Effect of chronic feline immunodeficiency virus infection on experimental feline calicivirus-induced disease

Performance and overview of clinically relevant areas of application of saliva testing in the cat

Introduction

The cat represents an important model in order to investigate basic physiological knowledge of salivary secretion as well as pharmacokinetics of active substances.

Objective

The aim of the study was to review in which diagnostic application areas saliva testing is routinely used and in which areas it could be further explored in the future.

Materials and methods

Literature relevant to the research question was collected in March 2022 using the Pubmed database.

Results

The diagnosis of infectious diseases in cat saliva is one of the most important fields of application. Saliva diagnostics may also indicate dental diseases, allergies or kidney and other metabolic diseases. Sexual and stress hormones can also be measured in cat saliva. A number of clinically relevant allergens in cat saliva that may cause allergies in humans has been investigated and described, in addition to infectious agents that can be transmitted from cats to humans.

Conclusions

Saliva testing in cats can be useful in many areas, including the detection of infectious diseases, allergies and dental disease. However, it is far from being used to its full potential within veterinary medicine.

Prevalence of feline chronic gingivostomatitis in feral cats and its risk factors

OBJECTIVES

This study investigated the prevalence of feline chronic gingivostomatitis in urban feral cats in South Korea and analysed its risk factors.

METHODS

Three hundred and forty-five feral cats that visited the hospital for neutering using a trap-neuter-return approach were screened for feline chronic gingivostomatitis based on clinical criteria. In addition, we determined if body weight, sex and the presence of tongue lesions are risk factors for feline chronic gingivostomatitis. The difference in severity due to the presence or absence of risk factors, and the relationship between gross findings and histopathological lesions, were analysed by grading lesion severity.

RESULTS

Feline chronic gingivostomatitis was diagnosed in 92 cats. Disease prevalence did not significantly differ with body weight and sex but was significantly related to tongue lesions.

CONCLUSIONS AND RELEVANCE

The prevalence of feline chronic gingivostomatitis in urban feral cats in South Korea was 26.6%. It was significantly more prevalent in cats that had tongue lesions. Severity was also significantly associated with tongue lesions. Feline chronic gingivostomatitis may be associated with an infectious agent that causes tongue lesions.

Lymphopenia Caused by Virus Infections and the Mechanisms Beyond

Viral infections can give rise to a systemic decrease in the total number of lymphocytes in the blood, referred to as lymphopenia. Lymphopenia may affect the host adaptive immune responses and impact the clinical course of acute viral infections. Detailed knowledge on how viruses induce lymphopenia would provide valuable information into the pathogenesis of viral infections and potential therapeutic targeting. In this review, the current progress of viruses-induced lymphopenia is summarized and the potential mechanisms and factors involved are discussed.

Modified-Live Feline Calicivirus Vaccination Reduces Viral RNA Loads, Duration of RNAemia, and the Severity of Clinical Signs after Heterologous Feline Calicivirus Challenge

Feline calicivirus (FCV) is a common cat virus causing clinical signs such as oral ulcerations, fever, reduced general condition, pneumonia, limping and occasionally virulent-systemic disease. Efficacious FCV vaccines protect against severe disease but not against infection. FCV is a highly mutagenic RNA virus whose high genetic diversity poses a challenge in vaccine design. The use of only one modified-live FCV strain over several decades might have driven the viral evolution towards more vaccine-resistant variants. The present study investigated the clinical signs, duration, and amount of FCV shedding, RNAemia, haematological changes and acute phase protein reaction in SPF cats after subcutaneous modified-live single strain FCV vaccination or placebo injection and two subsequent oronasal heterologous FCV challenge infections with two different field strains. Neither clinical signs nor FCV shedding from the oropharynx and FCV RNAemia were detected after vaccination. After the first experimental infection, vaccinated cats had significantly lower clinical scores, less increased body temperature and lower acute phase protein levels than control cats. The viral RNA loads from the oropharynx and duration and amount of RNAemia were significantly lower in the vaccinated animals. No clinical signs were observed in any of the cats after the second experimental infection. In conclusion, FCV vaccination was beneficial for protecting cats from severe clinical signs, reducing viral loads and inflammation after FCV challenge.

