Veterinary Biological Products

OREN E. HERL AND LEIGH T. GILTNER.

TO LOUIS PASTEUR mankind will always be in debt for his momentous work with biological products, which hold first place among medical accomplishments in preventing and treating infectious disease in man and animals.

The noted French chemist and biologist in 1881 published results of his first successful experiment in immunizing sheep against anthrax, an acute infectious disease that is caused by the anthrax bacillus and can attack all mammals, including cattle, sheep, and man.

Pasteur administered vaccine to the sheep. After a definite waiting period, the vaccinated animals were subjected to an infective culture of the anthrax organisms. Pasteur and his skeptical opponents waited to see what would happen. To the surprise of the doubters, the vaccinates remained well, but most of the controls, the unvaccinated animals that were kept for comparison and checking, died.

Following his first experiment, Pasteur began to study immunization against rabies. He reasoned that if he followed a pattern of preparation for rabies vaccine like the one he used for anthrax he should get similar results. He was disappointed, however. The new vaccine failed to stimulate immunity. The vaccinated animals, as well as the unvaccinated controls, contracted the disease when rabies virus was injected into them.

The reason was this: In the first instance, with sheep and anthrax, Pasteur was working with a bacterial organism. In the second, he was working with a virus. Later, however, he developed the famous Pasteur treatment for rabies.

Since the great Pasteur's time, scientists have been working eagerly to develop ways to immunize animals against disease-producing micro-organisms and viruses.

Three groups of disease-producing agents bacteria, viruses, and rickettsiae include most of the infective pathogens (disease-producing agents) that plague man and animals.

The bacterial organisms, such as anthrax and tubercle bacilli, can be seen under a microscope that magnifies a few hundred diameters.

Viruses, such as of hog cholera and rabies, may be seen only with the aid of an electron microscope, which gives a magnification of many thousands of diameters.

The rickettsiae are smaller than bacteria but larger than viruses; heart-water disease (Rickettsia ruminantium) in ruminants is an example.

Nature has given animals an immunizing mechanism whereby they may acquire immunity or resistance against such infective agents. The agents stimulate body tissues to produce protective substances, called antibodies, against the disease.

Scientific work to learn more about the antibodies and to make further use of them made slow progress at first.

It was a tremendous, unexplored field as unprobed but as challenging as atomic energy was in 1945 and outer space was in 1956. Then, to help the scientists, came better microscopes and laboratory equipment and a wider exchange of research findings through scientific journals and conferences, which summarize research work already performed, eliminate duplicate work, and stimulate new ideas and new products.

WHEN THE VIRUS-SERUM-TOXIN law went into effect in 1913, only a dozen or so veterinary biological products were being produced in the United States. Most of them were bacterins--inactivated bacteria.

The law provided for a licensing system to control the production and distribution of viruses, serums, toxins, and similar products intended for the treatment of domestic animals. It provided that no worthless, contaminated, dangerous, or harmful product may be produced and distributed in interstate trade.

Before the law was enacted, immunization of swine against hog cholera had been developed by Marion Dorset and his coworkers in the Department of Agriculture. Within 2 or 3 years, about 80 firms or individuals had applied for licenses for different products. Following this first rush for licenses and the establishment of a system of inspection for the products under the Office of Virus-Serum Control, progress was more orderly. In another 3 or 4 years, many of the less responsible producers had given up their licenses and gone out of production. Other, more progressive ones, met requirements, and over the years the number of licensed firms remained much the same.

On January 1, 1956, 70 firms held more than a thousand United States veterinary licenses covering more than 115 different products.

A GREAT CHANGE occurred in 1945, when the development of live-virus and modified live-virus vaccines took on new impetus. More vaccines and somewhat fewer serums and bacterins were produced. Serum production dropped from 70 million doses in 1950 to 50 million doses in 1955. Bacterin production dropped in doses from 84 million in 1950 to 75 million in 1955. Vaccines went up from 158 million doses in 1945 to 1,500 million doses in 1955. The greatest increases were in vaccines for Newcastle disease and infectious bronchitis for poultry, hog-cholera vaccine for swine, and bluetongue vaccine for sheep. Despite the trend toward the use of live-virus products, the continued demand for certain virus vaccines, such as rabies vaccine (phenol killed) and hog-cholera vaccine (killed-virus), remained.

