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Boxmeer (the Netherlands), January 27, 2011
– Intervet/Schering-Plough Animal Health
announced that it is entering the final stage
of development of a vaccine against Rhodococcus
equi, a bacteria that causes an acute and severe
pneumonia in foals. For the candidate vaccine,
which will be tested in a field trial in Germany,
a special, non-pathogenic bacterium strain has
been used of which four genes have been deleted
from the genome.
Currently, it is difficult to protect foals
against this potentially fatal disease as attempts
to develop a vaccine have not been successful
so far. However, there is an urgent veterinary
need for an efficacious and safe vaccine to
prevent infection with R. equi or to reduce
its symptoms because infections in foals can
currently only be managed with long-term antibiotic
treatment. Moreover, foals that recover from
the infection may be left with permanent pulmonary
lesions, which decrease their future performance
and cause financial losses to the breeding sector.
According to Dr. Rene Aerts, Vice President
Global Biologicals R&D at Intervet/Schering-Plough
Animal Health, the availability of a safe and
efficacious vaccine against R. equi would generate
several benefits: “The advantage for the
animals would be, that they are protected against
suffering from a severe and potentially fatal
disease. In addition, for horse owners and breeders
disease prevention would avoid significant economic
losses. Finally, the availability of a safe
and efficacious vaccine would lead to a reduction
of antibiotics prescription in animals”,
Dr. Aerts explained.
The candidate vaccine strain is derived from
a wild type R. equi bacterium which has lost
its virulence due to the deletion by genetic
modification of four genes which are crucial
for its pathogenicity. Extensive safety studies
have been performed, demonstrating the inability
of the vaccine strain to cause pneumonia in
foals. In addition, because the vaccine strain
is unable to survive in macrophages, it is expected
to be unable to cause disease in humans or other
animal species and its safety in calves, pigs,
chickens, mice and rats has been confirmed.
Based on these findings, health authorities
in the Netherlands have evaluated the safety
of this candidate vaccine and have concluded
that the risk of introducing this modified vaccine
strain is negligible for humans, animals and
the environment.
EU regulations require that candidate vaccines
are also tested for efficacy and safety under
practical conditions before any marketing authorization
will be granted. The execution of such field
trials needs prior governmental approval. Intervet/Schering-Plough
Animal Health has recently applied for permission
at the German BVL (Bundesamt für Verbraucherschutz
und Lebensmittelsicherheit) to perform a field
trial with the vaccine in Germany. The study
will be executed under strict biosafety measures
as required by German and EU legislation (in
particular Directive 2001/18/EC). In the first
phase of the study, a group of foals will be
vaccinated with the candidate vaccine and will
be compared to a goup of non-vaccinated foals.
The number of R. equi infections will be evaluated
in each group.
R. equi is a common gram-positive intracellular
bacterium which is found in soil (especially
where domesticated livestock graze). In addition
to soil, the bacterium may be recovered from
intestines of mammals and has a long survival
time in manure and soil. R. equi is a well-recognized
pathogen causing pneumonia with abscess formation
as well as other infections in foals, representing
a serious risk worldwide. Infection with the
bacterium is related to a high mortality in
foals left untreated. Foals are infected by
the bacterium while grazing or by inhalation
of contaminated soil dust. R. equi is primarily
pathogenic in young foals, whereas most of the
older equine population (above 6-8 months of
age) are unaffected.
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