Introduction
1. ANGIOSTRONGYLIASIS
Etiology:
The causative agent are
Angiostrongylus (Morerastrongylus) costaricensis, A. cantonensis, and A.
malaysiensis.
Infection in Man:
It is believed that the
parasite was introduced to the island some years ago by rats from a ship from
Asia. The clinical manifestations of abdominal angiostrongyliasis caused by A.
costaricensis are moderate but prolonged fever, abdominal pain on the right
side, and, frequently, anorexia, diarrhea, and vomiting.
Angiostrongyliasis caused
by A. cantonensis is generally expressed as eosinophilic meningitis, but there
have also been isolated outbreaks in which the spinal cord, spinal nerves, and
brain were extensively affected. The incubation period was 1 to 6 days, and the
disease lasted 10 weeks.
2. ANISAKIASIS
Etiology:
The agent of this
parasitosis is the larval stage of nematodes of the genera Anisakis,
Pseudoterranova (synonyms Porrocaecum, Terranova, Phocanema), or Contracaecum.
These parasites belong to the order Ascaridida, family Anisakidae.
Infection in Man:
Man is an aberrant host
in whom the larva ingested with raw fish or squid does not reach maturity.
There are two exceptions in which juvenile P. decipiens were recovered from
human hosts.
The larvae may remain in
the cavity of the stomach or intestine without penetrating the tissues, causing
an infection that is often asymptomatic. In general, asymptomatic or mild cases
are caused by Pseudoterranova spp. These infections are discovered when live
larvae are expelled by means of coughing, vomiting, or defecating.
3. ASCARIASIS
Etiology:
The agents of human
ascariasis are the nematode of humans, Ascaris lumbricoides, and occasionally,
the nematode of swine, A. suum.
Humans are the reservoir
of A. lumbricoides, as swine are for A. suum. The sources of infection include
soil (geohelminthiasis), edible plants, or drinking water contaminated with
fecal matter containing eggs of Ascaris. Transmission to man can occur directly
from the soil or indirectly, by means of dust, water, vegetables, or objects to
which the parasite’s eggs have adhered.
The course of the disease
and the symptomatology are similar in both humans and swine. Children and
suckling pigs are most affected. In the early age group, not only is the rate
of infection higher, but parasite burden is larger.
Infection in Man:
Mild infections are
generally asymptomatic; but when the parasite burden is larger, there may be
vague abdominal discomfort, colic, diarrhea, and vomiting. The most serious
complications in children include intestinal obstruction by a large mass of
parasites, obstruction of the pancreatic duct, and complications resulting from
the aberrant migration of adult parasites to various organs.
4. BAYLISASCARIASIS
Etiology:
The agents of this
infection are larvae of Baylisascaris procyonis, an ascarid found in the small
intestine of raccoons.
Infection in Man:
Man is an intermediate
rather than paratenic host. The human infection seems to be identical to that
found in laboratory animals, in which it has been shown that the B. procyonis
larvae continue to migrate, and that they molt and grow from 300 to 1,900 µm
until they develop into eosinophilic granulomas. B. procyonis causes visceral,
ocular, and cerebrospinal syndromes in man.
The severity of the disease depends on the
number, location, and activity of the larvae. A mild infection with a small
number of larvae, which mostly encapsulate in the connective and muscular
tissue, will probably not produce clinical manifestations. A more intense
infection can cause the typical signs of visceral larva migrans: fever,
leukocytosis, eosinophilia, hepatomegaly, and pneumonitis.
5.CUTANEOUS LARVA
MIGRANS
Etiology:
Cutaneous larva migrans is a clinical
description more than an etiologic diagnosis. The principal etiologic agent is
the infective larva of Ancylostoma braziliense, an ancylostomid of dogs, cats,
and other carnivores.
ZOONOTIC
ANCYLOSTOMIASIS
The agents
of these diseases are the nematodes Ancylostoma caninum (of dogs) and A.
ceylanicum (of cats).
A. braziliense occurs in
tropical and subtropical areas; A. caninum and B. phlebotomum, in temperate
climates; and U. stenocephala, in colder parts of temperate regions. Human
cutaneous larva migrans occurs more frequently in tropical and subtropical
areas.
Infection in Man:
Man is an aberrant host,
in which the infective larvae cannot complete their development cycle and
become adults. A. braziliense is a small species of Ancylostoma; the female
measures about 1 cm long by 0.37 mm wide.
The infective larva
produces a pruriginous papule upon penetrating the skin. In the days that
follow, the larva travels around in the germinal layer and produces sinuous
tunnels, advancing a few millimeters to several centimeters a day and forming
vesicles along the tunnels on the outer surface of the skin. The migration of
the larvae and the corresponding tissue reaction cause intense pruritus,
especially at night, and may keep the patient awake. Secondary bacterial
infections are also common. The lesion, which can be single or multiple, is
most often located on the lower extremities. The larvae usually remain alive
and travel in the skin for two to eight weeks, at the end of which the disease
is cured spontaneously. However, there have been patients in whom the infection
persisted for as long as 18 to 55 months.
