Mustafa Vora, DY Patil University Navi Mumbai
Malaria and the global problem it causes:
Malaria is one of the most infectious diseases that are a threat to the human race. The mode of transmission is from mosquito to humans by a parasite, Plasmodium falciparum. The infection is caused because the sporozoite enters the bloodstream of humans. In a report by WHO, during 2019 229 million clinical cases and around 400,000 deaths have been reported. Scientists all over the world are working to make a vaccine against this disease. Even after 140 years, since the causative agent for malaria has been discovered, no such vaccine could be discovered that can trigger a total immune response in humans. P. falciparum has a very complex genome as it consists of around 5,300 genes. Apart from this, the global diversity in P.falciparum strains has caused hindrance in developing a vaccine.
How is the infection caused?
Infection begins when the parasite from the salivary gland of mosquitoes is transmitted in humans and then to the liver and blood. The liver stage of this is not responsible for the symptoms of malaria. Within weeks of infection, the sporozoites mature and generate in a form that enters the red blood cells leading to death. The liver stage parasite and sporozoite together are called the pre-erythrocytic (P.E.) stage. The P.E stage is assigned by the scientists for the development of vaccines.
The development of malarial vaccine in the past:
Scientists have developed vaccines using the heat-killed version of P.falciparum. High doses of sporozoites weakened by radiation administered in humans can confer protection from subsequent infection by the parasite. Moreover, scientists focused on developing a malaria vaccine that targeted a single parasite protein (CSP) and expressed in the P.E stage of infection. This approach showed an improved level of protection against this infection. Although there was some improvement, the limitations of this approach far exceeded the application.
The present improved technique of malarial vaccine development:
To overcome the limitation posed by the approach, scientists moved to use whole and live PE stage parasites for inducing an immune response. The malarial vaccine was administered, along with a drug, such as chloroquine. Scientists have found a solution for such drawbacks, the aim is to genetically engineer the parasite such that no drug would be required to kill the parasite. This is only possible if the parasite after some generations of reproducing dies and does not reach the blood stage of infection. This will offer full immunization with no threat of malarial infection.
To develop such whole, live genetically engineered vaccines, there is a requirement for mass production of sporozoite from mosquitoes. This has faced a formidable challenge in scaling up the production of vaccines. To overcome this issue, investments in technologies that allow large-scale manufacturing of whole sporozoite vaccine can help. The sporozoites also need to be stored at low temperatures once harvested from the mosquito’s salivary glands. Storage at such a low temperature can be a limitation in resource-poor areas. Ultimately, several vaccines are needed for the fight against malaria.
Also read: Are “Too Clean” Homes leading to Poor Immunity In Children?
References:
- Minkah, N. K., & Kappe, S. H. I. (2021). Malaria vaccine gets a parasite boost in the liver. Nature, 595(7866), 173–174. https://doi.org/10.1038/d41586-021-01720-6
- Ledford, H. (2021). Vaccine made of live malaria parasites shows early success. Nature. https://doi.org/10.1038/d41586-021-01806-1
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