Scientists Discover Liver Parasite Behind Severe Lung Infection in Common Dolphin
In May 2023, a juvenile male common dolphin (Delphinus delphis), measuring 142 centimetres in length and weighing 25.7 kilograms, was found stranded on Isuntza beach in Spain’s Basque Country. While strandings are not uncommon along European coasts, this case reveals something scientists had never documented before.
Scientists have documented the first known case of the parasitic worm Brachycladium atlanticum, typically known for infecting the liver of striped dolphins, causing severe lung disease in a common dolphin (Delphinus delphis). Authors Andrea Estarrona, Gaizka Peñín, Xabier Lekube, Irune Valenciano, Oihane Díaz de Cerio, Manu Soto, Urtzi Izagirre, and Denis Benito presented this case in a paper published titled First confirmation of Brachycladium atlanticum as aetiological agent of pulmonary pathologies in a common dolphin (Delphinus delphis).
The discovery comes from a necropsy of a dolphin found stranded on Spain’s Basque coast, offering a rare glimpse into how parasites can dramatically affect the health of marine mammals. As they explained, the necropsy report included biological data, species identification, biometrics, age, sex, body condition, and conservation status.
The first documented case
The young dolphin showed signs of poor nutrition and generally weakened health. According to the report, “although fish remains were present in the stomach, and the dentition was in good condition, the thickness of the blubber and the depressions observed on the carcass indicated a poor nutritional status, suggesting that its condition may have been caused by a consumptive disease potentially linked to the multispecific parasitic infestation.”
But the most striking findings were in its lungs. “A cystic formation measuring approximately 4 cm in width and 5 cm in height was found in the right lung, which released a large amount of brown fluid and showed signs of necrosis. In the left lung, severe granulomas, nematodes, and necrotic tissue were present,” the researchers described. Tissue analysis revealed numerous parasite eggs embedded in lung tissue, along with inflammation, calcification, and abnormal blood vessel growth. To confirm the parasite’s identity, researchers combined traditional morphological analysis with modern genetic sequencing. The results were clear: the parasite was B. atlanticum. This marks the first documented case of this species infecting the lungs of a common dolphin, making the infection both unusual and scientifically significant.
“This finding can be considered of great importance, as the health impairments generated by the infestation might have reduced the animal’s chances of survival,” the researchers wrote.
How did the dolphin get infected, and what does that mean?
Scientists suggest the dolphin may have become infected by eating an intermediate host, likely a fish carrying the parasite’s larval stage. Another possibility is that adult parasites migrated abnormally from their usual location in the liver and pancreatic ducts into the lungs, where they later released eggs.
The discovery has broader implications for monitoring marine mammal health. Parasites like B. atlanticum can create multiple lung lesions, increase vulnerability to secondary infections, and reduce an animal’s chances of survival. The study also highlights the importance of combining traditional morphology with molecular techniques, since egg shape alone is often not enough for precise identification. The findings expand scientists’ understanding of brachycladiid trematodes and highlight potential risks for small dolphin species in the wild. Research like this helps scientists track the health of marine populations and may help inform conservation strategies, while revealing unexpected ways parasites can threaten their hosts.
“Furthermore, the new molecular data and evidence of the parasite’s underestimated pathogenicity help shed light on the little-known brachycladiid family and open new possibilities for future research,” the team concluded.
Image: NOAA NMFS, Public Domain
