18 | 04 | 2014
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DOG LICE and CAT LICE: biology, prevention and control

Lice are tiny microscopic insects that live on the body surface of many domestic and wild animals. Most species do not suck blood, but can cause considerable harm and anoyyance.

Adult Felicola subrostratus, the cat louse. Picture from M. Campos PereiraLice can plague dogs and cats as they do to humans and livestock. The good news is that lice species of dogs and cats, are also quite species specific. Consequently there is no risk that they are transmitted tu humans or to livestock, and vice versa, although some species may infect wild canids or felids (e.g. wolves, foxes, coyotes, etc. as well.

The most important lice species that affect dogs and cats are:

  • Felicola subrostratus, which occurs in cats worldwide. It is a rather small chewing lice, 1.2 to 1.3 mm long, i.e., it does not suck blood. It attacks mostly stray cats, but also old, neglected or otherwise weakened cats, especially longhaired breeds. It can transmit Dipylidium caninum, a parasitic tape worm of dogs and cats.
  • Heterodoxus spiniger, infests dogs almost worldwide except in Europe. It is a chewing lice, about 2.5 mm long. It is native from Australia: dingoes transmitted it to local dogs, which later spread it further. It can transmit Dipylidium caninum and Dipetalonema reconditum, two helminth parasites of pets.
  • Linognathus setosus, the dog sucking louse, occurs in dogs worldwide. It is a blood-sucking species 1.5 to 2.5 mm long. It is found often on the head (especially around the eyes and the ears), the neck and the breast of dogs.
  • Trichodectes canis infests dogs worldwide, 1.5 to 2 mm long. It is a chewing louse. It prefers the head, ears, neck and back of its hosts. It can transmit Dipylidium caninum, a parasitic tapeworm of dogs and cats.

Lice infestations are technically called pediculosis.


Biology and life cycle of lice on dogs and cats

All lice species are very small wingless insects, usually not lager than 3 mm. In contrast with mites, lice are visible to the naked eye. However, being so small they may look just like dirt, and not like living "bugs". Frequently the hair coat must be inspected deeply, down to the skin to find them. Lice eggs, called nits, are whitish, about 1 mm long and are glued to single hairs.

If a dog or cat shows vigorous scratching and/or licking and inspecting its hair-coat you find small spots of whitish dirt on the hairs or darker dirt elsewhere, such dirt may be lice.

Lice live on the surface of their hosts, i.e. in their hair coat, more or less close to the skin. They spend their whole life on the host, i.e. they are obligate parasites that cannot survive off the host and have no developmental stages living in the environment as fleas and ticks. If lice fall off the host, they won't survive more than a few days. They have an incomplete metamorphosis (i.e. they are hemimetabolic): larvae and nymphs are morphologically similar to adults, but smaller.

Their life cycle takes about 1 month to complete. Females glue their eggs individually to the hairs of the host. They can produce up to several hundred eggs during her lifetime. Adult life-span is 2-3 months, depending on the species and the environmental conditions.

Blood-sucking lice belong to the group called Anoplura. They may move around in the hair coat of their host searching a good place to bite.

Chewing lice do not suck blood and belong to the group called Mallophaga. They feed on skin scales or debris, or on body fluids that come out from small wounds they can produce with their mouthparts. They are rather static and usually do not move around in the hair coat, but remain close to the base of the hairs.

Transmission of dog and cat lice from one host to another one is by contact (typically from the mother to the litter). They are not transmitted through vectors such as flies, mosquitoes, etc. They do not jump from one host to another one as fleas may do. And they do not wait are crwal in the environment to find a host as ticks may do. This means that they are less infective than fleas or ticks. Lice can transmit a few diseases among dogs and cats, but not from pets to humans or livestock.

Lice infestations tend to be more frequent in the cold season, as for livestock.

Click here to learn more about the general biology of insects.


Harm caused by lice to dogs and cats

Linognatus setosus, the dog suking louse, adult male and female. Picture from M. Campos PereiraLice are more harming to weak (sick, undernourished, old, etc.) or neglected animals, or to puppies and kittens. Lice bites and feeding activity is highly itchy and the pets react with vigorous scratching, licking and even biting the affected areas. This can produce skin inflammation or thickening, hair loss and even wounds that can become infected with secondary bacteria. Massive infestations with bloodsucking lice can cause anemia as well.

As a general rule, lice are less harming to dogs and cats than fleas, ticks or mites and usually they are easier to control as well. However, in cold regions (e.g. Scandinavia, northern Canada, etc.), where weather conditions are not favourable for fleas or ticks, lice can become a major pest of dogs and cats.

Fatalities due to lice infestations are extremely infrequent.

As already mentioned, several lice species can also transmit pet diseases.


