Avian Influenza (AI) or Fowl Plague
is an endemic disease in poultry and
other birds around the world caused
by type A influenza virus. It is a devastating
disease that can cause high
mortality in infected flocks and causes
even more dramatic economic
effect on the trade of poultry products
between countries. Avian
Influenza exists in two forms. The
very virulent, (Highly Pathogenic) form that
causes high levels of mortality and
morbidity. Highly Pathogenic AI has only
been described for subtypes H5 and
H7. The Low Pathogenic form of the disease
occurs with infections of all subtypes
of AI. Mild respiratory signs, depression
and a reduction in egg production
in commercial layers
characterize infection with the
low path form.
The standard procedure
for eradicating outbreaks
of AI is depopulation of
the birds on the infected
premises followed by a
period of cleaning and
disinfection. Eradication
is time consuming,
expensive to conduct
and usually requires
an indemnification
payment to the
farmer for the
value of the birds.
The experiences with eradication
have raised questions about the cost
benefit of depopulation strategies as
the only way of handling large outbreaks
of thousands of birds.
The OIE and the FAO have recognized the that the use of vaccination is an important tool for the control of avian influenza along with target culling of infected flocks, surveillance and epidemiological monitoring of the spread of the disease.
Merial has a strong tradition
with the manufacture of inactivated
vaccine and is the only
manufacturer of a vector vaccine
for AI.
The Merial facilities in
France and Italy can
produce inactivated AI
vaccines. The vector vaccine
is produced in the
USA.
Vaccines containing different subtypes have been produced to control outbreaks in countries around the world. Emergency vaccines
containing other local AI isolates can
be requested.
Merial was the first company to
develop a vector live vaccine for AI
using a fowl pox virus as a
vector and expressing the hemagglutinin
gene from a subtype H5 virus.
The TROVAC AI H5 vaccine was
licensed by the USDA in 1998
and is being used widely to control the spread of AI in Mexico.
More than 2 billion doses have been sold
in the countries of Mexico,
El Salvador, Guatemala and Vietnam. A temporary marketing authorisation was issued for France.
TROVAC AI H5 is intended
for use in one-day-old chicks
or older birds that have not
received a primary inoculation with a
live pox vaccine. Development continues
for similar vaccines containing
subtypes H7 and H9.
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