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385
Journal of Wildlife Diseases, 24(3), 1988, pp. 385-ı-398
© Wildlife Disease Association 1988
CANINE DISTEMPER IN BLACK-FOOTED FERRETS
(MUSTELA NIGRIPES) FROM WYOMING
E. S. Williams, E. T. Thome,2 M. J. G. Appel,3 and D. W. Belitsky4
Department of Veterinary Sciences, University of Wyoming, 1190 Jackson, Laramie, Wyoming 82070, USA
2 Game and Rsh Department, Box 3312 University Station, Laramie, Wyoming 82071, USA
ı A. Baker Institute for Animal Health, Department of Microbiology,
New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
ı Game and Rsh Department, 260 Buena Vista, Lander, Wyoming 82520, USA

ABSTRACT: In September and October 1985, six black-footed ferrets (Mustela nigripes) were
captured from the only known population, located near Meeteetse, Wyoming for captive propagation.
Two days following capture an adult male showed signs of canine distemper and an adult
female displayed similar signs 7 days postcapture; these infections were undoubtedly acquired
prior to capture. Subsequently the four remaining captive black-footed ferrets also developed
canine distemper and all eventually died, Clinical signs included severe pruritus, hyperkeratosis
and progressive loss of body condition, A few animals had intermittent diarrhea and respiratory
disease, Intranuclear and intracytoplasmic inclusion bodies were numerous in epithelial tissues
and two black-footed ferrets had a mild to moderate meningoencephalitis. Canine distemper virus
was isolated from four animals and paramyxovirus nucleocapsids were observed by electron
microscopy of feces from all affected black-footed ferrets. Antibodies to canine distemper virus
were not detected in sera of sick black-footed ferrets. Antibodies to canine distemper virus were
found in sera of badgers (Taxidea taxus) and coyotes (Canis latrans) collected in the Meeteetse
area in 1986. Most free-ranging black-footed ferrets in the colony apparently died of canine
distemper during the summer and fall of 1985, An attempt was made to capture all surviving
animals in the affected area in order to abort the epizootic and provide black-footed ferrets for
captive propagation.
Key words: Mustela nigripes, black-footed ferret, endangered species, canine distemper, pathology,
serology, survey, case report.

INTRODUCTION
Canine distemper (CD) is a common,
highly infectious viral disease of domestic
and wild, free-ranging and captive Canidae,
Procyonidae, and Mustelidae (Budd,
1981). It is frequently diagnosed in Wyoming
in free-ranging striped skunks (Mephitis
mephitis) and raccoons (Proc yon lotor)
and less frequently in coyotes (Canis
latrans), badgers (Taxidea taxus), and
mink (Mustela vison) (Williams, 1982;
Thorne et al., 1985b).
In the fall of 1985, CD was diagnosed
in an adult male and an adult female blackfooted
ferret (Mustela nigripes)
shortly after
capture from the only known population.
Subsequently, four additional captive
black-footed ferrets developed CD. Most
of the free-ranging animals disappeared;
they presumably died from canine distemper
virus (CDV) infection
(Thorne, 1987).
This report documents the clinical and
pathologic features of CD in black-footed
ferrets and discusses the implications of
this disease for the captive and wild populations
of black-footed ferrets.

CASE HISTORY
[1] In September 1981, when black-footed
ferrets were thought to be near extinction
in the wild
, a colony of ferrets was found
in a large complex of white-tailed prairie
dog (Cynomys leucurus) colonies near
Meeteetse, Park County, Wyoming, USA
(44#{176}05’-44#{176}15’N,108#{176}55’-109#{176}15’W). Since
that time the population has been the subject
of intense study by state, federal, and
private biologists (Anderson and Inkley,
1985). The importance of disease to the
black-footed ferret colony was recognized
and precautions were initiated shortly af386
JOURNAL OF WILDLIFE DISEASES, VOL. 24, NO. 3, JULY 1988
ter their discovery to reduce the opportunity
for human-related disease introduction
(Thorne et al., 1985a; Thorne,
1987; Thorne, 1988).
Estimates of black-footed ferret numbers
were derived from litter surveys
conducted in late summer and mark-recapture
results (Forrest et al., 1988). Blackfooted
ferret numbers estimated in July
and early August were 61, 88, 129, and 58
in years 1982, 1983, 1984, and 1985, respectively,
and 15 animals in 1986
(Wyoming
Game and Fish Department, 1987;
Forrest et al., 1988; Belitsky, 1988). The
peak population estimate of 128 ± 25
black-footed ferrets in fall 1984 was followed
by a loss of black-footed ferrets over
the winter and spring (Belitsky, 1988;
Thorne, 1988) and an estimate of 58 by
litter survey in July and early August 1985
(Forrest et al., 1988). This decline was due,
in part, to juvenile dispersal and mortality,
which has been estimated to be between
60 and 80% each year when disease is not
a factor (Forrest et al., 1988) and as suggested
by the recapture in 1985 of 6 of 29
adults and none of 49 juvenile black-footed
ferrets eartagged in 1984 (Forrest et al.,
1988). The population declined further;
and by early October, it was estimated by
mark-recapture technique to contain 16 ±
4 animals
(Forrest et al., 1988).
