Feature Tropical Disease

What can India do about dengue fever?

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f643 (Published 04 February 2013) Cite this as: BMJ 2013;346:f643
  1. Mohuya Chaudhuri, freelance journalist, New Delhi
  1. mohuya.chaudhuri{at}gmail.com

Each year India’s dengue epidemic gets worse, with almost 50 000 cases reported in 2012. Mohuya Chaudhuri gives some reasons

It has taken several outbreaks for the government of India to realise that dengue fever is a serious public health problem. Every year, without fail, this tropical infectious disease affects thousands of Indian lives.

In the past decade, according to the National Vector Borne Disease Control Programme (NVBDCP), the number of cases has escalated steadily from 3306 in 2001 to 47 209 in 2012. Deaths have risen from 53 in 2001 to 242 in 2012. However, these figures were collected only from government hospitals and not the private sector. Scott Halstead, adjunct professor in the department of preventive medicine and biometrics at the Uniformed Services University of the Health Sciences, Bethesda, has stated that India has an estimated 37 million cases of dengue, with 227 500 hospitalisations.

Last year’s outbreak saw a sharp rise in cases of dengue hemorrhagic fever and dengue shock syndrome along with regular dengue fever. Hospitals in Tamil Nadu, Kerala, Andhra Pradesh, Maharashtra, and Bengal, the states with most cases, found it hard to cope with the number of patients affected.1

Size of the problem

Several studies have examined the size of the problem and why dengue has spread so rapidly.2 3 4

The findings show that initial outbreaks, from the late 90s until the beginning of the millennium, were limited to urban areas. As cities and towns modernised in an unplanned fashion, construction sites became breeding grounds for the Aedes aegypti mosquito, the commonest vector for dengue in India.

Dengue is no longer restricted to urban centres, with outbreaks now occurring in rural India. Nearly every state in India, including isolated islands such as Andaman and Nicobar, now reports cases.

P Vijayachari, director of Regional Medical Research Centre (a government body that maps diseases among tribal groups) said, “Dengue [types] 1 and 2 have begun to circulate in these islands and now new genotypes are coming up. We are tracking them.”

P Jambulingam, director of the Indian government’s Vector Control Research Centre, Puducherry, who studies vector ecology and management, told the BMJ, “Dengue is being disseminated across the country so widely because people travel extensively. Migrant populations, which are the fulcrum of infrastructural and labour activities, often fuel the transmission of dengue.”

The weather

Epidemiologists tracking dengue say that one of the main reasons for the increase in cases is changing climate patterns. High rainfall, high levels of humidity, inadequate water storage facilities, and poor sanitation have led to an increased distribution and density of the Aedes population, increasing the risk of dengue in these areas.5

V M Katoch, secretary of the Department of Health Research and director general of the Indian Council for Medical Research (the government body that oversees health research in the country) said that a long drawn out monsoon with incessant rain two years ago triggered a massive epidemic in Delhi.

S Vivek Adhish, professor at the National Institute of Health and Family Welfare (NIHFW), who is researching the economic impact of dengue in India, agrees. He says “So far no surveillance has been done to identify these high risk spots where mosquitoes breed or [to identify] weather related triggers for outbreaks. A Delphi study is being planned to understand the scale of the epidemic. Without that, it is not possible to contain the epidemic.”

Health officials at the state level say it’s a struggle to manage the upsurge of cases. According to the NIHFW, dengue viral infections tend to become more virulent epidemic after epidemic. Four strains circulate in the country, with different strains circulating in endemic zones every year.6 Experts think that as the circulation of the virus continues to increase, so too might the severity of disease, as happened in last year’s outbreak.

Randeep Guleria, professor of medicine at the All India Institute of Medical Sciences, New Delhi, says: “Although the first infection is usually mild, the second time, the immunological reaction in the body is far more severe, causing dengue hemorrhagic fever or dengue shock syndrome. Since dengue infections do not provide natural immunity, repeated outbreaks are responsible for more severe outcomes.”

