[Public Health] The 99% Solution

Pest management professionals often cringe over the thought of successfully navigating through the laborious logistics of a flea infestation. Perhaps the effective treatment solution for fleas has been so elusive due to high-gain emphasis on only one percent of the problem. Perhaps the effective treatment is the 99 percent solution.

With 2,200 or more flea species, about 95 percent of fleas parasitize mammals with the remaining 5 percent parasitizing birds (ecologically radiating the geographic habitats and ultimate niches serving these successful disease vectoring antagonists). Flea population developmental stages occur in a statistical distribution of approximately 35 percent eggs, 55 percent larvae, 9 percent pupae and 1 percent adults. Therefore, successful integrated treatments must refocus on the 99 percent of non-adult flea developmental stage populations.

FLEA BIOLOGY. Fleas are complete metamorphic insects, having developmental stages consisting of eggs, larvae, pupae and adults. Adult fleas are small (1 to 5 mm), laterally flattened, wingless insects that infest the pelage of mammals or the plumage of birds. Fleas have piercing mouthparts that are inserted into the capillary beds of their host for a blood feeding. In North America, a few species commonly parasitize dogs and cats: the ubiquitous cat flea, Ctenocephalides felis; the dog flea, Ctenocephalides canis; the small mammal flea, Pulex simulans; the human flea, Pulex irritans; and the poultry flea, Echidnophaga gallinacea.

Cat fleas cause severely emergent symptoms in animals, as well as man. Cat fleas are the cause for flea allergy dermatitis (FAD). In addition, fleas serve as a vector for typhus-like rickettsiae and are the intermediate host for filarid and cestode parasites. It is believed that cat fleas infest more than 50 different hosts worldwide. In North America, commonly infested hosts include domestic and feral dogs and cats, raccoons, opossums, skunks, bats, squirrels, rabbits, ferrets, rats and mice.

Cat fleas oviposit within the pelage of a given host. Flea eggs are whitish-oval with rounded ends and approximately 0.5mm in diameter. Host movements cause flea eggs to fall out of pelage in discernable patterns onto bedding, carpet, furniture and soil. Egg emergence occurs in approximately one week. Flea larvae are 3 to 5 mm long, cylindrical, white, segmented and intermittently covered with hairs. Larvae are precocial (e.g., capable of a high degree of independent activity from birth) and feed on organic types of debris found within their environment. Flea larvae avoid light and they actively move deep within carpet fibers or similar organic substrates.

In one or two weeks pupae are fully developed. These pre-emergent adult fleas breech the cocoon upon exogenous stimulation: carbon dioxide, movement or pressure on substrates and/or heat. Therefore, intensively repetitive vacuuming places considerable environmental stress on non-adult flea developmental stages. Pre-emergent adult flea populations residing within cocoons can significantly extend the longevity of interior flea pressures. If pre-emerged adult fleas do not receive the proper stimulus to emerge, they remain quiescent in the cocoon for extended periods until a host arrives. Pre-emerged adult fleas can survive up to six months within cocoons if protection from desiccation is in place. Emergent fleas move up in carpet pile or vegetation where a passing host is more likely encountered.

If emergent cat fleas do not immediately feed on a host, they can survive many days before needing a blood meal. Emergent-unfed fleas infest animals and bite people. Cat fleas that have obtained a preferential host (domestic and feral dogs and cats, raccoons, opossums, skunks, bats, squirrels, rabbits, ferrets, rats and mice) do not leave their host unless forced off by grooming activity or insecticides.

Temperature and humidity dependent, the complete life cycle of cat fleas can be completed in two weeks or delayed for six months. Under ambient household conditions, cat fleas complete their life cycle in about four weeks.

THE FLEA FEEDS. Once a host is found, cat fleas begin immediate feeding. Female cat fleas ingest 13.6 µL of blood on a daily basis. Upon blood digestion, the adult cat flea’s excreta or blood dries within seconds to form fecal pellets or long tubular coils commonly referred to as "flea-dirt." Within 24 hours of a blood-meal, adult cat fleas mate, protein conversion pathways are potentiated and egg production begins. Female cat fleas produce 40 to 50 eggs per day during peak production.

Since their roots are near the equator, adult cat fleas are extremely susceptible to cold. None of the cat flea life stages can survive exposure to less than 37°F over several days. Cat fleas survive seasonal cold temperatures in the adult stage on untreated dogs and cats or on feral mammals in urban environments. Feral animals passing through urban areas during spring migrations set up harborage sites in crawl spaces, attics, garages and sheds. Eggs placed by surviving female fleas drop off and, in turn, develop into adults. In addition, cat fleas survive seasonal cold as pre-emergent adults within sheltered microenvironments.

Cat fleas comprising dense populations cause iron deficiency anemia, especially amongst immature animals. It is indicated that fleas in the Genus Ctenocephalides produce anemia in poultry, dogs, cats, goats, sheep, cattle and horses.

