Seven employees of the Oregon Zoo in Portland have contracted a latent form of tuberculosis in 2013 from three of the Zoo’s elephants. This information was published by the Centers for Disease Control and Prevention (CDC) in Atlanta, USA, on 8 January.
Apparently the CDC report was issued due to the ruling of a judge in a lawsuit filed by the animal-rights group People for the Ethical Treatment of Animals (PETA) against the CDC’s parent organization the U.S. Department of Health and Human Services. Information on the tuberculosis investigation regarding the Oregon Zoo elephants had to be revealed. PETA wanted release of the information because of the risk involved when elephants would spread the potentially deadly disease to other elephants or to humans.
Tuberculosis (TB) is a respiratory disease that is spread through the air when a person — or in this case elephant — coughs, sneezes or otherwise spreads the pathogen, a bacteria. TB is a well-known disease and cause of death in elephants. The pathogen causing TB, Mycobacterium tuberculosis, is even implicated in the extinction of the American mastodon. The first zoo elephant death which reportedly was infected by TB was an Asian elephant at London Zoo in 1875. But African elephants can suffer from TB too, as it was first reported in 1962. Both the human form (Mycobacterium tuberculosis) and the bovine form (Mycobacterium bovis) can cause infection and disease in elephants. The avian form (Mycobacterium avium) is found in elephants but doesn’t cause disease.
In 1983 a circus elephant in North America was diagnosed with TB. Though nobody recognised it at the time, this report predicted a problem for captive elephants in North America and Europe that only would show more than a decade later. In 1996 TB re-emerged in elephants in the U.S. with the death of again two circus elephants. But more significant was the diagnosis of 5 new elephants with TB at 4 other facilities. And perhaps even more important, TB in elephants proved to be a zoonosis in 1997. Zoonotic transmission of TB from elephants to humans working in close proximity was described in the late 1990s. Obviously TB in captive elephant herds was an issue to be addressed seriously. So, the first guidelines for the control of TB in zoo elephants were produced in 1998.
In North America, approximately 5% of the captive Asian elephants are infected with M. tuberculosis, based on positive cultures of trunk washing samples or necropsy results. However, not only elephants in the USA are susceptible to TB. Until 2008 seven elephant TB cases have been reported in Europe, while 59 of 387 captive elephants had TB in four states of southern India.
TB in captive elephants is a re-emerging zoonotic disease. A zoonosis is an infection ‘shared in nature by man and animals’ according the definition of the World Health Organisation. Basically a disease is considered a zoonosis when the infection is transferred from animal to human, and as a reverse zoonosis when the infection is transferred from human to animal.
The 2013 Oregon Zoo case
In May 2013, a 20-year-old Asian elephant bull at the Oregon Zoo was diagnosed with TB during a routine annual culture of a sample from a trunk washing. In addition, two other bulls were detected with the same disease.
CDC Atlanta together with Oregon Zoo identified three different groups of people who had contact with these three elephants. Within the group of close contacts, 19 zoo employees, 6 persons testes positive for TB but were non-infectious. Retrospectively (back to 2010) another 22 close contacts were identified which resulted in another one TB positive non-infectious contact. A total of 7 persons were found to have a so-called latent TB infection.
Within the group of 39 casual contacts and a group of 20 contacts who had attended special events at which the elephants sprayed paint with their trunk onto canvases behind attendees, no persons were tested positive. But some time later another casual contact was identified. This turned out to be someone who had developed a pleural TB that probably wasn’t infectious. This patient had worked at the zoo intermittently during 2012, but had only limited contact with the elephants.
So, of all employees who have been found infected with this dormant type of TB, one showed symptoms (pleural TB) but none were contagious.
Rama, a 31-year-old Asian elephant (and son of Packy) known for his sweet disposition and Jackson Pollock-like painting technique, was humanely euthanized at the Oregon Zoo on 30 March 2015 after animal-care staff determined they could no longer help pain and mobility issues resulting from a 25-year-old leg injury:
(Source: Oregon Zoo YouTube channel)
Although subject to controversy among elephant veterinarians the CDC report suggests to improve screening for detecting TB in captive elephant herds because trunk-wash sample cultures, the standard for diagnosing active TB in elephants, are insensitive and limited by poor accuracy. Therefore, some cases of TB might be missed. In a 2009 article on highly accurate antibody testing for TB detection in elephants the authors say antibody testing will likely allow earlier and more efficient treatment, thus limiting transmission of infection to other susceptible animals and to humans. CDC agrees that further development of improved TB screening methods for elephants is needed to prevent exposure to humans with close and prolonged contact.
The cause of the outbreak is still unclear, but it could be that one of the elephants contracted TB from a human being. After all TB is a zoonosis whereby the pathogen can be transferred from human to animal as well.
Treatment of elephants
Elephants with TB typically are not euthanized, but isolated and treated to prevent infection of other animals and humans. Many elephants have apparently been treated successfully to date, but unfortunately the success rate is not 100%. The cost of treatment is around €50,000 per animal. Moreover there are additional costs for the lab work, the isolation and the employee’s time. It is a labour intensive treatment procedure.
The Oregon Zoo in Portland has announced that it will perform regular assessments on the elephants and the workers through at least June 2016.
Watch Packy, August 2014 — at 52 the oldest male Asian elephant in North America — starts his day by playing with a water cannon and tossing around a 500-pound log in the elephant swimming hole at the Oregon Zoo:
(Source: Oregon Zoo YouTube channel)
(Source: Reuters news release, 09.01.2016; CDC Morbidity and Mortality Weekly Report, 08.01.2016; Tuberculosis in elephants: a reverse zoonosis, by Arnon Shimshony in Healio, December 2008; website elephantcare; A Brief History of TB in Elephants by Susan K. Mikota; Review of Tuberculosis in Captive Elephants and Implications for Wild Populations by Susan K. Mikota in Gajah, 2008; Highly Accurate Antibody Assays for Early and Rapid Detection of Tuberculosis in African and Asian Elephants by Greenwald et al. in Clinical and Vaccine Immunology, 04.03.2009; Tuberculosis treatment protocols and complications for elephants by Genevieve Dumonceaux and Susan Mikota)