24 | New Scientist | 30 October 2021DiseaseWILD animals living close to cities
are more likely to carry the parasite
that causes toxoplasmosis, and
house cats may play a major role
in spreading it to wildlife.
Toxoplasmosis is caused by
the pathogen Toxoplasma gondii
and can infect any warm-blooded
animal, including us. Between 30
and 50 per cent of all humans have
been infected with T. gondii, with
most cases asymptomatic. But for
people and animals with weakened
immune systems, the infection can
lead to chronic illness or even death.
Wild and domestic cats are the
primary hosts of T. gondii, which
matures and reproduces inside
them. One of the most common
ways toxoplasmosis spreads is
through contact with cat faeces.
Amy Wilson at the University of
British Columbia in Canada and hercolleagues analysed 45,079 cases
of toxoplasmosis in 238 species of
wild mammals, from 202 published
studies. The researchers compared
rates of infection with factors such
as human population density,
annual rainfall and temperature
to identify the predictors of
toxoplasmosis prevalence.
They found a high prevalence
of the disease in wild mammals
living close to cities and a strong link
between warmer temperatures and
high infection rates (Proceedings
of the Royal Society B: Biological
Sciences, doi.org/g3dc).
The results support suggestions
that freely roaming pet cats are
a key driver of these infections,
says Wilson. She suggests that
responsible management of
domestic cats could help limit the
spread of the pathogen. Chen LyCats linked to toxoplasmosis
spike in wildlife near cities
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News In brief
MINIATURE human brain-like
structures have been grown in a
dish for more than a year, much
longer than possible before. This
was accomplished by growing
brain cells into a ball, then slicing
it up so that oxygen and nutrients
can reach all the cells, while
allowing the structure to retain
its internal tissue architecture.
The standard way to study
tissues kept alive in the lab is to
grow a single layer of cells in a
dish. Then it was found that if the
cells could be coaxed into a pea-
sized ball known as an organoid,
they mature into different cell
types that interact with each
other more naturally.
But such organoids tend to start
dying and breaking apart after a
few months because they have
no blood supply, so not enough
oxygen and nutrients can reach
the core. This makes it harder toNeurology^carry out experiments on them,
says András Lakatos at the
University of Cambridge.
While some groups are trying
to develop organoids with blood
vessels, Lakatos and his team tried
a new tactic: cutting up brain
organoids into slices about 10 cells
thick. They reported keeping the
mini-brains alive for eight months
(Nature Neuroscience, doi.org/
g3dg) – but Lakatos says some
have actually survived for just over
a year. “You still see quite good
cell diversity and architecture
resembling the fetal brain,” he says.
Some of the mini-brains were
made from cells taken from people
with motor neurone disease.
These behaved differently to those
made from cells taken from people
without the condition, which
may one day lead to new ways
to treat the illness, says Lakatos.
“You can capture the moment
when pathology occurs in the dish
in front of your eyes. If you know
how the disease starts, you might
be able to prevent it.” Clare WilsonMini-brains in a dish
kept alive for a yearA TINY crab is the first to be
found trapped in amber from
the dinosaur era. It lived in south-
east Asia 99 million years ago.
Remarkably similar to modern
crabs, the 5-millimetre-long
crustacean is fully preserved,
making it “the most complete crab
[fossil] ever discovered”, says Javier
Luque at Harvard University.
This new specimen, in amber
mined recently in Myanmar,Palaeontologyfills important knowledge gaps
about how crabs – including those
that can walk on land or live in
freshwater – evolved.
Although molecular estimates
set the origins of non-marine crabs
at about 130 million years ago,
we hadn’t found any evidence of
such crabs beyond 75 million years
ago. Because the fossil, named
Cretapsara athanata, appears to
be a freshwater crab, it potentially
extends the record of the group
back almost 25 million years
(Science Advances, doi.org/g3hd).
Luque and his team analysed
the specimen under a standard
microscope and X-ray micro-CT
scanner. They identified the
animal’s eyes, antennae, pincers,
mouthparts, fine hairs and all
eight legs. The crab’s gills suggest
it mostly lived in water. So how
did it end up caught in tree resin?
One possibility is that the crab
was making a brief, land-based
journey between two bodies of
water when it got trapped, says
LID Luque. Christa Lesté-LasserreA^ XINGGet face to face with
a crab from dino age