Download Flea Control Offers Better Protection For Pets, Humans

InFocus
Flea control offers better protection
for pets, humans from diseases
Advancements in technology enable veterinarians, owners
to eliminate fleas at most stages of development
By Lora Ballweber, DVM, MS
CONTRIBUTING AUTHOR
t one time fleas were an every day
fact of life – human infestations
were a result of living in close proximity to livestock and other animals as well as generally unkempt
environments that attracted rats
and other vermin.Humans were quite accustomed
to,although maybe not happy about infestions with
these ectoparasites,even going so far as to write poems
about them. Encountering fleas in many of today’s
societies, however, is more a byproduct of keeping
pets,rather than an inescapable fact of life.Without
pets, it is quite possible to never meet a flea despite
the presence of well over 2,000 species.
A
Diseases associated with fleas
Photo: Volpak USA
Fleas are the most common ectoparasitic problem
in dogs and cats throughout most of the world.Ctenocephalides felisis usually the species encountered and
is the least host specific, as many cat or dog owners
returning home from vacation to a house alive with
Fleas serve as
vectors for a
variety of human
pathogens.
hungry fleas can attest to.Clinical signs of infestation
in our pets can be mild and resolve once fleas are removed.However,uncontrolled infestations can lead
to pruritis,self-inflicted trauma and pyoderma.Certain animals are also allergic to salivary proteins of
fleas,which are released each time the flea feeds.The
allergic reaction also leads to pruritis,self-trauma and
secondary infections. In humans, papular urticaria
is often produced when a flea bites. These bites are
usually found around the ankles and wrists and tend
to just be itchy. However, some humans, just like
some dogs and cats,are allergic to the flea’s saliva and
severe, painful boil-like lesions may occur.
In addition,zoonotic diseases may be transmitted to humans through fleas.Fleas are the intermediate host for the tapeworm, Dipylidium caninum.
The definitive hosts for this parasite are cats and
dogs,but humans can become infected if an infected
flea is ingested. Obviously, the high-risk group is
children who tend to not notice what they put in
their mouths. Fleas are also vectors for a variety of
other human pathogens as well,including the agents
of murine typhus (Rickettsia typhi),sylvatic epidemic
typhus (Rickettsia prowazekii), cat scratch disease
(Bartonella henselae),plague (Yersinia pestis),and,a
relatively new-comer on the scene,murine typhuslike disease (Rickettsia felis).
The effects of fleas on the health of our pets, as
well as our own health,has led to a billion dollar industry centered on flea control products.Recent advances in our understanding of flea biology and in
product development has provided veterinarians
with many highly effective and safe flea control products with which to combat these voracious pests.
Types of activity
The latest developments in flea control center primarily on products that are given to the animal.Most
Continued on next page In Focus
june 2002 21
InFocus
The drug does not need to be ingested to
be effective;rather,it acts primarily as a contact poison passing through the exoskeleton of the flea. The time to peak effect is
six to 12 hours when used for the first time
and less than four hours in subsequent applications. Adults are generally killed before they can lay eggs.
Fipronil has also been combined with
methoprene, an IGR that is directly and
indirectly ovicidal,embryocidal and larvicidal.Female fleas exposed to methoprene
do not produce viable eggs and developing stages exposed in the environment do
not continue to develop.
Fipronil is also effective against ticks
(Rhipicephalus sangineus (brown dog tick);
Dermacentor variabilis(American dog tick);
Amblyomma americanum (lone star tick);
Ixodes ricinus(deer tick) killing them within
24-48 hours.This can be beneficial in controlling certain tick transmitted diseases
such as Lyme disease.
Photo: Volpak USA
of these products have adulticidal activity,
which is the lethal effect on fleas present on
the animal at the time of treatment. Some
of these products also have indirect larvicidal and ovicidal activity; that is,when trace
amounts are transferred to the animal’s surroundings through dermal debris, larvae
and ova contacting the debris are also killed.
Other products are insect growth regulators
(IGR). Some IGRs inhibit chitin synthesis
which disrupts the normal formation of cuticle and other chitnous structures. Others
are juvenile hormone analogs, binding to
insect juvenile hormone receptors and preventing the flea from molting from one stage
to the next.Finally,some products also have
anthelmintic properties or have been combined with anthelmintics to provide more
broad spectrum parasite control.
