Veterinary Epidemiology and Zoonosis

Strategies of prevention, control and eradication of zoonotic diseases

PREVENTION, CONTROL AND ERADICATION OF ZOONOTIC DISEASES

Prevention

• Prevention means inhibiting the introduction of a disease-producing agent into an area and a specific population group or an individual. It may be,
• Primary prevention: Quarantine and vaccination
• Secondary prevention: Test and slaughter and depopulation
• Tertiary prevention: Treatment

Quarantine

• The limitation of freedom of movement persons or animals exposed to communicable disease for a period of time not longer than the usual incubation period of the disease, in such manner as to prevent effective contact with those not so exposed.
• It is a prevention action related to separation of healthy population from the apparently healthy population but suspected to be exposed to an infection.
• A period of 14 days, in certain cases 90 days or more, is considered adequate quarantine period.
• Exhibit animals particularly carnivores and omnivores should be quarantined for a minimum of 180 days.
• Dogs on import should be quarantined for 4 months (anti-rabies vaccinated dogs) or 6 months (anti-rabies unvaccinated dogs) and 90^th day of quarantine one dose of rabies vaccination should be given.

Diagrammatic representation of application of preventive measures

Control

• Control means steps taken to reduce a disease problem to a tolerable level and maintain it at that level.

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Eradication

• Eradication means elimination of disease-producing agent from a defined population or geographical area. It may be,
• Total eradication: Complete removal of the agent. Example: Small pox from the world.
• Practical eradication: Elimination of infectious agents from the reservoirs of importance to humans or their domestic animals in defined geographical area and making ‘disease free zone’, rather than total eradication from the region. Example: Eradication of canine rabies, where eradication of rabies from wildlife reservoirs may not be possible.

Reservoir neutralization

• Isolation: Separation, for the period of communicability of infected persons or animals from others in such places and under such conditions, as to prevent or limit the direct or indirect transmission of the infectious agent from those infected to those who are susceptible or who may spread the agent to others.
• Test and slaughter: Deliberate killing of minority infected animals with test-positive from the majority non-infected animal population.
• Depopulation or ‘stamping out policy’: Deliberate killing of all the animals in the population from a defined geographical area without conducting laboratory diagnosis, if the disease-producing agent is highly contagious and/or spreading rapidly among animals in the population.
• Mass therapy: Immunization of at least 80 per cent of the population to maintain herd immunity or immune belt. This can be achieved by ‘ring vaccination programme or frontier vaccination programme’.

Reducing contact potential

• Increasing the herd immunity
• Disinfection and sanitation
• Niche filling: The concept is based on ‘epidemiological interference’. The presence of one organism within the niche can prevent its occupation by another organism. It has been experimentally investigated in poultry industry, the suspension of endogenous intestinal microbes have been fed to day-old chicks to prevent colonization of virulent Salmonella spp.

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Increasing host resistance

• Genetic selection
• Stress reduction
• Chemoprophylaxis
• Immunization

Consumer protection strategies

• Hazard Analysis Critical Control Point (HACCP)

Animal identification

• Identification and isolation of sick animals

Health maintenance

• Immunization
• Animal birth control programme
• Deworming
• Regular certification

Communication/liaison

• Notification and reporting to the local, regional, national and international authorities

Education

• Public health awareness

An effective preventive and control programme requires,

• Sound epidemiological knowledge of the disease: etiology, sources and reservoirs, magnitude, spatial and temporal distribution and dynamics of transmission
• Laboratory facilities for early diagnosis
• Community participation
• Financial resources
• Health care services
• Political support
• Active and passive surveillance
• Regular monitoring and notification
• Coordination between Medical-Veterinary-Public Health Departments
• Regular immunization programme and keeping the population with adequate herd immunity (about 80% of population should be protective), referred to as ‘immune belt’

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