Cats Provide Unusual Source for Potential Malaria Vaccine
Madison, Wisconsin — As scientific ideas go, this one sounds (and smells) pretty far out.
The contents of a cat's litter box have given microbiologist Laura Knoll, PhD, an idea about how to deliver a vaccine for malaria, one of the planet's worst infectious diseases.
But once the "eww" factor is set aside, there's solid scientific sleuthing at work. Knoll, an associate professor of medical microbiology and immunology at the University of Wisconsin-Madison, says what links the litter box to a potential malaria vaccine is something called toxoplasmosis.
This parasitic infection is usually acquired through contact with cats and their feces or by eating raw or undercooked meat. Most people don't notice the mild flu-like symptoms that accompany the very common infections.
But if a woman is pregnant when she is infected with the toxoplasma parasite, or "toxo," the infection can be transmitted from mother to fetus, with sometimes catastrophic consequences. People with immune systems that are compromised by AIDS, bone marrow transplants or some cancer treatments also are highly vulnerable.
As it turns out, toxo belongs to the family of parasites that also includes malaria and cryptosporidium. "Crypto" is a waterborne organism that typically causes diarrhea, if that. The mosquito-borne malaria, on the other hand, kills one to three million people each year. Most victims are young children in Africa.
In searching for a malaria vaccine, Knoll, an expert on these three parasitic diseases, and her collaborators have worked with toxo to see if it could induce protective immune reactions against malaria. She and her colleagues at the University of Wisconsin School of Medicine and Public Health have also analyzed and identified toxo genes important in initiating infection.
Knoll hatched the cat feces/vaccine idea when she "put on her bioterrorism hat."
"Toxoplasma is on the category B list of bioterrorism agents, and I wondered why, since it's not usually a terribly dangerous organism," she says.
Then she realized that the parasite was considered dangerous because during one part of its life cycle, it exists in the form of cysts that are highly resistant to the environment. The encapsulated "eggs," excreted in cat feces, are stable under any condition for up to two years.
"Some crazy cat lady might collect all her contaminated cat poop and poison municipal waters," Knoll says, although she recognizes how strange that sounds. Toxo-contaminated water would likely cause widespread panic, if not widespread disease.
"We want to see if an immune reaction to toxo would be useful in fighting malaria," Knoll says, noting that no vaccine currently exists for malaria.
Nowadays, as she contemplates how best to deliver a future vaccine, Knoll's thoughts turn frequently to the cat potty. How can we get the cat toxo cycle working so that we could mass produce the cysts? How to isolate and purify them?
"The toxo cyst could make a beautiful malaria vaccine base," Knoll says. "You wouldn't need refrigeration, you wouldn't need needles."
You would, however, need cats.
Date Published: 08/11/2009