Comparison of six in-house tests for the rapid diagnosis of feline immunodeficiency and feline leukaemia virus infections

Epidemiology of Pathogenic Retroviruses and Domestic Cat Hepadnavirus in Community and Client-Owned Cats in Hong Kong

Understanding the local epidemiology of feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) in Hong Kong will inform retrovirus prevention strategies. Domestic cat hepadnavirus (DCH), a novel hepatitis-B-like virus, is commonly detected among client-owned cats in Hong Kong, but community cats have not been studied. The aims of this study were to investigate the frequency and potential risk factors for (i) FeLV and FIV among community and client-owned cats and (ii) perform molecular detection of DCH among community cats in Hong Kong. Blood samples from 713 cats were obtained from client-owned (n = 415, residual diagnostic) and community cats (n = 298, at trap-neuter-return). Point-of-care (POC) testing for FeLV antigen and feline immunodeficiency virus (FIV) anti-p15 and p24 antibodies was performed. FeLV-positive samples were progressed to p27 sandwich enzyme-linked immunosorbent assay. Whole blood DNA was tested with qPCRs for FeLV U3 and gag, and nested PCRs where additional information was required. DCH qPCR was performed on a subset of community cats (n = 193). A single, regressive, FeLV infection was detected in a client-owned cat (1/415 FeLV U3 qPCR positive, 0.2%, 95% CI 0.0-1.3%). Five/415 client-owned cats tested presumably false FeLV-antigen positive (qPCR negative). No markers of FeLV infection were detected in community cats (0/298; 0%). FIV seroprevalence was much higher in community cats (46/298, 15.4%) than in client-owned cats (13/415, 3.1%) (p < 0.001). Mixed breed was a risk factor for FIV infection in client-owned cats. Neither sex nor age were associated with FIV infection. DCH DNA was detected in 34/193 (17.6%) community cats (median viral load 6.32 × 103 copies/reaction). FeLV infection is rare in Hong Kong, negatively impacting the positive predictive value of diagnostic tests. FeLV-antigen testing remains the screening test of choice, but confirmation of a positive result using FeLV qPCR is essential. FIV infection is common in community cats and the absence of a sex predisposition, seen previously in cats managed similarly, raises questions about virus-transmission dynamics in these groups. DCH infection is very common in Hong Kong, both in client-owned and community cats, highlighting the importance of understanding the pathogenic potential of this virus for cats.

Diagnostic Accuracy of a Point-of-Care Immunoassay for Feline Immunodeficiency Virus Antibodies, Feline Leukemia Virus Antigen, and Dirofilaria immitis Antigen

Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are retroviral infections of cats worldwide whose clinical manifestations range from mild to severe disease. In both cases, infected cats can live a long life with proper care and should be managed to prevent infection of other cats. Dirofilaria immitis, the nematode that causes heartworm disease, can infect cats in any region where dogs are infected. Though cats are more resistant to infection, clinical diseases in the form of heartworm-associated respiratory disease can cause death. Screening for these infectious diseases enables veterinarians to manage their cases and prevent the spread to other cats. We describe the diagnostic accuracy of a point-of-care immunoassay for FIV, FeLV, and heartworm, compared to reference methods commonly available through reference laboratories to the practicing veterinarian. For FIV, we report 100% sensitivity (95% confidence limits (CL): 96.2-100%) and 97.8% specificity (95% CL: 95.4-99.4%). For FeLV, we report 100% sensitivity (95% CL: 97.7-100%) and 99.2% specificity (95% CL: 97.1-99.9%). And for heartworm, we report 90.2% sensitivity (95% CL: 76.9-97.3%) and 100% specificity (95% CL: 98.3-100%). Veterinarians may expect this performance relative to the reference methods they use for confirmatory serological testing.