Some patients suffer a
transitory pneumonitis with eosinophilia (Loeffler syndrome), and in such cases
larvae may be found in the sputum. Ancylostoma larvae have also been found in
the cornea. This finding confirms the hypothesis that the larvae of animal
ancylostomids can sometimes produce visceral infections in man.
6.DIOCTOPHYMOSIS
Etiology:
Dioctophyma (Dioctophyme) renale is a large,
blood-red nematode that in the adult stage lodges in the kidneys of minks,
occasionally other mustelids, and at times, wild and domestic canids. In dogs,
the adult female of the parasite can reach up to 1 m long and 5–12 mm wide and
is therefore known as the “giant kidney worm.” The male is much smaller. The
size of the parasite depends on the host species; for example, in minks it is
not more than a few centimeters long.
The definitive host
eliminates the eggs of the parasite via the urine.
Infection in Man
The infection is very
rare in man. Until 1982, the literature described just 13 well-documented cases
of infections in the human kidney (Barriga, 1982). There are also three human
cases in which larvae of D. renale were found in ectopic locations (Gutiérrez
et al., 1989).
In humans and dogs, the
nematode usually locates in just one kidney, most often the right one, and in
most cases, only one parasite is found. As it grows, Dioctophyma destroys the
renal parenchyma and, in extreme cases, leaves only the capsule of the organ.
The most prominent symptoms include renal colic and hematuria or pyuria. In
some cases, the parasite migrates to the ureter or urethra and blocks the flow
of urine. In dogs, cases in which the parasite remains in the peritoneum are
usually asymptomatic, though this localization can occasionally cause
peritonitis. The healthy organ compensates for the loss of renal function and
generally hypertrophies.
7. DRACUNCULIASIS
Etiology:
The agent
of this infection is Dracunculus medinensis, one of the longest nematodes
known, despite its variable size.
In its
adult stage, D. medinensis parasitizes man and a variety of domestic and wild
animals, including monkeys, carnivores, cattle, and equines.
Infection in Man:
The prepatent period, from initial infection until
emergence of the parasite in the skin, lasts about a year and does not produce
any symptoms in the host.
Symptoms
appear when the parasite initiates its final migration to the skin surface.
Shortly before or at the same time the vesicle is formed, some of the following
allergic manifestations begin to develop: urticaria, pruritus, dyspnea,
vomiting, mild fever, and sometimes fainting. Once the vesicle is formed and
before the parasite emerges, the patient feels a strong burning sensation,
which he may try to alleviate by immersing the affected part in cold water.
The most
serious complications stem from secondary bacterial infections that gain entry
through the open lesion and can propagate along the length of the tunnel
excavated by the parasite.
Even when
there are no complications, many patients remain incapacitated for several
weeks or months. According to a study conducted in the district of Ibadan,
Nigeria, patients remained disabled for an average of 100 days. The degree of
incapacity was related to the number of parasites and their localization: sites
in the ankle and foot were the most serious.
8. ESOPHAGOSTOMIASIS
AND TERNIDENSIASIS
Etiology:
The agents of these diseases are strongylid
nematodes of the species Oesophagostomum bifurcum, O. stephanostomum, O.
aculeatum (O. apiostomum), and Ternidens deminutus. They live in the intestine
of nonhuman primates and sometimes humans, causing the formation of nodules in
the intestinal wall.
Infection in Man:
Mild human
infections caused by Oesophagostomum spp. go unnoticed. In clinical cases, the
symptoms range from vague abdominal pain to intestinal obstruction associated
with tumors. The disease can be mistaken for ameboma, carcinoma of the colon,
appendicitis, or ileocecal tuberculosis. A subcutaneous nodule caused by one of
these species has been reported in a human patient.
9. GNATHOSTOMIASIS
Etiology:
The agents
of this infection are larvae of Gnathostoma spinigerum, G. hispidum, G.
doloresi, and G. nipponicum.
G.
spinigerum is a spiruriod nematode parasite of dogs and domestic and wild
felines. It has been known since 1890 that it can infect man. G. hispidum is a
parasite of swine and wild boars, and has been known as a parasite of humans
since 1924. Only in 1989 was it recognized that G. doloresi, a parasite of
swine and wild boars, also infects man (Nawa et al., 1989). Around the same
time, it was found that G. nipponicum, a parasite of weasels, can also
occasionally infect man.
Infection in Man
Man is an
aberrant host in which the parasite only exceptionally reaches sexual maturity:
the larva continuously migrates and does not become established in the human
stomach. In most cases, a single larva is responsible for the clinical picture.
The most common symptoms are localized, intermittent, and sometimes migratory
swelling of the skin, often accompanied by pain, pruritis, and erythema. It can
also affect the internal organs.
The
movements of the larva inside the abdominal or thoracic organs can cause acute
pain of limited duration. The symptoms resemble cholecystitis, appendicitis,
cystitis, or other diseases, depending on the organ affected by the larvae
(internal or visceral gnathostomiasis). Approximately one month after the
infective food is eaten, the larva locates in the subcutaneous tissue, usually
of the abdomen, extremities, head, and chest. This is the beginning of the
chronic phase, in which the organic symptoms abate or disappear and
eosinophilia gradually decreases.
