In 2013, an outbreak of tuberculosis occurred in Oregon. The first patient discovered to have the disease was a 20-year-old male. His pale, cold, gray skin could have been a symptom of infection with the potentially deadly tuberculosis bacteria, but for Rama the elephant, it signaled that everything was normal. In fact, if it were not for a routine check-up, Rama's tuberculosis may have never been discovered. This lack of symptoms allowed the bacteria to spread to 3 other elephants and 6 humans in the Oregon zoo. Yes, that's right- not only was Rama infected with a human disease, but he was able to also spread it to humans.
While the possibility of catching a disease from an animal at your local zoo may seem rare, zoonotic diseases, or diseases that can be passed between humans and animals, are all too common. The Centers for Disease Control estimates that over 6 out of 10 known infectious diseases, and 3 out of every 4 new or emerging infectious diseases, are spread from animals. Humans can contract diseases from animals in many ways, including direct contact with infected animals, contaminated surfaces, or food. Insects that bite both humans and animals such as mosquito, ticks, or fleas, also contribute to the spread of zoonotic diseases.
Rama spread the bacteria responsible for causing tuberculosis through droplets that were released into the air when he sneezed. I have to admit, the image of an elephant sneezing is pretty cute, but that is the only funny thing about tuberculosis. The bacteria Rama carried currently plagues one out of every three people in the world; 1.8 million people died from tuberculosis (TB) last year alone. While public health agencies such as the Bill and Melinda Gates Foundation attribute the TB epidemic to co-infection with HIV or antibiotic resistance, the World Health Organization has recognized that zoonotic TB is also a major threat in the fight against tuberculosis.
Tuberculosis in animals is seen mainly in cows, although it is also found in deer, badgers, lions, and of course, elephants. While cows, like the elephants at the Oregon Zoo, can be infected with the human form of tuberculosis, the main zoonotic threat comes from the cow form of tuberculosis that can infect humans. Humans can contract bovine tuberculosis through direct contact with a cow, or through consumption of contaminated milk and cheese.
Fred Quinn, head of the Infectious Disease Department and a tuberculosis researcher at the University of Georgia, describes bovine tuberculosis as “Not only a plague, but an increasing one.â€
Bovine tuberculosis accounts for 1·4% of cases of human infection annually; however, in areas of the USA with large foreign-born populations (such as along the USA and Mexico border), the prevalence of bovine tuberculosis in people has been steadily increasing. In San Diego, CA, bovine tuberculosis accounted for 45% of tuberculosis cases in children and 6% of adult tuberculosis cases. These numbers, however, may not give an accurate picture of the problem.
“Part of the problem is we don't know how big the problem is,†says Quinn.
Bovine tuberculosis may be underestimated because reports of the disease mostly come from western countries with measures in place to control for outbreaks. In the United States, Canada, and England, herds are routinely tested, infected cows are slaughtered, and the farmer is reimbursed for financial loss associated with the cow. Pasteurization also kills bovine tuberculosis in milk products. In other parts of the world such as Asia, Africa, and South America, however, pasteurization and testing regulations may not exist, if the resources to do so are available at all. The social stigma and financial loss from an infected herd prevents farmers from testing or slaughtering their animals. Farmers are also reluctant to vaccinate their cattle since the test for tuberculosis cannot differentiate between an infected cow and a vaccinated cow, which may lead to unnecessary slaughtering. Without regulations and resources, bovine tuberculosis will continue to endanger cows and humans as long as infected animals survive, contaminated milk is sold, and the disease goes unreported.
The threat of bovine tuberculosis goes beyond its ability to spread. It also may require different treatments than human tuberculosis. Bovine tuberculosis is naturally resistant to pyrazinamide, one of the four antibiotics used to treat human tuberculosis.Additionally, bovine tuberculosis takes three months longer to treat than human strains,, so a misdiagnosed person will not take antibiotics long enough to kill all the bacteria. The bacteria that survive will be resistant to that antibiotic in the future. Further complications include the differences in the way bovine tuberculosis is spread and the way the disease manifests in the body. While human tuberculosis is inhaled from the air and primarily affects the lungs, Bovine tuberculosis is most often ingested through milk products and therefore affects the intestines, liver, and even lymphnodes of humans. All these factors affect how the disease needs to be diagnosed and treated in humans; however, the current test for tuberculosis gives a simple “infected†or “not infected†result and does not differentiate between human and bovine TB.
Recently, more attention is being given to a “one health†approach to treating diseases like tuberculosis. This approach recognizes that the health of people, animals, and the environment are interconnected and must be treated together. Researchers like Quinn are realizing the reality of treating disease with a zoonotic component:
“Just focusing on eliminating [the disease] from humans is not going to eliminate it from the human population.â€
In the case of tuberculosis, properly diagnosing the disease in cattle, wildlife, and humans through tests that differentiate bovine tuberculosis from the human form is the best place to start. Attention also needs to be paid to the economic and social factors that may prevent the diagnosis of the disease in developing countries. This one-health approach is already being implemented to control diseases such as influenza, ebola, and anthrax.
Rama and the tuberculosis outbreak he caused at the Oregon zoo are case study in a one-health approach. Routine testing and treatment of patients—animal and human—were successful in stopping the spread of disease. Although tuberculosis is far more complex and widespread on a global scale, enacting the one-health approach may provide the catalyst to end a disease that's been around for millennia.
About the Author
 Megan Prescott is a Ph.D candidate in the Department of Microbiology at the University of Georgia. She dedicates her time outside the lab to serving as President of UGA's Women in Science (WiSci) organization, volunteering with the Junior League of Athens, and continuously watching The Office on Netflix. She counts each day she leaves the lab without giving herself TB as a success. More from Megan Prescott. |
