Why Malaria Vaccine Is Taking So Long To Develop

Ever since vaccines were introduced, several vaccines have been developed. Many were able to stop the spread of deadly infection. Unfortunately, one of the most deadly diseases of all time malaria is yet to get a vaccine readily available. There are several factors that are contributing to the slow success of developing a vaccine for malaria.
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Vaccines are either live or attenuated microorganism. Unfortunately, this does not work with the malaria parasite. This is due to the complex malaria parasite life cycle and its ability to develop resistance. To understand whats scientist are up to, and the setbacks they face, let's take a look at the life cycle of this parasite.

Life Cycle Of Malaria Parasite

Plasmodium life cycle

There are five species of malaria parasite that cause infection. They are transmitted by the female Anopheles mosquito during a blood meal. The parasite known as a sporozoite of about 5-10 goes straight to the liver within a space of fewer than 60 minutes. In the liver, it multiplies and changes form into merozoites. This can last up to 2 weeks. They are later released into the bloodstream in a sac known as schizont. The schizoid burst opens releasing the merozoites. The merozoites infect red blood cell. They start multiplying before they rupture the red blood cell. The new merozoites reinfect more red blood cells. However, some of the newly released merozoites come out as gametophytes. During blood meals, a mosquito can pick up a female and male gametophyte. At the right temperature and condition, the gametophytes fuse to form an oocyst. The oocyst travel to the gut of the female Anopheles mosquito as a haploid sporozoite. Another blood meal is another infection.

Malaria Vaccine Target Sites And Setbacks

Several vaccines are currently at various stages of development. They all target different stages of the life cycle. The first target stage is the vector. Here it prevents transmission of the parasite from the mosquito to human. However, the feasibility of achieving this seems rocket science because it looks impossible to target all the mosquitos in the world.
The next two target stages are the body. Scientist tries to borrow a leaf from the body own natural immunity to Plasmodium infection. The body develops short term immunity against the infection after some level of exposure to the disease. The immunity does not last long. The immunity gives the body the ability to destroy the parasite (antiparasitic immunity) or prevent the manifestation of clinical symptoms known as antitoxin immunity which is the suppression of the immune response. Unfortunately, scientists are yet to understand how naturally acquired immunity works.
The first of the two-stage they target is the pre-erythrocytic stage. It take less than an hour for the sporozoites to get to the liver. It will require a vaccine with a fast onset of action to be able to curtail this. This prevents the parasite from either getting to the liver or infecting the red blood cells. A couple of vaccine devepement have gone far in this. This sound nice because it prevents clinical symptoms.
The last stage can reduce clinical symptoms. To achieve this, scientist needs the major histocompatibility complex molecule (MHC) expression on the surface of erythrocytes. Unfortunately, like other blood cells, this molecule is lacking. Instead, they express the antigen.
They say malaria parasite is diverse. That is true. They replicate fast and have the ability to resist drugs over some period of use. This can present a big challenge to the development of a good vaccine that can attack all forms of the parasite.
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One last thing. Every medical product goes through a series of test. It usually begins with laboratory studies before proceeding to animal models. Humans are the last set of persons that are exposed to any new product before they eventually hit the shelves. They are term stages from 1-4 with sub-stages. Unfortunately, most of the malaria parasites do not infect big animal models. This makes it difficult to use animals to study immunity against the infection and also develop a suitable vaccine using animals as case study. It is now left for the scientist to jump from theory and laboratory research to human testing. This is a big set back as fewer persons come to volunteer when presented with little or no safety evidence except laboratory jargons.
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