Healthy hogs for a healthy nation
Antibodies are always looking out for us, and this week we're taking a closer look at them. This is the fourth post in our Antibodies Week series. Read our other posts on pregnancy tests, an-tee-bodies t-shirts, and the plague.
On June 19, 1875, William Emerson Baker invited some 2,500 guests to his farm in Needham, Massachusetts, to celebrate the launching of his "sanitary piggery." As a "good-cheer souvenir" of the event, he created the "Porcineograph." This delightful lithograph, preserved in the collections of the Library of Congress, includes an unusual pig-shaped map of the United States (a geHOGgraphy!) with pigs cavorting around the border and banners proclaiming the pork-based dishes enjoyed in every state in the nation.
Baker, having made his fortune manufacturing sewing machines, was free to indulge his passion for public health and to promote his ideas on farming reform. His sanitary piggery, though decidedly eccentric in some respects, was based on the sound idea that clean, pure food would promote human health. Raising pigs in a sanitary environment would help keep them disease-free, and healthy pigs provide wholesome meat.
Control of disease in livestock, especially pigs, was a very real concern across much of the nation. A particularly virulent infectious disease had been decimating hogs in the Midwest as early as the 1830s. By the time of Baker's party, the disease had spread to 35 states and was causing millions of dollars in losses a year. The disease was known as hog cholera, swine fever, or sometimes swine plague. In 1884 the federal government responded to the growing threats to livestock with the establishment of the Bureau of Animal Industry (BAI) within the U.S. Department of Agriculture.
The bureau's investigations into livestock health were grounded in laboratory science and the emerging field of bacteriology. The period between Baker's party and the founding of the BAI had been a particularly fruitful time for medical science—the germ theory of disease had been established, and research into the diseases of animals had paved the way. In France, Louis Pasteur developed vaccines for chicken cholera (1879) and anthrax (1881), and in 1885, demonstrations of his rabies vaccine became front-page news.
In order to develop a vaccine for hog cholera, researchers at the bureau first had to identify the cause of the disease. In 1885 they thought they had the answer when they discovered a new genus of bacteria in the infected pigs. The bacteria, named Salmonella choleraesuis, turned out to be a red herring, but investigators continued to follow this lead for nearly 20 more years.
In 1903 BAI researchers Emil A. de Schweinitz and Marion Dorset discovered the real cause of hog cholera—a virus. Scientists at this time had no reliable tools for seeing viruses, which are 10 to 100 times smaller than bacteria. Instead, they used a very fine-pored porcelain filter to remove bacteria from samples, and then tested whether or not the samples were still infectious. They found that when blood from a pig with hog cholera was filtered, the bacteria-free filtrate was still capable of causing hog cholera in healthy pigs. This proved that hog cholera resulted from something smaller than bacteria—they called this something a "filterable virus."
With the identity of this new infectious agent confirmed, scientists could now work on a vaccine to defeat it. Injections of blood serum, drawn from hyper-immune pigs whose blood was rich with antibodies to hog cholera, proved to be an effective treatment, but failed to result in lasting immunity. However, when an injection of the antibody serum was followed by a dose of the live hog cholera virus, a long-lasting immunity was conferred. In 1906 Marion Dorset patented the method for manufacturing hog cholera serum, including instructions for the serum-virus technique of vaccination, and declared his invention free for use to all persons in the country.
The serum-virus vaccine was used on U.S. farms for about 50 years. A serious drawback to this method of vaccination was that it continuously reintroduced the live virus into the environment. As long as this technique continued, eradication of the disease was impossible. A better vaccine was needed, and researchers pursued two directions in vaccine development: a killed-virus vaccine, in which the virus has been completely inactivated, and a modified, or weakened, live-virus vaccine. Either approach can be successful, if the vaccine confers immunity without causing disease. During the 1940s researchers at the Lederle pharmaceutical firm developed a modified live-virus vaccine that was ready for the market by 1951.
Although the new vaccine was more effective than both the serum-virus method and the killed-virus vaccine, outbreaks of hog cholera continued to be a significant problem. In the 1950s a consortium of interests—the government, pork producers, veterinarians, and the animal vaccine industry—opted for a different strategy: they proposed a program of eradication. Authorized by an act of Congress signed by President John F. Kennedy in September 1961, the program entailed strict surveillance, quick diagnosis, quarantine, and eventually destruction of infected animals. In January 1978 the USDA was finally able to declare the country hog cholera-free. One hundred years after Baker launched his sanitary piggery, the geHOGraphy was a healthier place for pigs.
Diane Wendt is a curator in the Division of Medicine and Science at the National Museum of American History.
Explore the Antibody Initiative website to see the museum's rich collections, which span the entire history of antibody-based therapies and diagnostics.
The Antibody Initiative was made possible through the generous support of Genentech.