Encephalitis associated with giant cells in a cat with naturally occurring feline immunodeficiency virus infection demonstrated by in situ hybridization

Age-related cognitive impairments in domestic cats naturally infected with feline immunodeficiency virus

BACKGROUND

Age-related dementia has been documented in domestic cats; however, its interaction with naturally occurring feline immunodeficiency virus (FIV) infection has been investigated minimally.

METHODS

Visuospatial working memory (VSWM) and problem-solving (PS) ability were evaluated in FIV-infected (n = 37) and control cats (n = 39) using two cognitive tasks tested serially, which assessed the ability of cats to remember the location of a baited container after a set delay, then evaluated the capability of the cats to manipulate the container to obtain the food within a time limit. Cats were categorized using 7 years of age as a cut-off to determine age-related differences. The relationship between cognitive performance and FIV viral load was investigated using real-time PCR cycle threshold (C_t ) values.

RESULTS

Age significantly affected VSWM and PS ability. Younger cats had better VSWM performance and PS ability compared to older cats with the same FIV status. There was no difference between younger FIV-positive and negative cats in either part of the task. While older FIV-positive cats had significantly worse VSWM than older FIV-negative cats, no differences were found in PS ability. Additionally, C_t values predicted VSWM but not PS ability.

CONCLUSION

Age-related cognitive impairments and FIV infection appear synergetic, causing greater cognitive deficits in older FIV-infected cats.

Potential Causes of Increased Vocalisation in Elderly Cats with Cognitive Dysfunction Syndrome as Assessed by Their Owners

The objectives of this study were to explore owner perception of the causes of increased vocalisation in cats diagnosed with cognitive dysfunction syndrome (CDS) and consider what impact this vocalisation may have on the cat's household. Owners of cats diagnosed with CDS that presented with increased vocalisation were invited to complete an online survey. The survey consisted of 28 questions including the cat's signalment, its medical history, and questions pertaining to the owner's perception of what motivated their cat´s increased vocalisation. This was determined by looking at the cat's behaviour when vocalising, where it was looking when it was vocalising, and if the vocalisation stopped when the owner interacted with it, e.g., petting or feeding it. The owners were also asked how stressful they found their cat's vocalisation. There were 37 responses. The majority of owners reported that the main cause of their cat's vocalisation appeared to be disorientation (40.5%) or attention seeking (40.5%). Seeking a resource such as food was reported in 16.2%, and pain was perceived to be the cause in only 2.7% of cats. However, the majority of owners (64.8%) believed there was >1 cause of their cat's increased vocalisation. Importantly, when owners were asked how stressful they found their cat's increased vocalisation, 40.5% scored ≥3 (where 1 = not stressful; 5 = significantly stressful). This study provides novel insight into owner perception of feline CDS, as well as potential causes for increased vocalisation; this will allow veterinarians to better advise owners on how to manage their cat with CDS.

Immunopathologic Effects of Prednisolone and Cyclosporine A on Feline Immunodeficiency Virus Replication and Persistence

Feline immunodeficiency virus (FIV) induces opportunistic disease in chronically infected cats, and both prednisolone and cyclosporine A (CsA) are clinically used to treat complications such as lymphoma and stomatitis. However, the impact of these compounds on FIV infection are still unknown and understanding immunomodulatory effects on FIV replication and persistence is critical to guide safe and effective therapies. To determine the immunologic and virologic effects of prednisolone and CsA during FIV infection, FIV-positive cats were administered immunosuppressive doses of prednisolone (2 mg/kg) or CsA (5 mg/kg). Both prednisolone and CsA induced acute and transient increases in FIV DNA and RNA loads as detected by quantitative PCR. Changes in the proportion of lymphocyte immunophenotypes were also observed between FIV-infected and naïve cats treated with CsA and prednisolone, and both treatments caused acute increases in CD4+ lymphocytes that correlated with increased FIV RNA. CsA and prednisolone also produced alterations in cytokine expression that favored a shift toward a Th2 response. Pre-treatment with CsA slightly enhanced the efficacy of antiretroviral therapy but did not enhance clearance of FIV. Results highlight the potential for drug-induced perturbation of FIV infection and underscore the need for more information regarding immunopathologic consequences of therapeutic agents on concurrent viral infections.

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.

CNS disease in the cat: current knowledge of infectious causes

PRACTICAL RELEVANCE

Neurological disease is a relatively common reason for referral, constituting approximately 10% of the feline referral caseload. Nearly one-third to one-half of these cases may be infectious in origin. As such, an awareness of infectious diseases causing central nervous system (CNS) signs in cats, and their clinical diagnosis and management, is relevant to anyone dealing with cats on a regular basis.

GLOBAL IMPORTANCE

Some conditions (eg, rabies) are more common in certain countries than others. Conditions such as feline infectious peritonitis (FIP) and toxoplasmosis are of global significance.

PATIENT GROUP

Many infectious diseases may affect any feline population. Some, such as FIP, are more common in pedigree households, whereas others such as toxoplasmosis, feline immunodeficiency virus (FIV) or feline leukaemia virus (FeLV) infections, are more likely to affect a single cat with an outdoor lifestyle.

