When Dr Rachel Gray of the University of Sydney set out to save Australian sea lions she had no idea her tool would become the center of a culture war before the work was published. Now, however, the results are in, and she and her co-authors have shown a dab of ivermectin on the back of a sea lion pup's neck could be key to saving the species. Many other seals and sea lions may benefit as well.
A tragedy of the promotion of ivermectin against COVID-19 – based on a mix of flimsy and fraudulent evidence – is that it may harm the perception of a wonderful drug. There's a reason the discovery of ivermectin won a Nobel Prize, and its benefits extend to a wide range of mammals plagued by parasites, both internal and external.
Hookworms are so abundant among Australian sea lions (Neophoca cinerea) that 100 percent of young get infected via their mother's milk within days of birth. As many as 40 percent of pup deaths are directly linked to the anaemia the parasites induce, while slower growth makes the rest more vulnerable to other causes, contributing to a 64 percent decline in offspring in three generations. In the International Journal of Parasitology: Parasites and Wildlife Gray shows there is hope, however.
Other seals and sea lions also suffer hookworm infections, although Australian sea lions (N. cinerea) are particularly vulnerable because their numbers were so devastated by sealers. Previous research has shown an injection of ivermectin can form an effective treatment in related species. However, Gray told IFLScience, “anything that involves sharps in a field environment is a problem,” requiring a level of expertise that is not always available.
Gray and PhD student Scott Lindsay decided to test an easier solution, parting the fur on the back of a pup's neck and applying ivermectin in a viscous fluid to 27 pups at Dangerous Reef, South Australia. Another 29 received an ivermectin injection, while an equal number served as controls.
On subsequent recapturing the authors found both ivermectin groups were almost entirely freed of hookworm infection – topical ivermectin was 96.4 percent effective and injected was 96.8 percent. As a bonus, they were also largely protected from lice, which are not lethal but can exacerbate ill-health caused by other issues.
Gray told IFLScience she hopes rangers could apply the treatment to pups they encounter, although she is still looking for a method that would keep everyone well clear of the pups' very sharp teeth. Although the pups are distributed over 3,000 kilometers (1,864 miles) of Australia's shoreline – many in very inaccessible places – 40 percent are born and grow up on just four beaches, providing excellent opportunities to turn declining numbers around.
The sea lions and the hookworms have lived together for a long time, Gray told IFLScience, and it seems unlikely deaths were always so common. Pollutants or other stressors, even in a relatively untouched part of the world, are thought to be making the pups more vulnerable, but the exact cause is unknown, and therefore hard to fix.