In June 1985, sylvatic plague (Yersinia
pestis) was diagnosed in prairie dogs (Ubico
et al., 1988), the primary prey of the
black-footed ferrets (Sheets et al., 1972).
No more than 20% of the area of prairie
dog habitat was presumed lost to plague
from 1984 to 1985 (Forrest et al., 1988).
Domestic ferrets (Mustela putorius furo)
and Siberian polecats (Mustela eversrnanni)
were shown to be resistant to plague
(E. S. Williams et al., unpubl. data), and
there was no apparent evidence that plague
adversely affected the black-footed ferret
population (Forrest et al., 1988).
In late September and early October
1985, while and immediately after the
mark-recapture population estimate was
being made, six black-footed ferrets were
captured for captive propagation
at the
Wyoming Game and Fish Department’s
Sybille Wildlife Research and Conservation
Education Unit (Thorne, 1987). Blackfooted
ferrets were captured in tubular live
traps (Hillman, 1972), examined while in
the trap for condition, health, age, and sex
and placed individually into large wooden
boxes which contained burlap (Thorne et
al., 1985a). The animals were transported
from the Meeteetse area to Sybille in covered
vehicles within 18 hr of capture.
Two days following capture the last
caught black-footed ferret, an adult male,
was observed to be extremely pruritic and
an adult female became depressed 7 days
postcapture. The disease was diagnosed as
CD, and the other four captive black-f ooted
ferrets subsequently developed the disease.
Eventually all six captive and probably
most free-ranging black-footed ferrets
died of CD.
Following diagnosis of CD, a management
decision was made to attempt to capture
all black-footed ferrets remaining
, except
those that may have been present in
the outlying prairie dog colonies. This was
done in an attempt to further reduce the
population and interrupt the epizootic; to
remove infected animals, if captured, from
the population; and to provide animals for
captive propagation (Thorne, 1987;
Thorne, 1988). Six black-footed ferrets
were captured and placed in strict isolation;
they did not develop CD.
Surveys of the Meeteetse black-footed
ferret habitat during the winter of 1985-
1986 indicated minimal ferret activity
suggesting very few remaining wild blackfooted
ferrets
(Belitsky, 1988; Thorne,
1988). Additional surveys in the summer
of 1986 demonstrated approximately five
black-footed ferrets, including two females
that produced litters, escaped the
distemper epizootic
(Belitsky, 1988).

MATERIALS AND METHODS
The six captive black-footed ferrets that died
of CD were monitored visually twice daily for
signs of disease. They were housed in an 8.5 x
WILLIAMS ET AL-CANINE DISTEMPER IN BLACK-FOOTED FERRETS 387
2 m room with large windows and daylight spectrum
lighting adjusted to the natural photopenod.
Cages for individual black-footed ferrets
were 152 x 81 x 61 cm and constructed of
painted wood ends and floors with vinyl coated
wire mesh on tops, fronts, and backs. Cages were
arranged end to end in a row with two solid
plywood ends approximately 2.5 cm apart between
adjacent cages. The black-footed ferrets
that contracted CD in the wild were located in
cages 1 and 4. Initially, cages contained a layer
of clean dry sand. An unpainted two-chambered
wooden nest box was located 1 m below the
level of the main cage and was accessed by
brown plastic downspout pipe. Clean dry straw
or shredded white paper was supplied for nest
material, Temperature in the ferret room
was maintained between 7 and 18 C. Separate
sponges, spatulas, and rolls of paper towels were
used for cleaning individual cages; spatulas were
soaked in bactericidal and virucidal disinfectant
(Nolvasan Solution#{174}, Aveco Company, Inc., Fort
Dodge, Iowa 50501, USA) between uses. Access
to the black-footed ferrets was limited; a shower
and use of a face mask, cap, and clean overalls
was required for entry.
Most black-footed ferrets captured during
research activities since 1982 were vaccinated
subcutaneously with a beta propiolactone inactivated
Onderstepoort strain CDV vaccine
(supplied by M. J. G. Appel, James A. Baker
Institute for Animal Health, Department of Microbiology,
New York State College of Veterinary
Medicine, Cornell University, Ithaca, New
York 14853, USA) without adjuvant (Thorne et
al,, 1985a). One of the first six black-footed ferrets
captured for captive propagation was vaccinated
twice in the summer of 1984, and in
1985 all of the original captive black-footed ferrets
were vaccinated two or three times with
the same vaccine. During the course of disease,
these black-footed ferrets were vaccinated one
or two times each with the same inactivated
CDV vaccine but this time with adjuvant (Fort
Dodge Laboratories, Fort Dodge, Iowa 50501,
USA).
As soon as signs of CD were recognized, sick
black-footed ferrets were isolated from apparently
healthy animals by moving them to the
Veterinary Medical Research Center (Department
of Veterinary Sciences, University of Wyoming,
Laramie, Wyoming 82070, USA) and
monitored and treated twice daily. Monitoring
involved recording clinical signs, including food
and water intake, fecal consistency, evidence of
urination, attitude, behavior, appearance, and
periodic examination of feces by negative staining
techniques and electron microscopy for the
presence of viral particles morphologically consistent
with CDV (Nunamaker and Williams,
1987) and by floatation and direct examination
for internal parasites. Feces for parasitology were
preserved in 2% potassium dichromate.
