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SCIENCE & TECHNOLOGY
To a Louse, Typhus and More
By Max Sherman
The second stanza of Robert Burns’ poem, “To a
Louse,” describes a bug crawling on a woman’s
bonnet and in her hair as follows:
“Ye ugly, creepin, blastin wonner,
Detested. Shunned by saunt an’ sinner,
How daur ye set your fit upon her,
Sae fine a lady!
Gae somewhere else and seek your dinner,
On some poor body.”
Back in Robert Burns’ time (1759–1796), personal hygiene was not as big a deal as it is now,
and the bug he describes may not have been a
head louse. A louse is only the size of a sesame
seed. Chances are, however, that the woman he
described was infested. Although elegance of
manner and dress were cultivated in that period,
cleanliness was not.
Unfortunately, head lice are still most
common. In fact, Pediculosis capitus has been a
companion of the human species since antiquity.
In the US, head lice infestation is more prevalent
among children 5 to 11 years of age. It is endemic
worldwide and affects persons of all ages and
socioeconomic backgrounds.1
More important is that while head lice may
not cause fatal disease, they do cause great distress to the patient. The head louse effectively
infests only the human head, and thus is distinct
from body or pubic lice. It feeds by sucking blood,
simultaneously injecting saliva, which sometimes
causes itching of the scalp and, in neglected cases,
secondary infection and general malaise.2,3
Body lice (Pediculus humanus) are another
matter. They are responsible for epidemic typhus,
an acute, severe, febrile disease. The puncture
wound from the louse’s bite transfers the causative agent, Rickettsia prowazekii*, through the
skin by scratching. Dried louse feces may also
transfer the causative agent to the mucous membranes of the victim’s eyes or mouth.
Typhus remained endemic in the whole of
Europe from the 17th to the early 20th century.4
Approximately 20 million cases of true typhus
occurred in European Russia alone between 1917
and 1921, with from 2.5 to 3 million deaths.
Because lice are species specific, they are
important for another reason unrelated to disease
transmission. Biologists have used them to peer
back 130 million years in time, illuminating the
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catastrophic period during which dinosaurs perished and birds and animals rose.5 Lice have also
been genetically studied, and the analysis suggests that two distinct species of early humans
had close physical contact after a long period of
isolation.6 The history of lice, in essence, parallels
our own, and lice can be considered evolutionary
partners in tracking human origins.
Lineage
As mentioned above, lice are specialists, feeding
on a single species to whose fur, hair or feathers
their claws are adapted. The adaptation is so precise that when a louse’s host species evolves into a
new one, the louse will diversify into different species too. This information led to a reconstruction of
a family tree of lice. This tree stretches so far back
in time that the host of the first louse would have
been a dinosaur, probably one that was an ancestor of birds.7 Researchers used the recent discovery
of two fossil lice, one 44 million years old and the
other about 100 million years old, to calibrate a
molecular clock for louse evolution.
Evolutionary biologists have compared the
mitochondrial DNA from lice, primarily Pediculus
humanus, to existing data on human evolution.
They analyzed six louse species, including two
from humans, three from other primates and one
from a rodent. According to the parasites’ DNA,
lice specific to chimpanzees appeared 5.6 million
years ago, suggesting that the ancestors of chimps
and humans diverged at about this time.
According to one of the researchers, the
degree to which the louse tracks human history
is amazing. At the same time, it was apparent
that two genetically distinct lineages of P. humanus appeared about 1.18 million years ago. One
subspecies is now distributed worldwide and
infects either the head or the body, whereas the
other only inhabits the New World and only lives
on scalps. This means that the two subspecies
must have diverged at about the same time. Lice
thought to have been living on Homo erectus must
have migrated to H. sapiens at some point before
H. erectus became extinct some 30,000 years ago.8
Anatomy
Like most other insects, lice have three main
body parts: a head, a thorax and an abdomen,
and similar to other insects, lice have six legs
(three on each side). The legs originate from the
thorax. The louse’s legs are specially shaped for
gripping the host animal’s fur, hair or feathers.