A pilot study to evaluate the serum Alpha-1 acid glycoprotein response in cats suffering from feline chronic gingivostomatitis

BACKGROUND

Feline chronic gingivostomatitis (FCGS) is a multifactorial immune-mediated disease that can lead to chronic pain, anorexia, and weight loss and has substantial health and welfare effects. Currently, the recommended treatment includes dental extractions to decrease the inflammatory stimulation associated with dental plaque. However, complete remission is observed in less than half of the cases, and the majority need comprehensive medical management. This study aimed to evaluate the serum levels of the acute phase protein alpha-1 acid glycoprotein (AGP) in cats with FCGS and to examine whether dental extractions contribute to a significant decrease in the systemic inflammatory response at two postoperative time points.

RESULTS

AGP serum concentrations in the cats with FCGS were significantly higher at all time points than that in the control groups and were significantly correlated with the global caudal stomatitis score at day 0 but not at day 30 or 60. A significant improvement of some clinical scores, such as perceived comfort and global caudal stomatitis, was observed 60 days after the dental extraction. However, the levels of AGP did not significantly change over time.

CONCLUSIONS

Cats with FCGS were more likely to have a systemic inflammatory response compared with age- and dental disease-matched controls. Dental extractions, in most cases, did not contribute to a significant decrease of AGP both at 30 and 60 days. Therefore, this study reinforces the need to pursue comprehensive medical management after dental extractions to attenuate the systemic inflammatory response as a result of this disease.

Feline leishmaniosis: diagnosis, treatment and outcome in 16 cats

OBJECTIVES

Leishmaniosis is a vector-borne disease and in European countries is caused by Leishmania infantum. Cats are considered secondary reservoirs of the infection in endemic areas. The objective of this retrospective study is to describe the clinical findings, diagnosis, treatment and outcome of feline leishmaniosis (FeL) in 16 cats in Spain.

METHODS

Medical records of cats diagnosed with leishmaniosis were retrospectively reviewed for cases that met the following inclusion criteria: identification of Leishmania organisms and/or DNA on cytological and/or histological specimens and/or a high anti-Leishmania antibody titre, compatible clinical findings and pathological abnormalities.

RESULTS

Sixteen cats met the inclusion criteria, all of which were living in areas endemic for canine leishmaniosis. Systemic signs were present in 11 cases (68.8%). The most common clinical signs on presentation included cutaneous lesions in 12 cats (75%), ocular disease in six cats (37.5%) and anorexia in six cats (37.5%). A polyclonal gammopathy was noted in 12 cats (85.7%). Non-regenerative anaemia and renal abnormalities were present in six (37.5%) and five patients (31.3%), respectively. In nine cats (56.3%), immunosuppressive conditions/comorbidities were identified. The diagnosis was made in eight of the cats (50%) by cytology, but a combination of diagnostic tests was needed for definitive diagnosis in the remaining patients. Twelve cats (75%) were treated specifically for leishmaniosis. Five of the 12 cats (41.7%) did not improve with treatment. The median survival time in the group of patients treated specifically for leishmaniosis was 17 months. Median survival of patients treated with concomitant diseases was 13 months vs 41 months in those without, although this was not statistically significant (P = 0.557).

CONCLUSIONS AND RELEVANCE

Presentation of FeL appears to be similar to canine leishmaniosis but with some specific features: ulcerative and nodular skin lesions are the predominant cutaneous signs; cats with immunosuppressive conditions or coexisting diseases were more commonly present than typically seen in dogs (mainly feline immunodeficiency virus). A combination of diagnostic tests may be needed for definitive diagnosis.

Clinical, pathological, immunohistochemical and molecular characterization of feline chronic gingivostomatitis

Objectives This study presents the clinical, pathological, immunohistochemical and molecular characterization of 26 cats with feline chronic gingivostomatitis (FCG). Methods Oral mucosal biopsies, blood and swabs were collected from cats presenting with oral lesions. The tissue sections were submitted for histopathology and immunohistochemical analysis for feline calicivirus (FCV), feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV). The swabs were subjected to PCR analysis for FCV, and blood for FeLV and FIV. Results The main clinical findings were dysphagia (88.2%), halitosis (76.5%), sialorrhea (47.1%), weight loss (41.2%), intense oral discomfort (35.3%), oral hemorrhage (17.6%), and lackluster and fragile coat (11.8%). Gross inspection revealed bilateral lesions across the palatoglossal fold to the lateral tongue base. The lesions were diffuse, proliferative, intensely red and friable, and bled easily upon examination in 80.8% of cases. In 23.1% of cases, the lesions were multifocal to coalescent, at times forming multiple vesicles on a reddened, edematous palatoglossal fold. Microscopic examination showed that 15.4% of lesions had moderate (grade 2) and 84.6% had severe (grade 3) inflammation. Immunohistochemistry revealed the presence of FeLV antigens in the epithelium and the inflammatory infiltrate of 30.8% of the cats with FCG. FCV antigens were not detected in the FCG lesions. Conclusions and relevance The FCG cases analyzed could not be correlated with FCV. It is possible that FeLV plays a role as a causal agent of lesions in cases where the presence of the virus has been confirmed by immunohistochemistry in epithelial samples.