Supportive therapy given the black-footed
ferrets included subcutaneous administration of
lactated Ringer’s solution when needed for dehydration;
antibiotic treatment with lincomycin
(Upjohn Company, Kalamazoo, Michigan
49001, USA), gentamycin (Schening Corporation,
Bloomfield, New Jersey 07003, USA) or
tnibnissen (Burroughs Wellcome Company,
Kansas City, Missouri 64108, USA); and nutritional
support including skinned prairie dog
pieces, whole mice, and nutritional supplement
(Nutniıcal#{174}, Evsco Pharmaceuticals, Immunogenetics,
Inc., Buena, New jersey 08310, USA).
Canine distemper incubation periods were estimated
by two methods using development of
clinical signs as endpoints. A maximum incubation
period for four animals was estimated
from the date the first black-footed ferret developed
clinical CD to the date of development
of clinical signs in these four animals. Minimum
incubation periods were estimated from the date
of last exposure to an affected animal and development
of clinical signs.
Black-footed ferrets were necropsied minutes
to several hours after death. Blood was collected
by syringe from the heart or from severed peripheral
vessels and allowed to clot, and serum
was removed and frozen. Liver, lung, lymph
nodes and spleen were collected for virus isolation
and stored at -70 C until cultured for
viruses. Lung, liver and swabs of the external
auditory meatus were cultured by routine bacteriologic
methods for pathogenic bacteria. Portions
of a wide variety of organs were fixed in
10% neutral buffered formalin; embedded in
paraffin; sectioned at 6-7 ım; stained with hematoxylin
and eosin and, for selected tissues,
with periodic acid-Schiff techniques; and examined
by light microscopy. Impression smears
of urinary bladder and conjunctiva from two
animals were air dried and stained with Wright’s
stain and with hematoxylin and eosin.
Canine distemper virus isolations were made
in dog lung macrophage cultures in Leighton
tubes (Appel and Jones, 1967). A 10% suspension
in Eagles medium (Gibco Laboratories, Grand
Island, New York 14072, USA) was prepared
from lung tissues from four black-footed ferrets.
The presence of CDV caused syncytia formation
and was confirmed by specific immunofluorescence
(Appel and Jones, 1967; Appel and Gillespie,
1972), Virus titrations were made in dog
lung macrophage cultures in 96 well microplates
(Corning Glassware, Corning, New York 14830,
USA) in three-fold dilution steps. Isolated virus
was identified by neutralization with CDV antiserum
(Appel and Robson, 1973).
388 JOURNAL OF WiLDLIFE DISEASES, VOL. 24, NO. 3, JULY 1988
Three young adult CD susceptible domestic
ferrets were obtained (Marshall Farms, North
Rose, New York 14516, USA) and kept in isolation
units of the J. A. Baker Institute for Animal
Health (New York State College of Veterinary
Medicine, Cornell University, Ithaca,
New York 14853, USA). They were fed commercial
cat food (Purina Cat Chow, Ralston Purina
Company, St. Louis, Missouri 63164, USA)
and water. After a 3-wk observation period, each
domestic ferret was inoculated intraperitoneally
with 0.5 ml of a 10% black-footed ferret lung
suspension in Eagles medium. The lung suspension
had a virus titer of 1 x 1Oı mean infectious
doses/mI when titrated in dog lung macrophage
cultures. The animals were observed daily for
clinical signs of CD. At necropsy, imprints on
glass microscope slides were prepared from
lymph nodes and lungs and stained with CDV
specific fluorescent antibody for detection of
CDV antigen (Appel and Gillespie, 1972).
Canine distemper virus serum neutralizing
antibody titers were determined by serial dilutions
in 96 well microplates (Appel and Robson,
1973). Sera were collected from six healthy
black-footed ferrets which did not develop CD,
including one mature and five juvenile females
following subcutaneous vaccination. The mature
female received one dose of inactivated
CDV vaccine without adjuvant followed by two
doses of inactivated vaccine with adjuvant over
a 77-day period. One juvenile received two doses
of inactivated CDV vaccine without adjuvant
followed by two doses of inactivated vaccine
with adjuvant over a 51-day period. Sera were
collected from these animals 13 days after the
last vaccination, Three juvenile black-footed
ferrets were vaccinated three times with inactivated
CDV vaccine with adjuvant over a 23-
day period and sera were collected 19 days after
the last vaccination. One juvenile black-footed
ferret was vaccinated twice with inactivated
CDV vaccine with adjuvant over a 33-day penod
and serum was collected 8 days after the
last vaccination.
From December 1985 through September
1986, four skunks, four raccoons, 14 badgers, 10
coyotes and a long-tailed weasel (Mustela frenata)
from the Meeteetse area were shot or
trapped and killed to survey for diseases. Blood
was collected by syringe or by draining blood
into clean, dry glass tubes from the heart or
severed jugular vein or peripheral vessels. The
carcasses and blood samples were packed in ice
in styrofoam coolers and transported by air, generally
within 24 hr of death, from Cody, Wyoming
to Laramie where they were examined
for evidence of CDV infection. Serum was collected
and frozen, the animals were necropsied,
and tissues were collected for histopathology.