Prevalence of Infection of Canine Distemper Virus, Feline Immunodeficiency Virus, and Feline Leukemia Virus in Wild Ecuadorian Ocelots; Efficacy of Their Diagnosis, and Recovery from Infection

This retrospective study provides an analysis of the prevalence and detectability of canine distemper virus (CDV), feline leukemia virus (FeLV), and feline immunodeficiency virus (FIV) in ocelots (Leopardus pardalis) sheltered in a wild animal recovery center in Guayaquil, Ecuador. Blood samples of 19 rescued ocelots from 2019-20 were analyzed using FeLV p27 antigen enzyme-linked immunosorbent assays (ELISA) and commercial insulated isothermal reverse transcriptase PCR (iiRT-PCR) kits. Using this PCR we detected positive results for CDV (4/ 17; 23.5%) and FeLV (14/16; 87.5%), but not for FIV (0/8). Three previously positive cases of CDV and two of FeLV showed negative results on retesting 6 mo later. Moreover, a third analysis was conducted and was negative for CDV. Our results suggest that ocelots can recover from the local CDV and FeLV strains. An ELISA for the FeLV p27 antigen showed no capability to detect FeLV in ocelots that were confirmed positive by iiRT-PCR. Regional lineages, viral virulence, and host immune response capabilities should be addressed in further research to inform management and decision making for wildlife conservation.

[Feline leukemia virus infection - a guide to diagnosis]

Feline leukemia virus (FeLV) infection affects cats worldwide. The course of FeLV infection can change and vary over time. The complex pathogenesis, the availability of many different testing methods, and the interpretation of test results are often challenging for veterinarians. Cats with progressive infection (persistently p27 antigen-positive) shed FeLV mainly through saliva and are therefore considered a source of infection for uninfected cats. Diagnosing regressive infection is often challenging, since it usually cannot be detected by commonly used point of care-tests (p27 antigen test) and thus, it often remains undetected. Nevertheless, cats with regressive infection are FeLV carriers (provirus-positive) and when the immune system is suppressed, reactivation of the infection and FeLV-associated clinical signs can occur. Abortively infected cats are never viraemic, do not shed virus, and do not develop clinical signs. Abortive infection can solely be diagnosed via antibodies detection in blood. A new point-of-care test for the identification of antibodies against FeLV p15E antigen has recently been introduced on the European market and is currently being evaluated.

Feline leukaemia virus infection: A practical approach to diagnosis

PRACTICAL RELEVANCE

Feline leukaemia virus (FeLV) is a retrovirus of domestic cats worldwide. Cats lacking strong FeLV-specific immunity and undergoing progressive infection commonly develop fatal FeLV-associated disease. Many aspects of FeLV infection pathogenesis have been elucidated, some during more recent years using molecular techniques. It is recommended that the FeLV status of every cat is known, since FeLV infection can influence the prognosis and clinical management of every sick cat. Moreover, knowledge of a cat's FeLV status is of epidemiological importance to prevent further spread of the infection.

CLINICAL CHALLENGES

Diagnosing FeLV infection remains challenging due to different outcomes of infection, which can vary over time depending on the balance between the virus and the host's immune system. Furthermore, testing for FeLV infection has become more refined over the years and now includes diagnostic assays for different viral and immunological parameters. Knowledge of FeLV infection pathogenesis, as well as the particulars of FeLV detection methods, is an important prerequisite for correct interpretation of any test results and accurate determination of a cat's FeLV status.

AIMS

The current review presents recent knowledge on FeLV pathogenesis, key features to be determined in FeLV infection, and frequently used FeLV detection methods, and their characteristics and interpretation. An algorithm for the diagnosis of FeLV infection in a single cat, developed by the European Advisory Board on Cat Diseases, is included, and FeLV testing in specific situations is addressed. As well as increasing awareness of this deadly infection in domestic cats, the aim is to contribute diagnostic expertise to allow veterinarians in practice to improve their recognition, and further reduce the prevalence, of FeLV infection.

