Download Trichinella spiralis - comed.uobaghdad.edu.iq

Trichinella
Trichinella spiralis :
The adult worm of T.spiralis is the smallest nematodes which infects man.
Trichinella spiralis is a nematode parasite of humans that is cosmopolitan in
its geographical distribution. It is nearly unique among helminthic parasites
in that all stages of development occur within a single host; over 100 species
of mammals have been reported to be susceptible to infection. The infective
encysted larvae may remain viable in the host’s musculature for many years;
they may also survive long periods in decaying and putrefying muscle.
Trichinella spiralis causes trichinellosis, a zoonotic infection in human.
Humans are infected when parasite-infected meat (port in most instances) is
ingested.
The diseases that Trichinella spp. cause are collectively referred to
as trichinellosis.
This species is significantly higher in prevalence in people living in certain
parts of Europe, Asia, and Southeast Asia than in the United States. It is now
considered endemic in Japan and China. A large outbreak of trichinellosis
occurred in Lebanon in 1997.
Habitat: The adult worm inhabit the small intestine of pig , rat and man.
Morphology:
1.Adult worm: It is minute, whitish, thread like ,both male and female
worms are wider posteriorly than anteriorly. female worm is approximately
twice as long as male,the female is ovoviviparous which producing eggs
after fertilization that are immediately developed into larvae in the uterus
and then passed in the stools. The male is shorter than female and the
anterior end is delicate and filariform while posterior end bears two
conspicuous conical papillae .
Fig.(1): ♀of T.spiralis
Fig.(2):♂ of T.spiralis
1
2.Larvae : These are released in the intestine,from where they are carried
by systemic circulation and are deposite in various organs and tissues of the
body. The larvae becomes encysted in the striated muscles, and are infective
to other hosts. The larva in the cyst is coiled and hence the name spiralis in
species.
Figure(3): Infective first stage larva of Trichinella spiralis in its Nurse cell in muscle tissue.
Life Cycle of T.spiralis :
The typical life cycle for T. spiralis involves humans, pigs, and rodents.
Pigs become infected when they eat infectious cysts in raw meat, often pork
or rats (sylvatic cycle). Humans become infected when they eat raw or
undercooked infected pork (domestic cycle). After humans ingest the cysts
from infected undercooked meat, pepsin and hydrochloric acid help free the
larvae in the cysts in the stomach. All stages of development occur within a
single host such as humans, pigs, dogs, rats and cats. Adult worms reside in
small intestine, and larvae reside in skeletal muscle. However, two different
hosts are required to complete the life cycle.
Primary host: The pig is the primary host.
Natural host: rodents, carnivores and various other species of omnivorous
animals are other natural hosts.
Man is an accidental host and is the dead end for the parasite.
When man consumes raw or rare flesh infected with cysts of Trichinella, the
cysts are digested out of the muscle in the stomach; the larvae (first stage)
are resistant to gastric juice. After passing to the small intestine, the larvae
penetrate the villi of the small intestine, molt, and develop into mature adult
within 48 hours. After fertilization, the gravid female burrow deep into the
mucosa, discharging larvae beginning 5 to 46 days after infection and
continuing for 2 to 4 weeks or occasionally longer. Widely disseminated via
lymphatics and the bloodstream, larvae enter most organs, but persist only in
individual skeletal muscle fibers. The larval host cell becomes a nurse cell in
which the larvae will be encapsulated. The development of a capillary
network around the nurse cell completes encystation of the larvae.Although
the capsules calcify within six months to two years, the larvae within remain
viable for months to years, rarely for decades.
2
Nurse cell formation
This nematode is a multi-celular parasite that lives within a single muscle
cell, which it modifies according to its own requirements.
Trichinella spiralis larvae within the diaphragm muscle of a pig
Nurse cell formation in skeletal muscle tissue is mediated by the hypoxic
environment surrounding the new vessel formation.[4] The hypoxic
environment stimulates cells in the surrounding tissue to regulate up and
secrete angiogenic cytokines.
3
Clinical features:
The great majority of trichinosis infections have either minor or no
symptoms and no complications. There are two main phases for the
infection: enteral (affecting the intestines) and parenteral (outside the
intestines). The symptoms vary depending on the phase, species of
Trichinella, amount of encysted larvae ingested, age, gender, and host
immunity.
Enteral phase : A large burden of adult worms in the intestines promote
symptoms such as nausea, heartburn, dyspepsia, and diarrhea from two to
seven days after infection, while small worm burdens generally are
asymptomatic. Eosinophilia presents early and increases rapidly.
Parenteral phase : The severity of symptoms caused by larval
migration from the intestines depends on the number of larvae produced. As
the larvae migrate through tissue and vessels, the body's inflammatory
response results in edema, muscle pain, fever, and weakness. A classic sign
of trichinosis is periorbital edema, swelling around the eyes, which may be
caused by vasculitis. Splinter hemorrhage in the nails is also a common
symptom.
The most dangerous case is worms entering the central nervous system
(CNS). They cannot survive there, but they may cause enough damage to
produce serious neurological deficits (such as ataxia or respiratory
paralysis), and even death. The CNS is compromised by trichinosis in 1024% of reported cases of a rare form of stroke.[10] Trichinosis can be fatal
depending on the severity of the infection; death can occur 4–6 weeks after
the infection, and is usually caused by myocarditis, encephalitis, or
pneumonia.
Diagnosis :
Muscle biopsy is used for trichinosis detection. Several immunodiagnostic
tests are also available. In pigs, ELISA testing is possible as a method of
diagnosis. Anthelmintics can treat and prevent Trichinella infections
Acorrect diagnosis depend upon demonstration of Trichinella in the muscle
either biopsy or autopsy.Various tests useful in diagnosis:
1.DLC:shows marked eosinophelia up to 50 .
2.X-Rays examination :may show the presence of calcified cysts in the
muscles.
3.Increased levels of muscles enzymes:such as lactate dehydrogenase
,creatine phosphokinase due to muscles invasion .
4.muscles biopsy:This is the best way to demonstrate the presence
4
5