Download Pathology and Symptomatology

Diseases
•Strongyloidiasis
•Cochin-China diarrhea
People are the
principal hosts of S.
Stercoralis, but dogs
and monkeys have a
similar parasite. A
similar species, S.
fullerborni, can infest
higher primates and
humans.
•no male form has been reliably
identified in the parasitic stage
•female species reproduce in a
parthenogenetic manner
Description
•small colorless, semitransparent
filariform nematode with a finely
striated cuticle
•has s short buccal cavity and a
long, slender, cylindrical
esophagus
•paired uteri contain a single a
single file of thin-shelled,
transparent, sermented eggs
Action
The parasitic females penetrate the
mucosa of the intestinal villi, where they
burrow in serpentine channels in the mucosa,
depositing eggs and securing nourishment.
Eggs
• deposited in the intestinal mucosa
• hatched into rhabditiform larvae that penetrate
the glandular epithelium and pass into the lumen
of the intestine and out in the feces.
1. DIRECT CYCLE, like hookworm
After a short feeding period of 2 – 3 days in the soil, the
rhabditiform larva about 700 in length. The infective filaform
larvae penetrate the human skin, enter the venous
circulation, and pass through the right heart to the lungs,
where they penetrate into the alveoli. From the lungs, the
adolescent parasites ascend to the glottis, are swallowed and
reach the upper part of the small intestine, where they
develop into adults. Occasionally some larvae pass through
the pulmonary barrier into the arterial circulation and reach
various organs of the body. During
their migrationin the host the larvae
pass through two molts to become
adolescent worms. In about 28 days
after the initial infectionion, matuer
ovipositing females then develop.
2. INDIRECT CYCLE
In this cycle, the rhabdidtiform larvae
develop into sexually mature, free-living
males and females in the soil. After
fertilization, the free-living female produces
eggs that develop into rhabditiform larvae,
which may become infective filariform larvae
within a few days and enter new hosts, or
repeat the free-living generation. The
indirect method appears to be associated
with the optimal environmental conditions
for a free-living existence in tropical
countries, while the direct method is more
frequently followed in the less favorable,
colder regions. Strains may show chiefly one
or the other type of development or a
mixture of both types.
3. Autoinfection
At times the larvae may
develop rapidly into the filaform
stage in the intestine and, by penetrating the intestinal
mucosa or the perinial skin, establish a developmental
cycle within the host. Autoinfection explains persistent
strongyloidiases in patients living in nonendemic areas.
Several studies indicate that a substantial number of
British and Australian veterans of World War II who were
exposed in Southeast Asia have carries asymptomatic
Strongyloides infections for 30 years or more.
Autoinfection is also one of the few examples of
multiplication of a helminth within the host.
Epidemiology
• runs parallel to that of a hookworm, but its
prevalence is lower in temperate zones like the
tropical and subtropical areas where warmth,
moisture and lack of sanitation favor is free-living
Pathology and Symptomatology
• moderate infections may cause a burning, dull or
sharp, nonradiating midepigastric pain. Pressure to
this area may elicit pain and tenderness. Nausea
and vomiting may be present; diarrhea and
constipation alternate. The result in weight loss and
chronic dynestery accompanied by malabsorption
and steatorrhea.
Diseases
•ancylostomiasis
•Uncinariasis
•Necatoriasis
•Hookworm infection
Species
•Necator americanus
•Ancylostoma duodenale
•A. braziliense (rarely)
•A. caninum (rarely)
•A. ceylanicum (rarely)
Morphology
•adult hookworms are small, cylindrical,
fusiform, grayish white nematodes
• the female are larger than the males
• the worm has a relatively thick cuticle
• there are single male paired female
reproductive organs
• the posterior end of the male has a broad,
translucent, membranous caudal bursa with
riblike rays, which is used for attachment to the
female during copulation
The Egg
• has bluntly rounded
ends and a single thin
transparent hyaline
shell
• is unsegmented at
oviposition and in two
to eight cell stages of
division in fresh feces
The life cycles of the several species of hookworm
are similar. Humanity is almost the exclusive host of A.
duodenate and N. americanus, although these species have
been reported occasionally in primates and other mammals.
