Recovery of viral agents from the central nervous system of cats

Feline Foamy Virus Infection: Characterization of Experimental Infection and Prevalence of Natural Infection in Domestic Cats with and without Chronic Kidney Disease

Foamy viruses (FVs) are globally prevalent retroviruses that establish apparently apathogenic lifelong infections. Feline FV (FFV) has been isolated from domestic cats with concurrent diseases, including urinary syndromes. We experimentally infected five cats with FFV to study viral kinetics and tropism, peripheral blood mononuclear cell (PBMC) phenotype, urinary parameters, and histopathology. A persistent infection of primarily lymphoid tropism was detected with no evidence of immunological or hematologic perturbations. One cat with a significant negative correlation between lymphocytes and PBMC proviral load displayed an expanded FFV tissue tropism. Significantly increased blood urea nitrogen and ultrastructural kidney changes were noted in all experimentally infected cats, though chemistry parameters were not outside of normal ranges. Histopathological changes were observed in the brain, large intestine, and other tissues. In order to determine if there is an association of FFV with Chronic Kidney Disease, we additionally screened 125 Australian pet cats with and without CKD for FFV infection and found that FFV is highly prevalent in older cats, particularly in males with CKD, though this difference was not statistically significant compared to controls. Acute FFV infection was clinically silent, and while some measures indicated mild changes, there was no overt association of FFV infection with renal disease.

Detection of infectious canine parvovirus type 2 by mRNA real-time RT-PCR

A TaqMan real-time RT-PCR assay was developed for detection of RNA transcripts produced by replicating CPV-2. A pair of primers and a TaqMan probe targeting the spliced NS2 mRNA were designed. A synthetic DNA fragment was constructed to mimic the spliced NS2 mRNA by PCR-based gene assembly and was used for generation of standard RNAs. The detection limit of the assay was 1 × 10² RNA copies and standard curve displayed a linear range from 1 × 10² to 1 × 10⁹ copies and a good reproducibility. The assay was then applied to determine the mRNA loads in the tissues of dogs naturally infected by CPV-2. mRNA was detected in a variety of tissues, including the central nervous system.

Tissue distribution of the antigenic variants of canine parvovirus type 2 in dogs

Twelve dogs dead as consequence of natural infection caused by canine parvovirus (CPV) type 2a (n=4), type 2b (n=4) or type 2c (n=4) were investigated for determining the viral DNA loads in different tissue samples. By means of a real-time PCR assay, CPV DNA was detected in all tissues examined, with the highest titres observed in the lymphoid tissue and the lowest loads in the urinary tract. Surprisingly, the nervous tissue was found to contain considerable amounts of CPV nucleic acid. Similar patterns of tissue distribution were observed in all the examined dogs irrespective of the antigenic variant causing the disease.

Evidence of parvovirus replication in cerebral neurons of cats

The correlation between parvovirus infections and lesions in the central nervous system other than cerebellar hypoplasia was studied in 100 cats. The animals were necropsied with a history of various diseases, one third showing typical clinical and pathomorphological signs of panleukopenia. In 18 cats polyclonal antiserum against canine parvovirus consistently labeled neurons mainly in diencephalic regions, whereas the cerebellar cortex remained negative in all cases. In situ hybridization with digoxigenin-labeled minus-sense RNA probes, hybridizing with monomer-replicative form DNA or mRNA, revealed positive signals in nuclei of several neurons of the brain, again excluding the cerebellum. PCR applied to formalin-fixed and paraffin-embedded brain tissue and intestinal tissues of the diseased cats and subsequent DNA sequence analysis yielded canine parvovirus type 2 (CPV-2)-like sequences in the central nervous system. Two aspects of these findings are intriguing: (i). parvoviruses appear to be capable of replicating in neurons, cells that are considered to be terminally differentiated and (ii). CPV-like viruses of the old antigenic type CPV-2 appear to be able to infect cats.

Pathogenesis of virus-induced demyelination

Demyelination is a component of several viral diseases of humans. The best known of these are subacute sclerosing panencephalitis (SSPE) and progressive multifocal leukoencephalopathy (PML). There are a number of naturally occurring virus infections of animals that involve demyelination and many of these serve as instructive models for human demyelinating diseases. In addition to the naturally occurring diseases, many viruses have been shown to be capable of producing demyelination in experimental situations. In discussing virus-associated demyelinating disease, the chapter reviews the architecture and functional organization of the CNS and considers what is known of the interaction of viruses with CNS cells. It also discusses the immunology of the CNS that differs in several important aspects from that of the rest of the body. Experimental models of viral-induced demyelination have also been considered. Viruses capable of producing demyelinating disease have no common taxonomic features; they include both DNA and RNA viruses, enveloped and nonenveloped viruses. The chapter attempts to summarize the important factors influencing viral demyelination, their common features, and possible mechanisms.

Light and electron microscopical studies of the immunoperoxidase staining of multiple sclerosis plaques using antisera to a feline-derived agent and to galactocerebroside

Antibodies have been raised to two agents (CCA147 and MV631) that were isolated from central nervous tissue of cats. The cells co-cultivated with these agents are characterized by the presence of cytoplasmic inclusions consisting of 16-18 nm diameter tubular elements morphologically similar to inclusions seen in a demyelinating condition in cats and to inclusions described as 'curved linear profiles' in multiple sclerosis (MS) plaques. The peroxidase-labelled antibodies to CCA147 and MV631 stain these inclusions in MS plaques as well as small virus-like particles. The antisera do not stain normal white matter either in MS or non-MS brain tissue. The staining reaction of one agent is blocked by pretreatment with antisera to the other agent and also by pretreatment with MS sera but not by normal human sera. Peroxidase-labelled antibody to galactocerebroside stains normal myelin and myelin debris within MS plaques but does not stain the 'curved linear profiles' that are stained by the labelled antibodies to the feline-derived agents. The results show that the 'curved linear profiles' described in MS plaques are not myelin degradation products, but are comparable to the nucleocapsids of morbilliviruses. In addition, the small virus-like particles are morphologically similar to morbillivirus virions. The results are discussed with particular emphasis on the features of the morbilliviruses, canine distemper and measles viruses.

Primary demyelination in the central nervous system of cats

Primary demyelinating lesions have been observed in the central nervous system of 16 (approximately 7%) of a total of 235 clinically normal cats. The size of the lesions varied from small perivascular lesions in white matter to a large lesion occupying the diameter of an optic nerve. Intracytoplasmic inclusions consisting of tubular structures were common to all lesions examined by electron microscopy. The features of these feline lesions are briefly compared with those seen in multiple sclerosis.

Detection and prevalence of serotypes of feline syncytial spumaviruses

Three serotypes of feline syncytial virus (FSV) were detected by neutralisation tests: 906, a serotype of low prevalence and 702 and 951 which were serotypes of higher prevalence, between which a minor one-way antigenic difference was detected. Serum antibody in naturally-infected cats in some cases neutralised 951 but not 702 or 906 which suggested that 951 could be considered as a major distinct serotype. An increase in prevalence of antibody to FSV in cats over a 5 year period from 1977-1981 was detected by neutralisation, agar gel immunodiffusion, and fluorescent antibody techniques. Over the 5 year period the prevalence of antibody to the 951 serotype increased and the overall increase in prevalence of antibody to FSV during this period appeared to relate to dissemination of the 951 serotype.