Genetic diversity and phenotypic associations of feline caliciviruses from cats in Switzerland

Feline calicivirus (FCV) is a common viral pathogen in domestic cats worldwide. The variable regions of the capsid (VP1) gene of FCV have one of the highest recorded rates of molecular evolution. Understanding the genetic diversity and phylogeny of FCV is a prerequisite to exploring the epidemiology and pathogenesis of this virus and to the development of efficacious vaccine strategies. In this study, we undertook a nationwide molecular characterization of FCV using for the first time nearly complete capsid (VP1) gene sequences. Sequences from 66 FCV samples were used to investigate the correlation between viral phylogeny and several traits, including geographic origin, signalment, husbandry, FCV vaccination and co-infections. Codon-based nucleotide alignment showed that individual nucleotides and their corresponding amino acid sites were either invariant or highly variable. Using a threshold of 20 % genetic distance in variable region E, FCV samples were grouped into 52 strains, 10 of which comprised two to three samples. Significant associations between FCV phylogeny and host characteristics were found, specifically the pedigree status of the cats, and two well-supported lineages were identified in which the current FCV strain definition was confounded. No correlation between viral genetic distances and geographic distances was evident. The greater resolution of the FCV phylogeny in this study compared to previous studies can be attributed to our use of more conserved regions of the capsid (VP1) gene; nonetheless, our results were still hampered by sequence saturation. The study highlights the need for whole-genome sequences for FCV phylogeny studies.

Therapeutic Management of Feline Chronic Gingivostomatitis: A Systematic Review of the Literature

Feline chronic gingivostomatitis (FCGS) is a disease characterized by protracted and potentially debilitating oral inflammation in cats, the etiology of which is currently unknown. The purpose of this review is to apply an evidence-based medicine approach to systematically review and critically evaluate the scientific literature reporting the outcome of medical and surgical management of FCGS. Those articles meeting inclusion criteria were reviewed and assigned an "Experimental Design Grade" (EDG) and an "Evidence Grade" (EG) in order to score relative strength of study design and produced data. Studies were evaluated and compared, especially highlighting the treatments, the outcomes, and the therapeutic success rates. This review found a lack of consistency between articles' data, rendering direct comparison of results unreliable. The field of FCGS research, and ultimately patient care, would benefit from standardizing studies by adopting use of a consistent semi-quantitative scoring system and extending follow-up duration. Future researchers should commit to large prospective studies that compare existing treatments and demonstrate the promise of new treatments.

Contrasting clinical outcomes in two cohorts of cats naturally infected with feline immunodeficiency virus (FIV)

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Multi-cat household animals displayed 63% mortality rate.

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Lymphoma was the most common cause of death.

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The CD4:CD8 ratio failed to distinguish cats classified as healthy and not healthy.

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FIV load failed to distinguish cats classified as healthy and not healthy.

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Management and housing conditions impact on the progression of FIV infection.

Despite over 25 years of feline immunodeficiency virus (FIV) research, relatively little is known about the longitudinal course of FIV infection following natural infection. In contrast to published reports of experimental infections using lethal strains of the virus, clinical signs of naturally acquired FIV infection can be mild or inapparent, rather than life-threatening. In this prospective, longitudinal controlled study, based in Chicago, IL (n = 17) and Memphis, TN (n = 27), we investigated two cohorts of privately owned, naturally infected cats kept under different housing conditions. Cats in the Chicago cohort (Group 1) were kept in households of ≤2 cats, while the Memphis cohort (Group 2) comprised part of a large multi-cat household of over 60 cats kept indoors only, with unrestricted access to one another.

The majority of cats from Group 1 did not display clinical signs consistent with immunodeficiency during the 22-month observation period. In contrast, the outcome of infection in Group 2 was dramatically different; 17/27 (63%) of cats lost a median of 51.3% of their bodyweight (P < 0.0005) and died during the study period, with lymphoma being the most common cause of mortality.

