INTESTINAL PARASITES (Helminths)
NEMATODA Order: Strongylida

ANGIOSTRONGYLUS COSTARICENSIS

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Angiostrongylus costaricensis: abdominal angiostrongylosis,
caused by A. costaricensis (Morera and Céspedes, 1971
[Morerastrongylus costaricensis (Chabaud, 1972)]
is a parasitic disease characterized by
a granulomatous inflammatory reaction with heavy eosinophilic
infiltration of the intestinal wall,
especially in the ileocaecal region.
The inflammatory reaction, as well as vascular lesions,
can cause sub-occlusion, occlusion and/or perforation of the intestine.
Ectopic localization of the nematode may cause liver and testicle lesions.
Cost2: caudal end of the male of Angiostrongylus costaricensis
showing the copulatory bursa.

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A. costaricensis: although the parasite was described in 1971,
the disease has been observed in Costa Rican children
since the early 50's. Subsequently, the definitive and
intermediate hosts were identified and the life cycle was elucidated.
Since then, human cases of the disease have been reported
from the USA to Argentina, including some Caribbean Islands.
More recently an autochtonous case has been reported from Africa (Zaire).
In addition, naturally infected cotton rats (Sigmodon hispidus)
have been found in the United States.
Synonyms: Morerastrongylus costaricensis (Chabaud, 1972).
In some Latin American countries this parasitosis is named Morera's disease.
cost3: Ventral view of the copulatory bursa of Angiostrongylus costaricensis.
The cloaca is observed just in the middle of the bursa.

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A. costaricensis: A.costaricensis is a Metastrongylid
(super-family Metastronglyloidea, family Angiostrongylidae).
It is a filiform nematode that normally lives within
the mesenteric arteries of the definitive host.
cost7: Angiostrongylus costaricensis normally localize
within the mesenteric arteries, especially those
of the ileocaecal region of the natural definitive host.
The picture shows worms in a naturally infected cotton rat.

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A. costaricensis: in both sexes the oral
opening is surrounded by three small lips.
The male is 20 mm long with a copulatory bursa
and two spicules approximately 0,3 mm in length.
The female is 33 mm long, and the anus and
the vulva are located near the caudal end.
cost1: Caudal end of the female of Angiostrongylus costaricensis
showing the gonopore and the anus, close to the tip of the tail.

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A. costaricensis: in the natural definitive host (often rodents)
the adult worms live within the ileocaecal branches
of the anterior mesenteric artery.
Here, the parasites mate, the female oviposites
and the eggs are carried by the bloodstream
into the intestinal wall, where they embryonate.
The first stage larvae hatch in 4 days, migrate to the lumen through
the intestinal wall, and reach the soil within the rat feces.
cost8: Section through the caecal region of an infected cotton rat.
Eggs, embyos and larvae are observed in the lamina propria and in the submucosa.

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A. costaricensis: the molluscan intermediate host,
usually veronicellid slugs, become infected by eating the rat faeces.
Two molts take place in the molluscan fibromuscular tissues,
and after 18 days the infective third stage larva matures;
these larvae may remain within the mollusk for several
months or may be shed with its mucous secretion.
The definitive mammal host becomes infected by eating the infected mollusk.
The prepatent period is 24 days.
Although several mollusks are naturally infected,
veronicellid slugs are considered the main intermediate hosts.
Cost9: Section of and infected slug (Sarasinula plebeia).
Notice that the third stage infective larvae
are located near the surface of the mollusk,
in cavities that sometimes communicate to a slime excretory duct.
Thus, these larvae can go out of the mollusk with the slime.

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A. costaricensis: there is no evidence that people intentionally eat slugs;
however, small ones hidden in salad leaves could
be finely chopped and inadvertently eaten raw.
In addition, several cases are known of ingestion of these mollusks by infants.
Nevertheless, most human infections are probably caused by ingestion
of the infective larvae shed in the secretion of the mollusks.
Slugs have been found in ripe fruits that have fallen to the ground.
The characteristic mucous trails left by the mollusks
can be observed throughout the endemic areas.
The propensity for small children to put things in their mouths
could explain why they show the highest infection rates.
cost4: Normal life cycle of Angiostrongylus costaricensis