Prevention of lice on dogs and cats

Best prevention of lice infestations in dogs and cats is to keep the animals clean, healthy and well nourished, since lice tend to proliferate in weak and neglected animals. 

To prevent infestations it is not necessary to systematically treat the environment of the pets (beds, nests, carriers, crates, carpets, mattresses, cushions, coaches, cracks and crevices on floors, etc.) with lousicides, since lice spend all their life (including development) on the animals. The few nits that can fall off the animals won't survive long and lousicides are anyway ineffective against nits.

If a pet is already infested with lice, it is recommended to wash its bed or nest and textiles in very hot water, or dry-clean them at high temperature to accelerate death of possible lice or nits. If this is not possible, it may be better to replace them with uncontaminated fresh ones. If there is more than one pet in the same household it is also important to thoroughly clean or replace all tools or equipment used for pet care: combs, brushes, scissors, etc.


Vaccines, repellents and biological control of lice?

  • There are no vaccines against dog and cat lice. However, some people think that some medicines that are administered periodically (e.g. some spot-ons, injectables or tablets) are vaccines and write in blogs, chatrooms or forums about flea, tick or louse vaccines. Such products are not vaccines but classical insecticides that are administered periodically to prevent re-infestations.
  • There are no lice repellents, neither to prevent lice transmission from one pet to another one, nor to frighten off those that have already infested an animal. Most repellents may work to some extent against mosquitoes and certain flies, but certainly not against lice. To learn more about repellents click here.
  • There is no biological control method to effectively prevent or cure lice infestations on dogs or cats. Learn more about biological control of insects.

Natural, plant and homemade remedies to eliminate or prevent lice on dogs and cats

To begin with the conclusion, there are no natural and/or homemade remedies that will knockdown a serious lice infestation on dogs or cats. Lice population on the pet may be reduced, but the problem will not be solved. If ever effective, such remedies are frequently unreliable, i.e., they may work in a given place, on a given pet, for a certain time, but may not work elsewhere under different conditions.

There are numerous Internet sites with a lot of homemade remedies and recommendations, but almost none of them is supported by reliable investigations. Nevertheless, it may be worth trying them: usually they are not expensive and the risk of serious side effects is usually not too high. Many such remedies are based on do-it-yourself recipes based on plant extracts (citronella oil, neem, rosemary, lavender, lemon balm, etc.). Garlic is often mentioned as an effective lousicide, e.g. mixed with the pets food. Try them. If they work, fine. If they don't, try another one.

Click here if you are interested in medicinal plants for controlling lice and other external parasites of livestock and pets.

There are also countless so-called "natural" or "biological" commercial products containing natural insecticides or mixtures of plant extracts in the form of spot-ons, shampoos, soaps, lotions, sprays, etc. Many of them contain natural pyrethrins that are extracted from pyrethrum or similar flowers. Such products are usually substantially less effective against lice than synthetic lousicides. Besides being less effective, many of them have a very short residual effect, i.e., they protect no more than a few hours to a few days against re-infestation. The reason is that they are easily washed away by water (rain, washing, swimming, etc.) or break down by sunlight, or they simply evaporate very quickly.

Adult of Trichodectes canis, the dow chewing louse. Picture from M. Campos Pereira

It is good to know that most so-called "natural products" (e.g. plant extracts) are submitted to much less stringent regulations in many countries. This means that they don't need to proof their efficacy against parasites or their safety for the pets, users and the environment through such strict and thorough investigations as the products containing synthetic parasiticides. Many regulatory authorities seem to simply assume that being natural they are "good", or at least not harmful. Users will discover themselves whether they are effective or not... Obviously, the cost and the know-how to develop and market such "natural products" is substantially lower than for synthetic parasiticides and this explains their proliferation. It is not possible to deal with such products here in detail.


Products for chemical control of lice on dogs and cats

The chemical products used for the control of lice on dogs and cats are basically the same as for the control of fleas and/or ticks:

But be aware that not all products for flea and/or tick control will control lice and vice versa: read the label carefully.

Injectable macrocyclic lactones (e.g. ivermectin) are also efficient against pet lice. But in most countries they are not allowed for use on cats, and if ever allowed on dogs they must be used very carefully because several dog breeds have a reduced tolerance to macrocyclic lactones.

Since lice are easily transmitted among dogs or cats in the same household, it is usually necessary to treat all the animals in the same household.


Spot-ons against lice on dogs and cats

Nowadays spot-ons for flea and tick control are probably the most widely used antiparasitic products on dogs and cats. They contain one or more active ingredients in rather high concentrations (typically 10 to 40%) and are packed in ready-to-use, disposable vials of various sizes fitting to the pet's weight. The whole content of a vial has to be administered on one or more spots on the pet (e.g. on the back, or on the head, etc.) from where it spreads all around the body to reach the parasites where they are.