C. felis( left)
and C. canis
(right).
Compounds
Fipronil: Fipronil is a
phenylpyrazole compound that binds to gama-aminobutyric
acid (GABA) receptors of insects. GABA
is an inhibitory neurotransmitter in both
vertebrates and invertebrates. By blocking
GABA receptors,fipronil acts as an antagonist inhibiting the flux of chloride ions
into the nerve cell resulting in hyperexcitation of the nervous system and death.
The configuration of these receptors in insects is different than that in mammals
making this a very safe compound for use
in dogs and cats.
Fipronil is applied topically. The drug
dissolves in sebum,distributes through the
epidermis, and accumulates in the sebaceous glands from which it is slowly released by way of the follicular ducts. This
reservoir provides a long residual activity
allowing for monthly treatment intervals.
22 june 2002
Imidacloprid : Imidacloprid is a chloronicotinyl nitroguanidine that binds to the
postsynaptic nicotinic acetylcholine receptor thus preventing acetylcholine from binding.It is not degraded by acetylcholinesterase,
therefore, transmission of nerve impulses
is prevented resulting in paralysis and death
of the insect.It is a safe compound because
there is a higher concentration of nicotinic
acetylcholine receptors in insect nervous
tissue than in the central nervous system
(CNS) of mammals and it has a higher
affinity for insect receptors than vertebrate
receptors.
Imidacloprid is applied topically to a
single site in dogs and cats, although application of the dose to multiple sites in
dogs over 55 pounds is recommended. It
is translocated within eight hours and dries
as a microcrystal close to the follicles.Within
24 hours, it is completely distributed over
the body without any systemic absorption.
This drug also does not need to be ingested,
but acts as a contact poison. The time to
peak effect is under 12 hours in first time
applications, within two hours in subsequent applications and adults are generally killed before they can lay eggs.Monthly
applications are recommended.
Imidacloprid also has larvicidal activ-
ity.Larvae that contact dermal debris from
treated dogs will not develop and this inhibitory effect has been shown to last for
more than four weeks.
Selamectin: Selamectin is a semi-synthetic
avermectin compound that binds with postsynaptic glutamate receptors. This causes
the chloride channel to remain open and
chloride ions to flow into the nerve cell
blocking neurotransmission resulting in
paralysis.The blood brain barrier is generally effective in preventing the large molecule from passing into the CNS, even in
dogs with dose-related sensitivity to ivermectin, making this a safe drug.
Selamectin is applied topically.It is absorbed from the skin into the bloodstream
and redistributes into sebacious glands of
the skin. This compound also does not
need to be ingested by the flea, but acts as
a contact poison. The time for peak effect
is 24 to 36 hours in dogs and 12 to 24 hours
in cats with duration of activity good for
one month.Not only are adults killed,but
eggs which may be laid prior to death of
the selamectin-exposed flea tend to not develop and hatch. Additionally, dermal debris from treated dogs exhibits ovicidal activity for 21 days, larvicidal activity for 30
days and adulticidal activity for seven days.
Selamectin also has activity against
other parasites. It is approved for use in
the prevention of heartworms (Dirofilaria immitis) and the treatment and control of ear mites (Otodectes cynotis) in
dogs and cats. It is also approved for the
treatment and control of sarcoptic mange
(Sarcoptes scabei) and the control of the
American dog tick (D. variabilis) in dogs
and the treatment of intestinal roundworm (Toxocara cati) and hookworm
(Ancylostoma tubaeforme) in cats.