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A. costaricensis: the first non-Costa Rican case of abdominal
angiostrongylosis was found in Honduras.
During the 1970’s, several cases were reported from Venezuela, Mexico, and Brazil.
Today, the disease is being reported from USA to Argentina,
including some Caribbean Islands.
However, it has often been found as the result of the routine examination
of surgical specimens in pathology departments.
In addition, naturally infected cotton rats
(Sigmodon hispidus) have been found in the United States.
In areas where clinical knowledge and the methodology
for laboratory diagnosis have been improved,
it is becoming clear that this is quite a prevalent parasitic disease.
In 1993, more than 650 cases were diagnosed in Costa Rica (population: 3 million),
to give a probably underestimated rate of 21.6 cases per 100,000 persons per year.
In that country, its distribution is universal, from sea level to an altitude of 2000 m.
We think that in areas where physicians are unaware of the problem,
most clinical and subclinical cases probably go unrecognized or misdiagnosed.
Although the cotton rat S. hispidus is considered to be the most important
definitive host, 11 additional rodent species, one case of coati (Nasua narica)
and dogs in Costa Rica, and marmosets (Saguinus mystax) from Iquitos, Peru,
were also found to be naturally infected.
Studies carried out in Costa Rica showed that the highest infection rate
found for S. hispidus was 43.2%, similar to that found
in Panama (35.0%) for the same species.
cost5: The cotton rat Sigmodon hispidus, considered the most important
definitive host of Angiostrongylus costaricensis from the United States to Colombia.

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A. costaricensis: at least two species of veronicellid slugs in
Costa Rica, one in Ecuador and one in Brazil have been found
to be naturally infected with A. costaricensis;
50% of 6025 slugs from 20 Costa Rican localities,
from sea level to an altitude of 2000m, were found to be naturally infected;
more than 16,000 infective larvae were counted in a single specimen.
In addition, some aquatic and terrestrial snails have also
been found to be naturally infected.
Thus, the opportunities for humans, especially children, to become infected are high.
cost6: The veronicellid slug Sarasinula plebeia is considered the most important
definitive host of Angiostrongylus costaricensis in Central America.

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A. costaricensis: in most cases, the lesions are located in the ileaocaecal region.
They have also been observed in the hepatic flexure, descending colon,
regional lymph nodes, liver and testicles.
Two major pathogenetic mechanisms are clearly
distinguishable in the infections caused by A. costaricensis: first,
the adult worms living within the mesenteric arteries damage
the endothelium inducing thrombosis and, consequently,
necrosis of the tissues formerly irrigated by the vessel;
and second, eggs, embryos and larvae, as well as excretion/secretion products,
cause inflammatory reaction.
Combinations of these phenomena, as well as the patient's susceptibility,
and the number and localization of parasites,
determine the clinico-pathological differences,
ranging from cases in which only the appendix is damaged
to those in which major surgery is required.
Sero-epidemiological studies are being done demonstrating that in endemic areas,
many subclinical cases are present.
cost15: Eight cross sections of adult parasites
can be observed within a mesenteric artery.

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A. costaricensis: abdominal angiostrongylosis predominantly affects children.
From 116 patients studied in a pediatric hospital in Costa Rica,
53% were of school age; 37% were of preschool age and 10% were infants.
Of these patients, 64% were male and 34% female.
When the worms are located in the ileocaecal region,
most patients complain of pain in the right iliac fossa and the right flank.
Palpation in this area often causes pain.
Rectal examination is also painful in about half of the cases,
and most patients present with fever ranging from
38°C to 38.5°C (100.4F to 101.3F), rarely accompanied by chills.
In some children, intestinal bleeding can be confused with a Meckel diverticulum.
In chronic cases, a mild fever may persists for several weeks.
Anorexia, vomiting and constipation are also present in about one half of the patients.
A very important finding is a tumor-like mass that,
if present, can be palpated in the lower right quadrant
and may be confused with a malignancy.
Although a few patients have no hematological abnormalities,
leukocytosis and eosinophilia are usually present.
White blood cell counts usually range between
15,000 and 50,000/mm³ and eosinophilia from 20% to 50%.
The leukocytosis has been as high as 169,000/mm³, with 91% eosinophilia.
cost13: Section through the mucosa and sub-mucosa of a cecum surgical specimen.
Observe the strong inflammatory reaction and the three embryos of the parasite.

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Angiostrongylus costaricensis: an X-ray examination is often helpful
in making the clinical diagnosis.
Radiological changes are localized in the terminal ileum,
cecum, appendix and ascending colon.
The contrast medium shows incomplete filling and irritability of the involved areas.
The lumen is reduced by the thickening of the intestinal wall.
cost12: X-ray plate (with barium enema)
showing filling defects due to the inflammatory reaction.