Correct spreading of the administered product ist essential for the its efficacy, and this is mostly achieved by the formulation (i.e. by the non active ingredients) and not by the active ingredients. This means that two different brands with the same active ingredient (e.g. fipronil) manufactured by two different companies may be differently formulated, consequently they may have a different spreading behavior and thus a different efficacy. Spreading also depends on specific features of the particular animal (breed, hair coat, size, behavior, etc.), which explains why efficacy of a given product may not be the same on different animals, or on the same animal under changing conditions or behavior.

Spot-ons were already introduced almost 50 years ago, but they became very popular only at the beginning of this century with the arrival of highly effective flea control products.

Most widely spot-on brands for lice control on dogs and cats

The most common original spot-on brands for use on pets are the following ones (may not be available everywhere; may be marketed under different trade-names).

  • FRONTLINE (with fipronil) from MERIAL available for dogs and cats worldwide. It was introduced in the 1990's mainly against fleas. Fipronil is a broad-spectrum insecticide with activity against lice and several ticks species as well. The active ingredient fipronil belongs to the phenylpyrazoles. Fipronil is also broadly used as an agricultural pesticide. It is also used on livestock in some countries (mainly in South America). Numerous brands with generic fipronil, alone or combination with other active ingredients are already available in most countries. Other related brands from MERIAL are:
    • FRONTLINE PLUS = FRONTLINE COMBO are follow-up brands from MERIAL with a mixture of fipronil and methoprene. Methoprene is an insect development inhibitor that interferes with the development of fleas.
    • CERTIFECT is the latest follow-up brand from Merial with fipronil, methoprene and amitraz, only for dogs. Amitraz is a veteran generic tickicide already introduced in the 1960's and "reheated" by several Animal Health companies in the last years. Amitraz is also used as an agricultural pesticide. Amitraz is toxic to cats! Numerous brands with generic fipronil, alone or combination with other active ingredients are already available in most countries.
  • ADVANTAGE (with imidacloprid) from BAYER available for dogs and cats worldwide. It was introduced in the 1990's. The active ingredient imidacloprid is a broad-spectrum insecticide that belongs to the group of the neonicotinoids. It is highly effective against fleas and certain lice species, but not against ticks. It is extensively used as a pesticide against agricultural parasites and against domestic and public hygiene pests. It's us on livestock is very scarce. Numerous brands with generic imidacloprid, alone or in combination with other active ingredients are available in many countries. Other related brands from BAYER are:
    • ADVANTIX is a follow-up BAYER brand only for dogs that contains a mixture of imidacloprid and permethrin (a synthetic pyrethroid) and is also effective against ticks. Permethrin is another veteran generic pesticide already introduced in the 1970's and extensively used worldwide as a pesticide in agriculture, domestic and public hygiene as well as on livestock. Permethrin is toxic to cats!
    • K-9 DVANTIX is another BAYER follow-up dogs-only brand in some countries, containing imidacloprid, permethrin and pyriproxyfen, an insect development inhibitor that interferes with the development of fleas.
    • ADVOCATE = ADVOCATE MULTI is another BAYER brand containing imidacloprid and moxidectin. Moxidectin is an macrocyclic lactone effective against parasitic nematodes, mites and lice. It acts systemically, i.e. the active ingredient is absorbed through the skin, gets into the blood stream and is distributed throughout the whole body. Moxidectine is a veterinary medicine also used on livestock but not in agriculture or hygiene. Numerous brands with generic imidacloprid, alone or in combination with other active ingredients are available in many countries.
  • REVOLUTION = STRONGHOLD (with selamectin) from PFIZER available for dogs and cats worldwide. Selamectin is a macrocyclic lactone effective against several external parasites such as fleas and lice, as well as against internal parasites such as gastrointestinal nematodes, but only against a few ticks species. It acts systemically, i.e. the active ingredient is absorbed through the skin, gets into the blood stream and is distributed throughout the whole body. It kills the external parasites when they suck blood or other body fluids. Selamectin is a veterinary medicine use exclusively on dogs and cats. It was introduced in the late 1990's. So far no products with generic selamectin have been introduced.
  • PROMERIS DUO (a mixture of metaflumizone and amitraz) from FORT DODGE (= PFIZER = ZOETIS) available in numerous countries only for dogs. It is effective against fleas, certain lice species and ticks. Metaflumizone is a semicarbazone introduced around the year 2000 by BASF as an agricultural and hygiene pesticide. BASF does not market veterinary products. Metaflumizone is effective only against fleas. The efficacy of PROMERIS-DUO against certain lice species and ticks is due to the amitraz in the formulation. As already mentioned, amitraz is a veteran generic tickicide already introduced in the 1960's and "reheated" by several Animal Health companies in the last years, also used as an agricultural pesticide. Amitraz is toxic to cats!. PROMERIS is another FORT DODGE brand with metaflumizone but without amitraz, available for cats, effective only against fleas. So far no products with generic metaflumizone are available.
    • NOTICE: In 2011 FORT DODGE (= PFIZER = ZOETIS) announced the withdrawal of PROMERIS and PROMERIS DUO from the market for not fitting with their product range. The decission was perhaps related to reports that associated metaflumizone with a higher incidence of "pemphigus foliaceus" in pets, a type of autoimmune skin disorder. However, it is not clear whether this withdrawal has become effective worldwide. Some Fort Dodge websites (e.g. Brazil in January 2013) still include PROMERIS and PROMERIS DUO in their product range.