EQUIPMENT

All patients benefit from thorough history taking and clinical, neurological and ophthalmic examinations, which all require minimal equipment. Infectious diseases may often be diagnosed on blood samples; however, definitive diagnosis may require more extensive investigation involving cerebrospinal fluid analysis or advanced imaging necessitating access to computed tomography or magnetic resonance imaging.

EVIDENCE BASE

The information in this review, which summarises current knowledge of infectious diseases affecting the CNS, is collated from publications on the infectious diseases comprising previous research papers, review articles, case series, case reports and textbooks, supplemented by the clinical experience of the authors.

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.

Polyganglioradiculoneuritis in a young cat: clinical and histopathological findings

An 18-month-old European shorthair cat was presented with a two week history of progressive decrease in consciousness, ambulatory tetraparesis, moderate ataxia and generalised decreased-to-absent postural reactions. Bilateral facial and nasal hypalgesia, absent menace response and anisocoria were found, and segmental spinal reflexes were normal. Neurological signs progressed to nonambulatory tetraparesis, tremor and spinal hyperalgesia. Histopathological examination revealed a mild-to-moderate lymphoplasmacytic and histiocytic infiltration, predominantly in the dorsal spinal roots, cranial nerves and ganglia in association with marked demyelination and proliferation of Schwann cells. Neurons and axons were preserved. Lesions were multi-focal and varied in severity. A predominantly sensory polyganglioradiculoneuritis was diagnosed. This lesion has not been reported previously in cats. Rabies, herpesviruses, feline infectious peritonitis, feline immunodeficiency virus, Toxoplasma gondii and feline leukaemia virus were excluded as possible aetiologies. Infections by other viruses or an autoimmune disease are discussed.

Endothelial cell suppression of peripheral blood mononuclear cell trafficking in vitro during acute exposure to feline immunodeficiency virus

Trafficking of peripheral blood mononuclear cells (PBMCs) into the brain is a critical step in the initiation of human immunodeficiency virus (HIV)-associated central nervous system disease. To examine potential factors that control trafficking during the earliest stages of infection, PBMC transmigration across a cultured feline brain endothelial cell (BECs) monolayer was measured after selective exposure of various cell types to feline immunodeficiency virus (FIV). Infection of the PBMCs with FIV increased the trafficking of monocytes and CD4 and CD8 T cells. Additional exposure of the BECs to FIV suppressed mean monocyte, CD4 T cell, and CD8 T cell trafficking. B cell trafficking was unaltered by these changing conditions. Subsequent exposure of astrocytes or microglia to FIV altered transmigration of different PBMC subsets in different ways. Treated microglia compared with treated astrocytes decreased monocyte transmigration, whereas B cell transmigration was increased significantly. When both astrocytes and microglia were exposed to FIV, an increase in CD8 T cell transmigration relative to BECs alone, to BECs plus astrocytes, or to BECs plus microglia was demonstrated. Thus, initial exposure of PBMCs to FIV is sufficient to induce a general increase in trafficking, whereas initial exposure of endothelial cells to FIV tends to down-regulate this effect. Selectivity of trafficking of specific PBMC subsets is apparent only after exposure of cells of the central nervous system to FIV in co-culture with the endothelium.

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.

Non-suppurative meningoencephalitis of unknown origin in cats and dogs: an immunohistochemical study

Non-suppurative meningoencephalitis of unknown cause is a frequent finding in dogs and cats. Fifty-three dogs and 33 cats with non-suppurative meningoencephalitis of unknown aetiology were examined immunohistochemically for 18 different infectious agents, including viruses, bacteria and prion protein^Sc. In 14 (26%) of the dogs and 13 (39%) of the cats a causative agent was identified in the central nervous system (CNS), two dogs and one cat giving positive results for two infectious agents simultaneously. The study revealed infections with known causative agents (porcine herpes virus 1, feline infectious peritonitis virus, Escherichia coli) and a new disease pattern of parvovirus infection in the CNS of dogs and cats. Infection of the CNS with feline leukaemia virus was found in a cat. Five dogs and four cats gave positive results for West Nile virus (WNV) antigen. In one dog, canine parainfluenza virus antigen was detected in the brain. Four dogs and four cats gave positive results for encephalomyocarditis virus (EMCV). The significance of the detection of WNV and EMCV antigen requires further study. The aetiology remained undetermined in 39 dogs (74%) and 20 cats (61%). Although it is possible that non-infectious causes play a more important role than previously thought, infections with hitherto unrecognized agents cannot be ruled out.

Results of magnetic resonance imaging in 14 cats with meningoencephalitis

Medical records and magnetic resonance (MR) images of 14 cats with inflammatory diseases affecting the central nervous system (CNS) were reviewed retrospectively. Cases included eight cats with feline infectious peritonitis and two cats with toxoplasmosis. Abnormalities affecting the CNS were observed in MR images in 10 (71%) cats. Intracranial lesions appeared as slightly hypointense foci in T1-weighted images in two (14%) cats, as hyperintense foci in T2-weighted images in seven (50%) cats and as hyperintense foci after intravenous administration of a gadolinium-based contrast medium in 10 (71%) cats. In six cats with lesions in T1- and/or T2-weighted images, additional lesions were visible in T1-weighted images obtained after gadolinium-based contrast medium administration. In three cats, lesions were visible only after contrast medium administration. In our study, MR imaging (MRI) did not appear to detect all cases of CNS inflammation in the population of cats with inflammatory cerebrospinal fluid (CSF); however, MRI adds information about the sites and morphology of intracranial lesions that should help to distinguish between neoplasia and inflammatory conditions and, possibly, between different inflammatory conditions.

