High Security Animal Disease Laboratory,IVRI,Bhopal-462021(M.P.)

Zoonotic diseases represent one of the leading causes of illness and death from infectious disease. Worldwide, zoonotic diseases have a negative impact on commerce, travel, and economies. In most developing countries, zoonotic diseases are among those diseases of major public health significance and contribute significantly to an already overly burdened public health system. In industrialized nations, zoonotic diseases are of particular concern for at-risk groups such as the elderly, children, childbearing women, and immunocompromised individuals. The World Health Organization has defined zoonoses as, “diseases and infections naturally transmitted between nonhuman vertebrate animals and humans”, and emerging zoonotic disease as a "zoonosis that is newly recognized or newly evolved or that has occurred previously but shows an increase in incidence or expansion in geographical, host or vector range". However link between humans and animals with respect to diseases could be framed in many but slightly different ways. Strikingly, 75% of emerging infectious diseases have been identified as zoonotic in origin. Moreover if we could link the emergence of some diseases to animals, for e.g. AIDS then the number would be much higher. These agents have included some that maintain an ongoing reservoir life cycle in animals or arthropods, without the permanent establishment of a new life cycle in humans, as well as some “species jumpers” that derive from an ancient reservoir life cycle in animals but have subsequently established a new life cycle in humans that no longer involves an animal reservoir. Zoonotic diseases require rather different prevention and control strategies than diseases of etiologic agents employing only human-to-human transmission. Determinants discussed above have to be understood and dealt in proper perspective when it comes to the problem of zoonotic diseases. Different section of workers should collaborate their efforts against dreaded diseases, which are affecting mankind and animals and are continuously posing challenges. Multidisciplinary teams of ecologists, mammalogists, ornithologists, and entomologists, as well as physicians, epidemiologists, public health workers and veterinarians should join hands for intensive and sure success


Introduction
days and what are the factors for their emergence and re-emergence?. Both the developing and developed In recent years a number of new zoonoses have world has differences in their socio-economic status. emerged, in both developing and developed countries, Basically whole world could be divided into either and a number of known zoonoses have reemerged in following an agrarian or an industrialized setup. Both areas where they have been absent for decades or these kinds have different factors which will be dealt in have spread to animal species in which the pathogens following text to develop a basic understanding had not previously been detected.
behind the factors which affect the status of zoonotic The concept of emerging infectious diseases diseases. appeared in late 1980's, when major outbreaks Characteristics of the agrarian society that occurred around the globe and surprised many favours zoonotic transmission are mainly sharing same scientists who considered infectious diseases to be the environment with livestock, movement of animal maladies of past or limited to the under-developed population, limited human medical and veterinary world. However Charles Nicolle, in his book, "Infectious medical facilities, low literacy rate, poor Diseases Destiny" wrote more than half a century ago: sanitation/hygiene, environmental disaster/floods, "If human civilization persists, if it continues to develop earthquakes, civil unrest wars, AIDS epidemics and and expand, infectious diseases will increases in number in all regions of the earth".
other form of immunosuppression. This raises a question that why now emergence Characteristics of the industrialized society that of infectious diseases is a cause of great concern these favours zoonotic transmissions are mainly leisure time activities (camping, hunting), ownership of pets, Ecological factors usually precipitate emergence by suburban development intruding on indigenous animal placing people in contact with a natural reservoir or population, intensive animal production, human host for an infection hitherto unfamiliar but usually behavior, cultural trends and socio-economic already present, either by increasing proximity or, conditions. These are often as important as animal often, also by changing conditions so as to favor an related factors in determining zoonotic disease pattern increased population of the microbe or its natural host. in a community. As the role of animals in society Examples are of Japanese encephalitis closely changes, so does frequency of many zoonotic associated with rice field irrigation, creating large diseases. Centralized food processing and distribution bodies of stagnant water. Rift valley fever is associated system, AIDS and other immune-suppressive with dam construction and irrigation in heavily diseases also favours an aggravated sprung up of populated areas having naïve ruminant population. zoonotic diseases.
Proliferation of the rodent reservoir and phlebotome vector due to dam construction and agriculture Determinants in the Emergence of Zoonotic development has resulted in outbreak of cutaneous Disease Agentsleishmaniasis. Kyasanur forest disease, a tick borne Many different determinants act in a very complex way, encephalitis emerged due to grazing of deforestated with hard to predict results.
areas by cattle. The emergence of Lyme disease was 1) Human demographics and behavioral changesprobably due to largely to reforestation, which Human activities are the most potent factors increased the population of deer and the deer tick, the driving disease emergence. Due to changing sociovector of Lyme disease. The movement of people into economic conditions, human population has these areas placed a larger population in close interference in almost every sphere of nature.
proximity to the vector. Increased rodent population Urbanization leading to mass movement of rural due to ecological changes has resulted in outbreaks of population into cities has led to outbreaks of Lassa Hantavirus disease syndrome. fever due to increased rodent host in urban

