Scientists discover novel viruses in Galapagos giant tortoises

Scientists from the Charles Darwin Foundation (CDF), the Saint Louis Zoo Institute for Conservation Medicine (ICM), the Research Center for Animal Health (INIA-CISA), the Complutense University, and the European University of Madrid, together with technicians from the Galapagos National Park Directorate (GNPD) describe, for the first time, four novel viruses in giant tortoises from the Galapagos Islands.

This research determined that several species of giant tortoises living on different islands carry herpesviruses and adenoviruses, two viruses well-known for causing disease in turtles and tortoises around the world. These results were verified in a process that is similar to the Covid test we humans have become increasingly familiar with, but for tortoises, we collect a swab sample from the eyes, mouth, and the cloaca for PCR (molecular) analyses.

Scientists tested a total of 454 tortoises and assessed up to four infectious disease-causing agents that threaten turtles and tortoises around the world (herpesvirus, adenovirus, mycoplasma, and ranavirus); two of these (adenovirus and herpesvirus) were deemed positive in Galapagos tortoises.

"Infectious diseases have been reported as causes of mortality in turtles and tortoises globally, but previous to our study there was no information about the infectious diseases that may affect giant tortoises in Galapagos” explains Dr. Ainoa Nieto Claudín, first author of this work, Ph.D. candidate and researcher at the CDF and ICM.

Interestingly, not all tortoise species tested in this study carried viruses. For example, in Española island that is not inhabited by humans, no viruses were detected, whereas in Santa Cruz both adenovirus and herpesvirus were detected in the species more closely related to human activities.

“Giant tortoises act as sentinels of ecosystem health and the discovery of four viruses highlights the need for in-depth studies of infectious agents in the Galapagos wildlife”, adds Dr. Nieto Claudín.

Another research study recently conducted by the same group described how human activities in Galapagos are driving the transmission of antibiotic resistance in giant tortoises.

Dr. Sharon Deem, Director of the ICM and senior author of the paper comments: “In the era of Covid-19 it has become increasingly evident of the value for conducting health assessments of endemic wildlife species to detect novel and emerging diseases that may threat animal and human health alike.”

Dr. Fernando Esperón, co-author of the paper and professor at the European University of Madrid explains:

“More than 70% of the diseases that threaten human health are also shared with domestic and wild animals. By attending animal health and testing them for potential diseases we are also taking care of potential human health threats.”

But discovering new viruses is not necessarily a negative thing. These are most likely endemic viruses that have evolved with their hosts -the giant tortoises- for hundreds of years.

“Endemic pathogens that have evolved with a particular species do not usually cause harm or diseases to those species unless the virus jumps to another species, or if the animal harboring the virus suffers from other stressors that may compromise their immune system,” explains Dr. Deem.

Future viral screening of other tortoise species is crucial to determine if these viruses play a role in tortoise fitness, morbidity, and survival, and whether some tortoise species might be “virus-free” and therefore more susceptible to diseases if they get in contact with infected animals.

This information will allow researchers to provide proper recommendations to the Galapagos National Park Directorate and other institutions to improve the management and reintroduction plans for these unique species, which would include strategies to avoid the movement of potential pathogens across islands and populations not previously exposed to these viruses.

This research was published in the journal of Transboundary and Emerging Diseases, which can be accessed through this link.