The adults of A. braziliense, a parasite of wild domestic
felines and canines in the tropics, are infrequently found in
humans. A caninum, the common hookworm of dogs and
cats, is extremely rare intestinal parasite of humans.
The eggs passed in the feces, mature rapidly and
produce the rhabditiform larvae in 1 to 2 days under
favorable conditions and an optimal temperature of 23 to
33C.
Hookworm larvae remain within a few inches of where
they are deposited unless carried by floods or animals to
other locations.
The following factors favor hookworm maintenance and
dispersal:
1. Infected individuals who defecate on the soil in areas
frequented by others, fecal concentration in secluded areas
near the house. Return to this restricted area by members
of the family leads to family infection. The one-room school
without sanitary facilities is an excellent source of infection.
2. A shaded sandy or loam soil, which is a favorable
culture medium for hookworm larvae. Clay soil which
packs tightly, is unsuitable for the larvae.
3. A warm climate, which favors the development of the
eggs and larvae and promiscuous defecation. Cold,
snowy climes force people into shelter; hence the
widespread use of the privy in such areas.
4. Moisture, 30 – 50 inches of rain, especially during
the warm season of the year when egg and larval
development are possible.
5. A poor, ignorant population that does not wear
shoes. The population of half of the world does not
wear shoes, nor can they afford them.
Pathology and Symptomatology
When the larvae penetrate the skin they produce
maculopapules and localized erythema. Itching is often
severe, and as it is related to contact with the soil, especially
o the dewy mornings when the moisture prmits the larvae to
beat the surface.
Hookworm is essentially a chronic infection, and the
infected individual often shows no acute symptoms.
The hookworms attached to the mucosa of the small
intestine by their buccal capsules. The favorite site is the
upper small intestine, but in heavy infections the worms may
be present as far as the lower ileum. They suck the host’s
blood and mucosal substances by the tractile pull of the
contracting and expanding esophagus.
Disease
Creeping eruption is a dermatitis characterized
by serpiginous intracutaneous lesions caused by
migration of nematode larvae that normally do not
infect the human host.
Like the cerceriae of bird schistosomes, can
produce annoying skin eruptions known as
“swimmer’s itch” by allergic sensitization.
Epidemiology
Creeping eruption, which is prevalent in many
tropical and subtropical countries of the world is
caused by the filariform larvae of A. braziliense, which
lives as an adult in the intestine of humanity’s two
close animal friends, the dog and the cat. Hence, their
feces are ever available to pollute the human
environment. Sea and fresh-water batehrs who bask
in the sun on the beach while their dogs pollute it.
Pathology and Symptomatology
• indurated, reddish, itchy papules develop
• linear, slightly elevated, erythematous,
serpiginous, intracutaneous tunnels are
produced by the larvae
• vesicles form along the course of the
tunnels, and the surface becomes dry and
crusty
• itching is intense and scratching may lead
to secondary infection
Diseases
• Enterobiasis
• Oxyuriasis
• Pinworm
• Seatworm
Infection of the same or
another person may be affected
by (1) the important hand-tomouth transmission from
scratching the perianal areas of
from handling contaminated
Fomites, (2) inhalation of airborne eggs in dust, (3) rarely,
retroinfection through the anus. Eggs hatch in the perianal
region and the larvae migrate back into the large intestine.
Heavy infections are affected by the transference of eggs
from perianal region to the hands and thence to the mouth
directly or through contaminated food.
Pathology and Symptomatology
E. vermicularis is relatively innocuous and rarely
produces serioous lesions. The clinical symptoms are
due largely to the perianal, perineal, and vaginal
irritation caused by the migrations of the gravid female
worm, and less frequently to the intestinal activities of
the parasite. The local pruritus and discomfort produce
a cahin of secondary reflex symptoms that tend to
debilitate the patient – this debilitation is due to
disturbed sleep.
Diagnosis
Pinworm infection is suspected in
children who show perianal itching, insomnia,
and restlessness. Diagnosis is made by finding
the adult worms or eggs. Often the first
evidence of infection is the discovery of the
adult worms on the feces or in the perianal
region.