Feces were examined for particles consistent with
CDV nucleocapsids by electron microscopy.
ClInical signs

RESULTS
Minimum and maximum incubation
periods were calculated as days from the
most recent and earliest, respectively, exposure
to CDV until development of detectable
clinical signs of CD. Incubation
periods were estimated for four blackfooted
ferrets to be a minimum of 13 and
a maximum of 52 days, with incubation
period ranges for three animals determined
to be between 16 and 35 days. Two
black-footed ferrets were assumed to have
been incubating the disease when captured
and thus incubation periods could
not be estimated. The duration of clinical
disease prior to death ranged from 14 to
48 days (Table 1).
Clinical signs of CD in black-footed ferrets
are shown in Table 1. The most striking
initial clinical sign in most animals was
severe pruritus. Affected black-footed ferrets
rubbed their faces and trunk along the
wire of the cage, in the sand flooring, or
on the edges of the holes into the nest boxes.
Occasionally, black -footed ferrets
scratched the anterior portions of their
bodies with claws of their hind feet. Vigorous
head shaking was observed in two
black-footed ferrets.
Wrinkling and hyperemia of the skin of
the forehead and slight hyperemia of the
ears and chin were observed in all animals.
As the disease progressed the skin, ears,
nose, eyelids and footpads became increasingly
hyperkeratotic (Fig. 1). The ears frequently
became so hyperkeratotic they
cracked and most ear tags were dislodged.
A few animals lost considerable hair and
one female was diffusely hyperkeratotic
and nearly alopecic when she died (Fig.
1). Secretions of the anal scent glands of
the males were inspissated and the glands
were firm.
All sick black-footed ferrets became depressed
and often had a dull facial expresWILLIAMS
ET AL-CANINE DISTEMPER IN BLACK-FOOTED FERRETS 389
TABLE 1. Clinical signs and pathology of black-footed ferrets infected with canine distemper virus.
Ferret number
640 (3O)ı 649 (48) 65)3 (25) 680 (15) 684 (14) 686 (42)
Clinical signs
Hyperkeratosis +b + + + + +
Depression + + + + + +
Skin hyperemia + + + + + +
Pruritus + + + + + -
Diarrhea + + + - - +
Anorexia + - - + + +
Polydipsia - + + + - +
Alopecia - + - - - +
Nasal discharge - + + - - -
Photophobia - - + - - -
Conjunctivitis - - - - + -
Gross lesions
Hyperkeratosis + + + + + +
Emaciation + - + - + +
Intestinal hemorrhage - + + - + -
Alopecia - + - - - +
Gastric hemorrhage - - - + + -
Thymic atrophy - + - + - +
Chronic nephritis - - + - + -
Bronchopneumonia - + - - - -
Hepatic lipidosis - - - + - -
Dehydration - - - - + -
Conjunctivitis - - - - + -
Lymphadenopathy - + - - - -
Splenomegaly - + - - - -
Histopathologic lesions
Hyperkeratosis + + + + + +
Lymphoid depletion + + + + + +
Hepatic lipidosis + + + + + +
Dermatitis + + + + + +
Inclusions in epithelium + + + + + +
Inclusions in brain - + + + - +
Interstitial pneumonia - + + + - +
Bronchitis + + - - + -
Sialoadenitis - + - + + -
Intestinal protozoa + - + - + -
Pyelonephritis - - + - + -
Chronic nephritis - - + - + -
Nonsuppurative meningoencephalitis - + - - - +
Keratitis - - - - + -
Ureteritis - + - - - -
Suppurative bronchopneumonia - + - - - -
Tracheal protozoa + - - - - -
Muscle protozoa + - - - - -
Focal meningitis + - - - - -
Duration of clinical disease in days (d).
Sign or lesion present.
‘Sign or lesion not observed.

ı- ı
‘--5..
1’Lt.. ı.
FIGURE 1. Diffuse hyperkeratosis and alopecia in a black-footed ferret with canine distemper.
390 JOURNAL OF WILDLIFE DISEASES, VOL. 24. NO. 3, JULY 1988
sion. There was considerable individual
variation in black-footed ferret reaction to
human presence. Some black-footed ferrets,
especially adults, were relatively calm
during treatments while others were aggressive
until late in the course of disease.
Several black-footed ferrets were anorexic
from the initial stages of disease, some had
fluctuating appetites, and two black-footed
ferrets continued to eat relatively normal
quantities until several days before
death. Sick black-footed ferrets drank as
much as 50 ml of water in 24 hr, compared
to healthy captive black-footed ferrets
which drink relatively little water.
One black-footed ferret had a slight serous
nasal discharge in the early stages of
disease which disappeared within several
days. In the few days before death, two
animals showed evidence of respiratory
disease; one had a mild mucopurulent nasal
exudate and the other was slightly dyspneic.
