According to the World Health Organization, an estimated 429,000 people die from malaria annually. And while it's tempting to spray heavily for the mosquitoes that spread the disease, conventional insecticides are also toxic to humans and other animals. Now, however, a neurotoxin has been discovered that only kills the offending mosquitoes.

Malaria is transmitted to humans by Anopheles mosquitoes, which are themselves infected with Plasmodium parasites. Approximately 30 years ago, scientists identified a strain of Paraclostridium bifermentans bacteria that kills Anopheles, although its method of doing so was not understood. That has now changed, thanks to an international study led by Prof. Sarjeet Gill at the University of California, Riverside.

The researchers started by creating a mutant strain of the bacteria, that was not lethal to the mosquitoes. They then compared proteins present in that strain to those in regular P. bifermentans, finding a neurotoxin known as PMP1 in the latter. Additionally, the non-mutant bacteria also contained proteins that may protect the toxin as it's absorbed within a mosquito's gut.

Although PMP1 is related to the botulinum (aka botox) and tetanus toxins, both of which are highly toxic to humans, it itself doesn't affect vertebrates of any kind, or even other insects. When mice were directly injected with the neurotoxin, they showed no adverse reaction. Anopheles mosquitoes, on the other hand, die when exposed to it.

It is now hoped that industry partners could help develop a PNP1-based insecticide, for use in malaria-prone countries. Because that insecticide would be protein-based, it should harmlessly break down in the environment after being sprayed. And, unlike the case with synthetic chemical-based insecticides, the mosquitoes shouldn't develop a resistance to it.

A paper on the research, which also involved scientists from Sweden's Stockholm and Lund universities, was published this Friday in the journal Nature Communications.