Parasitic Roundworm Diseases, NIAID Fact Sheet: NIAID
Article title: Parasitic Roundworm Diseases, NIAID Fact Sheet: NIAID
Conditions: Roundworm, Parasite, Pinworm, Ascariasis, Hookworm Disease, Ancylostoma canium (type of Hookworm), Whipworm, Strongyloidiasis, Trichinosis
Source: NIAID
February 2001
Parasitic Roundworm Diseases
Overview
A parasite is a living being or organism that
exists by depending on another organism. Parasites that infect
humans are much more widespread than many people realize. These
diseases affect not only poverty-stricken peoples in remote areas of
the world, but they also can be important health problems for rich
and poor throughout the world, including the United
States.
As with other parasitic diseases, roundworm
infections are more common in warm climates than in cooler,
temperate areas. Many roundworm parasitic diseases result from human
carelessness and a lack of appropriate personal hygiene and
sanitation measures. Thus, the best solution to the problem rests in
preventing these infections rather than in curing
them.
Roundworms, or nematodes, are a group of invertebrates
(animals having no backbone) with long, round bodies. They range in
size from those plainly visible to the naked eye to those several
hundredths-of-an-inch long and visible only under a microscope. Most
roundworms or their eggs are found in the soil and can be picked up
on the hands and transferred to the mouth or can enter through the
skin. With the exception of the roundworm that causes trichinosis,
mature roundworms eventually end up or live in human intestines and
cause a variety of health problems.
Some of the most common
parasitic roundworms in humans are:
- Enterobius vermicularis, the pinworm that causes
enterobiasis;
- Ascaris lumbricoides, the large intestinal roundworm
that causes ascariasis;
- Necator and Ancylostoma, two types of
hookworms that cause ancylostomiasis;
- Trichuris trichiura, the whipworm that causes
trichuriasis;
- Strongyloides stercoralis that causes
strongyloidiasis; and
- Trichinella spiralis that causes
trichinosis.
We discuss roundworms that
infect human intestines only in this fact sheet.
Pinworm Infection (Enterobiasis)
A pinworm is the most
common roundworm parasite in temperate climates – even in areas with
high levels of sanitation. In the United States, it is the most
common of all parasitic roundworm infections, affecting up to
one-third of the country's children. Because pinworm infection is
spread mainly by children, it is found most often in family groups,
day-care centers, schools, and camps.
Pinworms are small,
threadlike roundworms found primarily in the colon and rectum. The
life cycle of the pinworm – egg, larva, and mature worm – takes
place inside the human body and requires from three to six weeks to
complete.
How do pinworms
get into the body?Pinworms enter the
body when eggs are swallowed. The female pinworm expels thousands of
eggs into the environment. Because the eggs are moist and a bit
resistant to drying, they may be able to infect someone for several
days after being distributed in dust. They can cling to the fingers
of children.
Exposure to infective eggs may occur when the
person who is infected scratches the contaminated area (the area
around the anus where the female worm deposits her eggs) and then
transfers the eggs to the fingertips and from there to the mouth.
The eggs may be scattered into the air from bed linen and clothing,
and can cling to doorknobs, furniture, tubs and faucets, and even
food. Although a person may have no symptoms over a long period,
episodes of infection may return repeatedly.
Folklore is
filled with fantastic descriptions of symptoms and abnormal behavior
blamed on pinworm infection. Actually, the symptoms are usually mild
and vague. Movement of egg-laden female worms from the anus will
often produce itching of the anus or vagina that, in some cases, may
become very intense and even interfere with
sleep.
How is pinworm
infection diagnosed?A doctor or other
health care worker can diagnose pinworm infection by finding the
eggs. The most common way to collect the eggs is a rather simple one
involving swabbing the anal area with the sticky side of a piece of
transparent cellophane tape. The tape is then transferred to a slide
where it can be looked at under a
microscope.
How can pinworm
infections be prevented?You can prevent
becoming infected or reinfected with pinworms by:
- Bathing frequently;
- Using clean underclothing, night clothes, and bed sheets; and
- Washing your hands routinely, particularly after using the
bathroom.
How are pinworm
infections treated?Some doctors believe
that no treatment is necessary for pinworm infections that have no
symptoms. This is because children usually outgrow the infection.
