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Types of
Insects and Bugs you may encounter, and facts about each are
here.
- Fleas
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Fleas are tiny, wingless insects.
The adult is an external parasite of people, dogs, cats, and
wild animals, including rodents and birds. Responsible in centuries
past for the plagues that killed millions of people, the flea
is now a far less serious but still troubling health threat and
nuisance to humans and animals.
Common Types:
Fleas are familiar to most people with a dog or cat. They are
the small, flat and normally hidden insects whose quest for blood
sets the animal to frantically snapping at its tail or scratching
its ears. Cat (and dog) fleas are the most familiar of well over
1,800 species and subspecies. A few other species have been instrumental
in spreading serous human diseases, such as bubonic plague. Others
pass diseases onto animals and a few burrow into the skin of
their hosts.
Fleas belong to the order Siphonaptera
and are subdivided into three superfamilies. Pulicoidea, with
about 25 genera, contains most species of medical and veterinary
importance such as the cat, Oriental rat and sticktight fleas.
Certopsylloidea is the largest superfamily with 150 genera that
are mostly Neotropical in distribution in southern Mexico, Central
and South America, and the West Indies.
The best known to North Americans
is the cat flea (Ctenocephalides felis), which pursues cats and
dogs. The very similar dog flea (C. canis) is far less common.
These fleas jump onto their hosts and remain there.
Few other flea species are familiar,
but the Oriental rat flea (Xenopsylla cheopis) which carries
the causative bacterium for the plague, retains notoriety for
several hundred cases occurring in wild rodents in the U.S. over
the last several decades.
Biology:
Adult fleas, which move by running or jumping, feed on the blood
of the host. The eggs hatch into worm-like larvae that develop
off the host and feed on detritus or the bloody excrement of
the adults. The flea structure, form and life cycle show perfect
adaptation to life on the host.
The Egg - Flea eggs are smooth
and white. Most species lay two to six eggs per day and can lay
hundreds over a lifetime. Eggs are normally laid in the host's
sleeping and resting areas. When laid on the host, as do cat
and dog fleas, the eggs fall out of the host coat, often at the
animal's sleeping quarters. (Hatching occurs in a few days if
humidity is above 70% and temperatures are between 65-80 degrees
Fahrenheit.) The flea embryo uses a sharp spine on its head,
called an egg burster, to cut and tumble out of the egg.
The larvae, blind, limbless worms
with circlets of hairs around each inter-segmental division,
have three molts. Normally intolerant of light, rarely seen but
quite mobile, larvae feed on debris on the floor of the nest
of their parents. Adult fleas supplement the debris under the
sleeping animal with undigested fecal blood of adult fleas.
The Pupa - The mature larva spins
a whitish, ovoid cocoon with debris embedded in it. This resting
stage allows a flea to survive for long periods until stimulated
to hatch by the appearance of a host. Pupae will not survive
if humidity is low (as low as 45% for the rat flea).
The Adult - The adult flea, normally
1.5 to 4 mm long, is wingless, flat and brown. The neck is short,
as are the antennae, which fit into a protective groove on the
head when not in use. The eyes are not well developed. Some species,
such as Leptopsylla segnis, the house-mouse flea, lack eyes entirely.
Many species have combs, arrays of stiff bristles to keep the
flea from being pulled out of the host's coat, and hind legs
adapted for jumping. Two notable exceptions to the active, jumping
flea are the sticktight fleas (Echidnaphaga gallinacea of chickens)
and the sand flea, chigoe, or jigger (Tunga penetrans) which
parasitizes man and animals. The females of these fleas burrow
into the skin of the host and remain attached for life.
Adult fleas feed by piercing
the host's skin with their mouth parts and penetrating a capillary
from which they suck blood, using one or more pumps to convey
the blood to the gut. If undisturbed, feeding is complete in
2-10 minutes. Female fleas take up about twice as much blood
as males.