Public awareness

Despite government attempts to increase public awareness of dengue and despite the high visibility of the disease, community engagement has been less than adequate. In endemic areas, local authorities are meant to fumigate public spaces to reduce the mosquito population before the arrival of the monsoons, but often these steps are taken only after a spike in cases.

V P Sharma, former director of the National Institute Malaria Research, says, “Whatever measures the local administration tries to implement—like spraying mosquito repellents—there is a lot of resistance from families who don’t want their homes or plants sprayed. People don’t even monitor or clean the vessels where they store water.”

In urban slums, families store water in metal drums, plastic pots, and buckets because of its scarcity. The stored water stagnates for weeks, allowing mosquitoes to breed. Even in richer households, water may collect in flowerpots, bird baths, water coolers, and overhead tanks, but the receptacles are not regularly cleaned. In public spaces, open drainage systems, pools of rainwater, and festering garbage dumps also provide the ideal habitat for the mosquito.

The vector also seems to be changing. B K Tyagi, director of the Centre for Research in Medical Entomology, Madurai, says, “Earlier, Aedes aegypti was the only vector causing dengue fever. Today, it is competing with Aedes albopictus, a more vicious vector, which has emerged as a predominant vector, replacing Aedes aegypti. The reason why Aedes albopictus breeds in close proximity to human habitation is because of its anthropogenic nature. It prefers to breed inside homes. It is imperative to understand vector biology to carry out preventive measures.”

According to the senior officials of NVBDCP, the Aedes mosquito used to bite once only for its blood meal. New data show that the vector needs to feed several times, so an infected mosquito is likely to bite more than one person.

The biggest challenge posed by dengue viral infections is early detection and treatment. During the 2012 outbreak, which began in February and peaked in October, the government reported that 247 patients became critically ill in a short space of time. Their platelet counts dropped dangerously low, and blood banks were swamped with requests for platelets.

But increased awareness of the disease has led to more rational management of cases. People now seek treatment earlier in the course of the disease. Challenges, however, remain.

Tests

In government hospitals, doctors depend for diagnosis on antibody tests, that lack sensitivity until patients are five or six days into their illness. This delay can be costly for patients with severe disease.

Navin Khanna, group leader at the Recombinant Gene Products Laboratory, International Centre for Genetic Engineering and Biotechnology—an international research organisation set up by the United Nations International Development Organization—says, “It is imperative to detect the virus early to manage the disease better, so that mortality and morbidity rates can be cut substantially.”

He says that rapid tests, such as the non-structural protein test, are needed to identify the antigen in the first few days of infection. These tests help doctors to track new cases that would otherwise slip through the net, as well as enabling differential diagnosis.

Diagnostic tests for dengue virus are not readily available in most parts of the country. In rural India, the prevalence of dengue is unknown, because no surveys are done and no cases are reported. Critically ill patients have to be brought to cities for treatment.

The government has not yet implemented a robust mechanism for tackling the dengue epidemic. Since dengue is not a notifiable disease, the actual burden of disease is hard to estimate. The NVBDCP continues to rely on data provided by government hospitals. In India, however, the private sector caters for almost 80% of healthcare, but their data are not shared with the government.7

N K Ganguly, an adviser at the Translational Health Science and Technology Institute, says: “The government needs a major strategy to tackle the annual outbreaks of dengue. First of all, there is a need to reduce mosquito breeding by using biological measures like introducing Wolbachia, a bacterium, in the environment, that can control mosquito populations. It is now being pre-tested globally. Alongside, we need better clinical management and new diagnostics to prevent deaths. But most importantly, there is a need to develop a vaccine that is appropriate for the Indian serotypes.”

At the moment, however, all the system is doing is bracing itself for an even greater onslaught of dengue cases in the future.

Notes

Cite this as: BMJ 2013;346:f643

Footnotes

  • Views and Reviews, doi:10.1136/bmj.e8574
  • Competing interests: I have read and understood the BMJ Group policy on declaration of interests and have no relevant interests to declare.

  • Provenance and peer review: Commissioned; not externally peer reviewed.

References