Molecular Detection of Feline Leukemia Virus in Oral, Conjunctival, and Rectal Mucosae Provides Results Comparable to Detection in Blood

Feline leukemia virus (FeLV) infection causes immunosuppression, degeneration of the hematopoietic system, and fatal neoplasms. FeLV transmission occurs mainly by close social contact of infected and susceptible cats. Developing procedures for the diagnosis of feline retroviruses is crucial to reduce negative impacts on cat health and increase the number of animals tested. Blood collection requires physical or chemical restraint and is usually a stressful procedure for cats. Our objective was to evaluate the use of samples obtained from oral, conjunctival, and rectal mucosae for the molecular diagnosis of FeLV. Whole blood and oral, conjunctival, and rectal swabs were collected from a total of 145 cats. All samples were subjected to the amplification of a fragment of the gag gene of proviral DNA. Compared to blood samples used in this study as a reference, the accuracies for each PCR were 91.72, 91.23, and 85.50% for samples obtained by oral, conjunctival, and rectal swabs, respectively. The diagnostic sensitivity and specificity were 86.11 and 97.26% for the oral swabs, 90 and 92.59% for the conjunctival swabs, and 74.24 and 95.77% for the rectal swabs, respectively. The kappa values for oral, conjunctival, and rectal swabs were 0.834, 0.824, and 0.705, respectively. The diagnosis of these samples showed the presence of proviral DNA of FeLV in oral and conjunctival mucosae. In conclusion, mucosal samples for the molecular diagnosis of FeLV are an excellent alternative to venipuncture and can be safely used. It is faster, less laborious, less expensive, and well received by the animal.

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

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

Performance of 4 Point-of-Care Screening Tests for Feline Leukemia Virus and Feline Immunodeficiency Virus

Background

More than 3 million cats in the United States are infected with FeLV or FIV. The cornerstone of control is identification and segregation of infected cats.

Hypothesis/Objectives

To compare test performance with well‐characterized clinical samples of currently available FeLV antigen/FIV antibody combination test kits.

Animals

Surplus serum and plasma from diagnostic samples submitted by animal shelters, diagnostic laboratories, veterinary clinics, and cat research colonies. None of the cats had been vaccinated against FIV. The final sample set included 146 FeLV+, 154 FeLV−, 94 FIV+, and 97 FIV− samples.

Methods

Prospective, blind comparison to a gold standard: Samples were evaluated in 4 different point‐of‐care tests by ELISA antigen plate tests (FeLV) and virus isolation (FIV) as the reference standards. All test results were visually read by 2 blinded observers.

Results

Sensitivity and specificity, respectively, for FeLV were SNAP^® (100%/100%), WITNESS^® (89.0%/95.5%), Anigen^® (91.8%/95.5%), and VetScan^® (85.6%/85.7%). Sensitivity and specificity for FIV were SNAP^® (97.9%/99.0%), WITNESS^® (94.7%/100%), Anigen^® (96.8%/99.0%), and VetScan^® (91.5%/99.0%).

Conclusions and Clinical Importance

The SNAP^® test had the best performance for FeLV, but there were no significant differences for FIV. In typical cat populations with seroprevalence of 1–5%, a majority of positive results reported by most point‐of‐care test devices would be false‐positives. This could result in unnecessary segregation or even euthanasia.

Opportunities and challenges for the application of microfluidic technologies in point-of-care veterinary diagnostics

There is a growing need for low-cost, rapid and reliable diagnostic results in veterinary medicine. Point-of-care (POC) tests have tremendous advantages over existing laboratory-based tests, due to their intrinsic low-cost and rapidity. A considerable number of POC tests are presently available, mostly in dipstick or lateral flow formats, allowing cost-effective and decentralised diagnosis of a wide range of infectious diseases and public health related threats. Although, extremely useful, these tests come with some limitations. Recent advances in the field of microfluidics have brought about new and exciting opportunities for human health diagnostics, and there is now great potential for these new technologies to be applied in the field of veterinary diagnostics. This review appraises currently available POC tests in veterinary medicine, taking into consideration their usefulness and limitations, whilst exploring possible applications for new and emerging technologies, in order to widen and improve the range of POC tests available.

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.