Health Issues:
Human Health Impact
Historically, the tiny rat flea has greatly impacted civilization
as carrier of the plague. The tropical or Oriental rat flea is
the main carrier of the plague bacterium, Yersinia pestis. Typically
feeding on the brown rat, Rattus rattus, and the black or roof
rat, R. norvegicus, the rat flea also readily feeds on people.
Plague has probably afflicted
humans since before the time of Christ. The Philistines are recorded
as suffering from a disease with symptoms like those of the bubonic
plague. The first pandemic of record was probably in the sixth
century, beginning in Egypt. During the late Middle Ages, the
Black Death laid waste to Europe in another pandemic. An estimated
25 million people died in the fourteenth century. From 1664 to
1666, 70,000 Londoners dies out of a population of 450,000. Civil
disorder broke out. Terrified neighbors even put plague victims
to death.
What made the disease so frightening
was that its cause was unknown. Only in the late 19th and early
20th centuries did a few brave researchers establish that the
rat flea had to be present to spread the disease. That discovery
came during the third pandemic, which began in China's Yunnan
Province in the 1890s and spread to the West Coast of the U.S.
and throughout the world. Deaths in the U.S. occurred in San
Francisco, Los Angeles and cities farther east, such as New Orleans.
The disease is characterized
by rapidly developing high fever, headache, prostration, fatigue
and delirium. By the second day, lesions know as bubos (hence
bubonic plague) appear in the groin and armpits. Mortality rates
are high.
Cases of plague still occur in
the U.S., primarily in wild rodents. In the western states, 334
cases were reported from 1970-1994.
Murine Typhus - Found worldwide,
several species of flea, including Xenopsylla cheopis (the main
vector), Nosopsylla fasciatus and Leptopsylla segnis carry murine
typhus. Flea feces transmit murine typhus when the host human
scratches his or her skin to alleviate itching caused by fleabites,
allowing the pathogen to enter the body. While thousands of cases
occurred each year early in the 20th century, the disease is
rare in the U.S., occurring primarily in the South. Symptoms
include sudden high fever, headache, nausea, coughing and a spotted
rash.
Flea-Caused Infections - The
female chigoe, jigger or sandflea bores into the skin, usually
of the feet, causing extreme irritation. If Tunga penetrans is
not removed, it can cause an infection, which may become gangrenous.
Chigoes are found in tropical Americas and Africa and are most
prevalent in people who walk barefoot.
Skin Irritation - Annoying to
some, fleabites can cause serious irritation in sensitive individuals.
Bird fleas may become a problem when construction disturbs bird
nests in buildings. The human flea (Pulex irritans) can also
cause irritation but is now much less frequently encountered
in the U.S. than cat and dog fleas.
Tapeworm - Young children may
be at risk if they play in areas where pet excrement is present
and the cat or dog has the tapeworm Dipylidium caninum. When
tapeworm eggs are defecated by a cat or dog, flea larvae may
feed on the excrement and ingest the eggs. The tapeworm eggs
hatch in the flea's larval gut. When the flea completes its development,
a cat or dog may ingest the adult flea during grooming or nipping.
A child coming into close contact with a pet may ingest a tapeworm-infected
adult flea from the pet.
Animal Health Impact
Cat and Dog Flea - The cat flea, which parasitizes both dogs
and cats and can transmit a species of tapeworm to pets, is the
main flea of concern to most North Americans. The less common
dog flea is similar to the cat flea.
Adult cat and dog fleas remain
on the host (rather than jumping on the animal only to feed),
causing severe irritation and vigorous scratching. This can lead
to severe coat loss and frequent visits to a veterinarian. Both
flea species may transmit the tapeworm Dipylidium caninum. The
tapeworm's eggs are defecated by the cat or dog and larval fleas
consume the feces.
Sticktight Flea - An important
poultry pest in subtropical America, the sticktight flea remains
attached to a chicken, causing ulcers in which flea eggs are
laid, and in heavy infestations, anemia. The sticktight flea
also will attack cats, dogs, horses and humans.