Only one black-footed ferret developed
keratoconjunctivitis; the other
animals had varying degrees of eyelid hyperkeratosis
without significant conjunctival
exudate.
Feces were usually of normal to soft consistency
throughout the course of disease.
Occasionally, diarrheic feces were passed
and three black-footed ferrets had melena
and/or bloody diarrhea at the time of
death.
Signs of nervous system disease were not
observed in these black-footed ferrets, with
the exception of one animal that bit at her
rear leg repeatedly for several minutes on
the day before she died and again just prior
to death. This behavior may have been an
attempt by a weak animal to bite the handler;
however, microscopic lesions were
present in the brain of this individual.
Results of examination of feces from 12
black-footed ferrets are shown in Table 2.
Canine distemper virus-like particles (Fig.
2) were detected in every fecal sample
tested from animals with clinical CD. In
one case, viral particles were detected 20
days prior to development of clinical signs
of CD (Table 2). Six healthy black-footed
ı: ı
ı,I
.zı.. ı “ı‘\ı,;
WILLIAMS ET AL-CANINE DISTEMPER IN BLACK-FOOTED FERRETS 391
TABLE 2. Results of examination of black-footed
ferret feces by electron microscopy for canine distemper
virus-like particles.
Animal Date clinical disease
number recognized
Date of fecal
examination Results
640 9 Nov 1985 11 Nov 1985 +ı
649 10 Nov 1985 21 Oct 1985
11 Nov 1985
27 Dec 1985
+
+
+
653 19 Oct 1985 21 Oct 1985
23 Oct 1985
+
+
680 6 Nov 1985 7 Nov 1985 +
684 8 Oct 1985 21 Oct 1985 +
686 27 Nov 1985 11 Nov 1985
1 Dec 1985
7 Jan 1986
+
+
Six clinically healthy 3 Dec 1985 -
black-footed ferrets 5 Dec 1985
10 Dec 1985
17 Dec 1985
2 Jan 1986
-
-
-
-
Canine distemper virus-like particles present.
Canine distemper virus-like particles not observed.
ferrets which did not develop CD were
always negative for these particles in their
feces.
Examination of feces for parasites
showed the presence of two species of Eimeria
in all sick black-footed ferrets, occasionally
in large numbers. Coccidian
oocysts, in low numbers, were present in
feces of approximately 30% of healthy animals.
Skin scrapings from several blackfooted
ferrets were negative for ectoparasites.

Pathology
Results of postmortem examinations are
shown in Table 1. Gross lesions included
severe hyperkeratosis of skin, foot pads,
eyelids, ears, and nose; emaciation; hemorrhagic
gastroenteritis in one black-footed
ferret; hemorrhagic colitis in two animals;
and focal bronchopneumonia in one
animal. Atrophy of the thymus was grossly
apparent in juvenile black-footed ferrets
and enlargement of mesenteric and peripheral
lymph nodes was observed in one
animal. Scattered pitting and irregularity
of the renal cortex was observed in two
black-footed ferrets and in one of these
FIGURE 2. Negatively stained transmission electron
micrograph of paramyxovirus-like nucleocapsids
in the feces of a ferret with clinical signs of canine
distemper.
animals the renal pelvis was gritty when
sectioned.
Microscopic examination of a variety of
organs revealed numerous large eosinophilic
cytoplasmic and intranuclear inclusion
bodies in epithelial cells of urinary
bladder (Fig. 3), renal pelvis, epididymis,
bronchi and bronchioles, bile ducts, pancreatic
ducts and islets, tongue, stomach,
skin, conjunctiva, ependyma and macrophages
in many locations in the body including
meninges. Impression smears of
conjunctiva and urinary bladder also contained
inclusion bodies in epithelial cells.
Skin lesions were characterized by
marked hyperkeratosis (Fig. 4), focal necrosis
with neutrophilic infiltration, and the
presence of bacterial colonies on the surface
and in hair follicles. Cytoplasmic
inclusion bodies were in cells of the epidermis
and multinucleated cells were occasionally
present.
In black-footed ferret 684, developmental
forms of a large Eimeria sp. were
present in many epithelial cells of the distal
one-half of the villi in jejunum and
ileum (Fig. 5). Crypt cells were seldom
parasitized. The lamina propria was lightly
infiltrated with lymphocytes and macrophages.
In another black-footed ferret
(640), developmental forms of a smaller
Eimeria sp. were scattered in epithelial
______ ı. __ f., . U ___
FIGURE 3. Typical intracytoplasmic inclusion bodies of canine distemper (arrows) in urinary bladder
epithelium of an affected black-footed ferret. H&E.
392 JOURNAL OF WILDLIFE DISEASES, VOL. 24, NO. 3, JULY 1988
cells of the distal small intestine. Inflammatory
reaction to this parasite was minimal.
Numerous comma shaped protozoa
that were identified as Giardia sp. on fecal
examination were present in the lumen of
the distal small intestine and colon of a
black-footed ferret (653).
