Dr. Wahied Khawar Balwan
Emerging and re-emerging diseases are on rising trend and have been threats to humans till date. Most of the emerging and re-emerging diseases noted since past three decades are of zoonotic nature, particularly of viral origin. The effects of these diseases have recently been emphasized by notable outbreaks as of those involving SARS-Cov2 (COVID-19), Nipah, Avian Influenza (H5N1), Swine Influenza (H1N1), West-Nile Fever, Ebola, Zika etc. Globally, the world of animals, humans and environment is interwined giving rise to number of benefits but also favouring for the spread of zoonotic diseases. According to the World Health Organization (WHO), zoonotic diseases (ZD) or zoonoses are defined as those diseases and infections, which are naturally transmissible between vertebrate animals and man. These diseases are fundamental determinants of community health because they cause major social and demographic changes with heavy burden of illness. As of now 58% (816) of human pathogens (1477) are zoonotic in nature which includes 208 viruses, 538 bacteria and rickettsia, 317 fungi, 287 helminths, and 57 protozoa .Outbreaks of emerging and re-emerging infectious diseases have surfaced in recent decades. Interestingly, all these outbreaks till date are likely to be zoonotic, particularly viral in origin. A study report revealed that 73% (130) of the total emerging pathogens were classified as zoonoses. Emerging zoonoses are defined as zoonotic diseases that are caused by either new etiological agents or previously recognized agents appearing in new places or in unsusceptible populations or in species which was previously unknown. These diseases have shown an increase in expansion geographically, host or vector range and pose a threat to public health and national economies. One of the recent example of emerging zoonoses is ongoing pandemic caused by SARS-CoV-2 (Covid-19) which has spread over 212 UN countries resulting in 4 crore human cases and 11 lakh deaths worldwide. Apart from this, there are many other notable outbreaks ofemerging zoonoses like Nipah virus, Crimean Congo hemorrhagic fever, Ebola virus, Zika virus, pandemic H1N1, H5N1 bird flu, severe acute respiratory syndrome corona virus (SARS- CoV), middle East respiratory syndrome corona virus (MERS-Cov) etc. Re-emerging zoonoses are referred to as diseases which are previously known and managed to a level that do not cause near danger but shows increase of infection and trend because of its reversal in due course of time. An example of re-emerging zoonosis is tuberculosis because of its association with HIV/ AIDS & drug resistant tuberculosis with other notable diseases are of Influenza pandemics of 1918, 1957, 1968, leptospirosis, plague etc. There are many factors involved in emergence of these zoonotic diseases but it is true to believe that favourable conditions for these diseases are due to complex interaction of rapidly evolving infectious agents, changes in environment and hosts. This article will give a fair view of transmission of pathogens, factors responsible for the emerging and re-emerging zoonoses with selected examples and a multidisciplinary approach to control these complex threats.
Transmission of zoonoses may be direct or indirect in nature. In both the cases, infected animals and contaminated materials are primary sources for transmission. Direct physical and sexual contact (brucellosis), air-borne transmission by droplets or droplet nuclei of infectious agents generated while sneezing or coughing (tuberculosis), bites or scratches by infected animals (rabies) and contact with contaminated materials (anthrax) are major pathways of direct transmission. Overcrowding, close proximity and poor ventilation will enhance spread of infectious pathogen particularly through air borne. On the other hand, indirect transmission includes intermediate vectors which are either animate (mosquito, ticks, fleas, lice) or inanimate objects (contaminated soil, surgical instruments etc.), air borne by infectious droplets in air (influenza) and vehicle borne through non-living things or substances such as food, water, blood, body fluids etc. Transmission by an arthropod vector between animals to human or human to human has been ranked as 1st for emerging zoonoses. Surprisingly, a study report revealed that 60% emerging pathogens are zoonotic in nature and of these pathogens more than 71% have a wildlife origins. We tried to depict the spill over of Nipah virus from bats to pigs and human being because of deforestation.
There are many causal factors which influence the dynamics associated with emergence and re-emergence of pathogens or zoonoses. These factors are complicated which include infectious origin, environmental, human and social factors namely:
1. Internal factors responsible for emergenceadaptation of the pathogen like the main strategies of viruses for genetic evolution and adaption are genetic reassortment, genetic recombination and mutations. These are mainly responsible for viruses to multiply, survive and also for their adaptation in respective hosts. A classical example of emerging and re-emerging zonoses by effect of genetic reassortment are outbreaks of Influenza A virus i.e. bird flu (H5N1) and swine flu (H1N1).The corona viruses also uses recombination and mutations as a strategy of evolving.
2. External factors include human factors such as population growth, urbanization, population movements, economic development, international travel and tourism, hunting, butchering, agricultural expansion, livestock production and trade, food production chain at global level, unsafe medical practices, breakdown of public health measures and social factors such as sexual behaviour, intravenous drug abuse, food habits, religious beliefs, war, inequality, poverty, war and bio-terroristic activities.
What Needs to be done?
The control of emerging zoonotic disease is hampered by lack of understanding the dynamics of their transmission. In addition to this, there are many gaps in understanding the role of animals in disease emergence because most of the times measures are taken against clinical cases of disease but not reservoirs. Therefore, thefundamental concept in prevention and control of diseases at the weakest link in chain of transmission are controlling the reservoir (animals), breaking the routes of transmission and immunization of susceptible hosts. Special policies and regulations are needed to be developed to focus on wild animal’s research because most of the emerged pathogens are due to unexpected spill over from wildlife. Food safety programmes like “farm to plate” to examine zoonotic diseases from environment to human are needed to be encouraged. Eventhough most of emerging diseases are of animal origin, research on human health and animal health are considered as independent disciplines. Therefore a strategy to predict, prevent and manage emerging zoonoses by developing a multidisciplinary, transboundary approach like “One Health” involving animal, human and environmental professionals has to be developed in order to address these complex human threats
Emerging and re-emerging zoonoses have surfaced over last two decades and became a part of constantly changing world causing unpredictable complications, increasing demand on national economies, health services. This is due to adaptation of agent to any circumstances, disturbances in environment due to increased human activities. Pandemics like COVID-19, SARS, Swine flu and Bird flu etc., clearly tells us the complexity of emerging diseases and their transmission. It could be said that in future many pandemics linked to zoonotic diseases will occur if proper emphasis on disease surveillance, intersectoral and interdisciplinary approaches like one health.
‘Any error in this manuscript is silent testimony of the fact that it was a human effort’
Dr. Wahied Khawar Balwan
Sr. Assistant Professor
Department of Zoology
Govt. Degree (PG) College Bhaderwah, J & K
Mob. No.: 9419369557
E-mail: [email protected]