Within multicat environments such as animal shelters, breeding catteries, cat shows, research colonies, and even multicat households, IURD (ie, rhinitis, pharyngitis, and keratoconjunctivitis caused by infectious organisms) is a common and major management problem.1 Although many infectious agents are likely involved, evidence gathered over many years on multiple continents suggests that the major pathogens are FHV-1, FCV, and Chlamydophila felis (previously Chlamydia psittaci).2 Of these, FHV-1 is believed to be the most common and to cause the most severe and recurrent disease. Infection of susceptible kittens with FHV-1 causes marked IURD, with approximately 100% morbidity. Illness may be fatal, particularly in young kittens.3 After primary infection, FHV-1 establishes lifelong neural latency in at least 80% of infected cats.3 Periodic viral reactivation and shedding take place throughout life in most cats and are associated with chronic rhinosinusitis and keratoconjunctivitis in many. Physiologic stressors such as intercurrent disease, pregnancy, lactation, and rehousing increase reactivation rates and ensure perpetuation of the virus in feline populations, particularly in cats housed in shelters.3 Therefore, latently infected cats represent the major source of infection for cats immunologically naïve to FHV-1. To date, medications that reduce establishment of latency or frequency of reactivation of FHV-1 in cats have not been identified.
The impact of IURD is perhaps greatest within shelter environments. In shelters, there is sometimes rapid turnover of large numbers of cats with variable vaccination and immune statuses and which are kept in conditions known to exacerbate shedding of some infectious respiratory pathogens.1,3 Methods for controlling the spread of IURD include quarantine, which consumes time, resources, and space; systemic administration of antiviral agents to newly infected cats, which is expensive and sometimes associated with considerable toxic effects;4 and vaccination, which is of unknown efficacy in latently infected cats. As a result, IURD is one of the major reasons for euthanasia or difficulty in rehousing cats from shelters. Because latently infected cats are the most important natural reservoir for infection of susceptible cats, the most logical means of control in shelter environments is reduction of viral shedding by carrier cats.
Encouraging data exist regarding antiviral effects of lysine against FHV-1 in vitro,5 in cats undergoing experimental primary herpetic infection treated with 500 mg of lysine every 12 hours,6 and in latently infected cats treated orally with 400 mg of lysine every 24 hours.7 Both of these in vivo studies6,7 involved investigation of the effect of bolus administration of lysine to small numbers of experimentally infected cats, and outcomes of a recent study8 suggest these data may not be directly applicable to larger groups of naturally infected cats. In that study,8 144 cats in a shelter received oral boluses of 250 mg (kittens) or 500 mg (adult cats) of lysine once daily for the duration of their stay at the shelter and outcomes were compared with those of an untreated control group. No significant treatment effect was detected on the incidence of IURD, the need for antimicrobial treatment for IURD, or the interval from admission to onset of IURD.8 Additionally, bolus administration of lysine to individual cats within multicat environments such as shelters, where FHV-1 is prevalent, may not be practical. It is also plausible that twice-daily handling of these cats may actually stimulate further viral reactivation through stress and cause transfer of pathogens between cats by shelter workers administering the lysine.
If bolus administration is not essential for efficacy of lysine in management of IURD, then dietary lysine supplementation would be an excellent means of providing additional lysine in multicat environments. We found that healthy cats fed a diet supplemented with up to 8.6% lysine developed no toxic effects and had significant increases in plasma lysine concentration, whereas plasma arginine concentration and food intake were unaffected.9 These results suggested that dietary lysine supplementation could be done safely and efficaciously in healthy cats. We then conducted a study10 in which 100 cats in a colony in which IURD was enzootic were rehoused to stimulate viral reactivation and fed a diet containing 1.1% or 5.1% lysine for 52 days. Compared with cats in the control group, cats fed the supplemented diet had a higher plasma lysine concentration but also had more severe disease and had FHV-1 DNA detected more often in swab specimens collected from the conjunctival fornix. However, increased disease severity and FHV-1 DNA detection were most noteworthy in a subpopulation of male cats that exhibited fighting behavior. Therefore, a definitive conclusion regarding the efficacy of dietary lysine supplementation for control of disease and shedding of FHV-1 in cats with enzootic IURD was not possible. In addition, we are unaware of any studies conducted to determine the effect of lysine on the replication, clinical severity, or shedding of other pathogens involved in feline IURD.
