The six-legged enemy

Malaria control in India is seriously affected by the fact that the knowledge once gained through painstaking research and fieldwork by entomologists is ignored.

Published : Sep 14, 2016 12:30 IST

A municipal employee spraying insecticide to repel mosquitoes, at a  slum  in Mumbai on February 17.

A municipal employee spraying insecticide to repel mosquitoes, at a slum in Mumbai on February 17.

THAT malaria persists even now in many pockets of India is no news. This is in spite of the best efforts of the government. The history of scientific malaria control dates back to 1898, when Ronald Ross in India demonstrated the role of mosquitoes in the transmission of the disease. This had led to a situation requiring the elimination of all mosquitoes. Intense studies on the habits and habitats of the vectors became necessary so that the weak points in their biology could be identified and appropriate measures taken to reduce their numbers. Though, as is well known, very spectacular success attended the efforts of William Gorgas and others in Panama, where in addition to the control of yellow fever they also undertook the control of malaria, it was at a very heavy cost. Attacking all mosquitoes was impossible, so a principle known as “species sanitation” was applied: attacks were launched only on the particular species of anopheles, which was the vector. This required the knowledge of the mosquitoes themselves, their habits and behaviour—an entomologist’s job. Also, what was required was not the complete elimination of mosquitoes but a reduction of their numbers below a certain level, now known as “critical density”, propounded by Ross.

Paul F. Russell and T. Ramachandra Rao (1942) were able to give a clear demonstration of the validity of the concept of “critical density” of the vector A. culicifacies . Many studies were made on the control of vectors, including on-source reduction. Efforts to control larvae with chemical larvicides such as Paris green and oil and by naturalistic and biological methods, including the use of Gambusia fish yielded mixed results. Malaria did not pose a major problem in cities but was difficult to control in rural areas. Then, in 1938, the “spray-killing” technique, using pyrethrum against the adults of Anopheles culicifacies , was demonstrated by Russell and Rao in Pattukottai, Tamil Nadu, with excellent results. But the method had discouraging results when applied against the vector A. fluviatilis . A. fluviatilis , though an efficient vector, rested out of doors in substantial numbers. DDT appeared on the scene at that time and revolutionised malaria control.

Success with DDT

In 1946, one of the largest malaria-control projects in the rural tropics, attempting to protect over one million people, was launched in North Kanara (Uttara Kannada) and Dharwad districts in Karnataka with remarkable success.

The subsequent history of malaria control all over the world, including India, has been described by several authors. It may be mentioned that the use of DDT (and similar insecticides) became the sole method of malaria control in India. Spectacular results followed in controlling practically all known vectors. The incidence of malaria came down in this country from about an estimated 75 million cases prior to the use of DDT to fewer than 2,00,000 cases in 1965. The battle against malaria seemed to have been won.

The usefulness of DDT prompted the launch of the National Malaria Control Programme (NMCP) in 1953. By 1958, the malaria-control programme had been extended to protect at least 165 million people from the disease. The programme had a tremendous impact, and the annual number of cases came down to 49,151 by 1961. The programme was renamed the National Malaria Eradication Programme (NMEP) in 1958 by A.P. Ray, a great malariologist, and it was believed that malaria could be eradicated in seven to nine years.

Soon, however, complacency set in, and malaria cases started appearing in increasing numbers in various parts of the country, crossing one million in 1965. Among several problems of an operational nature, one was that mosquitoes became resistant to the two commonly used insecticides, DDT and BHC. Unfortunately, all other methods of controlling malaria had by then been totally neglected as they did not seem to be necessary at all. Malaria research came practically to a standstill. There did not seem to be any more need for Indian Journal of Malariology , one of the foremost journals in the world, and it stopped publication. The history after 1965 is now well known. The number of cases detected rose steadily to over six million in 1976 and to 10 million in 1977. The modified Plan of Operations was then started, and the incidence rate stabilised at two million by 1985.

However, many focal outbreaks, particularly of Plasmodium falciparum malaria, and deaths from malaria occurred throughout India from the 1990s, and large-scale epidemics were also reported from eastern India and western Rajasthan from 1994. Many of these were related to irrigation projects. In 2004, the integrated National Vector Borne Disease Control Programme (NVBDCP) for the prevention and control of vector-borne diseases such as malaria, dengue, lymphatic filariasis, kala-azar and Japanese encephalitis was launched. It has since been changed to Enhanced Vector Borne Disease Control Programme (EVBDCP), with the World Bank’s support.