Although the decrease in CD4+ T cell count between enrolment and terminal disease was significant (P = 0.0017), the CD4:CD8 ratio at the time of enrolment did not reliably distinguish FIV-positive cats classified as ‘healthy’ and ‘not healthy’ at either cohort. FIV load at enrolment was significantly lower in Group 1 than in Group 2 (P < 0.0001), but there were no significant differences at enrolment between healthy and not healthy cats at either group.

In conclusion, the results of this study suggest that management and housing conditions impact on disease progression and survival times of FIV-positive cats.

Efficacy of Cyclosporine for Chronic, Refractory Stomatitis in Cats: A Randomized, Placebo-Controlled, Double-Blinded Clinical Study

Sixteen cats with chronic stomatitis, that had previously undergone premolar-molar or full-mouth extractions, were randomly assigned a group to receive 2.5 mg/kg cyclosporine or placebo orally twice daily. Neither the clinician nor the clients were aware of the group assignments. Cats were evaluated prior to treatment and every 2 weeks for 6 weeks using a 30 point Stomatitis Disease Activity Index (SDAI) score. Mean improvement in SDAI scores among cats in the treatment group after 6 weeks was 52.7 %. This was significantly different from the mean improvement (12.2 %) of cats in the placebo group. During the 6 week study period, 7 of the 9 cats in the treatment group (77.8 %) showed a > 40 % improvement in SDAI score, while 1 of 7 cats in placebo group (14.3 %) showed a > 40 % improvement in SDAI score. This difference was statistically significant. Individual variability in the absorption of orally-administered cyclosporine was high. Trough whole-blood cyclosporine levels ranged from 32.1 ng/ml to 1,576.2 ng/ml. At the end of the 6 week observation period, there was a statistically significant difference among cats with trough whole-blood cyclosporine levels > 300 ng/ml (72.3 % improvement) compared with cats with cyclosporine levels < 300 ng/ml (28.2 % improvement). Whole-blood cyclosporine levels > 300 ng/ml were associated with significant improvement in oral inflammation in cats with chronic stomatitis that had previously undergone premolar-molar or full-mouth extraction.

Clinical aspects of feline retroviruses: a review

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses with global impact on the health of domestic cats. The two viruses differ in their potential to cause disease. FeLV is more pathogenic, and was long considered to be responsible for more clinical syndromes than any other agent in cats. FeLV can cause tumors (mainly lymphoma), bone marrow suppression syndromes (mainly anemia), and lead to secondary infectious diseases caused by suppressive effects of the virus on bone marrow and the immune system. Today, FeLV is less commonly diagnosed than in the previous 20 years; prevalence has been decreasing in most countries. However, FeLV importance may be underestimated as it has been shown that regressively infected cats (that are negative in routinely used FeLV tests) also can develop clinical signs. FIV can cause an acquired immunodeficiency syndrome that increases the risk of opportunistic infections, neurological diseases, and tumors. In most naturally infected cats, however, FIV itself does not cause severe clinical signs, and FIV-infected cats may live many years without any health problems. This article provides a review of clinical syndromes in progressively and regressively FeLV-infected cats as well as in FIV-infected cats.

Clinical efficacy of the acyclic nucleoside phosphonate 9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine (PMPDAP) in the treatment of feline immunodeficiency virus-infected cats

In in vitro studies, the acyclic nucleoside phosphonate 9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine (PMPDAP) inhibited the replication of feline immunodeficiency virus (FIV). No information about its clinical efficacy is available so far. The aim of this prospective placebo-controlled, double-blinded study was to evaluate the antiviral efficacy of PMPDAP in cats naturally infected with FIV. Twenty cats were randomly assigned to two treatment groups receiving either PMPDAP (25 mg/kg) or placebo twice per week subcutaneously for 6 weeks. The general health status (Karnofsky's score), clinical signs, laboratory, immunological, and surrogate parameters were evaluated. No significant differences were found between PMPDAP- and placebo-treated cats, although cats treated with PMPDAP showed a tendency for improvement in their Karnofsky's score and clinical signs. Haematological side effects were noted in the PMPDAP-treated cats. Thus, PMPDAP may be an option in treating cats if it becomes available for veterinarians, but side effects have been monitored.

Feline respiratory disease complex

Feline respiratory disease complex (FRDC) refers to the characteristic acute presentation of a contagious respiratory or ocular disease caused by one or multiple pathogens. Environmental and host factors impact the transmission, clinical presentation, preventive strategy, and treatment of affected cats. The FRDC is especially problematic in settings where large numbers of cats cohabit, including animal shelters, catteries, and semi-feral colonies. Although elimination of FRDC is an unrealistic goal, improved understanding can lead to strategies to minimize disease impact.

