Encephalitic nematodiasis in a Douglas squirrel and a rock dove ascribed to Baylisascaris procyonis.

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Encephalitic nematodiasis in a Douglas squirrel
and a rock dove ascribed to Baylisascaris procyonis
John W. Coates, Judith Siegert, Victoria A. Bowes, Deirdre G. Steer
This report briefly describes the history, clinical signs,
treatment, and necropsy findings in a Douglas squir-
rel (Tamiasciurus douglasii) and 2 rock doves (Columba
livia), in which lesions observed within brain tissue
were caused by migrating ascarid larvae suspected of
being Baylisascaris procyonis, the raccoon roundworm.
Cross-species transmissibility of the migrating larvae
of the raccoon roundworm is briefly discussed.
One of 2 immature rock doves that had been under the
care of the Wildlife Rescue Association of British
Columbia in Burnaby for 6 wk suddenly developed
central nervous system (CNS) signs of head tremor,
incoordination, loss of balance, and torticollis. Three
weeks previously, the bird had received a routine, sin-
gle administration of 0.03 mg ivermectin (Ivomec,
MSD Agvet, Kirkland, Quebec), PO, as prophylaxis
against helminths. We suspected head trauma upon
onset of the CNS signs, so we administered 0.5 mg of
sodium dexamethasone phosphate (Dexamethasone 2,
Austin Laboratories, Juliet, Quebec), IM. Twelve hours
later, the bird's condition began to deteriorate rapidly,
and it was euthanized.
Necropsy failed to explain the CNS signs observed
clinically. Histopathological changes in tissues, includ-
ing serial brain sections, were not observed, though
portions of brain removed for viral culture had reduced
the quantity available for microscopic examination.
Tissue cultures for avian viruses, including avian
paramyxovirus (PMV-I), using separate cell cultures of
chick embryo fibroblasts and chick kidney cells were
also negative, as was toxicological analysis for lead.
Bacterial cultures were negative.
Prior to the bird becoming ill, about 40 rock doves had
been kept intermittently in the same outdoor pen. Over
the previous 4 to 5 y, groups of immature, orphaned rac-
coons (Procyon lotor) had been housed in this pen for
about 3 mo at a time. Within 24 h of admission, the
young raccoons were dewormed, using pyrantel pamoate
oral suspension (Strongid-T, rogar/STB Inc, London,
Ontario), PO, at 50 mg/ 7.5 kg body weight (BW), with
a 2nd worming 6 to 8 wk later. The floor of the pen was
composed of roughened cement, which had been washed
with a standard bleach solution (5.25% sodium hypochlo-
rite) and cleaned with pressurized steam following
release of the young raccoons. Walls in all the pens
consisted of an open wooden framework overlaid with
heavy-gauge wire mesh. This enclosure was immediately
Can Vet J 1995; 36: 566-569
Animal Health Centre, Ministry of Agriculture, Fisheries and
Food, 1874 Gladwin Road, PO Box 100, Abbotsford, British
Columbia V2S 4N8 (Coates, Bowes); 3240 Phillips Avenue,
Burnaby, British Columbia V5A 2W7 (Siegert); Wildlife
Rescue Association of British Columbia, 5216 Glencarin
Drive, Burnaby, British Columbia V5B 3C I (Steer).
|i_ f .' F:
.X
Figure 1. Photomicrograph of cerebral cortex from a Douglas
squirrel. Longitudinal and cross sectional views (arrows) of an
ascarid larva(e) consistent with Baylisascaris procyonis are seen
in conjunction with a moderate granulomatous inflammatory
response. Periodic acid-Schiff. Bar = 100gm.
adjacent to a pen containing a 6-month-old, female,
Douglas squirrel.
A week after the death of the rock dove, the Douglas
squirrel in the adjacent pen became ill. It developed
acute, progressively severe, CNS signs, characterized by
initial incoordination, followed by recumbency and
paddling of the limbs immediately prior to death.
