Transfer of animal cells, tissues or organs to humans is called Xenotransplantation. Which is likely to be a reality in the immediate future. The two important consequences of this would be (a) the transfer of Zoonotic agents present as silent/quiescent infection in the donor animal to a recipient made, (b) once the physical barrier between the two species is breached, establishment of a new infection results. WHO is concerned about this and is developing guidelines.
Breeding transgenic pigs provide a promising solution to acute and hyperacute Xeongraft rejection. Such pigs have been bred in which human complement-modulating protiens are expressed. Transplanted pig heart from CD55 transgenic pigs have survived 40 days.
However, the transgenic animals will be expressing human genes that serve as virus receptors. Also this might permit related porcine viruses to become pre-adapted for human in fections. Therefore veterinariens are expected to do screening of animals to be used for xenograft for known pathogens and aplly methods of raising germ-free animals, such as surgical delivery, isolation, raising in germ-free conditions.
EMERGENCE OF NEWER ZOONOSES
the population is facing the onslaughts of the environmental abuses. Exposure to pesticides and mycotoxins is affecting the natural defence mechanism of human system. Added to this is the increasing number of cases of Acquired Immunodeficiency Disease which is pandemic. The cases of cancers and surgical transplants are also on the increase. They are administered heavy doses of immunosuppressive drugs. Thus a considerable population is made immunocompromised naturally which presents a fertile soil for both relatively innocuous and infectious microorganisms.
Persistence of agents in the infected:
Persistence of agents in the infected individuals create problems for the population. They may continue to be symptomless shedder of infectious agents. Mechanism of persistence/latency is a challenging area of research. There are three implications of such latency.
Identification of an infected host/reservoir who do not manifest any clinical signs and symptoms of infection.
Abatement of symptoms and clinical recovery often satisfy the patient and the physician. The concerned individual, nevertheless continues to harbour the infective agents.
rapid industrial and technological advancements introduce new systems which have not been tested comprehensively for their consequential effects. The emergence of new variant of Creutzfeld Jacob Disease due to consumption of beef from mad cows is related to introduction of new technology for rendering offal.
Revelations of new reservoirs, vectors, agents and circumstances favoring infections add to the existing problems which stil continue as endemic and inadequtely attended. Outdoor defecation played a significant role in the transmission in human zones. Pigs, donkeys, black rats have been added in the list of dometic reservoirs.
Mechanics to evade containment measures
the agents adopt various mechanisms to evade the containment measures. e.g., drug resistence to evade chemotherapy. This and feding of drugs to meat food animals have created important zoonotic problems difficult to control. e.g., Multiple drug resistence tuberculosis, salmonellosis. Similarly infectious agents enter worms or parasites, pass through the metamorphic development cycle of these and thus evade the control measures directed to the reservoir hosts and known infectious stages of the vectors.
Agents crossing species barrier
The problem associated with the agents which cross over the species barrier is the example. Ebola, Marburg and Lassa viruses cause serious diseases in human beings. Recently examples of crossing over the species barrier by the infectious agents to human have come to light.
Wiess, magre and Takeuchi(2000) have mentioned that including Nipah virus, other dangerous strains of virus have been discovered during the last three years. Also new species of Mycobacterium affecting human beings have been recognized.
Infectious agents naturally maintained in vertebrates other than man often get detected on being translocated with their natural reservoir to a different environment.
Newer and serious pathological conditions not known earlier caused by zonnotic infections call for concerted efforts to contain such zoonoses.
Currently infections with viruses, bacteria and vaccination against Rabies and Swine Influenza precede GBS.
Zoonoses in hospital environment is a challenging area of epidemiology. The source of infection may be located in the immediate environment of the recipient(a patient admitted for a disease). Transmissions may be by direct/indirect contact or aerosol. The source could be located at a remote place and infectious agent is brought with he visitor or nurse who may be acting as a biological or paratenic vector.
This is a multifaceted programme which is to be very comprehensive for which a multidisciplinary think tank is required. However, it is necessary for epidemiologists and managers of zoonoses to prepare themselves for the emerging problems
Environmental alternations at the local levels to act as barriers in disease spread are always possible. For example, safe and frequent garbage disposal to prevent creation of a habitat for rodents, street dogs etc. water sanitation, management of drains, potholes and other sites where water accumulates favouring breeding of insect vectors etc.
National Programmee on Zoonoses control - directed to control endemic zoonoses e.g., rabies, Brucellosis. The zoonoses control programme may be run
Hospital Waste Management
it is expected that hospital waste is collected in a disposable container, sealed and incinerated. It is not done Immediate recipient of infectious agent is susceptible human. Time elapsed between open disposal and incineration being sufficient to allow access by a rodent/insect/dog/crow or any bird and thus exposure is likely to create a nidus of infection or spread infection. This has long lasting effect. Already there are evidences of creation of soil nidus of CL. botulinium at halts in the root of livestock trade and nidus of Salmonalliae in the liarage. The problem has accentuated because of innumerable hospitals/clinics and diagnostic laboratories.
ANIMAL HEALTH-RELATED (VETERINARY) PROGRAMMES
Following important programmes should be taken up
Programmes like management of livestock, zoos, veterinary hospitals and human hospitals with emphasis on preventive medicine should be taken up simultaneouly.
Slaughter house management - meat inspection to protect consumers, prevent animal diseases
disposal of the offal and rendering so as to prevent diseases originating from this source like parasitic diseases.
Management of street slaughter and slaughter houses - sight of slaughter and bleeding of animals, unhygienic, build up of nidus of infectious agents.
Integrating agricultural practices with health management programmes - Integrated pest management would be helpful in the containment of vector borne and parasitic zoonoses.
The difficulty begins increasing with the addition in the number of vertebrate hosts, intermediate hosts and vectors. Yet it is possible to 'control' a disease, but not to 'eradicate' . One must not be very enthusiastic in 'predicting eradication'.
KG Narayan (2000) - - - Indian Journal of Public Health
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