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In mid-1971, African swine fever suddenly appeared in Havana, Cuba, where over 12,000 pigs died. To ensure eradication of this disease, Cuba killed over 400,000 pigs in the providence of Havana. The Western Hemisphere remained free of the disease until 1978 when it was diagnosed in Brazil, the Dominican Republic, and Haiti, and again in Cuba in 1980. Extensive eradication programs were done in Cuba and the Dominican Republic with the slaughter of 1.5 million pigs in the Dominican Republic alone. An eradication program, through the efforts of the U.S., Mexico, and Canada, is scheduled to begin this year in Haiti. The U.S. Congress has appropriated $14.5 million for this program. It is estimated that if the virus were accidentally introduced into a major swine producing state, successful eradication could cost over $100 million, and the economic impacts of endemic African swine fever would run into the billions of dollars. The disease produces severe economic losses in pigs. Those that do not die are chronically infected and grow poorly. Attempts at development of vaccines have been relatively unsuccessful. Immunized pigs become carriers of the virus further complicating the epidemiological picture of this virus. SEA-AR has conducted research on the pathogenesis of the disease, improved methods to diagnose the disease, and on the immune response in hope of producing effective vaccines. Further research is needed on insect vectors, transmission of the virus, the immune response, and vaccine development.
Rift Valley fever
Rift Valley fever is another viral disease which had been confined to Africa for years. The virus now appears to have mutated and recently spread into Egypt and the Sinai Peninsula. It is a serious threat to the U.S. livestock industry, as the virus will infect humans who can unknowingly transport it from one continent to the next. Rift valley fever produces abortions and stillbirths in sheep and cattle and is highly fatal to young animals. The outbreak in Egypt in 1978 and 1979 resulted in a 25 percent reduction in livestock numbers and was responsible for the severe meat shortage in the area. SEA-AR has done research on developing diagnostic capabilities and a killed virus vaccine. Further research on insect vectors, transmission, and low cost vaccines are needed to adequately protect our livestock industry in the event of accidential introduction of the virus.
Viscerotropic velogenic Newcastle disease (WWND)
WND is exotic to the United States. Domestic strains of Newcastle disease have been known to be endemic in the United States since the 1940's. Vaccines have been developed for these less virulent strains, and except under unusual circumstances, they do not create significant economic losses in well-managed operations. In the late 1960's and early 1970's a more virulent exotic strain of Newcastle disease began to be detected around the world in the integrated poultry industry. The incidence of this exotic Newcastle Disease was apparently tied to the increased movement of Psittacine birds throughout the world.
Several smaller introductions of exotic Newcastle disease occurred and were contained in pet shops and some commercial poultry operations, especially along the U.S.-Mexican border. However, Exotic Newcastle disease was introduced into southern California in November 1971 and spread to the commercial egg producing industry. APHIS spent $56 million in task force and indemnity costs before it was eradicated 2 years later. More recently, outbreaks, now contained, have occurred involving wholesalers,
dealers, aviculturists, retail shops, and holding facilities for caged pet birds. These outbreaks were attributed to smuggled cage pet birds from Mexico and Central and South America. The import surveillance, diagnostic capability, eradication, and control efforts for Exotic Newcastle disease have cost more than $70 million in the past 10 years. SEA-AR research has provided diagnostic procedures, sampling methods, recommend use of disinfectants, and knowledge of the pathogenesis and epidemiology of the disease. Further research needs include development of an effective vaccine, improved diagnostic tests for virus characterization (it presently requires 9 to 15 days), further elucidation of the pathogenesis and viral shedding patterns of psittacine species, and better surveillance procedures for detection of the infection before spread occurs to our avian industries in the United States.
The major zoonotic diseases which are of public health significance are brucellosis and tuberculosis. An accelerated brucellosis eradication program was initiated in 1954 because of the extensive losses to the cattle industry due to abortions, and because of the public health problems associated with the handling of infected animals and animal products. In 1981, it is estimated that $150 million will be spent for the eradication program of which the Federal Government's share is $81.1 million. The research program for brucellosis is extensive and has included the development of improved methods of diagnosis, increased understanding of its pathogenesis and improved vaccines. Additional research is still needed to determine the duration of immunity following use of Strain 19 vaccine, to develop an inactivated vaccine and to determine how chronic infections are established. It is also necessary to develop methods to control brucellosis in the Alaskan reindeer.
