Endemic, emerging and re-emerging zoonotic diseases: The way forward!

As per the Second Report of the Joint World Health Organisation (WHO)/Food and Agricultural Organisation Expert Committee on Zoonoses, zoonotic diseases (zoonoses) are those diseases and infections, which are naturally transmitted between vertebrate animals and humans.^[1] Zoonotic disease transmission may occur directly or indirectly by means of vectors. Three classes of zoonoses are described in the WHO South-East Asia region.^[2] These include zoonoses that are present in many places and affect many people and animals (endemic zoonoses), zoonoses that are sporadic in temporal and spatial distribution (epidemic zoonoses) and zoonoses that are newly appearing in a population or have existed previously but are rapidly increasing in incidence or geographical range (emerging and re-emerging zoonoses).

Emerging zoonoses are ancient diseases that have been ‘forgotten’ and considered to be under control or extinct from a particular region or population and present with a new appearance. Their emergence is related to free-living wild animals and is driven by socio-economic, environmental and ecological factors. It is estimated that, of the 1400 species of infectious disease pathogens of humans, nearly 60% are derived from animal sources.^[3,4] Further, it is estimated that world over, about one billion cases of disease and millions of deaths occur annually from zoonoses, close to 60% of globally reported emerging infectious diseases; 75% of over 30 new human pathogens detected in the past three decades have originated in animals.^[5]

Due to several factors such as lack of awareness, misdiagnosis, insufficient laboratory diagnostic facilities and underreporting, the exact burden of zoonoses is difficult to estimate. Zoonotic diseases mainly affect the poor and marginalised populations that lack access to health services. While some of these zoonoses start in wildlife in remote areas, these diseases often move fast around the globe due to the rapid and frequent movement of people and animals and food products involved in transmission constantly crossing the international borders. Thus, as the world is increasingly interconnected, it is not surprising that zoonoses are encountered globally transcending the natural boundaries. Zoonotic diseases, therefore, have a potentially devastating impact with severe economic consequences for the countries across the globe through loss of trade, tourism and consumer confidence.

Several daunting organisational challenges exist in the control of zoonotic diseases, and these are influenced by social, economic, geographical and political forces. Beyond these, obstacles such as lack of integration between medical and veterinary researchers for the exchange of epidemiological and laboratory surveillance data of human health, non-existent disease surveillance systems and inadequate laboratory diagnostic capacity for diagnosis of zoonotic infections constitute important deterrents. Furthermore, hassles involved in the international transfer of samples, cross-border collaboration, surveillance information exchange and inadequate community involvement have impacted zoonotic control programmes. Public health policies and programmes apart, there is a need for sensitising clinicians regarding zoonotic diseases. Setting up and strengthening the laboratory network for their early rapid diagnosis, is of paramount importance for providing rational and scientific care to patients afflicted with zoonoses.

As per the analysis of the National Centre for Disease Control (NCDC), Directorate General of Health Services, Ministry of Health and Family Welfare and Government of India, 75% of emerging and re-emerging infections are due to zoonotic in nature.^[6] Since India has a vector, susceptible host and conducive environment for disease transmission, the country faces a potential threat from diseases such as yellow fever, severe acute respiratory syndrome, Hantavirus, Rift valley fever, Ebola and Marburg virus disease. Sensing the importance of the threat constituted by zoonotic diseases, the Government of India has adopted the ‘One Health’ approach, which provides an opportunity to the various stakeholders to identify their roles and responsibilities to address their challenges and prevent and control zoonotic diseases. The constitution of the District-Level and State-Level Zoonosis Committee is an important step in this direction to view the emerging threats with the ‘One Health’ vision and calls for a joint response from all stakeholders such as medical, veterinary and wildlife and environment sectors, including the formation of a District-Level Rapid Response Team. This cooperation and coordination are expected to channelise the efforts that to date have been occurring in silos into a unified approach.

A scheme on ‘strengthening of inter-sectoral coordination for prevention and control of zoonotic diseases’ was approved in the 12^th 5-year plan during 2012-13–2016-17 and is still continuing under the umbrella scheme of the NCDC.^[7] The main objectives of the program include establishing an inter-sectoral coordination at the national-, state- and district-level through Integrated Disease Surveillance Programme, sharing of necessary information among various sectors. Other objectives include laboratory capacity building, generating trained workforce and spreading awareness about the various important zoonotic diseases for early detection of zoonotic disease outbreaks at the earliest and institution of preventive measures to curtail their spread.

Zoonotic diseases still present researchers and clinicians with several challenges. Understanding of pathogenic mechanisms, development of point-of-care diagnostic tests for use in the field, available and affordable confirmatory molecular diagnostic tools, identification of biomarkers markers for disease severity, progression and treatment response and development of improved treatment regimens and vaccines for these zoonotic diseases are the tasks ahead.