In the case of many sucking lice species, the legs
are gripping claws exceptionally large in size,
compared to the size of the louse’s body, and
very strong.9
The adult head louse is 2–3 mm long, and
is usually tan to grayish white. The female lives
three to four weeks and, once mature, can lay
up to 10 eggs per day. These tiny eggs are firmly
attached to the base of the victim’s hair shaft
within approximately 4 mm of the scalp with a
glue-like substance produced by the louse. The
eggs are incubated by body heat and typically
hatch in 8–9 days. Once it hatches, a nymph
leaves the shell casing and passes through three
stages during the next 9–12 days to reach the
adult stage. The female louse can mate and begin
to lay viable eggs approximately 1.5 days after
becoming an adult. The louse feeds by injecting small amounts of saliva with vasodilatory
and anticoagulation properties and sucking
tiny amounts of blood from the scalp every few
hours.10
Body lice are similar in appearance to head
lice. Females are usually larger than males and
can lay up to eight eggs per day. Adult lice can
live up to 30 days on a person’s body. To live,
adult lice need to feed on blood several times a
day. Without blood meals from a host, the louse
will die within 1–2 days.
Transmission
Head lice transmission occurs mainly through
direct head-to-head contact and is common
within households. It is also thought to occur
through the sharing of combs, hair brushes or
hats, although supporting evidence is lacking.11
Adult lice can survive up to 55 hours without a
host, but probably become nonviable because of
dehydration long before death.12,13 Lice cannot
jump or fly; they crawl. Pets are not vectors.
Body lice live and lay eggs on clothing and
only move to the skin to feed, which occurs several times daily. The louse resides close to the
skin to maintain its body temperature. Lice are
spread most commonly by close person-to-person contact, but are generally limited to persons
who live under conditions of crowding and poor
hygiene.14 In the most severe cases, up to 30,000
body lice have been reported on one individual.15
Epidemic typhus, as with other Rickettsial
diseases, is transmitted to man by insects. The
body louse becomes infected with typhus by
biting an infected person who has the disease and then carrying the infection from one
human being to another. The louse takes up the
Rickettsia with infected blood and the organisms multiply in the cells lining the stomach
and intestinal walls, and finally appear in large
numbers in the feces. It takes about six days for
the louse to become infectious. The louse is a
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August 2011
relatively recent host of the Rickettsia and even
more susceptible than man. The louse will sicken
and die within two weeks.16
Epidemic Typhus
One of the earliest decisive typhus epidemics
occurred when the army of Maximilian II of
Germany was preparing 80,000 men to face the
Sultan Soliman in Hungary. In a camp at Komorn
in 1566, a disease broke out that was undoubtedly typhus. It was so violent and deadly that
the campaign against the Turks was ended.
Typhus has single-handedly played a part in
a number of major battles throughout the ages.
In 1632, during the Thirty Years War, Gustavus
Adolphus and Wallentine faced each other before
Nuremberg, which was the goal of both armies.
Typhus and scurvy killed 18,000 soldiers, whereupon both the opposing forces marched away
in the hope of escaping further ravages of the
pestilence.17 In November 1741, Prague was surrendered to the French army because 30,000 of
the opposing Austrians died of typhus.
Even Napoleon, thought to be the greatest
general, was helpless when pitted against the
tactics of typhus, dysentery and pneumonia.
