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A PREVIOUSLY unknown virus could be contributing to the global decline in
numbers of marine mammals.

Australian scientists have found that lice infesting southern elephant seals
carry a type of arbovirus that might infect the brains of seals already weakened
by pollution, causing them to beach. It鈥檚 the first arbovirus to be found in
marine mammals, and the first known to be transmitted by lice.

Many marine mammals are in decline, and several species, such as the
Mediterranean monk seal, are seriously endangered. Pollutants are suppressing
the animals鈥� immune systems, and several recent population crashes have been
blamed on previously unknown viral infections. The situation has prompted a
worldwide search for pathogens of seals.

Andreas Suhrbier from the Queensland Institute of Medical Research and his
colleagues decided to look on Macquarie Island, 2000 kilometres south of the
Australian mainland. The island is home to about 78,000 southern elephant seals,
but the population is inexplicably falling by about 1.5 per cent a year.

The seals are infested with the louse Lepidophthirus macrorhini.
Other blood-sucking parasites such as ticks and mosquitoes transmit a type of
virus called an arbovirus. Seals, whales and dolphins were thought to be safe
from arboviruses, but the researchers decided to check for them anyhow. 鈥淭his
was considered a ridiculous long shot, but it seemed like a good idea that night
when we met in the pub,鈥� says Suhrbier. Arboviruses are common in terrestrial
mammals, including people, and can cause diseases such as rheumatism and
encephalitis鈥攊nflammation of the brain.

The researchers took 12 lice from the seals back to the lab, and found a
previously unknown arbovirus in two of them. 鈥淲e were very surprised that these
lice carried virus,鈥� says Suhrbier. The researchers also studied blood samples
from some of the seals on the island and found that nearly all the seals over
two years of age had antibodies to the virus, suggesting that they had been
infected in the past.

None of the seals was ill, but seal virologist Albert Osterhaus of the
Erasmus University in Rotterdam says that the virus could be a danger if the
seals were immunosuppressed, or if it reached other more susceptible
populations. 鈥淚n general, virus infections will not pose a final threat,鈥� he
says. 鈥淏ut if a population is already on the brink of extinction then a virus
infection might make the difference.鈥� If arbovirus infection results in
encephalitis in seals or whales, it could cause them to beach, Suhrbier says.
鈥淲e are hoping to test the brains of beached animals for virus to check out this
possibility,鈥� he says.