Cat fleas are vectors of numerous diseases. Murine typhus, Rickettsia typhi, is a disease of humans with symptoms that include headaches, chills, skin-rashes and involvement of the kidneys and central nervous system. The primary transmission cycle and amplification of Murine typhus involves opossums and cat fleas. In addition, cat fleas serve as the intermediate host of the nonpathogenic subcutaneous filarid nematode of dogs, Dianimalalonema reconditum. Dipylidium caninum, an intestinal cestode of dogs, cats and sometimes children, develops as a tapeworm larva in dog, cat and human fleas. Flea larvae ingest tapeworm eggs which develop into cysticercoids within the flea. When dogs and cats groom themselves, they may ingest infected fleas and, with them, cysticercoids.

Flea allergy dermatitis (FAD), known as flea bite hypersensitivity, is the most common dermatologic disease of domestic dogs in the United States. In addition, cats are affected by FAD, which is one of the major causes of feline dermatitis. FAD is most prevalent in the summer. Cat fleas inject saliva that contains enzymes and histamine-like substances, resulting in irritation, itching and eventual hypersensitivity. Immunologic tolerance may be naturally occurring in dogs continuously exposed to flea bites.

CONTROL. Pest management efforts targeting the elimination of flea infestations are often challenging and laborious. Management solutions must be targeted toward elimination of adult fleas within the structure, but more importantly elimination of adult fleas on the animal and the three immature flea stages within the environment.

Prior to treating any animal or structure with insecticides, mechanical solutions must be implemented. Along structural exteriors and peripheries, dense vegetation that provides a damp microenvironment must be mowed, clipped or eliminated. Leaf litter organic debris and clutter must be removed to allow soil aeration and drying. Once obstructed areas are opened to sunlight, conditions are presented that are not conducive to flea development. Within structural interiors, mechanical solutions must include washing any animal bedding and animal carriers. In addition, intuitive knowledge and thorough vacuuming of animal resting and sleeping areas removes numerous flea eggs, larvae and stimulated mature pupae or pre-adults.

Dense interior flea populations can be controlled quite effectively through synergistic insecticide applications, usually pyrethroids, combined with an insect growth regulator (IGR). Insect growth regulators are compounds that inhibit molting or development of immature stages of fleas and other insects. Insect growth regulators are classified as either juvenile hormone analogs (metho-prene and fenoxycarb) or chitin synthesis inhibitors (also called insect developmental inhibitors such as lufenuron). IGR compounds inhibit viable development of flea eggs and larvae. IGRs can be used alone or in combination with insecticides in multiple formulations. Methoprene and fenoxycarb can be applied either to the environment or topically upon the animal. Lufenuron is administered orally to animals monthly.

Carpet density affects the penetrative ability of an insecticide into the fleas’ microenvironment. Flea larvae escape many insecticide treatments due to the fact that the compound fails to contact them at the base of carpet fibers where development occurs. Of interesting note is the fact that it requires two-and-a-half times more insecticide per gram of body weight to kill larvae as opposed to adults. However, IGRs effectively inhibit larval development in carpeting. In addition, borate-based carpet powders offer considerable larvicidal activity.

Insecticides and IGR synergists are applied by broadcast treatment method. Broadcast treatment is completed by using either a manual hand pump sprayer or ready-to-use pressurized aerosols. The application process requires that the surface of all rugs, carpets, related furniture upholstery and especially all animal resting and sleeping areas must be treated thoroughly. Emphasis must be directed toward flea ovae, larvae and pupae aggregation points. Aggregation points include, but are not limited to: carpet, cracks and crevices in hardwood floors, behind baseboards, under the edge of rugs, beneath furniture or furniture cushions and, especially in the case of cats, within closets. In very dense flea populations, thorough and persistent vacuuming will be required pursuant to continued emergence of adult fleas from cocoons hidden deep within carpets.

Flea pupae present a major problem for management solutions. When employing synergistic insecticide formulations containing an IGR, the balance of resident adult fleas are killed and further larval development is stopped. Conversely, without the integration of synergistic treatments, pupae will continue development and adult fleas will continue to emerge from cocoons for the next four weeks. Since most residual insecticides take hours to kill adult fleas, emerging fleas may re-infest animals or bite people before succumbing to insecticides.

Elimination of fleas in landscaping and the lawn is an important integration of a flea management solution. Exterior treatments must concentrate on main areas of flea development, including protected microhabitats such as dog houses, within garages, under porches and within animal resting areas beneath shrubs or other shaded areas. Entomopathogenic nematodes that parasitize flea larvae and pupae are available and can be used in these areas to inhibit flea populations. Broadcasting flea management products over large areas of a shade-free lawn generally is not beneficial. Multiple insecticidal solutions are commonly employed for exterior residual activity against emerging fleas. Some include; microencapsulated or capsular suspension pyrethroids and permethrin. These compounds have effective residual activity for several weeks.

CONCLUSION. Pest management professionals must certainly focus on the 1 percent of flea populations, the adults. But an overall integrated flea management solution must also equally focus on the remaining 99 percent of flea populations, the eggs, larvae and pupae, along with their accompanying unique biological characteristics. Bringing these two intuitions together will give pest management professionals and their clients 100 percent success.

The author is a Board Certified Entomologist and is technical director for Springer Pest Solutions, Des Moines, Iowa. He can be reached at smitchell@giemedia.com.