Because of the strong probability that small children will get
infected again outside the home, strenuous efforts to eliminate the
eggs from the household are of little help.
If the doctor
does prescribe medicine, all members of the household should take
it, regardless of whether they have symptoms. Drugs such as
mebendazole and pyrantel pamoate (Povan) are the most useful in
treating pinworm infections.
To relieve intense itching that
often accompanies pinworm infection, a doctor may prescribe a
soothing ointment or cream.
Ascariasis
The name
Ascaris lumbricoides reflects
the resemblance of this intestinal roundworm to the common earthworm
known as Lumbricus. Ranging in length from six to 13 inches, the
female worm may grow to be as thick as a pencil. Ascaris infections
are common throughout the world in both temperate and tropical
areas. In areas of poor sanitation, everyone may be harboring the
parasite. Amazingly, up to a hundred worms can infect one
person.
How is ascariasis
spread?Almost more than any other
parasitic disease, human carelessness causes ascaris. Human feces in
streets, fields, and yards are a major source of infective eggs in
heavily populated areas. The eggs of ascarids do not infect humans
when first excreted by the worm. The eggs are very resistant to
extremes of temperature and humidity. They usually are transmitted
by hand to mouth, although the use of human feces as fertilizer may
also permit transmission of infective eggs by food that is grown in
the soil and eaten without being thoroughly washed. The eggs require
several weeks to develop and become infective.
When a person
swallows the eggs, they pass into the intestine where they hatch
into larvae. The larvae then begin their journey through the body.
Once through the intestinal wall, they reach the lungs by means of
the blood or lymphatic system. In the lungs, they pass through the
air sacs, are carried up the bronchial tree, and are re-swallowed to
be returned to the small intestine where they grow, mature, and
mate. The worms become mature in about two
months.
Can pets transmit
these worms to humans?Other species of
ascarids such as
Toxocara, which infect dogs and cats, can,
under certain circumstances, be picked up by humans. In dogs and
cats, these ascarids have a migratory cycle similar to
A.
lumbricoides. In humans, however, they fail to reach the
intestine. Instead they remain active in other body tissue for some
time. This state of larval migration is known as visceral larva
migrans.
Young puppies and kittens contribute most to
contamination of soil by eggs that must incubate for some time in
the soil. Almost all dogs are infected at birth. Older dogs,
however, have usually become immune to the parasite.
What are the symptoms of
ascariasis?A few worms in the intestine
may cause no symptoms or may give rise only to vague or intermittent
abdominal pain. Heavy infection may cause partial or complete
blockage of the intestine resulting in severe abdominal pain,
vomiting, restlessness, and disturbed sleep. The heavier or greater
the worm infection, the more severe the symptoms are likely to be.
Occasionally, the first sign of infection may be the presence of a
worm in vomit or in the stool.
How is ascariasis
diagnosed?A large number of larvae
invading the lungs at one time may cause pneumonia. This stage of
the disease precedes the intestinal phase by weeks, and the symptoms
are difficult to diagnose. Once mature female worms are present in
the intestine, however, a doctor can diagnose the infection by
finding characteristic eggs in the stool.
How is ascariasis treated?
Doctors can treat ascariasis successfully with
mebendazole, albendazole, or pyrantel pamoate.
Hookworm Disease (Ancylostomiasis)
One of the most common
roundworm infections is hookworm. Like ascarids, people pick up
hookworms as a result of unsanitary conditions. Hookworm eggs are
passed in human feces onto the ground where they develop into
infective larvae. When the soil is cool, the worms crawl to the
nearest moist area and extend their bodies into the air. They remain
there – waving their bodies to and fro – until they come into
contact with the skin, usually on a bare foot, or until they are
driven back down by the heat.
Hookworm is widespread in those
tropical and subtropical countries in which people defecate on the
ground and soil moisture is most favorable.
Necator
americanus is the prevailing species in the southeastern United
States.
How is hookworm
disease spread?People usually get this
infection by walking barefoot over contaminated soil. In penetrating
the skin, the larvae may cause an allergic reaction. It is from the
itchy patch at the place where the larvae entered that the early
infection gets its nickname "ground itch." Once larvae have broken
through the skin, they enter the bloodstream and are carried to the
lungs. (Unlike ascarids, however, hookworms do not usually cause
pneumonia.) The larvae migrate from the lungs up the windpipe to be
swallowed and carried back down to the
intestine.
