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Malaria Eradication: Challenges, Progress, and the Future
Context:
The World Health Organisation (WHO) recently declared Georgia as the 45th country to eliminate malaria.
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- Despite progress, malaria persists, causing over 240 million cases and 600,000 deaths annually.
- Unlike smallpox, malaria has not been eradicated, and its vaccines are far less effective.
Overview of Malaria
- A life-threatening disease transmitted to humans by certain mosquitoes, primarily in tropical regions.
- Cause: Infection caused by Plasmodium parasites, spread through mosquito bites. It is not spread from person to person.
- Symptoms Occur within 10–15 days of a mosquito bite.
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- High-Risk Groups: Infants, children under 5 years, pregnant women, travellers, and people with HIV/AIDS.
- Malaria Treatment: Key antimalarial drugs include:
- Artemisinin-based combination therapies (artemether and artesunate) for Plasmodium falciparum, as well as atovaquone, chloroquine (where not resistant), doxycycline, mefloquine, quinine, and primaquine.
- The Government has launched the National Framework for Malaria Elimination (NFME) 2016-2030 to achieve zero indigenous cases of Malaria in the country by 2027 and to sustain elimination by 2030.
Discovery of Malaria Transmission
- Malaria was historically attributed to miasma (foul air from swamps).
- 1880: Alphonse Laveran identified the Plasmodium parasite as the cause of malaria.
- 1891: Patrick Manson hypothesised mosquitoes played a role in transmission but lacked proof.
- Giovanni Grassi confirmed that only female Anopheles mosquitoes transmitted Plasmodium.
- 1897: Ronald Ross proved Plasmodium completes its life cycle in mosquitoes, confirming their role as malaria vectors.
- This discovery facilitated European colonisation in Africa, reinforcing colonial rule rather than benefiting local populations.
Understanding the Malaria Parasite
- Life Cycle of Plasmodium: Infected mosquito injects sporozoites into the human bloodstream.
- Parasites invade liver cells, multiply undetected.
- Enter the bloodstream, infecting red blood cells (RBCs), causing fever and chills.
- Develop into gametocytes, which are picked up by mosquitoes.
- In the mosquito, they mature into infectious sporozoites, continuing the cycle.
- Comparison with Viruses: Viruses are simpler, with DNA/RNA in a protein shell.
- Plasmodium is a complex eukaryotic organism with multiple life cycle stages and surface antigens.
- Challenges in Immunity Development: Plasmodium constantly changes surface proteins, evading immune response.
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- It hides in liver and RBCs, making it hard for the immune system to detect.
- Reinfection is common due to lack of long-lasting immunity.
- Parasite evolves resistance quickly, complicating vaccine development.
Challenges in Malaria Vaccine Development
- Antigenic Variation: The parasite alters its proteins, making vaccines less effective.
- Complex Life Cycle: Vaccines must target multiple stages in humans and mosquitoes.
- Parasite Adaptability: Malaria parasite has evolved for 30 million years, adapting to immune responses.
Existing Malaria Vaccines
- RTS, S Vaccine: First malaria vaccine approved by WHO after 60 years of research. Targets liver stage, inducing immunity against circum-sporozoite protein (CSP).
- Efficacy: 36% reduction in cases over four years (much lower than 90-95% in viral vaccines).
- Requires multiple doses, creating logistical challenges.
- Next-Generation Vaccines:
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- R21/Matrix-M: Improved immune response, showing 77% efficacy over 12 months.
- PfSPZ Vaccine: Uses attenuated sporozoites to boost immunity against liver-stage infection.
- RH5-based Vaccines: Target blood-stage infection to prevent RBC invasion.
- Transmission-Blocking Vaccines: Prevent mosquito infection by targeting Pfs25 and Pfs230 proteins.
Challenges in Malaria Research and Control
- Underfunding: Malaria mainly affects low-income countries in Africa & South Asia, leading to limited research funding. Existing treatments reduce urgency for vaccine development.
- High research costs and low financial returns discourage pharmaceutical companies.
- Resurgence of Malaria: Shifting mosquito habitats due to climate change increases malaria risk. Requires integrated strategies: vaccines, mosquito control, and improved treatment.
WHO’s Vision for Malaria-Free World
- The WHO has launched initiatives like the Global Malaria Programme and the High Burden to High Impact (HBHI) initiative to support countries in their malaria elimination efforts.
- These programs focus on strengthening health systems, improving access to diagnosis and treatment, and promoting research and innovation.
- Several countries have made significant strides in eliminating malaria. According to the WHO, 15 countries have been certified malaria-free since 2015. Some of these countries include Algeria, Cabo Verde, Egypt, and Sri Lanka.
- The WHO has a goal to eliminate malaria in at least 30 countries by 2030. They have launched initiatives:
- E-2020 Initiative (2017): Included 21 countries with the potential to achieve zero indigenous malaria cases by 2020.
- E-2025 Initiative: Launched as a continuation of E-2020, reinforcing malaria elimination efforts.
Countries Certified Malaria-Free
- Azerbaijan and Tajikistan: The WHO certified Azerbaijan and Tajikistan as malaria-free in March 2023. Azerbaijan had not seen a locally transmitted case of Plasmodium vivax malaria since 2012, and Tajikistan since 2014.
- Cape Verde: WHO certified Cape Verde as malaria-free, making it the third African nation to achieve this status, following Mauritius (1973) and Algeria (2019). This brings the total number of malaria-free countries to 43 worldwide.
- El Salvador: El Salvador was declared malaria-free by the WHO, becoming the first country in Latin America to eliminate the disease.
