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Averting antimalarial drug resistance in India
In most malaria-endemic countries including India, Artemisinin-based antimalarial drugs are the first-line choice for malaria treatment especially against Plasmodium falciparum parasite which is responsible for almost all malaria-related deaths in the world. In recent years there is increasing evidence for the failure of artemisinin-based combination therapy for falciparum malaria either alone or with partner drugs.
On 23 September 2021, the New England Journal of Medicine published an article `Evidence of Artemisinin-Resistant Malaria in Africa’. The study described the presence of two mutations responsible for artemisinin resistance in Northern Uganda. The current report of artemisinin resistance in East Africa is a matter of great concern as this is the only drug that has saved several lives across the globe.
In India, after the failure of chloroquine to treat P. falciparum malaria successfully, artemisinin-based combination therapy was initially introduced in 117 districts that reported more than 90% falciparum burden in 2008.
In 2010, artesunate plus sulfadoxine-pyrimethamine (AS+SP) was introduced universally, but in 2013, in view of resistance to the partner drug SP in the seven North Eastern States, the combination partner was replaced by artemether-lumefantrine (AL) for these states. Currently, several combinations of artemisinin derivatives are registered in India.
Artemisinin-based combination therapy failure in India
In 2019, a report from Eastern India indicated the presence of two mutations in P. falciparum cases treated with artemisinin that linked to its presence of resistance.
Again in 2021, artemisinin-based combination therapy failure was reported from Central India where the partner drug SP showed triple mutations with artemisinin wild type.
This means the failure of artemisinin-based combination therapy may not be solely linked to artemisinin. Here it is needed to change the partner drug as has been done in NE states in 2013.
In the past, chloroquine was very effective for all types of malaria treatment in India. But it is no longer used for the treatment of falciparum malaria.
Though there have been some reports of chloroquine resistance in P. vivax malaria, this drug is still the effective choice to treat this species.
Reports of the presence of chloroquine resistance mutations in some vivax-dominated areas are a cause of concern and continued monitoring is needed.
History of drug resistance
In the 1950s chloroquine resistance came to light. Both chloroquine and pyrimethamine resistance originated from Southeast Asia following their migration to India and then on to Africa with disastrous consequences.
Similarly, artemisinin resistance developed from the six Southeast Asian countries and migrated to other continents, as is reported in India and Africa. It would not be out of context that artemisinin is following the same path as has been seen with chloroquine.
Now, the time has come to carry out Molecular Malaria Surveillance to find out the drug-resistant variants so that corrective measures can be undertaken in time to avert any consequences. Some experts even advocate using triple artemisinin-based combination therapies where the partner drug is less effective.
The first malaria vaccine
RTS,S/ASO1 (RTS.S), trade name Mosquirix, which was endorsed by the World Health Organisation (WHO) on 6 October 2021, is the first and, to date only, vaccine shown to have the capability of significantly reducing malaria, and life-threatening severe malaria, in tests on young African children.
The vaccine acts against P. falciparum, the most deadly malaria parasite globally, and the most prevalent in Africa. Among children who received 4 doses in large scale clinical trials, the vaccine was able to prevent approximately 4 in 10 cases of malaria over a 4-year period.
This is the first malaria vaccine that has completed the clinical development process, and received a positive scientific opinion from the European Medicines Agency (EMA).
It is also the first malaria vaccine to be introduced by three national ministries of health through their childhood immunization programmes — more than 800,000 children in Ghana, Kenya, and Malawi have been vaccinated, and are benefiting from the added protection provided by the vaccine as part of a pilot programme.
Other recent clinical evidence shows that strategic delivery of the vaccine just prior to the high malaria transmission season in areas where malaria is highly seasonal can optimize impact and markedly reduce mortality, especially when combined with other recommended malaria control interventions.
The global burden of malaria
Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. It is preventable and curable.
Still, in 2019, there were an estimated 229 million cases of malaria worldwide, and the estimated number of malaria deaths that year stood at 409,000.
Children aged under 5 years are the most vulnerable group affected by malaria; in 2019, they accounted for 67% (274,000) of all malaria deaths worldwide.
In 2019, India had an estimated 5.6 million cases of malaria compared to about 20 million cases in 2020, according to WHO.
How the vaccine can help
WHO’s recommendation is based on the advice of its two global advisory bodies, one for immunization and the other for malaria.
WHO has recommended that in the context of comprehensive malaria control, the RTS,S/AS01 malaria vaccine be used for the prevention of P. falciparum malaria in children living in regions with moderate to high transmission as defined by it.
The malaria vaccine should be provided in a schedule of 4 doses in children from 5 months of age for the reduction of malaria disease and burden.
The next steps for the WHO-recommended malaria vaccine will include funding decisions from the global health community for broader rollout in endemic countries, and country decision-making on whether to adopt the vaccine as part of national malaria control strategies.
A vaccine is a breakthrough addition to the malaria toolkit and can help get malaria control back on track.
Countries that have eliminated malaria
Globally, the elimination net is widening, with more countries moving towards the goal of zero malaria. In 2019, 27 countries reported fewer than 100 indigenous cases of the disease, up from 6 countries in 2000.