Clinical aspects of feline immunodeficiency and feline leukemia virus infection

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses with a global impact on the health of domestic cats. The two viruses differ in their potential to cause disease. FIV can cause an acquired immunodeficiency syndrome that increases the risk of developing opportunistic infections, neurological diseases, and tumors. In most naturally infected cats, however, FIV itself does not cause severe clinical signs, and FIV-infected cats may live many years without any health problems. FeLV is more pathogenic, and was long considered to be responsible for more clinical syndromes than any other agent in cats. FeLV can cause tumors (mainly lymphoma), bone marrow suppression syndromes (mainly anemia) and lead to secondary infectious diseases caused by suppressive effects of the virus on bone marrow and the immune system. Today, FeLV is less important as a deadly infectious agent as in the last 20 years prevalence has been decreasing in most countries.

When domestic cat (Felis silvestris catus) population structures interact with their viruses

Many theoretical studies have proposed different causal mechanisms by which the structure of a host population could have important implications for life history traits of pathogens. However, little information is available from real systems to test these hypotheses. The domestic cat, Felis silvestris catus, whose populations exhibit a great variability in social and spatial structure, represent an ideal case study to assess this question. In the present article, we show how cat population structure may have influenced the evolution of feline viruses and, in return, how these viruses may have modified the genetic structure of cat populations. To cite this article: D. Pontier et al., C. R. Biologies 332 (2009).

Concurrent oral shedding of feline calicivirus and feline herpesvirus 1 in cats with chronic gingivostomatitis

Oral mucosal salivary samples were collected from 25 cats with chronic gingivostomatitis and 24 cats with periodontal disease. Viral culture and isolation of feline calicivirus and feline herpesvirus 1 were performed. Eighty-eight per cent of cats with chronic gingivostomatitis were shedding both viruses, compared to 21% of cats without chronic oral inflammatory disease. Cats with chronic gingivostomatitis are significantly more likely to concurrently shed both feline calicivirus and feline herpesvirus 1 than are cats with classical periodontal disease.

Use of nested polymerase chain reaction (PCR) for detection of retroviruses from formalin-fixed, paraffin-embedded uveal melanomas in cats

Thirty-six formalin-fixed, paraffin-embedded enucleated globes from cats with a diagnosis of diffuse anterior uveal melanoma were obtained. Sections of tumor were excised, deparaffinized, and subjected to nested polymerase chain reaction (PCR) to identify proviral DNA sequences from the feline leukemia virus (FeLV)-feline sarcoma virus (FeSV; 36 eyes), and the feline immunodeficiency virus (FIV; 18 eyes). All samples tested were negative for FIV DNA. Three samples were positive for FeLV-FeSV DNA. This is the first reported evidence of a possible link between naturally occurring feline anterior uveal melanoma and the presence of FeLV-FeSV DNA.

Evaluation of formalin-fixed paraffin-embedded tissues obtained from vaccine site-associated sarcomas of cats for DNA of feline immunodeficiency virus

OBJECTIVE

To evaluate the use of a polymerase chain reaction (PCR) method for detection of feline immunodeficiency virus (FIV) DNA, using formalin-fixed paraffin-embedded (FFPE) tissues, and to use this method to evaluate tissues obtained from vaccine site-associated sarcomas (VSS) of cats for FIV DNA.

SAMPLE POPULATION

50 FFPE tissue blocks from VSS of cats and 50 FFPE tissue blocks from cutaneous non-vaccine site-associated fibrosarcomas (non-VSS) of cats.

PROCEDURE

DNA was extracted from FFPE sections of each tumor and regions of the gag gene of FIV were amplified by a PCR, using 3 sets of primers. Sensitivity of the method was compared between frozen and FFPE tissues, using splenic tissue obtained from a cat that had been experimentally infected with FIV.

RESULTS

We did not detect FIV DNA in VSS or non-VSS tissues. Sensitivity of the PCR method was identical for frozen or FFPE tissues.

CONCLUSIONS AND CLINICAL RELEVANCE

It is possible to detect FIV DNA in FFPE tissues by use of a PCR. We did not find evidence to support direct FIV involvement in the pathogenesis of VSS in cats.