The squirrel was hospitalized and initially treated
for suspected head injury with dexamethasone sodium
phosphate (Dexamethasone 5, Austin Laboratories),
0.3 mg, IM, q24h. By the next day, the squirrel's con-
dition had worsened. At this time, we recalled the CNS
signs shown by the rock dove from the adjacent pen only
I wk earlier, and that immature raccoons had been kept
in that enclosure until very recently. For these reasons,
we then suspected that migrating larvae of the raccoon
roundworm, B. procyonis, were causing the CNS signs
in the squirrel.
Ivermectin (Ivomec, MSD Agvet), 0.03 mg, PO, was
administered, followed by furosemide (Lasix, Hoechst-
Roussel, Sommerville, New Jersey), 0.05 mg, PO, qI 2h
for 3 d. Despite treatment, the squirrel's condition pro-
gressively deteriorated. It was finally euthanized 6 d fol-
lowing onset of clinical signs.
Necropsy of the squirrel failed to demonstrate any
gross visible lesions. Tissues from all major organs
and the brain were fixed in 10% neutral buffered for-
malin, embedded in paraffin, and then sectioned and
Can Vet J Volume 36, September 1995
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...t|
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....
Figure 2. Photomicrograph of cerebral cortex of a Douglas
squirrel from the same area as in Figure 1. Cross sectional
features, such as a single pair of lateral alae (small arrows),
paired excretory columns (larger arrow) and a prominent
central digestive canal (arrowhead), are typical of B. procyo-
nis. Periodic acid-Schiff. Bar = 50pm.
stained with hematoxylin and eosin (H&E) for histo-
logical examination. Brain sections were also stained with
periodic acid-Schiff (PAS). Portions of liver, lung, and
intestine were retained for bacterial culture; liver and kid-
ney were submitted for toxicological analysis for heavy
metals. Portions of fresh brain were kept and frozen for
subsequent viral studies, if other tests proved to be
negative. Bacterial cultures for pathogenic organisms
were negative, as was toxicological analysis on liver and
kidney samples for lead and cadmium.
Histological examination of sections from the brain
revealed multifocal, patchy areas of granulomatous
encephalitis in both the gray and the white matter of the
cerebral hemispheres (Figure 1). Gliosis with moderate
numbers of histiocytes, lymphocytes, plasma cells, and
a few granulocytic cells resembling eosinophils was
present in these malacic areas, as was prominent lym-
phohistiocytic cuffing of vessels. Brain sections stained
with H&E and PAS demonstrated multiple larval frag-
ments in these same foci within the cerebral hemi-
spheres (Figure 1).
Larval crosssections revealed a single pair of lateral
alae; paired lateral excretory columns, roughly triangular
in shape; and a prominent central digestive canal
(Figure 2). These features are characteristic of larvae of
Baylisascaris spp. within the family Ascarididae. The
greatest larval diameter measured on the sections exam-
ined was 60 to 65 ,um (Figure 2), which is consistent with
previously reported measurements of B. procyonis (1,2).
Larval diameters measured microscopically vary, depend-
ing upon the point and angle of sectioning, and with the
stage of development of the larva.
A 2nd rock dove, cage-mate of the I st one,became ill
10 d after the onset of illness in the squirrel. The bird,
which was initially observed as being lethargic and
disoriented, stopped eating and developed CNS signs
similar to those shown by the 1st bird, including poorly
coordinated attempts at flying. The dove was immediately
hospitalized and given nursing care. By the 5th d, the
dove's condition had worsened, and it was euthanized
and submitted for necropsy.
Examination of histological sections from the brain of
the 2nd dove revealed mutiple, patchy foci of mild
granulomatous encephalitis, malacia, edema, and glio-
sis, together with mild inflammatory perivascular cuffs
within the medulla, brain stem, and cerebellum. A sin-
gle ascarid larva observed in longitudinal and cross
sectional portions within the bird's cerebellar peduncles
was identical in size and morphology to the larvae pre-
viously seen in the squirrel's brain. The spinal cord
was not examined histologically in either the squirrel or
the doves. In retrospect, considering observed clinical
signs of weakness, incoordination, and recumbency,
lesions due to migrating ascarid larvae might have been
present in the spinal cord, as has been reported in other
cases (2).
