A malaria vaccine tried out in Mali in 2003 was not suited to protect people from the pathogen prevalent in the area, according to a joint study by researchers in Mali and the US.
The researchers studied samples from people in Bandiagara, a rural town in northeastern Mali, and found that before administering the vaccine, its possible effect on the strain of mosquito targeted was not taken into consideration.
Reporting the results of the study in the online journal Public Library of Science (plos) in November 2006, the researchers from University of Maryland School of Medicine, University of Bamako, Mali, and National Institutes of Health, Bethesda, said the results showed the importance of determining the genetics of the pathogens before starting vaccine trials.
The main vector in the Mali countryside is Anopheles gambiae, which spreads the pathogen Plasmodium falciparum. A variety of strains of Plasmodium can cause malaria and different strains produce different antigens. These antigen are used to make vaccines.
A vaccines is effective if it contains the same antigen as the parasite it has to produce antibodies against.
The research team collected 1,300 blood samples from malaria patients between July and January each year (1999-2001). They sequenced their DNA to examine the presence of a particular gene — msp-119. The vaccine had been developed against one of the variants of this gene —3 d7. Data from 14 different variants of msp- 119 were compared to find that 3d7 was present only in 16 per cent of the infections. Two other variants of the gene, fvo and fup, were present in about 40 per cent of the samples.
While 3d7-derived vaccine provides some protection against fvo and fup strains, it does not provide optimum immunity against them. Unfortunately, the 3d7-derived vaccine was tested in Mali where the other two variants were prevalent.
“We collected epidemiological data and samples between 1999-2001 and did the molecular analyses retrospectively in 2006,” said Christopher V Plowe, lead author and head of malaria section of the Center for Vaccine Development at University of Maryland School of Medicine.
Such epidemiological studies would ensure that potentially effective vaccines are not abandoned because they were tested on incorrect populations.
Preparations to test vaccines against falciparum malaria are underway even in India. The National Institute of Malaria Research (nimr), Delhi, has developed vaccine testing sites in Orissa and Madhya Pradesh. In Orissa, blood spots collected from people suffering from P. falciparum malaria showed that a total of 22 types of msp- 1 antigens and 24 of msp-2 were prevalent in the area. Trials are yet to begin. nimr deputy director Sukla Biswas said epidemiological studies were being carried out. “Trials on suitable vaccines that will work in the area will be allowed,” she says.
CSE/Down to Earth Feature Service

Cracking the code on mosquitoes
Meanwhile, scientists have released the draft sequence of the genome of Aedes aegypti, the mosquito that spreads dengue fever, yellow fever and chikungunya. The sequence is published online in the journal Science.
The genetic information could ultimately help control mosquito populations and the spread of disease, say the scientists.
"We expect that the genome sequence will accelerate basic research in the mosquito biology, particularly the ability of A. aegypti to transmit yellow fever, dengue and chikungunya," Vishvanath Nene from the US-based Institute for Genomics Research and author on the study told SciDev.Net.
The researchers expect it will help identify the genetic code of the receptors in A. aegypti's gut that the dengue virus attaches to.
The researchers were able to compare the A. aegypti genome with that of Anopheles gambiae, the mosquito that transmits malaria.  Nene says scientists can now begin to address questions such as why does A. gambiae transmit the malaria pathogen and A. aegypti the yellow fever, dengue and chikungunya pathogens.
Genetic differences may also explain their blood feeding preferences, the kind of hosts they seek and individual abilities to transmit certain pathogens.
According to the World Health Organization, there are 50 million cases of dengue fever each year. Yellow fever is a major problem in Africa and South America, with over 200,000 cases each year, and 30,000 deaths.
Meanwhile, scientists have identified a type of bacteria in mosquitoes that carry malaria, which could be used to attack the parasite.
The research was published in the Proceedings of the National Academy of Sciences recently.
Lead researcher Guido Favia and colleagues at the Italy-based University of Camerino found that bacteria of the genus Asaia inhabit the Anopheles stephensi mosquito. A. stephensi is an important mosquito vector of Plasmodium vivax - the parasite that causes malaria - in Asia. 
Favia told SciDev.Net that the bacteria are also present in the main African malaria mosquito vector, Anopheles gambiae.
The researchers say Asaia is an ideal candidate for malaria control because it has a symbiotic relationship with its mosquito host, can be passed between mosquitoes, and colonises the same parts of the mosquito as the malaria parasite.The researchers found that Asaia colonise the mosquitoes' gut and salivary glands.
These sites are also important for the malaria parasite - particularly for its development and ability to spread between mosquitoes.
The bacteria can also spread to mosquito offspring, as they were found in the eggs, ovaries and testes of mosquitoes and also in pupae and larvae.
 The malaria parasite has become resistant to drugs in some areas and attempts to create a vaccine have so far been unsuccessful.
The researchers suggest that the bacterium could be genetically altered to attack the malaria parasite by producing anti-parasite molecules.