More people, more cats, more parasites: Human population density and temperature variation predict the prevalence of Toxoplasma gondii oocyst shedding in free-ranging domestic and wild felids

Aim: Toxoplasma gondii is a ubiquitous zoonotic parasite that can infect
warm-blooded vertebrates, including humans. Felids, the definitive hosts,
drive T. gondii infections by shedding the environmentally resistant stage
of the parasite (oocysts) in their feces. Risk factors for oocyst shedding
are well-documented in domestic cats under controlled settings, but few
studies characterize the role of climate and anthropogenic factors in
oocyst shedding among free-ranging felids, which are responsible for the
majority of environmental contamination. We aimed to determine how climate
and anthropogenic factors influence the level of oocyst shedding in
free-ranging domestic cats and wild felids.  Location: Global
Time period: 1973-2021 Major taxa studied: Felidae, Toxoplasma gondii
Methods: We used generalized linear mixed models to determine the
association between climatic, ecological, and anthropogenic factors and T.
gondii oocyst shedding in free-ranging felids. T. gondii oocyst shedding
data from 47 studies were compiled for domestic cats and 6 wild felid
species, encompassing 256 positive samples out of 9,635 total fecal
samples.  Results: T. gondii shedding prevalence in domestic cats
and wild felids was positively associated with human population density at
the sampling location. Average annual temperature and total precipitation
were not associated with increased shedding, however, temperature
variables that reflected fluctuation on a smaller timescale were
associated with oocyst shedding. Larger mean diurnal range was associated
with higher T. gondii oocyst shedding prevalence in domestic cats, while
higher temperatures in the driest quarter were associated with lower
oocyst shedding in wild felids. Main conclusions: Anthropogenic factors
associated with increasing human population density and climate change in
the form of temperature fluctuation can exacerbate environmental
contamination with the protozoan parasite T. gondii. Direct or indirect
management of free-ranging domestic cats could lower the burden of
environmental oocysts due to their large population sizes and close
affinity with human settlements.