During his invasion of Russia, his army suffered
from a lack of water and insufficient changes
of clothing, making bodily cleanliness impossible. Fear of a Russian attack caused the men
to sleep close together in large groups. The lice
of infested hovels crept everywhere, clung to
the seams of clothing, to the hair, and bore with
them the organisms of typhus. Disease alone
robbed Napoleon’s army of more than one-fifth
of its effective strength during the first month
of the war.18 In 1914–15, Typhus was the disease
that prevented Austria from invading Serbia, an
incursion that could have changed the outcome
of World War I.19
Treatment
The first product used to treat head lice was
DDT. It was developed after World War II and
hailed as a breakthrough at the time. However,
because of environmental concerns, its use has
been curtailed. Currently, 1% permethrin lotion
is recommended as one of the drugs of choice
for head lice. It is a synthetic pyrethroid with
extremely low mammalian toxicity. In cases
where resistance to permethrin is common, or in
cases of treatment failures, malathion or benzyl
alcohol may be considered.20 These agents must
be used according to the product information to
maximize efficacy. Some experts feel that recurrence of lice is not due to resistance, but rather to
inappropriate use of the medications.
Antibiotics are used to treat epidemic
typhus. According to the Merck Manual, tetracyclines (doxycycline) and chloramphenical are
specifically effective; they are rickettsiostatic, not
rickettsicidal.21 Patients seriously ill with typhus
often have circulatory collapse, oliguria, anuria,
azotemia, hyponatremia, hypochloremia, edema
and coma. Fatalities are rare in children, but
mortality increases with age, and may reach 60%
in untreated persons.
7.
Final thoughts
8.
9.
There is no better way to close this article than to
quote from Hans Zinsser’s book written in 1935.22
It remains a masterpiece of science writing:
“Typhus is not dead. It will live on for centuries, and it will continue to break into the open
whenever human stupidity and brutality give it
a chance, as most likely they occasionally will.
But its freedom of action is being restricted, and
more and more it will be confined, like other
savage creatures, in the zoological gardens of
controlled diseases.”
*The organism responsible for epidemic typhus is named after
an American, Howard Taylor Ricketts, and an Australian,
Stanislaus Joseph von Prowazek, both of whom died while
investigating the disease.
References
1.
Roberts RJ. “Head lice.” The New England Journal of
Medicine. 2002; 346(21): 1645-50.
2.
Maunder JW. “An appreciation of lice.” Proceedings of the
Royal Institute. 1983; 55:1-31.
3.
Mumcuoglu KY, et al. “Clinical observations related to
head lice infestation.” Journal of the American Academy of
Dermatology. 1991; 25:248-51.
4.
Cartwright FF. Diseases and History. Dorset Press, New
York, 1972.
5.
6.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
Wade N. “As mammals supplanted dinosaurs, lice kept
pace.” New York Times, 6 April 2011.
Pennisi E. “Louse DNA suggests close contact between
early humans.” Science. 2004; 306:210.
Balter M. “Did feathered dinos spread lice?” Science Now.
6 April 2011.
Op cit 6.
HeadLice.Org. The Anatomy of Pediculus Humanus.
(http://headlice.org/news/research/anatomy.htm.)
Accessed 21 April 11.
Frankowski BL, et al. “Head lice.” Pediatrics. 2010;
126:392-403.
Op cit 1.
Lang JD. Biology and control of the head louse. PhD thesis. Tucson: University of Arizona Press, 1975.
Chunge RN, et al. “A pilot study to investigate transmission of head lice.” Canadian Journal of Public Health. 1991;
82:207-8.
Centers for Disease Control and Prevention. Parasites—
Lice—Body Lice. (http://cdc.gov/parasites/lice/body/
index.html). Accessed 27 April 11.
Stewart A. Wicked Bugs. Algonquin Books. Chapel Hill,
NC; 2011.
Zinsser H. Rats, Lice and History. Transaction Publishers.
New Brunswick, CT; 2008 (originally published in 1935).
Ibid.
Op cit 4.
Montana State University. Insects, Disease and History.
(http://scarab.msu.montana.edu/historybug) Accessed
21 April 11.
Op cit 10.
Merck Research Laboratories. The Merck Manual.
Seventeenth Edition. Whitehouse Station, NJ; 1999.
Op cit 16.
Author
Max Sherman is president of Sherman Consulting Services Inc.
He can be reached by email at [email protected].
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