Cats can spread deadly bird flu
19:00 02 September 2004
NewScientist.com news service
Cats can catch - and spread - the bird flu that has ravaged poultry
and killed at least 26 people across East Asia in 2004. This is the
first time cats have been known to get sick from flu, and means the
H5N1 virus has already acquired the ability to spread in some mammals.
The fear now is that cats, and perhaps other animals, could act as a
vessel for the virus to further evolve into a human pandemic.
Thijs Kuiken and colleagues at the Erasmus Medical Centre in
Rotterdam, the Netherlands did the study after three cats and a zoo
leopard living near sick poultry in Thailand were confirmed in
February 2004 to have died of H5N1.
A tiger in the same zoo got sick with H5N1 but recovered. Cats have
never been observed to get sick from flu infection before, Kuiken
told New Scientist.
The team infected three laboratory cats with H5N1 taken from a human
case in Vietnam. All got very sick with flu symptoms, and post mortems
showed they had the same lung damage as people.
Cats given a human flu virus, H3N2, stayed healthy. Other cats studied
caught H5N1 by eating infected birds, while two healthy cats housed
with the sick animals caught the disease, showing it spreads among
The results mean pet cats might give people H5N1 after eating one of
the many wild birds or poultry still infected across East Asia. But
more worrying than cats spreading the existing virus, says Kuiken, is
how cats might change its evolution.
H5N1 was already known to infect mammals 34 people, of whom 23 died,
were confirmed to have the virus before the Asian poultry outbreak was
largely controlled in March.
Three more deaths have since been confirmed in Vietnam, where H5N1 has
again broken out in poultry. But so far the virus seems unable to
spread from person to person.
If H5N1 acquires this ability, it could cause a lethal pandemic. The
World Health Organization fears the virus might do this by hybridising
with a human flu in a person infected with both.
Pigs also pose a theoretical risk as they catch both bird and human
flu. In August, Chen Hualan of Harbin University in China told a flu
conference in Beijing that H5N1 had been found in Chinese pigs in 2002
and 2003, which China had not previously reported.
What has received less attention, says Kuiken, is the possibility that
H5N1 could quietly evolve the ability to spread among humans by
itself, by infecting species that select for viruses better adapted to
Some researchers think this route - rather than bird flu combining
with a human flu - is how the lethal 1918 flu pandemic evolved. Chen
also reported in Beijing that her team had successfully infected mice
with H5N1 in the lab.
The more mammals the virus can infect, the greater the risk that it
will change to one that can transmit easily among mammals, says
Kuiken. The team is now checking whether cats can catch another bird
flu, H7N7, which broke out in the Netherlands in 2003, and can infect
Journal reference: Science (DOI: 10.1126/science.1102287)