Helminthic Pathogens Flashcards
Helminths
parasitic worms that feed on a living host to gain nourishment and protection,
while causing poor nutrient absorption, weakness and disease in the host
most common helminths recognized in the U.S.
primarily Intestinal Nematodes
Intestinal Nematodes
live in the small bowel (intestine) and are referred to as intestinal parasites
helminths classification
Nematodes or roundworms (large size an unsegmented body)
- Trematodes, which includes flukes or flatworms
- Cestodes or tapeworms
_______ all share a similar _______ and are _______ organisms that are _____ to the naked
eye.
Helminths all share a similar morphology and are multicellular organisms that are visible to the naked
eye.
How are Helminths caught?
The worms are usually caught through treading on contaminated soil, in warm, humid places
or countries that have poor sanitation and hygiene
If an infected person or animal has defecated on soil, helminth eggs present in their feces contaminate
the soil
-eggs mature and hatch to produce larvae that grow into adult worms of up to 13
mm in length.
- adult worms can penetrate human skin, which can happen if a person walks on
contaminated soil.
-worms then enter the bloodstream and migrate towards the lungs and also the throat where they are swallowed and transported to the gut.
Nematodes or roundworms
cylindrical, un-segmented and have lips, teeth and
dentary plates
-large size
-worms are either male or female
-live primarily as adult worm in the intestinal tract
-nematode infections are most commonly confirmed by detecting the characteristic eggs in feces.
Trematodes or flatworms
flat, leaf-shaped and un-segmented
- hermaphroditic (both male and female reproductive organs)
Cestodes or tapeworms are
segmented and hermaphroditic
-have a sucker
and a projecting, hooked rostellum (is a knob-like protrusion at the extreme anterior end of a tapeworm)
What do you look at to confirm nematodes?
- size and shape
- Thickness of shell
- Presence or absence of specialized structure: e.g. polar plugs, knobs, spines, opercula.
- The presence and characteristics of larvae within the eggs
Enterobius (Oxyuris) vermicularis (Human pinworm)
-Physiology & Structure: small (adult female: 8-13 mm) white worm found in perianal folds of an infected
child.
-Infection: it is initiated by ingestion of embryonated
eggs
-Eggs hatch in the small intestine and larva migrate to the large intestine, where they mature into adults
in 2 to 6 weeks
-Fertilization of the female by the male produces
the characteristic asymmetric eggs.
-eggs are laid in the perianal folds by the
migrating female (many as 20,000 eggs are
deposited)
-The eggs rapidly mature and are infectious within
hours
Where is Enterobius most common?
temperate region, where person-to-person
spread is greatest in crowded conditions, such as in day-care centers, schools and mental
institutions
How many cases of pinworm infection are reported worldwide?
500 million cases
-Most common helminthic infection in the U.S.
How does pinworm infection occur?
When the eggs are ingested and the larval worm is free to develop in the intestinal mucosa
- eggs may be transmitted from hand-to-mouth by children scratching the perianal folds in response to the irritation caused by the migrating, egg-laying, female worms,
- eggs may find their way to clothing and play objects in day-care centers
Eggs can also survive for _____ periods in the _____, and under ____ in the rooms inhabited by
infected people
long, dust, beds
Autoinfection (Retroinfection)
eggs hatch in the perianal
folds and the larval worms migrate into the rectum and large intestine.
True or False: An animal reservoir for Enterobius is known
False
Enterobius symptoms
-Many children and adults show no symptoms and serve only as carriers
-Patients who reacts to the secretions of the migrating worms experience:
o severe nocturnal perianal pruritus
o loss of sleep
o fatigue
-pruritus may cause repeated scratching of the irritated area and lead to secondary bacterial infection
-Worms that migrate to the genital area may produce genitourinary problems and granulomas
Diagnosis of Enterobius
suggested by the clinical manifestations and confirmed by detection of the characteristic eggs on the anal mucosa
-Occasionally, the adult worms are seen in stool sample
What is the method of choice for diagnosing enterobius?
anal swab with a sticky surface that picks
up the eggs for microscopic examination
-Sample should be collected when the child arises and before bathing and defecation to pick
up eggs laid by migrating worms during the night
How many swabbings may be required to detect eggs?
Three swabbing, one per day for 3 consecutive days, may be required to detect the diagnostic
eggs
-Eggs are rarely seen in fecal specimens
Enterobius vermicularis eggs
thin-walled eggs are 50 to 60 x 20 to 30 μm
-ovoid
-flattened on one side (not because children sit on them), but this is an easy way to correlate
the egg morphology with the epidemiology of the disease.