3) Microbial changescommunities and of brucellosis. Population explosion
The concept of the microbe as the cause of leading to intrusion of human to new areas such as the disease is inadequate and incomplete. But they are one that occurred in South America where major among the most mutable determinants of changing outbreaks of vampire bat rabies occurred when people status and pattern of zoonotic changes. Microbe settled in remote jungles. Human mortality followed changes to unpredictable forms either due to selective discontinuation of pig raising project which were natural or man made factors. Genetic reassortments destroyed being a threat to the crops. This raised the are more common in world of viruses. This is very well bat population which started feeding humans as their exemplified with influenza in which new variants due to source of blood was destroyed. Increased population genetic drifts and shifts are causing worldwide density resulted in greater generation of suitable pandemics. Another disease agent, i.e. Western factors such as unhygienic condition due to lack of equine encephalitis virus is thought of been aroused proper management, as number of people surpasses from recombination of Sindbis-like virus and Eastern the infrastructure facilities and accumulation of water equine encephalitis. which provides feeding ground for vectors. Examples Selection for antibiotic-resistant bacteria and include outbreaks of Dengue fever due to increased drug-resistant parasites has become frequent, driven mosquito population and cryptosporidium due to by the wide and sometimes inappropriate use of contaminated surface water. Change in lifestyle of antimicrobial drugs in a variety of applications. people such as close contact with pets along with Pathogens can also acquire new antibiotic resistance introduction of new pet animals Examples include genes from other, often nonpathogenic, species in the outbreaks of Congo-Crimean hemorrhagic fever environment, selected or perhaps even driven by the following introduction of ostriches as game farming selection pressure of antibiotics. The food and farming animals, tuberculosis from deers, epidemic of industries increasingly use antimicrobial agents and chorio-lympho-meningitis in pet hamster owner, other types of drugs to boost the efficiency of foodiguana related salmonellosis, all with many other producing animals and to prevent certain troublesome factors contribute to spread of zoonotic agents. organisms from reaching consumers. Use of these 2) Ecological Changeschemicals probably enhances the proliferation of Changes due to agrarian or industrial antibiotic-resistant microbes. In this category resistant development are most important factors which have strains of salmonella and E.coli are causing a major resulted in modification of natural niches and ecosystems. Several devastating outbreaks could be threat in surrounding environment of poultry, piggery attributed to the effect of change in ecosystem. and calf industry.

4) Technology changes-
of the diseases as emerging infections. Some of the diseases of humans are being considered to evolve Technology is changing at a very fast pace. Food animal veterinarians and technologists over the past from other species of animals. The "zoonotic pool" i.e. 30 or 40 years have adapted to revolutionary changes, introductions of microbes from other species is an important and potentially rich source of emerging driven by economics and technology, in the structure of diseases, some of which might become successful if animal agriculture right from procurement of raw given the right conditions. The human immunodefi-material from across the globe to processing of food up till its distribution. These changes include increasingly ciency virus (HIV) is a likely example of a zoonotic larger herd sizes, intensive production management introduction meeting this criterion. This virus has a very systems, improvement of but simultaneous narrowing close resemblance with other primate's lentiviruses. of the animal gene pool, vertical integration, and Which among the other primate lentiviruses, including innovations of housing and physical facilities. The some not yet identified, might have the potential to resulting production efficiencies have yielded an enter the human population and emerge as yet another increase in global trade of animals and animal HIV? Another example is that of Hanta virus which was products. present in rat species but possible ecological alteration Food borne zoonoses are increasing day by day caused an outbreak in human. Bovine spongiform in both developed and developing countries. Mass food encephalopathy (BSE) appeared as, probable processing technology allowing contamination of meat interspecies transfer of scrapie from sheep to cattle. has resulted in outbreaks of hemolytic uremic Changes in rendering processes, allowing incomplete syndrome caused by E.Coli O157:H7 strain. A change inactivation of scrapie agent in sheep byproducts fed to in rendering process of animal feed for short term cattle, may have been responsible. In any case, the use monetary gains has led to dramatic spread of BSE.
of such byproducts was clearly instrumental in Africa many of the secondary cases were hospital 6) Improved research acquired, most transmitted to other patients through Some disease agents are widely prevalent and contaminated hypodermic apparatus and some to the were already present in some or the other form.
health care staff by contact. Transmission of Lassa Although recent advances in diagnostic technology fever to health care workers has also been can also lead to new recognition of agents that are documented. Xenotransplantation (the transfer of already widespread. Recent example is the bacterium organs or other tissues from animals to humans) is yet Helicobacter pylori, a probable cause of gastric ulcers another ongoing research which if not carefully and some cancers. We have lived with these diseases executed could pose serious risks. for a long time without knowing their cause. Bacillary References angiomatosis, infection known since 1983, the etiology was detected as Bartonella henselae in 1990.