By Dr Amitav Banerjee, MD, Epidemiologist
In disease eradication, the last mile is crucial. Even a single case can keep smoldering and can start the fire with a vengeance, since immunity of the population goes down. In malaria, this immunity is weak and ill-defined and is called “premunity.” This is a form of incomplete protection that depends on low-level persistent infection, giving rise to “stable malaria” in endemic regions. Here there are no overt outbreaks, as survivors into adulthood have “premunity,” but these populations are likely to have high infant mortality rates due to malaria.
Half-hearted or incomplete malaria control measures in these regions can convert “stable malaria” into “unstable malaria” when adults lose this immunity due to interrupted transmission, and there are clusters of cases in adults giving rise to overt outbreaks. Most densely forested tribal regions in the country experience this phenomenon. Regarding diagnostic tests, the challenge is accessibility to health services rather than technology. Unless we have good-quality health services in these pockets, malaria eradication is a far cry.
A “stable malaria” situation can also turn into “unstable malaria” with the movement of large numbers of people from non-endemic regions to endemic regions. Troops moving into operations in highly infested regions are quite vulnerable and can encounter outbreaks.
It is two-way traffic. Labourers from these smoldering pockets often move to urban areas for projects. They may be carrying the infective stages of the malaria parasite (gametocytes) in their blood and serve as healthy carriers. In malaria-naïve regions, they can trigger outbreaks when gametocytes are picked up by vector mosquitoes and transmitted to people in non-endemic regions.
Drug resistance in Plasmodium vivax is not a big issue in India, with less than 2% of cases showing resistance to chloroquine, which can be managed by second-line drugs. Relapse in Plasmodium vivax malaria is mostly due to incomplete treatment, as a result of which liver phases of the parasite persist and give rise to relapses. All cases of malaria have to be treated with primaquine to prevent relapses. Primaquine not only eliminates the reservoir of the parasite in the liver but also kills the gametocytes in the blood that are responsible for community transmission.
Drug resistance is a major issue in the more severe, potentially fatal Plasmodium falciparum malaria, which is almost universally resistant to chloroquine and has to be treated with a 3-day course of artemisinin-based combination therapy (ACT), specifically Artesunate + Sulfadoxine-Pyrimethamine (AS+SP). This is combined with a single dose of primaquine (0.75 mg/kg) on the second day to stop transmission. Severe cases require prompt IV artesunate or quinine.
Drug resistance is dynamic and ever evolving. Continuous monitoring is required to cope with changing patterns of drug resistance.
There are six primary vectors of malaria in India. Anopheles culicifacies is predominantly a rural vector and prefers animal blood. The urban vector is Anopheles stephensi. Forest regions and foothills have a very high density of highly efficient vectors such as Anopheles fluviatilis and Anopheles minimus, which are outdoor-resting and therefore difficult to control by insecticide spraying of houses or insecticide-treated mosquito nets. Anopheles sundaicus is found in coastal regions, while Anopheles dirus, an efficient outdoor-resting vector, is found in the forests of the North East.
Note that the control of malaria in tribal regions poses many challenges, such as lack of accessibility to quality health care, nomadic behaviour of tribal populations, and outdoor-resting mosquitoes in forests. Lack of toilets is another contributing factor, and mosquitoes bite during dawn and dusk when people go for open-air defecation near forest streams where vectors like Anopheles fluviatilis and Anopheles minimus breed.
Insecticide resistance develops rapidly, and insecticides also have an environmental cost. DDT, which fetched the Nobel Prize for its inventor, Paul Müller, in 1948, was banned under the Stockholm Convention due to its severe adverse effects on human health, wildlife, and its extreme persistence in the environment. While initially hailed as a “miracle” insecticide during World War II for controlling malaria and typhus, its widespread agricultural use led to catastrophic ecological consequences.
Long-term control of malaria lies in overall development, with better housing, water management, access to quality medical care, toilets for all, including behavioural changes to ensure their use, and so on.
You cannot win a football match with all players concentrated in the forward line, with no half-backs, full-backs, and goalkeeper. Similarly, you cannot tackle a public health problem without proper placement of quality health services throughout the length and breadth of the country, including tribal areas. Most of our health services are concentrated in urban areas. There is massive migration from tribal and rural regions for jobs. Most of these migrants stay in overcrowded housing and poor surroundings and serve as moving reservoirs of malaria.
In this poor field placement, surveillance, data collection, and reporting remain on paper only, as there are no staff to carry out these activities where they are most needed, i.e., the epicentre of malaria transmission—the tribal areas.
The one-line answer is “equitable distribution of health services to carry out all these important anti-malarial activities.”
A detailed presentation on the dynamics of malaria transmission in tribal regions can be accessed at the following link: https://youtu.be/QnzODElU0rs?si=bcIi75IP369fj6tJ
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Dr Amitav Banerjee was an epidemiologist in the Indian Armed Forces who investigated the dynamics of malaria transmission extensively in tribal and counter-insurgency areas during his military career and was awarded for his work in tribal malaria while in service. Presently, he is Professor Emeritus at Dr DY Patil Medical College, Hospital and Research Centre, Pune, and Editor-in-Chief of the Medical Journal of Dr DY Patil Vidyapeeth
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