In the 1990s, the San Miguel Island fox faced a critical threat of extinction, with its population dwindling to just 15 individuals. A recovery initiative helped boost their numbers by 2010. However, between 2014 and 2018, the population decreased to just 30% of its peak level due to the emergence of a new acanthocephalan parasite, worsened by an extended drought. A cooperative research project used both morphological and molecular techniques, along with necropsy data, to identify the parasite and evaluate its effects on the foxes’ health.
The Channel Island fox (Urocyon littoralis), one of the smallest and most cherished island fox species in the United States, resides in California’s Channel Islands. While they are no longer listed as endangered, they still are regarded as a species of concern due to their important ecological role.
Throughout the 1990s, the population of the San Miguel Island fox was on the verge of extinction, reaching a mere 15 individuals. Fortunately, a recovery program helped restore their numbers by 2010. Sadly, between 2014 and 2018, the population dropped back to 30% of its peak as a new acanthocephalan parasite, commonly called thorny-headed worms, was discovered on the island. This situation coincided with a multi-year drought, complicating the assessment of the impact of the newly introduced parasite on the foxes of San Miguel.
A collaborative scientific study, involving a researcher from Florida Atlantic University, sought to identify this parasite and analyze its health implications for the fox population. They utilized both morphological and molecular methods to pinpoint the acanthocephalan parasites, in addition to a comprehensive collection of records from island fox necropsies and associated parasite data to explore how the parasite affected the overall health of individual foxes and the population as a whole.
The study’s findings, published in the International Journal for Parasitology, identified the parasite as Pachysentis canicola, which is commonly found in various carnivores in mainland North America. This parasite was detected in 69% of the necropsied foxes from San Miguel Island, but it was absent in the other five subspecies of Channel Island foxes.
Health problems associated with the acanthocephalan parasite, including severe intestinal damage and inflammation, were observed in 47% of infected foxes. Other parasites did not have a significant effect on the health or survival rates of the San Miguel Island foxes until the arrival of the acanthocephalan. Following 2018, improved rainfall may have contributed to the recovery of the foxes’ condition; however, it remained 27% below levels prior to the parasite outbreak, suggesting that both environmental influences and parasites play a role in shaping fox populations.
“We believe this parasite likely made its way to the island through infected arthropods, such as insects that were unintentionally transported by humans,” explained Ale Aleuy, DVM, MPVM, Ph.D., the senior author and an assistant professor in the FAU Department of Biological Sciences within the Charles E. Schmidt College of Science. “This finding raises concerns regarding human impact on isolated ecosystems and emphasizes the need for monitoring parasitic infections in at-risk wildlife populations.”
The research team utilized detailed data from 4,269 captures of 846 foxes to examine changes in their health and demographic trends before and after the parasite’s detection. They analyzed shifts in body condition and weight from 2006 to 2022. Prior to the arrival of the acanthocephalan, the foxes showed good health and low mortality despite the presence of other parasites.
“This parasite attaches itself to the host’s intestinal wall, which becomes particularly problematic for heavily infected foxes that exhibit serious health issues such as emaciation, enteritis, and potentially death,” stated Aleuy. “Following the parasite’s introduction, the foxes displayed poorer body condition and reduced weight, and these issues intensified during drought times. This situation underscores the importance of understanding the life cycle of this parasite and its impact on fox health, while also striving to prevent its spread to other Channel Islands.”
Environmental factors can influence disease dynamics, and even though foxes may manage to survive with P. canicola under favorable conditions, they may require additional support during droughts.
“The acanthocephalan parasite certainly posed significant health challenges for the foxes, leading to issues like weight loss and intestinal problems. Nonetheless, after the drought, we’ve observed a positive shift. While their condition has yet to reach pre-parasite levels, the overall health of the foxes seems to be stabilizing, showing encouraging signs of recovery,” said Aleuy. “This resilience inspires hope for their ongoing recovery.”
The researchers also propose the possibility that P. canicola was present before 2012 without detection, likely due to changes in the foxes’ diets that increased their exposure to intermediate hosts.
“Implementing suitable management strategies is essential for safeguarding this vital fox species’ health and longevity,” advised Aleuy. “Controlling the invertebrates that transmit the parasites could be beneficial, especially if they are non-native to the island.”
The primary objective is to prevent the parasite from spreading to other Channel Islands. The results of this study underscore the significance of biosecurity measures within Channel Islands National Park and highlight the need for further research on P. canicola and its effects on fox populations.
