Chapter 9 PRINCIPLES OF LIVESTOCK DISEASE ERADICATION  DR. SAUL T. WILSON, JR.

 

 

9.1 Objectives:

• A. Familiarize the students with the relationship between disease prevention, disease control, and disease eradication.
• B. Review the basic procedures used in livestock disease eradication.
• C. Acquaint the students with major diseases eradicated from the U.S. 

9.2 Introduction

Opposite the title page, in Schwabe's book, "Veterinary Medicine and Human Health", Daniel E. Salmon, D.V.M. (1850-1914) is cited as the "Father of disease eradication; Pioneer in public health practice and medical research, Discoverer of killed vaccines and of the Salmonellae, Experimental immunologist, Epidemiologist, Administrator, and Founder of the Bureau of Animal Industry."

Dr. Salmon is given credit for designing the first well-conceived program specifically to eliminate an important disease from an area until natural or defensible barriers to transmission were reached. This was the program to eradicate contagious bovine pleuropneumonia (CBPP) from the United States. Program procedures were:

• 1) systematic farm inspection for signs of the disease,
• 2) quarantine of infected premises, and
• 3) slaughter of affected and exposed cattle.

Eradication has been recognized since the 1982 success against CBPP in the United States as a theoretically and practically realizable goal for a number of infections. There are 14 animal diseases or animal pests that have been eradicated from the United States. A most notable achievement has been the world-wide eradication of human small pox. There are some diseases for which there is no possibility of eradication at present due to the nature of the reservoir.

Eradication implies action and completeness. A disease is not eradicated if it remains in a single host or in the environment with the capability of causing the disease. The term "eradication" has been loosely used and misused in both human and veterinary medicine. Misuse of the word can only serve to reduce the scientific credibility of public health officials, so stated Dr. D. A. Henderson, Director of the successful World Health Organization (WHO) International Smallpox Eradication Program.

The term eradication is frequently used when the term "control" is a more accurate description of the activity. It is important that the appropriate term be used when discussing disease intervention strategies of prevention, control and eradication.

9.3 Definitions

9.3.1 Prevention of Disease

• --AII measures to exclude disease from an unaffected population. Prevention includes:
• - Measures for exclusion of a disease agent from an area where disease is absent--Quarantine .
• - Measures to protect a given population from a disease that is present in the area--Mass immunization; mass prophylactic treatment; environmental control are measures for Prevention.

  9.3.2. Disease Control

  All measures used to reduce the frequency of illness associated with a disease already present in an area. Includes reduction of host parasite interactions, damage to host prevented, reduction in number of new cases, losses to owner negligible.

  9.3.3 Prevention

  Requires continuing effort. Means the inhibition of the introduction of a disease or disease producing agent into a regional population or to an individual.

  9.3.4 Control

  Requires a continuing effort, reduction of a disease to a level it is economically and socially tolerable - confining the disease to a designated area.

  9.3.5 Disease Eradication

  Complete elimination of a disease agent (extinction of species of infectious microorganism), so it does not reoccur unless reintroduced from outside. Effort and cost terminates with eradication.

  Accomplished by a combination of:

• - Case finding surveys - Mass treatment
• - Selective slaughter - Environmental control
• - Herd Depopulation - Biological control
• - Quarantine - Vector control
• - Mass immunization - Reservoir control

  9.3.6 Selective Slaughter

• 1. Deliberate killing of a minority of clinically ill or infected animals to protect the healthy 
• 2. Selective slaughter of reactors to a immunodiagnostic test. 

  Limiting Factors

  • 1. Percentage of animals involved initially
  • 2. Amount of disruption to the economy
  • 3. Availability of replacement animals
  • 4. Sensitivity and specificity of the diagnostic test. 

  9.3.7 Herd Depopulation

  Elimination of diseased animals and all normal appearing animals in contact with the diseased animal or previously in contact during the incubation period.

  Herd depopulation should be considered when:

  An affected population cannot be tested to carry out selective slaughter. Test and slaughter not cost effective when infection spreading too rapidly to cope with otherwise. Used for highly contagious diseases (Foot and Mouth Disease/FMD, African Swine Fever/ASF, Hog Cholera/HC), chronic diseases with long incubation (Tuberculosis/TB), and diseases that are difficult to diagnose, such as Scrapie.

  9.3.8 Quarantine

  Physical separation of sick animals and/or animals of unknown status from healthy animals.

  Applied at international level to prevent transmission of infection and vectors from one country to another.

  Office International des Epizootics (OIE) established in Paris, France in 1924 to standardize veterinary quarantine procedures and regulations around the world.

  OIE provides a forum to standardize veterinary quarantine procedures and regulations used by different countries around the world.

  9.3.9 Mass Treatment

  Depends upon availability of safe economical therapeutic agents.

  Examples: Tick eradication treatment with a regulatory-approved pesticide. Sheep scab eradication. Antibiotic treated feed to control psittacosis in imported birds. Coccidiosis in chickens. Sulfonamides in the feed of swine. 

  9.3.10 Mass Immunization

  Full potential may not be realized due to misuse of veterinary vaccines. Precautions must be taken to prevent vaccination crews and personnel from spreading the disease.

