Galápagos is home to the marine iguana (Amblyrhynchus cristatus), the world's only sea-going lizard. The conservation status of the species is vulnerable. One reason for this is the negative effect of El Niño events on their populations that can cause mortalities up to 85%. Other threats described include pollution and predation by invasive and domestic species.1
In early September 2013, Galápagos naturalist guides started reporting vomiting and deaths among marine iguanas from the colony at Tortuga Bay, Santa Cruz Island. The Galápagos National Park Directorate (GNPD) and the Charles Darwin Foundation (CDF) immediately began population monitoring onsite and in reference colonies. Around 300 individuals were captured, marked, measured and weighed. Complete health assessments were conducted, including exhaustive clinical exams, blood collection, and oral and fecal swabs. Oral cavity exams revealed stomatitis as a common finding in some of the affected animals. Initially this unusual mortality event (UME) was thought to be confined to Tortuga Bay. Unfortunately, in early October 2013, coinciding with male dispersal for mating season, new cases emerged among marine iguanas from other neighboring colonies. Between September and December 2013 about 160 individuals were found dead in a four-month period. It is likely that many more died, but these are the ones identified. CDF staff could perform necropsies on 20 dead specimens with carcasses between codes 1 and 3, revealing oral ulcerations, compacted stomachs full of undigested red and green algae (their normal food source), severe esophagitis, gastritis and enteritis. Histopathologic examination of 16 individuals revealed acute severe multifocal necrotizing glossitis with bacterial overgrowth, mild acute necrotizing esophagitis, mild interstitial pneumonia, acute congestion in the liver and spleen, and mild renal tubular necrosis in kidneys. The primary problem appeared to be the necrotizing lesions on the tongue and esophagus among 9 of the studied animals, presenting a pattern suggestive of infectious disease, particularly herpesvirus infection, although convincing inclusions were not seen. Death was likely due to endotoxic shock associated with bacterial overgrowth in the tongue. Preliminary electron microscopy (EM) results showed no viral presence but a second round is currently been performed. Molecular (PCR) and biotoxin analyses are being conducted at the time of writing. Preliminary results have revealed a novel alphaherpesvirus in one specimen; further study of other agents and of the clinical significance of the herpesvirus is pending.
The authors wish to thank the Galápagos National Park Directorate for supporting field work and samples exportation permits; Galápagos Conservancy, Lindblad/National Geographic, International Galápagos Tour Operators Association (IGTOA) for financial support. We also thank the collaboration of University of Florida, Northwest ZooPath, Houston Zoo, Inc. and the Charles Darwin Foundation.
* Presenting author
1. Nelson K, Snell H, Wikelski M. 2004. Amblyrhynchus cristatus. In: IUCN 2013. IUCN red list of threatened species. Version 2013.2. www.iucnredlist.org. Downloaded on 23 January 2014.