What are the
symptoms of hookworm disease?Diarrhea,
particularly in person who has never been infected, sometimes starts
as the worms mature in the intestines and before eggs appear in the
stool. Other signs and symptoms at this stage include vague
abdominal pain, intestinal cramps, colic, and
nausea.
Scientists have learned that people in good health
and on a diet containing adequate iron can tolerate the presence of
these worms in small or moderate numbers without having problems. In
chronic infections, if the number of parasites becomes great enough,
a person can develop serious anemia because of blood loss from the
worms attaching themselves to the intestine and sucking the blood
and tissue juices.
If humans come into contact with larvae of
the dog hookworm or the cat hookworm, or larvae of certain other
hookworms that do not infect humans, the larvae may penetrate the
skin. But these larvae cannot complete their migratory cycle in
humans. Instead, they move just below the skin producing snake-like
markings and intense itching. This is referred to as a creeping
eruption or cutaneous larva migrans.
Ancylostoma
canium, an illness caused by a particular species of dog
hookworm, has been described in Australia. This worm may almost
complete its development in the lower small intestine, but produces
a severe inflammatory reaction in the bowel, causing abdominal pain,
diarrhea, and an increase in certain white blood cells called
eosinophils.
How is hookworm
disease diagnosed?A laboratory worker
will examine stool specimens to look for and count the number of
eggs. If the egg output is large enough – more than 2,000 eggs per
gram of stool – the doctor will assume that the infection may cause
anemia and start treating the patient.
How is hookworm disease
treated?Once a person has been
diagnosed with hookworm disease, a doctor can prescribe medicines
such as mebendazole or albendazole. Frequently, the doctor will add
an iron supplement to this treatment.
Whipworm Disease (Trichuriasis)
This parasitic roundworm
infection of the large intestine often has no symptoms, but a doctor
usually can diagnose it by examining the stool and finding whipworm
eggs. Heavy infections may cause intermittent stomach pain, bloody
stools, diarrhea, and weight loss. The name whipworm comes from the
parasite's long, very thin, whiplike shape. Fertilized eggs develop
outside the body, and an embryonated egg is produced in three weeks
in a favorable environment; that is, warm, moist, shaded
soil.
Although the incidence of whipworm infection is high,
its intensity is usually light. In the United States, the infection
occurs principally in warm, moist climates, most frequently among
children. People can get infected by accidentally eating whipworm
eggs on their hands or in food or drink. Severe infections in young
children can result in serious disease with bloody diarrhea and a
condition called rectal prolapse.
Doctors treat whipworm
disease most often with mebendazole and albendazole.
Strongyloidiasis
The parasitic roundworm called
Strongyloides stercoralis mainly infects humans. This
parasite has different types of life cycles. One is direct, similar
to that of the hookworm. After a short feeding period and
development in the soil, the larvae penetrate human skin, enter the
blood stream, and pass through the right side of the heart to the
lungs. From the lungs, the adolescent parasites go up the windpipe
into the mouth, are swallowed, and reach the upper part of the small
intestine where they develop into mature worms.
Under
certain conditions, parasites may undergo an indirect life cycle in
which free-living mature male and female worms develop in the soil
and produce a new generation of large numbers of larvae.
At
times, the larvae may develop rapidly into the infective state in
the intestine where they penetrate the intestinal lining instead of
passing out of the body in the feces, as occurs normally. This
modification of the life cycle, called internal autoinfection,
explains persistent strongyloidiasis, as long as 40 years in
patients who have moved to areas where the disease is not generally
found. Autoinfection may produce heavy infections and severe
disease, especially in patients with reduced immunity such as those
receiving corticosteroids or other immunosuppressive drug
treatment.
What are the
symptoms of strongyloidiasis?Many
Strongyloides infections are mild and go unnoticed.
Moderate infections may cause a burning pain in the abdomen. Nausea
and vomiting may be present, and diarrhea and constipation
alternate. Severe infections result in anemia, weight loss, and
chronic diarrhea.
How is
strongyloidiasis diagnosed?Laboratory
diagnosis includes the examination of feces and duodenal contents
for larvae. Scientists at the National Institute of Allergy and
Infectious Diseases have developed a reliable blood test to detect
antibodies to
Strongyloides.
