FOR thousands of swimmers each year, a trip to the swimming pool means a bout
of diarrhoea, stomach cramps and fever. The culprit is often contamination with
faeces containing the protozoan Cryptosporidium, which is often brought
to the pool by sick babies. Now chemists Ric Pashley and Marilyn Karaman of the
Australian National University in Canberra have identified a crystalline
material that mops up the infectious form of the organism and destroys it.
So infectious is “crypto” that a single infected individual has the potential
to make up to 100 000 others ill. And while most infected people recover, crypto
can kill people whose immune systems are suppressed—for example, if they
have HIV or are undergoing chemotherapy.
Pashley will be in Britain this week to present the findings at the meeting
of the International Association of Colloid and Interface Scientists in Bristol.
Cryptosporidium becomes infectious when it forms an oocyst, an
intermediate stage in its reproductive cycle. Oocysts are resistant to the
chlorine in swimming pools. Water-treatment plants use complicated filtration
systems to remove the oocysts, which get into reservoirs from farm manure and
sewage overflow, but for reasons that are unclear these sometimes fail.
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To find a weak point, Pashley and Karaman studied the surface of the oocysts.
They found a scattering of phosphate and carboxylic acid groups, making the
oocysts highly negatively charged. A scanning electron microscope revealed that
an oocyst’s surface is made up of a series of plates. The researchers then
tested a number of materials until they found one that not only adsorbs oocysts,
but cracks them open, destroying the reproductive sporozoites lurking
within.
“They’ve found a chink in the Cryptosporidium armour,” says chemist
James Quirk of the University of Western Australia in Perth. “The material sucks
the oocyst onto its surface with such force that it collapses the whole thing.”
A swimming pool or drinking-water filter containing the material is cheap to
make and doesn’t reduce the water flow, says Pashley. The identity of this
crystalline material is not being revealed pending a patent application.