Why You Need to Worry About Cat Lice
[but not too much]
If you are a parent you probably have heard about lice. Maybe your kid has already got some at school.
Although a lice infestation doesn't cause serious health problems to cats, it may create an uncomfortable situation. And sometimes, schools require that infested children stay at home until they get rid of the parasites, to prevent the transmission of lice to other pupils.
The treatment usually takes a couple of days.
In cats, it is pretty much the same except that cats don't go to school and that the treatment is both quicker and fully effective.
Nevertheless, you need to take the problem seriously. If you do nothing, the situation will get worse and eventually affect your cat's health.
How do I know my cat has lice?
Lice are very small 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 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 are able to reproduce after a couple of days
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 places they can’t reach: the head and the neck. This is where you need to check, in priority.
Moreover, lice infestations are more often seen in longhaired or older cats that are no more able to groom themselves frequently.
To make sure your cat has lice, you’ll need to use a fine-toothed comb. This the same as those that are 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 i.e. 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?
Felicola subrostratus is the only louse that can be found in cats.
Cat lice (as all other lice) are very specific to their host. It means that cat lice are not the same as human lice or as dog lice. They can only be transmitted from one cat to another cat.
The practical consequence is that 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 between 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 the cat’s 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 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. On one hand because flea's larvae and adults don't develop in the same places. On the other hand 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?
Generally, anti-ticks and anti-fleas products are also effective against lice, if they have the opportunity to get in contact with the parasites.
It does not apply to systemic products, given orally or injected. Systemic products circulate in the cat's blood flow and reach blood-sucking parasites such as fleas or ticks. Such treatments won't do any harm to chewing lice which do not suck blood.
In practice, you should not see lice or nits on cats treated with topical products: sprays, spot-ons, or collars; even though very few of them are registered against lice.
Nevertheless, if you detect lice or lice eggs (nits) on your cat, you have a few options.
Only products containing fipronil (Frontline plus®, Fiproguard®, PetArmor®) are registered against chewing lice in cats. 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 is the active ingredient of Revolution®. It is registered in Europe under the name of Stronghold® or Chanhold® for the control of cat lice and its efficacy is documented in a published study .
The active ingredient spinosad is used in human medicine to treat head lice in children from the age of 4 . 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 that are quoted 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 might hear about natural treatments with vinegar, oil, and soap.
They probably wash out a majority of adults and nymphs, but not nits (lice eggs) which are strongly attached to the hair. These natural products have no remanence and it is very likely they won’t break the parasite’s lifecycle unless you are ready to repeat a daily application for several days.
Of course, if you have more than one cat, you should treat all of them at the same time to avoid new contamination.