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==Treatment==
==Treatment==
The control policy for CSF depends on the incidence and prevalence of the infection in
the domestic and wild pig populations, respectively. In countries with CSF endemic in
domestic pigs it is common practice to vaccinate against the disease, thereby, avoiding
serious losses. However, the simultaneous eradication of ®eld virus is improbable because
serological methods are no longer applicable for the detection of ®eld virus infections. It
is acknowledged that ®eld virus may be hidden under a `blanket' of general vaccination.
Taking this risk into account, importing countries in general do not allow the introduction
of pigs or pig products from countries that vaccinate against CSF. The preventive
measures adopted by the EU for trade with Third Countries stipulate that live pigs and
fresh pig meat can only be imported from regions or countries where no CSF has
occurred for 12 months and no vaccination against CSF was applied during the same
period. Nevertheless a policy of consistent and systematic prophylactic vaccination in
endemic situations may ultimately lead to a favourable starting point for a non
vaccination policy and the eradication of the virus. After the cessation of general
vaccination, eventual local outbreaks of residual ®eld virus must be dealt with by strict
measures to ensure prevention of virus spread and eradication of the virus.
Based on the above mentioned disadvantages of vaccination and a cost bene®t analysis
the EU banned vaccination against CSF at the end of the 1980s. Whereas most
neighbours of the EU have also adopted a similar policy, vaccination is allowed and
mostly routinely applied by many Central and Eastern European countries (Edwards
et al., 2000). In some of the latter countries only sick or clinically suspect animals are
destroyed in case of CSF outbreaks whereas all other animals of the infected herd, herds
in the neighbouring area and contact herds are vaccinated.
In case of an outbreak of CSF, all EU Member States and the other Western European
countries execute eradication measures according to the Council Directive 80/217/EEC
(Anonymous, 1980; Edwards et al., 2000). These are based on stamping out
(depopulation) of infected pig herds and possibly infected contact or (partially)
neighbouring herds, epidemiological investigations, clinical and virological investigations,
movement restrictions for live pigs, pig meat and other vectors which can transmit
CSF within zones surrounding the infected farm and restrictions on contact farms outside
these zones (Anonymous, 1980). Especially in areas with dense pig populations very
high numbers of pigs had to be destroyed in the course of the eradication measures
dealing with the outbreaks mentioned above. Only a minority of animals were killed due
to direct involvement with the infection. Most of the pigs had to be killed because of
welfare measures. The direct and indirect costs of recent CSF outbreaks in several EU
Member States so far amount to several billion Euro, and in the course of the CSF
epidemic in the Netherlands in 1997 approximately 10 million pigs were destroyed
(Saatkamp and Horst, 2000; Stegeman et al., 2000). Whereas in areas with a low density
pig population, the present control policy works very well it may well be questioned
whether it is sustainable in areas with a high density of pigs. There is a general consensus
that a number of measures must be introduced in order to reduce the vulnerability of
regions at risk, e.g., structural changes in the pig industry including trade. However,
implementation of appropriate programs might be dif®cult. Several parties, notably some
V. Moennig / Veterinary Microbiology 73 (2000) 93±102 99
national farmers' associations requested the reintroduction of a general or at least
regional vaccination.
In principle, emergency vaccination is in agreement with EU legislation (Anonymous,
1980). Requirements related to emergency vaccination campaigns against CSF virus have
been de®ned in the document `Guidelines for a Classical Swine Fever Emergency
Vaccination Programme' (Anonymous, 1994). However, by using conventional vaccines
and applying the mentioned guidelines, the Scienti®c Veterinary Committee of the
Commission has calculated that vaccinated animals would be excluded from the market
for up to 600 days (Anonymous, 1997). This is economically unacceptable and so far
emergency vaccination has never been used.
