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Malaria: A curse of the tropics

Infographic: Siddharth Kankaria / Research Matters

 

Did you know that nearly half of the world’s population is at the risk of malaria, a tropical disease caused by mosquito bites? A report by the World Health Organisation (WHO) states that in 2015, there were 212 million reported cases of malaria and almost half a million deaths around the globe due to malaria. While most of these occur in sub-Saharan Africa, in countries like Kenya, Uganda, Liberia, Ghana and others, parts of South-East Asia, Latin America and the Middle East are also at risk. The numbers in India too paint a gloomy picture with two million confirmed malaria cases and 1,000 deaths reported annually, making up 77% of the total malaria in South-East Asia.

Malaria is a disease caused by a protozoan belonging to the genus Plasmodium, and is spread from one person to another by the bite of female Anopheles mosquitoes. In the long course of human history, malaria has killed more humans than any other disease.

Thanks to sustained efforts at various levels by health workers, governments and organizations across the world, there has been a decline in the number of cases of malaria and related deaths since 2010. The 25th of April each year, is observed as ‘World Malaria Day’ (WMD) to spread awareness and recognise the efforts to control and eliminate this deadly disease. With the theme ‘let’s close the gap’ for 2017, the WHO is calling all of us to close the gap in malaria prevention. As a testimony to this, the WHO has announced that three African countries have been selected for the first ever large-scale trial of anti-malarial vaccines.

What causes malaria?

Malaria is a disease characterized by flu-like symptoms like high fever, shaking chills and sweating. In severe cases, it can also include headache, diarrhea, jaundice, kidney failure, seizure and coma followed by death. Of the 5 types of Plasmodium, P.vivax and P. falciparum are the most harmful species that affect humans.

When a female Anopheles mosquito bites a person infected with malaria, it picks up the protozoan Plasmodium from the infected person’s blood, which it sucks to nurture its eggs. Inside the mosquito, the protozoa reproduce and develop. When the same mosquito bites again, these protozoa present in its saliva, are injected into the blood of the person being bitten. Once inside humans, the protozoa grow and multiply in the liver cells and then successive broods of parasites move inside the red blood cells, destroying them in the process and releasing daughter parasites (merozoites) that continue the cycle by invading other red cells.

However, this is not the only cycle of malaria. Some of these protozoa living in the blood cells of an infected person can also reach a female Anopheles mosquito during a blood meal. To make matters worst, they start a different cycle of growth and multiplication in the mosquito. Found as sporozoites after 10-18 days inside the mosquito, they enter humans through a bite, infecting the liver cells and starting the damage.

But why is it only female mosquitoes that act as a vector? “Because, it is only the female mosquitoes that feed on human blood which is required for egg laying”, states Dr. Shalini Tiwari, Chief Medical Officer at Composite Hospital, Kolkata. “Each type of mosquito chooses a particular type of host depending on whose blood they consume, with each species having its own preferences”, she adds further.

The Anopheles mosquitoes are generally found in the tropics and breed in natural water collections. Hence, they grow in numbers during the rainy season when water collects in bottles, tins, coconut shells, buckets, tyres etc., that are thrown out in the open. In addition, open wells, ponds, water tanks and paddy fields -- all act as breeding grounds. In urban areas, water collected in construction sites, tanks and clogged drains also help breeding.

Cracking the malaria puzzle

Man’s association with malaria is as old as man himself. Ancient physicians believed that malaria was caused by smelling toxic vapours rising from marshes, giving rise to the name - ‘malaria’ - which in Italian translates to ‘bad air’. It was not until the 19th century that we understood the actual cause behind this fatal disease.

In the 1800s, it was observed that may soldiers deployed in tropical countries suffered from malaria which spread like wildfire, killing many. Dr Alphonse Laveran, a professor at the School of Military Medicine, Paris, was determined to identify the cause behind the untimely death of soldiers. Convinced by Louis Pasteur's ‘germ theory’ that says microbes are the cause of most infectious diseases, he observed, for the first time, black granules in the blood cells of infected soldiers, which he called ‘Laveran's bodies’. Though it was discovered that these black granules were the protozoa Plasmodium, there was no evidence found to link these protozoa to the marshlands, air, water or soil.