Myxomatosis - This flea-vectored
disease of rabbits wiped out nearly the entire rabbit population
of the United Kingdom in the 1950s, eliminating rabbit trapping
as an income source for many and reducing the food source of
raptorial birds and predatory animals. The disease has been deliberately
introduced in Australia as a means of controlling huge infestations
of rabbits.
Flea Control:
Sanitation, insecticides and common sense are keys to efforts
to control fleas. Good sanitation measures are important in conjunction
with appropriate flea control products used according to label
directions on the host or in the host's habitat.
Cat and Dog Fleas
Insecticidal pet shampoos and dips, flea collars and total release
aerosols, and powders can control cat fleas. Control is best
achieved by using several products concurrently so that the flea
infestation is attacked both on and off the host. Dipping or
shampooing coupled with fogging the home and fitting the treated
pets with flea collars is advisable.
Normally, no single product is
sufficient to control an infestation of cat fleas. For example,
treatment of the pet only will not combat fleas present in immature
stages in the carpet. The immature stages will emerge as adults
and cause reinfestations. Thus a combination of a pet treatment
and a house treatment, including the area where the pet sleeps,
is usually needed so the cycle can be prevented from recurring.
Pet Shampoos and Dips - A veterinarian,
professional groomer or the pet owner can apply these products
according to label directions. Shampoos are applied and rinsed
off after a short time. Dips are 'leave on' products.
Pet Flea Collars - Flea collars
are impregnated plastic strips that allow the slow release of
the active ingredient. Collars rely on migration of the active
ingredient over the coat of the pet, possibly aided by grooming,
to reach the fleas.
Total Release Aerosols - Foggers
are designed to fill a room with fine particles that settle on
exposed surfaces and can penetrate to hidden interior surfaces.
Fleas attacking the pet are often also found on the floor, especially
in carpet and places where the pet sleeps and rests. Use of a
total release aerosol is a convenient means of treating flea
infested rooms uniformly and completely. Of course, people and
pets should not be in the room during fogging. Be sure to read
and follow the directions.
In recent years insect growth
regulators have been added to foggers and to other flea control
products. These materials interrupt the flea's life cycle before
adult fleas emerge to become a nuisance. Because IGRs are slow
acting and do not affect the adult fleas, they are normally coupled
with a conventional insecticide so that adult fleas can be controlled
immediately.
Direct Aerosol Sprays - These
aerosol products have valves that allow the can to be used in
an inverted position so floor areas can be easily sprayed. They
are useful for treating limited areas or where foggers might
be inappropriate.
Powders - Powders applied to
the pet are the dry equivalent to dips in that the powder is
left on the animal. They also are easier to apply than dips.
Systemics - A successful innovation
in flea control has been an orally or dermally administered insect
growth regulator in pill form for dogs and liquid or gel for
cats. Available only from veterinarians, the IGR is administered
once a month, preventing eggs from hatching and breaking the
life cycle. Since a systemic has no effect on other life stages,
including adults, control is not immediate. A conventional adulticide
treatment is needed before the IGR can control an infestation.
Miscellaneous - Traps with small
lights aim at luring fleas to adhesive coated sheets to which
they are to become stuck. The impact of these types of traps
on flea infestations is unknown.
Public Health Control - Control
of fleas that may carry plague or other diseases is the responsibility
of state and federal public health authorities, which routinely
conduct surveys for plague, recording the incidence of plague
antibodies in wild and domestic hosts. When surveys have indicated
the need, dusting the burrows of rodent hosts with suitable insecticide
dusts has controlled potential plague-carrying fleas. The rodents
themselves may be controlled by rodenticides.
People in western states should
avoid contact with wild rodents because of the possibility of
contracting plague. Backpackers and campers should be particularly
careful. Use of an aerosol insecticide is a wise precaution against
rodent fleas. Wood piles and similar cover for the rodents near
dwellings should be removed.
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