Expert Speak Health Express
Published on Nov 10, 2016
Chikungunya is an example of what public health specialists call emerging or re-emerging infectious diseases in developing countries.
Chikungunya, dengue and emerging infectious diseases

Much has been written about threats to India’s security from across the border. But there is also another kind of threat to security — a threat that may not be immediately obvious but nevertheless can cause havoc in the long run. This is the threat of emerging infectious diseases.

In 2016, we saw the spread of chikungunya, a viral disease carried by the same mosquito that spreads dengue, as well as another virus in the news globally: zika. Dengue, chikungunya, zika and many others are example of what public health specialists call emerging/re-emerging infectious diseases — diseases that are either new to humans or new to a particular area or have emerged in that area after a long time.

Dengue epidemics are now common occurrences in India and indeed across Asia. The World Health Organisation estimates that there are 390 million dengue infections per year, of which 96 million manifest clinically. Dengue is not new; it was recorded in a Chinese encyclopedia of disease symptoms and remedies, first published during the Jin dynasty (265 to 420 AD) . Yet, before 1970, only nine countries had reported outbreaks of severe dengue. By 2014, however, severe outbreaks had been reported by over 100 countries.

According to one estimate published in 2014, the annual cost of direct medical care due to dengue in India is $521 million.

The chikungunya virus was first isolated from a patient with high fever in Tanzania in 1952-53. It is believed the word “chikungunya” is derived from the Swahili or Makonde word that means “to become contorted.” In some chikungunya patients, the pain can be so severe that they have a bent or stooping posture. The virus spread and outbreaks were recorded across Asia, including in India, where the last reported case was in 1973 in Barsi, Maharashtra. 

After that, there was a hiatus of more than 30 years till chikungunya was reported in 2006.  The 2006 outbreak affected more than 1.3 million people in 13 states, and according to research published by the Vector Control Research Centre, Puducherry, the national burden was 25,588 DALYs (Disability Adjusted Life Years, or years of “healthy” lives lost)  and a productivity loss of at least ₹391 million. The total burden due to the 2016 outbreak is not yet known. Chikungunya is now reported from over 60 countries and is growing as a major public health problem. 

The zika virus, which has not yet been reported in India, appears to closely follow the trend of chikungunya and dengue, according to an article published in Lancet last year. Till recently, human zika infections were only sporadically reported.  It has now spread across the world.

Approximately, a third of emerging infectious diseases are “vector-borne”, that is transmitted by a vector like a mosquito. Others could be viral or bacterial, and organisms resistant to drugs are also causing disease re-emergence.  Ebola in West Africa, MerS-CoV in the Middle East, influenza H7N9 in China, Nipah in South Asia, SARS in 2004, West Nile virus, Crimean-Congo Haemorrhagic Fever in Gujarat — the list of emerging or re-emerging diseases is extensive.

Even accounting for increased reporting, the number of emerging infectious diseases has increased substantially since the 1940s. We have more new diseases and are likely to have new diseases for which humans will not have immunity or adequate drugs.

A study in Nature in 2008 showed increased emerging infectious diseases were largely due to anthropogenic and demographic changes in the world. The rise in vector-borne diseases, including mosquito-borne diseases, has been shown to correspond to climate anomalies reported during the 1990s, such as severe weather, high temperatures and unusual rainfall. So it is possible that climate change is leading to an increase in these outbreaks.

Rapid population explosion and urbanisation also play a role, as it puts humans and vectors like mosquitoes in close proximity. Further, widespread construction due to urbanisation allows for an increasing number of breeding sites for mosquitoes like Aedes aegypti and Aedes albopictus, which transmit dengue, chikungunya and zika viruses.

Almost two third of emerging diseases that affect humans are from animals. Of these, the majority originate in wildlife. Understanding the factors that lead to an increase in contact between humans and animals is therefore important. Population growth and deforestation due to industrialisation and other reasons play a role in the emergence of new diseases. As forests are cut down, animals have no choice but to move to areas of human activity, leading to greater human-animal interaction.

For example, the cutting down of forests to build an international airport in Malaysia in the 1990s led to the devastating outbreak of Nipah virus disease, carried by forest bats that fled to agricultural land as their habitat was lost. Efforts to conserve rich wildlife diversity by decreasing human anthropogenic activity, on the other hand, are likely to reduce chances of a new disease emerging.

Agricultural practices can also play a part. For instance, many of the new influenza viruses that have emerged and infected human — such as AH5N1, popularly known as bird flu, and more recently A(H7N9) in China — were originally transmitted to humans from poultry.

The social impact of these diseases, particularly in developing countries, is enormous. In India, one medical emergency and consequent out-of-pocket expenses is all it could take to sink a lower middle class family back into poverty. And poor people, often the most under-nourished, are also more vulnerable to diseases.

Economically, the impact on a country is substantial. The loss of workers leads to loss of productivity, as even healthy workers stop going to work out of fear of the disease. In Sierra Leone, during the Ebola outbreak, healthy miners stopped going to diamond mines for fear of getting the disease. Drop in trade and tourism incurs heavy losses as well. During the SARS outbreak, China, Hong Kong, Singapore and Vietnam reported over $20 billion in lost GDP.

Tackling the enemy within is imperative. The first step is to know the enemy — creating a good surveillance system so that public health specialists know where the outbreak is occurring, how it’s spreading, and can make some predictions on its behaviour. Training of health workers is essential. It’s also important to ensure R&D to find ways to stop these diseases — including well-equipped laboratories. Finally, informing the public and making it an equal partner in these efforts is critical to ensuring success.

The author has worked in public health for fifteen years. She has a Ph.D in molecular biology from the University of London.

Gubler, D. (1998) Dengue and Dengue Hemorrhagic Fever, Clinical Microbiology Review 11 (3), 480-496 Shepard, D.S. et al (2014) Economic and Disease Burden of Dengue Illness in India Am J Trop Med Hyg. 2014 Dec 3; 91(6): 1235–1242. doi:  10.4269/ajtmh.14-0002 Padbidri VS, Gnaneswar TT. Epidemiological investigations of chikungunya epidemic at Barsi, Maharashtra State, India. J Hyg Epidemiol Microbiol Immunol. 1979;23:445–51. Lahatiya, C. and Pradhan, S.K. (2006) Emergence of chikungunya virus in Indian subcontinent after 32 years: a reviewJ Vect Borne Dis 43,151-160  Krishnamoorthy K et al (2009) Burden of chikungunya in India: estimates of disability adjusted life years (DALY) lost in 2006 epidemic J Vector Borne Dis 46, March 2009, pp. 26–35
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