Hand sanitizers and vitamins only get humans so far when it comes to warding off harmful illnesses; for elephants the options are even more limited. Researchers at the Smithsonian Conservation Biology Institute have turned, instead, to genetics to understand how Asian and African elephants fight infectious diseases and, perhaps, increase the animals’ ability to stay healthy.
The scientists analyzed part of the complex gene family that helps determine how resistant elephants are to the type of diseases that have devastated their species, including tuberculosis and the herpes virus. This gene family, called the major histocompatibility complex (MHC), is crucial to most vertebrates’ ability to fight off pathogens, and SCBI’s researchers and collaborators this year became the first in the world to “characterize,” or interpret and describe, these genes in elephants.
“Part of the excitement I feel is just the joy of discovering something new, especially when it involves overcoming major technical challenges to make the discovery,” said Robert Fleischer, head of SCBI’s Center for Conservation Genomics and a co-author on a paper about the work published in scientific journal Immunogenetics. “The other part is that it opens up a realm of additional research possibilities, from understanding the evolution of MHC genes in mammals to determining their precise role in disease resistance.”
Pairs of genes, known as alleles, determine traits such as eye color or, in this case, disease resistance. Proteins made by different alleles in the MHC recognize the proteins in harmful pathogens and attack them, so the more varied the alleles, the stronger the animals’ line of defense against disease.
SCBI’s researchers found about ten MHC-DQA alleles in the MHC of African and Asian elephants, compared to 20-50 alleles in other vertebrates and up to 100 in humans. One allele, however, was particularly common in the 30 African and three Asian elephants involved in the study, suggesting that elephants’ genes may have evolved in response to a past epidemic.
Of course, the DNA had to come from somewhere and SCBI scientists were fortunate to have resources at the National Zoo to help get the needed samples. Not only were the Zoo’s three Asian elephants, Shanthi, Kandula, and Ambika, among those included in the research, National Zoo head veterinarian Suzan Murray helped coordinate the collection of blood samples from other zoos.
“The more we can find out about genetic links to health and disease, the better,” said Murray, a co-author on the Immunogenetics paper. “There’s a lot genetic predisposition to diseases that we don’t yet know, but first you need a mapping of the genome, as well as the different immune complexes.”
MHC markers may also help researchers understand why elephants appear to recognize their own kin, preventing the type of inbreeding that could genetically weaken the species and affect their long-term viability.
“Elephants not only avoid maternal relatives but paternal relatives,” said Elizabeth Archie, former postdoctoral fellow at the National Zoo and lead author of the paper. “In other systems, MHC genes have been implicated in kin recognition. Scientists think animals can smell animals that are related to them by products of MHC genes.”
Although Asian and African elephants became two distinct genera at least six million years ago, the researchers found that these particular genes have not changed much between the two. This is unusual relative to other genes that have diverged naturally (like hemoglobin) and indicates that the elephants have had to fight off similar diseases over time.
Because of infectious disease, poaching, and habitat loss, the Endangered Species Act considers African elephants to be a threatened species and Asian elephants to be endangered. There are only an estimated 575,000 African elephants and 30,000 Asian elephants left in the wild—combined that’s less than the human population of El Paso, Texas. Elephants in captivity, meanwhile, have been plagued by elephant endotheliotropic herpesvirus, which is responsible for about half of the deaths of young elephants in zoos. One of the next steps for SCBI’s researchers is to determine whether the MHC affects susceptibility to this disease, which the National Zoo discovered was killing young elephants in zoos and at circuses.