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Surveillance, supported by comprehensive laboratory studies, is a key activity
underpinning all aspects of disease control and eradication, vaccine strain
selection and vaccine efficacy monitoring. Regardless of the nature of the samples,
it is important that collection is based on a properly defined plan so that the results
of laboratory assays will be meaningful and the samples useful.
Virus Sampling
Samples should be taken from as wide a variety of hosts (e.g., cattle, buffalo, sheep,
goats, pigs, and dominant wild species) and environments (e.g., areas of high stock
density, border areas and quarantine posts) as possible so that virus typing studies in
the laboratory will give a reasonably accurate picture of the distribution and
characteristics of the viruses in the field.
As with the vaccination teams and other officials/veterinarians, great care must be
taken by the sample collection teams to avoid spread of FMD from infected premises
to other premises covered by the investigation.
Serum Sampling
To ensure that vaccines are potent and have been properly used by field staff, it is
important to plan and implement a serum survey covering the vaccination campaign.
Care must be taken to avoid bias in sampling of livestock units; for example, choosing
only units within the same locality or vaccinated by the same vaccination team.
Ideally, serum sampling points should be as follows:
• Several days before or on the day of vaccination.
This will establish whether animals have any
pre-existing antibody, either from previous
infection or rounds of vaccination.
Apparent absence of antibody does not
necessarily indicate that there has been no
previous exposure but rather that titres may
have declined below measurable levels.
• Five days after vaccination.
Rapid increases in titre within five days
following vaccination are a strong indication
of an anamnestic response and, therefore,
previous infection or rounds of vaccination.
• Twenty-one days after vaccination.
For primovaccinates using aluminium
hydroxide-saponin vaccines, the antibody titre
at 21 days post vaccination is commonly
used to assess the protective capacity of a
vaccine. The rate of antibody development
with some oil-adjuvanted vaccines is slower
and sampling at 28 days post vaccination
may be more meaningful.
• Three months after vaccination.
This will give some indication of the duration
of the immune response.
Other useful sampling points include:
• After the second vaccination of young animals
(i.e., one month after primovaccination).
• Different dates post-partum to assess
titres of maternally derived antibodies.
• Other dates to assess longer term immunity in frequently vaccinated
animals.
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