In older
infections, the edemas recur at longer intervals. The larva can survive in the
human body for a long time; and one case lasting 16 years has been recorded.
10. STRONGYLOIDIASIS
Etiology:
The agents
of this disease are the nematodes Strongyloides stercoralis and S. fuelleborni.
Although man can be infected experimentally with the swine parasite S. ransomi,
this latter infection does not appear to occur in humans spontaneously in
nature.
In man,
there are two forms of superinfection (acquisition of a new infection on top of
a previous one): hyperinfection and autoinfection. In hyperinfection, the
rhabditiform larvae turn into infective filariform larvae in the upper part of
the intestine; penetrate the mucosa in the lower part of the ileum or the
colon; migrate to the lungs, trachea, and esophagus; and, finally, are carried
by the bloodstream back to the intestine, where they mature. In autoinfection,
some of the filariform larvae shed with the feces remain in the perianal or
perineal region long enough to repenetrate the skin of the same host.
Infection in Man:
In a high proportion of human patients, S.
stercoralis infection can be of very long duration. The evidence suggests that,
even though host immunity inhibits the development and pathogenicity of larvae,
it does not terminate the infection. These hypobiotic larvae can remain in the
patient’s tissues for years as an asymptomatic and overlooked infection, until
a breakdown of immunity enables them to resume their development and become
pathogenic once again.
Mild
infections are usually well tolerated in immunocompetent individuals and
produce no symptoms at all, or at most only vague and variable intestinal
complaints. However, in persons with large parasite burdens or lowered
immunity, the clinical picture can be cutaneous, pulmonary, or digestive,
depending on the localization of the parasite, and the seriousness of the
infection can range from mild to fatal.
11. THELAZIASIS
Etiology:
The agents
of this disease are Thelazia callipaeda, T. californiensis, and T. rhodesii.
The
intermediate hosts of Thelazia are various species of Musca.
The female
lays embryonated eggs in the conjunctival sac, and the first-stage larvae are
released and deposited on the conjunctiva. To continue their development,
Thelazia spp. require a fly as an intermediate host. The flies, by sucking
conjunctival secretions, ingest the larvae (or the eggs containing them). These
larvae develop inside the insect for several weeks, until they become infective
third-stage larvae. The infective larvae migrate to the proboscis of the fly
and infect new conjunctiva when the arthropods resume sucking conjunctival
secretions. In 2 to 6 weeks, the third-stage larva matures into an adult and
begins to produce eggs.
Infection in Man:
In man,
Thelazia sp. lodge in the conjunctival sac, where they cause irritation,
lacrimation, conjunctivitis, and sometimes, corneal scarring and opacity. Some
infections manifested only as a bothersome sensation of a foreign body in the
affected eye.
12. TRICHINOSIS
Etiology:
The agents
of this disease are nematodes of the genus Trichinella, particularly T.
spiralis. This species is a small nematode of the intestine of predatory
mammals and the muscles of mammals preyed upon by other animals.
Infection in Man:
Human
trichinosis is still widespread in many parts of the world, but morbidity rates
are low and declining. Only a small proportion of infections—those that are
intense—are manifested clinically. It is thought that man needs 10 to 100
parasites per gram of muscle in order to show symptoms. Many sporadic cases
pass unnoticed or are confused with other diseases.
13. TRICHURIASIS OF
ANIMAL ORIGIN
Etiology:
The agent
of trichuriasis is Trichuris vulpis of canids and, secondarily, T. suis of
swine. Trichuris trichiura is a species that parasitizes man.
Infection in Man
Trichuriasis
is very similar in humans and canines. The infection is much more common than
the disease and much more prevalent in young individuals. In infections with a
large number of parasites, there may be abdominal pain and distension as well
as diarrhea, which is sometimes bloody. In very heavy infections in children
(hundreds or thousands of parasites), there can be strong tenesmus and rectal
prolapse. Massive parasitoses occur mainly in tropical regions, in children 2
to 5 years old who are usually malnourished and often infected by other
intestinal parasites and microorganisms.
14. VISCERAL LARVA
MIGRANS AND TOXOCARIASIS
Etiology:
Visceral larva migrans refers to the presence
of parasite larvae that travel in the systemic tissues of man but not in the
skin. However, the term visceral larva migrans is usually reserved for
extraintestinal visceral infections caused by nematodes of the genus Toxocara,
especially Toxocara canis.
The
reservoir of larva migrans for man is infected dogs. The source of infection is
soil contaminated with infective eggs, and the mechanism of transmission is the
ingestion of these eggs in contaminated food or water, or via contaminated
hands.
Infection in Man
Toxocariasis
is caused by the presence of T. canis or T. cati larvae in various human
tissues. These larvae produce small tunnels of traumatic, inflammatory, and
necrotic lesions in the course of their migration, followed by a granulomatous
reaction with an abundance of eosinophils, and sometimes abscesses, once the
larvae settle in a particular site. Toxocariasis is basically an allergic
disorder. Originally two forms were described (visceral and ocular), but later
four clinical forms were recognized: visceral (perhaps better referred to as
systemic), ocular, neurological, and covert.
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