Lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats: a systematic review

Abstract

BackgroundFeline herpesvirus 1 is a highly contagious virus that affects many cats. Virus infection presents with flu-like signs and irritation of ocular and nasal regions. While cats can recover from active infections without medical treatment, examination by a veterinarian is recommended. Lysine supplementation appears to be a popular intervention (recommended by > 90 % of veterinarians in cat hospitals). We investigated the scientific merit of lysine supplementation by systematically reviewing all relevant literature.MethodsNCBI’s PubMed database was used to search for published work on lysine and feline herpesvirus 1, as well as lysine and human herpesvirus 1. Seven studies on lysine and feline herpesvirus 1 (two in vitro studies and 5 studies with cats), and 10 publications on lysine and human herpesvirus 1 (three in vitro studies and 7 clinical trials) were included for qualitative analysis.ResultsThere is evidence at multiple levels that lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats. Lysine does not have any antiviral properties, but is believed to act by lowering arginine levels. However, lysine does not antagonize arginine in cats, and evidence that low intracellular arginine concentrations would inhibit viral replication is lacking. Furthermore, lowering arginine levels is highly undesirable since cats cannot synthesize this amino acid themselves. Arginine deficiency will result in hyperammonemia, which may be fatal. In vitro studies with feline herpesvirus 1 showed that lysine has no effect on the replication kinetics of the virus. Finally, and most importantly, several clinical studies with cats have shown that lysine is not effective for the prevention or the treatment of feline herpesvirus 1 infection, and some even reported increased infection frequency and disease severity in cats receiving lysine supplementation.ConclusionWe recommend an immediate stop of lysine supplementation because of the complete lack of any scientific evidence for its efficacy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-015-0594-3) contains supplementary material, which is available to authorized users.

Effects of free amino acids on cytokine secretion and proliferative activity of feline T cells in an in vitro study using the cell line MYA-1

“…Considering the effects of lysine in the present investigation, further in vivo studies on its immunomodulating potential seem to be interesting. Dietary lysine supplementation has been recommended for cats infected with feline herpesvirus 1 for a long time, however, current data could not prove antiviral effects of lysine (Maggs et al 2006;Rees and Lubinski 2008;Drazenovich et al 2009;Bol and Bunnik 2015). Stiles et al (2002) could demonstrate some beneficial effects of dietary lysine supplementation in cats with feline herpesvirus conjunctivitis, whereas the study of Maggs et al (2003) could not support this observation.…”

A review of antiviral drugs and other compounds with activity against feline herpesvirus type 1

“…Lysine's antiviral effect is believed to arise because arginine is an essential amino acid for FHV‐1 and HSV‐1 replication, and assumes that lysine antagonizes arginine availability to or utilization by these viruses during protein synthesis. This was originally hypothesized to affect protein synthesis of the virus more than the host because viral proteins had a higher arginine‐to‐lysine content than did human (and feline) proteins; however, recent analysis suggests that the difference in feline vs. FHV‐1 protein amino acid content is minimal . Markedly elevated lysine concentrations in combination with notably low arginine concentrations suppress HSV‐1 and FHV‐1 replication in vitro .…”

A novel herpesvirus associated with chronic superficial keratitis and proliferative conjunctivitis in a great horned owl (Bubo virginianus)

“…Cidofovir, which was administered in this GHOW, has been previously shown to reduce viral shedding and clinical signs in cats with induced ocular infection with feline herpesvirus, although its effectiveness in birds in general and against the specific virus isolated remains undetermined. l ‐lysine was administered as it was regarded as a benign therapeutic; however, recent studies indicate that lysine is not efficacious for control of feline herpesvirus 1, as well as human herpesvirus 1 . As clinical disease associated with herpesviral disease is often waxing and waning, it is possible that resolution of clinical signs may have occurred without any therapy.…”