The tuberculosis eradication program was started in 1917 and is currently costing approximately $14 million annually of which $5.9 million is contributed by the Federal Government. Extensive testing programs at time of slaughter are used to identify infected herds. Further research is needed to develop simplified diagnostic tests for use at slaughter and to develop methods of positively identifying the origin of infected animals.
Production associated diseases
The third group of diseases is the production associated diseases. Despite the fact that most developed countries including the U.S. have been successful in controlling many serious epidemic infectious diseases, losses to productivity from other livestock diseases remain high. These diseases are complex epidemiologically and have infectious toxic, genetic, metabolic, and nutritional etiologies or combinations of these. The diseases generally result from several etiologic factors acting in concert with environmental and production factors. This group includes: (1) infectious diseases and disease complexes, such as pseudorabies, bluetongue, mastitis, neonatal disease, multiple gastrointestinal and other parasitisms; (2) reproductive disorders; (3) stress related syndromes such as the bovine respiratory disease complex, salmonellosis, and transport tetany; (4) metabolic imbalances such as ketosis and hypomagnesemic tetany; (5) digestive system disorders, such as bloat and lactic acidosis; (6) nutritional disorders and marginal malnutrition-infectious disease complexes provoked by deficiencies in minerals and other essential nutrients; (7) toxicoses caused by industrial and agricultural chemicals and wastes, poisonous plants and mycotoxins; (8) combinations of two or more of the above.
Some production diseases are capable of killing large numbers of animals, and others may produce high morbidity in affected herds. However, as a class, they cause their greatest reduction in productivity of livestock enterprises often without producing clinical signs of disease.
Pseudorabies is a specific example of an infectious disease which causes severe production losses. It is a viral disease that can affect most farm animals, but its major impact is in swine. Pseudorabies in swine has been present in this country for many years. Within the past 5 years, there has been a marked increase in the incidence and severity of the disease. In a recent study, the pseudorabies virus was isolated from 10 percent of swine at slaughter. It appears that stress may be one factor causing outbreaks in swine herds. The incidence of pseudorabies is widespread throughout all of the major swine producing areas of the U.S. The implementation of programs to control the disease has created market barriers for purebred swine producers. The disease can occur in swine herds without warning producing abortions and heavy losses of baby pigs. As the result of a research program initiated in the past 5 years, an attenuated vaccine has been produced and has proven effective in reducing the mortality on farms that have had outbreaks. In addition, a killed vaccine has also been produced. Both types of vaccines are commercially available. Varying degrees of success are reported for both vaccines; however, continued research is needed to determine the incidence of the disease in the major swine producing areas and the latency of the virus in normal (carrier) swine. One of the most important research needs is to develop an effective killed vaccine. Also, research is needed to characterize the different types of viruses that are responsible for the outbreaks of pseudorabies. Characterization of specific herpesviruses would aid in diagnosis and help to determine how pseudorabies is spread and permit the development of vaccines that would arrest the onset of the disease in swine herds.
Bluetongue was formerly thought to be primarily a disease of sheep. There are over 20 antigenically distinct strains of which four occur in the United States. In sheep, bluetongue will produce severe cyanotic mouth lesions, death, abortions, and stillbirths. It is now apparent that cattle can have a mild form of the disease; however, the virus is increasingly implicated in abortions, stillbirths, and weak calves. A similar viral agent, epizootic hemorrhagic disease of deer, appears to produce complications similar to bluetongue in cattle. The SEA-AR research has primarily been to develop methods of typing bluetongue virus, study pathogenesis of bluetongue disease, improve virus isolation and diagnostic tests, and develop attenuated live and killed bluetongue virus vaccines. Research to develop improved methods of determining whether an animal is infected or not is needed to certify livestock for export. This research is difficult as virus isolations are difficult and antibody is not always present in carrier animals. Research is also needed to determine how much of the reproduction failures of cattle are due to these viruses and to develop improved vaccines and, insect control procedures.