One should be aware of the true state of affairs. The statistics dished out by the official channels have to be taken with a large pinch of salt. This is what the World Malaria Report, December 9, 2014, London, states: “As many as 111 crore Indians are at risk of getting infected with malaria, and 28 crore have been found to be at the highest risk. The World Health Organisation said India had 12.8 crore suspected malaria cases. However, India recorded 8.81 lakh confirmed cases. This means that only 7 per cent of malaria cases are being confirmed in the country. A report in a leading daily, The Hindu , highlighted the main reasons: ‘Threadbare and chronically understaffed clinics often turn sick patients away or refer them to overcrowded district hospitals. Mosquito nets and pesticide sprays are seldom deployed on time or in sufficient quantities. Overworked laboratory technicians race to keep up with unexamined stacks of blood tests for malaria in public health laboratories. The country also faced a shortage of anti-malarial drugs in 2014, and a longer shortage of life-saving mosquito nets—both apparent during our field visits. Meanwhile, we learned that government officials responsible for the programme succumbed to a culture of fear, afraid to report poor progress to their supervisors.’”

“Why does under-reporting happen? A very simple reason: wanting to please your bosses,” said V.P. Sharma, a former director of the National Institute of Malaria Research who received the Padma Bhushan for his ground-breaking work on the disease. He passed away in October 2015.

The epidemiology of malaria is quite complex. The malaria parasite, the mosquito, man and his environment are all intimately interwoven. Involved in it are four species of human plasmodia with very different biology, numerous vector anophelines, each with its own peculiar bionomics and ecology, and man himself, varying in his social habits and his susceptibility to the disease, and finally the environment with an infinite variety of features. It was therefore a most remarkable accomplishment that one single method, the use of indoor residual sprays of DDT, was able to circumvent all the intricacies of the epidemiology. By simply reducing the length of the life of the vector, it nearly eradicated the disease.

I do not think we need any more reasons to emphasise at this time the importance of entomologists. Vector control is impossible without entomologists. Major successes in the fight against vector-transmitted diseases like malaria, Japanese encephalitis, filariasis, dengue and chikungunya have been achieved because of efforts aimed at killing mosquitoes. In the push towards control of these diseases, we need to get smarter in the way we wage war against our six-legged enemy.

In earlier times, entomologists, a dying or dead breed in India, spent hundreds—if not thousands—of hours trekking through muddy villages, inspecting watery holes for young mosquito larvae, and collecting mosquitoes resting on walls of huts or among bushes in forests. Such fieldwork-oriented experts are no longer available. Essential information on mosquito behaviour and knowledge of which anti-mosquito tools to use where and at what time can be obtained only by an entomologist. It can be a matter of choosing a tool that will have high impact or no impact, a decision that can amount to millions of dollars and thousands of lives.

As a belated recognition, the Malaria Policy Advisory Committee of the WHO, in September 2013, urged all “countries to ensure the presence of a functional intersectoral coordination mechanism with a subcommittee for capacity building, responsible for developing a long range strategic plan for building human resources and systems for public health entomology and vector control including malaria; to start in-service training programmes to ensure that public health entomology and vector control (including epidemiology and management) is included in curricula and educational activities; to ensure that posts and career development and structures for entomology and vector control experts are established at national and sub national levels within ministries of health or other appropriate government structures; to establish institutional arrangements among universities, training and research institutions and the national malaria control programme to support ongoing training and support for entomologists and vector control experts”. The development of a cadre of individuals with entomological skills, as well as corresponding infrastructure to support them, has been especially neglected; and potential entomologists have few opportunities for training and generally poor prospects for employment once trained.

But these important recommendations are yet to be followed up and implemented, particularly in India. There is thus a dire shortage of entomologists. India at present has a small number of experienced and expert entomologists. Their services are not used by the authorities since the system is dominated by medical people. The country has no entomology programmes at the undergraduate/university level these days, though some medical/public health entomology courses have been started by some institutes in recent times. But, since the degree is awarded by a university, restrictions have been placed on the syllabi, making the course itself more or less useless for work in the field. The net result is that only a limited few of those who take these courses are utilised by the programme. Specialising at a higher level is impossible without guidance from experienced mentors, of whom there are precious few.