Countries that have achieved at least 3 consecutive years of zero indigenous cases of malaria are eligible to apply for the WHO certification of malaria elimination. Over the last two decades, 11 countries have been certified by the WHO Director-General as malaria-free: United Arab Emirates (2007), Morocco (2010), Turkmenistan (2010), Armenia (2011), Sri Lanka (2016), Kyrgyzstan (2016), Paraguay (2018), Uzbekistan (2018), Algeria (2019), Argentina (2019), and El Salvador (2021).
Difficulty in developing a vaccine
The World Health Organisation on 6 October 2021 allowed the “widespread use” of the world’s first vaccine against malaria, a common mosquito-borne disease that claims more than four lakh lives every year. Developed by GlaxoSmithKline, the vaccine, known as RTS,S/AS01, has already been administered to nearly 8 lakh children in Ghana, Kenya and Malawi as part of a pilot programme since 2019.
The WHO endorsement paves the way for the use of this vaccine outside the pilot programme, in all areas where malaria is known to be widely prevalent. But the RTS.S/AS01 vaccine, known by its brand name of Mosquirix, is considered only the first step towards effective immunisation of the global population against malaria. This vaccine is able to prevent severe cases of malaria in only 30 percent of the cases, and the quest for more effective vaccines is still underway.
Biggest killer
Malaria is known to be one of the deadliest diseases in human history, having claimed millions of lives. Even now, the disease kills over four lakh every year, according to WHO figures. This is still a huge improvement from twenty years ago, when close to double the number of people were succumbing to the disease.
Malaria is most endemic in Africa, with Nigeria, Congo, Tanzania, Mozambique, Niger and Burkina Faso together accounting for over half the yearly deaths.
India is one of the countries badly affected by the disease. Deaths due to malaria has come down sharply in the last few years — officially these are only in hundreds now — but infections continue to be in millions.
Lack of vaccine
Despite decades of research, scientists have been unable to develop an effective vaccine for malaria, though over 20 candidates have entered clinical trials in the last few years.
To date, the best prevention of malaria remains the use of mosquito nets. However, this does nothing to eradicate the disease.
Scientists cite a variety of reasons for the failure to develop a malaria vaccine, the foremost being the complexity of the life-cycle of the malaria-causing parasite, a part of which is spent in the human host.
“The difficulty in developing effective malaria vaccines stems largely from the complexity of the malaria-causing parasites’ life cycle, which includes mosquitoes, human liver, and human blood stages, and subsequent antigenic variations of the parasite. These parasites are also able to hide inside human cells to avoid being recognised by the immune system, creating further challenges,” wrote a group of Australian and Chinese researchers in an open-access journal last year.
“Another challenge faced in malaria vaccine development is that the common human malaria-causing parasite, P. falciparum, is not a rodent pathogen. The most common mouse models of malaria employ the rodent-specific parasite species P. berghei, P. yoelii, and P. chabaudi. These species generate unique pathologies and immune responses. While they are still employed to model various manifestations of human disease, the immune response patterns observed in these models are not fully transferable to humans,” the researchers wrote.
Mosquirix itself is the result of more than 30 years of research and development, and yet has only modest efficacy. Other scientists, like Navneet Arora, Lokhesh Anbalagan and Ashok Pannu, researchers from Postgraduate Institute of Medical Education and Research (PGIMER) in Chandigarh point to other reasons like the lack of funding and interest in developing a malaria vaccine.
“Because malaria disproportionately affects LMIC (low and middle income countries) lacking the robust health infrastructure, the vaccine manufacturers have little incentive for malaria vaccines and continued targeting vaccines for industrialized world markets,” the three researchers wrote in a paper in an open-access journal last year.
Other scientists have also mentioned that research for malaria vaccine never received the same kind of attention as, say, HIV/AIDS.
Malaria on decline
However, significant progress has been made in the last few years in reducing the impact of malaria. A few countries have also been able to eliminate malaria, mainly through spray of insecticides to kill the mosquitoes, and cleaning up areas where mosquitoes breed. In the last twenty years, 11 countries have been declared by WHO to have become malaria free, after zero cases were recorded in these countries for three consecutive years. These countries include United Arab Emirates, Morocco, Sri Lanka and Argentina. In 2019, as many as 27 countries reported less than 100 cases of malaria. Two decades ago, only six countries had less than this number.
Newer vaccines
Several other vaccines are being tested. One of them has also shown some promise. In May this year, a malaria vaccine candidate undergoing phase two trials reported an efficacy of 77 per cent. This vaccine, R21/Matrix M, is a modified version of Mosquirix, and has been developed by researchers at the University of Oxford. Lead researcher Adrian Hill, director of Jenner Institute and professor of vaccinology at Oxford University, had said he believed this vaccine was the first to reach WHO’s goal of at least 75 per cent efficacy.
Dr V S Chauhan, a former director of Delhi-based International Centre for Genetic Engineering and Biology, and well known for his efforts to develop a recombinant malaria vaccine, said R21/Matrix M held a lot of promise. “This vaccine is definitely a big hope, but it still has to undergo phase three trials,” he said.
POSTED ON 29-11-2021 BY ADMIN
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