  Improper storage--improper administration--inadequate potency and safety control can preclude total elimination of an agent through use of vaccines. Mass immunization can complicate surveillance, control, and monitoring programs based upon serologic testing.

  9.3.11 Environmental Control

  Measures directed against invertebrate vectors such as arthropods or snails frequently can be carried out with little or no involvement of owner.

  Concerns--Development of vector resistance to insecticides; pesticide toxicity to man, animal, birds, etc. 

  9.3.12 Education

  - Categories of Disease Control Programs

• 1. Compulsory government-run programs
• 2. Voluntary government-run programs-under state authority and/or federal authority
• 3. Voluntary private or Cooperatives Programs
• 4. Private programs for individual farms or small groups of related units, such as nucleus herds, and multiple herd within a company.

  - Eradication of individual disease achieved mainly by:

• (a) detection,
• (b) notification and slaughter,
• (c) cleaning and disinfection

  M. Ancillary Measures

• 1. restricting movement,
• 2. cooking garbage,
• 3. disinfecting premises, trucks, etc. 

9.4 Contagious diseases are controlled by:

• A. Creating a physical barrier between diseases and susceptible animals
• B. Eliminating the source of infection
• C. Protecting susceptible animals through vaccinations and prophylaxis

  - Eliminating slaughter--Lansci, Italy 1712---Bates, England 1714.

  - Chemicals to control ticks used in late 1800. 

  - Vaccines introduced in 1800.

  - No single procedure can be used to control all diseases. 

  - Effective--Practical programs must be tailored for each parasite and host in a given environment.

  - During surveillance and inspections for disease management purposes:

• 1. Animals should be observed with sufficient regularity and detail to detect abnormalities in an individual or group at the earliest possible moment. Timing and scrutiny are determined by the risk and severity of anticipated abnormalities.
• 2. An early accurate diagnosis is a major step toward prevention and control.
• - Factors to be satisfied before an eradication program is terminated:
• 1. Clearly establishing that the last case has occurred
• 2. Means of internal spread identified and neutralized
• 3. Survey inspection, surveillance testing, mandatory reporting, laboratory support maintained
• 4. Barriers to reintroduction in place 

9.5 Animal Health Programs

Animal Diseases Eradicated From the United States

9.6 Features of Selected Government Eradication Programs:

9.6.1 Hog Cholera Eradication

9.6.1.1 Phase l--Preparation

State authorities in existence to require reporting or hog cholera, cooking of garbage fed to swine, regulate swine movement, quarantine, inspect, and disinfect infected premises, and control use of hog cholera biologics.

• --Establishment of State and County hog cholera eradication committees
• --Establishment of a system for prompt reporting of suspected outbreaks
• --Investigation of reported suspicious outbreaks
• --Disposition of each report through a standard diagnostic procedure 

  9.6.1.2 Phase II-- Reduction of Incidence

• --Quarantine of suspect herds until final diagnosis and maintenance of quarantine on infected herds as long as danger to other herds remained
• --No movement from quarantined herds except to slaughter under regulator controls
• --Inspection of swine entering markets that returned to farms
• --Maintenance of records of origin and disposition by dealers in swine 

  9.6.1.3 Phase IlI--Elimination of Outbreaks

• --Elimination of infected herds in their entirety with payment of indemnities from State and Federal agencies as necessary to accomplish that purpose
• --Operational plans for handling disposal of infected and exposed swine; inspection of swine in infected areas and those exposed in market channels
• --Arrangements for cleaning and disinfection of infected premises and swine-handling facilities 

  9.6.1.4 Phase IV--Protection Against Reinfection

• --Active operation of a reporting and search program for 1 year, with no hog cholera diagnosed in the State
• --No vaccination with live virus hog cholera vaccines, with all vaccination with inactivated vaccines to be reported to the State
• --Swine imported for feeding and breeding purposes to be subject to 21- day isolation after arrival unless originating in another "hog cholera free" State

9.6.2 Tuberculosis (TB) Eradication Program

• All cattle to be tuberculin tested
• All reactors slaughtered and subjected to post-mortem (PM) examination
• All infected premises cleansed and disinfected (C&D)
• All infected herds quarantined until negative to two complete herd tests
• All movement traced to infected herds and herds of origin

Exposure-tested, TB-lesioned animals found at slaughter traced to herds of origin and herds tested

9.6.3 Brucellosis Eradication Program

Restriction on cattle movement based upon State classifications according to cattle herd infection rate and market cattle reactor prevalence rate during previous 12 months: 

State Market Cattle 

Classification Herd Inf. Rate Reactor Rate

Free No infected herds Not more 0.050%

• A Not more than 0.250% Not more 0.100%
• B Not more than 1.500% Not more 0.300%
• C Exceed 1.500% Exceed 0.300% 

9.6.4 VEE Eradication

• Mosquito control
• Vaccination of Equine animals and man
• Quarantine-restriction on equine movements in infected areas
• Improper vaccine storage--improper vaccine administration--inadequate vaccine potency and safety control can preclude total elimination of an agent, through use of vaccines.

Mass immunization can complicate surveillance and control monitoring programs that use serologic testing.