Baylisascaris procyonis is the common roundworm in
the small intestine of raccoons. The parasite is similar in
appearance and life cycle to the roundworm of skunks
(B. columnaris); in morphology, it superficially resem-
bles the canine roundworm Toxocara canis (1). The
raccoon roundworm is well recognized as a potentially
serious pathogen when its eggs are ingested by other
species. Lesions attributed to larval migration of this par-
asite have been described within brain or spinal cord in
over 40 mammalian and avian species, including the grey
fox (1), red squirrels (1), mourning doves (1), chin-
chillas (5), cottontail rabbits and woodchucks (6), dogs
(7), ratites (3,8), and humans (9). Rodents including
squirrels, as well as birds and rabbits, are considered to
be the natural intermediate hosts for B. procyonis (1).
Several other Baylisascaris spp., including B. colum-
naris of skunks and B. transfuga of bears, as well as those
of badgers, fishers, and martens, are also capable of
causing animal or human disease of a similar nature
(1,2,9). A few species, including cats and larger domes-
tic livestock, such as sheep and swine, are evidently only
marginally susceptible to B. procyonis (1).
The roundworm is a common parasite of raccoons;
in
detected in raccoon scats taken from both rural and
urban areas varied from 27% to 31% (10). Other animal
species, including man, may become infected by ingest-
ing infective eggs from contaminated soil, water, air, or
fomites (9).
We suspect that the ascarid larvae detected within the
brain tissues of the Douglas squirrel and the 2nd rock
dove were those of B. procyonis. The rock doves had
been caged in an outdoor aviary pen previously occupied
for several months by immature raccoons, and it is
likely that the floor of this pen, and that of the adjacent
pen that contained the Douglas squirrel, had become
contaminated with eggs from the raccoon roundworm.
In retrospect, the initial administration of an anthelmintic
to the young raccoons upon admission would not have
prevented the release of ascarid eggs and subsequent
contamination of the pen within the first 24 h following
treatment.
1 report, the prevalence of eggs of B. procyonis
567
Can Vet J Volume 36, September1995

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Migrating larvae of the raccoon roundworm have a
tropism for nervous tissue in other species (1,4). Larvae
are believed to reach the brain via the arterial blood
stream, leaving small arteries where their diameter
approximates that of the blood vessel. Larvae then pen-
etrate the brain from the subarachnoid space and
choroidal membranes (4). A single ascarid larva wan-
dering haphazardly through the brain or spinal cord of
either a natural intermediate host, or an accidental host,
may produce severe and fatal damage. Unlike the larvae
of Toxocara spp., migrating larvae of the raccoon round-
worm continue to grow in size upon reaching the brain
(1,4). Earlier reports link the granulomatous inflam-
matory response observed within nervous tissue to
mechanical trauma caused by larval movement and
actual growth, and to the parasite's release of antigenic
enzymes and metabolic wastes (1-4).
In this case, preventing the development of lesions
attributed to B. procyonis neural larva migrans in both
the 2nd rock dove and the squirrel by a single oral pro-
phylactic treatment with ivermectin upon admission to
the Wildlife Rescue Care Centre was unsuccessful. The
effectiveness of veterinary treatment of the condition
in animals, including the administration of either
anthelmintics, steroids, or both for acute cases of CNS
larva migrans caused by this parasite, is still a quandary
(2,9); additional study is needed.
Though steroids are known to exacerbate parasitic
infections in host-parasite relationships, some authors
believe them to be of value in cases of cross-species larva
migrans, since they reduce inflammatory reactions and
eosinophil degranulation, which may be serious and
even life-threatening (9). The CNS certainly has limited
tolerance to either the trauma caused by the migrating
larvae or the deleterious effects of the inflammatory
reaction that the parasite generates.