Lufenuron: Lufenuron is a benzoylphenylurea compound that disrupts the synthesis and deposition of chitin by blocking the
enzyme chitin synthetase. Chitin is essential for the survival of both ova and larvae;
consequently, this drug has both ovicidal
and larvicidal activity. Flea feces, an important component of the larval diet, will
contain a sufficient amount of lufenuron
to inhibit larval development.Fleas take up
www.dvmnewsmagazine.com
Product
Route of
administration
Approved for
of control*
Spectrum
Fipronil+methoprene
Topical
Dogs and cats
Adult fleas and eggs, ticks
Topical
Dogs and cats
Adult fleas
Topical
Dogs and cats
Cats: Adult fleas and eggs; heartworms, ear mites,
hookworms, roundworms
Dogs: Adult fleas and eggs, heartworms, ear mites,
sarcoptic mange, ticks
Injection
Cats
Flea eggs
Oral
Dogs and cats
Flea eggs
Dogs
Flea eggs, heartworms, hookworms,
roundworms, whipworms
Dogs and cats
Adult fleas
(Frontline Plus®)
Imidacloprid
InFocus
Table 1: Flea Control Options in 2002
(Advantage®)
Selamectin
(Revolution®)
Lufenuron
(Program®/6-month injectable)
Lufenuron
(Program Flavor Tabs)
Lufenuron+milbemycin oxime Oral
(Sentinel Flavor Tabs)
Nitenpyram
Oral
(Capstar)
Hundreds of products are available to control fleas on pets. This table is a summary of just some of the recently marketed products available for flea control.
*See text for specific names of parasites.
the drug with the bloodmeal and transfer
it to their eggs.It does not have adulticidal
activity; consequently, it may take five to
eight weeks to achieve good flea control
when used alone. Significant reduction in
environmental flea burdens can be achieved
with development inhibition lasting for up
to 45 days after a single dose.
Lufenuron is administered orally (cats
and dogs) or through subcutaneous injection (cats only). This is a highly lipophilic
compound that concentrates in adipose
tissues from where it is slowly released into
the blood.Oral formulations are given on
a monthly basis while the injectable formulation provides six months protection.
Given that mammals do not have chitin,
this is a very safe compound.
A combination product of lufenuron
with milbemycin oxime is available for use
in dogs.Milbemycin oxime,a macrocyclic
anthelmintic,eliminates the tissue stage of
heartworm, and the adult stage of hookworm (Ancylostoma caninum),roundworm
(Toxocara canis and Toxascaris leonina),
and whipworm (Trichuris vulpis).
Nitenpyram: Nitenpyram is a neonicoti-
noid compound that binds and inhibits
nicotinic acetylcholine receptors.It is rapidly
absorbed and eliminated with maximum
blood levels reached within 1.2 hours in
dogs and 0.6 hours in cats. The half-life is
about three hours in dogs and about eight
hours in cats. Effective blood concentrations are only maintained for approximately
one day after administration. This compound has adulticidal activity with most
adult fleas killed within four to six hours.
This compound is also very safe – it can be
administered every 24 hours if necessary.It
can also be safely combined with lufenuron.
Suggested reading
Taylor MA. 2001. Recent developments in ectoparasiticides. The Veterinary Journal 161:253-268.
A two-part series by Barragry T. 2001. Pharmacological developments in flea control. Irish Veterinary Journal 54:457-459 and 54:523-529.
Ruiz A. 2001. Plague in the Americas. Emerging Infectious Diseases 7:539-540 (conference panel
summary giving brief overview of plague).
In Focus
The future
Even with the major advancements in the
area of flea control, successful ectoparasite control programs still rely heavily on
the use of chemicals.Worry over the possible development of resistance to parasiticides,coupled with human,animal and
environmental safety concerns, emphasize the need for continued research into
discovery of compounds with novel modes
of action or improved formulations of existing compounds. The long developmental time and high costs required to
bring new products to market,only stresses
the importance of using our current products in a wise and judicious manner.Failure to do so may result in their loss before alternatives become available and,
should that happen, we may once again
be writing poems to the flea.
DVM
Dr. Ballweber is an associate professor in
the College of Veterinary Medicine at
Mississippi State University. She joined
the faculty in 1993 where her research
focuses on parasites of ruminants and
llamas, as well as a variety of wildlife. She also shares responsibility for teaching veterinary parasitology to veterinary students. She received her veterinary degree from
Oregon State University in 1992 and a master’s degree in
parasitology from the University of Wyoming in 1982 and
a master’s degree in veterinary science (epidemiology) from
Oregon State University in 1989.
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