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Angiostrongylus costaricensis: sometimes the patient complains of pain
in the upper right quadrant; in these cases,
the liver is almost always enlarged and tender to palpation.
At laparoscopy, small yellowish spots are seen on the surface of the liver.
Most patients have hepatic involvement along with intestinal angiostrongylosis.
When the testicle is involved, the most remarkable findings are acute pain,
accompanied by redness that later change to purple.
Eosinophilia and leukocytosis are also conspicuous.
All patients with testicular necrosis have been misdiagnosed
as having testicular torsion, and the correct diagnosis was only
made following surgery. In non-surgical intestinal infections,
the symptomatology could last from a few weeks to a few months.
cost10: Surgical specimen. Notice the thickening of the intestinal wall,
especially in the area of the ileocaecal valve and cecum.

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A. costaricensis: in humans, as well as in the rodent natural host,
the adult parasites are located within the mesenteric arteries.
In most cases, the lesions are located in the ileocaecal region.
They have also been observed in the hepatic flexure,
descending colon, regional lymph nodes, liver and testicles.
The gross examination of surgical specimens shows a hardened
and thickened intestinal wall with yellowish foci
on the serosal surface and in the mesentery.
The intestinal lumen is reduced, sometimes causing partial or complete obstruction.
When necrotic areas are present, they could lead to perforation and peritonitis.
cost16: Two worms could be observed within a mesenteric artery.
The intimate is edematous and the endothelium is damaged.

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A. costaricensis: in many cases, even though only an appendectomy is performed,
the surgeon observes lesions on the cecum.
Histopathology demonstrates granulomatous inflammatory reaction
with heavy eosinophilic infiltration, especially in the mucosa and submucosa;
the serosa and muscular layers are often involved to a lesser degree.
Eggs, embryos and larvae appear in small cavities lined by endothelium.
Unfertilized eggs usually degenerate and are difficult to recognize.
These structures as well as excretion/secretion antigens are easily identified
by immunochemical techniques within microscopic areas of necrosis.
Large necrotic areas are caused by arterial thrombosis.
cost17: Mesenteric arteries totally occluded by thrombus;
observe cross sections of adult parasites trapped within the thrombus.

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A. costaricensis: Eggs and embryos are also present in the mesenteric lymph nodes,
which show reticuloendothelial hyperplasia and eosinophilic infiltration.
Hepatic lesions caused by A. costaricensis are similar
to those caused by Toxocara canis.
However, the finding of eggs, embryos and even adult worms
in the hepatic parenchyma establishes the diagnosis.
In excised necrotic testicles histologically showing
extensive parenchymal hemorrhagic necrosis,
worms could be observed obstructing the arteries of the spermatic cord.
cost: 14: Granulomatous inflammatory reaction with heavy eosinophilic inflitration.
Microscopic necrotic areas can also be observed.

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A. costaricensis: the clinical diagnosis is based on the above mentioned features.
The symptoms and other clinical findings can be confused with appendicitis.
Sometimes the diagnosis is made after surgery.
Barium enema examination can show filling defects
of the colon that often resembles a malignancy.
In infected rats, the first-stage larvae can be easily identified in the stools;
however, this is not true in humans.
In man, an immunological test should therefore be used to confirm suspected cases.
Immunoelectrophoresis and Ouchterlony immunodiffusion test give good results.
However, an inexpensive and rapid latex-beads agglutination test
also gives high sensitivity and specificity rates.
During the last 20 years, more than 20,000 Costa Rican
potential patients have been examined with this test.
In more than 97% of the cases, no cross-reactions,
nor false positive or negative results have been observed.
cost18: Two embryos can be observed in a mesenteric lymph node
of a patient with angiostrongylosis.

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A. costaricensis: surgery, when necessary,
is the treatment of choice for abdominal angiostrongylosis.
However, as knowledge of this often self-limited disease increases,
more non-surgical cases are being followed.
Three drugs, diethylcarbamazine, thiabendazole and albendazole,
have been used with "remission" of symptoms reported. However,
there was no objective evidence to prove that cure was attributable to the drugs.
In fact, in vitro, and in vivo trials in experimentally infected rats,
demonstrate that the parasites are excited by the drugs instead of being killed,
causing erratic migrations and worsening of the lesions.
Thus, chemotherapy is not recommended until experimental studies
demonstrate a more efficacious drug.
Non-surgical patients should therefore be observed carefully;
well-controlled palliative treatment could be used.
Some patients may present with remission of the symptoms;
others could eventually develop an acute syndrome that requires surgery.
cost11: Surgical specimen showing thickening
of the colon and a huge mass in the cecum area.
Necrotic areas can also be observed.