Investigation of recombinant human insulin-like growth factor type I in thymus regeneration in the acute stage of experimental FIV infection in juvenile cats

Thymus involvement and the development of thymic lesions in HIV-1 infection is hypothesized to suppress thymus function and limit T cell maturation and replenishment of the peripheral lymphoid pool. Therapeutic modulation to protect or enhance thymus function may therefore ameliorate peripheral lymphocytopenia and retard disease progression. Thymotrophic agents, such as insulin-like growth factor type I (IGF-I), may therefore represent adjunctive but important methods of treatment to protect or promote thymus function. The assessment of rhIGF-I in lentiviral infection and its impact on the thymus was performed using the feline immunodeficiency virus (FIV) model. Regeneration of the thymus in juvenile cats and amelioration of the thymic lesion after FIV infection was assessed by multiple measurements including thymic weight, stereologic analysis of the thymus cortex and medulla, histologic and immunohistologic analysis, quantitation of thymocyte and peripheral lymphocyte subsets, and quantitative competitive RT-PCR. Evidence of thymic cortical regeneration was observed in FIV-inoculated cats after 12 and 20 weeks of rhIGF-I treatment. Inflammation in the thymus was reduced during this period of treatment in this group of rhIGF-I/FIV-inoculated cats as evidenced by the reduced numbers of B cells detected. Viral replication rates in peripheral lymph nodes were not altered by rhIGF-I treatment and were decreased by 1 log in the thymus after 20 weeks of treatment. Peripheral blood CD4+ T cell counts also increased after 14 weeks of treatment. This suggests that rhIGF-I treatment can enhance thymus function and replenishment of the peripheral T cell pool.

Immunopathologic changes in the thymus during the acute stage of experimentally induced feline immunodeficiency virus infection in juvenile cats

The feline thymus is a target organ and site of viral replication during the acute stage of feline immunodeficiency virus (FIV) infection. This was demonstrated by histologic, immunohistologic, flow cytometric, and virologic tests. Thymic lesions developed after 28 days postinoculation (p.i.) and included thymitis, premature cortical involution, and medullary B-cell hyperplasia with germinal center formation and epithelial distortion. Alterations in thymocyte subsets also developed. Fewer CD4+ CD8- cells were detected at 28 days p.i., while an increase in CD4- CD8+ cells resulted in an inversion of the thymic CD4/CD8 ratio of single-positive cells, similar to events in peripheral blood. Provirus was present in all thymocyte subpopulations including cortical CD1(hi), CD1(lo), and B cells. The CD1(hi) thymocyte proviral burden increased markedly after 56 days p.i., coincident with the presence of infiltrating inflammatory cells. Increased levels of provirus in the CD1(lo) thymocyte subpopulation were detected prior to 56 days p.i. This was likely due to inclusion of infected infiltrating inflammatory cells which could not be differentiated from mature, medullary thymocytes. Proviral levels in B cells also increased from 70 days p.i. Morphologic alterations, productive viral infection, and altered thymocyte subpopulations suggest that thymic function is compromised, thus contributing to the inability of FIV-infected cats to replenish the peripheral T-cell pool.

Toxicity associated with high dosage 9-[(2R,5R-2,5-dihydro-5-phosphonomethoxy)-2-furanyl]adenine therapy off attempts to abort early FIV infection

9-[(2R,5R-2,5-dihydro-5-phosphonomethoxy)-2-furanyl]adenine, or D4API, was tested in the feline immunodeficiency virus (FIV) infection model and found to be significantly more inhibitory in vitro than its parent compound 9-phosphonylmethoxethyl adenine (PMEA). Cytotoxicity was less than for PMEA or azidothymidine (AZT) for culture periods of 7 days, but more toxic after 10 days. D4API was rapidly absorbed by cats following subcutaneous inoculation, with a plasma half-life of less than 1 h after intravenous inoculation and between 2 and 3 h after subcutaneous injection. Peripheral blood mononuclear cells collected from cats given a single dose of D4API were refractory, however, to FIV infection in vitro for up to 24 h. Given its prolonged intracellular phase and high selectivity index, high dose D4API therapy was tested for its ability to abort an acute (i.e. 2 week) FIV infection. A divided daily dose of D4API, which was one-fourth the toxic dose and 125 times the concentration that would totally inhibit virus replication in vitro, completely abrogated the anticipated viremia and antibody responses. Unfortunately, a majority of treated/uninfected and treated/infected test cats died acutely of drug toxicity after 47 days of treatment. Toxicity in vivo mirrored what was observed in vitro, being precipitous and cumulative in nature. Toxic signs included widespread hepatic and lymphoid necrosis. A surviving treated/FIV infected cat remained healthy to day 175 when the study was terminated; antibodies appeared 2 months later than in untreated/infected cats and virus was only detectable at low levels on day 175. In contrast, untreated/infected cats were viremic and antibody positive from 3 to 4 weeks post-infection onwards. Therefore, it was possible to alter, but not abort, an early FIV infection with prolonged, high-dose D4API treatment.