In black-footed ferret 640, epithelial cells
lining the trachea, a large bronchus and
associated glands contained schizonts of a
protozoan parasite. Impression smears of
urinary bladder from 684 revealed numerous
epithelial cells containing protozoal
zoites. Cysts of a protozoan parasite
resembling Sarcocystis sp. were present in
skeletal muscle of black-footed ferret 640.
The anterior portion of the lung of one
black-footed ferret contained an alveolar
and bronchiolar infiltrate of a few neutrophils.
Bronchi and bronchioles contained
macrophages and neutrophils in several
animals. Alveolar septae were hypercellular
and capillaries were congested in four
black-footed ferrets. Depletion and necrosis
of lymphocytes in germinal centers of
lymph nodes and spleen occurred in many
black-footed ferrets; sinus histiocytosis and
the presence of multinucleated cells were
common; and thinning of the thymic cortex
occurred in juvenile black-footed ferrets.
A mild lymphocytic infiltrate was observed
in the meninges of one animal.
Nonsuppurative meningoencephalitis occurred
in the two black-footed ferrets with
the longest duration of clinical disease. Degenerative
changes were observed in testicles
of the males and spermatozoa were
not present.
Lesions in the kidneys of two black-f ooted
ferrets were characterized by interstitial
fibrosis and a mild mononuclear inflammatory
cell infiltrate, and dilated
tubules with mineralization of debris within
distal tubules and at the renal pelvis.

Virus isolation
Canine distemper virus was isolated
from lungs of all four affected black-footed
ferrets on which virus isolation was attempted.
Virus titers were between 1 x
10ı and 1 x 1062 mean cell culture infectious
doses/ml of 10% suspension. The
isolated virus was neutralized by CDV specific
antiserum.
..ı.-,,: -
FIGURE 5. Developmental stages of the large Elmeria
sp. in the small intestine of a ferret with canine
distemper. H&E.
WILLIAMS ET AL-CANINE DISTEMPER IN BLACK-FOOTED FERRETS 393
FIGURE 4. Follicular and epidermal hyperkeratosis
and dermatitis in a black-footed ferret. H&E.

Domestic ferret inoculations
The three inoculated domestic ferrets
died between 21 and 23 days postinoculation.
The first signs of disease were seen
between 12 and 19 days postinoculation
and consisted of anorexia and mucous discharge
with crust formation around the
eyes. The animals gradually became dehydrated
and moribund 4 to 8 days after
the appearance of first clinical signs. Imprints
from lymphatic tissues and lungs of
all domestic ferrets showed CDV antigen
by immunofluorescence with specific CDV
conjugate.

Serology
Sera from four black-footed ferrets that
died of CD did not contain neutralizing
antibodies to CDV. Sera from six healthy
black-footed ferrets had CDV neutralizing
antibody titers of 1:60 to 1:1,000 following
vaccination with the inactivated vaccine
with adjuvant.

Carnivore survey
Canine distemper virus was not detected
in feces and there was no gross or microscopic
evidence of active CD in any of
the carnivores collected at Meeteetse. Two
of 14 badgers and five of 10 coyotes had
serum neutralizing antibodies to CDV
ranging between approximately 1:100 to
1:1,000. Antibodies to CDV were found
only in adult animals. Skunks, raccoons and
the weasel were negative for CDV antibodies.

DISCUSSION
[2] Canine distemper caused 100% mortality
in six recently captured black-footed
ferrets in Wyoming in 1985-1986. Distemper
is a well known, usually fatal infection
of wild mustelids (Budd, 1981) and the
disease is considered essentially 100% fatal
in domestic ferrets (Appel et al., 1981;
Bernard et al., 1984; Davidson, 1986).
Black-footed ferrets may be exceptionally
susceptible to CD
as shown by their fatal
response to a modified-live CDV vaccine
demonstrated to be safe in domestic ferrets
and Siberian polecats (Carpenter et al.,
1976).
The estimated minimum and maximum
incubation periods of CD in these black394
JOURNAL OF WILDLIFE DISEASES, VOL. 24, NO. 3, JULY 1988
footed ferrets, 13 to 52 days, were probably
longer than the incubation period (not
reported) in the four black-footed ferrets
which died within 21 days following inoculation
with a CDV vaccine strain (Carpenter
et al., 1976). Incubation periods are
difficult to determine during an epizootic
in contrast to incubation periods derived
from experimental exposure in a controlled
study, because exact time of exposure
is unknown. Our estimates do not
take into account possible exposure of
healthy black-footed ferrets to CDV shed
by subclinically affected animals. Controlled
studies would be necessary to determine
routes and duration of CDV shedding
during the course of the disease.
Exposure was assumed to have been by
aerosol or fomites as black-footed ferrets
were never in direct contact. One blackfooted
ferret shed CDV for at least 20 days
before developing clinical CD. Incubation
periods of 7 to 10 days are common in
domestic ferrets (Ryland and Gorham,
1978). There is considerable biological
variation between CDV strains, which may
influence incubation periods (Appel et al.,
1981). Another explanation for the relatively
long incubation period in these blackfooted
ferrets is that some animals may
have had a marginal immune response to
CDV stimulated by the inactivated CDV
vaccine.
