Malaria vaccine : Blocking transmission of Malaria

Malaria has been epidemic, not only in India but in many countries like China, Indonesia etc. The discovery of chloroquine was a revolution in treating malaria, but gradually resistant cases started emerging and now more than 20% of cases are chloroquine resistant malaria.

As the vector for malaria, the female anopheles mosquito reside at clean and stored water, it was very difficult to prevent malaria merely by maintaining hygiene. This lead to the need of something which can block the spread or transmission of malaria, and this need forced scientists to work on malaria vaccine.

Possible targets of malaria vaccine development

In human beings the asexual cycle of malarial parasites occurs while in mosquitoes the sexual cycle occurs, this makes the possible target in blocking transmission of malaria or malaria vaccines as

Pre erythrocytic malaria vaccine

The preerythrocytic malarial vaccine can prevent
i. Sporozoites inoculated by the infected mosquito during the blood meal before they invade the liver cells.

ii. Sporozoites multiplying within the liver cells to give rise to merozoites.

Blood stage malaria vaccine

i. Inside the red cells merozoites transform into trophozoites, grow and then divide finally to give dozens of merozoites, which reinvade the new red cells after bursting of the infected cells. These merozoites can be the vaccine target.

ii. During intracellular growth of the parasites they express some antigens on the surface of red cells which may be the vaccine target.

Transmission blocking malaria vaccine

Vaccines targeted against gametocyte or gametes are known as transmission blocking vaccines. Some trophozoites differentiate into sexual form, male and female gametocytes which mature to gametes in the digestive system of mosquito.

What are pre erythrocytic malaria vaccine

Pre-erythrocytic malarial vaccine have focussed largely on circumsporozoite protein which is the major surface protein of the sporozoites. The basic aim is to generate humoral immune response which will neutralize the sporozite and prevent it from invading the hepatocytes.

Once sporozoite reached the relatively immuno protected intracellular haven of a hepatocyte then cell mediated immunity is called upon to contain the infection.

A successful pre-erythrocytic vaccine will either kill the sporozoite before they invade hepatocytes or destroy it once they are inside the hepatocyte. This result in a disease preventing vaccine, an ideal vaccine, which will result in sterile immunity. Also it will be an ideal vaccine for the travellers as it would prevent clinical disease.

What are blood stage malaria vaccine

Blood stage malarial vaccine will either destroy the merozoites in the short time before they invade red cells or target malarial antigens expressed on red cell surface by invading parasites. Protection offered by these vaccines will be both antibody dependent and cell mediated immunity. These vaccines will suppress the exponential growth of dividing merozoites there by reducing the disease manifestation ie disease reduction vaccine. They will simulate natural immunity that is found in highly endemic zones.

What are transmission blocking malaria vaccine

Antibodies produced by these vaccines against gametocytes will be taken up by the mosquito during its blood meal along with the gametocytes. Within the mosquito the antigens become exposed to antibody thereby neutralizing the sexual stages.

These vaccines are termed altruistics, since they mediate their action within the mosquito and would protect not the vaccinee, but the next person beaten by that mosquito. Reduction in transmission rate could radically alter the incidence of the disease particularly in areas of low or moderate endemicity.

Chinese malarial vaccine

A China developed malaria vaccine is under trial in Shanghai, this is a move China hopes it will contribute to global prevention efforts of the deadly disease.

Seventy healthy volunteers will recieve the vaccine, code named PfCP2.9, at the Changhai hospital in shanghai, if the eight month trial is successful, full clinical trials will be conducted on adults and children where malaria is most prevalent.

The trials are funded by the worldwide non-profit fund PATH, and its malaria vaccine initiative. Shanghai based Wanxing Biological Pharmacy Co. Ltd. is also engaged in the research and development of the vaccine. The two organizations signed a agreement to carry out the clinical trials in Shanghai.

The trial will recieve 2 million US dollars from PATH which will also provide technical support and data analysis.

The PfCP2.9 malaria vaccine, developed by medical experts with the Shanghai No. 2 medical college of the Chinese people's Liberation Army (PLA), is one of 20 new malaria vaccine around the world which have recieved funding from PATH for clinical trials.

Numerous trials are also going on simultaneously and hundred vaccine development teams had applied for funding. We expect a full proof preventive vaccine very soon which will not only prevent from clinical disease but also prevent transmission.