Comparison of the primary signs induced by experimental exposure to either a pneumotrophic or a 'limping' strain of feline calicivirus

Two strains of feline calicivirus, one reportedly pneumotrophic (FPV 255) and the other associated with a limping syndrome (2280) were compared with respect to the signs induced in kittens after oronasal exposure. Neither strain induced severe upper respiratory symptoms, and both caused oral ulcers and lameness. However oral ulcers were more prevalent, and lameness and depression were more pronounced in the kittens which received strain 2280. Kittens which exhibited lameness also had elevated blood levels of alpha 1-acid glycoprotein. A decline in lymphocyte count was noted only in kittens which received strain 2280. These data demonstrate that despite reported antigenic and genetic differences between these strains, no distinct differences in pathogenicity could be determined.

Two related strains of feline infectious peritonitis virus isolated from immunocompromised cats infected with a feline enteric coronavirus

Two groups of cats were experimentally infected orally with the cat-passaged RM strain of feline enteric coronavirus (FECV-RM). One group of cats (n = 19) had been chronically infected with feline immunodeficiency virus (FIV) for over 6 years, while a second control group (n = 20) consisted of FIV-naive siblings. Fecal virus shedding of FECV occurred in both groups starting on day 3 postinfection, nearly ceased by 4 weeks in FIV-uninfected cats, but remained at high levels in FIV-infected animals. FIV-infected cats shed virus for a longer period of time and at levels 10 to 100 times greater than those for FIV-uninfected cats. The coronavirus antibody response of the FIV-infected cats was delayed and of reduced titer compared with that of the FIV-uninfected animals. Cats in both groups remained asymptomatic for the first two months following FECV-RM infection; however, 8 to 10 weeks postinfection two cats in the FIV-infected group developed feline infectious peritonitis (FIP). The FIP viruses (designated FIPV-UCD9 and -UCD10) isolated from these two cats had almost complete genetic homology to each other and to the infecting FECV-RM. However, unlike FECV-RM, they readily induced FIP when inoculated intraperitoneally into specific-pathogen-free cats. This study confirms that FIPVs are frequently and rapidly arising mutants of FECV. Immunosuppression caused by chronic FIV infection may have enhanced the creation and selection of FIPV mutants by increasing the rate of FECV replication in the bowel and inhibiting the host's ability to combat the mutant viruses once they occurred.

Proviral burden and infection kinetics of feline immunodeficiency virus in lymphocyte subsets of blood and lymph node

Feline immunodeficiency virus (FIV) is similar to human immunodeficiency virus type 1 virologically and induces a clinical syndrome in cats comparable to human immunodeficiency virus type 1 syndrome in humans. To determine the lymphoid target cells of FIV, populations of CD4+ lymphocytes, CD8+ lymphocytes, and CD21+ lymphocytes (B cells) were enriched to more than 96.5% purity and then analyzed for FIV provirus by semiquantitative DNA amplification. We found FIV provirus in CD4+, CD8+, and B lymphocytes. In cats infected for <4 months, proviral burden was greatest in CD4+ cells, followed by B cells and then by CD8+ cells. In cats infected for more than 5 years, proviral burden was greatest in B cells, followed by CD4+ cells and then by CD8+ cells. The total proviral burden was > 1 log10 higher in acutely infected cats than in chronically infected cats, primarily because of a higher level of CD4+ infection in the acutely infected cats. A comparison of proviral loads in mesenteric lymph node and peripheral blood mononuclear cells in acutely or chronically infected cats revealed no significant difference. A kinetics study of FIV infection demonstrated that all lymphocyte subpopulations were infected by 4 weeks postinoculation. Virus was isolated from CD4+, CD8+, and B cells in vitro, and reverse transcriptase PCR demonstrated that all subsets contained viral RNA in vivo and therefore are productive reservoirs for FIV.

