The Cat Flea: biology, ecology and control

This article, The Cat Flea: biology, ecology and control is a follow on from the earlier: Cat Flea Treatment. Its purpose is to try and provide some insights into how best to control the cat flea. Fleas are a major nuisance for cat keepers and a major irritant and possible health hazard for our cats. The article is centered around USA life as it was written by Americans – apologies to international visitors.

This article is exclusively based on a scientific study of the same title authored by Michael W. Dryden and Michael K. Rust working out of the Department of Pathology and Microbiology at Kansas State University and the Department of Entomology at the University of California. It was published in 1994.

The Flea and Health Issues

Almost all cat fleas are the species, Ctenocephalides felis felis. This species is also found on dogs a lot. For example, in north-central Florida, USA, 92.4% of the fleas on dogs were C.felis felis. In Virginia all the fleas on cats and dogs were C.felis felis.

There are four subspecies of Ctenocephalides felis. The other three are:

1. Ctenocephalides felis strongylus – Africa
2. Ctenocephalides felis damarensis – Africa
3. Ctenocephalides felis orientis – Southeast Asia and East Indies

Tackling the flea is important as it:

• causes irritation in animals
• can cause anemia in animals
• can cause allergic dermatitis (Flea Allergic Dermatitis – FAD). See Feline Miliary Dermatitis too.
• acts as a vector (carrier) for “typus-like rickettsia” and:
• is the intermediate host for filarids and cestodes. Filarids are parasites living in the blood vessels of animals. Cestodes are tapeworms living in the digestive tract of vertebrates. Fleas ingest the larva of tapeworms. A cat (or dog) ingest fleas infected with the larvae of tapeworms. The larva is released inside the cat.
• the cat flea has been “implicated as a vector” in human plague.

FAD is caused by the saliva of the flea that contains antigens that the cat’s immune system responds to. FAD is the most common dermatological disease in cats and dogs worldwide. It is a major cause of feline miliary dermatitis. The symptoms are an intense itch resulting in scratching, licking and chewing. This damages the skin, which in turn can lead to an infection.

The flea is an hematophagous insect. Hematophagous animals have mouth parts and chemical agents for penetrating vascular structures in the skin of hosts, mostly of mammals, birds, and fish allowing them to feed on blood. They can therefore cause iron deficiency anemia in heavy infestations. Young animals are particularly vulnerable. An example is barn calves that were severely infested causing anemia and death.

Rickettsia typhi is an organism that causes murine typhus. The signs are headches, chills and rashes. It occurs in humans and other animals. C.felis has been shown to be the vector for this illness. A vector in this context means: an organism, often an invertebrate arthropod, that transmits a pathogen from reservoir to host. Murine typhus occurs in south-eastern, south-western and the gulf states of the USA.

Cat Flea Eggs

70% of eggs laid in the fur of cats fall off the cat within 7 hours. They fall off and hatch within 1-6 days depending on temperature and relative humidity (RH). They accumulate around the area where the cat sleeps/rests. The optimum temp/RH combination for hatching is: 50% and 27°C.

Cat Flea Larvae

The eggs hatch into larvae. The larvae hide from light in the substrate (the surface on which the larva grows or is attached). That is why they develop at the base of carpet fibres, which makes them harder to kill through the application of insecticides. Flea larvae are very light, temperature and RH dependent for development:

• “Flea larvae will simply not develop in areas exposed to hot sun”;
• “Larvae are extremely susceptible to desiccation” (drying out). An RH of less than 33% is lethal.

Cat flea development outdoors is promoted by an RH greater than 50%, a soil moist level of less than 20% and a temperature that is between 4°C and 35°C.  In short: moderate temperatures and a high RH. This is quite specific and many places don’t support this requirement.

Larvae require a source of adult flea fecal blood (the blood excreted by the adult flea having fed on the host cat or other animal).

Larvae hardly move when developing in a household’s carpet; most moving less than 20 cms. They crawl to avoid light.

Flea larvae tend to survive cat flea treatments for adult fleas that is applied to carpet because:

• they are at the base of the carpet
• they require more insecticide to kill them than adult fleas.

The study provides some analysis of insecticides. I have selected some:

• residual deposits of methoprene provided 75-100% reduction in flea larval development even after 1.5 years after treatment.
• aerosol applications of “fenoxycarb (at 2.2 mg per sq. ft.) and methoprene (at 0.6 mg per sq. ft.) provided 100 and 70% inhibition of adult emergence at 60 days, respectively”.
• 186 mg per sq.ft. of granular or powdered boric acid applied to carpet killed all the larvae.
• D-limonene, a naturally occurring chemical (in fresh peel of citrus fruit) is toxic to larvae at 210 mg per square foot.  D-limonene can be bought over the internet as a standard household cleaner (left below) and for use in a spray (right below):

Two useful tags. Click either to see the articles: Toxic to cats | Dangers to cats

The authors make no confirmatory statement about the effectiveness of borate treatment of carpets, which are advertised as effective.

