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Infectious Disease

A novel solution for an invisible enemy

Saul Tzipori, director of the Division of Infectious Diseases Photo: Ed Malitsky

Earlier this year, 18 people died in Walkerton, a rural community in Ontario. The catastophic event is thought to be the worst case of a waterborne outbreak reported so far in North America.

It is also just one of the recent outbreaks of illness from food products or contaminated water with the virulent strain of the bacterium Escherichia coli, or E. coli O157:H7. While all animals and humans have natural colonies of E. coli living in their intestines, E. coli O157:H7, discovered in 1982, ranks among the most-fearedfood-borne pathogens.

These bacteria liberate toxins that are absorbed from the intestine into the bloodstream, where they cause kidney failure and often brain damage, which can be fatal. The outcome is known as hemolytic uremic syndrome or HUS, the leading cause of kidney failure in children.

An estimated 100,000 cases of E. coli, mostly O157:H7 with some similar but non-O157:H7 strains, occur annually, with 2,100 hospitalizations in the United States resulting in three to five percent deaths. According to the Centers for Disease Control and Prevention (CDC), disease-causing microorganisms like E. coli are difficult public-health enemies that are invisible, furtive and gaining in strength and numbers.

At Tufts, scientists at the Division of Infectious Diseases at the School of Veterinary Medicine have developed what may be the first effective defense against the toxin producing E. coli O157:H7 and similar E. coli. After five years of study, researchers have developed an antitoxin therapy that inactivates the toxins in the bloodstream and will most likely prevent kidney failure and death in affected children.

"Since the treatment is directed against the liberated toxins and not the bacteria," says division director Saul Tzipori, "the bacteria will not be able to develop resistance as they do against antibiotics. These are human antibodies, which were produced in transgenic mice and are very safe to use in children at risk of developing kidney disease. Their efficacy has recently been demonstrated in animals infected with the E. coli O157:H7."

After some initial evaluation the human antitoxins are now ready for production for phase I and phase II clinical trials in humans. They will be administered to children at risk of HUS and to those who come in contact with them. Typically, within two to four days after consuming contaminated food or water, individuals may experience the onset of bloody diarrhea, which in some may lead to anemia, kidney failure and sometimes death. Researchers postulate that E. coli bacteria injure the intestinal tract, which causes diarrhea, and the toxins are absorbed into the bloodstream through the injured lining of the gut.

Tzipori says the development of this product promises to be the first effective solution to a "nasty disease" that tends to strike in clusters and in certain geographic locations.

"Food safety is a deep concern, and people are becoming more aware of precautions needed to handle meat and other animal products," he says. "There is growing hypersensitivity around meat monitoring, but it is not an easy thing to do. You can monitor a bulk of meat and not detect contamination. We believe that this treatment will be a significant contribution toward greater protection. It is certainly the best option available at the moment for treating and protecting exposed children against HUS."

Such progress, he adds, offers hopeful signs that more advances will be made to treat this significant but yet untreatable disease. "We got our first grant in 1996 from the National Institutes of Health (NIH) for five years," he notes, "and we just were awarded a second NIH grant for another five years for $1.7 million to develop molecular techniques to amplify these antibodies for large-scale commercial production. We are encouraged by the strong NIH support we have received for this project."

The advancements with E. coli also mark a milestone for the Division of Infectious Diseases, a little-known aspect of the Veterinary School and, indeed, of Tufts, but whose brief ten-year history is marked by impressive growth and vitality. It began inauspiciously when Gerald Keusch, chief of the Division of Geographic Medicine/Infectious Disease at the New England Medical Center (NEMC), persuaded Tzipori, then associate director of the International Centre for Diarrheal Diseases Research in Dhaka, Bangladesh (ICDDR,B), to come to the Veterinary School as a visiting professor.

Tzipori's international reputation in the investigation, diagnosis and treatment of infectious diseases in animals and humans made him a natural choice. Tzipori graduated with top honors in veterinary medicine from the University of Queensland, Australia, where he also earned a Ph.D. From 1975 until 1985 he directed the microbiology section at a Melbourne research institute, during which time he identified important enteric infectious agents previously either unknown or ill-defined in Australia and elsewhere; he also developed two new veterinary vaccines. From 1985 to 1990 he directed the Department of Microbiology at the Royal Children's Hospital in Melbourne from which he was eventually recruited to Tufts.

When his four months were up, Tzipori was offered a joint appointment to initiate a program in infectious disease, a position funded initially by the Veterinary School and NEMC. In January 1991 he was made full professor.

"I had an established career in Australia and some of my colleagues thought I was taking too big a risk in moving to the highly competitive and unfamiliar U.S. biomedical environment," says Tzipori. "The reputation of Tufts and NEMC for interdisciplinary biomedical research, however, particularly in the field of gastroenteritis, was well recognized and potentially could draw resources. I figured the challenge was worth the risk."

That challenge soon began to pay off. In less than three years, drawing entirely on external funding, Tzipori expanded his research staff to 15, and the group was recognized as an official division within the Veterinary School. Today, the staff has grown to nearly 35, including 20 scientists, ten of whom are faculty. Now occupying the entire second floor of Building 20 and part of 21 at the Veterinary School, the division is the largest single research entity at the University, and Tzipori the largest funded individual at Tufts. Grant writing has secured some $15 million to fund current research and over the next five years from sources such as the NIH, the U.S. Department of Agriculture, the CDC, the Federal Drug Administration and the Environmental Protection Agency.

Still, Tzipori is quick to point out that the success is not measured in dollars alone. Members of the division are charged with the task of directing and teaching immunology, molecular biology, microbial pathogenesis, parasitology and public health at the Veterinary School. This year Tzipori also was instrumental in helping launch the first Ph.D. program at the school.

"In a relatively short time we've created a highly productive and integrated group," says Tzipori. "It took a lot of hard work, but as it turned out, it was worth it." The E. coli program is only one pioneering effort by the division, noted for its multidisciplinary approach to science.

One major initiative, also funded by NIH, investigates Cryptosporidium parvum, a waterborne protozoa that causes diarrhea in both humans and animals, and can be fatal to malnourished children made weak by diarrhea, and to people whose immune system is compromised, including the elderly and those with AIDS. Tzipori was one of the first to demonstrate in 1980 that Cryptosporidium was a serious cause of diarrhea in animals and humans and that humans can be infected from contact with animals.

"When I came across this protozoa while working in Scotland, not much was known about it. It became clear that this may turn out to be a serious cause of disease in calves," he says. "Then, surprisingly, when we started looking for it in other domestic animals, we found it in every species we looked at, including humans."

There is no effective treatment for Cryptosporidium, but scientists at the division, who have received an award to sequence the nucleotides of the entire Cryptosporidium genome, hope to help identify molecular targets for development of therapeutic agents.

Other key research programs include a collaborative investigation in Uganda to identify links between Cryptosporidium and Microsporidium, another microorganism associated with chronic diarrhea and immune impairment due to malnutrition and chronic diarrhea and wasting in young children. Together with the Tufts School of Medicine and the New England Primate Center, the division is involved in defining the contribution of nutritional factors, direct effect of the AIDS virus on the gut, and opportunistic infections to wasting and metabolic disorders associated with AIDS.

"We are very excited about the newly developed and funded programs in our division," says Tzipori. "With the drive to recruit three new talented faculty members, the division is entering its second growth phase. Our division has come a tremendous distance since it began, and we look forward to the next decade, which we hope will be just as scientifically rewarding and productive as the first."

Laura Ferguson

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