Herpes virus infection is a common illness in cats. Along with other infective organisms, it is responsible for the highly contagious cat flu. Infection causes upper respiratory signs including sneezing and runny eyes; many cats also develop a fever and go off their food. Some cats develop ulcers on their cornea and vulnerable young kittens can succumb to pneumonia.
For many years, the amino acid L-Lysine has been recommended as a treatment for herpes virus in cats. It has also been used to prevent infection. This recommendation was based on some studies in humans that suggested that L-Lysine inhibits herpes virus replication inside cells. However, a recent literature review suggests that it’s not as useful as once thought.
L-Lysine has no actual antiviral properties, but is thought to affect viruses by lowering the amount of the amino acid arginine that is available to them. Arginine is another amino acid that is used not only in normal cell processes, but specifically in virus-infected cells because it plays a role in virus replication. The 2015 literature review conducted by scientists from the University of California found that supplementation with L-Lysine was not at all effective in either preventing or treating feline herpes virus infection. It appears that L-Lysine didn’t affect arginine levels, and indeed reducing the amount of arginine didn’t stop viral replication. The other issue that’s important here is that cats can become ill from insufficient arginine so it’s not a good idea to try to lower the levels of this amino acid.
With L-Lysine no longer recommended for treating herpes virus in cats, what are the options available to veterinarians and pet parents?
Human antiviral drugs such as famciclovir and acyclovir have been used in cats with good results. They reduce the period of illness and cats tolerate them very well. Topical antiviral drugs can be used on corneal ulcers -- one example is idoxuridine -- but they need to be administered frequently, sometimes every three hours. This can be difficult in a busy working family.
Antibiotics are appropriate in some cases. Even though these drugs don’t kill viruses, they can help with the secondary bacterial infections that often occur.
Symptomatic treatment is also important. Intravenous fluids to maintain hydration, steam therapy to clear mucus from the nose, and appetite stimulants to encourage a sick cat to eat can play a role in recovery. When a cat feels unwell, sometimes the simplest thing such as washing their face can make them feel better. Tender loving care is always a good method of therapy.
Herpes virus is a persistent infection in cats, and when they are stressed, the virus can reactivate and symptoms recur. This means that cats can become ill with these symptoms repeatedly throughout their life. Reducing stress can lessen the chance of further outbreaks.
Prevention of illness is better than cure and to that end, cats should be vaccinated to protect them from this disease. Kittens need to have multiple vaccinations over their first few months of life; thereafter, their veterinarian can recommend an appropriate schedule of boosters to make sure that they stay protected.