Credit: Jason Rasgon lab
A virus that infects a species of malaria-transmitting mosquito could help scientists gain a better understanding of mosquito biology and eventually could lead to methods for stopping or slowing the spread of the disease, according to a researcher in Penn State's College of Agricultural Sciences.
Jason Rasgon, professor of entomology, has received a grant of $1.9 million from the National Institutes of Health to study the virus, called AgDNV. The goal of the five-year project is to develop a toolset that would enable researchers to genetically modify mosquitoes more easily, with an eye toward examining the influence of specific genes on mosquito phenotypes and developing malaria-control strategies.
"This project involves Anopheles gambiae, the main mosquito vector of malaria in Africa," Rasgon said. "Routine genetic manipulation of this species has proven challenging, so the development of novel tools for genetic modification is critical for both applied strategies for malaria control and for basic research into this mosquito's genetics and host-pathogen interactions."
To prove the feasibility of this concept, the research team will insert specific genes into a densonucleosis virus — known as a "densovirus" — which will infect the mosquito's tissues and express those genes.
"This virus is distantly related to the virus used in human gene therapy," Rasgon said. "So it's almost like gene therapy in the mosquito." He explained that the densovirus is a tiny virus — it contains only three genes and about 4,100 nucleotides — and its entire genome can be synthesized artificially and placed into a plasmid, which is a circular piece of DNA.
"Once in that form, we easily can manipulate it and transfect it into insect cells in a dish, where it will make live, infectious virus that will have whatever genetic modifications we've put into it," said Rasgon.
Researchers then can infect mosquitoes either by putting the virus into water with mosquito larvae or by injecting it into adult mosquitoes. The virus then will infect them, and whatever gene was inserted will be expressed.
Rasgon said this system would have great value as a laboratory tool. "If you want to test a gene by turning it on or off, you wouldn't need to develop a transgenic mosquito. You just could pop it into the virus, and it will express that gene in the mosquito for you."
It also could become a biocontrol agent, he said. "You could insert genes that would make the mosquito unable to transmit the malaria parasite or that would kill the mosquito or shorten its lifespan."
This specific virus occurs naturally and would be very safe as a control agent, Rasgon noted. The virus is not a human pathogen and is host-specific, meaning it infects only Anopheles gambiae and not other mosquitoes or nontarget organisms such as vertebrates.
In addition, once infected by the modified virus, adult female mosquitoes can transmit it to larvae by inoculating it into the water when laying eggs. Rasgon's lab also has found that male adult mosquitoes can transmit the virus to females during mating.
Rasgon maintains that this line of research illustrates the unpredictability and serendipity of science — he discovered the existence of the virus by accident about 10 years ago.
"We were looking for a particular bacterium in a mosquito cell line using PCR [polymerase chain reaction], and we got a weird band where there shouldn't have been one," he said. "We wanted to know what it was so we sequenced it, and it turned out to be this virus.
"We've been unsuccessfully seeking funding to study it further for 10 years. So receiving this grant also is a testament to the value of persistence in science," he said.
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