Vector-control efforts should be directed towards improved entomological surveillance for more efficient and well-monitored vector-control operations. One must be able to forecast an epidemic like Japanese encephalitis or a flare-up of malaria in an area previously unaffected by it through constant surveillance that can tell whether a mosquito population is about to reach the threshold density. Programmes must adapt to the emerging threat of insecticide resistance in cases of outdoor and early vector biting and to shifting transmission patterns brought about by changing ecologies owing to deforestation, agricultural and infrastructural development and urbanisation. All vector-borne disease control programmes, as they move from control towards elimination, need robust mosquito surveillance in order to ensure cost-effective use of resources and interventions. Entomological surveillance and a clear understanding of the local transmission ecology are critical for reducing receptivity and preventing the reintroduction of transmission in areas where malaria has been eliminated.

There are many newly emerging vector-borne diseases in the country that are not receiving adequate attention. There are many neglected tropical vector-borne diseases such as scrub typhus and Kyasanur Forest disease that are ignored by the medically dominated disease-control programmes. There is panic only when an epidemic with disastrous consequences occurs. High-power meetings are held and enormous funds are sanctioned. If 10 per cent of the knowledge already available is applied in time, epidemics can be prevented.

Disease surveillance Another important aspect is disease surveillance. There was a report in March from Swaziland in Africa, which was once highly malarious but where malaria is now totally eradicated. What distinguishes Swaziland the most is its surveillance mechanisms. These include “active case detection”, which sends officers to the site of every new case to test everyone living in the vicinity of patient zero. This is crucial because communities in which malaria thrives tend to be isolated and inhabitants often develop resistance, meaning they have few symptoms and are unlikely to go to a hospital. Surveillance is thus the key word, whether it is malaria, yellow fever or zika.

Waste of resources

Many African countries are doing much better work than India, whether it is malaria control or virus isolation. Resources are now wasted through inappropriate or ineffective measures such as using an insecticide for indoor residual spray where there is resistance, investing in larvicide where there is no evidence of impact or in LLINs (long-lasting insecticide-impregnated nets) where many tribal people just do not sleep under nets, and in using indoor residual sprays where there is very limited or no transmission. Newer drugs are advocated, but how do you ensure that the drugs are taken by the patients? There has also been wrong diagnosis of malaria cases as dengue. There must be a vast improvement in the operations, particularly in remote areas. One can say that, even though malaria is still occurring in most parts of India, though in pockets in most places, it is now a forgotten disease. Other diseases such as dengue, chikungunya and now zika have claimed the attention of research workers and operational people.

It is over a century now since Dr William Gorgas wiped out yellow fever in Havana and Panama, and thereby in an entire continent, and more than half a century since Fred Soper led the eradication of anopheles gambiae in north-east Brazil. Their names are little known, their boots-on-the-ground methods, which they described in detail, are not read. The mistakes they warned of and the assumptions that they discovered to be useless and ineffectual in the field against disease-bearing mosquitoes are repeated today. What they found to be effective and efficient in real-life conditions are routinely ignored and avoidable errors are repeated.

In the battle against malaria, to be ignorant of Gorgas’ and Soper’s work is to be hobbled by the lack of hard-earned field knowledge and the practical and effective discoveries they made, which remain completely relevant.

Where malaria eradication is concerned, Soper underlined the achievements in terms of populations protected from the disease, discussed the epidemiology of disappearing malaria, underlined the successes of certain countries, but regretted the failures of surveillance activities in others (such as India?).

I would like to end this write-up by quoting from what the late Dr Wilbur Downs, a great malariologist and virologist, said at a Fred Soper Memorial Lecture a few decades ago. These views hold good even today. Our researchers should take a look at this.

“Over 40 years, including the decades of the malaria eradication efforts, I have seen how discussions of what to do with immediate local epidemiological problems of malaria have been tabled and projects denied funding. Only when some particular eradication project has encountered heavy going has any work gone on to find why. Meanwhile projects relating to new drugs, enhancement of immunity by vaccines, genetic studies of parasites, hosts and vectors, and new insecticides have gone on apace. These latter studies are fascinating. They are the new scientific approach. They are also illusory. They deflect attention from the here and now. The ‘here and now’ is that today there are millions of villagers in thousands of villages for whom the application of knowledge and means already at hand—an adequate supply of antimalarial drugs, simple control procedures carried out on the local problem, and differentiation of malaria from other diseases—is still awaited. Yesterday came and went. Today comes and goes. Tomorrow will come and go. Malaria remains unshaken.”

Dr P.K. Rajagopalan is former Director, Vector Control Research Centre, Puducherry, an institute of the Indian Council of Medical Research.

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