Detection of active and latent feline herpesvirus 1 infections using the polymerase chain reaction

Abstract

A polymerase chain reaction (PCR) assay was developed to detect the thymidine kinase gene of feline herpesvirus 1 (FHV-1) and to study the active and latent carrier state in a group of naturally FHV-1 infected specific pathogen free (SPF) cats. The detection limit of PCR products on ethidium bromide stained gels was 390 fg or about 3 x 10(3) copies of the FHV-1 genome. The PCR was 25% more sensitive than conventional cell culture based virus isolation techniques in detecting FHV-1 in oral/ocular swabs and 100 times more sensitive in detecting virus in cell culture supernatants. Sites of FHV-1 latency in FHV-1 carriers as determined by PCR were mainly tissues of the head, especially the trigeminal ganglia, optic nerves, olfactory bulbs and corneas. Oral fauces, salivary glands, lacrimal glands, cerebellum and conjunctiva were less consistently positive. The cerebral cortex, thymus, trachea, lung, liver, spleen, kidney, and peripheral blood mononuclear cells were consistently negative for FHV-1 genome. The distribution of FHV-1 DNA in the tissues of the head was similar whether or not corticosteroid-induced virus shedding was occurring at the time the tissues were collected. Infectious virus was never recovered from tissue homogenates regardless of the PCR status of the tissues.

Feline herpesvirus

“…Latent infection has been demonstrated in trigeminal ganglia, using extended culture techniques such as explant or organ culture [35,94]. FeHV-1 DNA, indicative of the presence of viral genome, has also been detected in trigeminal ganglia and in some other sites by PCR [111,130,146]. However, detection of latency associated transcripts (LATs) is probably the most accurate way to determine whether the virus is truly in a latent state: such transcripts, produced from the complementary strand to the immediate early gene(s), are expressed in relative abundance compared to other genes by alphaherpesviruses during latency.…”

“…However, viral DNA has also been detected by PCR in other neurological sites (including olfactory bulb, optic nerve and cerebrum), and also in various ocular and respiratory tissues (including nasal turbinates and cornea, and less consistently, oral fauces, conjunctivae, lacrimal and salivary glands, tonsils and submandibular lymph nodes) [28,111,146]. Whether FeHV-1 is truly latent in such tissues, or whether low grade viral reactivation is being detected is not clear.…”

“…shed virus under natural conditions, and even then, transmission to susceptible animals is not necessarily easily achieved [30,34]. More recent studies using PCR, including realtime PCR, have shown a higher sensitivity for detecting carriers, with a more prolonged presence of viral DNA in the secretions of infected cats [8,45,83,111,125,131,141,146,147]. Whilst such molecular techniques help identify carriers, the epidemiological significance of cats in which viral genome can be detected by PCR, but from which infectious virus cannot be isolated is not clear, as transmission studies have not been performed.…”

Clinical and antiviral effect of a single oral dose of famciclovir administered to cats at intake to a shelter

“…At least 80% of infected cats remain persistently infected, since the virus becomes latent in neural tissue, especially within the trigeminal ganglia, as well as the optic nerves, olfactory bulbs and corneas (Reubel et al, 1993). This helps to account for its estimated seroprevalence of 50-97% in feline populations worldwide (Studdert and Martin, 1970;Ellis, 1981;Maggs et al, 1999;Bannasch and Foley, 2005;Byeong-Teck and Hee-Myung, 2008;Blanco et al, 2009).…”

Quantification of Feline Herpesvirus 1 DNA in Ocular Fluid Samples of Clinically Diseased Cats by Real-Time TaqMan PCR

“…Unfortunately, during chronic and recurrent infections both tests often yield negative results (8). Therefore, DNA detection techniques, e.g., PCR, have become extremely useful in the diagnosis of FeHV-1 (3,12,26,29,35).…”