Mechanisms for persistence of acute and chronic feline calicivirus infections in the face of vaccination

The study was concerned with possible reasons for the persistence of both acute and chronic feline calicivirus (FCV)-induced disease and sustained oral carriage in the field in the face of routine FCV immunization. It was concluded from this study that: 1) the original FCV-F9 strain, which is the basis of most live vaccines, still generates cross-reactive antibodies against almost all field strains in California, 2) vaccine strains derived from FCV-F9 may not be as broadly cross-protective as the parent strain, 3) whole inactivated FCV-2280 vaccine evokes high virus neutralizing antibody titers with an equally broad spectrum of cross-reactivity as FCV-F9, 4) all vaccine strains of FCV cause acute disease signs and protracted oral shedding when administered orally, 5) strains isolated from the mouth five to ten weeks following oral inoculation can differ from parental virus, usually appearing more vaccine resistant, 6) cats previously infected with field or vaccine strains develop much less severe acute illness when subsequently infected with heterologous FCV strains but are not protected against the chronic carrier state. Therefore, the persistence of FCV in the field cannot be explained solely by the emergence of vaccine resistant strains and vaccine virus itself may contribute to both acute and chronic infection and disease.

FIV vaccine studies. I. Immune response to recombinant FIV env gene products and outcome after challenge infection

We have vaccinated five groups of cats (n = 25) four times with five preparations of recombinant feline immunodeficiency virus (FIV) env gene products; one group (n = 7) served as control. The vaccine formulations were as follows: (1) envelope glycoprotein of FIV Zurich 2 (FIV Z2) expressed in a Baculovirus system and isolated by gel electroelution (denatured form); (2) insect cells expressing FIV Z2 glycoprotein; (3) envelope glycoprotein of a Boston strain (FIV Bangston) expressed in insect cells and isolated by gel electroelution (denatured form); (4) glycosylated Bangston envelope protein made in insect cells and isolated in a native form; (5) non-glycosylated Bangston envelope protein made in Escherichia coli. All cats were challenged with 20 50% cat infective doses (CID50) of FIV Z2 previously titrated in cats. All vaccinated cats developed high enzyme-linked immunosorbent assay (ELISA) antibodies to the homologous antigen; crossreactivity to heterologous antigens was seen at a lower level. Virus neutralizing antibodies (tested with Petaluma virus) reached titers up to 32. After challenge, all cats seroconverted (as judged by anti gag antibodies in Western blot) and became infected (as judged by virus isolation and/or polymerase chain reaction) between 4 and 11 weeks with the exception of one cat. It is concluded that it is relatively easy to induce high ELISA antibody titers using recombinant env gene products, ELISA antibody titers do not correlate with virus neutralization or with protection.

An experimental study of primary feline immunodeficiency virus infection in cats and a historical comparison to acute simian and human immunodeficiency virus diseases

Sixteen adolescent specific pathogen free cats were inoculated with the Petaluma strain of feline immunodeficiency virus (FIV) and two cats were then necropsied at each of 5, 10, 21, 28, 42, 56, 70, and 84 day time points following infection. Lymphadenopathy gradually increased starting at Day 10 and persisted for the duration. Gross clinical signs of fever, mild to severe malaise, anorexia, diarrhea, dehydration, and generalized soreness appeared around Day 42, peaked at Day 56, and disappeared by Days 70-84 post-infection. Leukopenia, associated initially with a mild lymphopenia and later by both a mild lymphopenia and a severe neutropenia, appeared 14-28 days following infection, troughed at Day 56, and persisted thereafter. The CD4+:CD8+ T cell ratio started to decrease around Day 28, reaching a nadir at Days 56-70. This decrease was due to a decline in the absolute numbers and percentage of CD4+ T cells and an increase in the percentage of CD8+ T cells. Significant histopathologic lesions included myeloid hyperplasia between Days 56-70 post-infection; thymitis with cortical involution and follicular hyperplasia starting at Day 42; lymphoid hyperplasia of peripheral and mesenteric nodes, spleen and tonsils beginning around Day 42; typhlitis most evident from Day 56 onward, and an interstitial nephritis and pneumonitis that was most intense after Day 42. Virus was isolated from peripheral blood mononuclear cells (PBMC) beginning 2 weeks post-infection, and plasma viremia appeared 1 week later. Plasma and PBMC-associated viremia peaked at 42-56 days following infection and decreased abruptly thereafter. Proviral DNA was detectable as early as 5 days after infection in blood leukocytes and after 10 days in other organs. The central nervous system, lungs, thymus, tonsils and mesenteric lymph nodes were the earliest sites of virus localization. Antibodies to the FIV capsid protein appeared 14 days following infection and reached peak levels by Days 42-56. Abnormalities occurring during the primary stage of FIV infection were consistent with those described for acute simian and human immunodeficiency virus-induced disease.