Steroids have been used together with anthelmintics
in the treatment of toxocaral visceral larva migrans in
children, including ocular larva migrans (9). Unfortu-
nately, success in treating neural larva migrans due to
Baylisascaris spp. in animals or humans is much less
satisfactory. Larvae of B. procyonis can enter the brain
within the 1st wk of infection, and significant CNS
damage usually occurs prior to the onset of clinical
signs (2,9).
Embryonated eggs of B. procyonis are extremely
resistant to environmental conditions and to common
disinfectants (1,3), including the combination of bleach
solution and pressurized steam used here following the
release of the young raccoons, but prior to the occurrence
of the cases. The effectiveness of steam is likely influ-
enced by its pressure and the duration of its application.
Decontamination of pens or enclosures can be achieved
by other forms of heat, including boiling water or the dry
heat of a propane torch (3). Autoclaving of feed bowls,
etc., should be done where applicable.
Most chemicals are an unsatisfactory means of
destroying Baylisascaris eggs. The use of bleach solu-
tion to clean pens does not kill the eggs but renders
them nonadherent, so that they can be rinsed away (9).
This likely leads to further contamination of the imme-
diate environment. Chemicals, such as 1:1 xylene:
ethanol or 120 ppm aqueous iodine, will kill the
eggs but are impractical for general environmental
use (9).
With adequate moisture and humidity, eggs of B. pro-
cyonis may survive for years in soil (1,3). For this rea-
son, complete removal of contaminated surface soil
within enclosures that previously contained raccoons has
been recommended (1). Removal and disposal of feces
and bedding from pens previously occupied by raccoons
is an additional practical step to reduce the likelihood
of inadvertent mechanical transport and contamina-
tion of nearby pens (3). Feed storage areas should be
raccoon-proof.
After postmortem studies on the Douglas squirrel
and the 2nd rock dove confirmed the presence of ascarid
larva migrans, the pen that had previously contained
raccoons, together with the adjacent pen, were flamed
with a propane torch to kill roundworm eggs. All wooden
or disposable material remaining in the 2 pens that held
the rock doves and the Douglas squirrel was incinerated.
Immature raccoons placed in enclosures previously
occupied by older raccoons easily become reinfected with
eggs, despite an initial program of deworming, as was
attempted in this case. Baylisascaris procyonis evi-
dently undergoes a prolonged developmental period in
the intestine in 2-month-old raccoons, when eggs will not
be found in feces with the flotation method. Immature
raccoons thus pose problems for the control of round-
worms, since they may have false negative results on
fecal examination, only to shed eggs at a later date (1).
In our view, the knowledge gleaned from this case
clearly indicates the importance of housing raccoons
separately and at a distance from other animals in zoos,
game farms, wildlife refuges, rehabilitation centers, or
similar facilities to prevent contamination by raccoon
scats. In this case, it appears that direct contamination
of the squirrel's and birds' pens with roundworm-
contaminated scats from the orphaned raccoons led to
cross-species infection with B. procyonis.
Specific pens at the Wildlife Rescue Care Centre are
now designated for holding raccoons, and all fecal and
bedding material from these pens is incinerated after
removal. Individuals attending the animals wear pro-
tective and disposable outer clothing and footwear.
Raccoons are now dewormed immediately during an
initial 24-hour quarantine, followed by additional
dewormings at 10- to 14-d intervals, as has been recom-
mended (9). Fecal examinations are carried out con-
currently with dewormings, so that individuals shedding
ascarid eggs can be indentified.
Veterinary practitioners caring for wildlife species
should be aware that larva migrans of B. procyonis is an
important differential when determining the origin of ner-
vous signs in mammals or birds, especially if the case his-
tory indicates previous habitation in pens or dirt lots
where exposure to raccoon scats may have occurred.
Public education by veterinarians concerning the
zoonotic danger of the raccoon roundworm is an ongo-
ing responsibility. Keeping pet raccoons should be dis-
couraged. Handlers of raccoons in zoos, game farms, or
wildlife rehabilitation centers should be informed of
the potential health hazard this parasite poses to them-
selves, to unsuspecting patrons, and to animal species
under their care.
cvJ
Can Vet J Volume 36, September 1995
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