The purpose of the study reported here was to test the hypothesis that dietary lysine supplementation of cats housed in a shelter in which IURD was enzootic would reduce detection of specific microbial nucleic acids and clinical signs of IURD in the cats. Our objectives were to determine the effect of dietary lysine supplementation on the development and severity of clinical signs of IURD and on detection at ocular and oropharyngeal surfaces of nucleic acids from FHV-1 along with 2 other organisms commonly associated with IURD (C felis and FCV) in cats in a shelter environment in which IURD was enzootic.
Feline herpesvirus type 1
Hazard rate ratio
Infectious upper respiratory disease
Snap FIV/FeLV Combo test, IDEXX Laboratories Inc, Westbrook, Me.
Dacron swab, Fisher Scientific USA, Pittsburgh, Pa.
Nucleic acid purification lysis solution, Applied Biosystems, Foster City, Calif.
TestDiet, Division of Land O'Lakes Purina Feed LCC, Richmond, Ind.
Biochrom 30, Biochrom Ltd, Cambridge, England.
ABI Nucleic Acid PrepStation, Applied Biosystems, Foster City, Calif.
Eclipse-4, Schering-Plough Animal Health Corp, Omaha, Neb.
RNase-free DNase I, Roche Diagnostics, Indianapolis, Ind.
SuperScript III RT, Invitrogen, Carlsbad, Calif.
Random Hexamers, Invitrogen, Carlsbad, Calif.
RNase inhibitor, Invitrogen, Carlsbad, Calif.
Invitrogen, Carlsbad, Calif.
ABI Primer Express 2, Invitrogen, Carlsbad, Calif.
SYBR Green PCR Master Mix, Applied Biosystems, Foster City, Calif.
7700 ABI PRISM SDS instrument, Applied Biosystems, Foster City, Calif.
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Proximate composition (g/kg of diet) of experimental diets as reported by the manufacturer.
|Nutrient||Basal diet*||Lysine-supplemented diet†|
The basal diet was composed of the following ingredients (g/kg of diet): corn gluten meal (219.2), ground brown rice (200), poultry by-product meal (184.3), corn flour (174.2), porcine animal fat preserved with butylated hydroxyanisole (62.1), fish meal (58.1), soybean oil (50), dicalcium phosphate (15.8), potassium chloride (8.5), sodium chloride (5.8), phosphoric acid (4.7), calcium carbonate (3.1), choline chloride (2.5), taurine (1.9), L-arginine (1.8), pyridoxine hydrochloride (1.3), menadione dimethylpyrimidinol bisulfite (1.0), DL-methionine (1.0), L-tryptophan (0.7), thiamin mononitrate (0.7), vitamin A acetate (0.6), zinc sulfate (0.5), cholecalciferol (0.4), DL-α-tocopheryl acetate (0.3), magnesium potassium sulfate (0.3), biotin (0.2), folic acid (0.2), manganese sulfate (0.2), calcium pantothenate (0.1), riboflavin (0.1), cyanocobalamin (0.1), nicotinic acid (0.1), copper sulfate (0.1), calcium iodate (0.05), and sodium selenite (0.001).
The lysine-supplemented diet was composed of the following ingredients (g/kg of diet): corn gluten meal (230.0), ground brown rice (200.0), poultry by-product meal (154.3), corn flour (141.8), porcine animal fat preserved with butylated hydroxyanisole (68.9), L-lysine acetate (56.4), soybean oil (50.0), fish meal (33.5), dicalcium phosphate (19.4), potassium chloride (8.5), phosphoric acid (7.5), calcium carbonate (6.5), sodium chloride (5.8), L-arginine (3.7), choline chloride (2.5), taurine (1.9), pyridoxine hydrochloride (1.3), magnesium potassium sulfate (1.1), menadione dimethylpyrimidinol bisulfite (1.1), DL-methionine (1), L-tryptophan (1), thiamin mononitrate (0.7), vitamin A acetate (0.6), zinc sulfate (0.5), cholecalciferol (0.4), DL-α-tocopheryl acetate (0.4), biotin (0.2), folic acid (0.2), manganese sulfate (0.2), calcium pantothenate (0.1), riboflavin (0.1), cyanocobalamin (0.1), nicotinic acid (0.1), copper sulfate (0.1), calcium iodate (0.05), and sodium selenite (0.001).