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Arthropoda: Insecta PHTHIRAPTERA Old = ANOPLURA (Sucking Lice) (Contact) Please CLICK on underlined links to view images To Search for Subject
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see: Phthiraptera Key] .
The mouthparts are
adapted for piercing and sucking blood.
The biting lice, Mallophaga, that are not of great
medical importance to humans, have chewing mouthparts that feed on scales,
feathers, and skin waste (Matheson 1950). Sucking lice are all permanent
ectoparasites of mammals. They have
highly modified mouthparts, which
when at rest are pulled back within a diverticulum that opens into the lower
part of the pharynx at its anterior end.
The thoracic segments are fused save for the genus Haematomysus. The tarsi have only one segment and end in
a single claw that is adapted for grasping and clinging to hair. Eggs are attached to the host's hair (Fig. 4). LIFE CYCLE Both male and female lice suck blood
during days and nights from their hosts.
They spend their entire lifetime on their hosts and in the case of
humans on clothing as well. The eggs,
which have been called "nits", are white and 1 mm. or less
long. The eggs hatch in 5-11 days if
located on the body. If warm hatching
conditions are not available, the eggs may survive more than a month. There is a hemimetabolous life cycle in
which nymphs resembling small adults hatch.
The nymphs can suck blood and pass three stages, which take about two
weeks. Nymphs that have left the body
for clothing require a longer time to complete their development. Service (2008) noted that lice deprived of
a blood meal couldn't live more than four days, whereas those that are able
to take 3-5 blood meals daily can live for about a month. Those hosts with a fever of about 40 deg.
Centigrade are not suitable for louse survival. Usually there are less than 100 lice
on a single person, but some people may harbor an infestation of up to 500
lice on their bodies and clothing.
Service (2008) even refers to an exceptionally high infestation of
20,000 lice being recorded! MEDICAL IMPORTANCE All
Phthiraptera are bloodsucking ectoparasites of mammals, and among the four
families only the Pediculidae have species that are of medical importance to
humans. Humans develop a rash from the salivary secretions. Pediculus
humanus, the body louse is associated with the spread
of many diseases, such as Ricketts,
Typhus and Relapsing Fever. This insect also
transmitted the disease known as Trench
Fever, which reduced Napoleon's Army and was prevalent in all war
areas during World War I (see ent79):
The group
as a whole includes the most important vectors of Typhus Fever. During
World War II, DDT treatment of the Italian population was required to rid it
of a louse epidemic. Although the crab
louse is not a disease vector, it can be acquired either through
bodily contact or indirectly from bedding, etc. It is known to attack only humans and wild gorillas in Africa. DISTINGUISHING CHARACTERISTICS (Derived
from Service 2008) Pediculus humanus- Body Louse The adults are small brown or grey
and wingless, with a soft but tough integument. The males average 2-3 mm and females larger at 3-4 mm. Two black eyes are present and short
antennae with 5 segments. The thorax
consists of three fused segments and the legs are proportionately large and
well developed. There is a short spur
on the tibia that also bears a tiny spine.
The legs are all very close in size. The mouthparts are distinctive
because there is no extended proboscis but rather a sucking snout that projects
into the haustellum. This bears tiny
teeth that are able to grip the skin.
The stylets pierce the skin and saliva is injected to the wound to
deter clotting while the blood is sucked out to where it enters the stomach. The darkened sides of the abdomen are
sclerotized. Males have dark bands on
the abdominal dorsum and the posterior is round, which contrasts with females
where it is forked, which aids in holding fast during oviposition. Both sexes draw blood at any time
during the day or night, and both adults and immatures pass their lives
entirely on humans that includes their clothing. The eggs, known as nits, are ovoid, white and about 1 mm. in
length. There are openings on the egg
that allow air to enter for breathing and for egg expansion at hatching. Females may live for 2-4 weeks during
which 150-300 eggs can be laid. Some
humans may actually sustain as many as 500 lice on their body and clothing. Pediculus capitis - Head Louse There are few morphological
differences between P. capitis
and P. humanus, but rather
their location on the body distinguish them.
The life cycles are also similar but the eggs of P. capitis are usually glued to single
hairs located on the head with hatching occurring within seven days. Most infestations do not exceed 20 lice on
a head, but there are exceptions.
Female lice generally lay about eight eggs per day with not more than
150 per lifetime, which is not more than two weeks. Eggs hatch in 5-10 days. Head lice can be of serious public
health concern all over the world.
Overcrowding contributes to the louse population size in any given
area. However, unlike body lice that
are vectors of typhus, head lice may only be minor vectors of a relapsing
fever. Pthirus pubis - Pubic Louse Pubic lice are smaller than those in
the Pediculus genus, and their
bodies are almost completely round.
The legs also differ as the middle legs are thicker than the front
legs and they possess large claws, which gives them the common name of
"crab lice". Females lay
only about three eggs per day, totaling not more than 200 during their
lifetime. The eggs are a bit smaller
than the other two species, and their location is primarily in the pubic area
of humans, although other parts of the body are occasionally infested. Their activity is much less than the other
species. CONTROL Sucking lice rank number one in
livestock pests with three different species attacking cattle, two species
goats and one species hogs. Cleanliness is of the utmost importance in
keeping down infestations of sucking lice.
Because the eggs will not survive for more than a month infested
clothing not worn for over a month should be louse-free. For livestock it is important to maintain
the animals in a healthy state. Rotenone applied twice
a year in autumn and spring has been effective for the control of both adults
and eggs. = = = = = = = = = = = = Key
References: <medvet.ref.htm> <Hexapoda> Burgess, I. F.
1998. Head lice: developing a
practical approach. The Practitioner
242: 126-69. Burgess, I. F.
2004. Lice and their
control. Ann. Rev. Ent. 49: 457-81. Burgess,
I. F., C. M. Brown & P. N. Lee.
2005. Treatment of head louse
infestation with 4% dimeticone lotion:
randomised controlled
equivalence trial. BMJ 330:
1423-25. Buxton,
P. A. 1948. The Louse: An Account
of the Lice which Infest Man, Their Medical Importance & Control, 2nd
ed., Edward Arnold,
London. Chetwyn,
K. N. 1996. An overview of mass disinfestation procedures as a means to
prevent epidemic typhus. IN: Proc. 2nd Intern. Conf. on
Insect Pests in the Urban Environment. ICIPUE: pp 421-416. Matheson, R. 1950. Medical Entomology.
Comstock Publ. Co, Inc. 610 p. Service, M.
2008. Medical Entomology For
Students. Cambridge Univ. Press. 289 p Meinking, T., C. N.
Burkhart & C. G. Burkhart.
1999. Ectoparasitic diseases
in dermatology: reassessment of
scabies and pediculosis. Adv.
Dermatology 15: 77-108. Nuttall, G. H. G. 1917. The biology of Pediculus humanus. Parasitology 10: 80-185. Orkin, M. & H. I. Maibach (eds.). 1985.
Cutaneous Infestations & Insect Bites. Marcel Dekker, NY., Chapt. 19-26. Service,
M. W. (ed.). 2001. The Encyclopedia of Arthropod-transmitted
Infections of Man & Domesticated Animals. CABI: pp. 70-3, 170-4, 295- 9. Zinsser, H. 1935. Rats, lice
and history. Boston Globe. Zinsser, H. 1937. The rickettsia diseases: varieties, epidemiology and geographical
distribution. Amer. J. Hyg.
25: 430-63. |
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