A survey of feline leukaemia virus antigenaemia among cats in eastern Austria: a retrospective analysis of serum samples routinely tested between 1996 and 2011

Objectives

The aim of this retrospective analysis was to determine the seroprevalence of feline leukaemia virus (FeLV) antigenaemia among owned cats in Vienna and the surrounding area.

Methods

Samples were tested between 1996 and 2011 by the Department of Clinical Virology at the University of Veterinary Medicine, Vienna, Austria. All samples were sent to the university as part of routine diagnostic procedures, either to determine infection in clinically symptomatic individuals or to rule out infection prior to vaccination. To allow for statistical comparison, samples analysed between 2008 and 2011 were pooled into one population (n = 444) and evaluated against samples tested in 1996 (n = 840). Furthermore, analyses of subgroups were undertaken to determine the effect of sex and age on the prevalence of FeLV antigenaemia.

Results

With respect to the samples tested at the University of Veterinary Medicine in Vienna, it was determined that the level of FeLV antigenaemia in eastern Austria between 1996 and 2011 was 5.6%. The proportion of FeLV antigenaemic cats was highly variable and has not fallen significantly over this period, despite advances in vaccination, and the education of pet owners and animal welfare charities.

Conclusions and relevance

This study confirms the importance of continued and regular vaccination against FeLV among Austrian cats, particularly those allowed access to the outdoors. Within the remit of this retrospective study, it was not possible to follow-up results of repeat testing or of other assays (PCR) of individual cats. As a result of this, no conclusions can be drawn as to the possibility of transient antigenaemic cats or false-positive enzyme-linked immunosorbent assay results.

Development and clinical evaluation of a rapid diagnostic kit for feline leukemia virus infection

Feline leukemia virus (FeLV) causes a range of neoplastic and degenerative diseases in cats. To obtain a more sensitive and convenient diagnosis of the disease, we prepared monoclonal antibodies specific for the FeLV p27 to develop a rapid diagnostic test with enhanced sensitivity and specificity. Among these antibodies, we identified two clones (hybridomas 8F8B5 and 8G7D1) that specifically bound to FeLV and were very suitable for a diagnostic kit. The affinity constants for 8F8B5 and 8G7D1 were 0.35 × 10⁹ and 0.86 × 10⁹, respectively. To investigate the diagnostic abilities of the rapid kit using these antibodies, we performed several clinical studies. Assessment of analytical sensitivity revealed that the detection threshold of the rapid diagnostic test was 2 ng/mL for recombinant p27 and 12.5 × 10⁴ IU/mL for FeLV. When evaluating 252 cat sera samples, the kit was found to have a kappa value of 0.88 compared to polymerase chain reaction (PCR), indicating a significant correlation between data from the rapid diagnostic test and PCR. Sensitivity and specificity of the kit were 95.2% (20/21) and 98.5% (257/261), respectively. Our results demonstrated that the rapid diagnostic test would be a suitable diagnostic tool for the rapid detection of FeLV infection in cats.

Survey of the feline leukemia virus infection status of cats in Southern Germany

Most studies that investigate the prevalence of infections with feline leukemia virus (FeLV) are based on the detection of p27 antigen in blood, but they do not detect proviral DNA to identify the prevalence of regressive FeLV infections. The aim of the present study was to assess the prevalence and status of FeLV infection in cats in Southern Germany. P27 antigen enzyme-linked immunosorbent assay (ELISA), anti-p45 antibody ELISA, DNA polymerase chain reaction (PCR) of blood and RNA PCR of saliva were performed. Nine out of 495 cats were progressively (persistently) infected (1.8%) and six were regressively (latently) infected (1.2%). Cats with regressive infections are defined as cats that have been able to overcome antigenemia but provirus can be detected by PCR. Twenty-two unvaccinated cats likely had abortive infections (regressor cats), testing FeLV antigen- and provirus-negative but anti-p45 antibody-positive. Most of the FeLV-vaccinated cats did not have anti-FeLV antibodies. Both progressive, as well as regressive infections seem to be rare in Germany today.

