One Earth, One Health, One Future

22 Sep, 2020

(Re) Emerging infectious disease outbreaks in India

By: Dibyendu Mandal, Technical Expert, GIZ

In January 2001 patients with high fever and altered sensorium (inability to think or concentrate) were admitted to hospitals in the town of Siliguri situated in the foothills of Northern West Bengal. The doctors initially suspected Japanese encephalitis, endemic to the area. But the disease primarily affects children. Subsequently, they checked for other diseases due to variations in the epidemiological features of the disease and the affected age groups. By 23 February 2001, 45 patients, mostly hospital staff or primary caregivers, had died due to this unknown disease with a very high case fatality rate of 74%. Available samples were collected and checked for Malaria, Dengue, and other bacterial diseases; West Nile Virus, and Hanta Virus. What unfolded next was the startling identification of the first Nipah virus (NiV) outbreak in India1. This disease re-emerged in India in 2007 in West Bengal and 2018 in the southern state of Kerala. The Kerala NiV outbreak and consequent state response to contain the epidemic was powerful enough to find its way into public discourse through the well-acclaimed 2019 Malayalam film ‘Virus’!

Forest Fragmentation in the Terai Arc landscape, India (Source: Google Earth Image)

NiV was first recognised in 1998-99 in Malaysia during a disease outbreak among pig farmers. Large fruit bats of the genus Pteropus are the natural reservoirs of NiV. The saliva of infected fruit bats in the half-eaten fruits or their faeces/urine transmitted the disease to pigs. Infected pigs passed on the disease to humans2. Yet the question remains: why and how does a virus present in bats suddenly emerge in humans? Pteropus is largely distributed in the tropics and sub-tropics of Asia, Australia, East Africa, and some islands in the Indian and Pacific Ocean. Habitat fragmentation and loss in these areas is leading to an ever-increasing interface primarily between animals and humans. This complex interplay between habitat loss, animals’ ecological need of resource-provisioning, animal husbandry, consumption and use of wildlife coupled with global trade is slowly bringing animals closer to humans, resulting in disease spill over. Half-eaten fruit with saliva consumed by humans may have transmitted the disease in Kerala where 19% of bats were found to be NiV positive around the house of the index patient3. In Malaysia, pigs transmitted the disease to humans. Animal husbandry practices especially larger farms also provide emerging pathogens a lot of intermediate animal hosts in one place to evolve and spread to humans. Avian influenza (H5N1) usually infected poultry animals and pigs, and was assumed as a non-human virus due to difference in receptors. However, changes in the virus and the emergence of novel Z strain caused infections in people in Vietnam in 20034. The 2009 H1N1 influenza virus (formerly referred to as swine flu) resulted from reassortment, where two or more influenza virus exchange genetic information by infecting a single host. In this case, reassortment occurred between influenza viruses present in North American and European pigs connected through international trade5.

Sars-Cov-1 and SARS-CoV-2 (or COVID 19) both have ecological origin in bats. There is limited contact of human with bats. It is likely that these diseases infect intermediate animal hosts which are more likely to be handled by humans and may cause outbreaks6. COVID 19 has also been reported in pangolins7 which are one of the most trafficked animals in the world. Their scales are used in traditional medicine and meat considered a delicacy8. In an ideal world, the interface of bats with pigs/ pangolin/ civet and human would have been difficult and unlikely. Poaching, illegal trade of wildlife, zoonotic disease spread, and consequent persecution of certain species are all aspects of human wildlife conflict. This phenomenon is not new and has been observed worldwide.

Civets were persecuted following the SARS outbreak in 2003 and bats have been blamed for disease outbreaks in the last two decades and also face persecution to their population. However, zoonotic diseases are emerging from several other animals which were not previously detected in humans. Over 30 new infectious diseases have been detected globally in the last four decades- 2/3rd of which were zoonotic in origin, i.e. passed on from animals to humans9. India has seen the outbreak of eight such emerging/re-emerging diseases, six of which were zoonotic, i.e. passed on from animals to humans. There are three major categories of emerging viral infections in India: respiratory viral infections, arboviral infections and bat-borne viral infections. Pandemic influenza, highly pathogenic avian influenza (AI) infection (H5N1) and the Middle East respiratory syndrome coronaviruses (MERS-CoV) are examples of respiratory viral infections. Dengue, chikungunya, Japanese encephalitis and Kyasanur forest disease (KFD) are arboviral infectious diseases. NiV, Ebola and COVID-19 are bat-borne diseases. Apart from these other pathogens such as bacteria (e.g. Bovine Tuberculosis and Brucellosis), fungi, and protozoa cause human diseases.