How is strongyloidiasis
treated?Thiabendazole (Mintezol) given
twice daily for two or three days is the one of the treatments
doctors recommend. Ivermectin given in one or two days, or
albendazole given in two courses 10 days apart also are effective.
Trichinosis
Trichinosis is an infection by the larvae of a
most versatile roundworm,
Trichinella spiralis. This
parasite can infect virtually every meat-eating mammal. Unlike the
other parasitic roundworm diseases that have been discussed,
trichinosis is not an intestinal infection in the usual sense. It is
the migration of
T. spiralis larvae through the body and
their encystment (becoming enclosed in a capsule) in a muscle that
creates serious problems. The parasite is especially common in rats
and in swine that feed on uncooked garbage. The disease occurs in
humans when they eat undercooked infected pork.
Although
trichinosis is sometimes found in cities, it is much more common in
rural areas, particularly in the hog-raising areas of the United
States. Because many states have adopted laws requiring that all
garbage fed to hogs be sterilized, fewer people get
trichinosis.
Typically, the life cycle of the parasite begins
when a person or an animal eats contaminated meat containing larvae.
Digestive juices from the stomach dissolve the capsule-like cyst and
release the parasites. The larvae then penetrate into the intestine
where they mature and mate. Female worms then pass larvae into the
blood stream where they make their way through the capillaries (tiny
blood vessels) into the muscle fibers. Once in the muscle fibers,
they encyst again and begin a sometimes long
life.
What are the symptoms
of trichinosis?The average case of
trichinosis is not severe and produces no noticeable discomfort. It
can produce symptoms that are frequently overlooked or ignored – a
slight stomachache and achy muscles and joints. Invasion by a large
number of parasites, however, produces symptoms that mimic food
poisoning followed by severe "muscular
rheumatism."
How is
trichinosis diagnosed?Although a doctor
may suspect that a patient has trichinosis on the basis of clinical
signs, it is usually diagnosed as the result of: 1) a blood test
that shows an increase in the number of eosinophils, a type of white
blood cell; or 2) microscopic examination of muscle tissue to look
for the larvae.
How is
trichinosis treated?A doctor can
prescribe medicine only to relieve symptoms. There is no treatment
for the infection. If the doctor diagnoses infection while the
patient is still having digestive symptoms, standard antiparasite
drugs can be used to dislodge some of the worms. Once encystment of
the parasite has begun, treatment is for any symptoms. In most
cases, the chances of recovery are good.
Thiabendazole may
help patients with trichinosis if treatment is begun very early,
during the incubation state. Corticosteroids can relieve the
inflammatory reaction during the larval migration state, and the
patient should take them with thiabenazole. Steroids could, however,
prolong the intestinal phase of the
infection.
How is trichinosis
prevented?Researchers and health care
providers have known all the basic facts necessary for preventing
trichinosis in humans for years. You can kill the parasite by
cooking (allowing all parts of the meat to reach at least 150
degrees Fahrenheit), freezing (16 degrees Fahrenheit for 36 hours).
Irradiation can also kill T. spiralis. Smoking, pickling, and other
methods of processing or preserving meats do not kill the parasite.
Research
Researchers at the National Institute of Allergy
and Infectious (NIAID) diseases are conducting basic and clinical
research on the prevention, control, and treatment of a variety of
parasitic diseases, including some caused by parasitic roundworms.
NIAID scientists are trying to determine the factors that allow
Strongyloides stercoralis roundworms to infect humans and
cause disease. The findings from this research may help scientists
develop a skin test to diagnose stronglyloidiasis.
NIAID is a component of the National Institutes
of Health (NIH). NIAID supports basic and applied research to
prevent, diagnose, and treat infectious and immune-mediated
illnesses, including HIV/AIDS and other sexually transmitted
diseases, tuberculosis, malaria, autoimmune disorders, asthma and
allergies. NIH and CDC are agencies of the U.S. Department of
Health and Human Services.
Prepared by:
Office of
Communications and Public Liaison
National Institute of Allergy
and Infectious Diseases
National Institutes of
Health
Bethesda, MD 20892
Public Health Service
U.S.
Department of Health and Human Services
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Pelvic Inflammatory Disease, NIAID Fact Sheet: NIAID
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