Parasites

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Parasites of the Urinary System and the eye
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There are two nematodes that occur as parasites
of the urinary system in small animals,
Dioctophyma renale and Capillaria plica. Both are
of rare incidence.
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Dioctophyma renale in situ
The adult worm occurs in the kidney parenchyma
and occasionally the peritoneal cavity of dogs,
mink and other wild carnivores. There is no
possibility of confusion in the identification of
this worm because of its spectacular size and
location. It is the largest parasite nematode of
domestic animals.
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Dioctophyma renale in situ
Dioctophyma renale ultimately destroys the
kidney, leaving only a thickened capsule.
Unilateral infections are the rule and the right
kidney is most commonly involved. Most unilateral
infections are asymptomatic, with compensatory
hypertrophy of the unaffected kidney. Bilateral
infections are fatal.
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Dioctophyma renale
D. renale is robust and red in color. Female
worms measure 20-100 cm in length and males
measure 14-45 cm. One to three worms may occupy a
kidney.
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Dioctophyma renale eggs
Distinctive eggs are shed in the urine of
infected animals. They measure 75m by 45m, are
ovoid, brown in color and have a deeply pitted
shell with a plug at either end. Eggs are long
lived and eggs become infective in several weeks.
Infective eggs must then be ingested by a fresh
water annelid which lives as a commensal on
crayfish. Dogs and other hosts may become
infected in two ways 1) by ingestion of
infective larvae in annelids (usually on
crayfish) or 2) by ingestion of encysted larval
in freshwater fish which act as paratenic hosts.
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Dioctophyma renale eggs
Worms are thought to migrate directly through the
wall of the duodenum to the kidney. The duodenum
is on the right side and this probably accounts
for the high incidence in the right kidney. Worms
become adult in 1-3 months and are thought to
live 1-3 years. In some cases worms may develop
in the peritoneal cavity of dogs.
Although infections are rare in dogs, a high
incidence may occur in mink and other wild
animals (i.e. 8 of mink in Michigan). It is
cosmopolitan in the U.S. and has been reported
from Louisiana. Outbreaks on mink farms have been
reported from feeding raw fish scraps.
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Capillaria plica life cycle
Capillaria plica occurs uncommonly in the urinary
bladder and sometimes kidney pelvis of dogs, wild
canids and occasionally the cat. It is not
considered to be pathogenic and diagnosis is
often made by the incidental finding of
characteristic eggs in sediment of routine
urinalysis specimens.
The life cycle is poorly understood but is
thought to be indirect. Eggs are ingested by
earthworms in which they become infective for the
final host. After ingestion of infected
earthworms, a complex developmental migration to
the urinary bladder is thought to take place.
Larvae penetrate the mucosa to the hepatic portal
blood and enter the general circulation via the
liver and lungs. Larvae enter the kidneys by way
of the renal arteries and migrate through
Bowman's capsule and tubular nephrons to the
renal pelvis, and finally descend to the bladder
via the ureter. Patency occurs 2 months after
infection. Female worms measure 3 to 6 cm males
measure 1.5 to 3 cm.
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Capillaria plica egg
Typical double plugged, yellowish eggs are
diagnostic if found in the urine. They measure
60-68 by 24- 30 m and have some resemblance to
whipworm eggs except for the smaller size,
lighter color, and the rougher, more irregular
shell morphology of C. plica. Treatment is not
warranted.
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Thelazia californiensis
Thelazia califoiniensis is an eyeworm about 1-2
cm in length. It occurs beneath the nictitating
membrane, and in the conjunctival sac and tear
ducts of dogs. Other hosts include the sheep,
deer, jackrabbit, coyote, black bear, and cats.
Rare cases are reported in man. Incidence
Thelazia was originally recorded in California
and has since been found in Oregon, Nevada,
Arizona and New Mexico. In California, endemic
areas of high incidence occur along the coastal
mountains and the Sierras. Seasonal occurence in
the summer months correspond to the fly season of
June through September. Thelazia is found most
often in rural dogs, probably because these dogs
are outside more and exposed to more flies or
because they are closer to wildlife reservoir
hosts.
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Thelazia californiensis
Life cyc1e Vectors of eyeworms are the Muscidae
houseflies. In the United States, Fannia spp have
been incriminated although there is some question
about other possible vectors. The Fannia species
involved is called the lesser housefly because
of its small size and slender abdomen. These
f1ies can be distinguished from the domestic
housefly by their habit of hovering and darting
about in mid-air in the middle of a room or in
their outdoor habitat. The life cycle has not
been completely worked out for Thelazia
californiensis, but it is probab1y that of other
Thelazia spp. Embryonated eggs in lacrimal
secretions are ingested by flies and develop to
third stage larvae in 2-4 weeks in the insect.
They then migrate to the proboscis and transfer
to a new host at feeding. Egg-laying adults are
found in the eye in 2-3 weeks for a total life
cycle of 1-2 months. Worms can live several
months to a year in the eye.
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Clinical Signs Usually there are only mild
symptoms of lacrimation, photophobia, and mild
conjunctivitis. Rarely, there is secondary
infection, supporation and ulcerative keratitis.
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Thelazia californiensis in a dogs eye
Worms are difficult to see where the eyelids and
nictitating membrane are in place, but are easily
visualized by retracting the third eyelid after
local anesthesia.
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Removal of Thelazia californiensis
Parasites can be removed manually with local
topical anesthesia. However, there is danger to
the animal due to restraint problems and sharp
instruments and it is more common to lightly
anesthetize the dog with a short acting
barbiturate in addition to topjcal ophtha1mic
anesthesia. Several repeats of this process may
be necessary to remove all eyeworms (either early
reinfection occurs or young forms are missed).
Soulsby (1995) has recommended various topical
chemotherapy drugs (I 500 Caracide solution,
12000 Iodine, 0.05 HgCl, or 2-3 boric acid).
These topical drugs may aid in climating immature
forms not readily seen during removal of adult
worms.