With the development of a ®rst generation marker vaccine against CSF the possibility
of an amendment of the existing EU emergency vaccination regulations seems feasible. A
restricted application of a marker vaccine would require extensive serological testing in
the vaccinated population in order to detect hidden ®eld virus infections. At present no
marker vaccine has been licensed within the EU and EU Member States demand welldocumented
data on the safety and ef®cacy of the vaccine before its potential use in
emergency situations. It is understood that the criteria for the use of the marker vaccine
will be very stringent. Provided that all safety requirements are met, the period of
exclusion from the market could be considerably shortened at least for pig products after
a CSF outbreak (Anonymous, 1997). As soon as marker vaccines are suf®ciently
investigated and licensed, the `Guidelines for a Classical Swine Fever Emergency
Vaccination Programme' (Anonymous, 1994) are to be amended. The possible use of an
emergency vaccination with marker vaccines is expected to avoid the ethically
questionable and expensive large scale pre-emptive slaughter of pigs. Thereby, the
public acceptance of the eradication policy will increase and costs will decrease. Under
these circumstances the use of emergency vaccination using marker vaccines could be a
useful tool of the non-vaccination policy.
A still unresolved problem is the control of CSF in wild boar (Laddomada, 2000).
Both the prolonged persistence of virus in wildlife populations and the constant threat
of domestic pig holdings in the respective areas require an ef®cient control strategy.
Comprehensive information about the current situation in wild boar populations
is essential and new strategies have to be devised. They have to take into account
current knowledge about factors in¯uencing CSF epidemiology, e.g., wild boar
behaviour; population dynamics; in¯uence of hunting strategies; in¯uence of geographic
pro®les.
An ef®cient surveillance system must be an integral part of the control strategy. The
EU Commission has held a workshop dedicated to this topic (Anonymous, 1998) and a
working group of the Scienti®c Committee on Animal Health and Animal Welfare will
prepare a recommendation.
===Vaccination===
From the beginning of the century attempts have been made to develop vaccines
against CSF. However, the safety and ef®cacy of the ®rst generations of vaccines were
poor. In the 1940s ®rst experiments were made to attenuate CSFV by adapting it to
rabbits (Baker, 1946; Koprowski et al., 1946). After initial setbacks, this development
ultimately led to a very ef®cient and safe generation of live vaccines. Most attenuated
vaccines are based on the China-strain (C-strain) of lapinized CSF virus. C-strain
vaccines were and are still being used world-wide for the control of CSF in domestic pigs.
It is also used at least on an experimental basis for the oral immunisation to control CSF
in wild boar (Kaden et al., 2000). C-strain vaccines induce high titres of neutralising
antibodies and they are safe when used on pregnant animals. Their ef®cacy is
demonstrated by the observation that vaccinated pigs are protected against infections with
virulent CSF virus as early as ®ve days after vaccination. The animals are immune
throughout their economic life. However, with respect to today's global trade policy there
is a severe disadvantage in using live attenuated vaccines against CSF: Vaccinated and
®eld-virus-infected animals cannot be distinguished because the antibody pattern induced
by the vaccine virus resembles that of reconvalescent animals.
A way out of this dilemma may be the development and use of so-called marker
vaccines, e.g., subunit vaccines consisting of single viral surface proteins, which are suf-
®cient for the induction of protective immunity. At present two subunit vaccines containing
the viral glycoprotein E2 are under scrutiny. The respective gene is expressed in baculoviruses
grown in insect cells (Van Rijn et al., 1996). Since these cells are able to glycosylate
proteins, the resulting viral glycoprotein is expressed in a `natural'way.CSF subunit vaccines
are safe and so far their protective potency is promising, though inferior to live vaccines.
Vaccinated animals may be distinguished from infected pigs using an ELISA based on a
different viral protein as diagnostic antigen, e.g., the surface glycoprotein Erns or the
nonstructural protein NS2-3. However, not all criteria for the emergency use of marker
vaccines are well de®ned yet, and the technical merits of these vaccines have not yet been
established. More data are expected to be available during the year 1999.
Technically there is the potential for further improving CSF marker vaccines by
developing, e.g., viral vector vaccines (RuÈmenapf et al., 1991; Van Zijl et al., 1991; Hooft
van Iddekinge et al., 1996), DNA vaccines and molecularly altered infectious cDNA
clones of CSF virus (Meyers et al., 1996, Moormann et al., 1996, Ruggli et al., 1996).
==Prognosis==
==Prognosis==