A serological test is highly accurate at finding tuberculosis infection in elephants, and can determine such infection years before culture, according to a study in the August Clinical and Vaccine Immunology. The issue is critical not only for elephants, which are an endangered species, but for human public health, because elephants are among the very rare animal species which are commonly infected by human strains of tuberculosis, says first author Konstantin P. Lyashchenko of Chembio Diagnostic Systems, Inc., Medford, NY.
Elephants are unusual when it comes to diagnosing M. tuberculosis. Generally, bacterial infections can be diagnosed much earlier with culture than with serology. "Serology is considered to be a late diagnostic marker of tuberculosis in humans and various animal species," says Lyashchenko. "However, efforts to isolate M. tuberculosis from live, infected elephants have proven very disappointing, whereas antibody assays in such animals showed promise for early detection of TB," says Lyashchenko.
Lyashchenko and his collaborators first realized the promise of serology for diagnosing TB in elephants, in 2004, when they were asked to test serum samples from a zoo elephant that had been diagnosed with M. tuberculosis in 2000. They requested serum samples going back 10 years, and discovered the elephant had become antibody positive in 1996. Later, they found that all 26 elephants that had been culture confirmed as infected tested antibody positive for M. tuberculosis.
The novelty in the new paper is that instead of conducting serological tests in elephants that were known, via culture, to be infected with M. tuberculosis, the researchers began conducting serology in elephants that were not known to be infected, deflecting criticisms that interpretations of antibody test results might be biased by the knowledge that the elephants were infected, says Lyashchenko.
That is important, because the earlier research and development leading to approval of the Chembio antibody assays by the United States Department of Agriculture (USDA) in 2007, resulted in USDA's implementing a requirement by the USDA two years ago that all ~450 elephants in the US be tested annually using the Chembio serology. When elephants are diagnosed with tuberculosis, and confirmed by culture, their owners have a choice of treating, quarantining, or euthanising the elephants. Treatment takes around a year, and is very expensive, partly because such large animals require proportionately large quantities of drugs.
The incidence of TB appears to be higher in circus elephants than in zoos, says Lyashchenko. He notes that TB has more opportunity to spread among circus elephants than in zoo or sanctuary elephants, because they travel together more frequently and are both kept in closer proximity to, and exposed to greater numbers of people and other animals.
Positive cultures for M. tuberculosis are difficult to obtain because bacterial shedding occurs only intermittently, so that "trunk wash" samples, from which cultures are grown, must be taken repeatedly before success is achieved. Further slowing diagnosis, elephants can be infected with M. tuberculosis for a number of years before showing signs of disease.
"Very interesting and potentially right up my alley," says Suzan Murray, head veterinarian at the National Zoo. "We are beginning to do more field work with elephants and this could be very helpful."
(K.P. Lyashchenko, R. Greenwald, J. Esfandiari, S. Mikota, M. Miller, T. Moller, L. Vogelnest, K.P. Gairhe, HS. Robbe-Austerman, J. Gai, and W. Ray Waters, 2012. Field application of serodiagnostics to identify elephants with tuberculosis prior to case confirmation by culture. Clin Vaccine Immunol. 19:1269-1275.)