Photo source: Pexels, Karolina Grabowska

Yet the challenge remains: how can we prevent these emerging and re-emerging disease outbreaks? Many experts are supporting the idea of One Health. One Health is "the collaborative efforts of multiple disciplines working locally, nationally, and globally, to attain optimal health for people, animals and our environment", as defined by the One Health Initiative Task Force (OHITF) formed by the American Initiative10. It is an effective way to fight health issues at the human-animal-environment interface, including zoonotic diseases. In 2012, a wildlife sanctuary staff trained in wildlife disease surveillance program discovered six dead howler monkeys near the park in Bolivia. Post-mortem and diagnostic tests indicated flavivirus infection (which causes Yellow Fever). Flavivirus are arbovirus and primarily transmitted by infected arthropod such as a mosquito and tick and causes fever in non-human primates. Although, yellow fever was never detected in Bolivian primates, authorities were able to implement preventive measures such as YF human vaccination, public education and outreach, mosquito control to reduce infection risk in surrounding areas rapidly. Consequently, no human mortality has been reported from Bolivia indicating the importance of disease surveillance programme and early warning11. Rwanda and Tanzania launched National One Health Strategic Plan recently. It helped National One Health Steering committee of Rwanda to implement timely response during the avian influenza outbreak in neighbouring Uganda in 201711.

India sustains nearly 18% of the global human population in just 2.4% of the global landmass12. Human density in India (382/km2) is much higher than other parts of the world. Infectious diseases spread quickly in densely populated areas which creates the need for an integrated approach to manage such a situation, like One Health. India also supports tremendous biodiversity in its forests. But these forests are small and fragmented due to human settlements inside forested areas and the periphery; often dissected by linear infrastructure. As a result, a growing number of people and livestock now live in proximity to wildlife. There is a growing need to map such areas with high risks of spill overs. While forest fragmentation has been well documented in India, there is limited research on diseases in wild animals, livestock, and the transmission risk from wild animals to livestock. Most Indian livestock is reared without adequate veterinary care, and wild animal health receives lesser attention due to fewer veterinarians entering in the field of wildlife. Many reserves in India lack veterinary experts or the appropriate infrastructure for disease surveillance programmes.

©GIZ/Nakul Jain

The mapping of disease transmission risk for Nipah Virus in South and Southeast Asia by Deka and Morshed (2018) was successful in predicting the outbreak in Southern India even before the outbreak event occurred13. Though the article was published days before the actual outbreak and the concerned authorities could not act in time, it definitely shows the potential of such modelling in predicting and preparing the local authorities across the suspected distribution range to either have a preventive strategy or quick response plan in place in case of future outbreaks.

Though the 2005 H5N1 influenza outbreak in India led to the conceptualisation of multisectoral linkages between human, animal and wildlife health sectors to combat the problem, the scope of these coordination mechanisms remains limited and have not been extended to cover the wider sets of issues emerging at the human-animal-wildlife interface. Several zoonotic disease events occurring in India such as Rabies, Crimean-Congo Haemorrhagic Fever, Nipah Viral Encephalitis, and Zika Viral Disease are yet to be addressed with an intersectoral coordinated effort. Further, with the absence of a national One Health strategy in India, there is also a likelihood in duplication of efforts and inefficient utilisation of funds and resources in one health research and implementation. There are over 300 institutions across different streams, engaged in epidemiological research on zoonotic infections in India. For example, the National Centre for Disease Control (NCDC) which comes under Ministry of Health & Family Welfare, Government of India issues a detailed weekly outbreak report and a monthly (human) disease alert for over a decade now. Department of Animal Husbandry and Dairying has a Livestock Health and Disease Control Division which looks after diseases in livestock and poultry animals in the country. ICAR-Indian Veterinary Research Institute supports disease diagnosis, critical healthcare services, and disease surveillance for both captive and wild animals. National Institute of Virology (NIV) has expertise and specialised labs to run diagnostic tests.

On a positive note, the Indian Council of Medical Research (ICMR) has started discussions around setting up of a Centre for Zoonoses Research, in partnership with the Indian Council of Agricultural Research (ICAR). A One Health Initiative was launched on February 18, 2019 at the “One Health India Conference”14. While the initiative aims in bringing Indian as well as global expertise in dealing with such threats, it also envisages to provide a platform for governmental, public and private sectors to integrate knowledge and identify needs and opportunities to better coordinate the One Health activities in India.

Currently lack of training, manpower at the field level, and inter-departmental coordination may hinder detection, early warning, and response. The newly formed One Health Initiative of India may be operationalised for better coordination among different departments, training, and overall response mechanism. India needs to urgently formulate an effective national One Health action plan and strategy to contain zoonotic disease at its source and invest substantially to establish regional centres for disease surveillance, map disease risk zones; and train a pool of doctors, veterinary experts and ecologists to work on it.


The views expressed in this post are purely those of the author.



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