PRO/AH/EDR> Avian influenza (166): Americas (Peru) H5N1, sea lion, conservation concern


A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases

Date: Sun 5 Nov 2023
Source: News Medical [edited]

In a recent early-release research letter published in Emerging
Infectious Diseases by the United States Centers for Disease Control
and Prevention (CDC), researchers report their recordings of a
synchronized mass mortality of over 5000 Peruvian sea lions (Otaria
) presenting symptoms characteristic of avian influenza A
(H5N1) infection. Herein, the researchers estimate that about 5% of
Peru’s entire sea lion population perished to the virus in a matter of

These findings emphasize that urgent research and conservation
interventions are needed to prevent these colonially breeding animals
from further population collapse.

H5N1 is a highly virulent and extremely infectious pathogen,
particularly in birds. First discovered and isolated in 1996 from
geese in Guangdong Province, China, H5N1 has repeatedly mutated,
reassorted, and spread throughout Asia, Europe, North America, and,
most recently, Africa. Along with its sister strain A (H5N2), H5N1 has
been responsible for over 200 million avian deaths since 2002.

Avian influenza is panzootic, affecting not only birds but also
mammals, including humans. While person-to-person transmission is
rare, contact with infected birds has resulted in 878 reported cases
of human infections since early 2003, 458 of which were fatal, thus
leading to a human mortality rate of 52%. The impact of H5N1 on
livestock and wildlife is even more severe, with H1N5 claiming the
lives of hundreds of thousands of mice, ferrets, and pigs globally.

The global transmission of avian flu is primarily attributed to the
long-distance migrations of wild waterfowl, ducks, geese, and swans.
In December 2022, H5N1 reached South America and, within only 3
months, resulted in the deaths of over 200 000 Peruvian birds. Species
that were more significantly affected included the Peruvian boobies
(Sula variegata), Peruvian pelicans (Pelecanus thagus), and guanay
cormorants (Leucocarbo bougainvilliorum).

Similar to zoonotic spillover events reported in New England seals in
the United States, the sizeable infected biomass of dead marine birds
may have caused H5N1 to be transmitted from birds to Peruvian sea
lions (Otaria flavescens), thus resulting in unprecedented mortality
in the species.

In the present research letter, researchers conduct detailed
surveillance of agonal and dead sea lions in Peru’s protected areas
between January and April 2023. A total of 5224 dead animals were
recorded in 4 months, 1112 of which were found on San Gallán Island.
These numbers represent about 5% of Peru’s entire sea lion population
and form a significant portion of the global estimate of 225 500
extant mature individuals.

Due to restrictions implemented by Peruvian national health
authorities, researchers were only able to perform one necropsy, while
other study findings were derived from veterinarians’ observations.
These observations included signs of respiratory distress such as
dyspnea, tachypnea, and buccal and nasal secretions.

The single necropsy revealed lung congestions alongside hemorrhagic
focus, which were suggestive of interstitial pneumonia. Brain tissue
similarly exhibited congestion and hemorrhagic focus that was
suggestive of encephalitis.

Proximity to infected H5N1 avian carcasses led researchers to
hypothesize that zoonotic spillover caused this ‘massive mortality’ of
sea lions, later confirmed in clinical studies. Alarmingly, novel H5N1
substrains were discovered in sea lion carcasses, thus alluding to the
continued and rapid evolution of H5N1 and the potential for further
damage to marine life.

Research in Chile reported thousands of infected and dying sea lions
along their shores that were attributed to the December-May [2023] breeding season of these animals.

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