Poultry immunization was improved when methods using sprays, dusts, and drinking water were developed for mass vaccination against Newcastle disease and infectious bronchitis. The methods were authorized in 1954. They make unnecessary the handling of each bird individually in fact, the chicks treat themselves when they breathe the spray or dust or drink the water containing the vaccine. Also unnecessary, when they are used, is the employment of vaccinating crews, who go from farm to farm and who may carry disease from one flock to another. The new methods enable one person to vaccinate thousands of birds in an hour. Costs are greatly reduced, and results are good if the user follows strictly the manufacturer's directions.

Veterinary biological products may be classified generally as antiserums, antitoxins, bacterins, mixed bacterins, diagnostics, diagnostic antigens, and vaccines and viruses.

The production procedures for antiserums and antitoxins are much alike. For antiserum, the producing animals are injected with appropriate amounts of an antigen to stimulate the tissues to create antibodies. In the production of anti-hog-cholera serum, the hog-cholera virus is the antigen and is produced from the blood of pigs that become sick from inoculation with hog-cholera virus.

In the instance of tetanus antitoxin, the tetanus toxin is the antigen (antibody stimulating substance). It is produced as a byproduct by growing the tetanus organism on artificial liquid media. After the production animals for these types of products are injected with adequate quantities of the appropriate antigen and enough time (which varies with the product as much as 10 days to 3 months) is allowed for the injected animals to develop sizable quantities of antibodies, bleedings are collected from the production animals and are processed into antiserums and antitoxins, respectively.

The antiserums and antitoxins contain large amounts of antibodies. They are used to give immediate, brief protection, which may last 2 to 6 weeks. They have curative value when given in large doses. Antiserums may be used simultaneously with viruses or vaccines in certain instances to stimulate a more lasting immunity. The use of antitoxins simultaneously with toxins or toxoids (detoxified toxin) is not a common practice in veterinary medicine, however.

Bacterins and mixed bacterins are produced from bacterial organisms grown on artificial media, such as nutrient agar or broth preparations. After incubation, the growth is harvested. It is inactivated by chemicals or other means, standardized to contain a required number of organisms, and put into containers.

Bacterins may contain 1, 2, or 3 different organisms designed to stimulate immunity in animals against specific disease conditions. They are referred to as named bacterins. Mixed bacterins are prepared from four or more bacterial organisms using much the same procedure as outlined for the named bacterins. Since it has not been demonstrated that this type of product possesses antigenic value for any specific disease, the recommendations for use have been restricted to a phrase like, "for use in the prevention of conditions attributed to the organism used in producing the product."

Diagnostics and diagnostic antigens are used for the detection and diagnosis of diseases. They are produced in much the same way as bacterins. They are designed and developed to detect specific disease conditions.

Some diagnostics, such as tuberculin and mallein, when injected or appropriately applied to an animal infected with either tuberculosis or glanders, will cause a reaction indicating the infection.

Diagnostic antigens are used for making serological tests for the detection of disease in the laboratory or in the field in some instances on samples of blood collected from the suspected animals. Certain reactions indicate positive infection. Negative, reactions indicate no infection.

Eighteen different diagnostics and diagnostic antigens were produced in 1955. They are a valuable weapon in the hands of the Federal and State agencies in the control and eradication of disease. By the use of tuberculin in an eradication program which began a few decades ago, tuberculosis in cattle was reduced from 5 percent infection in the beginning to less than 0.011 percent infection in 1952. That figure had remained practically unchanged through 1955.

Vaccines and viruses embrace a large number of important biological products, which are becoming increasingly more in demand for use in the prevention and control of diseases in livestock and poultry. More than fifty forms of vaccines or viruses were being produced on January 1, 1956. They vary greatly as to origin, composition, combination, virulence, (relative infectiveness), attenuation (made less virulent), and modification. Thus different methods of preparation as well as special techniques and methods of application are sometimes necessary. Fowlpox and fowl-laryngotracheitis vaccines, for example, are processed from the natural viruses that cause those diseases. Yet by administration of the pox vaccine by the wing-web puncture method and the laryngotracheitis vaccine by brushing it on the membranes of the vent, immunity is established without the danger of causing disease.