Enterobius vermicularis treatment and control
Albendazole or Mebendazole keeps the worm from absorbing sugar
(blocks glucose uptake), so that the worm loses energy and dies
-One dose initially (two times a day for 28 days: 1 cycle) and repeat treatment after 2 weeks for a total of three cycles
-Personal hygiene, clipping of fingernails, washing of bed cloths and prompt treatment of
infected individuals all contribute to control
How to avoid reintroduction of organism and reinfection in family environment?
common to treat the entire family simultaneously
-Reinfections are common
Ascaris Lumbricoides (Roundworm)
large (20 to 35 cm in length) pink worms that have a complex
life cycle
Roundworm infection
ingested infective egg releases a larval worm
that penetrates the duodenal wall, enters the
blood stream, is carried to the liver and heart, and
then enters the pulmonary circulation
-larvae break free in the alveoli of the lungs,
where they grow and molt
-In about 2-3 weeks, the larvae pass from the
respiratory system to be coughed up, swallowed,
and returned to the small intestine
Where do male and female worms mature?
small intestine (primarily jejunum)
-fertilization of
the female by the male initiates egg production
-Up to200,000 eggs/day for as long as a year.
-Female worms can also produce unfertilized eggs
in the absence of males
-Eggs are found in the feces 60 to 65 days after the
initial infection
-Fertilized eggs become infectious after approx. 2 weeks in the soil
Ascaris Lumbricoides (Roundworm) Epidemiology
prevalent in areas where sanitation is poor and where human feces are
used as fertilizer
-this parasite (more than
any other) affects the world’s population because food and water are contaminated
True or False: No animal reservoir is know for A. lumbricoides
True
-Although an almost identical species from
pigs (A. suum) can infect humans
______ eggs are quite hardy and can survive extreme ______ and persist for several _____ in _____ and _____
Ascaris, temperatures, months, feces, sewage
What is the most common helminth infection worldwide?
Ascariasis
-estimated 1 billion people infected.
Ascaris Lumbricoides (Roundworm) clinical symptoms
infection caused by ingestion of only a few eggs may produce no symptoms
- single adult Ascaris worm may be dangerous since it can migrate into the bile duct and the liver and damage the tissue
- worm has a tough, flexible body occasionally allows it to perforate the intestine, creating peritonitis with secondary bacterial infection.
True or False: adult worms attach to the intestinal mucosa
False
-depend on constant motion to
maintain their position within the bowel lumen
After infection with many larvae, migration of worms to the lungs can produce
pneumonitis
In some cases, accumulation of worms in the intestine can cause
obstruction, perforation and
occlusion of the appendix
Patients with many larvae may also experience
abdominal tenderness, fever, distention and
vomiting.
Ascaris Lumbricoides (Roundworm) diagnosis
Examination of the sediment of concentrated stool reveals the knobby-coated, bile-stained, fertilized and unfertilized eggs
- Eggs are oval
- 55 to 75 μm long
- 50 μm wide
- Occasionally, adult worms pass with the feces, dramatic because of large size
decorticated egg
thick-walled outer shell can be partially
removed
Ascaris Lumbricoides (Roundworm) treatment
Treatment of symptomatic infection is highly effective
-Albendazole or Mebendazole
-Pyrantel pamoate (depolarizing neuromuscular blocking agent, thereby causing sudden contraction, followed by paralysis, of the helminths) and piperazine are alternatives
-Patients with mixed parasitic infections should be treated for
ascariasis first to avoid provoking worm migration and possible intestinal
perforation
-Eggs can persist in contaminated soil for 3 years or more
Trichuris trichiura (Whipworm)
resembles the handle and lash of a whip -Ingested eggs hatch into a larval worm in the small intestine and then migrate to the cecum (the first section of the large intestine), where they penetrate the mucosa and mature to adults -About 3 months after the initial infection, the fertilized female worm starts laying eggs and may produce 3,000 to 10,000 eggs/day -Female worms can live for as long as 8 years -Eggs passed into the soil mature and become infectious in 3 weeks
Trichuris trichiura eggs
distinctive with dark bile staining, a barrel shape, and the presence of polar plugs in the egg shell
- measuring 50x24 μm
- thick wall
What is T. trichiura worldwide distribution, and prevalence directly correlated with?
poor sanitation and the use of human feces as fertilizer
True or False: There is a recognized animal reservoir for T. trichiura
False
Clinical Symptoms of T. trichiura
generally related to the intensity of the worm burden
-usually asymptomatic with small number
-secondary bacterial infection may occur because the heads of the worms penetrate deep into the intestinal mucosa
-Infections with many larvae may produce abdominal pain and distention, bloody diarrhea, weakness, and weight loss
-Appendicitis may occur as worms fill the lumen, and prolapse of the rectum is seen in
children because of the irritation and straining during defecation
-Anemia and Eosinophillia are also seen in severe infections
Trichuris trichiura diagnosis
Stool examination reveals the characteristic bile-stained eggs with polar plugs
-Light infestations may be difficult to detect because of the paucity of eggs in the stool specimens
Trichuris trichiura treatment and control
Albendazole or Mebendazol
-prevention depends on education, good personal hygiene, adequate sanitation, and
avoidance of the use of human feces as fertilizer