Clinical signs of CD in these black-f ooted
ferrets were somewhat different than
those reported for vaccine-induced CD by
Carpenter et al. (1976). Severe pruritus was
the most striking early sign of disease we
observed; however, pruritus was not described
as a sign of vaccine-induced CD
in black-footed ferrets (Carpenter et al.,
1976) and only rarely is described in domestic
ferrets (Davidson, 1986). Ocular and
nasal discharges are frequently described
in domestic ferrets and were reported previously
in black-footed ferrets with vaccine-
induced CD (Carpenter et al., 1976).
Ocular discharge was observed in only one
of this group of black-footed ferrets; one
of the six animals had a transient serous
nasal discharge early in the course of disease,
and one had a mild mucopurulent
nasal discharge shortly before death. Pneumonia
was observed in all black-footed ferrets
with vaccine-induced CD and often is
present in domestic ferrets (Budd, 1981).
However, one of these six black-footed ferrets
had grossly apparent pneumonia and
only mild bronchitis and/or interstitial
pneumonia were observed microscopically
in the other animals. Absence of severe
pulmonary disease may have been due to
the aggressive antibiotic therapy used in
these black-footed ferrets, thereby reducing
the opportunity for secondary bacteria-
induced pneumonia. Secondary bronchopneumonia
is a commonly recognized
sequela of CD in many species (Jubb et
al., 1985).
Signs of nervous system disease were not
observed in five black-footed ferrets and
were equivocal in one animal. Nervous
signs were observed in all black-footed ferrets
with vaccine-induced CD (Carpenter
et al., 1976) and are commonly observed
in affected domestic ferrets. Occurrence
of nervous signs may be related to the strain
of CDV (Appel et al., 1981).
Two Eimeria spp. were within the intestines
of some of the black-footed ferrets
with CD. Carpenter and Hillman (1979)
reported coccidia in captive black-footed
ferrets, but the parasites were not identified.
Similar, possibly the same, species of
Eimeria were described by Hoare (1927)
in a colony of domestic ferrets during an
outbreak of CD. Intestinal lesions associated
with the coccidia were mild in blackfooted
ferrets and were similar to those
described in domestic ferrets (Hoare, 1935).
The presence of schizonts of a protozoan
parasite in the epithelial cells of the trachea
and bronchi is noteworthy as we are
not aware of protozoa being reported from
this location in mustelids. Systemic infection
by this parasite and the proliferation
of coccidia and Gi.ardia sp. in the intestinal
tract may be associated with immunosuppression
caused by CDV (Kauffman et
a!., 1982) as has been observed with ToxWILLIAMS
ET AL-CANINE DISTEMPER IN BLACK-FOOTED FERRETS 395
oplasma gondii in other carnivores infected
with CDV (Moller and Nielsen,
1964; Diters and Nielsen, 1978).
Hemorrhagic gastroenteritis and colitis
were present as terminal events in three
of the black-footed ferrets. These lesions
are commonly observed in severely stressed
mustelids (Wallach and Boever, 1983).
None of the affected black-footed ferrets
developed demonstrable serum antibodies
to CDV by the time of death even
though they had been vaccinated repeatedly
with the inactivated CDV vaccine
without adjuvant and the same vaccine in
adjuvant. This inactivated CDV vaccine
has been used in red pandas (Ailurus fulgens)
which are known to be susceptible
to vaccine-induced CD, even though data
indicated lack of high virus neutralizing
antibody response to the vaccine (Montali
et a!., 1983). Addition of the adjuvant to
the inactivated vaccine resulted in neutralizing
antibody titers in six healthy
black-footed ferrets after two or three doses
of vaccine. Thus, black-footed ferrets
are capable of responding with serum antibodies
to CDV antigens. It is not known
if these antibodies would be protective
against CDV challenge.
It is not known how or when CDV was
introduced into the free-ranging blackfooted
ferret colony. Many susceptible
species are present at the Meeteetse site,
including skunks, raccoons, coyotes, red
fox (Vulpes vu! pes), badgers, weasels (M.
frenata, M. errnina) and occasional ranch
dogs. At the time of the CD outbreak in
black-footed ferrets there was no evidence
of other susceptible species being affected.
However, it was later learned that in July
1985 a cowboy observed a disoriented
ataxic badger with matted eyelids in close
proximity (approximately 2 km) to the
black-footed ferret colony. The badger was
discarded and not available for postmortem
examination. The clinical signs described
suggest the badger had CD (Armstrong,
1942; Farrell, 1957). Evidence from
the carnivore survey confirms the involvement
of badgers and coyotes in the distemper
epizootic. These species could have
served to amplify and spread the disease
into new regions of black-footed ferret
habitat. Lack of evidence of CD in skunks,
raccoons and weasels may have been due
to the small number tested, their use of
different habitats and lack of exposure, or
high mortality induced by CD in these
species. The presence of antibodies to CDV
only in adult animals, and lack of evidence
of active CD in any animal during the
carnivore survey suggests the epizootic did
not recur in 1986.
