Proceedings of the fifth mountain lion workshop: 27

30 PROCEEDINGS OF THE FIFTH MOUNTAIN LION WORKSHOP
Finally, host populations are vulnerable only if they
are exposed to disease, due to individual movement into
infected areas, exposure to vectors, and interaction with
alternate hosts of the disease. For many diseases, feral cats
represent a significant alternate host to mountain lions, and
we might therefore anticipate increased rates of infection due
to some of these pathogens in semi-urban populations, such
as parts of southern California. Below, 6 infectious disease
agents are reviewed, with descriptions of basic biology,
clinical presentation and testing interpretations, and potential
impact on western mountain lion populations.
RABIES
Rabies is a fatal, viral infection of all mammals
which has strains that are adapted to certain hosts in certain
geographical locations. Western foci of rabies currently
exists in striped skunk (Mephitis mephitis) in California and
Texas, gray foxes (Urocyon cinereoargenteus) in Arizona
and Texas, and coyotes (Canis latrans) in Texas (Krebs et al.
1995). Each year, individuals of numerous other species are
incidentally infected with rabies, including opossums
(Didelphis virginianus), raccoons (Procyon lotor), rodents,
deer (Odocoileus hemionus), bobcats, cats and dogs (Canis
domesticus), and in 1994, a single mountain lion near
Covelo, California. Disease progression occurs differently
in different species, with some reports suggesting a more
chronic, "atypical" disease course in skunks and bats,
compared with dogs. Chronic and/or latent infections,
sometimes with the infected animal shedding infectious
virus, have been described for cats and striped skunks (Perl
et al. 1977, Murphy et al. 1980). Infection can occur when
an animal is bitten by an infected animal, transplacentally in
some species, and by ingestion of infected meat (Fischman
and Ward 1968).
Testing for rabies infection is less straight-forward
than for some of the other diseases discussed here, because
classical diagnosis requires pathological visualization of
brain tissue. The traditional test is documentation of Negri
bodies, which are cytoplasmic inclusion bodies consisting of
aggregates of internally budding membrane bound virus
particles. More modern testing procedures include
immunofluorescent antibody (IFA) on brain tissue, DNAbased
polymerase chain reaction (PCR) tests, and mouse and
mouse cell line inoculation.
Compiling reports of rabies cases and
seroprevalence assays into an accurate picture of rabies risk
to mountain lions is an extremely difficult task. There is
significant evidence that most infections in other wildlife and
domestic species due to chance, sporadic contact with the
major host species in that geographical region (i.e. striped
skunks in California and coyotes in southern Texas) (Krebs
et al. 1995). The 2 likely explanations for this phenomenon
are ecological isolation among species and virus strain-host
species evolutionary adaptations (Smith 1989). It is
unreasonable to assume significant ecological isolation
between mountain lions and most medium mammal species,
because lions efficiently prey upon many available species.
However, earlier data showed that rabies virus strains that
were adapted to foxes were distinctly less pathogenic to
skunks, and that experimentally inoculated foxes shed
amounts of virus in their saliva which would often be
sufficient to effectively create an infection in a skunk (Smith
1989). If a large number of skunks eventually acquired a fox
rabies strain in an area with endemic fox rabies, those skunks
might excrete higher salivary viral loads and create a
secondary skunk rabies cycle, a prediction consistent with
observed patterns. Another example of distinct host speciesrabies
cycles is gray fox and skunk rabies in Arizona and
Texas, where monoclonal antibody analysis of the N protein
revealed clear distinctions between the virus strains associated
with the major host species.
The implication of these findings for potential rabies
in mountain lions is that we might anticipate one of two
possible patterns: sporadic cases in mountain lions often due
to interaction with infected major host species, or the unlikely
possibility of a lion-specific cycle developing within the
primary host-species cycles. The biology of skunk, fox, and
coyote rabies strains when inoculated into mountain lions has
not been explored, but the worst-case scenario for mountain
lion-adapted rabies would be if lions developed high salivary
viral loads after inoculation, and had frequent exposure to the
primary host species. Additionally, rabies in domestic cats
might be efficiently spread to mountain lion predators.
CANINE DISTEMPER
Until recently, canine distemper virus (CDV) was
rarely associated with disease in cats. Isolated incidences of
canine distemper were reported for captive snow leopards
(Panthera uncia) already affected by panleucopenia (Fix et al.
1989), and a captive Bengal tiger (Panthera tigris) (Blythe et
al. 1983). In 1994, a report appeared in "Science"
documenting a fatal epidemic of canine distemper in African
lions in the Serengeti (Morell 1994). The total mortality loss
due to CDV in Masai Mara lions approached 30% (Roelke-
Parker et al. 1996). In Kenya, canine distemper has been
described in feral dogs with seroprevalence at one time point
of 76% (Alexander and Appel 1994). In the United State,
distemper occurs frequently in domestic dogs, coyotes, and
gray foxes (Davidson et al. 1992). Cases of canine distemper
in felids in the Americas have included a possible case in an
African lion in Canada (Wood et al. 1995): in captive leopards
(Panthera pardus), tigers, African lions, and a jaguar
(Panthera onca) in southern California: and in captive black
leopards in Illinois (Appel et al. 1994). The source of the
disease in southern California cats was believed to be
raccoons.
Infection with CDV in dogs produces respiratory,
gastrointestinal, and neurological clinical signs, commonly