Sensitivity and specificity of a nested polymerase chain reaction for detection of lentivirus infection in lions (Panthera leo)

Feline immunodeficiency virus (FIV) is a lentivirus in the Retroviridae family that causes lifelong infection in domestic cats. The lentivirus of African lions (Panthera leo), referred to as FIVple, is endemic in certain lion populations in eastern and southern Africa. Lentivirus infection leads to immunologic dysfunction and immunosuppressive disease in domestic cats; however, little is known about the pathogenic effects of infection in lions, nor about the epidemiologic impact on free-ranging and captive populations. Whole blood and serum samples were collected opportunistically from free-ranging lions in Kruger National Park, Republic of South Africa (RSA). Whole blood and serum samples were also collected from captive wild lions in the RSA. A nested polymerase chain reaction (PCR) assay for detection of FIV was performed on all whole blood samples. In addition, serum samples were tested for cross-reactive antibodies to domestic feline lentivirus antigens and puma lentivirus synthetic envelope peptide antigen. The PCR assay successfully amplified the lion lentivirus from African lions. The relative sensitivity and relative specificity were 79% and 100%, respectively, and the positive and negative predictive values were 100% and 67%, respectively. This research represents the first study to compare genetic material with antibody-based methods of lentivirus detection on lions in RSA. Using PCR as an additional diagnostic test for FIV in lions will increase screening sensitivity and will allow viral characterization among circulating isolates and monitoring of changes in the viral epidemiology within geographic regions and populations over time.

Prevalence of feline immunodeficiency virus and feline leukaemia virus among client-owned cats and risk factors for infection in Germany

This study was conducted to determine prevalence and risk factors for retrovirus infection of infected cats in a large cat population in Germany by evaluation of 17,462 client-owned cats that were tested for the presence of feline immunodeficiency virus (FIV) antibodies or feline leukaemia virus (FeLV) antigen. The owners of a subset of 100 cats were contacted to determine their cat's survival times. Prevalence of FIV and FeLV was 3.2% and 3.6%, respectively, remaining stable for FIV, but decreasing for FeLV (6-1%) over 10 years. Median age was 6 years in FIV- and 3 years in FeLV-infected cats. Risk factors for FIV infection were male gender, older age, mixed breed, access to outdoor, aggressive behaviour, and FeLV co-infection; and for FeLV infection contact to other cats, aggressive behaviour, and FIV co-infection. Median survival time of FIV-infected cats was not significantly different to non-infected cats, whereas FeLV-infected cats had significantly shorter median survival times than non-infected cats.

Feline leukaemia. ABCD guidelines on prevention and management

OVERVIEW

Feline leukaemia virus (FeLV) is a retrovirus that may induce depression of the immune system, anaemia and/or lymphoma. Over the past 25 years, the prevalence of FeLV infection has decreased considerably, thanks both to reliable tests for the identification of viraemic carriers and to effective vaccines.

INFECTION

Transmission between cats occurs mainly through friendly contacts, but also through biting. In large groups of non-vaccinated cats, around 30-40% will develop persistent viraemia, 30-40% show transient viraemia and 20-30% seroconvert. Young kittens are especially susceptible to FeLV infection.

DISEASE SIGNS

The most common signs of persistent FeLV viraemia are immune suppression, anaemia and lymphoma. Less common signs are immune-mediated disease, chronic enteritis, reproductive disorders and peripheral neuropathies. Most persistently viraemic cats die within 2-3 years.

DIAGNOSIS

In low-prevalence areas there may be a risk of false-positive results; a doubtful positive test result in a healthy cat should therefore be confirmed, preferably by PCR for provirus. Asymptomatic FeLV-positive cats should be retested.

DISEASE MANAGEMENT

Supportive therapy and good nursing care are required. Secondary infections should be treated promptly. Cats infected with FeLV should remain indoors. Vaccination against common pathogens should be maintained. Inactivated vaccines are recommended. The virus does not survive for long outside the host.

