Editor's Note: It is with great sadness that we report the death of Dr. Charles Thoen, professor of veterinary microbiology and preventive medicine, on Monday, May 8, 2017.
During his half-century- long career in veterinary medicine, Dr. Charles Thoen has worked with food- producing animals, companion animals, nonhuman primates, elk, buffalo and even elephants. Early in his career he was a veterinary medical epidemiologist for the United States Department of Agriculture (USDA). He later chaired the department of Veterinary Microbiology and Preventive Medicine at Iowa State University, International Union Against Tuberculosis and Lung Disease Scientific Committee on Tuberculosis in Animals, and World Health Organization Committee on Animal Tuberculosis.
He’s been a consultant to the Smithsonian Institution, National Institutes of Health, Centers for Disease Control and Prevention, Pan American Health Organization, National Aquarium in Baltimore, International Elephant Foundation, and agricultural departments in the United States and countries including Egypt, New Zealand, South Africa, Colombia and Serbia.
Dr. Thoen has served as president of the American Veterinary Epidemiology Society and was invited by the World Veterinary Association to provide content for its educational portal on tuberculosis (TB) in animals and humans. In 2014 he received the Distinguished Research Alumnus award from the University of Minnesota College of Veterinary Medicine for his accomplishments on TB and clinically significant pathogenic mycobacteria. He’s been an editor of seven textbooks on infectious disease that are used by scientists worldwide.
He credits his training at Mayo Clinic for providing him with research skills, and a childhood pet for sparking his lifelong interest in infectious diseases in animals and humans.
Dr. Thoen grew up on a farm in Harmony−Lanesboro, Minnesota. When his dog, Trixie, contracted an infectious disease and died, the 10-year-old boy wanted to learn more about what killed his pet. He talked to the local veterinarian and “was hooked,” he says.
Dr. Thoen recently edited the third edition of Zoonotic Tuberculosis: Mycobacterium bovis and Other Pathogenic Mycobacteria, a comprehensive review of the state-of-the-art control and elimination of infections caused by Mycobacterium tuberculosis complex in animals and humans.
Intermingling of the species
“Infectious diseases can be transmitted from animals to humans, and from humans back to animals,” says Dr. Thoen. TB in particular causes disease in humans, elephants and several nonhuman primates. He says this information is especially important because TB is a re-emerging disease in both humans and animals worldwide and is a risk when they intermingle.
“Advanced TB is highly contagious and a significant concern to public health officials,” says Dr. Thoen. “Molecular techniques can trace outbreaks, including genotyping the TB organisms to identify strains and determine if isolates from human patients are similar to those of animals they were exposed to — or vice versa. If the isolates are the same, we can suspect transmission from one species to another, which helps identify the source of infection.”
Employees at animal parks and animal training centers have contracted the disease from elephants and primates. TB isn’t common among U.S. cattle but does occur in cattle imported from Mexico, exposing domestic cattle to the disease.
“Suspected animals are tested, but they only shed the organism in advanced stages of disease, so tests have limitations,” he says. “Public health officials are very concerned about animal-to-human transmission. People who come in contact with elephants may be at risk of contracting TB. Infected animals that expel air in proximity to people can infect them. Some studies show that 13 percent of captive elephants are infected with TB.”
When TB was first diagnosed in captive elephants in 1996, Dr. Thoen worked with a national group of elephant owners and the USDA to set up guidelines for testing, treatment and monitoring the disease. It was the start of 20 years of working with elephants. Some of his trainees became pioneers in the process of collecting samples for testing from the inside of the animals’ trunks — similar to a sputum sample. His team also determined the drug treatment protocols for elephants infected with TB.
“Initially the drug is given orally in grape juice, but elephants quickly lose interest in it,” he says. “We developed a suppository pack, which is now the standard treatment for uncooperative elephants.”
Costly treatment — in dollars and death
Some strains of TB in both humans and animals are resistant to two or more first-line drugs, and others are resistant to multiple drugs. The cost of treating TB is considerable. According to Dr. Thoen, in humans it’s $20,000 for a normal strain of TB and $135,000 to $400,000 for drug- resistant strains, with no guarantee — drug-resistant cases are often fatal. Treating infected animals is just as costly — $100,000 over 18 months for an elephant and as much as $400,000 if it is extensively drug-resistant.
“When an outbreak occurs in other animal populations, we don’t treat the disease,” says Dr. Thoen. “Instead, we remove the animals from the population and do follow- up tests for three and five or more years in those who were exposed.”
Dr. Thoen points out that when TB occurs in developing countries, it’s often not treated in humans, let alone animals, due to the high cost, which contributes to the spread of the disease. Some experts fear TB in animals could lead to the extinction of endangered species.
Dr. Thoen is an advocate for the One Health initiative and has authored content on its educational portal. One Health recognizes that human health, animal health and the environment are inextricably linked and encourages worldwide interdisciplinary collaboration in health care for humans, animals and the environment to defend the health and well-being of all species.
“Tuberculosis doesn’t know if it’s in an animal or a human and doesn’t care who it infects next,” he says. “We need better diagnostic tests and procedures.”
Reprinted from Mayo Clinic Alumni Magazine, Issue 3, pp 28 to 30. 2016. electronic Alumni magazine