A retrospective study of 286 cases of neurological disorders of the cat

Archive central nervous tissue from 286 cats with neurological disorders was reviewed for histological evidence of feline spongiform encephalopathy (FSE), which may have occurred before it was first recognized in 1990. The following six categories of disease were identified: congenital; degenerative; inflammatory; neoplastic; FSE; lesion-free. The largest category (inflammatory) contained 92 cats, of which 47 were considered to be consistent with infection by feline infectious peritonitis (FIP) virus. Six cats showed evidence of more than one disease process; thus, one cat with FIP also had toxocara infection of the lateral ventricles and five cats with FSE also showed perivascular cuffing suggestive of concurrent viral infection. In only two cases did the diagnosis on review differ significantly from the original interpretation. There was no evidence of FSE before the original case was recognized in April 1990.

Infectious diseases of the central nervous system

Neurologic disease is seen commonly in cats, with infectious causes accounting for 30-45% of cases. However, since a specific infection cannot be identified in 12-40% of these cases, it is essential that we try to understand these cases better in the hope that we can eventually identify the cause(s), and so determine how best to treat and/or prevent them.

Immunohistochemical localization of feline immunodeficiency virus using native species antibodies

Feline immunodeficiency virus (FIV) is the feline analog of human immunodeficiency virus and a small animal model of human acquired immune deficiency syndrome (AIDS). We sought to identify early in vivo target cells in cats infected with clade B or C FIV. In tissues, however, neither mouse monoclonal nor rabbit polyclonal antibodies suitably detected FIV because of either insensitivity or lack of specificity. We therefore developed an immunohistochemical protocol using high-antibody-titer serum from cats chronically infected with FIV(Petaluma). Native species anti-FIV antibodies were labeled with biotinylated protein A before placement on tissues, and downstream signal was tyramide-amplified. This method revealed many productively infected cells in bone marrow, lymph node, thymus, mucosal-associated lymphoid tissue, and spleen, but few such cells in liver and none in kidney or brain. Concurrent labeling for virus and cell phenotype revealed that antigen-bearing populations were primarily T lymphocytes but included macrophages and dendritic cells. Our results demonstrate that FIV: 1) expands rapidly in T cells, 2) targets long-lived reservoir populations, and 3) is replicatively quiescent in brain at 3 weeks after infection. Use of native species antibodies for immunohistochemical detection of infectious antigens has application to other settings in which xenotypic (eg, mouse and rabbit) antibody sources are inadequate or unavailable.

The feline model of neuroAIDS: understanding the progression towards AIDS dementia

Feline immunodeficiency virus (FIV) is a neurotropic lentivirus that produces a protracted state of immunodeficiency and encephalopathy in the cat. Recent evidence has shown several similarities to the natural progression of human immunodeficiency virus infection (HIV-1) associated degenerative effects on the central and peripheral nervous systems. Similar to HIV-1, FIV-induced encephalopathy neurovirulence is strain dependent, results in progressive immunodeficiency and increasing early peripheral but not brain viral load, preferentially affects the developing nervous system, produces quantifiable behavioural and neurophysiological impairment that is not directly linked to neuronal infectivity, and induces neuronal injury and loss both in vivo and in vitro. This paper highlights the cumulative scientific body of evidence supporting the use of the feline model of neuroAIDS.

Axonal sprouting in hippocampus of cats infected with feline immunodeficiency virus (FIV)

Neurologic dysfunction and neuropathology are common findings in patients infected with HIV and in cats infected with feline immunodeficiency virus (FIV). The pathogenesis of lentivirus-associated alterations in the central nervous system (CNS) is multifactorial. Because seizures, alterations in memory, and behavioral changes are clinical manifestations in adults and children infected with HIV, we explored the possibility that changes in neuronal structure may occur in the hippocampus. To do this, we examined the dentate gyrus of FIV-infected cats, an animal model of HIV infection. Neuropathologic findings included gliosis within the hilus of the dentate gyrus and granule cell axonal sprouting. Using the Timm's method, which labels axons of dentate gyrus granule cells, abnormally high amounts of staining were observed in the inner one third of the molecular layer in 45% of FIV-infected cats (n = 11) and in none of the controls (n = 19). Prominent axonal sprouting was seen in three FIV-infected cats that were infected as kittens, suggesting that younger cats may be more susceptible. Axon reorganization of the dentate granule cells has been hypothesized to underlie complex partial seizure activity in human temporal lobe epilepsy. These results suggest that FIV infection causes granule cell axon reorganization in the hippocampus of cats. A similar neuropathogenetic mechanism may contribute to neurologic dysfunction in HIV-infected patients.