Spot-on safety

Correctly used spot-ons are usually not a safety hazard for pet owners and their families. However it is advisable, especially for children, to avoid close and intense contact with pets recently treated with such spot-ons.

Serious intoxication of pets after been treated with spot-ons has been reported worldwide, especially on cats and small dogs. An investigation by the US EPA from 2010 reports that most problems have been noticed with spot-ons containing permethrin, fenothrin or amitraz used on cats, despite not being allowed for cats. Such use on cats may happen if users inadvertently apply dog-only spot-ons on cats. Intoxication or severe side effects have also happened on small dogs (puppies, small breeds) after using spot-ons for larger dogs on small ones due to erros in estimating the dog's weight, or after splitting a large spot-on to treat several smaller dogs or one dog in successive administrations. It also seems that some small dogs may simply have a more sensitive skin than larger ones and can react stronger to the treatment.

Another cause of pet intoxication or intolerance seems to be due to certain solvents in the formulations not sufficiently investigated regarding their tolerance for pets: they seem to be not as harmless as initially assumed.


Insecticide impregnated collars for lice control on dogs and cats

Before the introduction of spot-ons in the mid 1990's, insecticide impregnated collars for pets where rather popular. Most collars consist in a plastic or textile matrix impregnated with various contact insecticides, most of them rather old ones belonging to the organophosphates (e.g. diazinon), carbamates (e.g. propoxur), amidines (mostly amitraz) or synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin, etc.). Today some collars contain a mixture of such insecticides with insect development inhibitors (e.g. methoprene, methoprene, etc.). There are also collars impregnated with natural insecticides such as pyrethrins, d-limonene, linalool, etc. All these active ingredients, whether synthetic or natural, act by contact.

Collars are easy and convenient to use, and mostly cheaper than spot-ons. Some collars (especially those with organophosphates) may smell badly. Other collars may cause irritation around the neck of the pet.

Primary target of such collars are usually fleasticks or mosquitoes and not lice. They may provide some relief against lice, but they are seldom sufficient to control established lice populations.

Safety of collars against lice

Froom the safety point-of-view collars are similar to spot-ons. However, collars frequently contain older active ingredients, e.g. organophosphates or carbamates that may be more toxic than modern insecticides. Application erros such as those described for spot-ons are less likely to occur with collars.


Shampoos, soaps, lotions, spray, powders, etc., for lice control on dogs and cats

These kind of products have usually only a curative effect, and almost no protection against re-infestation, or only a few hours, if ever. As collars and spot-ons they target mainly fleas and ticks, and their efficacy against lice may be poor, although they may provide some relief.

Most shampoos, soaps, powders, etc. contain various contact insecticides, most of them rather old ones belonging to the  organophosphates (e.g. diazinon), carbamates (e.g. propoxur), amidines (mostly amitraz) or synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin, etc.), sometimes mixed with a synergist (e.g. PBO = piperonyl butoxide), which is added to overcome a possible resistance of the parasite to the insecticide.

Some products are ready to use (shampoos, soaps, lotions, etc.), others need to be diluted before use. Normally they are quite convenient and easy to handle, but application erros are more likely, because it is not always clear how much shampoo, soap or powder has to be used for a particular pet, and some parts of the body may not be properly treated.

From the safety perspective special care must be taken with concentrates that have to be diluted before use, especially those with organophosphates or carbamates. Mistakes in the dilution may cause overdosing and toxic effects for the pet, or underdosing and subsequenty inefficacy.


Insecticide resistance of dog and cat lice

So far there are almost no reports on confirmed resistance of dog or cat lice to lousicides.

This means that if a particular product has not achieved the expected control, it is most likely because the product is not adequate or it was not used correctly, not because lice have become resistant.

Learn more about parasite resistance and how it develops.

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