VACCINATION RECOMMENDATIONS

All cats with an uncertain FeLV status should be tested prior to vaccination. All healthy cats at potential risk of exposure should be vaccinated against FeLV. Kittens should be vaccinated at 8-9 weeks of age, with a second vaccination at 12 weeks, followed by a booster 1 year later. The ABCD suggests that, in cats older than 3-4 years of age, a booster every 2-3 years suffices, in view of the significantly lower susceptibility of older cats.

2008 American Association of Feline Practitioners' feline retrovirus management guidelines

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are among the most common infectious diseases of cats. Although vaccines are available for both viruses, identification and segregation of infected cats form the cornerstone for preventing new infections. Guidelines in this report have been developed for diagnosis, prevention, treatment, and management of FeLV and FIV infections. All cats should be tested for FeLV and FIV infections at appropriate intervals based on individual risk assessments. This includes testing at the time of acquisition, following exposure to an infected cat or a cat of unknown infection status, prior to vaccination against FeLV or FIV, prior to entering group housing, and when cats become sick. No test is 100% accurate at all times under all conditions; results should be interpreted along with the patient's health and risk factors. Retroviral tests can diagnose only infection, not clinical disease, and cats infected with FeLV or FIV may live for many years. A decision for euthanasia should never be based solely on whether or not the cat is infected. Vaccination against FeLV is highly recommended in kittens. In adult cats, antiretroviral vaccines are considered non-core and should be administered only if a risk assessment indicates they are appropriate. Few large controlled studies have been performed using antiviral or immunomodulating drugs for the treatment of naturally infected cats. More research is needed to identify best practices to improve long-term outcomes following retroviral infections in cats.

Prevalence and risk factors for hemoplasmas in domestic cats naturally infected with feline immunodeficiency virus and/or feline leukemia virus in Rio de Janeiro--Brazil

The aim of this study was to determine the prevalence and risk factors for Mycoplasma haemofelis (Mhf) and 'Candidatus Mycoplasma haemominutum' (Mhm) infections in domestic cats tested for feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) with a commercial enzyme-linked immunosorbent assay (ELISA) kit. Based on serological testing, cats were grouped as i) FIV-positive (n=25); ii) FeLV-positive (n=39); iii) FIV/FeLV-positive (n=8); and iv) FIV/FeLV-negative (n=77). Complete blood counts were followed by DNA extraction, species-specific polymerase chain reaction (16S rRNA gene) for Mhf and Mhm and Southern blotting for all animals. Mhf DNA was found in 4.0, 2.6, 12.5 and 7.8% of the cats from groups i, ii, iii and iv, respectively, while 32, 5.1, 50 and 5.2% of these animals had an Mhm infection. Cats with FIV (OR=4.25, P=0.009) and both FIV and FeLV (OR=7.56, P=0.014) were at greater risk of being hemoplasma infected than retroviral-negative cats, mainly due to Mhm infection (OR=8.59, P=0.001 and OR=18.25, P=0.001, respectively). Among pure-breed cats, FIV-positive status was associated with hemoplasma infection (OR 45.0, P=0.001).

Quality of different in-clinic test systems for feline immunodeficiency virus and feline leukaemia virus infection

Many new diagnostic in-house tests for identification of feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infection have been licensed for use in veterinary practice, and the question of the relative merits of these kits has prompted comparative studies. This study was designed to define the strengths and weaknesses of seven FIV and eight FeLV tests that are commercially available. In this study, 536 serum samples from randomly selected cats were tested. Those samples reacting FIV-positive in at least one of the tests were confirmed by Western blot, and those reacting FeLV-positive were confirmed by virus isolation. In addition, a random selection of samples testing negative in all test systems was re-tested by Western blot (100 samples) and by virus isolation (81 samples). Specificity, sensitivity, positive and negative predictive values of each test and the quality of the results were compared.

New challenges for the diagnosis of feline immunodeficiency virus infection

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

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.

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.

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.

