Genome May Mean Vaccine

October 24, 2002
By Michelle Vachon
The Cambodia Daily

The news that researchers have uncovered the genetic code of both the parasite and the mosquito that transmit malaria raise the hope that, one day, an inexpensive and effective vaccine will be available, said Sean Hewitt, malaria adviser with the European Commission Malaria Control Project in Cambodia.

"But I'm afraid it will be many, many years before the most vulnerable groups living in malaria countries feel the benefits resulting from practical applications," he said. "Malaria parasites and the way they interact with their human and mosquito hosts is extremely complex, so [a vaccine] seems a good way off."

Plasmodium falciparum, a deadly form of malaria, and the mosquito host Anopheles gambiae, whose genetic sequences have been mapped out, are responsible for most malaria deaths in Africa, Hewitt said.

One of the researchers' goals is to engineer a "trans-genic" mosquito that would be incapable of transmitting malaria, he said. This mosquito would have to outperform natural species, and spread to the most remote locations in order to progressively replace the malaria-transmitting species, Hewitt said.

In Africa, mosquitoes can travel long distances on the wind over grasslands, which is not the case in Cambodia, he said. Here, malaria-carrying mosquitoes, which only bite monkeys and humans, stay in specific locations and don't travel from one area to the next. If trans-genic mosquitoes were used to fight malaria in Cambodia, it would mean transporting them by truck, along good and bad roads, deep into the jungle where most malaria cases occur. It's already hard to transport medicine to remote corners of Cambodia, let alone live mosquitoes, Hewitt said.

"They would die in the heat," he said.

A vaccine would have to be "multi-valent" to be effective against the various strains of the parasite, Hewitt said. Each time parasites reproduce inside mosquitoes, they produce slightly different strains not unlike parents giving life to children who look differently.

Since mosquitoes in Cambodia stay at one spot, the malaria strains they carry may vary from one village to the next, Hewitt said.

And malaria strains evolve so quickly, people would need to be vaccinated every month or so to build resistance against the latest strain of the disease, he said.

While a person who survives smallpox becomes immune for life, immunity against a malaria strain may last about six months, Hewitt said.

According to Associated Press, Neil Hall, who led the research team on the malaria genome at the Wellcome Trust Sanger Institute in the UK, compared the malaria gene map to a haystack in which one will have to find the needle to produce malaria vaccine or medicine.

"It contains every possible vaccine target and every possible drug target," he said earlier this month at a press conference in London. More than 160 scientists in 10 countries were involved in the parasite and mosquito genetic code project.