent CD4⁺; 15·2 [6·3] per cent CD8⁺). The CD4⁺/CD8⁺ ratio was reduced to 1·5 (0·7), compared with 3·0 (1·5) in 39 FeLv- and FIV-negative control cats. Differences from control values were significant, but there was no significant difference between CD4⁺ and CD8⁺ lymphocytes of FeLV- versus FIV-infected cats. These findings indicate that FeLv and FIV have similar effects on T lymphocyte subsets. Both retrovirus infections can induce immunodeficiency, both viruses infect a broad range of lymphohaemopoietic cells, despite having different primary target cells, and can induce the killing of lymphocytic cells in vitro. It is concluded that a decreased CD4⁺/CD8⁺ ratio is not restricted to FIV infections but may also occur in FeLv infection.     

Diagnosing feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infection: an update for clinicians

With the commercial release in Australia in 2004 of a vaccine against feline immunodeficiency virus (FIV; Fel‐O‐Vax FIV®), the landscape for FIV diagnostics shifted substantially. Point‐of‐care (PoC) antibody detection kits, which had been the mainstay for diagnosing FIV infection since the early 1990s, were no longer considered accurate to use in FIV‐vaccinated cats, because of the production of vaccine‐induced antibodies that were considered indistinguishable from those produced in natural FIV infections. Consequently, attention shifted to alternative diagnostic methods such as nucleic acid detection. However, over the past 5 years we have published a series of studies emphasising that FIV PoC test kits vary in their methodology, resulting in differing accuracy in FIV‐vaccinated cats. Importantly, we demonstrated that two commercially available FIV antibody test kits (Witness? and Anigen Rapid?) were able to accurately distinguish between FIV‐vaccinated and FIV‐infected cats, concluding that testing with either kit offers an alternative to PCR testing. This review summarises pertinent findings from our work published in a variety of peer‐reviewed research journals to inform veterinarians (particularly veterinarians in Australia, New Zealand and Japan, where the FIV vaccine is currently commercially available) about how the approach to the diagnosis of FIV infection has shifted. Included in this review is our work investigating the performance of three commercially available FIV PoC test kits in FIV‐vaccinated cats and our recommendations for the diagnosis of FIV infection; the effect of primary FIV vaccination (three FIV vaccines, 4 weeks apart) on PoC test kit performance; our recommendations regarding annual testing of FIV‐vaccinated cats to detect ‘vaccine breakthroughs’; and the potential off‐label use of saliva for the diagnosis of FIV infection using some FIV PoC test kits. We also investigated the accuracy of the same three brands of test kits for feline leukaemia virus (FeLV) diagnosis, using both blood and saliva as diagnostic specimens. Based on these results, we discuss our recommendations for confirmatory testing when veterinarians are presented with a positive FeLV PoC test kit result. Finally, we conclude with our results from the largest and most recent FIV and FeLV seroprevalence study conducted in Australia to date.     

Long-term impact on a closed household of pet cats of natural infection with feline coronavirus, feline leukaemia virus and feline immunodeficiency virus

A closed household of 26 cats in which feline coronavirus (FCoV), feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) were endemic was observed for 10 years. Each cat was seropositive for FCoV on at least one occasion and the infection was maintained by reinfection. After 10 years, three of six surviving cats were still seropositive. Only one cat, which was also infected with FIV, developed feline infectious peritonitis (FIP). Rising anti-FCoV antibody titres did not indicate that the cat would develop FIP. The FeLV infection was self-limiting because all seven of the initially viraemic cats died within five years and the remainder were immune. However, FeLV had the greatest impact on mortality. Nine cats were initially FIV-positive and six more cats became infected during the course of the study, without evidence of having been bitten. The FIV infection did not adversely affect the cats' life expectancy.