Low-dose interferon-alpha treatment for feline immunodeficiency virus infection

Feline immunodeficiency virus sustains an AIDS-like syndrome in cats, which is considered a relevant model for human AIDS. Under precise enrolment requirements, 30 naturally infected cats showing overt disease were included in a trial of low-dose, oral human interferon-alpha treatment. Twenty-four of them received 10 IU/Kg of human interferon-alpha and 6 placebo only on a daily basis under veterinary supervision. The low-dose human interferon-alpha treatment significantly prolonged the survival of virus-infected cats (p<0.01) and brought to a rapid improvement of disease conditions in the infected hosts. Amelioration of clinical conditions was neither correlated with plasma viremia, nor with proviral load in leukocytes. A good survival of CD4+ T cells and a slow increase of CD8+ T cells were also observed in human interferon-alpha-treated cats. Interestingly, the improvement of the total leukocyte counts showed a much stronger correlation with the recovery from serious opportunistic infections. As shown in other models of low-dose interferon-alpha treatment, there was a rapid regression of overt immunopathological conditions in virus-infected cats. This hints at a major role of interferon-alpha in the control circuits of inflammatory cytokines, which was probably the very foundation of the improved clinical score and survival despite the unabated persistence of virus and virus-infected cells.

Development of recombinant capsid antigen/transmembrane epitope fusion proteins for serological diagnosis of animal lentivirus infections

Among animal lentiviruses, Feline immunodeficiency virus (FIV), Equine infectious anaemia virus (EIAV) and Small ruminant lentiviruses (SRLV) are important pathogens associated with a variety of clinical pictures including immunodeficiency, anaemia, arthritis, pneumonia. The detection of viral antibody response represents a practical diagnostic approach in all lentivirus infections since they remain detectable long life. Capsid antigen (CA) is the major viral core protein and specific antibodies against this antigen are usually first recognised in infected sheep, goat and horse, remaining detectable for long period. Transmembrane (TM) domain of envelope glycoprotein contains a well conserved motif known to form an immunodominant epitope in several lentiviruses. In this study a simple strategy was developed to express the entire CA and the TM epitope in a single fusion protein from equine, feline and small ruminant lentiviruses in prokaryotic system and evaluated the diagnostic utility of a purified preparation in an indirect ELISA for each of the three infections. Results demonstrate that, for FIV and SRLV infections, the combination of CA and TM fractions increases the sensitivity of diagnostic tests based only on CA. The corresponding CA/TM antigen from EIAV showed excellent agreement with Coggins test.

FIV vaccine development and its importance to veterinary and human medicine: a review FIV vaccine 2002 update and review

Feline immunodeficiency virus (FIV) is a natural infection of domestic cats that results in acquired immunodeficiency syndrome resembling human immunodeficiency virus (HIV) infection in humans. The worldwide prevalence of FIV infection in domestic cats has been reported to range from 1 to 28%. Hence, an effective FIV vaccine will have an important impact on veterinary medicine in addition to being used as a small animal AIDS model for humans. Since the discovery of FIV reported in 1987, FIV vaccine research has pursued both molecular and conventional vaccine approaches toward the development of a commercial product. Published FIV vaccine trial results from 1998 to the present have been compiled to update the veterinary clinical and research communities on the immunologic and experimental efficacy status of these vaccines. A brief report is included on the outcome of the 10 years of collaborative work between industry and academia which led to recent USDA approval of the first animal lentivirus vaccine, the dual-subtype FIV vaccine. The immunogenicity and efficacy of the experimental prototype, dual-subtype FIV vaccine and the efficacy of the currently approved commercial, dual-subtype FIV vaccine (Fel-O-Vax FIV) are discussed. Potential cross-reactivity complications between commercial FIV diagnostic tests, Idexx Snap Combo Test and Western blot assays, and sera from previously vaccinated cats are also discussed. Finally, recommendations are made for unbiased critical testing of new FIV vaccines, the currently USDA approved vaccine, and future vaccines in development.

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.