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Study Finds Feral Cats Likely Driving Disease Among Deer
By The Wildlife Society Government Affairs
Posted on December 27, 2014
Free-roaming domestic cats (Felis catus)
are widely understood to have substantial negative impacts on wildlife.
The International Union for the Conservation of Nature (IUCN) lists
cats among the
world’s worst non-native invasive species, and cats on islands
worldwide have contributed to 33 species extinctions (Lowe
et al. 2000, Medina et al. 2011). In the United States
free-roaming cats are the top source of direct anthropogenic mortality
to birds and mammals, killing approximately 2.4 billion birds and 12.3
billion mammals each year (Loss
et al. 2013).
The
indirect impacts of cats on wildlife are less obvious, but one of the
greatest emerging threats from free-roaming cats is infection with
Toxoplasma gondii. T. gondii is a parasitic protozoan that
can infect all warm-blooded species but relies on felids to complete
its life cycle. According to a
new study published in
EcoHealth, feral cats are likely driving white-tailed deer (Odocoileus virginianus) infections in northeastern Ohio (Ballash
et al. 2014). Cats that host T. gondii excrete oocysts
into the environment in their feces, and a single cat can deposit
hundreds of millions of oocysts, which may remain infectious for up to
18 months (Tenter
et al. 2000).
The
study’s authors collected white-tailed deer samples at the Cleveland
Metroparks as part of a deer management program. Cat serum samples were
collected from cats in a trap, neuter, release (TNR) program
in the Greater Cleveland area. TNR programs spay/neuter feral cats and
then release them into the environment. Nearly 60% of white-tailed deer
and 52% of feral cats tested positive for
T. gondii. Older deer and deer in urban environments were more
likely to be infected, suggesting horizontal transmission from
environmental exposure.
The
study’s findings have implications for people as well. Widespread
environmental contamination increases the likelihood of human
infections. In people, infection has been linked to schizophrenia and
can lead to miscarriages, blindness, memory loss, and death (Torrey and
Yolken 2013, Gajewski
et al. 2014). Due to the creation of tissue cysts in infected deer, people that consume undercooked venison can also acquire
T. gondii and the subsequent disease, toxoplasmosis.
The Wildlife Society actively supports the humane removal of feral cats from native ecosystems. See our
position statement
and fact sheet for more information on how feral and free-ranging domestic cats impact wildlife.
This article was written in cooperation with the American Bird Conservancy.
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