What You Need To Know About Cat Lice
If you have kids, you probably have heard about lice. Maybe they have already got some at school.
Although a lice infestation doesn't cause serious health problems, it may create an uncomfortable situation. And sometimes, schools require that infested children stay home until they get rid of the parasites to prevent lice transmission to other pupils.
The treatment usually takes a couple of days.
In cats, it is more or less the same situation, except cats don't go to school, and the treatment is both faster and fully effective.
Nevertheless, you need to take the problem seriously. If you do nothing, the infestation will develop and eventually affect your cat's health.
How do I know my cat has lice?
Lice are tiny insects with no wings. They are very sedentary and spend their entire life on the same host (in this case, on the same cat), where they hatch, molt 3 times, and reproduce.
Lice appear in 3 different forms:
- eggs (also called nits) are oval-shaped sticky balls that are attached to the hair. They are 0.8 mm long and 0.3 mm wide
- nymphs are identical to adults in every way. But they are smaller and they can't reproduce
- the last molt gives birth to adults, which can reproduce after a couple of days. They are 2 to 4 mm long
Lice can’t fly or jump. They just creep slowly on the cat’s skin or hair.
At the beginning of the infestation, lice often remain unnoticed. But as they reproduce continually, the female laying one to two eggs per day, the population grows fast.
By grooming regularly, cats limit this growth. But there are some places they cannot reach: the head and the neck. You need to check these areas as a priority.
Moreover, lice infestations are more present in long-haired or older cats who cannot groom themselves as frequently.
You have to use a fine-toothed comb to ensure your cat has lice. They are the same as those used for humans, children, or adults. You'll pass the comb carefully through your cat's hair, preferably in the neck area.
Then, while keeping the comb horizontal, you'll examine what you've got on the comb's teeth. Nits may be confused with skin flakes or dandruff. But if you see forms moving slowly along the teeth, it means you caught some lice: you need to consider treating your cat.
How do lice harm cats?
Cat lice are Mallophaga or chewing lice. They have relatively large mandibles that allow them to chew and swallow what they can find on cats’ skin: skin flakes or sebaceous secretions.
A few lice do not represent a threat to your cat’s health. But when they are present in large numbers, lice may cause considerable irritation and itching. In some cases, allergic reactions may occur.
How can lice be transmitted to cats?
Felicola subrostratus is the only cat louse.
Cat lice (like all other lice) are very specific to their host. Cat lice are not the same as human or dog lice.
As a consequence, a cat can only be contaminated by another cat.
Cats can’t be infested by human or dog lice. And vice versa, cats can’t transmit lice to humans and dogs.
But it is very contagious among cats. In a household of several cats, it is very likely that when one cat is infested, the others are infested as well.
The complete life cycle is about 4 weeks.
Lice can’t live for more than 1 to 2 days away from their host; eggs and mobile forms can't stand the cold. Thus lice in the environment are not a source of contamination for your cat.
Repeated infestations by lice often indicate poor hygiene conditions, or that the cat meets regularly other cats that are themselves infested
How can I differentiate lice from fleas?
Fleas and lice share common characteristics. Both fleas and lice are insects. Both are about the same size. Both cause itching and sometimes allergy. Both can transmit Dipylidium caninum worms: the worms that look like rice grains in cats' feces.
Their bodies are both flattened, but not in the same direction:
- A louse body is flat and wide
- A flea body is tall and narrow: it helps it find its way among the hair easily and quickly
Lice creep slowly along the hair, while fleas move quickly and can jump very high.
Fleas bite to suck their host's blood, while lice only eat skin flakes.
Both species are sensitive to the same antiparasitic medicine. But fighting a flea infestation is much more challenging. First because flea's larvae and adults don't develop in the same places. And then because an adult flea can live on hosts from different species (cats, dogs, rats, birds, wild animals, and occasionally humans).
How do I treat lice on my cat?
Flea and tick treatments that work by contact with the insect or mite will also generally be effective against lice. These products are sold as sprays, spot-on, or collars.
The others are systemic products: they circulate in the bloodstream and kill ticks and fleas when they start to bite. They cannot affect chewing lice, which do not bite and do not consume the blood of animals.
Only products that contain fipronil (Frontline plus®, Fiproguard®, PetArmor®) are registered against cat lice. According to the legal leaflet, they “kill chewing lice for at least one month”.
Other active ingredients may also be recommended by your vet, but their use is "off-label":
- imidacloprid (Advantage®, Seresto®) based products are registered against chewing lice in dogs. They should also rapidly eliminate lice infestations in cats, 
- selamectin, the active ingredient of Revolution®, is registered in Europe under the names Stronghold® or Chanhold® for the control of cat lice. Its efficacy is documented in a published study.
The active ingredient spinosad is used in human medicine to treat head lice in children from 4 years of age. But the only veterinary dosage forms (Comfortis®, Trifexis®) are adminstered orally. They shouldn't be able to kill chewing lice 
There is no treatment against nits (eggs). But as all the products listed here are persistent for several days (up to one month), all first-stage nymphs that hatch out of their eggs will be killed. So, you should expect a total control of the infestation after a single product application.
DO NOT USE products containing PERMETHRIN as they are toxic to cats.
Here and there, you may hear about natural treatments based on vinegar, oil, and soap.
They probably wash out most adults and nymphs but not nits (lice eggs) because they are firmly attached to the hair. These natural products have no remanence. It is most likely that they will not break the parasite lifecycle unless you are ready to repeat a daily application for many days.
Of course, if you have more than one cat, you should treat all of them to avoid them contaminating each other again.
1. Companion Animal Parasite Council. Guidelines on pet lice
2. Rania Gollakner. Imidacloprid – Topical. VCA Hospitals
3. Stanneck, D., Kruedewagen, E.M., Fourie, J.J. et al. Efficacy of an imidacloprid/flumethrin collar against fleas, ticks, mites and lice on dogs. Parasites Vectors 5, 102 (2012)
4. D J Shanks et al. Efficacy of selamectin against biting lice on dogs and cats. Veterinary Record. 2003 Feb 22;152(8):234-7
5. MedlinePlus. Spinosad Topical