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Ectoparasites 225

vectors and transmit diseases through their bites. Typhus syndrome, sometimes fatal to children. Both adult and
is a disease that may be spread by both lice bites or flea nymphal forms of ticks may be vectors for transmitting
bites and is a rickettsial disease, which invades the lining infectious diseases and transmit a significant number
of blood vessels and smooth muscles. of diseases including Rocky Mountain spotted fever,
Two species of the human body louse—Pediculus Q fever, borreliosis, ehrlichiosis, tularemia, babesiosis,
humanus corporis, known as the body louse, and Pedicu- and Lyme disease.
lus humanus capitis, the head louse—attach themselves Fleas are mostly found on furry and hairy animals
to the hairs of the head, and causes outbreaks in schools but humans may also be affected. They are vectors for
and daycare centers. The pubic or crab louse, Phthirus several human diseases including tularemia, typhus, and
pubis, is usually sexually transmitted and can also infect brucellosis. Rats in large cities harbor fleas that transmit
any hairy areas such as the eyebrows, eyelashes, and diseases to humans and apparently were responsible for
beards. the deaths of hundreds of thousands of Europeans with
Other common ectoparasites include a group called the plague several centuries ago.
mites. Some members of the order Acarina are parasitic Jigger is a common name for a parasitic flea called
and may affect both humans and domestic animals and a Tunga penetrans. Parasitic infestations of this organism
few mites even transmit viruses and bacteria and at least typically involve pigs, dogs, and those humans who tradi-
a few species of tapeworms may be transmitted by mites. tionally go barefoot. These fleas are found in the tropical
Other complications include allergic reactions to the and subtropical Americas and Africa. Complications of
infestation, which may exacerbate or cause respiratory ulcerations and attendant infections sometimes require
problems such as asthma. amputation if early treatment is not obtained.
Mites are often called chiggers or redbugs and bur- Other common parasites include the bedbug Cimex
row into the skin, causing intense itching and skin irrita- lectularius. This “bug” contains an irritating chemical in
tion. Itch mites (Sarcoptes scabiei) cause a skin condition its saliva that causes irritating skin reactions, and feeds
known as scabies. Symptoms include intense itching, on humans at night. Bedding may be infected and remain
which occurs mostly at night accompanied by a rash on so until the next victim arrives at some point in the future
the hands, arms, armpits, and genitalia. There are two so scrupulous cleaning is necessary to control the infes-
varieties of S. scabiei organisms. Both varieties spread tation of a dwelling. These organisms are prevalent and
rapidly in households and among intimate partners. may be found in transient motels and homeless shelters
Dust mites, including mostly Dermatophagoides where the personal hygiene of the residents may be poor.
pteronyssinum or D. farinae, ingest human skin cells that Blood loss leading to anemia in protracted cases and the
are shed or may be abraded by scratching. Face mites or transmission of hepatitis B are possible complications to
follicle mites (Demodex brevis and D. folliculorum), are infestations of this bug.
found as a normal organism of the face. These organisms Leeches are not known to transmit any types of dis-
can only be seen with the help of a microscope, and may eases to human hosts and they often infect other mam-
cause mild allergic reactions and contribute to asthma in mals that enter the water. The term leech is applied to
humans. any of the annelids from the class Hirudinea, especially
Three species of chiggers are commonly called the Hirudo medicinalis. Some species are bloodsuckers and
“redbug” in some areas of the country. Chiggers attach were once used to draw blood out of those who were ill.
to the skin and bite the host, causing intense itching and Tooth amoebae, Entamoeba gingivalis, are micro-
severe dermatitis. Irritation of the skin may be due to al- scopic parasites able to hide in the tiny crevices where
lergic reactions to the saliva of the mite. These mites also the teeth meet the gums. Brushing does not remove them
act as vectors for scrub typhus. because of their ability to assume different shapes, en-
Two kinds of ticks, “hard” and “soft,” each carry abling them to fit into minuscule hiding places. These
different diseases. Soft ticks (family Ixodidae) do not organisms may be considered beneficial organisms, as
burrow into the skin, but hard ticks (family Argasidae) they eat mouth bacteria that may cause inflammation.
do and require great care in removing them to avoid leav- But with poor mouth hygiene, their numbers may pro-
ing the head imbedded in the skin. Dog ticks are known liferate and they may become harmful when the lack of
to cause paralysis similar to that of the Guillain-Barre hygiene forces them to multiply too quickly.