In 1897, an Indian Medical Service Officer, Dr. Ronald Ross from Begumpet, Hyderabad, collaborated with Dr. Patrick Manson from Scotland, to find out the exact cause of malaria. Called the ‘father of tropical medicine’, Dr. Manson had worked for 24 years on tropical diseases and was the first to discover that an insect could be a vector for a human disease. Guided by Dr. Manson’s work, Dr. Ross studied mosquitoes in his small lab in Begumpet for two years and discovered that female Anopheles mosquitoes carry the malarial protozoa in their saliva.

This was the first time a link between protozoa, mosquito bites and malaria was established. For their pathbreaking research that identified the protozoa causing malaria and the mosquito acting as a vector, Dr. Laveran and Dr. Ross were both awarded the Nobel Prize in Medicine.

The fight against malaria

The first cure for malaria dates back to 1600 when Jesuit missionaries in Peru used the bark of cinchona, a tree found in tropics, containing quinine, a medicine still used to cure malaria. Later, Artemisinin, a Chinese herb that was used to treat fevers for over 1000 years, was found to work better than quinine. In fact, Tu Youyou was awarded the 2015 Nobel Prize in Medicine for developing an antimalarial drug from Artemisinin.

Since the 20th century, many compounds have been identified to act against various stages in the life cycle of Plasmodium, like chloroquine, amodiaquine, pyrimethamine, proguanil, clindamycin and others. However, the development of drug-resistant strains of Plasmodium have increasingly posed a serious threat in the recent past.

“There has been a progressive increase in frequencies of drug-resistance genes”, remarks Dr. Tiwari. “Drug resistant P.falciparum hide in red blood cells in a state that is naturally less vulnerable to drugs. These protozoa are also thought to increase their capacity to repair the damage caused by the anti-malarial drug, which gives them a higher chance of survival. Since many of the available drugs are more effective in the later stage of its lifecycle, the protozoa slow down their growth in order to survive longer”, she adds.

In areas with high risk of malaria, drug-resistant strains cause chronic infections with increasing risk of severe anemia. An early switch to other drugs could be a life-saving decision in most cases, says Dr. Tiwari, adding that these measures certainly add to the economic burden of the country.

The control of malaria in India

India’s tryst with fighting malaria dates back to 1953 with the launch of National Malaria Control Programme (NMCP). “The spectacular success of NMCP enthused health planners to convert it into an Eradication Programme (NMEP) in 1958. However, this success was short lived due to constraints on financial, logistic, administrative and technical capabilities”, recollects Dr. Tiwari. The country witnessed a resurgence of malaria after 1964, which reached its peak in 1975 with thousands of cases recorded.

The Modified Plan of Operation introduced in 1977 led to significant reduction in malaria cases, which was maintained until 1986. This again did not last long and during 1995-96, numerous incidents of malaria outbreaks and deaths were reported from many tribal parts of the country. However, after the programme was converted into National Vector Borne Disease Control Programme in 2003, the cases of malaria are on the decline.

In addition to government policies, hospitals and health-care providers have a major role in controlling the spread of malaria. “Hospitals have to devise strategies to control, detect and treat the disease early”, opines Dr. Tiwari.  One of the important strategy intervention has been the ‘Early case Detection and Prompt Treatment (EDPT)’ aimed to control the spread of the disease. In addition, numerous Drug Distribution Centres (DDCs) and Fever Treatment Depots (FTDs) have to be established in rural areas for providing easy access to antimalarial drugs. Fogging of Malathion (an insecticide) during outbreaks and biological control of mosquitoes by using larvivorous fish in ornamental tanks and fountains can also go a long way in controlling malaria.

The community at large also needs to shoulder this responsibility by using prescribed prophylactic drugs (medicines taken to prevent a disease) and avoiding creating a breeding ground for mosquitoes. “Simple things like using mosquito repellent creams, liquids and coils, screening of the houses with wired mesh, use of bednets treated with insecticides and wearing clothes that cover maximum surface area of the body can greatly help one from contacting the disease”, says Dr. Tiwari. In addition, community participation in spreading the awareness of the disease and detecting Anopheles breeding places can help too.

The battle against malaria is never won without closing the gaps that exists in eliminating the disease from the face of the planet. So what can each of us do? “Let us join hands to fight the malaria menace and extend full co-operation to our government to make the National Vector Borne Disease Control Programme a success by individual and community level participation”, signs off Dr. Tiwari.