Another source of the disease could have
been humans acting as fomites during sylvatic
plague control measures. This seems
to be an unlikely source due to the fragility
of the virus in the environment (Gorham,
1966) and the remote possibility that blackfooted
ferrets or other susceptible species
would have come into direct contact with
people or their equipment. All personnel
involved with the ferret project were advised
not to handle dogs for 24 hr prior to
work at Meeteetse or to transport dogs to
the site (Thorne et al., 1985a), although it
is possible that ranch hands or oilfield
workers transported dogs into the area or
that feral dogs were present. Extensive
precautions were taken by all biologists to
avoid introduction of disease when trapping
and handling black-footed ferrets for
research purposes (Thorne et al., 1985a).
The dynamics of distemper in the colony
are not clear. The survey for blackfooted
ferret litters in July and August 1985
indicated a reduction of approximately
50% compared to the same time in 1984
(Forrest et al., 1988). Estimates of ferret
numbers dropped to approximately 16 animals
by early October 1985. By late October
and early November 1985, only six
black-footed ferrets could be found. These
were captured in an attempt to obtain animals
for captive propagation and to interrupt
transmission of disease to remaining
black-footed ferrets believed to live in
more remote, outlying prairie dog colonies
(Thorne, 1987; Thorne, 1988). The presence
of a small number of untagged black-
footed ferrets in 1986 in areas known to
have been severely affected by CD and
where most black-footed ferrets were ear
tagged in 1984 and 1985
(Thorne, 1987;
Forrest et al., 1988) suggests this was successful.
It is possible the black-footed ferrets
alive in 1986 occupied outlying prairie
dog towns in 1985 and survived the CD
epizootic by not being exposed to the virus.
The presence of sylvatic plague in prairie
dogs complicated interpretation of
black-footed ferret numbers obtained during
the summer of 1985. It has been suggested
that reduction of the food base due
to plague may have reduced the resistance
of the black-footed ferrets to CD (May,
1986). However, no ferrets were known to
have died directly or indirectly due to the
effects of sylvatic plague (Thorne, 1987;
Forrest et a!., 1988). As prairie dog towns
became less active, it is likely that blackfooted
ferrets moved to adjacent, more active
prairie dog towns, rather than stay
where prey was less abundant. Nutritional
status probably has little influence on the
100% fatality rate of CD in black-footed
or domestic ferrets, no more than 20% of
the occupied prairie dogs habitat was lost
to plague (Forrest et al., 1988), and expansion
of prairie dogs into new areas
(Belitsky, 1988) may have partially compensated
for that loss.
Canine distemper had a severe impact
on the captive and wild populations of
black-footed ferrets. The disease compromised
breeding programs both times these
animals were brought into captivity and it
continues to be a significant threat to blackfooted
ferrets now in captivity. Use of the
inactivated CD vaccine with adjuvant may
provide some protection against the disease
and strict isolation procedures may
prevent introduction of CD into the captive
colony. Once captive propagation of
black-footed ferrets is successful, management
of CD will be of major importance
to reintroduction of the species into the
wild.
The historic impact of CD on wild populations
of black-footed ferrets is difficult
to assess. The dramatic decline of blackfooted
ferret numbers at Meeteetse in late
summer and fall 1985 was probably due
to CD. It seems likely that similar epizootics
could have occurred in other freeranging
black-footed ferret colonies in the
past. Loss of black-footed ferret habitat
due to widespread prairie dog control programs
is thought to be largely responsible
for the near extinction of the black-footed
ferret (Nowak and Paradiso, 1983). It also
seems possible that CD has played a significant
role in the demise of the blackfooted
ferret, considering the ubiquity of
the virus in domestic and wild species and
the extreme susceptibility of black-footed
ferrets to the disease.
Continuing attention to preventing and
controlling diseases in captive and reintroduced
black-footed ferret populations will
be necessary to insure survival of the
species. The diseases of major concern to
managers of black-footed ferrets have been
reviewed (Carpenter and Hillman, 1979;
Thorne, 1985a) and in addition to CD, include
human influenza, Aleutian disease,
rabies, and a variety of bacterial and parasitic
diseases. An understanding of the diseases
of prairie dogs also will be necessary
because of the dependency of black-footed
ferrets on prairie dogs. Management of
disease is of critical importance when populations
of animals become small (Dobson
and May, 1986) and will continue to be of
concern during the recovery of this and
other endangered species.

ACKNOWLEDGMENTS
This report was funded in part by the U.S.
Fish and Wildlife Service to the Wyoming Game
and Fish Department under authority of Section
VI of the Endangered Species Act of 1973 and
Federal Aid to Wildlife Restoration, Wyoming,
Pittman-Robertson Project FW-17-P; the U.S.
Fish and Wildlife Service, National Ecology
Center, Fort Collins, Colorado; and the Department
of Veterinary Sciences, University of
Wyoming. We would like to thank N. Kingston
and W. Jolley for assistance with parasitology,
K. Mills for bacteriology, and J. Yost, I. Johnson,
C. Nunamaker, and S. Anderson for technical
WILLIAMS ET AL-CANINE DISTEMPER IN BLACK-FOOTED FERRETS 397
assistance. We appreciate also the trapping efforts
of J. Hanna and A. McKinney. Fort Dodge
Laboratories kindly provided the adjuvant.

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