Sea Turtles: Old Viruses and New Tricks Dispatch

Emerging diseases seemed to enter the nightmares of mainstream culture with the ebola and hantavirus scares of the 1990s. Since then, emerging diseases have become a major health concern in human populations, with such diseases as severe acute respiratory syndrome (SARS), avian influenza and West Nile virus disease sickening and scaring people around the globe. Most people do not realize that emerging diseases are also a problem for wildlife and may be a major threat to endangered species [1]. In the last decade, there has been an increase in the number of cases of a wide spectrum of diseases in populations of diverse species of plants and animals [1,2]. Emerging diseases in wildlife are important for the obvious reason that they can cause population declines in the susceptible species. But these diseases in wildlife are important from a human health standpoint too, because many of the emerging diseases in humans have been linked to wildlife species that serve as reservoirs of the pathogen. Furthermore, the study of emerging diseases in wildlife may well provide general insights that help us to understand the dynamics of emerging diseases in human populations. As reported in a paper just published in Current Biology, Herbst et al. [3] investigated the cause of the recent outbreak of marine turtle fibropapillomatosis by examining the evolution of the virus that causes the disease. This disease affects mainly the green sea turtle (Figure 1), but cases have also been documented in loggerhead, olive ridley and now Kemp’s ridley sea turtles. The fibrous growths typical of fibropapillomatosis were first described in 1938 and reports of the disease were relatively rare until after 1980 [4]. Now, fibropapillomatosis occurs around the globe and in one recent sample from the Hawaiian Islands more than 90% of green turtles showed symptoms of the illness [4]. From the standpoint of a wildlife enthusiast, fibropapillomatosis is a heinous disease, marring the usually noble appearance of the beloved sea turtles. The growths associated with the disease occur mainly on the soft skin of the turtle, but they can appear internally as well. The growths can be so large that they interfere with normal mobility, vision, feeding and organ function. In addition to these gross mechanical effects, the disease appears to result in suppression of the immune system and a susceptibility to bacteremia [5,6]. Consequently, death is the ultimate outcome for many of the turtles affected by the disease. All the current evidence suggests that marine turtle fibropapillomatosis is caused by a herpesvirus that has been shown to be associated with the growths [7] (although definitive experiments involving cultured virus particles have not yet been possible). But why does the virus causes so much harm now compared to 50 years ago? Two non-exclusive hypotheses can explain the sudden increase in frequency of fibropapillomatosis (and most other emerging diseases in wildlife for that matter). One possibility is that a change in the environment caused the host species to become extremely susceptible to a previously harmless strain of virus, for example, as a consequence of immune suppression, a new vector and so on. The other possibility is that the disease is Current Biology, Vol. 14, R842–R843, October 5, 2004, ©2004 Elsevier Ltd. All rights reserved. DOI 10.1016/j.cub.2004.09.038