Much is known about some of the remaining production diseases and surprisingly little about others. Reliable means of control are available for a few, whereas, prevention and control procedures are disturbingly inadequate for most of the others. For example, despite all that has been learned about calf diarrhea since the classical studies of over a half century ago, it continues to be one of the most important causes of neonatal losses in animals throughout the world. Similarly, a great deal has been learned about mastitis through research during the past 50 years, yet it is still one of the world's most costly diseases. Essentially, the same situation applies to reproductive inefficiencies, mixed parasite infections, and many other insidious disease complexes.
For the production diseases, research is need to: (1) Develop combined disease and production monitoring systems which interface data with diseases, disease determinants and production practices in the production environment; (2) Develop integrated (interdisciplinary-multifactorial) methods to determine and quantify various factors and interactions responsible for loss and inefficiencies in the production environment; (3) Devise analytical systems to develop practical strategies for effective control of production disease; (4) Examine under controlled conditions the causative interactions and their effects to substantiate on-the-farm assessments to improve strategies of disease control; and (5) Develop computer simulation models for production diseases to assist in the development of control procedure and to predict biologic and economic consequences of particular strategies for disease control.
Insect pests cause losses because of their direct effect on animals and because they may transmit infectious diseases. Major livestock insect pests are screwworm, cattle fever tick and imported fire ants.
The screwworm is an outstanding example of a major livestock pest that has been suppressed through the application of research. After SEA-AR research established the classic sterile insect release method, APHIS employed this new technology to eradicate screwworms from the United States. The eradication of screwworms has resulted in an estimated annual savings of $100 million in direct losses and $300 million in losses to consumers and indirect costs. In order to prevent the reintroduction of screwworms into the United States, the program will proceed southward through Mexico until a barrier zone is established at the Isthmus of Tehuantepec. Research has always underpinned the eradication Program since its inception.
Research scientists develop new competitive screwworm strains each year for use in the sterile male production facility. AR scientists developed the screwworm adult suppression system (SWASS) as a supplement to the sterile insect release method and have developed attractants for surveillance and control. Ecological and genetic studies in the United States and Mexico continue. Research needs include the continual development of new competitive screwworm strains, the investigation of SWASS to make sure that it is effective in all parts of Mexico, the development of a system to kill screwworm females so that males only will be mass reared, the genetic characterization of geographic populations of screwworms, and the development of better attractants of adult screwworms for use in control and surveillance systems.
Cattle fever tick
Another extremely important pest of livestock, the cattle fever tick, has also been the subject of an eradication program which has a cost/benefit ratio of 1:20. APHIS has a successful eradication program that has limited this tick to a small area of Texas and to the island of Puerto Rico. The basis for the evaluation procedures was provided by research. Furthermore, research scientists have developed pesticides and methods of pesticide application which are central to the eradication effort. Research that still needs to be accomplished to further reduce losses includes the development of new, environmentally-safe pesticides and methods of their application; the discovery of new technologies for tick control, such as sterile hybrid ticks as a supplemental eradication technique; and the acquisition of information about the biology and ecology of the cattle fever tick not only in Texas, but particularly on the island of Puerto Rico.
Imported fire ant
Imported fire ants attack people, inflicting painful stings which frequently require medical attention; attack livestock, reportedly causing some deaths of newborn animals; and cause significant losses in crop production. They have spread from their point of introduction in Alabama to Texas, Louisiana, Arkansas, Mississippi, Georgia, Florida, North Carolina and South Carolina. Research has been conducted at Gainesville, Florida, on chemical and biological control, the ecology, and the impact of imported fire ants on agriculture and human health. At Gulfport, Mississippi, research has emphasized biology, behavior, reproduction, and pheromones. With the withdrawal of mirex registration in June 1978, a search was made to discover a suitable replacement. Excellent progress has been made. One bait has received conditional registration for use on noncrop areas. A second bait toxicant will receive an experimental use permit in the near future. A third compound has shown excellent activity as a toxicant and reproductive inhibitor. A fourth promising toxicant is under investigation. Research needs for the future center on the development of highly effective, safe, and inexpensive imported fire ant toxicants, the initiation of a full-scale research program on biocontrol, and the intensification of research on pheromones, insect growth regulators, and attractants with the goal of integrating these chemicals into a more efficient and safe toxic bait system.