Pupae

Mature larva transform to pupa within a cocoon although the process can take place without a cocoon. The cocoon is 0.5 mm long, white and ovoid. The cocoon is sticky and bits stick to it. They are found in soil, in carpets, in cat’s bedding, under furniture and on vegetation.

The pupal stage lasts for 6-7 days. Pupa are resistant to drying out. The products illustrated above are less toxic to pupae than to adult cat fleas.

Pupae, though, absorb insecticide so they can be killed. The main barrier to killing pupae is the fact that they occupy the base of the carpet where insecticide does not reach.

Pupa can stay “quiescent” (quiet) for long periods (up to 140 days). In autumn the period before emergence as as an adult can be 20-30 weeks. “Mechanical pressure and increased temperatures stimulated emergence “ of the adult flea. Vacuuming stimulates adult fleas to emerge and are “extremely effective” in collecting fleas. Th e authors say that, “vacuuming after treatment forces the pre-emerged adults to emerge…”. The average time for emergence in households is 3-5 weeks.

Adult flea seeking a host

Adult fleas jump onto passing hosts such as your cat. The flea locates a host through “visual and thermal clues” (vision and heat). Fleas are color blind! They are most sensitive to green light. Fleas congregate near vents, crawl spaces and window sills. This is a response to the light.

C.felis orientates towards light and is likely to jump onto a host on the temporary interruption to the light as this indicates a passing animal that throws a shadow. C.felis differentiates between ambient heat and heat from a “target” (potential host animal). The adult cat flea moves from the base of the carpet or vegetation to the top in readiness for jumping.  A cat flea can survive for several days without finding a host. Temperature and RH dictate length of survival for newly emerged adult fleas.

Adult-host associations

Once the adult flea has jumped onto a cat it feeds “almost immediately”. It produces feces within 8-9 mins after starting feeding. Reproduction requires feeding to take place first. After feeding fleas mate. Egg production begins within 24-48 hrs after females have feed for the first time. Eggs are laid in the cat’s fur. They drop off. Within 8 hours 70% of the eggs have dropped off the host.

C.felis has a “large reproductive capacity” (it breeds fast!). This compensates for high loss rates in larvae due to extremes of temperature and RH.

Dependant of the cat’s grooming, which interferes with reproduction, the female flea can produce 40-50 eggs per day max. When cats groom they remove fleas by inadvertently eating the  flea or dislodging it.

Flea control on the cat is very much dependent on flea control of the environment in which the cat finds itself. This is commonsense but sometimes forgotten. “On host” and “in environment” flea treatments go hand in hand and in parallel.

See Cat Flea Treatment for more on this.

I’ll add some of the authors’ useful comments on cat flea treatments:

Flea products that work by ingesting blood that has insecticide in it such as Frontline Spot treatment kills more female than male fleas as females drink more blood than males! “The efficacy of orally administered cythioate after two doses was 82.8% and 33.4% against female and male C.felis respectively.” Cythioate is an organothiophosphate chemical used as an insecticide and anthelmintic. It has been sold under the trade names Cyflee and Proban, under which form it has been used for veterinary purposes against fleas¹.

Cats are apparently more commonly undertreated for fleas than dogs because of the inability of “many cat owners to restrain and treat their cats”.

The fleas reproductive process can be prevented by topical or systemically acting insect growth regulators (IGR). “Topical” means the treatment is applied to a localized area of the body or to the surface of a body part. While  “systemically” means affecting a particular body system in this context, as I understand it.

Insecticides are, however, unpopular today for good reason. Instructions must be strictly adhered to for obvious reasons. Some alternatives are not effective though:

• ultrasound producing devices don’t repel fleas. Worse, the sound produced can be picked up by the cat causing altered behaviour.
• Brewer’s yeast and;
• B-complex vitamins and;
• elemental sulphur flea repellents are all ineffective.

Recurrence of infestations

This is thought to be due to:

• prolonged survival of pre-emerged adults (see pupae above)
• lack of penetration of carpets by insecticides
• the wide host range of C.felis. Non-domestic hosts include: coyotes, red and grey foxes, bobcats, skunks, rodents, raccoons, opossums and ferrets. These can live close to humans and pets and be a continual source of C.felis.
• As to the gradual resistance C.felis to insecticides this has yet to be determined but may be a factor.

Conclusions

Flea populations survive because of fast reproduction. Suitable environments are limited for the fleas development. Control of infestations is conducted by treating the host (e.g. cat) and environment. The environment should be treated with IGRs to “eliminate further larval development” and the application of insecticides against adult fleas which should be re-applied within 1-3 weeks. The use of topical and systemically acting IGRs are recommended on the pet.

A typical topical treatment is Frontline drops. Examples of systemic treatments are Program® flea control for cats and Capstar. Both are pills that are given orally.

The Cat Flea biology ecology and control — Note:

1. wikipedia.org/wiki/Cythioate

From The Cat Flea biology ecology and control to Cat Health Problems