Cerebrospinal fluid is an efficient route for establishing brain infection with feline immunodeficiency virus and transfering infectious virus to the periphery.

Like human immunodeficiency virus (HIV), feline immunodeficiency virus (FIV) invades and infects the central nervous system (CNS) soon after peripheral infection. The appearance of viral RNA is particularly prominent in the cerebrospinal fluid (CSF), suggesting an efficient route of virus transfer across the blood-CSF barrier. This raises the concern whether this route can establish a stable viral reservoir and also be a source of virus capable of reseeding peripheral systems. To examine this possibility, 200 mul of cell-free NCSU1 FIV or FIV-infected choroid plexus macrophages (ChP-Mac) was directly injected into the right lateral ventricle of the brain. Negative controls were sham inoculated with uninfected ChP-Mac or virus-free culture supernatant and positive controls were infected systemically by intraperitoneal (i.p.) injection. Intracerebroventricular (i.c.v.) inoculation with cell-free FIV resulted in high levels of plasma FIV RNA detected as early as 1 to 2 weeks post inoculation in all cats. In each case, the plasma viremia preceded the detection of CSF viral RNA. Compared to i.p. cats, i.c.v. cats had 32-fold higher CSF viral loads, 8-fold higher ratios of CSF to plasma viral load, and a 23-fold greater content of FIV proviral DNA in the brain. No FIV RNA was detected in plasma or CSF from the cats inoculated with FIV-infected ChP-Mac but an acute inflammatory response and a slight suppression of the CD4+:CD8+ ratio were observed. These results indicate that free FIV circulating in the CSF promotes infection of the CNS and provides a highly efficient pathway for the transfer of infectious virus to the periphery.

Compartmentalization and evolution of feline immunodeficiency virus between the central nervous system and periphery following intracerebroventricular or systemic inoculation.

The emergence of distinct neuropathogenic strains resulting from the adaptation and the unique evolution of human immunodeficiency virus (HIV) in the brain may contribute to the development of HIV-induced neurological diseases. In this study, the authors tracked early changes in virus evolution and compartmentalization between peripheral tissues and the central nervous system (CNS) after intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) inoculation of animals with cell-free feline immunodeficiency virus (FIV). Using the FIV-NCSU1 envelope V3-V4 heteroduplex tracking assay (HTA), the authors observed a rapid compartmentalization of envelope variants between the CNS and periphery. Animals receiving the i.c.v. inoculation showed two peaks of viral RNA in the cerebrospinal fluid (CSF) with very different HTA patterns. Compared to the initial viral peak in CSF, the second peak showed an increased compartmentalization from plasma, reduced viral diversity, and more divergence from the proviral DNA in peripheral blood mononuclear cells (PBMCs) and the choroid plexus. In contrast, changes in plasma over the same time period were small. Different animals harbored different FIV DNA genotypes with varied regional compartmentalization within the brain. These results demonstrated that the virus within the CNS experienced a relatively independent but variable evolution from the periphery. Initial penetration of virus into the CSF facilitated the development of brain-specific reservoirs and viral diversification within the CNS.

AIDS-associated encephalopathy with experimental feline immunodeficiency virus infection.

Experimental intravenous challenge of 8-week-old kittens with the feline immunodeficiency virus Maryland isolate (FIV-MD) was investigated for its ability to infect the central nervous system (CNS) and induce neurologic abnormalities. Six cats were inoculated with 1,000 TCID50 units of FIV-MD isolate, with six age-matched cats serving as uninfected controls. Clinical and immunological evaluation documented that challenged cats developed immunodeficiency and growth delay. Neurologic examination revealed an abnormal stereotypic motor behavior consisting of repetitive, compulsive roaming that developed as early as 4 weeks postinfection (PI) and persisted throughout the 16-month study in three cats. Serial neuroelectrodiagnostic evaluation revealed persistent abnormal electroencephalographic recordings in three infected cats. Serial evoked potential (EP) recordings at 3, 8, and 12 months PI demonstrated significantly prolonged interpeak latencies III-V at 3 months PI and I-III at 12 months PI for brainstem EP recordings. Alterations of visual EPs were detected only at the 3-month time period. Retinocortical time, however, was significantly different from that in control cats at 3 and 12 months PI. Magnetic resonance imaging evaluation of FIV-MD-infected cats at 12 months PI revealed cortical atrophy, mild ventricular enlargement, and discrete white matter lesions. At 16 months PI, however, histopathological examination of brain tissue indicated only mild lesions limited to satellitosis and perivascular lymphocytic infiltrates. Virus was detected in the CNS by reverse transcriptase, immunofluorescence, and antigen capture. Evaluation of the cerebrospinal fluid revealed intrathecal anti-FIV-MD antibody despite lack of detectable viremia in five challenged cats. Collectively, these findings demonstrate the induction of virus-associated neurologic disease following parenteral FIV challenge in conjunction with an immunodeficiency state. The nature of the nervous system infection is analogous to HIV-1 pediatric encephalopathy.

Antibody responses to Toxoplasma gondii antigens in aqueous and cerebrospinal fluids of cats infected with T. gondii and FIV.

Antibodies to antigens of Toxoplasma gondii were measured in the aqueous and cerebrospinal fluid (CSF) of 16 specific-pathogen free kittens experimentally infected with feline immunodeficiency virus (FIV), T. gondii, or both pathogens. The results indicated that all cats infected with T. gondii had antibody responses to antigens of T. gondii in both aqueous fluids and CSF. Co-infection with FIV did not affect antibody levels. Aqueous fluids from eyes of cats with toxoplasmic retinochoroiditis did not necessarily have higher antibody levels than those from eyes without lesions. Antibodies to T. gondii were also detected in the CSF of two cats from whose brains no parasites were isolated by in vivo mouse inoculation. Total IgG did not increase significantly in the aqueous fluids and CSF of cats infected with T. gondii whether or not they were also infected with FIV.